Piston compression..........

[B450r]

wht is the highest compression u can use while using pump gas.......... like 12:1 or 12.5:1

let me know..
THANX

[stocktires]

on a 450r, 13.5:1 is the highest one should go with pump fuel.

[krt400ex]

Originally posted by stocktires
on a 450r, 13.5:1 is the highest one should go with pump fuel.

DO NOT GO THAT HIGH!!!!! THAT IS REDICULOUS!!!!

12:1 is right about ur the highest u want to go. 12.5:1 is border line. i know a guy who is a professional engine builder and he races a 450R. he had no race gas one day so he ran pump gas on a 12.5:1 comp piston, his jetting was correct, and he burnt up his piston and rings. he has learned from experiance and i am passing it on to u. 12:1 is it.

[stocktires]

Originally posted by krt400ex
DO NOT GO THAT HIGH!!!!! THAT IS REDICULOUS!!!!

12:1 is right about ur the highest u want to go. 12.5:1 is border line. i know a guy who is a professional engine builder and he races a 450R. he had no race gas one day so he ran pump gas on a 12.5:1 comp piston, his jetting was correct, and he burnt up his piston and rings. he has learned from experiance and i am passing it on to u. 12:1 is it.

I disagree on this topic again, but I will say that for an everyday weekend warrior type of rider, a 12.5:1 should be the perfect set-up. 12:5:1 in a 450r motor is not NEARLY pushing the limits. Its not a 400ex krt, these CRF style motors can take MUCH more than a XR based motor.
You engine builder buddy is an idiot.

[stocktires]

http://www.thumpertalk.com/forum/showthread.php?t=385561&highlight=race+gas

Very good thread, please check it out!

[stocktires]

Originally posted by krt400ex
DO NOT GO THAT HIGH!!!!! THAT IS REDICULOUS!!!!

12:1 is right about ur the highest u want to go. 12.5:1 is border line. i know a guy who is a professional engine builder and he races a 450R. he had no race gas one day so he ran pump gas on a 12.5:1 comp piston, his jetting was correct, and he burnt up his piston and rings. he has learned from experiance and i am passing it on to u. 12:1 is it.

His jetting was NOT correct, you can't just change fuels like underwear.

[krt400ex]

Originally posted by stocktires
His jetting was NOT correct, you can't just change fuels like underwear.


#1, with race fuel u will need to lean out ur jetting a little, so his jetting was a little rich. that would not hurt a motor if anything it will help.

#2, i am finished argueing, i answered u in the other post we were arguing over. the guy i know is not an idiot. in fact he is one of the very few sponsored privateers racing. i would say that it would take some experience on and off the track to achieve something like that.

[400eXr1d3rZ]

krt400ex, he burnt up his piston and rings? How were the conditions outside? If it's extremly hot, your bike will run hot, hotter<overheat<detonation. Higher octane gas is a good idea whens it's 98+ degrees outside. But not mandatory.

[dork]

there are many variables that control how much compression you can get away with on pump gas: cam duration, chamber turbulence, rpm, elevation, engine load, jetting, etc. so if someone's gonna make a blanket statement about it, then it should be on the conservative side. in the case of a 450r, 12 to 12.5:1 is reasonable. 13-13.5 is race gas territory for, at least 50/50 mix. also you don't always jet leaner on race gas, it depends on the specific gravity of the fuel and whether or not its oxygenated.

[krt400ex]

Originally posted by dork
also you don't always jet leaner on race gas, it depends on the specific gravity of the fuel and whether or not its oxygenated.

u r right, ogenated fuels go richer, but he doesn't run that.


he was running a sparks full race motor. basically the same one that john natalie ran, but his compression was lower. he is now running a 14:1 comp, u know stocktires, he should be just fine on pump gas...right?

[B450r]

THANX guys

i think i will use 12:1.......you don't have to change ur jetting or anything like that do u? jus wondering

[400eXr1d3rZ]

Yes, richen your jetting.

Order from C&D Racing, site sponser, they have good prices. Colby, or whomever you talk too, will tell you the correct jets.

[stocktires]

Originally posted by krt400ex
u r right, ogenated fuels go richer, but he doesn't run that.


he was running a sparks full race motor. basically the same one that john natalie ran, but his compression was lower. he is now running a 14:1 comp, u know stocktires, he should be just fine on pump gas...right?


