Shelby standard block question

[JohnN-1BADFE]

To convert a Shelby standard block to a big bore block it has to be bored from 4.500" to 4.625" so a 4.625" OD sleeve will go into the block.

Is that all the difference(s) there is between a standard and big bore Shelby block?

Can much /  far can a standard block be bored?  More than 4.310?

Are there things to take into consideration on a big bore block such as, less rigidity, strength, etc.,  etc.?

Thanks,

JohnN

[jayb]

I believe that the overbore is all that is required for the big bore Shelby block.  As far as how big you can go on the bore, this is going to depend on how comfortable you are with the thickness of the sleeve.  At a 4.31" ID and a 4.50" OD, the sleeves are 0.095" thick.  Since they are made of much better material than cast iron, that's certainly an acceptable thickness, although thicker is always better.  The guy who designed the Shelby block, Mike LeFevers, told me that he has run those sleeves down as thick as .0625" (1/16").  I don't think I'd go that low, but I'm currently running my race car engine at 0.085".

[CaptCobrajet]

In an aluminum "shell", I would rather have some integrity behind the sleeve, and the thickest sleeve I could retain.  I think the gains in cubic inches are more than negated by the loss of roundness and straightness when it is running.  The Shelby blocks are top notch, as far as aluminum blocks go.  In their most stable form, they are about 20 HP down from iron, which is offset by the weight benefits.  Doing things to further compromise ring seal will give diminishing returns, in my opinion.

[blykins]

Never been an aluminum block fan.  Too much trouble for no benefit. 

[jayb]

I beg to differ   Aluminum blocks are easier to repair, and it is also easy to swap out a sleeve and get back to the original bore size, if you want to do that.  Plus taking over 100 pounds off the nose of the car makes for better handling, and negates any power advantage that the cast iron block may have.  For me, aluminum blocks are the best way to go.

[blykins]

Wait until you get a couple new blocks in that are porous and leak through the lifter bores, then you have to explain why you're sending the customer's new block back to the manufacturer, or having to put lifter bore bushings in.   

I've also found that the blocks squirm around a lot more during heat cycles than their cast iron counterparts, so the chance for an oil leak is greater.

Most of my customers wanting aluminum blocks are the Cobra guys, where the block sits pretty far behind the front axle centerline, so I don't think the weight savings is really worth it in that case.  If it's sitting in the front of a Mustang or Galaxie, then I agree, you would probably notice it. 

While speaking with Robert Pond, I remember him saying that the aluminum block "squirming" goes up with horsepower as well.  So as horsepower goes up, you lose more and more power to loss of ring seal due to the block flexing. 

The fact that they're easily welded up is a nice plus.  Sleeves are nice too....when they don't drop. 

I'm just not a fan.  To each their own though.

[jayb]

I have five aluminum blocks, and I've never experienced a porous aluminum block.  I've heard of porous Dove blocks, though...

I think the squirming you refer to, at least internally, is specific to Pond blocks.  Every time I revamped my Pond block, there was evidence of the mains squirming around.  I think the Pond aluminum block doesn't have enough support for the main bearings in the block.  Having said that, though, I've run the Pond aluminum block up to 840 HP without any problems.

Also, just to be clear, the sleeves can't drop out of an aluminum block because they have a flange on top.  I think you are referring to the flange being pressed down into the block so that its top is below the deck of the block.  That's a machining issue, of course, but it can be easily corrected by decking the block with the sleeves in it.  Again I haven't seen that problem on any of my blocks (4 Shelby, 1 Pond), but I can see it could be a problem.

I will say again, aluminum blocks are the best way to go, aside from the financial considerations.

[blykins]

I’m a lot harder to convince... 

Aluminum blocks have cost me a lot of time, money, and labor over the years and I personally just don’t see a reason for manufacturing them.

The problems go up with the sample size.  I’ve had 3 bad aluminum blocks.  Fixed one, returned two.  There’s a lot of aluminum fe blocks running around with lifter bore bushings....not because the build required bushings but were needed to keep the block from leaking.

I think Barry sends all his aluminum blocks out to be coated inside but that’s just another step and another reason for me to hate them....lol

Give me a stout cast iron piece with thick cylinders any day.

[Heo]

When will we see the first compacted graphite iron Fe block?

