How much power can the 996TTs make using 91 Octane
#62
11-11-2009, 07:27 PM
[quote=ttboost;2616601]
A 7 liter V8 does not need forced induction to make good power (defined in my book as 600 whp or more). A 3.6 liter 6 cylinder does.
The big NA motor will benefit from better gas, of course, but should easily be able to make 600 on 91 pump.
The small motor that relies on FI (there is no replacement for displacement...except a turbo) is riding a much finer line in terms of risk for detonation and thus is more dependent on high quality gas.
Smaller forced induction engines require gas that resists detonation. Thus our cars are very limited if forced to use CA 91 octane.quote]
This limitation is a fact for ALL engines. As Law Jolla has said, MANY things can cause a motor to detonate, not just low octane fuel. If an engine has been exposed to detonation for a long period of time, it will naturally be more susceptible to detonation as the pitting and such become hot spots aiding preignition. The answer to the original question is: whatever level the tuner feels the engine can operate safely at, which won't be known until the tuning process after many logs are reviewed.
This limitation is a fact for ALL engines. As Law Jolla has said, MANY things can cause a motor to detonate, not just low octane fuel. If an engine has been exposed to detonation for a long period of time, it will naturally be more susceptible to detonation as the pitting and such become hot spots aiding preignition. The answer to the original question is: whatever level the tuner feels the engine can operate safely at, which won't be known until the tuning process after many logs are reviewed.
The big NA motor will benefit from better gas, of course, but should easily be able to make 600 on 91 pump.
The small motor that relies on FI (there is no replacement for displacement...except a turbo) is riding a much finer line in terms of risk for detonation and thus is more dependent on high quality gas.
#63
11-11-2009, 07:43 PM
I see a couple of things here I'd like to comment on... For one the question is what can be made on the 996TT safely. Certainly you can make HUGE amounts of power if you're using say a BBC with a turbo but the concern here is this specific engine, stock compression, bolt-ons. This isn't just "how much power can be made on X octane".
Another thing I see is talk of specific boost levels as safe or not. Folks, "boost" is a measure of restriction. Port the heads, swap cams, run the same level of "boost" and you get more power. Why? Because the restriction was lowered, the engine ingested more air, and the W/G compensated by spinning the turbos harder to reach that same pressure! Likewise, a different turbo may present a lower backpressure on the exhaust side and allow for more power at the same pressure. You may also see lower IATs from the slower spinning larger turbo moving more air. The lesson being you should be careful not to equate intake restriction\boost with safe or not. It's simply not that simple...
The real concern is cylinder pressure. Sadly measuring this isn't trivial. Retarding timing may allow for more boost\less detonation but there's diminishing returns and the side effects of a retarded mixture include higher EGT as late burning fuel exits the exhaust port.
Oh, it's been mentioned that you could run say 87octane and the ECU would retard and you'd be "safe". IMO "leaning" on the knock sensor is a dangerous game. Knock sensors get their name because they detect knock - it has to have already happened for it to detect it! Depending on the ECU the timing will advance to see if the coast is clear and then retard again when it senses knock AGAIN. On a high performance engine this just isn't a good idea. Is it any wonder that some folks who do this notice not only a lack of performance but reduced MPG too?! It's because the engine isn't running as efficiently as it should, the octane compromises things due to it's volatility. Likewise running super high octane doesn't always help if the cylinder pressures are low. BTW, I recall reading about at least one Supra owner unknowingly leaning on their knock sensor who got a nasty lesson when their knock sensor went bad - pop!
Another thing I see is talk of specific boost levels as safe or not. Folks, "boost" is a measure of restriction. Port the heads, swap cams, run the same level of "boost" and you get more power. Why? Because the restriction was lowered, the engine ingested more air, and the W/G compensated by spinning the turbos harder to reach that same pressure! Likewise, a different turbo may present a lower backpressure on the exhaust side and allow for more power at the same pressure. You may also see lower IATs from the slower spinning larger turbo moving more air. The lesson being you should be careful not to equate intake restriction\boost with safe or not. It's simply not that simple...
The real concern is cylinder pressure. Sadly measuring this isn't trivial. Retarding timing may allow for more boost\less detonation but there's diminishing returns and the side effects of a retarded mixture include higher EGT as late burning fuel exits the exhaust port.
Oh, it's been mentioned that you could run say 87octane and the ECU would retard and you'd be "safe". IMO "leaning" on the knock sensor is a dangerous game. Knock sensors get their name because they detect knock - it has to have already happened for it to detect it! Depending on the ECU the timing will advance to see if the coast is clear and then retard again when it senses knock AGAIN. On a high performance engine this just isn't a good idea. Is it any wonder that some folks who do this notice not only a lack of performance but reduced MPG too?! It's because the engine isn't running as efficiently as it should, the octane compromises things due to it's volatility. Likewise running super high octane doesn't always help if the cylinder pressures are low. BTW, I recall reading about at least one Supra owner unknowingly leaning on their knock sensor who got a nasty lesson when their knock sensor went bad - pop!
