Recommended 390 build for obnoxious street strip 1970 f250

[Blackmamba]

I am new to the forum and am seeking advise from the FE gurus. I am relatively mechanically inclined and have done a few basic SBC rebuilds many moons ago. I have a very rough looking 1970 f250 the “blackmamba” which I have fell in love with it character and would like to build up for a strong running street/ strip ride.

I have a donor 390 and c6 trans from another 1971 truck that I will be using for the build.  I plan on posting the build in the correct forum sub section in hopes to seek advise as the build progresses and also share the build with others.

I’d like to get into the 600hp range on pump gas but also have the ability to have the option of a procharger power adder and get another 100-150 hp.

I’m seeking help in compiling a parts lists to achieve this goal. From my internet surfing I’m liking the idea of a 445 and also using set of trick flow heads.

I have the donor 390 which has a edlebrock rpm manifold and looks to be new set of jegs stainless adjustable rocker arms.

Any guidance is much appreciated, I’m just barely smart and humble enough to know that it’s always best to seek advise from other that have been there done that and got the T-shirt.

[blykins]

I can get you the 600 hp naturally aspirated with a 445, but when you start getting much past that, you need to start looking at an aftermarket block.

[Sand hauler]

Times 2 with Brent.

[Sand hauler]

It's definitely doable, still tweeking and tuning on mine

[Blackmamba]

Thanks for that info Brent, maybe it would be wise to scrap the procharger idea. I’d prefer to use the stock block that I have available. Out of curiosity what is the weak link on the block? Would the stock block be ok with around 600hp naturally aspirated and adding the occasional 100-150hp shot of nitrous?

Brent if you don’t mind sharing build list for a 600hp range engine that I’m looking to build that would be awesome. Would most likely be going they you for the parts being that I see from this forum you are a wealth of knowledge.

[blykins]

The weak link is the design of the block itself.  It will split between the mains and the cam tunnel. 

There's not an "X" hp number where a switch is flipped and blocks fail, but I would say trying to put 700-750 hp through a 390 block, whether it's forced induction or naturally aspirated, is a catastrophe waiting to happen, especially when tossing around a longer stroke. 

A 445 with TFS heads, Track Heat/Victor intake, and one of my custom hydraulic rollers will get you to 600, but just know it will be rowdy....

[TJ]

Would it be possible to put together a 445 with a pro charger and get a torque curve like a 3.5 eco boost?  Around 1.8 lb ft per cube from 1500 rpms to 5200 rpms and then it drops straight down? Keep it under 600 hp but with 800 or so lb ft?  Could the 390 or an aftermarket block handle it? (Truly an academic question for me since I have enough lb ft to twist up my truck if I pushed it… just call me curious.)

Let’s say it is possible, would it idle like a kitten?

[jayb]

Getting to even 1.5 lb-ft per cube with a naturally aspirated engine is very, very difficult.  I've only seen one on my dyno, after 150+ FEs on there.  The supercharger or turbocharger gets you the added torque.

I'm going to disagree, a little, with the consensus that you shouldn't go more than 600 HP with a 390 block.  I think that if you crossbolt or girdle the block, and are certain that the bores are solid, and you are running on street tires (not sticky race slicks), and you are not dumping the clutch all the time, it may be possible to make 650-700 HP from a 390 block and still live on the street.  I'm working on a project right now to test out that theory.  When I get the engine built and on the dyno I will share all the glorious or gory details 

[blykins]

……and you are running on street tires (not sticky race slicks), and you are not dumping the clutch all the time…..

Well that doesn’t sound like much fun……..

I think the longer stroke cranks cause a lot of issues.  Lots of threads on the other forum of both cross bolted 390/428 blocks and factory 427 blocks failing at the #2 and #4 main saddles with longer strokes and high hp naturally aspirated or blown setups..  Cracks develop in the saddles where it’s thin around the oil holes and then they split and dump oil pressure.

Like anything else, you can’t really count on it doing it every time but by the time you buy a factory block, machine for cross bolted caps, or a girdle, it would be worthwhile to glance at an aftermarket block.  I think even with cross bolted caps it’s not a guarantee that it will last. 

