View Full Version : Most boost I can safely run with a stock engine??

04-12-2002, 09:23 PM
Whats the most boost I can run without have any problems?? Any input on the subject will help.Thanks.

04-12-2002, 09:42 PM
I would say 9-10 LBs. I ran 12 lb and lifted the heads.

04-12-2002, 10:09 PM
Was the 576rwhp with the bigger pulley?

04-13-2002, 04:22 PM

there is no official number for a safe boost level.

you need to specify timing, fuel system, octane requirements, etc.

you can easily toast a stock motor on 5 or 6 psi if you don't do things right.

Teddy D
04-14-2002, 01:43 AM
This is another statement that needs more depth to answer properly. When you say "how much boost" you have to realize this depends on octane, fuel pump, injectors and tunning with FMU or maft.

Teddy D
04-15-2002, 12:29 PM
Most places that sell supercharger kits, or turbo kits and install them should know the limits.

I understand you wanted this to be an easy question, so I am sorry for the elaboration but this stuff is never simple. If you want super simple pay the cash and play then get a 420+ cube motor.

If you want to make max power with a stock engine and 93 octane, then you will need a better fuel pump(or puller pump in addition to stock) and bigger injectors. This is the stuff you will need to ask the shop you are planning on buy from.

04-16-2002, 12:06 AM
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by VINCE:
<strong>Was the 576rwhp with the bigger pulley?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">That was with the smaller pulley (2.75"
It was running very lean 14.2:1 over 6k rpms.

04-16-2002, 09:31 PM
A C5 just burnt up a piston running 12#.

8-9 is where I'd be ok.

Black LS1 T/A
04-21-2002, 08:45 PM
My vote is 7 or 8 lbs max is safe.

Any higher, you have to keep up with increased octane requirements and the margin for error is narrower.

Also, the head gasket stresses. That's what I'm hearing guys say.

My 2cents. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

04-21-2002, 09:51 PM
I agree that 8lbs is around max for stock bottomend.. If you had a forged setup then you could boost more, but then more pcm programming is required.. Fuel requirement is a biggie as well.. So many things that come in to play when it comes to FI, but when it is done right you will never stop smiling..

04-21-2002, 09:53 PM
Is it really boost related tho?
What if you have long tubes, hi-flow cats, etc and use a 10# pulley but only see 7-8#?

Still safe? Does less boost put less stress on the engine and have less detonation even when flowing more air at lower psi with better airflow?

04-21-2002, 10:18 PM
You just answered your own questions? If you put a 10# pulley on the car, but only see 8#'s then you are only running 8#'s of boost. If the car is running fine then you are o.k. If you try to get the 10lbs out of it you might have to make some other adjustments to reduce any possible complications..

04-22-2002, 01:30 AM
Guess so.. Just thinking out loud, LOL!
Lowering the psi thru airflow reduces detonation/tuning complications, eh?

But still hard on the bottom end past a certain point.. as much as the bottom end can handle rwhp. Guess you just separate the tuning issues from what the engine itself can handle without blowing up on the rotating assembly.

Less chance of burnt pistons, rings, running lean, etc..

More flow would give the same power and reduce fuel requirements? Not sure about that one.. What does the LS6 intake flow anyhow?

04-22-2002, 01:50 AM
I do not know how much the ls6 intake flows, but others say it is a must for FI..

Black LS1 T/A
04-22-2002, 07:54 AM
While it can be true that FI can make an actually softer hit on pistons, etc, than an equivalent powered heads/cam setup where the Static Compression Ratio matches the Static Compression of the h/c.

But, Jason of Golden West Performance tells me when your motor is producing in excess of 600 RWHP (an approximate figure for sake of argument), you can STILL have issues such as lifting heads, etc, even if your boost is nominal (say 5 to 8 PSI), such as may be the case with a stroker/borer.

Just a side-thought, there... <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

04-24-2002, 02:32 AM
The question is how do you prevent the lifting of the heads?