[troublemaker427]

There is a reason NHRA Pro Stock engine builders use iron blocks in place of aluminum.  The weight savings is not worth the horsepower loss because of the loss of ring seal and block squirm.  An iron block will always make more power than an aluminum block.  If weight is a huge concern then you have to weigh your options. 

[scott foxwell]

There is a reason NHRA Pro Stock engine builders use iron blocks in place of aluminum.  The weight savings is not worth the horsepower loss because of the loss of ring seal and block squirm.  An iron block will always make more power than an aluminum block.  If weight is a huge concern then you have to weigh your options.

This. There are a few racing venues where weight trumps power and the weight savings is justifiable but there will always be a power sacrifice.
Also, sleeves "dropping" isn't the issue...the problem usually comes from when the sleeves are decked even with the block, the block can expand more than the sleeves leaving them "in the hole". The other scenario is the sleeves don't get installed to their full depth and will "settle" after the engine is run. Both scenarios are very common with aluminum blocks. It's usually recommended to leave the sleeve up a couple thou on a new build, but if you have to deck the block for some reason, it's usually not real practical to remove sleeves before you do it, re-install sleeves, then deck them to a different height. At that point, the engine has run, the sleeves are settled, and zero decking them usually isn't an issue.

[blykins]

There is a reason NHRA Pro Stock engine builders use iron blocks in place of aluminum.  The weight savings is not worth the horsepower loss because of the loss of ring seal and block squirm.  An iron block will always make more power than an aluminum block.  If weight is a huge concern then you have to weigh your options.

This. There are a few racing venues where weight trumps power and the weight savings is justifiable but there will always be a power sacrifice.
Also, sleeves "dropping" isn't the issue...the problem usually comes from when the sleeves are decked even with the block, the block can expand more than the sleeves leaving them "in the hole". The other scenario is the sleeves don't get installed to their full depth and will "settle" after the engine is run. Both scenarios are very common with aluminum blocks. It's usually recommended to leave the sleeve up a couple thou on a new build, but if you have to deck the block for some reason, it's usually not real practical to remove sleeves before you do it, re-install sleeves, then deck them to a different height. At that point, the engine has run, the sleeves are settled, and zero decking them usually isn't an issue.

Which is what happened to one of my builds. 

We take the new blocks out of the box, clamp a head gasket and torque plate to each side, and put them in an oven to get the sleeves to take a set, to try to eliminate that "settling" that can happen after the engine is ran.  The sleeves are still usually proud a couple thou and match up perfectly with the fire ring in the head gasket, but the issue is that the block's decks aren't always perfectly square/straight/parallel with the crank, so the decks need cut. 

So this particular block had the sleeves set, decks cut, and "dropped" a sleeve on the dyno, just far enough to necessitate pulling the engine down again.  On an aluminum block, the deck height actually grows, so if you have a sleeve drop and then the block grows up around it even more, it's not a good scenario. 

I'm not convinced that ring seal isn't always compromised, especially with a different running temperature/condition than when the block was machined.  I've pulled fresh all-aluminum FE's off the dyno, and have yanked the heads to see what I would call a "shadow" in some of the cylinders, almost like the block had never been torque plate honed.  I could see how these engines would automatically be down for a little oil usage right off the bat. 

Complicating all of this is the fact that there are no aluminum FE block manufacturers who can push out enough quantity to justify some real hard core durability testing, like the OEM has.....or even like Dart/World would have.  That's why we see porosity/flaws/etc. on larger sample sizes of blocks. 

A CGI block would be where it's at, if you could take advantage of the weight reduction capabilities. 

[jayb]

Its amazing to me that you guys are so opposed to aluminum blocks.  I have never had any of the problems that you describe, and I have five aluminum blocks that I have run hard, starting in 2004.  I also do not believe that the power loss from aluminum block ring seal trumps the weight loss.  We are talking about 100 pounds here, on the front end of the car.  It would take a 20 HP loss from ring seal to make that up, and you would still be behind as far as handling and suspension go.  And as long as we are discussing that, somebody please point me to a back to back comparison between a cast iron block and an aluminum block, for power.  As far as I know, no one has made such a comparison.  So there is no data to support the "theory" that cast iron blocks make more power than aluminum blocks.  It's all just a guess. 

