372xp build, need some guidance

[subhunter]

No one can offer any advice on the timing numbers? Or help on what to change?

 

[AUSSIE1]

Joseph, your ex being 160° and your saying your inlet is 170°?

It's sounding like you are probably better off milling the barrel and 372 piston for increased compression and do the piston porting others have been doing.

Go your 160° at the exhaust, 158-160° at your inlet. Do your lowers and typical port widening.

Get as much out of the ex as you can for as much area as possible while keep curvature at the top.

 

[subhunter]

So you are saying that with the 266 piston it just in not going to be possible or not worth it?

 

[AUSSIE1]

So you are saying that with the 266 piston it just in not going to be possible or not worth it?

If you are raising the barrel to decrease the inlet timing and end up not being able to do a popup and still left with 170° inlet, it's no good.

I thought others may have used the 266 piston before but don't quote me, so is there a possibility your no's are out?

Most of my playing has been with the BB kit's and 064 piston.

.020-.030 popup's are nice in these saws.

 

[subhunter]

I am unsure of what the numbers actually mean. I knew from what I have read my EX number looks good. I was hoping to use the .050 gasket, mill the jug down .015 and make a .015 -.020 pop up. The thing that confuses me is the actual durations.

I have also read that others have used a 266 piston and made a nice running saw

 

[subhunter]

OK checked the numbers with the stock piston no base gasket.Squish was .026. Ex 99* {162 duration} X-fer 122* {116 duration} INtake77* {154 duration}

To me the numbers do not seem that far apart, but then again I dont really know what I am doing here :msp_w00t:

 

[tlandrum]

i would keep the 372 piston and window it.the 266 piston is putting the intake way too high. you dont want more than 160 on the intake. i would widen the intake and exhaust and lower the intake to get the timing to 160.

 

[subhunter]

What are the draw backs of the high intake duration?

 

[AUSSIE1]

Joseph, your Ex seems a little high for stock and gasket removed. Make sure you have TDC spot on before any measuring and grinding.

Keep turning the crank back and forth with the piston stop fitted making sure you have exactly the same reading side to side. Take your reading JUST as the port opens. Your no's are looking close. Don't worry about your trans if you don't have a right angle cutter. As you have done, only bother recording the opening no's.

Being new to this and for ease stick with the oem piston. If you can get the barrel and piston machined, go this route.

 

[komatsuvarna]

i would keep the 372 piston and window it.the 266 piston is putting the intake way too high. you dont want more than 160 on the intake. i would widen the intake and exhaust and lower the intake to get the timing to 160.

I agree. Sounds like a good plan.

What are the draw backs of the high intake duration?

I probably cant explain it that good, but the saw will be sickly with 170 degrees of intake duration.

 

[tlandrum]

when you get over 160 they seem to really start to come up slow on the throttle

 

[komatsuvarna]

when you get over 160 they seem to really start to come up slow on the throttle

Yep, and if you get the intake wider than the piston skirts it does too.:bang:

 

[AUSSIE1]

Yep, and if you get the intake wider than the piston skirts it does too.:bang:

Lol, don't WE know it!

 

[subhunter]

Alright

Well I think I am getting somewhere. I got some more time to work on this saw. My timing numbers now are EX-158 trans-124 IN-162, squish was .022. I have raised the lower transfers to 1mm above the base and am using the 266xp piston. I have yet to do anything to the exhaust or intake ports. I put it together to see how "slow" the throttle response was going to be with the extra 2* on intake and to me it seemed pretty good. I have not put it in wood yet.

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[komatsuvarna]

162 should be fine. Mine ended up a little over that and it still revs up as fast as it always did.

 

[tlandrum]

i would widen the intake and not touch the top or bottm other than to clean up the flash. do not touch the transfers, at 124 thats pretty good. the closer you get to 130 the more torque youll lose. it will be a high rev 8x8 saw. you can raise the exhaust a few degrees and stiil be ok. id shoot for 164-165 widen the exhaust and you will have a pretty nice running saw. but im not a pro and my advice isnt worth too much. maybe someone with more experience will kick in som info

 

[subhunter]

Put it in some wood just to see how it runs before I do the grinding. It seems to run pretty good:hmm3grin2orange:



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[blsnelling]

I made a .050 base gasket making my squish on the 266's piston .021. The timing numbers were EX= 100 in=85 transfer 126.

My timing numbers now are EX-158 trans-124 IN-162, squish was .022. I have raised the lower transfers to 1mm above the base and am using the 266xp piston.

So how did you loose all that intake duration? I'm looking at the same thing on the 266 piston. The skirts on a 266 piston are 3.5mm shorter than on a 372 piston. I don't see how a 266/268 piston can be used and not have at least 170° of intake duration.

 

[subhunter]

Well I am no expert by any means, and it is possible that I have read the degree wheel wrong{ more than once :msp_unsure:} but I have made a base gasket that is right at .060 thick. I think I have made around 10-12 gaskets fooling around with this project.

EDIT: When I first started I was using cork gasket material and it was squishing too much and it was giving me false readings.

 

[AUSSIE1]

Joseph so you have raised the barrel .060 to get the .022 squish with the 266 piston? This would mean you have similar/same compression as stock. It would be nice to get your exhaust up near your inlet in duration but it sounds like you will loose too much needed compression. If you have your durations correct, I would think you would be better off with the stock piston windowed, no base gasket. Raise your lowers up to the divider. Leave the divider alone. No sharp edges. Durations around 158/158 to 160/160 for a strong work saw. Save the 266 piston for when you have more of a grasp on the duration side of things. Raising/lowering cyl's etc can confuse things more when learning to use a degree wheel.

All you have to do is make sure you have your correct TDC then just post your opening no's.