I will start this off by letting everyone know that I know very little about forced induction builds, I am just reading and learning and that this is going to be a few years before I build this due to other financial requirements.

Recently finished a new NA 408 build, spent a ton even though I built it all myself, minus machining, purchased really nice parts. so I thought that I would be able to save a bit and use the heads that were on my previous motor. I knew that they were a bit small for a 408, but really realized it after the dyno graphs, and driving it on the street, and reading the boards. So this has led me to wanting more power.

I am running PRC stage 2.5 ls6 heads with the 10mm yella terras. These are too small for the NA 408, but I see people running stock 317 heads on a turbo 408, all the up to some 235's, then even ls3 heads. For the people running untouched 317, that makes me think my cnc'd ls6 heads wouldn't be horrible. Am I thinking wrong? I can always get a nice set of 0823 ls3 heads which would flow a lot more and not cost a fortune. What are your thoughts? I would love to get 1000 to the wheels. I do need to compete with my bro's car which should be around 1400 rwhp. But only if I gut the hell out of my car, or throw it into a tin can mustang.

As you can see I am just starting my research on this.

Thank you for your opinions.

-Mark jr.

 

Bad cylinder heads can easily be covered up by forcing air through them. Doing your thing N/A..........the cam/head/intake/exhaust combo is really the deciding factor on how it runs.

Thats why you see guys with stock 799/243/317 heads forcing 2-3 atmospheres of boost through them and they seem like such great heads.

 

From your post, looks to me that the operative word is "seems".

What's your opinion on 0821 / 0823 heads for forced induction? I cannot afford $5-7 k primo heads at this point in my life, I'm just a little fish in the pond. I could wait for a decent deal on heads and an intake, run them on my current motor for a few years, and they would also be good to crossover when I am ready to step things up.

Thank you

-Mark jr.

 

TFS 235cc heads would be great on that setup.

 

For 1k just ran what you've got, try not to make 1000ftlb at 3500rpm though, with that many cubes you'll lift them

 

I'm just trying to figure things out a bit now since I made some not so good decisions with my last build. Learned from my mistakes. So even with ls3 heads, there is still a lifting problem at the 1000+ mark, and though I could get better flowing heads which would allow me to make the power easier, they are still limited until I go with an aftermarket block and 6 bolt heads.

If I could lighten my car a lot with 1000 rwhp, I should be somewhat competitive, I just have to come to terms with really gutting a clean low mile car.

I was also thinking about saving these heads for a smaller motor, I have a 35k mile ls1 from my car, and also an ls2.

Thank you for the replies, some things to think about and a lot of reading and learning.

 

You mentioned competitive... Is this gonna be a class car? You'd be better off spinning 8500 rpm on your heads with good valvetrain and bringing the power later on than trying to make a thick casting live at inmense cylinder pressures that come with low end tq, if you do go 6bolt in the future, that valvetrain will still be good for it, a torched good head will not.

 

QI thought that I had the valvetrain sorted out, lunati high rpm link bars, Manton 11/32 series 5 pushrods, 10mm yella terras, good valve springs, but didn't realize my valves were too heavy for high rpm, and saw some valve float @6500 on the dyno. Power was already dropping off by then so the limiter is @6250. Thought I researched good, but apparently didn't. First performance car, always just fabbed and fixed cars.


What I meant by competitive was between my bro and I, and another buddy.

Little backstory, I had my heads / cam 346, th400, 9" car that ran pretty good, and my bro has been building his car for 8 years. When he finally got it done we would race each other and when he could hook, he could beat me on the launch, but from a roll, it was crazy how dead even we were. You could high five each other on the highway without anyone pulling away from each other. He was disappointed since he was running a 461 BBC in a 300# lighter car.

Running my buddy, his was 300# lighter, 460 to the wheels, all wheel drive. No comparison. But he just purchases car built by others, so I wasn't really mad, I could have done that myself to.

So I decided to build this 408, but didn't think my current heads would be so bad. 450/430, and doesn't feel much quicker than before, just added more weight. But as I was building mine, my bro knew that I would be faster again so he started his new engine build.

But instead of a nice competition of upgrading parts, running each other, then keep going that way, he decided to just shut me down for many years. He decided to do an A2w intercooled, 540 dart BBC with an F2 which should be in the 1300-1400 on 93.

After spending almost 13k building this motor ( doing all work myself minus machining and tuning) I just cannot go that crazy, so I figured I a few years if life's decides to go my way, either turn my car into a gutted tin can with 1000 to the wheels (his will always be a full interior car, sleeper) I would be able to compete. I can get my car lighter to help offset the power diff. Or if I can get a bigger place, get a notchback mustang like everyone else and go even lighter. All dreams, just reading and trying to get a better idea on what I would need to do.

Thank you for the reply

-Mark jr.

 

So, with my small flowing heads and running my stock block 408 would require a larger turbo to force that air since heads aren't optimum to get to 1000 to the wheels, than if I had better flowing heads which at least in my head, would be able to use a smaller turbo to make the same power since they could flow more?

 

No, you're overthinking it, ARP studs, LS9 gaskets and a good tune, and I'm thinking you may wanna stop at about 800, which you probably arent gonna be able to hook since you mentioned dig racing

 

Overthinking is my only talent in life

ARP heads studs are no problem, I'm already using them. Need to change Pistons since I am 11.5-1. This summer I am doing some paint and resto work on the car, and depending on time, I may be mini tubbing the car. I am currently running MT 275/60/15 et streets and am very close to rubbing. And now that they discontinued those tires, I am unsure how a different MT will fit. I may be forced to mini tub. Besides upgrading the th400 and 9"

I have a lot of reading to do, at least a year of research. I want to do this build better this time.

Thanks

-Mark jr.

 

The highest HP 408 I've ever been involved with made 1300+ rwhp on an aborted run at 6300rpm with Frankenstein Racing Heads TFS 248cc cathedral port heads.

Had the pull continued and been allowed to make peak power where it was being made on lower power pulls at 6700rpm I guarantee it would of made over 1400rwhp.

This particular engine made 925rwhp on just 14psi of manifold pressure and 1130rwhp on 25psi of manifold pressure and 13-14* ignition timing. Pump gas + meth for fuel.

Good heads absolutely make a difference even with boost. The reason people can make big power on inferior heads such as unported stock castings with boost is because the engine is moving much more air mass due to the turbochargers compressing the incoming intake charge making it denser. Denser charge means more air mass and more fuel can be burned resulting in higher cylinder pressures.

 

the TFS 235 or + would be the only way to go on that. The 243 is no where near enough cylinder head for that deal. And trying to get around it will only lead to more bad decisions.

 

I am just going to have to wait until I come across a great deal on some heads and just drive my slow car for a few years before I go FI. If I find them, I could always put them on my motor along with some diff. Length pushrods and enjoy them until the future and have 500rwhp, though I am sure that I won't even feel that.

Need to step back from expensive mods, would like to own a house some day. Any huge difference between AFR, Trick Flow, PRC, Mast 235's

Thanks for the replys.

-Mark jr.