As far as the blocks being able to hold up to power, I will take a Shelby aluminum block over any cast iron block that is available now or in the past.  My big SOHC makes over 1000 HP with the Shelby block, my Mach 1 with the supercharger made 1200+ with the Shelby block, and my twin turbo SOHC will make close to 2000 HP with the Shelby block.  I'm not worried about the block one bit. 

I often wonder if the professional engine builders out there prefer the cast iron blocks because they are easier and more conventional to machine and assemble than the aluminum blocks...

[scott foxwell]

Its amazing to me that you guys are so opposed to aluminum blocks.  I have never had any of the problems that you describe, and I have five aluminum blocks that I have run hard, starting in 2004.  I also do not believe that the power loss from aluminum block ring seal trumps the weight loss.  We are talking about 100 pounds here, on the front end of the car.  It would take a 20 HP loss from ring seal to make that up, and you would still be behind as far as handling and suspension go.  And as long as we are discussing that, somebody please point me to a back to back comparison between a cast iron block and an aluminum block, for power.  As far as I know, no one has made such a comparison.  So there is no data to support the "theory" that cast iron blocks make more power than aluminum blocks.  It's all just a guess. 

As far as the blocks being able to hold up to power, I will take a Shelby aluminum block over any cast iron block that is available now or in the past.  My big SOHC makes over 1000 HP with the Shelby block, my Mach 1 with the supercharger made 1200+ with the Shelby block, and my twin turbo SOHC will make close to 2000 HP with the Shelby block.  I'm not worried about the block one bit. 

I often wonder if the professional engine builders out there prefer the cast iron blocks because they are easier and more conventional to machine and assemble than the aluminum blocks...

The fact that you can argue with the power difference between an alum block vs iron makes me wonder... are you talking about just FE's here, or in general? A good alum. block may very well make as much power as a factory FE block but in the "big" world of racing and performance, the difference is well known and don't ask for documentation. I'm sure it's out there somewhere from decades ago. You don't have to throw a rock in the water to know it'll sink these days. I've seen 30+hp just from one iron block to another iron block. There is no way on God's green Earth any aluminum block will make near the HP a Pro Stock iron block does. If weight was an issue and block integrity wasn't, they would all be running GM blocks that weigh a couple hundred pounds less. Heck, a Dart BigM can handle 1400hp and weighs a heck of a lot less than a DRCE block but try and make 1400hp @ 10,5 rpm with a Big M @ 500ci. Aint gonna happen.
Forced induction or power adder with an alum block is not part of the argument. That covers a lot of sin...
I worked for Dart and Rich Maskin when they came out with the Rocket small block. We did a little test...back to back, as close as was humanly possible...a 400" Bowtie block SB Chevy vs the Rocket block, on the dyno, and switched as many common parts as possible between the two. Cam, pistons, rods, crank, heads, intake, etc. The Rocket block made almost 40hp more than the Bowtie. Consensus was, it was just a better, thicker, more rigid block.

[blykins]

I think Blair has back to back between cast iron and aluminum builds.  I think Robert Pond has data too.  It's not a theory, it's something that's talked about quite often.

I prefer the cast iron because I don't have trouble with them.  Yes, they're easier to machine and take less assembly time, but as I mentioned earlier, I've experienced a good bit of down time and loss of profit because of aluminum blocks.  I'm a one-man shop and having to pull an engine off the dyno, disassemble it, cut the decks, buy all new gaskets, etc., then reassemble is a good chunk of time that's taken away from other builds.

The chances of problems go up with the quantity of blocks used.  I've used a lot more than 5 aluminum blocks and didn't have any trouble with the first few, but there's a bell curve to any statistical sample.   Keith Craft and I had quite a few discussions about this when he was building.  He had quite a few blocks that didn't pass the pressure test as well, and a lot of his blocks ended up with lifter bore bushings.  I sent mine back. 

I've had troubles with all aftermarket FE blocks, cast iron and aluminum, but I've had more trouble with aluminum blocks by far.   

The fact that I can almost buy 2 new cast iron blocks for the price of 1 aluminum is the nail in the coffin.

