when i install a turboback, do you think i'll see 1 or 2 psi decrease? that would put me into a safer boost range.

 

No, the boost will go higher due to less backprssure, but it doesn't matter - you have an MBC, so you can set your boost wherever you want. Not sure why you'd be hoping that the exhaust would lower your boost when you already have full control of boost.

 

I've been running 24.5 - 25 psi for six months now with 92 octane on the stock exhaust. Sure, its not ideal, but it works fine for street use and does not cause any tuning issues. I'm knock-free (ok 1 or 2 knock counts) throughout the entire boost range (2500-7000 rpm). I've seen way more knock counts on my friend's VIII that is custom DynoFlash tuned for 22.5 psi and is running a Buschur TBE.

I just switched over to a Random Tech HFC a few weeks ago and noticed better top end performance.

 

Doesn't mean it's a good idea. In fact, it's a very poor idea to do that on 92oct. You can make plenty of power with normal boost levels - those are race gas boost levels. Whatever power you're gaining from running the turbo so hard is being lost in the required conservative tune. It's a give and take, so why not have a more aggressive tune with more reasonable boost levels. Shoving all that boost through the stock exhaust just doesn't make sense - not sure why you'd want to do that.

 

prior to actually getting the tune i expected the results to be about 23psi, i think i'll be turning it down for now. long shot, but who was worked with the AMS MBC and how much of a turn do you think it would be to drop 2-3 psi? 1/4 turn? 1/2 turn? i didn't actually touch it for the tuning and at install we left it at the lowest possible setting.

 

Not sure what 92 octane has to do with it being a poor idea when there is no knock. The real issue is whether I'm pushing up the EGTs by using the stock exhaust with this much boost. I'm sure that the EGTs are higher with a stock exhaust (compared to a 3" exhaust), but as I said, for street use, its fine. I rarely boost for long periods of time. Yes, my car runs less ignition advance to deal with the higher boost levels. The optimum balance between boost and ignition advance for maximum power is far from clear cut. I've seen no proof that less boost and more advance can yield more power than a higher boost tune.

 

Okay I am not gonna jump in the middle of the fight about stock exhaust being bad and such, but I am gonna just add some tech.

High boost and less advance by itself dramatically affects EGT's
Corked exhaust with a high backpressure co-efficient raises EGT's as well.

So everything added together is that while you CAN do it, might not do it for long stretches, can do it without knock, IT will in fact shorten the life of the turbo.

Warr-I am used to seeing NW cars that are all 20.16psi like the brochure says. 19psi is lower than 20.16. It is obviously a fact that all IX's are not equal. I will quit assuming that all IX's are like my freak of an MR. Thank you for the reminder about assumptions.

John

 

I'm sure it common knowledge but see now that you are saying that some IXs are rated low. What kind of enviroment were these stock IXs in when they were dyno'd high? I'm sure that not all IXs are going to be high on the dyno due to what kind of dyno, enviroment, control measures, etc, so where does this leave the issue? Only with a ballpark of what a completely stock IX whp is? Probably beating this topic a little to death now but just want to get it straight.

 

I asked this question to, cause I thought I was boosting really high for all stock, I bought my car in AZ and it maxed a little above 21 almost 22 PSI, I currently live in DC and it still maxes a little above 21 PSI, a hair lower than AZ

 

sorry i forgot to repy to your PM on h-i but i'm not too sure with ams's boost controller. it's really just different for every boost controller. you're going to have to turn it down a few clicks, check your boost, repeat. i know with my forge boost controller, turning it like 5 clicks barely moves the boost at all. it moves in fractions so it'll probably be at least a good 10-15 clicks if you want to knock it down 3 psi.

sorry, but i really have to disagree with you KevinD. That is really a lot of boost to push through stock headstuds. My friend on here, Lowness, boosts high on race gas as well but even he knows it's not a terribly smart idea and doesn't do it too often. I'm hoping he will get some headstuds soon because I don't want him to have to go through the headache of blowing something up because he took someone like your's advice.

 

haha kee1pride, how much of a difference do you think there is on the strain of the headstuds between 23psi and 25 psi?

as an example, evo8RA on here runs 28psi regularly with race gas autocrossing. completely stock engine, stock turbo, no problems.

 

I didn't say the other way would yield more power. I said it would yield AS MUCH POWER while being at much safer, more reasonable boost levels. That's without even getting into the EGT issue. If you even know that your method is bad for EGTs, then why do you do it? Your justification is because you don't boost often? Not a very good justification, imo, and a poor example for others who don't know any better.

Hurley, if you have the MBC set to the LOWEST SETTING and are hitting 25psi, then you have a problem. The lowest setting should put you at minimum boost, which is 11psi. Are you sure you don't have it at the maximum setting?

 

If you're running over stock boost it just makes sense to replace the stock head bolts that are in place to hold up to the forces being seen under the oem pressures. Can you at least see the logic in this?

Many don't wan't to get their hands dirty with their Evos, they think that magic will prevent failure. Sadly the only way to come to the realization that there is no fairy god mother keeping your car together is when you personally experience a mechanical failure.

Comparing the safety margin of an evo running high boost on pump gas and one running the same on race fuel is not logical. Then again, the mentality behind running 28psi on stock turbo is one I don't really want to delve too deeply into. Sure people do it but most of them don't care much about badly they are pushing the compressor past it's efficiency range.

 

question, have either of you ever bench tested a head stud to check its yield strength? it would be awsome to get an engineering student to compare a stock head stud to an aftermarket headstud. anyone have an instron in their garage?

personally i don't replace parts just because i've moved beyond OEM. i would never do it because a salesman or shop told me to either. if that were the case we wouldn't be using the stock internals either now would we? we would all have fully built engines with stock turbos.

 

nice.