Has anyone cc'd a stock 64U head?

Storbeck · Feb 11, 2020

It's like walking into a bar and being amazed that nobody knows the local zoning ordinance. You're asking about something not many people care about, modifying stock heads is not very common.

Big Chris · Feb 11, 2020

And you deleted the post where you stated the front and rear domes had a different volume. Then said this. All I was looking to do was verify what "stock" was. Never mind, I found out what I needed to know.

waxhead said:
My bad I was looking at this and seeing 760 head not stock 701 head. yes I have cc.ed a stock head and no i am not saying which model comes with a smaller cc chamber because that's a trick in lites racing

waxhead · Feb 11, 2020

Big Chris said:
And you deleted the post where you stated the front and rear domes had a different volume. Then said this.

yes Chris because I was talking about a 760 head where the compressions are different and there is certain castings that have a smaller combustion chamber that are legal in lites class racing, like putting a gx160 head on a gx200. What are you actually here for on this site ?? is it to puff your chest and try to prove something. You have already had a go at me in a private message for some reason to which i just deleted your instant message. Let it go dude, no one gives a toss its a friendly site, go and find one where people can be bothered to argue with you

Storbeck · Feb 11, 2020

You can be sure if I was racing lites id be measuring every casting I could legally use! I'd probably know a thing or two about gaskets too.

Big Kahuna · Feb 12, 2020

Storbeck said:
You can be sure if I was racing lites id be measuring every casting I could legally use! I'd probably know a thing or two about gaskets too.

Yup, like finding the thickest base gasket within tolerance, thinnest headgasket, head that has the smallest domes, squish, etc - within tolerance........

Chris, one thing that is very common here, is we are all enthusiast. We all have different strengths of knowledge. And many many times one topic starts off about A, and ends up about D. That is what happened, the topic went from 701 heads to 760 heads. Hence, the conversations about there being staggered dome sizes. Yamaha does this to keep heat down on the rear piston. They found in runabouts (AKA Waveraiders) that the rear pistons would heat up more due to loads to the pump so they lowered the compression and also jetted richer to keep the rear temps down. This is what Wax was referring to... And he is also correct. Most of us dump the stock heads. I have not ran one since 2002 or 2003.

hornedogg79 · Feb 12, 2020

Big Chris said:
I made mention early in this thread that I build national level karting engines, I didn't get to this level without testing everything that has ever been written on a forum regarding karting engines.

You better have a really really thick wallet and some patience if you wanna do that here. And the motor is only half the battle.

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dillmu967 · Jul 1, 2020

Can anyone tell me what the differences are between a 61x head and a 64u? Building a 760 to race and I have the 64x 760 with the different compression per cylinder which is not ideal. I read on a different forum that you have to use a 64u head on the 760 can not use the 61x but can not find the reasoning why. Moral of the story I have a 61x head sitting on the shelf and I don’t wanna run out and buy a 64u if I don’t have too

MTRHEAD · Sep 6, 2020

Woke up and decided to watch mxgp and cc some more oem superjet heads. One head off a 2017’ silver and other head off a 1996 gray I think. 31mm thick so no decking. Sanded with 800grit to clean and ensure seal with thin baby oil. Oem spark plugs and yes they filled the cavity. I used very thin Baby oil. Note I also did it with water and found absolutely no difference just so people wouldn’t complain Need to do the math with the pictures. Didn’t start at zero so someone would think calibration was off. Just pure CC
All 4 domes 33.5-34cc. Same as last time I did it.

subnsxr · Sep 6, 2020

180psi 91octane and WOT as long as I can hang on with no issues. I ran it one time at 190psa and it detonated pretty bad.

Joe Superjet · Sep 9, 2020

The stock exhaust is probably higher quality than the factory pipes at least. I bought a used ski with a factory pipe, expansion chamber cracked in multiple places, exhaust manifold cracked, had to deck manifold etc. welded exp chamber and hoping jb weld holds up on the manifold

jrddillon · Sep 27, 2020

hornedogg79 said:
Haven't cc'd a stock superjet head (64u) but yours appears uncut. The ridge around the perimeter of the dome is normally gone after it's been cut. Stock should be around 33cc. Gasket will add around 7cc. I have an old WC head with interchangeable domes that still uses a gasket. Their chart read something like this. 27cc=190psi 29cc=185psi 30cc=170psi

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can you find and post that chart

kevbo · Sep 28, 2020

Those WC domes arent big enough to cover much more than an 81mm bore. Its shell is drilled for a 61x gasket, newer style gaskets need cooling holes drilled to match. As I remember their 29cc domes made around 180 on a new stock 61x cyl.

jpswift1 · Feb 3, 2021

Great thread, and lots of useful information! Thanks for sharing this.

Has anyone cc'd a stock 64U head?

Storbeck

Big Chris

waxhead

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hornedogg79

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MTRHEAD

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