[plovett]

Can the power loss with an aluminum block be minimized with thicker sleeves?  Just wondering.

paulie

[blykins]

Depends on the block and how strong the block is behind the sleeves.   The fact that the aluminum moves so much with heat doesn't help. 

Here's a couple of quotes that I dug up from a conversation that we had about aluminum FE blocks on Club Cobra:

This one is a quote from Dave Shoe where he had interviewed Robert Pond:

"The horsepower differences between iron and aluminum blocks have been repeatedly characterized by Robert Pond, though I am necessarily distorting his claims because I lack sufficient experience to fully comprehend all his findings. He has been particularly interested in horsepower gains as small as a single horsepower, as his Stock Eliminator racing engines are constrained in the modifications which are allowed. I've spoken to Robert a little bit about "free horsepower", and he strongly contends that the block, all by itself, can provide dozens of free horsepower between the 600 to 1000 horsepower levels, just by its cylinder rigidity characteristics."

And from Barry Rabotnick from his F-M days....

"Well - - I can add a little fuel to the fire.  I supply rings and bearings to a large percentage of Pro Stock, Cup, and fastest street car competitors. In virtually 100% of situations where the weight is not critical (meaning that they would have to add ballast to offset any weight benefit from aluminum to meet a mandated minimum) these competitors ALL run an iron block of some sort.

Iron blocks simply make more power. Every time. The commonly bandied about number is somewhere between 15 and 30 - depending on the power level and the particular engine in question. Big beefy billet caps on aluminum blocks are kinda like a super strong steel lid on a cardboard box - when they're stronger than the parent material the value is limited. Ultimate power handling potential is not an issue - both materials have been proven at levels beyond anything feasable in an FE (I have seen numbers near 3000HP).

When properly prepped and designed, neither material will show bearing issues - but aluminum does require tighter cold clearances. Fuel motors don't count - - repairability is more important than the nominal power difference when you're at that level. The sole benefits to an aluminum block are identical to those of aluminum heads - weight ease of modification and repairability."

[scott foxwell]

I think Blair has back to back between cast iron and aluminum builds.  I think Robert Pond has data too.  It's not a theory, it's something that's talked about quite often.

I prefer the cast iron because I don't have trouble with them.  Yes, they're easier to machine and take less assembly time, but as I mentioned earlier, I've experienced a good bit of down time and loss of profit because of aluminum blocks.  I'm a one-man shop and having to pull an engine off the dyno, disassemble it, cut the decks, buy all new gaskets, etc., then reassemble is a good chunk of time that's taken away from other builds.

The chances of problems go up with the quantity of blocks used.  I've used a lot more than 5 aluminum blocks and didn't have any trouble with the first few, but there's a bell curve to any statistical sample.   Keith Craft and I had quite a few discussions about this when he was building.  He had quite a few blocks that didn't pass the pressure test as well, and a lot of his blocks ended up with lifter bore bushings.  I sent mine back. 

I've had troubles with all aftermarket FE blocks, cast iron and aluminum, but I've had more trouble with aluminum blocks by far.   

The fact that I can almost buy 2 new cast iron blocks for the price of 1 aluminum is the nail in the coffin.

My first Shelby block was a disaster. 'Course, it was one of the first ones. The bores in the block were nice and round...the sleeves were nice and round, but put the sleeves in the block and everything when haywire, and I mean by .002-3". I looked at every possible reason...in the end, Mike LeFevers fixed it for me..along with the main studs that pulled out of the block when I torqued them. 
Water blocks are obviously going to be the worst, but when I was at Alan Johnsons, we always used gapless rings, even in the solid blocks like the KB or Rodack because of the fact that the cylinders are always moving around. Aluminum blocks are about the only place I use gapless rings, but ALWAYS in alum.

[Nightmist66]

Water blocks are obviously going to be the worst, but when I was at Alan Johnsons, we always used gapless rings, even in the solid blocks like the KB or Rodack because of the fact that the cylinders are always moving around. Aluminum blocks are about the only place I use gapless rings, but ALWAYS in alum.

Gapless rings can benefit in an engine running on alcohol, to keep from diluting the oil.

[fekbmax]

So with all thats been said,
Opinions on whats a better choice?
Assuming both are properly prepared and machined.
A nicely repaired pond aluminum block or a good factory cross bolt block with pro gram caps and properly applied block fill for 850 to 900 Hp.