SURE! Why not go 15:1 while your at it!

Seriously, I'd say no, If you read I have said 13.5:1 is the limit on the CRF style motor. 14:1 may work, but that's pushing it too much for me in any motor. Seriously, read that thread, you may LEARN something, lol.

[Architects]

I wouldnt go past low 12:1 without race gas. 13:1 up is definately race gas territory

[krt400ex]

Originally posted by stocktires
SURE! Why not go 15:1 while your at it!

Seriously, I'd say no, If you read I have said 13.5:1 is the limit on the CRF style motor. 14:1 may work, but that's pushing it too much for me in any motor. Seriously, read that thread, you may LEARN something, lol.


no duh...

[400exrider707]

No way no how would I run pump gas on 13.5:1 compression. I usually mix some race gas in with pump for 12.5:1. 12:1 is about as high as I would go with straight pump. Dork hit the nail on the head though, there are too many variables to just make a flat out statement for it. If your running a cam with monster overlap then you can run even lower octane, and so on and so on.

Originally posted by 400exrider707
No way no how would I run pump gas on 13.5:1 compression. I usually mix some race gas in with pump for 12.5:1. 12:1 is about as high as I would go with straight pump. Dork hit the nail on the head though, there are too many variables to just make a flat out statement for it. If your running a cam with monster overlap then you can run even lower octane, and so on and so on.

I always heard that highest for air cooled is 11:1 but that wasn't that safe so 10:1 should be the highest for air cooled relibility so i heard.
For liquid cooled i heard 12:1 is the highest on pump.

My motor is 12.5:1 if I did go to a 13:1 would it gain much more hp? My motor runs really hot and starts to over heat with in about 20 min. Is it cause i should be running race gas? I already have a PWR radiator. Im told that yz426 motors dont like race gas.

[stocktires]

Originally posted by slow
I always heard that highest for air cooled is 11:1 but that wasn't that safe so 10:1 should be the highest for air cooled relibility so i heard.
For liquid cooled i heard 12:1 is the highest on pump.

My motor is 12.5:1 if I did go to a 13:1 would it gain much more hp? My motor runs really hot and starts to over heat with in about 20 min. Is it cause i should be running race gas? I already have a PWR radiator. Im told that yz426 motors dont like race gas.

YZF motors run hot. Is it in a hybrid? Race gas isn't needed for a 12.5:1 is a yzf. What kinda radiator are you running? I wouldn't buy a new piston for just half a pound of compression, not really that worth it IMO.

[krt400ex]

Originally posted by stocktires
YZF motors run hot. Is it in a hybrid? Race gas isn't needed for a 12.5:1 is a yzf. What kinda radiator are you running? I wouldn't buy a new piston for just half a pound of compression, not really that worth it IMO.


#1 don't listen to stocktires. he is misleading u because he himself has been mislead.

#2 u will fell a diff between a 12.5:1 and a 12:1 com piston. is it worth it? i don't think so unless u want that every little bit of performance possible. if u do go that high and ur motor already runs hot, u should start mixing race and pump fuel.

[stocktires]

Slow, please get some info else where. This whole thread is childish, including some of my own posts. Any good information I have will just be screwed up because of krt.

http://www.thumpertalk.com/forum/showthread.php?t=385561&highlight=race+gas

Please check that out, your motor is a bike motor and this will answer ALL your questions.

[Toadz400]

Originally posted by krt400ex
#1 don't listen to stocktires. he is misleading u because he himself has been mislead.

#2 u will fell a diff between a 12.5:1 and a 12:1 com piston. is it worth it? i don't think so unless u want that every little bit of performance possible. if u do go that high and ur motor already runs hot, u should start mixing race and pump fuel.

And who made you the expert? I'd trust stocktires over you anyday after seeing some of your posts/suggestions.

There are WAY too many variables to determine a safe point for using pump gas. You would need to give us all your modifications, elevation, temperature, etc. to really get a good suggestion on whether or not to run race gas.

With a 450 engine I would probably not go over 12.5:1 without mixing or running race gas. You know why? YFZ's came with 11.9:1 compression on the '04 and '05's, so that's not that big of a jump. 450R's I believe came with 12:1 compression so once again a jump to 12.5:1 isn't going to make quite a difference. But once again temperature, mods, and elevation make a HUGE difference on what you can run in your engine.

