I'll take the bet on 45psi on the stock LS1. But I want to see 45psi to the back of the intake valve, not with a restrictor in front of the throttle body where you are taking your boost reading.

CFM is airflow and is what makes power. But one can infer greater air flow with higher intake pressure one the same engine. Said differently, on the same engine in the same conditions, 8 psi will flow more air than 5 psi. In nearly all cases, it's neither cfm, nor boost pressure that kills an engine, it's cylinder pressure and/or heat.

To the original poster, you can run as much boost as you like so long as you don't run lean or detonate. I can infer that your stock engine is fundamentally the same as my stock engine therefore speaking in terms of manifold pressure is a legitimate and easy way to discuss infered air flow. At roughly 8 psi of properly intercooled air, I can make a safe assumption that the minute differences in years will not have a great enough effect that you cannot run a good tune and 91 octane fuel. At 12 psi of properly intercooled air, I can make the make the assumption that you should be safe on a good tune and 101 octane fuel. Why can I say this? Because your engine is fundamentally the same as mine and I've done it on more than one fundamentally the same engine.

 

Regarding Fiero and 45psi or 100psi or any other nonsense number he is throwing out...it is nonsense...ignore it.

Compressor flow maps and efficiency at this airflow vs this pressure vs intake restriction are all meaningless. IF the intake manifold saw that level of pressure there would HAVE to be a certain commensurate amount of airflow (CFM) to even get that much pressure into the intake. In any kind of remotely-realisitic situation you'd have a bomb on your hands.

The only edit needed for the first few answers to the original poster was "I think you can run xxxpsi safely as long as your car is well tuned and properly monitored with the right gauges and a smart driver."

 

Yeah, thats well put. And as other forums would say.."it's all in the tune". But in Fiero's defense, we should not associate a motor's limit with a certain amount of boost UNLESS this is a very specific and detailed turbo setup and tune (whether it be conservative or race tune) that has been tested time and time again with a pattern of similar results.

Otherwise, it's much more accurate to associate a certain HP & TQ curve produced given a completely bone stock setup, including RPM's to the stock motors limit. Just like with a rear-end, or a clutch..the individual parts in the motor have a ballpark limit depending upon a few factors such as quality of tune, driving habits, as well as RPM's. Such things are key in how long your stock motor setup will last under any given boost setup.

For instance, it's well understood that a certain specific Honda motor, say a B18C can handle 300whp-320whp boosted for a limited time of say about 20K miles or so before the ringlands, pistons or rods or all three give in. Now how you go about making that 300whp is up to you, and might take you 14 psi with a GT28 or it might take you only 6psi with a GT35R. So you see, in a way, Fiero was exactly right in that psi is not the way to measure a motors limit, but rather...how much freaking HP and TQ your planned on making. The HP reflects the TQ and RPM, the TQ and RPM reflect everything else discussed in this thread, including boost amounts, compression, etc. This is why you need to go to a dyno shop so that someone can make sense of how your motor is running...why? Because the gauges and the TQ curve tell it all. So there you have it.

 

Yup, and the fact is that we have nine years of FI LSx history and experience to draw from, so there is a certain amount of common knowledge that folks use.

So 15 is double the amount air, so a 150hp engine might make.... 300hp... So a 400hp engine might make... 800hp (at the crank).

The differences between a 1.8 and a 5.7 are significant.

 

Good point, but if the intake valve is the proximate restriction on the induction side (And who could argue otherwise), then why can't that be more of a restriction on some cars? It can be, and is, everyday. That's why a BMW M3 makes the same HP as a F-body LS1, down 2.5l. Because the proximate, and subordinate, induction restrictions are not nearly as bad. So he said nothing about what heads he's running, what valves, and what has been done to them. So we should just assume and give him a number? Sounds reasonable to me. How much boost can my 3.4 handle?

Fact is, if his heads aren't stock, they probably flow more. Now his 15psi is getting A LOT more air into the cylinder. So 15psi is safe on my LS1, and just chucked a rod out the side of his.

As I said. You are correct about the airflow statements, but the engines aren't the same. We don't know what intake he is running, we don't know what heads he's running, we don't know anything about the VE of his setup. And you're correct on what blows engines, barring my exceptions said earlier.

Assuming his is fundamentally the same, of which we don't know, then you can make those inferences. But we don't know this, he didn't specify. Furthermore, he's at altitude, and 15psi at sea level is A LOT different than 15psi at elevation. Trust me, I live in Colorado, and run boosted motors up here. I turn my boost up 5psi for 7,000ft just to put down the same dyno numbers. Secondly, he can't run as much boost as he wants so long as the tune is good. I think the OP was more questioning short block strength than his tune. And it is quite plausible to blow up an LS1 without running lean or detonating, just from too much power. The factory castings can only take so much.

