"Safe" PSI Questions

[ScottsVaporGT]

I have been trying to find definitive answers on this but I am not having much luck. I am trying to learn about the FI route and have questions about PSI. When running a FI setup, on a stock motor, more hp for less psi is desired correct? So if I have supporting mods (bolt ons) and can make say 500rwhp on 9 psi, is that better than having no bolt ons and making 500rwhp on 11 psi? I am just throwing out some numbers to try and help me understand, so they are probably not accurate. What I am trying to figure out is, is it a "safer" 500rwhp by going bolt ons and lower psi or just going straight boost?.....or am I completely off all together, and those situations cannot happen?

 

[dysan]

This is a question that's asked quite often and there is no real definitive answer. You've got things like slight differences in tolerances in each engine, how your engine in your car has worn during it's use, and the tune plays a HUGE role in reliability as well.

I believe you're better off with lower boost and adding supporting mods to get you where you want to be. LT's, cams, etc.

There are many people on here that know a ton more than I do (since what I know is from reading everyone else's posts) so hopefully some others will chime in.

 

[JeremyH]

When running a FI setup, on a stock motor, more hp for less psi is desired correct?

Depends, thumbrules: 10psi or less, less than 500rwhp. Are considered "safe" but as stated that all depends on tune and timing and every car's tolerance and engine characteristics will be different. Car may run for a year at 500rwhp, where car b may blow after a month at 475rwhp...

So if I have supporting mods (bolt ons) and can make say 500rwhp on 9 psi, is that better than having no bolt ons and making 500rwhp on 11 psi?

Heres the deal psi or boost is a measure of restriction at the manifold.
An otherwise stock engine with a blower will make lets say 450rwhp on 10psi. Make the engine less restrictive (ported heads, high lift cams, longtubes, no cats, etc) And now it will reads less boost 7-8lbs but makes more power lets say 500rwhp. Granted the boost u read is less the extra power is what u gota pay attention to. Too much hp and torque on the stock engine as well as heat (detonation) is what is going to kill the engine.

So basicly keep it at 10psi or less and 500rwhp or less with a good/safe tune ie: average timing 15* max and a good air/fuel 11.7-11.5. And that will help keep the engine together lol

 

[LuckyH]

Stress is the main failure of a stock block s197. To be more specific, the rods typically break first. A certain amount of boost isn't the end all be all sign of how safe your car is. Things like shock (often seen in drag racing) will have an impact, as well as how high you are revving the motor. The amount of force put on a rod is a lot higher at 7000rpm than it is at 6000rpm. Not to mention with an rpm based power adder, one could be producing 10lbs of boost at 6000rpm while another is producing the same at 6800rpm. Same boost, different amount of stress being put on the rotating assembly. Also the duration of the stress is a factor, a road course car could depending how driven put more stress on parts due to the longevity of run time under duress. Road course cars can generate lots of heat for long periods of time, even if oil coolers are used. Same being said, a road course car will see smoother inputs (i.e. less shocking) than a drag car. So there are trade offs and too many variables to get an exact figure on what's "safe".

 

[Bullitt3478]

The limit on our stock internals is a mixed result here for sure.Some people say 450 rwhp but others are making far more with good results.Now if you achieve this magical limit number with bolt ons and low boost I personnally would think it would be less stressful on the motor.With that being said I am not an expert and this is just my opinion....As far as expense you can bolt on just about any supercharger or turbo system on the market and make enough power to blow these motors sky high and you dont have to turn up the boost too high to do it.There are a whole lot of guys on here that know far more than me and who can tell give you more first hand knowledge than me.Just my

 

[US-1]

Safe psi on stock shortblock = 0

 

[LAllison20]

OP, the main thing(s) ive learned about reading the many posts on this topic is this. If you cant afford to replace an engine, stay away from F/I. Do it the right way the first time, forged internals are your friend, and choose who tunes your engine wisely.

 

[ScottsVaporGT]

Heres the deal psi or boost is a measure of restriction at the manifold.
An otherwise stock engine with a blower will make lets say 450rwhp on 10psi. Make the engine less restrictive (ported heads, high lift cams, longtubes, no cats, etc) And now it will reads less boost 7-8lbs but makes more power lets say 500rwhp. Granted the boost u read is less the extra power is what u gota pay attention to. Too much hp and torque on the stock engine as well as heat (detonation) is what is going to kill the engine.

So basicly keep it at 10psi or less and 500rwhp or less with a good/safe tune ie: average timing 15* max and a good air/fuel 11.7-11.5. And that will help keep the engine together lol

So your saying that the actual hp number is also a factor, not only the boost?

I see so many sigs with people running "x" amount of boost and making "y" rwhp and people running "z" boost making the same. I was just wondering what factors made one produce more, and if one is better/safer than the other. Through reading I do understand that FI is not good for the motor by any means, and that there is a general rule and breaking point, but I was not sure if it was the actual hp numbers or boost that is making the problems.

So IF we could make our motors have 500 rwhp n/a (just throwing a number out) would there be less of a chance of blowing, as apposed to a FI motor making the same power?

 

[kahmann]

Safe psi on stock shortblock = 0

This.

OP, the main thing(s) ive learned about reading the many posts on this topic is this. If you cant afford to replace an engine, stay away from F/I. Do it the right way the first time, forged internals are your friend, and choose who tunes your engine wisely.

This.

So your saying that the actual hp number is also a factor, not only the boost?

Yes.

I see so many sigs with people running "x" amount of boost and making "y" rwhp and people running "z" boost making the same. I was just wondering what factors made one produce more, and if one is better/safer than the other.

Your original post contains the answer to this question.
You can make more power with less boost depending on your supporting mods. Does that make 500 rwhp inherently 'safe' on a stock block? Nope.
Good luck.