High Octane Fuel

MB-Monkey · #1 (**permalink**) 12-18-2008, 12:22 AM

-General question-

i know these engines will run on 87 octane but seeing as high octane fuel burns cleaner i am wondering if high test 97 or greater would be beneficial

. We have Race fuel 110 Octane here available at the pump.

Any input is welcomed.

Technocyclist · #2 (**permalink**) 12-18-2008, 02:14 AM

High octane fuel is designed for high compression engines. The HT engine has only 6:1 compression ratio. Engine modifications are required to have the full benefits of high octane fuel.

The engine will run on high octane fuel, but there won't be any real substantial benefits...

**Bikeguy Joe** · #3 (**permalink**) 12-18-2008, 04:57 AM

It will actually make marginally less power.

machiasmort · #4 (**permalink**) 12-18-2008, 05:58 AM

Anybody ever measure the compression on a HT with the Base gasket removed. The gasket between the block and cylinder head... My bike is nasty!!! I run the higher octane and it does make a noteable difference.

**Bikeguy Joe** · #5 (**permalink**) 12-18-2008, 06:05 AM

You said "base gasket" then you said "the gasket between the block and the cylinder head". So, which one is it?

How much would that raise the compression, maybe to a whopping 7.5 to 1? High octane doesn't do anything until you are just a little higher than that- say 10 or 10.5 to 1. If you are running the chinese engine @ 10.5:1 I don't think that it will last very long.

What is a "noteable difference"? Compared to what?

Just askin', not arguing.

ZnsaneRyder · #6 (**permalink**) 12-18-2008, 06:35 AM

Ever since removing my RPM limiter, I run 93 octane. With 87 octane, it works fine, but doesn't rev as high or smooth as with premium.

*87 octane has more low-end torque, but I lose high-end HP compared to premium gas.

I get about 45-46mph max on 87 while I get over 50mph with 93 octane. Even if the engine has low compression, 93 octane works better and is quieter at high RPM.

Also the less chance of spark knock, the better. The few extra cents paid at the pump ensures the engine lasts longer.

Now as far as using race fuel, it won't make much difference unless your engine was REALLY hotrodded with high compression and aggressive timing. Just stick with premium, that's good enough for our bicycle engines.

**Bikeguy Joe** · #7 (**permalink**) 12-18-2008, 06:41 AM

Z- I think he's asking about octane in the 2 cycle chinese engines....

machiasmort · #8 (**permalink**) 12-18-2008, 01:56 PM

It's my impression that the base gasket is the gasket between the block and the cylinder head. I only removed one! It's a 2strk HT.

I notice a difference between 87oct. and 93oct. Quieter and faster top end. The bike kicks over real hard? How long will it last like this??? 500miles no probs yet!

jasonh · #9 (**permalink**) 12-18-2008, 02:02 PM

You may be running a bit lean which is why the 93 would do better.

The base gasket is the one between the crankcase and the cylinder. Then you have a head gasket between the cylinder and head.

These motors really don't need higher octane since the compression is so low. In a low compression motor, high octane is actually more inefficient than lower octane.