[jayb]

I wouldn't run the Pond aluminum block that high, Keith.  As mentioned previously the main webbing on the Pond aluminum block is the same as their cast iron block.  It needs to be thicker.  I would have no issues with a Shelby block at those power levels (been there, done that), but I'd worry about the Pond block.  A filled iron block would be better, I think.

[Leny Mason]

Hi, Nick Arias said his aluminum blocks need to be run till they burn to much oil three times before the blocks stop moving around, on his by the time you put the third set of sleeves in it it will stop using oil, now that is in a speed boat it may be different  because of the water temperature is cool all the time, that is his story. Leny Mason

[stangbuilder]

   I will chime in here..I have a all alum fe in a resto mod mustang that i have been running for about 12 years and appox 50.000 miles..It has been blown up 1 time dropped a valve.  And rebuilt two other times because it burned oil..As we speak car uses about a qt every 400mi..I have tried every thing i know to fix it.different rings.honing ect ect..So at this point on this engine it been driven for appox 20.000 mi runs perfect hauls ass
 i just add oil..believe me i hate it..I have pretty much given up trying to fix it.

 stats on car 67 F/B shelby gt 500 car weights 3100 w/o me in it 477in all alum fe
 blairs pro ports and victor with fast xfi sportsman EFI
 Mike jones S/F/T Cam tremic 5 speed close ratio
 
  Know what people are thinking crappy mach work last machine shop that did my motor was shaver specialties in torrance calif..At the time i felt if anybody know anything about working with allum blocks he would ..

[BH107]

Lance Smith down at Craft Performance did a back to back test with Pond blocks. First one was 711hp cast iron. All of the components were swapped into an aluminum block and it was down almost 40hp.

[blykins]

Y'all keep talking, just makes me hate 'em more.......LOL

[Posi67]

Lance Smith down at Craft Performance did a back to back test with Pond blocks. First one was 711hp cast iron. All of the components were swapped into an aluminum block and it was down almost 40hp.

The fix is easy... I have a goal of let's say 750 HP in an Aluminum BBM block. I don't care if the Iron would make more so I'll just toss enough parts at the Aluminum to reach my target. If I decide at some point I need more HP then an Iron block upgrade is an option. 100# off the front of my car is appealing.

[blykins]

Lance Smith down at Craft Performance did a back to back test with Pond blocks. First one was 711hp cast iron. All of the components were swapped into an aluminum block and it was down almost 40hp.

The fix is easy... I have a goal of let's say 750 HP in an Aluminum BBM block. I don't care if the Iron would make more so I'll just toss enough parts at the Aluminum to reach my target. If I decide at some point I need more HP then an Iron block upgrade is an option. 100# off the front of my car is appealing.

Spend $5k for an aluminum block, pay more for prep, and make 750 hp......or spend $3500 for an iron block and make 800 hp. 

Numbers are theoretical for the sake of argument, but the points are still valid.  LOL

[Joe-JDC]

Y'all keep talking, just makes me hate 'em more.......LOL

Something doesn't sound right with this whole argument.  If what some of you are claiming is true, no new car manufacturer would build an engine with aluminum block and heads.  I know they are on a weight savings mandate to improve fuel mileage, but the easiest way to improve fuel mileage is compression, and good fuel.  Also, if Lance Smith did R&R the internals from an iron block and install them in an aluminum block, did he blueprint the aluminum block just a carefully as the iron block, did he use new rings, bearings, did he heat the oil, water, engine cycles to the same amount before testing?  Did he do this on the same day? Weather the same, barometer the same?  Etc., etc., I have to say that with all my years of experience, automotive degree, teaching experience, have I ever heard such an argument that cannot be substantiated with back to back dyno testing in a laboratory environment to eliminate all differences but the material used in the block.  A simple gasket mismatch in the intake tract can change the horsepower level on a highly tuned engine, and I have seen 20 hp difference back to back with that situation on the dyno.  I have also seen 20 hp difference with spacers turned around differently, or different timing, fuel pressures, different oil level in oil pan, all make differences in back to back horsepower testing to find the ultimate combination.  A carburetor not opening fully and not caught when installing on the dyno.  I have to call this an argument that I cannot agree with until I see it performed under the same testing environment on the same day with identically prepared engines, and have all the same pulls to break in, all the same temperatures, and same individuals monitoring the testing procedures to verify.  JMO, but skeptical to say the least at 20-40hp level.  Joe-JDC

[blykins]

I understand your concerns on keeping everything consistent, Joe, but the horsepower difference has been well documented by many others besides Lance Smith. 