More ignorance. Remember kids, compressor maps, efficiency levels, airflow vs pressure ratio, and induction restriction are all meaningless bullsh!t. Just put a T25 on your LS1, because flow numbers don't mean ****, and the T25 weighs less than a GT67. Who cares that a T25 can't break 62% AE? Who cares that the wastegate is about as accurate as your temp gauge? Who cares that it is too small for a 140hp V6? All that **** don't matter!

What are the right gauges? Because I'll agree if they include an accurate airflow monitor, IAT gauge, and a WBO2 reading.

Agreed 100%.

I agree, but we don't know his setup, and therein lies the problem. We don't know his VE, we don't know his heads/cam/intake, so why assume and throw out numbers when it can easily cost him his engine?

Furthermore, your math is way wrong. Just because you double ambient pressure, doesn't mean you double power. I watched a stock 3.4 dyno 176whp, then with the turbocharger, make just over 415whp at 13psi. So explain to me how he more than doubled factory whp, in fact gained 135%, with LESS than double ambient pressure? It's quite simple, your assumptions are not taking into account the variables that affect power.

 

My point as a play on your 45psi statement. I knew where you are going with it. No stock ls1 will survive 45psi if you have that pressure at the back of the intake. Cylinder pressure alone rip the stock head bolts off let alone the bottom end handling it. He did say something about the heads he is running. He said they were bone stock per the title of his thread. And how much can your 3.4 handle? I'm a good person to ask since you bought it from me. Remember my CBR?

That fact is irrelevant. The title of his thread says bone stock engine. To me that means bone stock heads. If he says bone stock engine and has a set of heads flowing twice that of stock and chucks a rod, it's his fault not mine. My advice is based on the information he gave.

Sure we do. He's running a bone stock intake and bone stock heads. If he says so and is running otherwise, again, if he blows it up, it's on him, not me. The advice I gave him was based on my experience with a bone stock engine.

Sure he did. It's in the title of his thread.

That's only somewhat true. It's true if you consider 15psi over ambient pressure. However you have to put X amount of pressure on the wastegate diaphragm to open the gate. At higher altitude where the air is thinner and pressure is less, the turbo has to work harder to get that 15psi but it's the same density in the intake. The is the same reason a supercharged car, which is RPM dependant, makes less boost (psi in the intake) at altitude. Because turbos are decoupled and will spin until a certain pressure is archived, all things being equal, you will have the same airflow/density through the engine.

Perhaps but that wasn't the point of my post. My suggestion is that he focus on his tune. I'm not here to hold his hand through the development of his install. I feel safe making the assumption that he isn't going to try for 1200hp on a stock engine. My post also gave him suggestions of boost level that have been proven said with due diligence.

It's interesting that you turn up your boost up 5psi to put the same numbers down because I change altitude 2000 feet and put roughly the same power down at the same boost level, for the reasons listed above.

 

the same way some people on here are making 500 rwhp @ 5psi while other are making only 450 rwhp. just like you say, there are variables. but....

the math is right but it never works out that way due to, like you say the other variables. but its just a common rule of thumb for guessing. but it does make perfect sense. but nobody can magically double their ambient pressure without mods. the math would maybe be spot on if you took a stock engine, dyno it, then using a external source, add a constant one bar of pressure and you "should" have doubled your power. engine= air pump. double air= double power.

i have another question. on topic and off. some are saying between 500-600 rwhp is reliable. is this different for a n02 ls1? im just wondering cause that is my goal with cam/spray. about 420-430 rwhp on motor / 550+ rwhp w/spray. again, it must be reliable. its a DD car. it wont see the spray that much.

 

Agreed, and I knew where you were coming from.

No way! I completely forgot your CBR. I can't remember at all a speedometer climbing faster than the readout could keep up, front wheel lifting in every gear I tried, my hands shaking uncontrollably for a half hour after I shut it off, and almost not being able to go wide open because that f*cker was pulling so damn hard

I remember. Goddamn do I remember. Like it was yesterday. I'll drop you a PM on the Fiero 3.4 stuff, no need to go into details in this thread. And I've got a LS1 now too

I should try reading more. I = owned.

You're right. However the reason for the lack of power at altitude, is not because the air is thinner but because the actual oxygen content of the air is lower at higher altitudes. It does have to work harder to get to max boost, I'll spool about 500-800rpm later than at sea level. I did the calculations a while back, and at 6,000ft altitude (~CO average), a turbo car would lose about 11% from sea level, and a N/A or supercharged car would lose around 21%.

