Why are we limited to 15psi on pump
 

A few of my buddies have EVO's and they have all the bolt-ons plus a remapped ECU and they are running 22-23 psi on pump gas. I know alot of the supra guys are running around this level of boost on pump also. My ex-girlfriends 1.8T GTI that I had rechipped for her also ran around this level of boost on pump gas. This got me thinking.

Why is it that we are limited to about 15psi on pump gas? If you have enough fuel and proper timing for the desired boost, why is it that 15psi seems to be the "universal" safe limit on our cars? Im not limiting this to the stock twins either as I know they become very inefficient much past 15psi, but most of the single guys also use this as the safe threshold for pump gas.

Is it due to the "fragile" nature of apex seals and ppl use this as an extra margin of safety? Is it due to the excessive heat generated by the rotary that makes it more prone to detonation at a given psi vs. a piston engine?

I know running water/alky injection raises this level, im talking strictly pump gas.

1. The other cars you mentioned have effective knock sensors, the FD no longer does once you have a standalone ecu.

2. Piston engines are more durable to knock than rotaries.

3. Detonation is more prevalent in a rotary due to the combustion chamber design -- IIRC.

BTW, the Evo may boost high but it also rolls off the boost at higher rpm to save the motor (in stock form anyway). That goes double for the VWs. Also, despite what you "hear", people with those cars blow engines too.

I figured it was the nature of the motor that factored into this. I never really thought of the combustion chamber design as a factor though, but very good point. And yeah, piston motors are alot more tolerant of knock, oh and believe me, i know of a few guys that have popped piston motors.

The remap on the EVO's and the GTI all hold the boost at that level to redline. Kinda crazy if you ask me, considering both those vehicles have relatively small turbos. AIT's must be sky high at those levels.

^ excellent response!

And yes, I have personally seen a piston engine with holes in the pistons from overboosting.

Over boosting is not only reason why iston engine with holes.

Too much timing
Poor octane
not enough fuel
high compression
heat

And poor tuning.

Piston engine have head gasket (s) to give...rotor doesn't.

if there running 22-23 psi on a pistons engine with a good size turbo...they better have a built motor, and a great tune....or that engine is going bye bye....

i know around here alot of jackass's that turn up boost, and there like
" im running 18psi"....thats fine but the turbo is the size of a peanut....

rotaries react much better to boost than piston engines, just like turbo diesels can run 100+PSI(keep in mind most turbo diesels are close to 6.0liters or larger before accusing this of being false) but their boost does not add on as much as gasoline piston engines, it is related to airflow paths, compression ratios and combustion cycles. piston engines can sustain under harsher environments like pre-ignition better than a rotary can but that is still very limited and has nothing to do with this, considering both engines are tuned to close to their pre-ignition phases they are still both limited equally.

rotaries will gain more HP per PSI than a comparable piston engine and turbo will, our engines are not huge but we can strap huge turbos on them and benefit very well.

the other reason rotary engines cannot boost much higher than 18PSI on pump fuels is due to the internal temps of the engine, you all realize the exhaust is pushing out 1300-1800F+ correct? well the internals are fractionally as hot as that, it all relates to the flash points of the fuel, lower octane fuels probably couldn't handle 10PSI due to heat and their lower flash point where 91-93octane can handle up to about 17PSI in most rotary applications before it will pre-ignite under the harsh temperatures in the engine.

you can effectively reduce the chance of pre-ignition by cooling the intake temps but that can only help so much.

the best thing you can do is up the octane even more by either running race fuel or adding in an AI(auxiliary injection) source such as alcohol injection or methanol injection which basically turns your pump fuels into race fuel for a fraction of the price of a full tank of race fuel.

the AI section here on the forum is already starting to bust with threads about AI systems because it was an untapped resource that most people didn't realize how crucial it was to making high HP numbers. for example J-Rat who lives in Arizona is pushing out close to 500RWHP with the help of AI in the desert heat with the help of Ethanol, Methanol supposedly has even higher anti-knock suppression capabilities, and yes i will agree the REW engine has more potential than a 13BT does so you can expect even better numbers.

i hope that cleared up a few things. :)

From what i've seen and who i've spoke with the threshold of maximum boost on 13 b's is more like 17-18 psi. Anyone else hear this? Regardless our engines cannot handle the extra stress like piston engines, because of many reasons regarding resistance to knock, detonation, and thermodynamic charactaristics.

17-18 on 91 octane is true, i have already managed to crack 2 irons testing this theory.

i am joining the AI bandwagon as soon as i get it set up and installed, i just wish there was more meth dealers around. wait, what am i saying? olivehurst was the meth capital of the world for a while there. :)

I think it really depends on intake temp, ignition timing, and ofcourse a/f ratio.

I know of people running 23psi on pump gas with over 15k miles already with no problems.

I'm currentlying running 18psi on my 60-1 tuned around 10.5-11.0 a/f.

I have seen people run crazy amounts of boost on pump gas (20+) with no problems, a few with locked dizzys pretty well advanced.

But, one f*ck up on the ecu's part or injector, fuel pressure drop from stereo, fan etc.. . and at those boost levels your engine is done for.