As far as what's used in the OEM, they have millions and millions of dollars invested in research and testing, and produce literally millions of blocks on high levels of quality standards.   The FE aftermarket doesn't have any of that.  Actually, none of it.  I couldn't even get 5 aluminum FE blocks in a row that didn't have issues. 

On another note, just because it's used in the OEM doesn't mean it's right.  If you want to look at how flimsy OEM aluminum can be, take a Teksid 4.6 modular block and see if you can turn the crankshaft until all the main caps are torqued.   However, I would imagine that you had a good point about weight savings, fuel economy, and the EPA.....

[BH107]

Y'all keep talking, just makes me hate 'em more.......LOL

Something doesn't sound right with this whole argument.  If what some of you are claiming is true, no new car manufacturer would build an engine with aluminum block and heads.  I know they are on a weight savings mandate to improve fuel mileage, but the easiest way to improve fuel mileage is compression, and good fuel.  Also, if Lance Smith did R&R the internals from an iron block and install them in an aluminum block, did he blueprint the aluminum block just a carefully as the iron block, did he use new rings, bearings, did he heat the oil, water, engine cycles to the same amount before testing?  Did he do this on the same day? Weather the same, barometer the same?  Etc., etc., I have to say that with all my years of experience, automotive degree, teaching experience, have I ever heard such an argument that cannot be substantiated with back to back dyno testing in a laboratory environment to eliminate all differences but the material used in the block.  A simple gasket mismatch in the intake tract can change the horsepower level on a highly tuned engine, and I have seen 20 hp difference back to back with that situation on the dyno.  I have also seen 20 hp difference with spacers turned around differently, or different timing, fuel pressures, different oil level in oil pan, all make differences in back to back horsepower testing to find the ultimate combination.  A carburetor not opening fully and not caught when installing on the dyno.  I have to call this an argument that I cannot agree with until I see it performed under the same testing environment on the same day with identically prepared engines, and have all the same pulls to break in, all the same temperatures, and same individuals monitoring the testing procedures to verify.  JMO, but skeptical to say the least at 20-40hp level.  Joe-JDC

This wasn’t just something mentioned in passing, it was something Lance actually advertised with dyno sheets.

“We often have people ask what the horsepower difference is between cast iron and aluminum blocks. It often depends on the engine specs, but here is one that we ran on the dyno in a cast iron Pond block then swapped everything to a Pond aluminum. This is a 482ci, 11.5:1 comp, Stage III Edelbrock heads, and a street solid roller camshaft. Torque was basically the same but hp definitely dropped off on the aluminum. Back to back dyno play is always fun. — at Craft Performance Engines LLC.”

“I think there are several factors. Heat rejection being one, unlike cylinder heads, in a cylinder heat is power. The aluminum will distort more than cast iron under load and rpm, distorted cylinders = ring seal loss.  I believe this is the 4th back to back we have done and they are normally 25-40 hp difference depending on engine specs.”

[stangbuilder]

Y'all keep talking, just makes me hate 'em more.......LOL

Something doesn't sound right with this whole argument.  If what some of you are claiming is true, no new car manufacturer would build an engine with aluminum block and heads.  I know they are on a weight savings mandate to improve fuel mileage, but the easiest way to improve fuel mileage is compression, and good fuel.  Also, if Lance Smith did R&R the internals from an iron block and install them in an aluminum block, did he blueprint the aluminum block just a carefully as the iron block, did he use new rings, bearings, did he heat the oil, water, engine cycles to the same amount before testing?  Did he do this on the same day? Weather the same, barometer the same?  Etc., etc., I have to say that with all my years of experience, automotive degree, teaching experience, have I ever heard such an argument that cannot be substantiated with back to back dyno testing in a laboratory environment to eliminate all differences but the material used in the block.  A simple gasket mismatch in the intake tract can change the horsepower level on a highly tuned engine, and I have seen 20 hp difference back to back with that situation on the dyno.  I have also seen 20 hp difference with spacers turned around differently, or different timing, fuel pressures, different oil level in oil pan, all make differences in back to back horsepower testing to find the ultimate combination.  A carburetor not opening fully and not caught when installing on the dyno.  I have to call this an argument that I cannot agree with until I see it performed under the same testing environment on the same day with identically prepared engines, and have all the same pulls to break in, all the same temperatures, and same individuals monitoring the testing procedures to verify.  JMO, but skeptical to say the least at 20-40hp level.  Joe-JDC

So what is the fact its well documented that they burn oil??

