N/A build discussion
By greengoblin
#233939
If you have a REALLY good tuner ... no you don't. But you should to be on the safe side. Octane only prevents detonation ... which is good. I've seen a 13.5:1 motor run on 87 octane, but that guy was a crazy good tuner. For the rest of us ... stick with higher octane fuel.


Even with a good tuner, 87 octane is too low, no one will ever tune a high 13 comp at the pump, not even me. With 87, the engine will definitely be knocking even though you cant hear it. If you have an easy supply of e-85 that would be the best way to go and its still pump gas. You will gain more torque, run cooler, and less chance of detonation.
By AutoXCivic
#234049
greengoblin wrote:
If you have a REALLY good tuner ... no you don't. But you should to be on the safe side. Octane only prevents detonation ... which is good. I've seen a 13.5:1 motor run on 87 octane, but that guy was a crazy good tuner. For the rest of us ... stick with higher octane fuel.


Even with a good tuner, 87 octane is too low, no one will ever tune a high 13 comp at the pump, not even me. With 87, the engine will definitely be knocking even though you cant hear it. If you have an easy supply of e-85 that would be the best way to go and its still pump gas. You will gain more torque, run cooler, and less chance of detonation.


Whoops sorry my bad. It's 12.5:1 CR, just looked at the post again. But a lot of people would argue that CR is too high for 87 octane too. But it's not. Guy makes good power and torque, nice smooth power band ... and NO PINGING.

Take a look.

Visuals on page 2. Some people are so smart it makes my head hurt.
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By LaosToaster
#234323 just learned something new here. thanks guys 8)
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By poorman type-r
#236041 Its all in the tune bro. Lol my friend ran 14.4:1 comp on 93 without a problem so im sure you can run 89 or 91 with a good tune.
By AutoXCivic
#237063 The D-series motors make it much easier to run higher compression on pump gas than a B-series. This is due to the smaller bore of the cylinder which aid in resisting detonation. Motorcycles run 12.5 - 13:1 CR on pump gas in stock trim. They are able to do this, partially, because of the tiny little cylinders they have.
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By suspendedHatch
#237092 This is silly.

By "good tune" you mean that there is a serious compromise made to the ignition timing. You are not making maximum torque.

You want to run at least 91 (USA) even when tuning a stock engine so you can find max torque. A dyno shop will have race gas for tuning a built motor even if you plan to run it on pump gas. Once you find max torque, you can back off the timing for engine safety. The last thing you want is to start having random pinging when you're trying to tune the motor.
By AutoXCivic
#237568
suspendedHatch wrote:This is silly.

By "good tune" you mean that there is a serious compromise made to the ignition timing. You are not making maximum torque.

You want to run at least 91 (USA) even when tuning a stock engine so you can find max torque. A dyno shop will have race gas for tuning a built motor even if you plan to run it on pump gas. Once you find max torque, you can back off the timing for engine safety. The last thing you want is to start having random pinging when you're trying to tune the motor.


No that's a "conservative tune" a good tune is one that takes the best of both worlds. It manages to give you a good balance between power and survivability. At least that's how I would define a good tune. Yes you can tune on the ragged edge to extract every last drop of power and torque from the engine, but then you run a higher risk of catastrophic failure. And yes you can tune it so there is little to no risk of anything ever going boom, but then it's no fun, because it doesn't make any power. A good tuner will find a balance between these two especially if you are looking to make a DD. In a race car, you might not be nearly as worried about survivability since the engine is probably going to be rebuilt every season anyway, and breaking something is kind of par for the course. But for the most part you will want to have a good balance between "Wheee" and "worry".

Too much "whee" and you worry too much about "boom" to have any fun.
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By suspendedHatch
#237859 That's not the same thing as what was being discussed in this thread. What you're saying now is basically what I said. You're describing how a car is tuned. You find max torque and then back the ignition timing down a bit for safety. Set up knock protection. Smooth the map so you don't have any sudden changes in timing from one cell to the next.

Running low octane on a built motor can only result in compromised power and risk to the engine. There's no getting around it. There's no magic tuning.
By AutoXCivic
#238541 Power wasn't being discussed at all. The OP asked what octane was needed. I was merely stating that he didn't need to run 93 octane depending on how the car is tuned. I didn't say it was the best way to go, just stating that there are other options and then I gave my reference, which shows that you can make good power and torque on a higher compression motor (than OP) using low octane fuel.