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.