Recently have been making some changes to my pickup. I was doing a cam swap, fuel system and some other changes. I have an master power t76 turbo now. At 12-13psi with 8.8 compression runs consistent 12.20's. I had planned to turn up the boost with a new fuel system, but I pulled the pan and low and behold I didn't have the crank and rods I was told was in the motor. Now I'm nervous to push higher boost on the stock rods.

So here's my dilemma. I don't have enough money to buy a new rotating assembly and new hot pipes to go with the 408 so I can run a bigger turbo. I had planned on putting on a turbonetics 76/76. I'm pretty sure that is the biggest I can run with my pipes. So could I run that 76/76 on a 408?
Or... Do I just buy a new 370 assembly and stick to my plan? I was hoping for 18-20psi with the 370. Shooting for anything 800+. My goal is 11.50's or better.

Would the shorter stroke 370 be faster than the 408? I am running the 317 heads and with 15cc dished pistons the 408 would be higher than planned compression around 9.8. Where my 370 will stay at 8.8.

Any advice or opinions appreciated. Just don't know which way to go now.

 

I think 800+HP is a reasonable goal for a 370. IMO you don't need a 408 to make that.

 

I would stick with the 370. Lots of guys hitting big numbers on 370s. Also leaves you some room to rebuild if it blows up. Think about it this way. Boost is a matter of simple percentages. In a perfectly efficient world roughly 15lbs of boost will increase your power by 100% vs NA. 7.5lbs will increase power by 50%. You get the idea. This means if a 370" makes 400hp NA then with 15lbs it should make 800hp. A 408" makes 450hp NA then with 15lbs it should make 900hp. Of course we don't live in a perfect world and variables will effect this situation. I think with your current turbo and funds situation swap in some better rods and crank up the boost a little bit. Your stock crank should be fine at the 800hp level.

 

Basically for every atmosphere of air is 100% hp increase. I get that. Makes sense. You wouldn't use a forged crank? Just arp mains?

 

Stock crank will be fine. I would stick some ARP mains in it if it was me.

 

Every additional atmosphere doubles the ci size of the engine.
370ci @ 15psi is 740ci
408ci @ 15psi is 816ci

 

I'd do the 370, but bump that compression ratio up to at least 9.5:1, tune the **** out of it & let it eat. Your 11.50's should be in the bag.

Stock crank will be fine, get some forged rods for peace of mind. I think the turbo you already have will get it done.

 

What rods do you have. They changed around 04ish. The later ones are better than the early ones.

 

They appear to be the stock 03 rods. The pistons are diamond -15cc with factory wrist pins for the stock rods.

I am really debating just putting in a full rotating assembly. If I have to buy rods, then pistons to match the aftermarket rods, might as well put in a forged crank too.

I went to a different machine shop today and the owner told me he could get some scat rods that would go on my pistons. And he thinks like most of you to keep my stock crank.
He also told me about a forged Chinese crank that he gets. They come raw and he machines them out. He said they are the same cranks that eagle and another brand use. I'm not sure if this is true or not but he told me I could get that crank for a smoking price. Which scares me. But he has a few trucks around here running them and I talked to one today. He is running this same crank in two cars. A 9 second camaro am a lifted 408. They guy said they have both been tested pretty hardcore with boost under turbos.

I still can't believe my motor has made it this far with just aftermarket pistons in it. I have been running around 13psi for over 40k miles in extreme weather. And before that, it ran for about 10k miles with a sts setup at 8 psi. To me that kinda proves to me how strong these things are.

 

I was a little off. This is good info. Thanks. Now I just need a lsx 454 running about 30psi! That would move out nicely!