[Posi67]

"Spend $5k for an aluminum block, pay more for prep, and make 750 hp......or spend $3500 for an iron block and make 800 hp. 

Numbers are theoretical for the sake of argument, but the points are still valid.  LOL"

Well, in my case I didn't spend quite that much on a block and with my setup the 100# off the nose is worth money. I could be wrong but don't expect block prep will be a deal breaker since both the Iron and Aluminum need similar work. I'm not arguing the fact Iron is the material of choice for the serious go fast guys. I have other ways to reduce weight or make a few HP but I prefer to keep my car somewhat "stockish" looking. Results may vary... 

[TJ]

I don't think new car makers using aluminum blocks/heads is contradictory to the notion iron makes more hp than aluminum.  Looks like FE iron vs aluminum makes a difference of 20-40 hp (about 3-6%).  The Craft engine was 482 cubes while the average family car is roughly 220 cubes.  So 3-6% difference in hp for a family car size motor is around 15 hp at most ...not likely noticeable to a consumer.  Add to that all the gizmos and do-dads (like variable cam timing) on modern family cars and the consumer is so pleased by the higher revving/higher hp aluminum block that the iron block of yesterday is not missed.

[JohnN-1BADFE]

Would it be fair to say the Shelby block is superior vs. all other alum blocks?....

Fully redesigned, the Shelby 427 Alloy FE block is 45 percent lighter, yet stronger than the factory cast iron version.

The Shelby block offers these premium performance features:

Deep lifter valley reinforcing webs combined with thick oil pan rails and main webs maximize block strength.
Thick 0.750-inch deck delivers the foundation needed for maximum head gasket sealing and retention.
Priority main oiling system. With the oil gallery raised adjacent to the camshaft bore, oil flow is directed to main bearings first, before going to the cam bearing. Crank life is maximized.
Strong enough to support over 1500 horsepower outputs.
Shelby's FE alloy block delivers superior bottom end stability at high rpm.

This is accomplished by:

Extended skirt design.
2,3,4 main caps are cross bolted with 4 cross bolts. Main caps are billet steel and cap alignment is further enhanced by integral dowel section in the main studs.
Steel caps allow moderate bearing clearances for cold starts.

Centrifugally cast duplicate iron. cylinder sleeves are fitted in the block, with an interference step fit that creates precise, non shift sleeves positioning. Cylinder walls are stained and revised cooling passages make street or race track cooling problems a thing of the past.

The block requires special Shelby head studs, available separately. Unlike a stock block, where the head bolt threads start at the deck surface, the Shelby stud threads are positioned adjacent to the cylinder bore bottom. This configuration delivers maximum gasket seal/retention and minimum cylinder bore distortion when the head is torqued to the block.

[Posi67]

Yes, that is fair to say and they are priced accordingly. I wouldn't trust any of the other brands to take the HP the Shelby does but then they weren't designed to compete in that area. Sorry for joining in the thread hijack which is of course what happens with almost every thread. 

[blykins]

"Spend $5k for an aluminum block, pay more for prep, and make 750 hp......or spend $3500 for an iron block and make 800 hp. 

Numbers are theoretical for the sake of argument, but the points are still valid.  LOL"

Well, in my case I didn't spend quite that much on a block and with my setup the 100# off the nose is worth money. I could be wrong but don't expect block prep will be a deal breaker since both the Iron and Aluminum need similar work. I'm not arguing the fact Iron is the material of choice for the serious go fast guys. I have other ways to reduce weight or make a few HP but I prefer to keep my car somewhat "stockish" looking. Results may vary...

