Why can my sv with 11.5:1 run on 87, but say a GSR/ITR with 11.5:1 is recommended to run 91/92(at least)?. Just thought about it and was curious. Does it have to do with the head design, because i was under the impression that our honda heads are great from factory.

 

good question, i was thinking about that earlier today and couldnt really think of a good explination. maybe somebody on here will give us some insight.

 

I think higher revs might have something to do with it, but good question.

 

Maybe has something to do with timing, it might be a tid more conservative on a bike than on a car. That's the best I could come up with. Or if a bike has v-tech you can run like 15:1 compression on 87 octane too.

 

please say that was a joke

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by papa_smurf &raquo;</TD></TR><TR><TD CLASS="quote">please say that was a joke</TD></TR></TABLE>

yeah...definitely a joke! But vtek is the made note Anyway, ttt to see if we can get an answer.

 

with all the expertise on this site, someone has got to know.

 

It has to do with timing, fuel curves, fuel pressure, and the overall weight of the vehicle related to the size of the engine.

That's why.

 

load being much less do to weight on the engine. i guess i was just looking at it as an engine being an engine and didnt think about that. also didnt think it would have that big of an effect.

 

I've always wondered the same thing...but I wanted to tell you you've got a nice bike. I'd like to upgrade to an SV1000 naked in hopefully a yr. I Vtwins.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Ag-Eng &raquo;</TD></TR><TR><TD CLASS="quote">It has to do with timing, fuel curves, fuel pressure, and the overall weight of the vehicle related to the size of the engine.

That's why.</TD></TR></TABLE>

bam! i am going to say this is the best answer.

the power/weight ratio is so much better on a bike...basically there is less force resisting the piston from descending when the air/fuel mixture ignites. in a car, all the mass of the car is resisting the acceleration, and this means you have to generate a lot more pressure to force the piston down. more pressure means higher temps and more likely to detonate. bike combustion chambers would see lower pressures at the same compression ratio, so they raise the compression to get the most oomph per liter of displacement.

bikes with similar compression ratios to cars can run much leaner before they ping for the same reasons.

good discussion.

 

interesting discussion. I really can't say off the top of my head. I guess I'll bring it up sometime next season. It's always nice to learn new things

 

Static Compression Ratio != Dynamic Compression Ratio

While the bike might have more static compression ratio(i.e. volume of totally filled cylinder versus volume of combustion chamber - piston dome), its dynamic compression ratio is lower due to much more aggressive cams and a better flowing head given its displacement.

What this does is make the cylinder fill less for conditions in which detonation is most likely - namely low engine speed, high load conditions like going up a hill at a low RPM. This also gives bikes their VERY rev happy nature by having much better volumetric efficiency in higher RPMs due to the aggressive cams and very good flow capacity from the ports.

Larry at Endyn used a pretty good analogy to describe this on his board ( http://www.theoldone.com ), but I can't remember it now. Red bull and vodka after finals =


I'll probably forget to watch this topic since I've been drinking a little, but feel free to IM me if I wasn't clear enough.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Def &raquo;</TD></TR><TR><TD CLASS="quote">Static Compression Ratio != Dynamic Compression Ratio

While the bike might have more static compression ratio(i.e. volume of totally filled cylinder versus volume of combustion chamber - piston dome), its dynamic compression ratio is lower due to much more aggressive cams and a better flowing head given its displacement.

What this does is make the cylinder fill less for conditions in which detonation is most likely - namely low engine speed, high load conditions like going up a hill at a low RPM. This also gives bikes their VERY rev happy nature by having much better volumetric efficiency in higher RPMs due to the aggressive cams and very good flow capacity from the ports.

Larry at Endyn used a pretty good analogy to describe this on his board ( http://www.theoldone.com ), but I can't remember it now. Red bull and vodka after finals =


I'll probably forget to watch this topic since I've been drinking a little, but feel free to IM me if I wasn't clear enough.</TD></TR></TABLE>

interesting. cant wait to learn more when i sit in on the ME internal combustion engine class next semester. Met up with my buddy yesterday outside his last final classroom with some whiskey/pepsi, i am so happy this break is here now.

 

Watch out for the red bull and vodka... couple of guys got really messed up on that. I've got enough red bull in me for a week. Gotta try to stay away from the vodka