The guy who blew his engine on that one race just by switching to pump gas obviously had some other issues inside his engine he did not know about. It was NOT caused by running that pump gas, unless he was running a 13.5:1 or higher piston with some pretty radical modifications. And what kind of professional engine builder that races would go to a race without race gas (if he needed it)?

[Toadz400]

And slow, your jetting is probably too lean. Have you considered taking it to a dyno to have it properly jetted?

[krt400ex]

Originally posted by Toadz400
And who made you the expert? I'd trust stocktires over you anyday after seeing some of your posts/suggestions.

There are WAY too many variables to determine a safe point for using pump gas. You would need to give us all your modifications, elevation, temperature, etc. to really get a good suggestion on whether or not to run race gas.

With a 450 engine I would probably not go over 12.5:1 without mixing or running race gas. You know why? YFZ's came with 11.9:1 compression on the '04 and '05's, so that's not that big of a jump. 450R's I believe came with 12:1 compression so once again a jump to 12.5:1 isn't going to make quite a difference. But once again temperature, mods, and elevation make a HUGE difference on what you can run in your engine.

The guy who blew his engine on that one race just by switching to pump gas obviously had some other issues inside his engine he did not know about. It was NOT caused by running that pump gas, unless he was running a 13.5:1 or higher piston with some pretty radical modifications. And what kind of professional engine builder that races would go to a race without race gas (if he needed it)?


what kinds of post/suggestions r those? start listing. ya, ive been wrong before, but:

#1 i have learned alot and

#2 i know that i am correct.

i will say that i made a mistake about the bike he was riding though. i talked to him today. he was on a 265R. the compression was 220psi and he was running pump gas because he ran out of race gas. he didn't burn up his piston nad rings, he melted a hole through the piston and melted the spark plug.

he has been building engines for over ten yrs, so he has some experience under his belt.

[B450r]

i have an 05 450r and the stock is 10.5:1

i have a pro circuit T-4 slip on, dyno jetting, and a 13 tooth front sprocket.

i think im going to use a 12:1 with 93 octane.
also goin to get re jetting. should i get a cam, if so what kind stage 1 or 2.
is that a good idea?

THANX

[Toadz400]

Originally posted by krt400ex
i will say that i made a mistake about the bike he was riding though. i talked to him today. he was on a 265R. the compression was 220psi and he was running pump gas because he ran out of race gas. he didn't burn up his piston nad rings, he melted a hole through the piston and melted the spark plug.

he has been building engines for over ten yrs, so he has some experience under his belt.

I don't believe you made a "mistake" talking about the engine builder racing. Sounds like you deliberately said a 450R with 12.5:1 compression was what he was riding just so you could TRY and prove stocktires wrong. How else could you confuse a 450R running 12.5:1 compression with a 265R at 220PSI. The only thing that's the same is the R at the end of the name! There's quite a difference. I could believe an R burning up a piston running on pump gas with 220 PSI of compression, that is some major compression to be pumping out in a 2-stroke. My previous engine builder ran 220 PSI in his 265R and he could go no lower than 110 octane. He did run it at either 50:1 or 100:1 depending on what he was using it for (50:1 for the trails and 100:1 for racing) and he never had a single problem, every time he tore it apart it looked brand new. If he has 10 years under his belt, shouldn't he know that running pump gas on his high compression 2-stroke would ultimately lead to destruction?

Now away from that bickering. I guess I'll admit I was wrong on the 450R compression, I did say "I believe" because I wasn't sure, as B450R says it's 10.5:1. Did they change the compression on the '06 450R's to 12:1 or anywhere near that? I remember hearing from someone that they did...or maybe I heard wrong or the person was wrong. Anyway, 12.5:1 on a 450R should be safe running on pump gas as long as there are no other radical engine modifications. But if you do experience detonation obviously you should run a mix or race gas depending on how bad it is, that is really the only for sure way to know; by running it. I know on a YFZ there are many people running 12.5:1 on pump gas and have never had any problems. Now anything above 12.5:1 I would suggest running race gas or at least a mix of it. This is where I don't exactly agree with stocktires as I have never heard anyone have a problem with mixing race gas with pump gas or giving any reason as to why it wouldn't mix properly.

*Edit* - The compression was changed to 12.0:1 for the '06 and '07 450R.

