max compression for 50/50 mix? 12.5

[f150mann]

if i ran a 50/50 mix of 92 octane and 110, whats my max piston compression i could run? 12.5????? anyone know? or anyone with 12.5 pistons what fuel do you run

[zrpilot]

depends on the cam selection, but in general a 12:1 is going to require 110 octane.

Mixing is a gamble. I remember reading somewhere that mixing on a molecular level never really produces the results desired.

[f150mann]

full 110 is only 12:1? that doesnt sounds right... if 11:1 runs on 92, 12:1 shouldnt take 18 more octane.

it will be with a hotcam stage one.

im building a 440, hotcam stage 2, just not sure on compression yet. hd studs are a given.

[underpowered]

12.5 would be pushing it on mix.

i have to run mix at a minimum on my 11:1 426, it pings on straight 93 with my setup. so i would run straight race to be safe, and even if you went with 11:1 i would mix atleast.

[zrpilot]

Originally posted by underpowered
12.5 would be pushing it on mix.

i have to run mix at a minimum on my 11:1 426, it pings on straight 93 with my setup. so i would run straight race to be safe, and even if you went with 11:1 i would mix atleast.

Yup me too. MY 11:1 416 has detonation on 93 octane, but runs nicely with 110.

It all depends!!!

Available gas in your area!
Dynamic compression ratio
Outside Temp
accuracy of jetting
Exhaust system (most exhaust full exhaust systems for the 400EX lean out the A/F around 2000-3000 RPM due to unequal runner length) Could require higher octane

[REDRIDDER]

I've run 110 in my 400ex when it was stock and i thought that the throttle response was a little crisper.....or it was just a placebo lol..

[JOEX]

Originally posted by zrpilot
...
Exhaust system (most exhaust full exhaust systems for the 400EX lean out the A/F around 2000-3000 RPM due to unequal runner length) Could require higher octane
Do you have any more info on this? People have mentioned the unequal runner length a couple of times but I haven't heard anything else about it and how it affects performance.

[zrpilot]

Originally posted by JOEX
Do you have any more info on this? People have mentioned the unequal runner length a couple of times but I haven't heard anything else about it and how it affects performance.

I have witnessed it first hand and spoke to Laz at GT Thunder about this issue on my 416EX. He has told me the best exhaust to run that reduces this hesitation is the Sparks X6.

Here is a quote directly from an exhaust test he did:

" For all of you who have ridden a 400ex that is modified in any way I am sure you have noticed a hesitation and or coughing at 2-3000 rpm if you peg the throttle. I will try to explain the best I can what I have observed on this subject.

When I first modified a 400 I noticed this and I also noticed this on the dyno graphs from dynojet that came with the K&N jet kit. When I built my first exhaust for this bike I wanted to build both head pipes the same length but had trouble fitting it to the bike nicely. On the first DMC system I noticed that they had the tuned length the same on both pipes and that the dip in the power was gone on the dyno.

On my latest system that I built I have the tuned length within 3/4 inch the same tuned length. with this system there is also no dip in the power on the track or on the dyno.

I have also noticed that if the header pipes are tuned to the same length the collector needs to be larger than if the head pipes are of a different tuned length. I believe that I know the reason for this and have spoken to several tuners about this and will be asking two of them to write an article on this subject. I have contacted a company to build an exhaust to solve this problem as I don’t have time to build exhausts other than for R&D."

[JOEX]

Thanks:)

How long ago was that?

[zrpilot]

I'm guessing based on Laz's '80s hair, it was 2000?

here is the link:

gt thunder (http://www.geocities.com/gtthunder.geo/shootout.html)

[Big - D Racing]

I have 12:1 and run VP C-12 straight, which is 108 octane. I would never use mixed gas. With 11:1 I would only run 50/50 mix, I wouldn't even mess with 93