10:1 vs 11:1?

[jimmy7120]

I am about to buy the wiseco piston 416 kit for my 400ex and there are two options; 10:1 and 11:1 compression. I had a few questions before a bought the kit.

Would the 10:1 be more reliable due to the lower compression?

Would the 11:1 still run with premium gas (93).

Why would someone choose the 10:1 over the 11:1 and vise verse.

I race xc and possible may be purchasing a new cam as well.

Any info would be helpful.

Also what are your thoughts on the EBC clutchs.

Thanks,

Jimmy

[Glamis400ex]

With the 11:1 you'll need head studs. 10:1...probably not. You can run the 11:1 on 93 pump. I run mine in the sand so I choose to mix with VP C12 for extra insurance.

Glamis

[jimmy7120]

Thanks for the quick reply.

[THE 400EX DUNER]

my 400ex has a wiseco 11:1 piston and i have to run a 50 50 mix of 110 octane and pump gas or the preignition is very noticable. keep in mind i am at 2500 ft. in the desert, but even in winter the preigniton is there. on a side note: dont run aviation fuel, as this is another topic all together. if you dont want to have to run race fuel stick with the 10:1 piston, but the 11:1 with the hot cam makes a world of difference from experience first hand.

[northwest Texas]

Originally posted by THE 400EX DUNER
on a side note: dont run aviation fuel, as this is another topic all together. Why? Explain please.

[ImplodedMindZ]

I run 11:1 piston and i run 91 octane gas in it and i have no problems whatsoever. although im only at 1200ft elevation. from what iv heard u dont need head studs until u go to like 12.5:1 or so compression. I dont have em, the guy that built my engine thats what he said too.

[flauge]

What about added stress on the rod and crank, would i have to worry about that if i ran 11:1?
Also, im just wondering would you be able to notice the difference in power between the two.? In a 416 kit, that is..
If there aint that much of a difference then I'll just get a 10:1 then.

[slipp]

i have a 2002

im running 11:1 compression wiesco piston..
i run on 93 octane.. runs fine
i dont know my elivation, but i live in south louisiana, im about 10ft or so below sea lvl.. so that should give you an idea. i dont have head studs or anything like that, i have been thinking to my self if i should do somthing to reinforce.. not sure yet though.. i am slighly concerned about long term damage, but.. none yet so..

[GPracer2500]

I've got a 10.8:1 JE 416 with a HC stg 2 (old version) and it pumps 180psi on my gauge. That's enough compression to knock pretty bad on the 91 pump fuel available in the Phoenix metro area.

AZ uses it's own blend of "boutique" fuel--and it sucks. Other blends of "boutique" fuels are used in various population centers around the country. Areas deemed "non-attainment" areas by the EPA must use reformulated gasoline. My point is that the sticker on the pump that shows the octane rating isn't the end-all be-all indication of it's performance in our engines. Joe Blow's 91 might not offer the same overall knock resistence as your 91.

I run mostly at the dunes in CA which are at about 200ft with low humidity (low humidity increases the engine's octane requirement). If I head up to the mountains (3000+ feet) here in AZ and don't ride too hard then the 91 is ok (sorta). When/if it knocks I can back off the gas and it stops.

At the dunes I run a 50/50 race/pump mix but switch to a 66/33 race/pump mix if it's hot (90+ degrees). That's what it takes to keep it from knocking on those long steep bowls and climbs.

As far as the rod and crank holding up to 11:1, I wouldn't loose sleep over it. Stay on top of your oil changes and I'd expect a reasonable engine life. 12:1 or higher and I'd be a lot less comfortable with the stock rod and crank.

[flauge]

Thats what im afraid of, it gets pretty hot here Ga in the summertime and im scared itll knock with 93. Im at sea level so that prolly wont help either..
10:1 might be my best bet huh?
But What about using an octane booster tho. GPracer i remember you said in another thread somewhere that there was some stuff by Kemco that really works..That'd be good enough for 11:1 wouldnt it?
Im still wondering if the power difference is noticeable btween the two. Is it noticeable?

