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Bryanthehunter November 22nd, 2013 01:44 PM

boost on lower end
I've heard to many different answers on this question and I have used the search on here and many other forums so please don't say "ever heard of the search bar".

what psi can the stock lower end with stock internals handle safely? it's an 87gt.

What psi have you pushed it to?

flattusmaximus78 November 22nd, 2013 02:21 PM

Psi is 100% irrelevant to longevity.

Z)OoM November 22nd, 2013 02:42 PM


Originally Posted by flattusmaximus78 (Post 6468794)
Psi is 100% irrelevant to longevity.

^-- This.

On another note, the 302 block splits around 500whp.

Bryanthehunter November 22nd, 2013 07:43 PM

I understand that and I do know they tend to split anywhere from 450-550whp but I'm really just looking to see what everyone else has done on stock lowers and how long it lasted.

WillyT November 22nd, 2013 08:20 PM

30 pounds. Lasted 5 years.

---------- Post added at 07:20 PM ---------- Previous post was at 07:15 PM ----------

No, but seriously, there's no good way to answer that. It depends on a lot of variables:

1) How the car was treated since day 1

2) How the engine is tuned after the boosty boost is added

3a) How the car is driven once the boosty boost is applied
3b) How far up into the RPM range you push it
3c) How you shift

You may get years of enjoyment, you make get 30 seconds of enjoyment and then tears of rage as you leave a trail of oil and bearings behind your car.

TPowers6 November 22nd, 2013 08:35 PM

I think its more in the tune and how hard you drive it.
I know people that run past the 500 mark with no issues.
and some that blew well under that.
Mine has been at 9 psi for 4 years and that put it past the "safe zone"
with no issues.

rhino0487 November 23rd, 2013 03:48 PM

My bud has ran 12-13 psi (maybe 14 on cool nights) with gt40's on a stock bottom end with 110,000 miles. He drives the sh## out of it and it just keeps going. Its been a little over two years and he drives it for three seasons a year almost daily and sees the track every 2 weeks. He would not be doing it if he didn't have a second motor waiting to go in though. The stock bottom end can take plenty of abuse if your engine is in good shape and your tune is decent but you should only push what you feel safe doing. I have another buds that took a dive at 9 psi so pressure is only one factor.

Old man November 24th, 2013 06:27 PM

You will get all sorts of answers because blocks split from pressure on the crank more than any other factor. If you put soda straw port heads on a block and a small cam, you can run 15 pounds of boost and not have much cylinder pressure pushing things apart.

They do not fly apart based on horsepower or boost. They fall apart depending on the particular block, the tune, and how much pressure the pistons are pushing down with.

If you have a good crank and make torque at high RPM, you get a lot of power without splitting a block. If you have a low RPM engine and use nitrous or boost to make power, you can break a block with less than 450 HP. It will just push apart.

I had a stock 100,000 mile 1989 302 (stock has forged pistons). I put TFS heads and other good parts on it, and an F cam. I ran 8-10 lbs of boost and it was fine. At 14-15 lbs it would constantly lift the heads off the block. It eventually broke the block.

I'm sure if it had small port heads and less cam, it would have been OK at 15 lbs. But better flowing intake and heads means the boost gets into the cylinder, and the pressure on the power stroke goes way up. This greatly increases torque, but it also pushes the crank downwards and the heads upwards in proportion to that extra torque making pressure.

If you don't let the air in, the boost is not nearly as relevant.

Bryanthehunter November 26th, 2013 05:15 PM

well Im sure some of you have seen my other threads but I'll be running

ford racing x303 64cc heads
cobra lower intake
and kenne bell 1.5 with water meth inj.
full exhaust

I think the most I could really run with the kb1.5 is 10psi so from what I'm getting that should be just fine without high compression heads.

nxcoupe November 27th, 2013 01:35 PM

I installed a D1 procharger on a stock except for exhaust 93 coupe. It made 15 psi. It lasted for 2 years and then we put in a 331 Rblock. Engine was tired when we pulled it.

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