Going to have to call BS on that one, especially if you are talking 91 octane.

The boost may be that high, but the knock sensors in the ignition system retard the ignition timing so far back to keep from detonating that the engine isn't even close to putting out the power that it could with the right conditions.

i would probably agree with as high as 20PSI but not 23, if it is surviving then i doubt for long. i'm betting his boost gauge is inaccurate or he is running a dinky stock S4 turbo which is doing nothing for performance at that point. it has to do with compression ratios vs boost and internal engine temps... just one hot day and the intake temps rise enough and POP!

just because someone claims something does not mean it is safe, quit giving people ideas that it is ok.

I CANT BELIEVE U PEOPLE ARE AGREEING TO ThatT WE ARE NOT LIMITIED TO 15 . I THINK MANY PEOPLE FEEL THAT WE ARE LIMITED AT 15 LBS. DUE TO THE NATURE THE ROTARY HAS (NOT BEING ABLE TO TAKE DETONATION AS MUCH AS PISTON MOTORS) MANY TUNERS LOWER THE LIMIT TO RUN HIGHER BOOST AS A SAFETY MARGIN....MANY PEOPLE ON THE EAST COAST RUN 18 PSI ALL DAY AVEN CLOSE TO 20 especially at the track.....i only say this because ive seen this w my own eyeS, i currently run 10 lbs but i will be tuned for 13 low and 17-18 high. i feel we just need more people w more knowledge and GOOD tuners across the country. AND WE WONT HAVE AS MANY BLOWN MOTORS. IT IS NOT EASY FOR THE AVG JOE TO TUNE OUR MOTORS FOR HIGH BOOST W/O DETONATION. BUT IS DEFINATELY POSSIBLE ON PUMP!

dude shut up, you hurt my ears.

this is about safe levels not what your brothers friend's sister's brother runs ALL DAY LONG AT TE TRACK!!!!1!!1


i have personally experienced pre-ignition at varying levels with varying octanes of fuel. believe what you want but quit telling people it is safe to run 20PSI on pump gas safely, you're full of shit.

Yeah, I'm betting 50% of these running high boost on pump stories actually go like this --

guys drives like a grandma on the street running 13-15 psi, he only runs 15+ psi once in a blue moon after filling up with race gas.

The other 50% are bullshit.

EDIT --

5% are really running high boost and not blowing up
20% are really running high boost and blowing up
25% remaining people are full of shit

i have dozens of trophies from various detonations over the past year from various customers engines, ranging from collapsed rotors to 4mm deep gouges in rotor housings to 1" chunks missing out of rear irons.

if you want to play, you gotta pay. i just hope people don't really feel like pushing the limits of their engine for just a mere 20HP more.

karak first off show some respect dont start this internet shit seriously show some respect!

ryenberg so u would tell me that if i ran 18 psi all day i would blow my motor?
so u seriously dnt believe that a rotary cant run 18 psi al day w good tuning andfuel management?

karack i still believe our "SAFE" LEVEL IS MORE THAN 15LBS MANY PEOPLE ON THE FORUM HAVE PROVEN THAT!...ALSO I MENTIONED I KNEW PEOPL WHO RAN 20PSI AT THE TRACK BUT I NEVER ONCE SAID THAT WAS SAFE!!!....I BELIEVE WE CAN RUN 18LBS SAFELY ON PUMP..... ACTUALLY GOODFELLAS RUNS 17.5 ALL DAY ON PUMP AND HES ALL OVER THE FORUM

So just a quick one,,, how well do our cars respond to increase in boost ( i must admit i wound my escort turbo from 8psi to 18psi with aftermarket ECU and the power increase was massive). If my RX7 is running 10psi now and i can only wind it up to 14PSI dont sound like im gonna get that much power? ,mmmmm???

Respect is earned....and you're not going to earn it posting like that.

Rich (Goodfellas) runs 17 psi ON WATER INJECTION. Big difference. He is also running 94 octane, not 91 like we get out here.

And yeah, if you run 18 psi every day on pump gas and ACTUALLY repeatedly hit 18 psi at WOT (see my grandma comment above), then yes your motor is on borrowed time. Good tuning doesn't make up for simple physics.

Depends on a LOT of factors....but 15 rwhp per psi would be a rough ballpark.

ACTUALLY RESPECT IS ALWAYS DUE I MADE A POINT BECAUSE OF WHAT I SEE IN W MY OWN EYES. REGUARDLESS, ITS FUNNY HOW PEOPLE TALK OUT THIER MOUTH OVER THE NET THAT SHIT KILLS ME!!!
actually from my understanding goodfellas DID NOT ALWAYS HAVE WI. AND SECONDLY I FORGOT U GUYS GET 91...i run on 93-94 that may be the difference but on 93-94 we can run 18 on pump w/o detonation and its been proven many times!!

^^ Quit typing in caps holy fuck

Yeah you guys in Cali cant get 93. Just like njstrreetrx7 said i have personal friends who run 18 psi on pump gas but it's only on 93 octane . Never never do we dare put anything less in. If we could only get 91 that 18 would probably be 14 but because we have access to higer octane pumps we can run that high boost.