Why is it that tuners feel a need to tune street cars running on pump gas to 22psi. It seems to me once you get to that level you would be pulling so much timing that you are in fact increasing the cylinder temps to the point that its not good for the motor in the long term. Note this post is not accusatory. I just wonder what your tuning philosophy is in regards to pump gas timing and boost. Matt
I dont know the exact tuning reasons as I am not a tuner but as a customer here is my take on it: I've got a car with a bigger turbo and intercooler so I'd expect to be boosting more than stock. I'm tuned for 19psi but I hardly ever go completely wide open in the car so the motor never sees all of that. My boost tapers towards redline down to I believe 14 or 15psi to help preserve the piston rings, I'm not sure how my tune is setup exactly with regards to timing. I know that high revs + high boost + lots of timing is a good start for some detonation but reducing the boost should let you keep the timing pretty even while staying reliable. I drive a turbo car and it's nice having the option for more power by just laying into the gas and getting more boost on demand. My car sees full boost very rarely since most of my driving is around town. If I had a car with a turbo that is most efficient in a certain boost range I would tune the car for that boost and play with the timing in order to make the most power on whatever octane I planned on using in the car.
good answer bobby. i say wait a few years after the introduction of a new motor for a few people to blow it up and then stick with the tried and true methods and reputable tuners.
Bobby 19 psi is fine especially since it tapers towards redline. Atlanta is a lucky place because there are a lot of good tuners here. I just see all these people running 22-23 psi on pump gas and I have to wonder if people realize that to run that level of boost on pump that you have to pull a lot of timing which is increasing cylinder temps. I'm just curious why people feel a need to push the limit with pump gas when its completely unnecessary. Come on Alex out with it, I posted this because I want people to think for themselves. There is so much misinformation on other boards that its unbelievable. I'm not saying that there aren't situations that you cant run 22 psi on pump.
Coming from the guy with the Supra :keke: I didnt know the effects that timing had on cylinder temps, I would have thought it to be the other way around, that more advance would lean out the A/F mixture and increase temps. Tuning is something I'd love to learn but I'd really prefer to test it out on some beater, not a daily driver.
Retarding the timing, depending on how much increases cylinder temps. Its kind of a tricky subject that's why I was hoping the resident tuners would chime in. Unless of course they want to secretive about the black art of tuning. LMAO
siegel is currently travelling but im sure he will chime in when he gets back... i have wondered about this recently as well and i meant to ask him a similar question... now i dont know much about engine tuning at all but here's my take... please correct me if im wrong i believe timing is everything since thats when u decide the mixture ignites... theres an optimal point when u would like it to ignite in order to exert maximum force on a piston at a given boost level... as slowwrx mentioned, if u raise boost, ur mixture is hotter for 2 reasons...(1) turbo is working harder and getting hotter and (2) more pressure inside the block makes it hotter... so u would have to compromise timing... so if what i said is true, y would u set a target boost and work timing into it vs chosing a desired timing plot and adding as much boost as possible but still maintain the timing like i said, my knowledge of tuning is extremely minimal so if anyone could throw light on this topic or tell me why im wrong, i would appreciate it
I'm working on a post to better explain the combustion process, so that those that arent that familar with it can understand, it may take me a while though. I will through it up as soon as I'm done. Matt
My 2 pennys: 22 on pump can be good and bad. A big part of it is combustion efficincy and of course cooling. A big turbo that is still very efficient (both hot and cold side) at 22 combined with a nice IC and heat management (oil, coolant, as well as heat soak/absorbtion both outside and inside the motor) may be just as healthy a smaller turbo at 18 psi. The above big turbo setup may not require to pull much timing either. Of course, the above setup isn't really that streetable; its more of a race setup. We all know the 4g63 has a more efficient combustion than an EJ; many 4g's seem to live happily for a while at ~22 psi on pump on even smaller turbos. For the average setup though (stock EJ block with decent supporting mods) I would agree that 22 on pump is a little overkill. Of course, plenty of folks come to tuners and say I want a bunch of power on pump gas. FOr my up and coming setup I plan to run 18 psi on pump, around 22 or so for track events / practice with pump and meth and maybe 25 for competition with meth plus race fuel. OF course, those are just some ball park nubers that I personally am comfortable with (nice way of saying I pulled them out of my arse). Ultimately, I will rely on Doug's judgement as he is a great tuner and understands the loading/abuse that a road course car will see. FYI, I don't really play with the car on the street though so 18 psi is pretty erelavent. I would have it tuned at 14 psi if the wastegate / boost control could manage that as well as manage 25 psi 'perfectly'... my two pennies
This says it all. Smaller turbos running out of their efficientcy range at 22 psi will cause high charge temps. A big turbo running 22 psi will have the same charge temp or possibly cooler than the small turbo at 18 psi.