04-24-2002, 09:50 AM
im hoping studs will help along with no detonation

04-24-2002, 07:23 PM
I melted a piston with the Vortech #9 (No pulley change), reading 6 p.s.i.. I had detonation briefly at about 6000 r.p.m. while racing and then had an engine miss which turned out to be the piston. I had 93 octane with 104+ octane boost. I am a mechanic, but am new to this forced induction game. I was suprised at how quickly and easily the damage was done. I'm in the process now of getting my car running again. Whichever way I go it will be with forged dished pistons.

04-24-2002, 07:32 PM
Stock pistons will go in a heartbeat. I found that out with high compression heads.. I always run 93 octane, but ruined 3 pistons in a matter of seconds.. I am having my shortblock built right now with forged internals.. I am going to be ready for that detonation this time.. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

04-25-2002, 01:34 AM
Yep. You have to realize that power is a result of controlled combustion pressure anyway you look at it. You always trade power for longevity.

Car Craft had a cool article about Top Fuel cars, how many passes each part lasts and how much they cost.

I think pistons lasted 12 runs. Plugs for 3.

Andy West
04-25-2002, 06:46 AM
I learned that supercharging is very tempting but not always good, eventually most people fry their motor. I spent the extra cash and bought a 383 LT4 with really beefy rotating assymblies, converted splain 4 bolt mains... (the works) I even got it 9.1:1 CR and matching cam if I ever want to supercharge it.
I found that my 383 with LT4 heads, etc. makes as much power as a 6-8 psi supercharged stock LT-1 and I REALLY doubt I will be frying anypart of my motor anytime soon.

My opinon: supercharged stock LT-1 or LS-1 x time equals needs new LS-1 which equals, alot more money than i spent for 450 Horsepower.

04-25-2002, 07:38 AM
If longevity is what you are looking for then stay NA and keep the compression down. I was a NA person myself until I started having engine problems. This time I am building a stronger shortblock. Boost will come later...

04-25-2002, 04:59 PM
You must remember, boost deserves respect

While some FI setups are more reliable than others, mechanically that is, they all require some thought.

You can't bolt them on, turn up the wick, and expect things to live happily.

You must maintain a well tuned setup. Proper fueling, advance, boost, and octane. The second you don't stick to the requirements you break things.

I ran a stock longblock to nearly 600 RWHP for 25k+ miles, daily driving it. But i kept the setup the same. Low timing, plenty of fuel, and mixing 110 in EVERY TANK. That was on 10 to 12 psi, every day.

I could have run straight pump gas on 8 psi, and made 500 RWHP if i felt the need. If i wasn't near the stations with good fuel, i turned down the boost. Simple as that.

You must respect boost, especially on stock parts.

04-25-2002, 05:24 PM
I agree.. I respect the boost..

04-25-2002, 06:13 PM
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by VINCE:
<strong>I agree.. I respect the boost..</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yup, and inject Alky for an extra margin of safety!!


04-25-2002, 08:05 PM
What this alky I keep hearing everyone talk about? How much does it cost? Do you guys run it all the time? What does it bring your octane up too?

Black LS1 T/A
04-27-2002, 06:46 AM
Vince, The guys that are tying it are saying they beleive all the gains to be due to increased ignition advance, true. They say the water/alcohol slows down the combustion process, much like high octane gasoline, but I don't know that you can say the octane of the gasoline is raised.

One guy said he heard audible knock on hot days without the injection, yet never heard another "ping", no matter how hot the engine got or the ambient temperature, after the injection system.

04-27-2002, 07:41 AM
Is this a system or what? What money are we talking about?

04-27-2002, 09:23 AM
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by VINCE:
<strong>Is this a system or what? What money are we talking about?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Do a search on Alcohol Injection. There are a couple of individuals on this site that pioneered inexpesive systems that allow them to turn up the boost without causing problems.

The Alcohol has a cooling effect on the intake charge. One person dropped significant heat from the intake charge and stayed out of detonation.

It's what I'll end up with after the single turbo install.


04-27-2002, 12:13 PM
That sounds like a winner..