Originally posted by stocktires
YZF motors run hot. Is it in a hybrid? Race gas isn't needed for a 12.5:1 is a yzf. What kinda radiator are you running? I wouldn't buy a new piston for just half a pound of compression, not really that worth it IMO.

I run a 250r PWR Radiator. I though 400ex's ran hot and liquid cooled ran much cooler like said. Well this motor i have runs just as hot if not hotter.

Im running normal quad coolant. Should i switch to engine ice? Its said to lower temps by 30.

i looked in a 04 mag and the 450r was like 10:1 or somthing like that compression. Did it get bumped up over the years??

Every time i drive i let it cool like every 20 min cause at about that amout of time theirs a little coolant bubling out the top cap and out the water pump cover. Do i have to take brakes or is it safe to run for a while?

[Toadz400]

Originally posted by slow
I run a 250r PWR Radiator. I though 400ex's ran hot and liquid cooled ran much cooler like said. Well this motor i have runs just as hot if not hotter.

Im running normal quad coolant. Should i switch to engine ice? Its said to lower temps by 30.

i looked in a 04 mag and the 450r was like 10:1 or somthing like that compression. Did it get bumped up over the years??

Every time i drive i let it cool like every 20 min cause at about that amout of time theirs a little coolant bubling out the top cap and out the water pump cover. Do i have to take brakes or is it safe to run for a while?

The 450 engines come lean from the factory to meet emissions. It's usually recommend that you rejet as soon as you bring it home. That's why they run hot. I wouldn't worry about switching coolants, rejet your carb and you should be fine on temperature as long as you are moving.

Since it sounds like you need help getting this done, what quad do you have? What year? What's your mods? What's your elevation? Temperature? Current jetting? This should help us help you get your jetting right on.

The '04 and '05 450R had the lower compression, they bumped it up to 12:1 for the '06 and '07.

[Mike[socal]]

A riding buddy of mine rides an 05 crf450. He recently rebuilt the top end with a J&E 12.5:1 piston and runs pump CA 91 without any problems. We ride at or below sea level.

[krt400ex]

Originally posted by Toadz400
I don't believe you made a "mistake" talking about the engine builder racing. Sounds like you deliberately said a 450R with 12.5:1 compression was what he was riding just so you could TRY and prove stocktires wrong. How else could you confuse a 450R running 12.5:1 compression with a 265R at 220PSI. The only thing that's the same is the R at the end of the name! There's quite a difference. I could believe an R burning up a piston running on pump gas with 220 PSI of compression, that is some major compression to be pumping out in a 2-stroke. My previous engine builder ran 220 PSI in his 265R and he could go no lower than 110 octane. He did run it at either 50:1 or 100:1 depending on what he was using it for (50:1 for the trails and 100:1 for racing) and he never had a single problem, every time he tore it apart it looked brand new. If he has 10 years under his belt, shouldn't he know that running pump gas on his high compression 2-stroke would ultimately lead to destruction?

Now away from that bickering. I guess I'll admit I was wrong on the 450R compression, I did say "I believe" because I wasn't sure, as B450R says it's 10.5:1. Did they change the compression on the '06 450R's to 12:1 or anywhere near that? I remember hearing from someone that they did...or maybe I heard wrong or the person was wrong. Anyway, 12.5:1 on a 450R should be safe running on pump gas as long as there are no other radical engine modifications. But if you do experience detonation obviously you should run a mix or race gas depending on how bad it is, that is really the only for sure way to know; by running it. I know on a YFZ there are many people running 12.5:1 on pump gas and have never had any problems. Now anything above 12.5:1 I would suggest running race gas or at least a mix of it. This is where I don't exactly agree with stocktires as I have never heard anyone have a problem with mixing race gas with pump gas or giving any reason as to why it wouldn't mix properly.