While cooler temps help it still doesnt really have an effect on overall cylinder pressure. Overall cylinder pressure is kind of what effects timing. Its kind of hard to explain unless you know a good bit about tuning and engines in general.
Hmmm... Anyone want to go into the basics for me, mainly about boost and "timing" and what the effects of changing their values are?
Basically, The more boost you run the less timing you can run. Generally when you have to retard the timing severely you end up with higher cylinder temps. Mind you this is all dependant on the octane rating of the fuel you are using. Higher octane fuels burn slower so you can advance the timing even further with high octane fuels. Well you can advance the timing or add boost. Most motors about 18psi seems to be the safe limit after that you start having problems. The EJ series of motors is not especially tolerant of detonation so I am not sure why people insist on running these motors on the ragged edge with pump gas. Matt Edit: There are lots of variables that contribute and I didn't mention all of them. Because honestly most people on here aren't going to be tuning there on car so it doesn't matter all that much.
timing is the point at which you fire the spark plug. Its usally in degrees. The degree refers to the amount of time before the piston reaches top dead center. Matt
How does the static compression ratio affect cylinder temps? With a higher CR you could run less boost and make the same amount of power correct?
Yerrow is correct, the thing is there are so many factors that contribute that it is hard to seperate them. The EJ series motor is a strange beast, I mean really its a stupid design, but I dont really want to get into that. We will just assume that it is just like any other inline 4 cylinder, If you increase the compression ratio you will quicken the spool and ultimately make more power at the same boost levels if you have enough octane. Ill work on a better explaination. Matt
lol, I just found the post that likely modivated this thread. That looks like a case of someone that isn't really familiar with motors/tuning that walked into a shop with a list of desires (a strange list: stupid power out of a 4 cyl on pump) and the shop sold him the most expensive thing they had....
25psi on 91 oct: (note, I don't know what the CR is on the R4, could be lower but why go that far for pump only use? must be a Cali thang) http://forums.nasioc.com/forums/showthread.php?t=948750
That actually wasnt why, however that is a perfect example. That motor is a ticking time bomb. I speed and crawford are stupid for even posting that crap. What makes it even worse is that its not even good numbers. By the time you convert their flywheel numbers to wheel horsepower, they made less than I did on a bone stock 2.0, I mean seriously good job. Matt
Within reason, all a combustion chamber "sees" are 3 things: 1) a certain amount of air, with turbo cars this can be loosely defined with boost 2) a certain amount of fuel, generally defined with AFR 3) spark timing, how far Before Top Dead Center (BTDC) the spark plug fires other things that matter are, intake air temp, octane, cam timing, and few other little things. The bigger turbos can make more boost with more efficiency, which keeps the intake charge cooler. More intercooling further reduces the intake charge temp. Meth injection of course DRAMATICALLY reduces intake charge temp. You are correct that more boost generally needs less timing. Leaner mixtures also run less timing. Obviously you get more power with: 1) more boost 2) leaner AFRs (in and of themselves, not counting it's effect on timing) 3) more timing More of any one of those generally equals less of the others. You need to decide how much of each is appropriate. "Fortunately" some things have an appropriate "efficiency" curve. Tuners generally keep the turbos in their efficiency range. Sometimes this means they can make big boost down low, while still being VERY efficient. Plenty of the VF34 FMIC cars that run just over 20 psi down low, still NEVER fall under 17-18 degrees of timing. I *ALWAYS* taper ej20's boost up top, so we're generally near 30 degrees of timing up top. So generally one picks a boost curve based on the effiency. There is almost always an appropriate fueling curve. Most people go a bit richer right at torque peak and then taper the afr's up to keep the power on up top. Just how far you go depends on how much timing the car is willing to run as you lean out, and what the EGT's do, and how the car will be used. There is a "general" timing curve that's expected. If the car will run a good bit of boost at a reasonable fueling curve, an still run an expected amount of timing, then it's fine. If somebody had some strange desire to run a set amount of boost, and had to pull huge timing to do it, it would be a bad idea... I guess I'm getting away from the topic... basically, some cars can very efficiently run 21 psi at lower revs, will keep lots of timing, and make lots of torque. Most ej20's with VF34's and FMIC run just over 20 psi down low, and never fall under 17 degrees... 22 is a lot on straight pump... SS
thanks for your response scott... just a reminder to all... PLEASE keep this a discussion... if this turns into an argument, this thread will be locked immediately and the moderators will take necessary action
There's one thing I don't understand about compressor efficiency. Basically heat = pressure and pressure = heat. So it just seems to me that hot air is still just hot air no matter what machine you used to make it with. What I'm missing is why some compressors are able to make a given amount of boost easier or with less heat than others. Help!
