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Bonneville speed trials

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justbummin1:
After having a terrible week top speed wise at the Bub speed trials at Bonneville I found you guys on line in my search for knowledge and answers.

 So here's the short version of the back story. We bought a 2007 GS-500F and decided to run in the production class this year at Bonneville (we are also running a ZX10 and a Hayabusa in the stock production classes). The record is 112 and change so after getting all the safety requirements done, carb work done and a couple dyno runs to prove that this record was a joke and didn't understand why it was so low and that we would be leaving with an new record!!!

WRONG!!! Reality is a Buddha Loves You and this is way harder then we ever thought it would be. We got in 12 runs over the 5 days with a blazing 104.905 as our fastest of the week. We made 2 front sprocket and 3 rear sprocket changes, 5th gear passes, 6th gear passes and most all of the runs where in the 100 to 102 mph range. We where having a fuel feed problem with the stock fuel petcock (now after the fact I see here that this is a common issue with the GS500's) so I don't know if on the extended full throttle run we where leaning out the motor and just starving it??? We did a plug check at the end of a run and they looked good so i think we where jetted right for the altitude but I am lost on why that was as much speed as we could get???

Any suggestions on what changes we need to start making for next year would be much appreciated but being in the production/production class we cant make any real changes from "factory stock"

Thanks, Rob

BTW: be gentle with me I'm new here!

burning1:
You're asking an interesting question... Will do a little reading/thinking and get back to you. Need to look into the speed week rules.

Off the top of my head though, 112MPH is pretty close to the maximum achievable speed of the GS500 on pavement... It's my understanding that you don't normally see a vehicle's maximum road speed on the salts, is that correct?

I can say, that on the local road race circuit, my maximum GPS confirmed speed was ~102MPH down the .4 mile front straight section of track (production bike, 100% stock intake, engine, exhaust, jetting.) I know the bike can do better than that, but an additional 12 MPH might be too much to ask, even with prod legal mods.

The Buddha:
Sorry to break it to ya ... but ... that's the rules, I dont make them, I only follow them ... but its OK you're new we can give you some slack right guys and gals ... So on behalf of the whole world of gstwin ... Pics ... or it didn't happen.

Cool.
Buddha.

justbummin1:
burning 1 - You are correct about losing top speed on the salt. I think most people figure about 2 to 5% slip depending on salt conditions which adds up quicker then you think. My dad rode the bike this year (72 year old guys are not real flexible to get down on the tank right) and the plan is for my son to run it next year so we should pick up a little there since he is smaller and can get tucked up better to get out of the air. When you are only working with 40 horse power wind resistance really counts.

Buddha - If I can figure out how I will get some pictures up tomorrow.

Currently we are trying to find out how much work we can do inside the motor and keep it legal. Don't know if they only check bore and stroke or if they do compression also??? Since you guys are the experts would polishing the intake/exhaust and shaving the head to bump up the compression get me any gain or would i just be pissing money away?

Rob

burning1:
Knowing what you can do legally would be a huge help. I tried to find the rules for your class, but it looks like I'd have to order the rulebook. If you happen to know of an online copy, I'll review.

The GS500 is a pretty low compression engine; 9:1 or so. Machining the heads/block will give you some power. An aftermarket exhaust (~$200-$300,) intake, jetting, cams, etc. could help a lot as well, especially if you port. But it depends on how much you're willing to put into the engine, and what the rules permit.

Stock, the GS500 puts out about 40 horsepower or so, at the rear wheel. I've seen race bikes that can put out 60 or so with the stock bore/stroke. Most of those engines have:

- Airbox removed, pods or intake trumpets
- Cams, shim-over-bucket, springs, etc.
- Full exhaust
- High comp pistons
- Rebalanced, lightened crank
- Rejet and/or flat slide carbs
- Balancer shaft removal

Cost on all that is probably ~$2000.

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