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WILLIAMS37

Race motor, what can I expect?

24 posts in this topic

Well, did about half the research I should have but cracked the wallet open anyways. I have a crosworth 13.75:1 piston and gytr cams on their way for my 08 yz450f. Few questions some of you might be able to help me with. Any issues using an oem head gasket? Or oem valve springs? What will these parts do to my jetting? And what octane fuel can I get away with at sea level? Any help at all would be great as I'm not finding much with this compression ratio and cam specs.

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Problems and headaches that otherwise would never have been... That is what you should expect :)

 

All cynicism aside, the bike will no doubt perform better. I just never understand why, especially on a 450, anyone would sacrifice a proven motor like this for a little bit of extra power.

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Thanks for ur input

So is it common to have problems with high compression pistons then ?

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So is it common to have problems with high compression pistons then ?

 

It has been my experience, both personally and through proxy, that any time you start changing things with the engine beyond the OEM spec you will create problems for yourself. My input is nothing more than me speculating as I can't say for sure if these specific mods will be an issue or not. So, take it for what it's worth, which isn't a whole lot in this case.

 

That said, it's a freakin 450! It's already a beast. 

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Ok thanks a lot

Think I'm just going to keep standard for a while

Mines 426 though not 450

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Appreciate the heads up, but I have a stock 450 to ride whenever this will be for racing only, so it's not like I'm expecting 400 hours out of it. But some insight on tuning it in would be mighty helpful. Most of these parts are getting pretty close on the shipping tracker! Btw this build is a motor learning experience, I know it wont sound practical to most.

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If the listing for the GYT-R cams don't specify that certain springs must be used, fresh OEM springs are good.  The OEM head gasket, correctly installed, is also plenty well up to the job.  High compression will generally tend to richen the very low end, and not particularly affect the high end.  Cams?  Just have to run it and see.

 

Pump gas works in most cases, but 13.75 is a little high, and together with sea level riding, you might have to go up a point or two.  Pump gas is AKI 91/92, which would give it an approximate Motor Octane of about 87/88, or a Research octane of 95/96.  If you go with race gas, look for one blended for 4-stroke bikes that has a Motor number in the 90-95 range. (Research Octane, ~100)

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If the listing for the GYT-R cams don't specify that certain springs must be used, fresh OEM springs are good.  The OEM head gasket, correctly installed, is also plenty well up to the job.  High compression will generally tend to richen the very low end, and not particularly affect the high end.  Cams?  Just have to run it and see.

 

Pump gas works in most cases, but 13.75 is a little high, and together with sea level riding, you might have to go up a point or two.  Pump gas is AKI 91/92, which would give it an approximate Motor Octane of about 87/88, or a Research octane of 95/96.  If you go with race gas, look for one blended for 4-stroke bikes that has a Motor number in the 90-95 range.

Appreciate your valuable input Gray, doesn't seem as daunting or impractical as I first assumed. Shipping date changed from friday to august 5th to torture me no doubt.  I live in an area where I have access to vp and sunoco race fuel, sounds like ill be doing some reading up on research octane, but happy I may be able to get by with a mix of 93 pump and u4.4. 

 

This whole project came about because I assumed and set money aside to replace my warped head.  After tearing it down though,  I found my head to be still perfectly flat, but the cylinder had wear marks on opposite sides of the wall where it had worn completely through the nikasil.  I didn't install the piston but I can only assume that attention wasn't given to the correct way the rings go on.  Learning as I go,  but I know I care about my bike more than someone who is on the clock and wanting to go home.  Should hopefully make some power without being the deepest sounding 2 stroke on the track now  :banghead:

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25 years ago, any engine that had worn that far into a plated cylinder would have peeled off a chunk of it and blown parts all over a 30 foot radius.  The improvements made in last several years are stunning, taken in context.

 

I doubt it had anything to do with ring orientation.  More likely just simple wear; too much time on the thing.

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If the listing for the GYT-R cams don't specify that certain springs must be used, fresh OEM springs are good. The OEM head gasket, correctly installed, is also plenty well up to the job. High compression will generally tend to richen the very low end, and not particularly affect the high end. Cams? Just have to run it and see.