*Edit* - The compression was changed to 12.0:1 for the '06 and '07 450R.

ok, i didn't confuse those 2 on purpose. he told me this the first time like 1 yr ago, and he didn't say which bike when he told me, so i assumed it was his 450R. he owns a 265 and 450. sry about that. i corrected myself after i talked to him on tuesday. i was asking him questions to make sure i had my facts right and that is when i founf out i was mistaken. he ran out of race gas in the first moto, and he didn't want to DNF, tht is why he ran the pump gas.

if i did that on purpose, do u think i would have gone back and corrected myself??

the whole time i have been arguing with stocktires it has been over that fact that i think u should not go over 12.5:1 on pump gas. i said that was pushing it. and i have been arguing about the 50:50 mix of race fuel anf pump gas. i think that u can mix them just fine. u won't end up with something like mixxing water and oil. if u read back, u will see that everything here u just posted is what i have been trying to say.

and yes, the '06 and up 450Rs have 12.0:1 comp.

i am finished here, my point has been made over and over again.

[stocktires]

Originally posted by krt400ex
ok, i didn't confuse those 2 on purpose. he told me this the first time like 1 yr ago, and he didn't say which bike when he told me, so i assumed it was his 450R. he owns a 265 and 450. sry about that. i corrected myself after i talked to him on tuesday. i was asking him questions to make sure i had my facts right and that is when i founf out i was mistaken. he ran out of race gas in the first moto, and he didn't want to DNF, tht is why he ran the pump gas.

if i did that on purpose, do u think i would have gone back and corrected myself??

the whole time i have been arguing with stocktires it has been over that fact that i think u should not go over 12.5:1 on pump gas. i said that was pushing it. and i have been arguing about the 50:50 mix of race fuel anf pump gas. i think that u can mix them just fine. u won't end up with something like mixxing water and oil. if u read back, u will see that everything here u just posted is what i have been trying to say.

and yes, the '06 and up 450Rs have 12.0:1 comp.

i am finished here, my point has been made over and over again.


Please just stop running in circles, your "point has been maybe" so stop wasting everyones time. You need to understand that a compression ratio means maybe 50% of what gas you need to run, probably less. You also need to understand that every motor is completely different. Like the 450r vs. the 400ex. The 450r and most other modern 4-strokes with F1 inspired valvetrains can EASILY run much higher CR's on pump because of the very efficient combustion chambers and their large overlap cams do not trap cylinder pressure and there for they can use a low octane fuel...whew, that was a long sentence.
ALSO, mixing fuel is so 1970! You ruin both! The pump gas makes the consistency and cleaness of the race gas suck. With not needing the octane of the race gas (which you don't because you can run pump with 13.5:1, unless your pro), the race gas is a waste of money! Buy one or the other.
KRT, you are working and talking with old wives tales that hold no weight here with this F1 4 stroke crowd (dirtbikes and 450 quads). The 400ex crowd (like yourself) is a bit different, which i give you credit for because your argueing from that standpoint, while I'M talking about a 450r (which the guy is asking about).
Although it seems like your arguing just to win...

[krt400ex]

Originally posted by stocktires
Please just stop running in circles, your "point has been maybe" so stop wasting everyones time. You need to understand that a compression ratio means maybe 50% of what gas you need to run, probably less. You also need to understand that every motor is completely different. Like the 450r vs. the 400ex. The 450r and most other modern 4-strokes with F1 inspired valvetrains can EASILY run much higher CR's on pump because of the very efficient combustion chambers and their large overlap cams do not trap cylinder pressure and there for they can use a low octane fuel...whew, that was a long sentence.
ALSO, mixing fuel is so 1970! You ruin both! The pump gas makes the consistency and cleaness of the race gas suck. With not needing the octane of the race gas (which you don't because you can run pump with 13.5:1, unless your pro), the race gas is a waste of money! Buy one or the other.
KRT, you are working and talking with old wives tales that hold no weight here with this F1 4 stroke crowd (dirtbikes and 450 quads). The 400ex crowd (like yourself) is a bit different, which i give you credit for because your argueing from that standpoint, while I'M talking about a 450r (which the guy is asking about).
Although it seems like your arguing just to win...


i am not arguing about a 400ex. i know what the guy asked. i am tired of this. u r an @$$hole

[400eXr1d3rZ]

Originally posted by krt400ex
i am not arguing about a 400ex. i know what the guy asked. i am tired of this. u r an @$$hole

Why is he an *******? Because he's proving a point?

Have you ever had a high compression piston? Why do you think you need race fuel or 50/50 mix? Just because some guy who happens to " have 10 years under his belt" thinks he knows what he's talking about doesn't make him right.

[B450r]

lets jus stop the ARGUING...

i think all of u have made a point on wht to use so i will use 12:1

end of story.....

THANX GUYS