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.

sorry for caps....i take my fustration out on the key pads...thats why i hate postin my opinion....im dne here ill post resulyts when i geet there

The 23psi is on a block with GSL-SE rotors, on a GTR35R.. boost measurements taken from the microtech.

Perhaps Rene Franco will chime in, as I know he seems to tune pretty on high on pump gas alot of motors, and I have yet to hear of a failure.. even on his drag car that is boosting 40psi. On a T91, aiwth 1.25 hotside.

But for stock FD motor with high comp rotors, I wouldn't pesonally push more then 18psi on pump.

i still find that hard to believe, i have seen and experienced too many failures to think otherwise unless the octane is increased somehow.

tuning has little to do with it once you start pushing the limits of the build, if he can manage to keep his intake temps icy cold it may sustain for a single run but back to back on the streets is a completely different story and hardly true to real world situations.

Hey Wan,

I do run 17 psi on 93 octane, but that is with my water injection system. I typically used to run 15 or so psi on straight pump gas. Back in 2002 or so I briefly ran 17 psi on straight 93 octane, but I decided against that because, quite frankly, pump gas is shit. You never know what you're going to get with it. I popped a motor back in 2003 on a bad tank of supposed 93.

People running 20 psi on pump gas are running on borrowed time---you can be the best tuner in the world, but when that tank of 93 really turns out to be 89.......

or internal temps rise even a tad, most people just are ignorant to what pre-ignition is. in simple it is combustion without a spark from hot spots in the engine, rotaries run hot as hell internally so any of a number of factors can raise internal temps beyond the point of pump gas' handling characteristics when enough boost is added, ask any tuner and they will say the same.

and yeah GoodfellaFD3S i wouldn't doubt there is quite a number of shady gas pump owners who sell 89 and market it as 91 or higher. most cars on the road will not have ill effects on it but if you are tuned for it and don't get the correct octane, well we all know what happens then. ;)

is there a way to tell if u were cheated gas?? besides the blown motor a couple miles back?? like how the car reacts and such

it'll run kind of lumpy/choppy. when I fill up I typically don't go out and starting making redline pulls right away, I'll drive the car easy and boost it slowly to make sure it feels ok. Hell, who I am fooling? lol. Maybe I used to do that, now I don't really worry about it, esp with the water injection.

Ha, for sure. I used to do the same thing till I got WI. It is definitly fun to light them up after filling up and having some guy ask if "thats a viper?"

goodfellas i definately understand ur point u neve know what u can get...or even iof something may go wrong w ur fuel! im not goin the WI way but hopefuly i will have luck at 17 on pump.....Wi requires u to keep it maintained...and i daily my car.lol

and lastly i dnt think andybody should run over 15lbs all the time for what?

you mean to tell me after all my thought out posts on what kills these motors you don't even know the real reason why you tried to bitch me out about why it's not safe to push over 15-17PSI on pump fuels?

i thought the 15 psi limit was cause of the map sensor. and going back to the evos and pistons. alot of times thats their peak hp, which usually goes down a few psi at readline.(dunno if that was mentioned or not)

and wan, stop picking internet fights.lol

the stock map sensor is only part of the problem but that is a good point, the stock map sensor becomes innacurate after those levels since it was never originally inteded to see that much boost. even with an EMS though the limitations on pump octane fuels is still the limiting factor.

so technically with a 3 bar map sensor and fuel upgrades you can run round 18 psi on pump gas, but youll have to cut back on the timing, making the extra psi not worth it.

As far as the EVO thing I mentioned in my initial post, with the stock ecu, the car does drop the boost level towards redline. But with the reflash, it eliminates this, so it holds full boost till it hits the rev limiter. But along with that reflash, its tuned octane specific. My 2 friends got flashed for 93, so they can get away with the 22-23 psi I suppose. And the ex's 1.8T GTI, i also had a choice between a 91 and 93 reflash, picking the 93 for the extra 20-30 WHP it provided.

And yeah, being on the east coast, i can get 93 octane at any station and 94 at Sunoco. So that might have a bit to do with ppl on the east coast running a bit higher boost. Even though, i would rather be safe than sorry and just stick with 15psi as a good pump gas tune, then up it a bit with some water/methanol injection or have a race gas tune.

i tried to explain what pre-ignition is in my earlier posts but most people don't understand what pre-ignition is. in short you don't need a spark for pre-ignition to happen, it is internal temperature sensative so when internal temps rise enough then the fuel will ignite on it's own prior to the spark plugs igniting the fuel mixture. in pre-ignition cases in a rotary engine it will cause detonation, detonation is very catastrophic in these engines and will break components if there is enough pressure in the chamber when it occurs.

octane is directly related to pre-ignition, higher octane will help prevent pre-ignition from happening. so the truth of the matter is, no matter how safe you tune your ignition maps you still are limited to the internal temps of the engine vs the octane of the fuel at X amount of boost, higher pressures in the combustion chamber(higher boost levels) will increase internal engine temps increasing the chance of pre-ignition.

karack i dont undersatnd ur last post..but my point is that 15 psi is NOT our limit on 93-94 octane. i would say our safety margin is still above 15 (16-18) i believe we can run up to about 20 psi on pump w good tuning and proper fuel management w no room for error!.. i beleive anything over 20 is not safe on pump...

you could probably run 18PSI relatively safely on 93 octane if the AFRs are clean, that is dependent on your cooling system and intercooler though. if the engine is operating too hot with improper cooling than even 15PSI can be unsafe on 93 octane fuels, in the right setup you probably could squeeze out 20PSI but that would probably be the limit even with a great intercooler, cooling system and oil cooler.

double post
 

karack i dont undersatnd ur last post..but my point is that 15 psi is NOT our limit on 93-94 octane. i would say our safety margin is still above 15 (16-18) i believe we can run up to about 20 psi on pump w good tuning and proper fuel management w no room for error!.. i beleive anything over 20 is not safe on pump...

so i guess we are on the same page now

safe levels are in the setup, most people say 15PSI because alot of people still run stock intercoolers and cooling systems, that is a very big limitation since stock FDs run hot as hell in my opinion. with a lot of money and time invested in the cooling systems you could push those numbers up but not by much. each setup will have different limitations so as a generalization it's good not to tell people it's ok to run the peak because people will believe it and wind up with a 200lb brick sitting in their engine bay.

so youd have to run colder plugs, very conservative timing and fatten the map a bit to keep temps down. great ill just make same power at 20psi as at 15 just so i can tell ppl im running 20psi on pump.

something like that right?

basically yes there is ways to deter pre-ignition but it is at the cost of power, with the exception of raising the octane level.

Just to clarify here: Pre-ignition doesn't cause detonation, they are two different problems. Pre-ignition is just that, premature ignition of the intake mixture due to excessive combustion chamber metal temps, "hot spots" like the surface edges in the combustion chamber or components/areas that aren't getting sufficient cooling. Detonation is a premature (and very uncontrolled) ignition of the intake mixture caused by excessive temps in the mixture itself.

Well that depends a lot on the motor. I routinely run 25 psi on pump gas on my bone stock 188k mile motor. Provided the proper bolt-ons and tuning this is not a problem.