110 octane XC motor options?

[MtnEX]

If I am going to commit to 110 octane race fuel... what are my options on the engine build?

Good XC motor, not a hand grenade...

[Zakradu398]

12.5:1 piston, HD studs, stg 3 HotCam or Webcam, CRF timing chain, Hd clutch, +1 valves, Port and polish..

[ish416]

12.5:1 would be the absolute limit in my opinion.

The thing with the EX is the cooling. 12:1 might be more ideal for XC racing. Consider if your quad gets covered in mud and can't expel the heat efficiently. You are going to end up with a dead engine or a significant loss in power.

If I were to build an XC EX engine it would be:

12:1 standard bore, stg 2 hotcam (for mid-range power and overall ride-ability), ported head with possibly +1 valves, CRF timing chain, HD studs, a billet clutch basket and pressure plate, FCR carb (better throttle response and light throttle pull), full exhaust (likely a hybrid exhaust like I currently have. WB E-series slip-on with FMF Powerbomb header), cooling mods (over-sized oil tank, larger oil cooler and spal fan).

[MtnEX]

Thanks for the info so far.


Tired of dealing with pump gas problems. I am having good luck with the 110 in other applications. So I am thinking about just bumping up the compression on the 400 to run it too when I do it. Won't cost any more.

[JOHNDOE83]

In my opinion you dont start creating a "hand grenade" until you start raising the compression.

High compression with race gas isnt "unreliable" but it will lead to the possibility of malfunction under extended hardcore riding, more so then any other mod.

MX, XC and drag racing motors arent any different from eachother, the only difference is how open your air filter is to the element's.

Basically, your just looking to build a race motor.

Start with the basic's, bore/compression, cam, carb. Only do valve's if you really wanna go big and have the money to do so, you could do a mild port and polish for now to make up for it.

A stage 3 cam is specifically designed for a stroker motor and isnt recommended for non stroker application's, although there's a few people out there using them in non stroker's with good result's you might as well build it right so you dont have a "grenade".

I reccomend a 426 or a 440 with a stage 2 cam and a 450r carb with a valve job. Get a white bro's rev box and jett using the jetsrus method for main jet tunning and you'll be amazed at the performance gain.

If money is a issue, get high compression with a 450r carb and tune it right then get some upgraded shocks, most important for XC.

[MtnEX]

Well, I am playing with a few ideas... which is the nice thing about a Honda... there are lots of options and choices.

The thought I am having is that I'd like to freshen up the 400. I will have to open it up though before any real final decisions are made.

But I was thinking it would be nice to bring it up where it could serve as a race quad or backup/practice. Clearly it don't have to be another 450 to be competitive in a 2 hour XC race. Power/Fatigue is a trade off in my opinion. I just do not know if "I" can successfully switch back and forth if wanted/needed. But that is another subject of it's own.

Back to the motor... so many options. I could just do one of those bolt on 440 kits or I could just go with whatever cc the original cylinder needs to be... it may not need anything and I may can stay stock bore but was thinking of a 416.

Anyways, cams... it's getting a cam. Something mild. It's an XC quad so useful power that is in the lower RPMs and don't wear the body out is what I am looking for. I DON'T WANT TO BUILD A 450-ISH MANNERED MOTOR. I already have a decked out 450. I want the good nature of the 400 to stay. I just want a bit more power on top when my thumb reaches for it.

I have now found a pump of 93 octane pure gasoline (so it's marked anyways). It's the Shell 93 pure gas. But it still would not hurt my feelings to have enough compression to run the 110 octane. Enough compression to get a good burn on it but not so much that there is not some overkill there for bad conditions.

Is the compression recommendation any different for a 440cc? Or no?