compression ratio

[93dirtrider400]

As yall know i have been wanting to put a 416 je piston kit in my 400.... could I put in 12.0.1 compression ratio and just use 91 octane pump fuel or would I have to use racing fuel? What compression ratio would be the best? Thanks.....

[riotact]

If you put the 12:1 in it you will have to run race fuel for sure.If you want to run pump gas I would run 10 or 10.5:1.

[slightlybent47]

Agreed

[gojk]

I have an 11:1 Wiseco, and I get away with pump(91) most of the time. If I am at the dunes with paddles or it is really hot outside, I have to run race gas mix.

[93dirtrider400]

alright with the 10 could you run 91 pump? whats yals suggestion? i do a lot of track riding and dune riding and wanting a decent increase in power!

[jasonwayne222]

ive got 11:1 and i live in louisiana and i run supreme most of the time but when its real hot outside itll overheat a lot quicker and lose power without race fuel.

[slightlybent47]

It’s not a big deal to use race fuel and if you mix it, it’s not that much more money.
I buy 5 gallons of race fuel and mix it 50-50 which will give me 10 gallons. You can ride a long time on 10 gallons of fuel. There is probably not that much deference between a 11:1 and 12:1 as far as performance, some but not a lot. I have 12:1 in mine and love it, but I do have to run a higher octane. But I only use about two to three gallons a week so I don’t spend a lot on fuel. And I live in Houston so race fuel is easy to get.

[93dirtrider400]

alright so i could go with a 12 1 ratio and used mixed racing fuel i wouldn't have to use straight? how much is the durability brought down on the engine? what brand of race fuel would you go with and is there different octanes or is it all the same?

[tri5ron]

Originally posted by 93dirtrider400
alright so i could go with a 12 1 ratio and used mixed racing fuel i wouldn't have to use straight? how much is the durability brought down on the engine? what brand of race fuel would you go with and is there different octanes or is it all the same? 12:1 without HD studs, will have the same durability as a tissue-paper raincoat.

[93dirtrider400]

so your saying you wouldn't do that?

[tri5ron]

Originally posted by 93dirtrider400
so your saying you wouldn't do that?
What I'm saying is,
If you want to go ANYTHING over 10.5:1 compression ratio,

AND you want Durability/Reliability,....
You MUST use the HD studs.

If you DO NOT use the HD studs,
properly installed,
by a shop,
using ROLL FORMED threads,
you WILL eventually yank the OEM studs right out of the cylinder.

The stock, OEM, factory cylinder studs, CAN NOT handle a compression ratio of 11:1 or 12:1, for very long.

LOTS of guys on here, have already learned this the hard, (and MORE EXPENSIVE), way. The only ones that will argue with that, are the ones who have yet to blow up their motor.
but make no mistake about it, it WILL happen.

When the time comes for me to bore mine,...
I will only be going to a 416, at 10.5:1,
and I will be putting in the HD studs at that time, just to play it safe.
Durability and Reliability is what mine is all about.
No 440,
No 12:1 compression,
No rev box,
No BS

The 400ex is a Bulletproof Woods/Trail/Desert bike, when properly built and maintained.
It no longer is a top contender "Race" bike, without pouring ungodly amounts of cash into it.

If you want a RACE bike, start over with a 450.
That's just the way it is.

Remember this,...
It is always safer to err on the side of caution.

[slightlybent47]

I’ve had a 416 with12:1 and stage 2 cam with a P&P in mine for the past year and I’ve had no problems with the stock studs what so ever.
If you torque the studs right they will last a long time. If I went over a 416 I’d do the studs.
In the winter I use VP U4.2 which is a strait pore in with no mixing needed and is 102 octane. But the U4.2 is an oxygenated fuel and runs a little hot in an air cooled engine so that’s why I only use it when it’s cold.
In the summer I use VP 110 or 114 and mix it half and half with 93 pump and that puts it close to 100- 104 octane.