[Gaugster]

I'm hoping for a glorious result so that I can apply it to my girdled street build auto on drag radials.

[Blackmamba]

Thanks for the info. Being that I’m not conservative with my right foot, I’d agree to go with something that has a better chance of holding together for longer.  How much power would I be sacrificing if I used the existing edelbrock rpm 7105 manifold that I already have available for use?

[blykins]

Thanks for the info. Being that I’m not conservative with my right foot, I’d agree to go with something that has a better chance of holding together for longer.  How much power would I be sacrificing if I used the existing edelbrock rpm 7105 manifold that I already have available for use?

If you do decide to stay with a 390, I'd try to aim for the lightest rotating assembly pieces that you can get your hands on.  A good engine builder buddy of mine says, "Once you hit the ignition switch, everything that's inside of an engine is trying to get out."  That's a good way of thinking about it and the heavier parts put a lot more stress on the blocks.  With that being said, I just wouldn't be comfortable with hitting 700-750 hp with a factory block.   I see plenty of factory 428 blocks that are cracked in the mains just from normal usage.  The aftermarket blocks add a lot of meat in the main saddles and bulkheads, which is a trouble area for factory pieces.  They just weren't designed with that kind of power in mind, whereas the new stuff will take 1000 hp without thinking.

As for the Performer RPM, it kinda depends on the rest of the application.  I normally make about 550 hp and 590 lb-ft with a 445, TFS heads, a Performer RPM, and a fairly mild hydraulic roller that has enough vacuum to pull about 15" on a gauge.  That's a 5500 rpm engine.  I think we could make 25-30 hp over that with some careful part selection, while using your Performer RPM.  The RPM is actually a really good manifold, but there's a point where other manifolds begin to shine. 

Also, keep in mind that the cylinder head has a big bearing on the horsepower and how much camshaft it takes to hit a specific point.  We offer ported TFS heads that flow around 360 cfm with a 178cc port and then Jay has his street heads coming out that will do around that as well.  When you add a high performing head into the mix, it makes it easier to hit higher goals.  I'm a big TFS fan, but I have a feeling based on what I've seen from Jay's testing that I may be switching teams once they're plentiful.

[machoneman]

"I think the longer stroke cranks cause a lot of issues.  Lots of threads on the other forum of both cross bolted 390/428 blocks and factory 427 blocks failing at the #2 and #4 main saddles with longer strokes and high hp naturally aspirated or blown setups..  Cracks develop in the saddles where it’s thin around the oil holes and then they split and dump oil pressure."

It's not just the FE series that has this same issue. Later model say post 1975 or so Ford small blocks, especially 5.0 302s, also develop cracks in the mains that lead up to the cam tunnel. Seems like OEM Ford engineers in multiple engine series were more concerned about weight savings than designing thick block bulkheads, valley bottoms and cam tunnels. Having been a mod on the old 'Net 54 SBF Forum, I saw loads of pics of cracked 5.0's which of course did not benefit from cross-bolted mains. Even with the advent (and widespread use) of girdles, they seemed to do little for nitrous, blower or turbo engines so popular during the Fox body era where thousands of guys were building big SBF power. Moral is: whether its an FE or SBF, if one wants to build a high hp and bullet proof engine, get an aftermarket block.   

[Blackmamba]

Thanks for all the great info. I don’t plan on getting an aftermarket block, so that route is not option. Which leaves me with a 445, or a possibly a stock 390 stroke.  If one was to use a stock 390 block, crank, rods and pistons. With a set of trick flow heads, good matching cam,  could you get it into the 500hp range? And would this in theory hold up better to abuse comparative to a 445?

[blykins]

Thanks for all the great info. I don’t plan on getting an aftermarket block, so that route is not option. Which leaves me with a 445, or a possibly a stock 390 stroke.  If one was to use a stock 390 block, crank, rods and pistons. With a set of trick flow heads, good matching cam,  could you get it into the 500hp range? And would this in theory hold up better to abuse comparative to a 445?

Last 390 I did with TFS heads, Performer RPM, and a fairly aggressive hydraulic roller, made 540 hp.  He spins it to 7000.