What Gas Should I Use?
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Joined: Apr 2002
Posts: 870
From: NASA/JSC - Clear Lake, TX
Originally Posted by j9fd3s' date='Apr 29 2003, 01:43 PM
[quote name='RX-7Aggie' date='Apr 29 2003, 11:34 AM'] if the compressed air due to the intercooler is cooled back down to ambient temperature, T_o, before entering the combustion chamber, then the change in pressure within the engine delta P due to compression will increase the temperautre of the AF mixture just like a NA engine. only if the compressed air from the turbo is too high will it auto detinate or knock.
i belive it's the compression ratio of the pistons/rotors that determines the gas type, not necessarily the use of a turbo. i understand on blown cars w/o a intercooler that premium gas would be needed, but i dont see about other cars.
PV=nRT --> if T is the same for both a TII and a NA due to intercooling, and compresion or change in pressure is the same, and we know displacement is the same, then the change in temperature has to be the same, resulting in a final gas temperature that is the same between a TII and a NA, assuming the intercooler is sufficient and the initial temperature entering the engine is the same.
i belive it's the compression ratio of the pistons/rotors that determines the gas type, not necessarily the use of a turbo. i understand on blown cars w/o a intercooler that premium gas would be needed, but i dont see about other cars.
PV=nRT --> if T is the same for both a TII and a NA due to intercooling, and compresion or change in pressure is the same, and we know displacement is the same, then the change in temperature has to be the same, resulting in a final gas temperature that is the same between a TII and a NA, assuming the intercooler is sufficient and the initial temperature entering the engine is the same.
mike [/quote]
yes, but the TII has a lower compression ratio, 8.5:1 compared to an NA compression ration of 9.4:1 (FSM Engine section). this should compensate for the increase in temperature due to turbocharging combined with a undersized TMIC, should it not?
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Joined: May 2002
Posts: 22,465
From: California
no its doesnt, the turbo "adds" compression. just the ratio of largest chamber volume to smalest chamber volume does not tell you what octane you can run, nor what cylinder pressures are gonna be like. i think a stock t2 will run on 87 cause they cant have the think blow up if you put the wrong gas in the tank, but they recommend 92+ octane in the book.
mike
mike
Thread Starter
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Joined: Apr 2003
Posts: 51
wow nice responses everyone, i was wondering for my dad and i. we've always run 87 on it and its run fine, its been breaking up a little around 2000-3000 rpm under light pedal pressure (Just enough to keep it rolling when in traffic speeds or like cruise control). So i was thinking that maybe it was because of the gas, we'll start running 93 which sucks $$$ wise but oh well, got to keep her running well. Thanks for the plugs also.
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Joined: Apr 2002
Posts: 870
From: NASA/JSC - Clear Lake, TX
like i said previously, the turbo adds compression BEFORE the engine intake, and it is cooled BEFORE the intake. The cause of detonation is high AF mixture temperature, not pressure within the chamber. If a car is intercooled and the ENGINE compression ratio is decrease, there is no reason why a turbo car cant run on low grade gas.
when you say the turbo adds to the overall compression of the air, you are correct. however, you could compress the intake air with a ratio of 20:1, properly cool it down to ambient temps, and compress it again in the engine 8.5:1, resulting in an overall ratio of 28:5:1 and NOT have detonation until spark. you have to look at air cooling and AF mixture temperatures, NOT just pressures
when you say the turbo adds to the overall compression of the air, you are correct. however, you could compress the intake air with a ratio of 20:1, properly cool it down to ambient temps, and compress it again in the engine 8.5:1, resulting in an overall ratio of 28:5:1 and NOT have detonation until spark. you have to look at air cooling and AF mixture temperatures, NOT just pressures
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Joined: Apr 2002
Posts: 870
From: NASA/JSC - Clear Lake, TX
Originally Posted by ChainSawOnSteroids' date='Apr 29 2003, 06:45 PM
you didnt get it then, if you have an N/A it is better to use 87! better for the engine it runs better, and better gas mileage
for turbo its the other way around 93
for turbo its the other way around 93
i have heard somehting about adding 2 cycle oil to the mix, or something like that. what's that all about?
Senior Member
Joined: Apr 2002
Posts: 870
From: NASA/JSC - Clear Lake, TX
Originally Posted by j9fd3s' date='Apr 29 2003, 04:40 PM
no its doesnt, the turbo "adds" compression. just the ratio of largest chamber volume to smalest chamber volume does not tell you what octane you can run, nor what cylinder pressures are gonna be like. i think a stock t2 will run on 87 cause they cant have the think blow up if you put the wrong gas in the tank, but they recommend 92+ octane in the book.
mike
mike
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Joined: Aug 2002
Posts: 1,801
From: Eastern PA
Its not that you cant run low octane on a boosted car (especially stock)... its just safer to run higher octane which is why most manufacturers recommend it. I remember boosting to 15psi on 93 was the best I could do before mild detonation and the ecu cutting fuel to avoid a blow up (DSM)... At the track, I put in 104 octane and ran 17psi no problem.