Pump gas works in most cases, but 13.75 is a little high, and together with sea level riding, you might have to go up a point or two. Pump gas is AKI 91/92, which would give it an approximate Motor Octane of about 87/88, or a Research octane of 95/96. If you go with race gas, look for one blended for 4-stroke bikes that has a Motor number in the 90-95 range. (Research Octane, ~100)

All dirt bikes call for 91 octane at the pump, nothin less. And if your going to run 110 octane or race fuel. It's best to mix a 5 gallon can with half 91 octane and the other half 110 octane. This will allow the higher octane fuel

To still burn good and clean but it won't be straight 110 that's sitting there burning up your motor. That's what I do and I race desert all the time. I learned my lesson when I ran straight race fuel and held my bike wide open on a lake bed during a race. Ya kaboom went the too end. Since then I mix half and half. Never had another motor blow on me thankfully

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If the listing for the GYT-R cams don't specify that certain springs must be used, fresh OEM springs are good. The OEM head gasket, correctly installed, is also plenty well up to the job. High compression will generally tend to richen the very low end, and not particularly affect the high end. Cams? Just have to run it and see.

Pump gas works in most cases, but 13.75 is a little high, and together with sea level riding, you might have to go up a point or two. Pump gas is AKI 91/92, which would give it an approximate Motor Octane of about 87/88, or a Research octane of 95/96. If you go with race gas, look for one blended for 4-stroke bikes that has a Motor number in the 90-95 range. (Research Octane, ~100)

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All dirt bikes call for 91 octane at the pump, nothin less. And if your going to run 110 octane or race fuel. It's best to mix a 5 gallon can with half 91 octane and the other half 110 octane. This will allow the higher octane fuel

To still burn good and clean but it won't be straight 110 that's sitting there burning up your motor. That's what I do and I race desert all the time. I learned my lesson when I ran straight race fuel and held my bike wide open on a lake bed during a race. Ya kaboom went the too end. Since then I mix half and half. Never had another motor blow on me thankfully

Octane rating is related to a fuels resistance to ignition. The higher the octane number the more difficult the fuel is to ignite.  Having a significantly higher octane rating than needed for the air fuel ratio, engine compression and other related engine operating parameters will actually reduce an engine performance when compared to a lower octane that is appropriate for those parameters.  I think your engine blew for reasons other than your fuel octane.   I do agree that running a 50/50 mix of (91 - 93) pump gas and high octane race fuel will be good for 13.5:1 compression with the correct jetting. 

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You guys replying to a two year old thread? The original poster has stopped riding and taken up non competitive badminton.

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You guys replying to a two year old thread? The original poster has stopped riding and taken up non competitive badminton.

I did not see that.  That is really funny!!!

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Octane rating is related to a fuels resistance to ignition.

 

Half true: Octane number is the fuel's resistance to ignition by any source other than open flame or spark

 

The higher the octane number the more difficult the fuel is to ignite.

 

Again, half true only.  See above.

 

Having a significantly higher octane rating than needed for the air fuel ratio, engine compression and other related engine operating parameters will actually reduce an engine performance when compared to a lower octane that is appropriate for those parameters.

Not true. Octane has no direct effect on ANY attribute of a fuel other than its resistance to detonation.

I think your engine blew for reasons other than your fuel octane.

The only way a fuel's octane could be connected to an engine failure is if it was low enough to allow significant detonation

 

 

Read:

www.thumpertalk.com/wiki/_/octane-ratings-higher-better-performance-right-r605?pg=1

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After more research, my comment on reduction in power with excessive octane was incorrect.  There are many variables and differences in fuels, other than octane that can impact the output power of an engine. 

 

gray- my other points were correct. We are talking about an internal combustion engine not an open flame ignition of fuel. 

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No one is talking about anything other than internal combustion engines.  Combustion of the fuel is supposed to be initiated by direct exposure to the spark at the plug ONLY.  Following that, the open flame from the small cluster of gasoline droplets ignited by the plug is what is supposed to ignite the rest of it, nothing else. 

 

High octane fuels are NO MORE DIFFICULT TO IGNITE by exposure to flame or spark than low octane fuels are, so those of your statements marked as half true were exactly that.

 

Go back and read the article again. 

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​OK I stand corrected (thrice).  Octane is the resistance to detonation, not ignition.  Thank you for the clarification. 

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