There is a little more work with the aluminum blocks.  Sleeves need to be set and provisions need to be made to make sure they don't leak due to porosity issues.  I think Barry sends all of his off to have them coated internally which adds to the cost of the machine work/prep work.   I don't have them coated, but do a pressure test first.  If they don't pass, they go back.  If they do pass, then I include a bottle of ceramic seal with the engine after it's dyno'd and sent out.   I should be talking in past tense as I haven't taken any aluminum block builds in over a year and really don't intend to do any more.

[blykins]

Would it be fair to say the Shelby block is superior vs. all other alum blocks?....

Fully redesigned, the Shelby 427 Alloy FE block is 45 percent lighter, yet stronger than the factory cast iron version.

The Shelby block offers these premium performance features:

Deep lifter valley reinforcing webs combined with thick oil pan rails and main webs maximize block strength.
Thick 0.750-inch deck delivers the foundation needed for maximum head gasket sealing and retention.
Priority main oiling system. With the oil gallery raised adjacent to the camshaft bore, oil flow is directed to main bearings first, before going to the cam bearing. Crank life is maximized.
Strong enough to support over 1500 horsepower outputs.
Shelby's FE alloy block delivers superior bottom end stability at high rpm.

This is accomplished by:

Extended skirt design.
2,3,4 main caps are cross bolted with 4 cross bolts. Main caps are billet steel and cap alignment is further enhanced by integral dowel section in the main studs.
Steel caps allow moderate bearing clearances for cold starts.

Centrifugally cast duplicate iron. cylinder sleeves are fitted in the block, with an interference step fit that creates precise, non shift sleeves positioning. Cylinder walls are stained and revised cooling passages make street or race track cooling problems a thing of the past.

The block requires special Shelby head studs, available separately. Unlike a stock block, where the head bolt threads start at the deck surface, the Shelby stud threads are positioned adjacent to the cylinder bore bottom. This configuration delivers maximum gasket seal/retention and minimum cylinder bore distortion when the head is torqued to the block.

I would agree that the Shelby block is superior, although I have heard of several 1000+ hp Pond aluminum block builds.

The underlying argument here though is not how much hp they will withstand, but if an aluminum block’s pros outweigh the cons.  I would argue that any aftermarket FE block would hold 1000+ hp as they all have provisions for priority oiling, billet steel caps, increased structural support, etc. 

[machoneman]

I wonder what actually causes the excessive oil consumption? Is it oil slipping past the sleeve to cylinder head junction, then getting burned in the chamber? Blowby primarily? Would not the spark plugs get fouled pretty quickly then? Or is it the sleeves flexing against piston/ring movement?

I've oft considered an aluminum block (sorry, a 351W design, stoked to maybe a 408-427) to reduce nose and overall weight for my Mach 1 but the cost is damned high as killer, big-bore 4.125" iron blocks are readily available and the overall cost/prep work is far cheaper. Based on all these great comments, I may stick with the OEM iron block as a 358 CID engine. 

[blykins]

I would assume it’s the cylinder not being able to stay straight and round because the support around it is flexing and moving.  We torque plate hone blocks but I have taken all-aluminum FEs back apart after dynoing to do head work and have seen shadows in the cylinders.

You also raise a good point about oil slipping past the sleeve, as when an aluminum block gets hot, it will grow up around the sleeve. 

[machoneman]

I would assume it’s the cylinder not being able to stay straight and round because the support around it is flexing and moving.  We torque plate hone blocks but I have taken all-aluminum FEs back apart after dynoing to do head work and have seen shadows in the cylinders.

Ah, thanks Brent and also for the fast reply! That makes perfect sense. Have zero exeperience with modern aluminum blocks but crewed on a 417 Donovan alky motored dragster long ago. Those sleeves and modern 426 Hemi-based fuel engines of today have super thick sleeves, now in solid blocks that I guess have near zero flex. The Donovan sleeve's bores always looked good save an engine blow-up or a backsided piston due usually to a too-lean tune-up. 

[Leny Mason]

On Nick Arias Engines they were six hundred inch and bigger and maybe the cubic inch has something to do with it, but it was all better after new sleeves the third time, we are doing a Nissan V eight now it is cool it has an intake port for every valve and a lot of valves anyway the sleeves are cast into the aluminum maybe that is why they work. Leny Mason