I agree that he focus on his tune, but to blindly put 8psi in it thinking it will be fine is not what I'd do. I'd much rather trust the power numbers, and try not to exceed the 500rwhp mark (Assuming that's the safe max). I wouldn't worry where the psi gauge is at to do that.

My friend's GT30r Cavalier needed the same thing. This altitude crap sucks! I'll figure out the DA when I get time, because I bet is is significantly higher than altitude alone.

 

Running off at the mouth again I see. My contest with you is the 45psi and a small throttle body nonsense. This contest has nothing to do with your "T-too-small that could make 45psi on an LS1." This is about ANY combination, on this planet, that could put 45psi in the intake manifold of an LS1...that combination would make nothing more than a grenade.

You quoting flow numbers to me is nonsense (as I said), because a T25 couldn't make 45psi on a 5.7L V8, ever heard of 'compressor stall?' That little weed-eater turbo would be such a restriction that I doubt a large V-8 would even run with one...oh wait, you didn't mean that as a serious example, right? You sir, should spend less time telling others that THEY are wrong and try to share some useful information.

There is a reason many domestic guys hate imports, and a reason they hate guys that drive funny little cars...it's because those who drive them have an attitude that doesn't lend well to the community at large (Neither does that Brospeed exhaust tip, by the way).

 

It'd only be a grenade if that 45psi made it into the cylinder. But with even a stock LS1 you aren't going to get more than 36psi past the intake valve.

A T25 could easily make 45psi on a 5.7l V8. Just put a 2" plate to block off 67% of the throttle body. If that doesn't work, use a 2.5" plate.

Maybe do a little research. My "funny little car with that Brospeed exhaust tip, aka highly sought after SLP CME":

 

I don't think that anyone is getting help from this thread anymore. Mods please close this pissing contest.

 

I'm kinda feelin' like you guys took Fiero's post about "45psi into an LS1" and ran with it for miles. I believe he was alittle over the top, but his point was not that 45psi was possible, and especially in a bone stock LS1, but rather that 45psi in Garrett's smallest line of turbo's is probably puttin' out an 8th or 10th of the total HP of 45psi in Garrett's largest line of turbo's. (With the assumption that a baby turbo could even operate in those pressures, although in reality it cant.)

The first impression I got from this statement was that psi doesn't matter, but more so CFM in this case. And yes, I realize CFM is not the sole indicator of the engine's reliabilty..but CFM IS a good indicator of the amount of HP your making, or at least what you could be making, right?

Well, then..let's brain storm a bit..if CFM is an indicator of HP potential...not PSI..you guys already know what I think about HP..I think the HP ultimately reflects how the rest of your setup is working...and also..this is where PSI get's it's nifty credit...

If you make good HP on such a low boost, then you have a good tune..therefore you'll more than likely have a pretty reliable setup, or at least a fully functioning setup. If you make bad HP on a rather high boost, then you probably have a bad tune, which means your reliabilty is more than likely bad.

We shouldn't generalize so much to the OP when the surrounding influences of this "bone stock LS1" setup is so general. But since this thread is so generalized..I'll be glad to add alittle detail to my thoughts.

He's using a T67, right? Well, this ain't no slouch..and with two I can imagine a potential 1200rwhp setup. My point..it will be very easy for him to see 500-600rwhp (which to me is the limits of the LS1 in stock form assuming you want to count on the fact that it will crank everyday and get you to where you are going)..much sooner that 15psi..probably more like 7-8psi..but it really depends upon how competent his tuner is. I would tell the OP to start as low as possible with a boost controller and work my way up to 550whp..then immediately go buy some meth injection and slap it on-->call it a day. Don't ruin your motor by taking advice blindy and solely from people telling you to boost 12psi on that kinda turbo setup. Seriously..stay in low boost, stay away from heat..and tune good. Besides..if you have a good tuner..he won't let you boost any higher (HP wise) than what I'm telling you without warning you first of the possible consequences.

All of you have some good info..but pertaining to the thread..Fiero clearly overrides with his point about measuring reliability...seriously..boost numbers are ALWAYS generalized, because there are so many factors which are different for everyone's setup. It's not accurate to say a certain boost range is safe for the motor in this particular case, unless you include ALL of the boost range, from 0-15psi.

Mr. OP- Your turbo's are not gonna start working to their full potential till about 16psi or more. These turbo's are a handful for a stock LS1, keep that in mind when you go to boostin'.

 

yeah, I'm about to take a dump on this thread as of now.

 

They are specifically talking about the STS t67 on stock motor, so it's ok. He does need more fuel though.