Compression ratio for new build?

[dsm_racing]

I'm about to build a reverse motor for my bike and I'm trying to decide what compression ratio to go with. Here's the mod list:

Wiseco 440
Stage 2 Hotcam
K&N open air box
Either full LRD exhaust or Two Brothers slip-on (I have both)
Rev box

I have the choice of either 11:1 or 12.5:1. I have motors with both set-ups, so I can pull the jug off either one.

My question is, can I run 93 octane on 12.5:1? When I bought the bike in question, the guy I bought it from ran 100 low lead, so that's what I've always done. I've never tried to see if it was possible to re-jet and run pump gas. For this motor, I'm sure I don't want to hassle with 100 octane. I want to be able to run the same 93 that I run in my 700xx and my RZR. Just for convenience.

[trailrider894]

Originally posted by dsm_racing
My question is, can I run 93 octane on 12.5:1? When I bought the bike in question, the guy I bought it from ran 100 low lead, so that's what I've always done. I've never tried to see if it was possible to re-jet and run pump gas. For this motor, I'm sure I don't want to hassle with 100 octane. I want to be able to run the same 93 that I run in my 700xx and my RZR. Just for convenience.

No you can not run 93 in a 12.5:1. Re-jetting is not going to fix it, it is a detonation issue.

[bherriman]

Yea 93 is a no go for 12.5:1, however if you do go with the 12.5 I would run something with lead in it. The lead helps lubricate the upper cylinder.

[honda400ex2003]

it sounds like 11:1 is the way to go if you want to run the same gas as your other machines. steve

[dsm_racing]

Yeah, I was pretty sure that was going to be the case. I didn't think that I could pull off the 12.5:1 on 93. I just don't think the little bit of extra compression and a few horsepower is worth the hassle of having to deal with buying and storing high octane. Especially when traveling. I think I'll just go with the 11:1 and stick with pump gas for the convenience.

[honda400ex2003]

<a href="http://www.myemoticons.com/"><img src="http://www.myemoticons.com/images/emotions/happy/raise-the-roof-1.gif" border="0" alt="raise-the-roof-1" title="raise-the-roof-1" /></a>

sounds like a done deal then. :D
steve

[400exshop]

Originally posted by dsm_racing
Yeah, I was pretty sure that was going to be the case. I didn't think that I could pull off the 12.5:1 on 93. I just don't think the little bit of extra compression and a few horsepower is worth the hassle of having to deal with buying and storing high octane. Especially when traveling. I think I'll just go with the 11:1 and stick with pump gas for the convenience.
have you run the 440ex in the 1/8 mile to see what it will do ? I see you ran the car.

[dsm_racing]

No, I've never taken either of the bikes to the strip. These are my way of unwinding and I try not to get competitive about it. I do plan to dyno tune this one once I get it going, though. I want to make sure I've got the a/f ratio right once I get it jetted and I want to see if there is a noticable difference between my full LRD exhaust and the Two Brothers slip-on.