I think that I am pretty much in agreement with Scott. It just seems like there is a trend developing lately to see who can run the most boost on pump gas. If you want to make big power then run race gas. Bottom Line 22psi is just too much for pump gas. Its too close to the edge. Unless your running a very big turbo and honestly even then I feel like your pushing your luck.
I rarely break 20 psi by much on straight pump. Even with meth on the ej20's we only go to near 23 psi... If you look at a compressor map you will see the efficiency "islands." If the turbo were 100% efficient it would follow pv=nrt exactly, increasing temp linearly with pressure. So with 14.5 psi atmospheric, to get 14.5 psi boost you are taking the 14.5 atmospheric and doubling it to 29 absolute = double the absolute pressure, with 100% efficiency it would "only" double the temperature. The gap from 100% to the actual efficiency is how much MORE it heats the air than double. Most turbos are at MOST 75% efficient, it's easy to get to 50% efficiency pushing them too hard, so even 14.5 psi of boost is taking 80 degree intake to 200 degrees. You can imagine at 22 psi = 1.5 times the pressure it's making 300+ degree air. Yes we have intercoolers, but they are at best in the 80% efficiency... SS
Standard "Prodrive Stage III" curve. 19 psi peak to 14.5 at 6k, to 12.5 at 7k. We could run a touch more at 7k, but that curve still makes 235+ whp 245+ wlb-ft... SS
MY 2 cents With big turbo's you can get away with runing more boost because there is less back pressure inside the exhaust manifold, causing less contamination(sp) inside the combustion chamber. As fuel heats up it becomes less stable, higher the octane the more stable the gas is, which is why your can run more timing and higher boost on race gas. But if your getting alot of backpressue inside the exhaust manifold your going to get alot of contaimination inside of the combustion from burnt gasses going back into the power stroke process. It is these cases that runing high boost is a bad idea . If you want to do a fun test insert a boost gauge coming from the exhaust manifold an turn the boost up, you will find that the car will run alot of timing up until the point were there is more pressure inside the exhaust manifold than the intake manifold side. It is at this point you reach the turbos delta, and from that point you will have to pull more timing as you raise the boost level, or run a higher octane fuel. So 22lbs on the a gt35r is much safer then runing 22 lbs on say an TDO5 18g well that is if your block can handle the power the car is making. Compressor wheel effiency has little to do with anything when runing 21-22lbs, where as the exhaust turbine wheel has everything to do with it. 22lbs to redline on a turbo that is blowing through a straw = bad, but on a turbo thats has a large AR turbine side its no problem.
That's interesting Doug. I was thinking since turbine wheel and compressor wheel are carefully matched, even in hybrids, that the compressor wheel effiency would still be important here. But I can see how the compressors outlet affects things quite a lot.
At 21psi not really here are two different compressor maps for two totally different turbos. Now if both turbos were run at 21 psi and both made around 400bhp they would have a pressure ratio of around 2.42. You can see that even thought the size is extremely different the efficiency at the level is about the same. No if you were to turn the boost up to say 28psi then the smaller turbo would be way out of is range.
Even with the 16g compressor map, 21psi is not out of the range of the turbo. Like I said above the difference is in the exhaust side, it is for that reason the 35r will make more power at the same boost level, and is much safer runing 22psi.
Its nice to have a bunch of knowledgeable people share their knowledge without getting into a battle... Oh I love WRXatlanta :bigthumb:
I wanted some the day after the 555 party.....is that bad :coolugh: Why cant they build a chipotle closer to me, i just might have to move.
So higher octane fuel is more stable because it has a higher flash point and doesn't ignite until it's near a higher temperature (than lower octane fuels) So why if someone starting boosting more would they need a cooler sparkplug?
I'm not sure the flash point is really relative here. Higher octane fuels burn slower. First you have to understand what ignition timing is. Ignition timing is how many degrees of crankshaft rotation before the piston reaches TDC that the spark is lit. When you lite the spark its starts the flame front moving down the cylinder. As the flame front moves down the cylinder the piston is coming up towards the top. If your ignition timing is perfect then the piston compresses the mixture right as it gets a nice big shove from the flame. The more stable\higher octane the fuel is the more degrees of timing you can add. More timing bigger push. I simplified this a lot, I can get more complex with it if we need too. Pump gas is more of a bang than a push. As far as boost and pump gas goes its ultimately about cylinder pressure and I don't care if its a 35r or not its just not worth it to run 22lbs on pump gas. Cylinder Pressure- who wants to try this one Matt
cooler plugs pull more heat out of the combustion, in turn making the fuel more stable... but the effect is very small.