Has anyone cc'd a stock 64U head?

[Big Kahuna]

760 motors had a larger dome volume at the rear to achieve a lower compression.

From GP760 owners manual specs
Compression ratios: Front 7.2 Rear 6.8
This means that the front psi should be higher than the rear on a good engine.

 

[SXIPro]

Reading a thread like this makes me feel stupid, and thankful there are guys like Paul, Chris, Blue, Harrison, and the rest of you brainiacs to reach out to. Otherwise I'd be screwed.

 

[Storbeck]

760 motors had a larger dome volume at the rear to achieve a lower compression.

From GP760 owners manual specs
Compression ratios: Front 7.2 Rear 6.8
This means that the front psi should be higher than the rear on a good engine.

But, again, 64u is a superjet head, not a 760. 64x is a 760.

 

[Big Kahuna]

But, again, 64u is a superjet head, not a 760. 64x is a 760.

Just responding about the 760 had different dome sizes.

 

[MTRHEAD]

Then there must be differences in the 64U castings. Or the more obvious, is are the head volumes different between the front and the rear. You appear to have done the front, and I appear to have done the rear. I measured this before, and I was pretty sure I got the same volume from both. I'll recheck.

See below.

Interesting - I will do it again this weekend and use similar oil. Both front and rear. My heads were all late model SJ’s. 13’+ I have another one that I haven’t test that’s off a 15’

I did note visual difference in squish depth. Not much but a touch. (Cast angle edge depth).

 

[fastgtfairlane]

never cc'd a 64u head but did do a 62t and 6m6 head. the 62t came in at 33cc and the 6m6 at 31cc. im running the 6m6 head on my 62t engine with a c4 chamber all stock and it blew 169psi per cylinder with fresh rings after breakin on stock 81mm bore

 

[Big Chris]

Front cylinder measures out at 35.7-35.8 cc. As demonstrated in post #20, the rear cylinder measures out at 36 cc. That's a .2-.3 cc difference, I'm gonna go ahead and call them approximately equal. If we express this as a percentage (.3/36 x 100% = 0.8%) we have a 0.8% difference between the front and rear dome volumes on the 64U head casting. This is from a '13 SJ.

I make the statement in the beginning of this video about "air vent or air bleed for the exhaust". I believe the purpose of this small hose is so when the engine is shut off, there is an air vent (via the stock exhaust) to allow the cylinder's water jacket to drain back out through the hull and ultimately the pump, so as to prevent potential damage from freezing. Of course when the jet pump is moving water, there is water flowing out of this into the stock exhaust.

Also if you plan to mill this head, here are some insights I learned through this exercise.

 

[Storbeck]

I always thought the little tube was to prevent an air locked area in the head, basically to help it bleed.

 

[waxhead]

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]

Front cylinder measures out at 35.7-35.8 cc. As demonstrated in post #20, the rear cylinder measures out at 36 cc. That's a .2-.3 cc difference, I'm gonna go ahead and call them approximately equal. If we express this as a percentage (.3/36 x 100% = 0.8%) we have a 0.8% difference between the front and rear dome volumes on the 64U head casting. This is from a '13 SJ.

I make the statement in the beginning of this video about "air vent or air bleed for the exhaust". I believe the purpose of this small hose is so when the engine is shut off, there is an air vent (via the stock exhaust) to allow the cylinder's water jacket to drain back out through the hull and ultimately the pump, so as to prevent potential damage from freezing. Of course when the jet pump is moving water, there is water flowing out of this into the stock exhaust.

Also if you plan to mill this head, here are some insights I learned through this exercise.

Im a throw in the dumpster guy hahaha.
But good on you for having a go at it. I watched the video of you setting up the mill, I have just got into milling stuff and found it interesting.

 

[Big Chris]

The Stock OEM 650/701 Exhaust System is a Dry Pipe Type, meaning it's double-walled to keep the Cooling Water separated from the Exhaust Gases keeping the Exhaust Dry and thus yield improved performance.

The small (1/8"?) Cylinder Head Barb is the Stinger Water Injection source.

Na bro, simply not true.

Seriously folks, if you don't know something to be an absolute fact, please don't comment. 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. While I am new to the 701 platform, I am completely blown away at the lack of actual good info that I've come across in this one simple thread.

www.rperacing.com

 

[Storbeck]

So... What's up with the video then? Something wrong with his particular exhaust?

 

[Storbeck]

Isn't the thing you just said about the gap in gasket 29 different than the thing you said earlier that the 1/8" line is the water injection for the stinger?

 

[Big Kahuna]

All this over a pipe 90% of us remove as soon as possible..............

 

[Storbeck]

All this over a pipe 90% of us remove as soon as possible..............

I've actually never owned a ski with a stock superjet exhaust lol.

 

[Big Kahuna]

Isn't the thing you just said about the gap in gasket 29 different than the thing you said earlier that the 1/8" line is the water injection for the stinger?

I am honestly not sure if that small line is not letting water get to the head from the exhaust to prevent a hot spot or if it is to send water to the exhaust and a specific point injecting water into the exhaust stream to help meter the exhaust temp. Never really paid too much attention to the stock system. @MTRHEAD , any insite?

 

[waxhead]

Yup I think there is a special place in the landfill dedicated to stock exhausts.

 

[Big Chris]

Nice try Bro but you're still wrong.

Disassemble the Exhaust System and you will see that it is in fact a Double-Wall System aka Jacketed Pipe aka Dry Pipe.

And the 1/8 Fitting from the Head to the Stinger is water injection.

Too much confidence and pride can prevent a Man from seeing the facts.

Three points:

The first, JC SuperJet is correct that this is a dry exhaust. I stand corrected.

The second, the 1/8" fitting from the head is not the primary source of water injection, it is a vent. There are multiple passages in part number 29 in the diagram above that provide the water flow through the exhaust.

The third, none of you could give me an accurate number for the title of this thread, a question I asked 3 weeks ago.

 

[user_error]

Very informative video, thanks for taking the time to do that. I’m sure it will help many people get a better understanding of the stock exhaust setup!

 

[waxhead]

Three points:

The first, JC SuperJet is correct that this is a dry exhaust. I stand corrected.

The second, the 1/8" fitting from the head is not the primary source of water injection, it is a vent. There are multiple passages in part number 29 in the diagram above that provide the water flow through the exhaust.

The third, none of you could give me an accurate number for the title of this thread, a question I asked 3 weeks ago.

That's because unless you are building a lites boat no one cares. No one on here races the lites class its a free-ride/freestyle site. we simply pull the head off throw it in the bin and get an aftermarket head that holds the cylinder together. The 61x cylinder is known for its ability to crack when you start making power.