Ok so i am wanting to know what the limits of a 408 are NA on pump gas. Also what top end could do it. I was thinking something along the lines of small bore LS7 heads and a spec'd cam with matching intake but i just dont lnow. Im trying to get 600rwhp NA. Now i saw one of Tony Mamo's 383 put down 525rwhp NA. Now my thoughts are if one can squeeze 500 hp NA out of a 383 couldnt one get 600 out of a 408? Whats Techs opinion on this?

 

What's your definition of pump gas? Does that include E85?

If you go with like a 13.0 CR and the best heads available and a cam in the 26x/27x with a sheet metal intake spinning close to 8k you might get there.

 

I havent really thought about e85. I was think more along the lines of 91 octane. I know the highest u can go with that is 12.0:1. If my math is correct i would need 690hp at the crank to get 600rwhp with a 15% parasitic drive train loss.

 

On a happy dyno I think it's very possible

 

You could, but you would need expensive parts and expensive people. That power per cubic inch is pushing the limits of pump gas.

 

I know i need a new very pricey top end. But is a forged bottom end too heavy?

 

Um what? Why would you think that? What do you think goes into 1000hp NA race engines?

 

Because ive read some threads on here that say u sometimes need expensive light weight rotating assemblies. Am i missing something?

 

I have a feeling that you'll be missing lots of $$$. Forget NA at that power level, too expensive, look at FI instead.

 

i got 724HP 602 ft. lb torque out of 425 cu. in. LS2 block. Eagle rotator. LS3 heads ported by bowers out of Ft. Collins. Holley tall efi intake, 92mm intake. I think we used 45# injectors. 91 Octane at 3800 ft. elevation. Gibbs oil. lots of dyno time. Lots of ZOTARS $$$$$$ The holley tall efi intake is a tight SOB in a fourth gen.

 

Not really a need for that. Just shelf rods and pistons will be fine. The extra attention needs to be paid to the top end, but that's not to say that the shortblock needs to be assembled properly with respect to frictional losses.

 

I appreciate everyones advice. Now my 408 is a fully forged short block with arp 2000 fasteners used. The short block was built by Thompson Motorsports. As it is right now it has a 11.2:1 compression ratio with LSA heads so id imagine i could bump compression quite a bit with a smaller chamber.

Now i have looked into Forced Induction and it would cost about 7300 for the procharger, injectors, fuel pump, intercooler ect. My issue with FI is my compression ratio is a bit high, id run out of octane on 91, and i could only run about 10 lbs boost before i exceeded the rating on my short block. I would imagine 7300 would get me pretty close to my NA power desire. And if i wanted to run a power adder i could run direct port and spray my way to my goals for about 3300.

How does one determine a max rpm for a engine if u take the valve train out of the equation?

 

Also what heads would give me the best chance of hitting this? Like what is a good head to start with then have it thoroughly worked over.

 

A buddy made 540 rwhp on a Mustang dyno with a 410 six speed 12 bolt combo, that's 560-570 on a Dynojet through a full 4 inch Mufflex ex.

ETP LS7 style heads, stock LS7 intake.

So he's in the upper 600's.

 

Just don't spray my way

 

Where would one find ETP LS7 heads cause i keep hearing about them but i can never find a website for them.

 

Mast Motorsports bought ETP.

 

Mustang dynos can be calibrated to read within a certain percent of a dyno jet, and usually are. Still impressive.

 

So can i buy a set from Mast because i checked Mast's website and the only small bore heads i saw were for a 4.060" bore.

 

Making that kind of power is going to require about $6500 in heads and intake. Solid roller. so another $1200 in cam and lifters. 8000 rpm Nothing gets cheap about it. Trust me I am looking at $5000 out of pocket to sell my stuff and put a set of full tilt mast heads that will make 760-770

Tim