[troutman561]

It gets hot in Ga yes, but he said low humidity is what makes it knock and require higher octain, Ga has high humidity so maybe that will make 93 alright then?

[GPracer2500]

I'd say the difference is noticable.

If you look at pumping pressures in PSI then 11:1 vs. 10:1 is about the same as going up 4500ft in elevation. That's a difference most people are going to be able to feel. It's not a perfect analogy because air density and the engine's ability to compress don't have exactly the same affect on performance. But it's sorta the same thing and significant elevation changes is something many folks have experienced. That's why I mention it.

10:1 = HD head studs aren't needed and I can't imagine deto taking place while using premium pump even under the most deto-prone conditions. Still almost a full point of static compression higher than stock.

11:1 = HD head studs are a must (in my opinion) and deto is a possibility depending on the quality of premium pump fuel in your area and the riding conditions. But most poeple choose 11:1 because it's a good middle ground between reliabilty and power.

Using stock gaskets (or gaskets of that same thickness) can make a difference. Cometic offers several different gasket kits (including a hi-comp kit--you don't want that) and can actually make you a custom thickness gasket (I'm thinking of a thicker base gasket here). When you're right on the edge of what pump gas will handle, getting the right gaskets can make all the difference. Using a Stg 2 cam and not a Stg 1 will help too (longer intake valve duration will reduce pumping pressures).

If the premium pump fuel available is 93, it's not a reformulated or boutique blend (which it's probably not if it's 93), and you're not drag racing up sand hills most of the time then you'll probably be fine.

I'd get the 11:1 and on the outside chance that it does knock you can deal with it. It'll just cost a little more to run the quad cause you'll have to either tear it down and change something or better yet, find a way to increase the octane rating of the fuel you use. If you're absolutely sure you don't want ANY chance of having to "deal with it" then just accept the reduced performance of 10:1 and have the piece of mind that you've got a low(er) stress engine.

All you can really do is try and consider all of the factors at play, make your choices, put it together, see what you've ended up with, and go from there.

[400exmkt]

I had the 10:1 on my 426 and then stepped it up to the 11:1. I run 93 with no problems. Plus i have factory studs with no problems. The 11:1 made a noticable improvment in my opinion, Go with that.

[ImplodedMindZ]

I am qurious why alot of people have to run 50/50 race gas on the 400ex when their compression ration is 11:1 or so, when outta the box the 450r has 12:1 and the, yfz450s have 11.4:1. Are these guys runnin 50/50 race gas outta the box w/ these quads. My friend uses 91octane in is yfz w/ no problems. Whats the big difference here that w/ a lower compression ration motor that we have to run higher octane fuel than any other quad w/ higher compression ration piston like the ones i listed above.

[GPracer2500]

Originally posted by ImplodedMindZ
I am qurious why alot of people have to run 50/50 race gas on the 400ex when their compression ration is 11:1 or so, when outta the box the 450r has 12:1 and the, yfz450s have 11.4:1. Are these guys runnin 50/50 race gas outta the box w/ these quads. My friend uses 91octane in is yfz w/ no problems. Whats the big difference here that w/ a lower compression ration motor that we have to run higher octane fuel than any other quad w/ higher compression ration piston like the ones i listed above.

Static compression ratio doesn't really mean all that much. Dynamic compression is what matters. Liquid cooling vs. air cooling and combustion chamber design makes a significant difference too.

I don't know the stock YFZ cam specs but with a Hotcams intake cam the YFZ intakes are left open unitil 64.5 degrees ABDC. What does that mean? A YFZ doesn't really have much (if any--and maybe less!) dynamic compression than a typical 11:1 400EX--even though the YFZ's static compression ratio might be higher.

[flauge]

Hmm. I think im just going to go for it and get the 11:1, but i am going to get hd studs tho. It is real humid around here in the summer so that'll prolly help.