High vs Low Compression...

[YFZ-FoFiddy-TC]

Okay I cannot decide which route I want to go, so I'm wondering people's opinion and the pro's/con's of each.

How are maintenance and rebuild intervals affected with a 14:1 vs 12.5:1 piston? Also with a 14:1, would I want to run a 50/50 mix of premium pump and VP110?

Thanks,
Anthony

[chronicsmoke]

Well, how readily available is race fuel, how often do you ride, and how deep are your pockets?

I mix 50/50 with a 13:1, but I'm being generous. I could get away leaner than that, but a little extra assurance is always appreciated. Do you trail ride at all? that might pose an issue.

I only run my quad at the track, so while I do notice the extra cost of the race fuel, I only used 3 5-gallon pails so far this year. (80 bucks a pail up here)

Def. worth the extra oomff you get though.

[CJM]

Depends on how much you want to spend on gas. Compression means power, more compression more power you get. If its just your trail quad choose the highest you can go and still run on pump gas, if its race onyl you want the most power period and want to win so race fuel and its cost is justified.

Ex: Going up from stock compression on my 400EX of 9:1 397cc to 11:1 416cc yielded quite alot of power. Riding a stock 400EX makes me feel SLOW as hell vs mine. The small bump in overall cylinder size definately didnt cause it, its to small to really matter at less than 20cc.

BUT in the above example I set up my 400 to run on 93 octane. This was a huge limiting factor inmy book as race gas is $$$ and harder to find. My tanks only like 2.5 gallons and it costs 10 bucks just to fill itusing 93, I cant imagine what 100 + octane would cost me.

[chronicsmoke]

Originally posted by CJM
My tanks only like 2.5 gallons and it costs 10 bucks just to fill itusing 93, I cant imagine what 100 + octane would cost me.

I'd estimate probably arpund 25-30$ per tank of fuel mixing 50/50

Too lazy to do math right now

[CJM]

Originally posted by chronicsmoke
I'd estimate probably arpund 25-30$ per tank of fuel mixing 50/50

Too lazy to do math right now

Ill do it, figure even if its only 8/gal thats 20 bucks right there, Id imagine the cost is higher-I havent bought any race type of fuel in a LONG time.

[chronicsmoke]

Originally posted by CJM
Ill do it, figure even if its only 8/gal thats 20 bucks right there, Id imagine the cost is higher-I havent bought any race type of fuel in a LONG time.

Buying it by the pail runs me 100$ (20$/gal) and the cost of 91-94 is $1.30/liter ($4.90/Gal)

TRX450R tank is 3.1 Gal which would mean ~$38-40 bucks a tank (mixed 50/50) :eek2: now i remember why I never did the math!

But I just found a guy who sells 'D12' for about 60$ (bring your own pails though) which would make it ~26 bucks for a tank (mixed 50/50)

I've just discouraged myself for the day..

[CJM]

You discouraged yourself? hell you just discouraged me lol..

[Honda#4]

My turbo blue runs $6.00/gal and I only buy 5 gallons at a time, but I don't run my quad quite as much anymore so I don't mind spending on race gas, but for others it's a different story I guess.

[Balaz_73*00]

With a 14:1 you will definately have to run stright race fuel. All 14:1 pistons are single ring so youre looking at 12-15 hr life outa them for optimum performance. Unless you have 2 bikes, one race and one practice, Id stay away from the 14:1 unless you like rebuilding your top end often. Yes itll have mad "pop" and power, but its not worth it imo. If you want high compression, why not look into a 13:1 or 13.5:1? Why limit yourself to a 12.5:1 or 14:1? After this season will be 2 years on my 13:1. I run stright av100LL fuel and which is reasonably priced. My 13:1 is also dual ringed so I have a lil more reliability. Im more than happy with the power and reliability. My motor internals always look perfect running the av fuel too. 0.02

[YFZ-FoFiddy-TC]

I'm also considering a 13:1, I was just curious what people think of 14:1. VP110 is readily available here and is $7 a gallon if I bring my own cans. I think I'll go with a 13.25:1 and run a 50/50 mix.

Edit- I ride mostly dunes and rarely ride trails with it. Plan is to have a Grizzly 700 for trail riding by next season.

[400exrip]

Anything between12:5:1 and 13:1 comp ratio, I run straight race gas 110 to 112 octane

Now for those wild motors with 14:1 to 16:1 comp ratio, I run Straight race gas 114 to 116 octane and up.

Sunoco or VP race fuels are the best

[YFZ-FoFiddy-TC]

Originally posted by 400exrip
Anything between12:5:1 and 13:1 comp ratio, I run straight race gas 110 to 112 octane

Now for those wild motors with 14:1 to 16:1 comp ratio, I run Straight race gas 114 to 116 octane and up.

Sunoco or VP race fuels are the best

I called VP Tech and they don't recommend running straight VP110 unless it's 14:1 or higher. They tried selling me on U4.4 but that stuff is ungodly expensive.

[400exrip]

What Octane is the VP U4.4? I know a lot of the guys at the track run that fuel. And it smells like sour apple.

You can run 110 in a moped motor and not have any troubles out of it. But what I have always heard is if you have a motor that makes 12:1 comp ratio or more, to run race fuel. VP 100 octane is good fuel also

[YFZ-FoFiddy-TC]

Originally posted by 400exrip
What Octane is the VP U4.4? I know a lot of the guys at the track run that fuel. And it smells like sour apple.

You can run 110 in a moped motor and not have any troubles out of it. But what I have always heard is if you have a motor that makes 12:1 comp ratio or more, to run race fuel. VP 100 octane is good fuel also

They said you're fine with pump until you hit 13:1. The U4.4 is like 98 I think?

[400exrider707]

First of all, every motor is different, so you can't just generalize it and say at 13:1 you need to start running race fuel. There are a lot of factors. The octane is only there to prevent detonation or pre-ignition.

I ran an 11:1 in my 400ex for years and ran 87 octane with a cometic thin head gasket too, never once had an issue, but the 400ex is a different breed (if you've had the motor apart and know where the piston sits at TDC, you'll know why I got away running 87).

The last 450R we built, we did a baldwin 14:1. The bottom end power was just plain awesome. That piston with a stage 3 hotcam got us about 47hp on the dyno with a stock head and stock carb.

A race bike... I would definitely run the 14:1 again, I loved it.

A trail bike, pump gas only for me. I'd be running somewhere around 12:1 on a 450R or YFZ.