what octane?

[mymastifftucker]

I have started building a 04 450r I just bought. I ordered a 13.1 Wiesco piston and am going to use a stg. 2 hotcam. Can I still run 93 octane pump fuel or do I need race fuel?

[MAD450r]

No, anything over 12:1 you will at the very least want to mix 50/50 93 and race fule.

I plan on going with a 14:1 piston once I open my 04. Then I'll still run 50/50 I think. But I run the hrc cam which has alot of overlap I guess they call it so I can still get away with no detonation. That is what I have read here though. Anyone know if this is incorrect please chime in.

[MR.BIG]

Originally posted by MAD450r
No, anything over 12:1 you will at the very least want to mix 50/50 93 and race fule.

I plan on going with a 14:1 piston once I open my 04. Then I'll still run 50/50 I think. But I run the hrc cam which has alot of overlap I guess they call it so I can still get away with no detonation. That is what I have read here though. Anyone know if this is incorrect please chime in.

With a 14:1 piston I would run at least 110 octane to be on the safe side even with the Hrc cam.

[Smidgy]

give this a read, it will make you better understand what gas types you can or should run at what compressions. It also describes compression pretty good

http://members.uia.net/pkelley2/DynamicCR.html

[mustangflyboy]

great info!!

[Smidgy]

it all depends on what you are using for a cam, whether or not you can, even though you are putting a 13:1 piston in, and that is what you will tell everyone because everyone elses enigine is speced that way too, it doesn't mean that you are going to have 13:1 actual compression. So you have to do some calcs before you can say what octane you should use

[ghott]

All depends on your dynamic CR. Cam profile....piston....elevation.

In short, you probably "could" get away with 93 pumper if you are above 1000 ft. elevation....and stay above 1000 feet.

Would I do it? HELL NO. Detonation is not worth it.

If I were you, I would mix pump gas, with race fuel to have a final octane rating of AT LEAST 100.

This will provide plenty of detonation resistance for that new piston, cam combo.

I personally use a 13.1:1 Wiseco piston in conjuction with a Hot Cams Stage 2, and I run straight leaded 110 Sunoco Purple :).

Good Luck!

[mymastifftucker]

What other engine work do you have done? I am building this just for a fast trail bike, and maybe an trip to the track every now and then. Do you think this set up will work well together, and not sacrifice the reliability? Is it going to be harder to start after the mods or will it be OK as long as it is jetted right. Should I just rejet the stock carb, or look into a aftermarket one? Thanks for all the info.

[ghott]

Are you sure you want to have to buy race fuel for your trail bike? That should be the question you are asking yourself at this point. The 13.1:1 will be reliable...and she'll start just fine as long as your carb is jetted correctly.

If you're wanting to run straight pump gas...look into a piston that has a static compression ratio of 12.5:1 or lower.

The stock carb will suit you just fine. I don't think you want to spend hundreds of dollars on an FCR.

[mymastifftucker]

This is just a fun project if that makes any sense. If a aftermarket carb is going to help with this set-up, than I would buy one. I have already ordered the piston, so that part is done. I dont mind the race fuel part. I was actually thinking about changing the valves and having a port/polish done, do you think its worth it? What do you think about the Dynatek?

[ghott]

Dyna non-programmable CDI actually hinders power. Brian @ WPP Racing did a lot of dyno testing with the Dyna non-prog CDI, and he found out that he actually lost over a full 1 HORSEPOWER going from the stock CDI to the DYNA non-programmable.

He now runs the Dynatek PROGRAMMABLE CDI on his machine. He programmed it to the STOCK Curve with an extended rev limit.

So the answer to that question is....do NOT buy the Dyna non-programmable CDI....if you are going to purchase a CDI, then get the Dyna programmable and set it to the stock curve with extended rev limit.

Is it worth it? I would say NO unless you had extensive engine work done, and your engine was very top end biased.

And...unless you have Heavy Duty aftermarket springs, an extended rev limit is a very big gamble. Stock springs weren't meant for 11,000 RPMs.

_____

An aftermarket carb will most likely help your build. If you decide to purchase an aftermarket carb, a Keihin FCR would be the way to go. They have EXCELLENT throttle response, and they can be bored up to 43.5mm for a gain of approx 1.5-2hp across the entire powerband.

_____________

If you decide to have your head ported and polished, do yourself a favor and send it to a respected company such as DASA, RAGE, Rossier, or WPP/Wicked Racing. These guys are making Dyno proven power consistently. I hear Chad502ex (drg) also ports a pretty nice head also :).

IMO, I would go ahead and have new intake valves installed at the very least while the head is off. Stock intakes are very soft, and aren't the longest lasting valves in the world. Both Ferrea and Kibblewhite make very nice Stainless Steel valves. I know WPP, DASA, and RAGE all offer 3-angle SREDI valve jobs along with their head porting service as well....this would be a good way to round out a nice head.

Hope this helps.