#65
11-12-2009, 04:26 AM
A 7 liter V8 does not need forced induction to make good power (defined in my book as 600 whp or more). A 3.6 liter 6 cylinder does.
The big NA motor will benefit from better gas, of course, but should easily be able to make 600 on 91 pump.
The small motor that relies on FI (there is no replacement for displacement...except a turbo) is riding a much finer line in terms of risk for detonation and thus is more dependent on high quality gas.
The big NA motor will benefit from better gas, of course, but should easily be able to make 600 on 91 pump.
The small motor that relies on FI (there is no replacement for displacement...except a turbo) is riding a much finer line in terms of risk for detonation and thus is more dependent on high quality gas.
Last edited by ttboost; 11-12-2009 at 04:29 AM.
#66
11-12-2009, 06:11 AM
oh yes they can. Another fallacy is believing that on 91 you can only run .9 bar.
Not every big motor is equal either. A 7 liter ZO6 motor makes 505 bhp and it can be taken up much higher with head work and cam. possibly 600-650 and it might just be streetable, any more and can you say pro stock lope. A carrera GT 5.5L motor can make over 660 bhp without going into the engine. hmm, so there are no absolutes. you can tune higher for higher octane and get even more power out of both.
I wonder if you reflashed a Veyron ECU to run VP109, how much more power it would make
but alas we are back to main point. I'd still like to see a 3L turbo motor that can run on 91 octane and make 860 whp. Any motor that will do that has a useless pro level ski slope power curve. Only good for drag racing, and even then I would not believe it until I saw it. It was mentioned that it was done, but there are those in here that can barely squeeze that kind of power out using vp109 or better. So I'd like to see this, but I doubt it really exists. So who has seen a 3L 860 whp 91 octane motor?
So basically performance based data is where it is at if you want to know what really happens and if you want to know that the text book applies. Some just will never get it.
#67
11-12-2009, 03:10 PM
It depends on the set up. With smaller turbos and tuning, yes you can run more than .9. With my turbos and tuning, .9 is as high as I would go.
#68
11-12-2009, 05:35 PM
doesn't KPG have GT30's? if so he's pushing 1.36 bar on 93 octane. According to this dyno sheet, if I read it correctly
#69
11-12-2009, 05:42 PM
KPG's motor has custom heads and cams, and flows a lot more air than Sean's does. Thus, he can run more boost on lower octane than Sean can.
My GT2 has a stock motor and is running 30 size (T3s) turbos as well; and .8 to .9 BAR is the maximum boost I will run on 93. That's wastegate spring pressure with the EBC turned off.
Last edited by Divexxtreme; 11-12-2009 at 05:49 PM.
#70
11-12-2009, 06:04 PM
The compression ratio of any modified motor would play a significant part in the answer. If you were to lower the compression ratio you could run significantly more boost than .9 bar on 91 octane.
Last edited by cjv; 11-13-2009 at 02:32 AM.
#72
11-12-2009, 07:09 PM
built motor verses stock...and I was talking about CA 91 craptane.
Scott, I have been running 1.1 on our Tx 93 for over a year now with no prob, although Todd K is more comfortable w/ 1 even.
Scott, I have been running 1.1 on our Tx 93 for over a year now with no prob, although Todd K is more comfortable w/ 1 even.
#74
11-14-2009, 03:34 PM
I'm with you, bro. But I'm very conservative with pump gas. Since I can get 100 octane out of the pump right near my house, I see no reason to push the limits on 93.
#75
11-14-2009, 05:16 PM
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Law jolla, BLKMGK great posts glad to have you guys here
i think it all boils down to how long you want to leave your ***** on the chopping block to repair your 25k engine for an extra 30hp pushing the timing limits on horrible fuel.
if you want to push it on pump gas you should look into meth injection at least its inexpensive compared to an engine rebuild.
the question is, is pushing the limits and testing the engineering limits of the rods from detonation, worth the 30hp gain or so that costs 25k to fix when the whole package hiccups n detonates the last time?
i think it all boils down to how long you want to leave your ***** on the chopping block to repair your 25k engine for an extra 30hp pushing the timing limits on horrible fuel.
if you want to push it on pump gas you should look into meth injection at least its inexpensive compared to an engine rebuild.
the question is, is pushing the limits and testing the engineering limits of the rods from detonation, worth the 30hp gain or so that costs 25k to fix when the whole package hiccups n detonates the last time?