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Discussion Starter · #1 ·
Just wondering what is the determining factor for requiring race fuel. Is it how much power is made or how much boost you're pushing? I mean there are supercharged vette's out there running 15psi boost and putting down 600-700hp or more and still running pump gas. Then you have some Supras needing 28psi to hit that same power level but needs race fuel.

Reason I'm asking is because I just upped the boost in my car to 20psi and still running on pump gas. I did a few hard pulls while monitoring the AEM and I don't get any significant knock events.

So, for those of you running at higher power levels...please share your fuel situation :)
 

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There are a few factors...like engine size for one. Those vettes are running V8's. We have 6's. You can get more power out of a bigger engine on pump gas, thats just a simple fact. I know on suprastore.com they list that basically to get over 600 you need some sort of race gas/higher octane. Evo's have to use higher octance with even lower numbers because of the smaller engine. 25 psi on a 6 cyc is way different than a 4 cyc or 8 cyc. Also, a v8 is making power all the time during its cycle. A lot of people here are using c16 or something else to achieve the 600+ range safely.

Hope this helps.
 

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You dont need to run on race fuel unless you want to squeeze out some more HP.

As far as the corvette needing less boost than a supra to make the same HP... you have to consider that the vette has 2 extra cyclinders and has about double the displacement
 

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Discussion Starter · #4 ·
Sorry to mention that. I forgot to type what you guys just said. Bigger engine needs less boost to make same power. To be more specific. Is there a general PSI number where race fuel is needed on the 2JZ?

Or to be really specific....is it relatively safe to run daily at 20psi on pump gas? Keep in mind I run a GTE so the setup might differ a bit from you guys that have head gasket on a GE.
 

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While I'm pretty sure this is right, I'd wait for the experts to chime in.
The amount of boost you can run is going to depend on your specific situation. For example if you have two GTE motors, one with a small turbo one with a big one. The smaller one will knock first because it will compress and heat intake charge more, to get the same volume of air. Timing, headwork, squish etc will all determine the limits, so each situation will be different, but if you don't have significant knock then you can stay where you are, otherwise you need a higher octane fuel. Hope that is useful.
 

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2JZ's are know to run a maximum of 23/24 psi on pump gas (spraying meth/water)

ANything above that (25+ psi) will require race gas.
 

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On str8 pump its best to keep it under 18-19 psi (which is pushing it) Detonation is a fine line away. 16 psi would be ideal. Big reason why is that you'll never know when you will get bad batch of gas. Octane ratings do go down overtime. The race gas helps keep things cooler and detonation away and provides a better combustion.
 

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Discussion Starter · #8 ·
Damn, I guess I need to get off my lazy ass and hook up the methanol injection lol. 21psi is just too much fun ;)
 

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I wouldnt run anymore then 16-17psi max personally on 93oct on conservative timing/af's, too much chance of small spike or crappy gas to push it at 18-19psi..Unless your running a direct port meth injection you run the risk of popping a motor, just takes one good long pull with uneven cylinder distribution as a couple local people here have come to find out :/...Spend hundreds and thousand of dollars on parts, tuning, not to mention downtime just to cheap out on good race fuel is ashame..

Like already mentioned, bigger motors create much more power on much lower boost levels..A buddy of mine has a fully built 427ci TT vette on low boost will push 800+rwhp safely on pump gas, but how long you think that motors gonna last? He was told be very lucky to hit 20k street miles, HG's will pop left and right and the aluminum block won't like the higher boost he wants to run..
 

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While I'm pretty sure this is right, I'd wait for the experts to chime in.
The amount of boost you can run is going to depend on your specific situation. For example if you have two GTE motors, one with a small turbo one with a big one. The smaller one will knock first because it will compress and heat intake charge more, to get the same volume of air. Timing, headwork, squish etc will all determine the limits, so each situation will be different, but if you don't have significant knock then you can stay where you are, otherwise you need a higher octane fuel. Hope that is useful.
This is probably the best explaination of when race gas is needed or not needed.

Monitor your knock, and keep the timing conservative. Set your EMS to pull timing when too much knock is seen. Make sure your base timing (using timing light) is the same as what your EMS is reading. As someone said, a bad batch of pump gas can take out the motor even at safer boost levels and timing levels. Trust me, I know what can happen ;)
 

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Discussion Starter · #11 ·
htekwo, did you happen to be that red IS300 at TK2k8? I couldn't find the owner of it when I was there.

BTW...this is my daily driver so I can't exactly run around all day using race fuel lol. The only reason I'm running at 20-21psi is because I just happened to have a wastegate spring laying around. I can't bring it down a tick or anything heh. Worse case, I'll just pull it out and throw a boost controller on it later on.
 

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htekwo, did you happen to be that red IS300 at TK2k8? I couldn't find the owner of it when I was there.

BTW...this is my daily driver so I can't exactly run around all day using race fuel lol. The only reason I'm running at 20-21psi is because I just happened to have a wastegate spring laying around. I can't bring it down a tick or anything heh. Worse case, I'll just pull it out and throw a boost controller on it later on.
Yes, that was me. You must have seen it in staging lanes. The shut down the Test and Tune and I left it there until the Tech guy could get to it.

Worse case for you running 20psi on pump, I would never get gas from a 'discount' station. I would always use Texaco, Exon, Shell, etc. You run a better chance of always getting 'good' gas. Manual boost controllers are pretty cheap, I would get one ASAP ;)
 
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