Stroking a Dolmar 7900

[Fruecrue]

123/ 95 would probly be enough, forgot you were goin that high on ex

I figure the stroke gets me a little torque back and it’s purpose built for 24” white pine with a good chain (hopefully), not a long bar build. Why not raise the roof some.

 

[Chainsaw Jim]

I wouldn't take that big of bite all at once with the exhaust.

 

[mettee]

I say keep the thick spacer, remover the stock gasket, that will take your squish from .023(-.015) to approx .008. Then I would cut the squish back in removing .012 or so to get you .020 squish. No need for a pop up at that point or any piston changes, right?

That move will keep you where you are, and the porting will not be too crazy(within .020 of where you started). You are gonna be close to 200 psi I would think, but the exhaust being high that might bleed off and be the 190 you are looking for.

 

[mettee]

It would be nice to have wider skirts I have been told...

 

[Redfin]

Pretty high trans on a 7900

Not really.

 

[mettee]

Primary transfers on these are supposed to be good opening at 28 degrees blow down, then you can have the secondaries open 3 degrees past that.

 

[Deets066]

Not really.

Wood bee if the xsawst wuz @ 102

 

[Redfin]

Light bulb.
Sorry, I’m slow.
That would still leave me a bit short on compression me thinks.

.015” from band and 96 ex nets 190lbs at 2100’

 

[mdavlee]

I’ve not noticed a huge drop in compression at 92-96 on exhaust in these. They’ll still be 180-200 with .025-030” from the band

 

[mettee]

I’ve not noticed a huge drop in compression at 92-96 on exhaust in these. They’ll still be 180-200 with .025-030” from the band

You mean that the band is measuring .025 to .030 squish?

 

[Deets066]

You mean that the band is measuring .025 to .030 squish?

Cutting that much from the squish band and lowering the jug accordingly

 

[mettee]

This one is going to be complex to hit the numbers without some kind of cutting and porting.

Do the gasket and spacer measure .058, or is it 58+15?

 

[Fruecrue]

This one is going to be complex to hit the numbers without some kind of cutting and porting.

Do the gasket and spacer measure .058, or is it 58+15?

There will be porting and there may be cutting of band and base, not against it.
Not in a hurry to make a decision either.
I have a handful of 52mm pistons here.
.058” plus the gasket.

 

[mdavlee]

This one is going to be complex to hit the numbers without some kind of cutting and porting.

Do the gasket and spacer measure .058, or is it 58+15?

To run a 46 piston you need about .085” of gasket and spacer without machining. This is best I can remember from 2.5 years ago now.

 

[mettee]

Is this on a solo chassis?

Fruecrue is using a 058 solo gasket/spacer with a sock 014 dolmar gasket as far as I know. So that kinda lost me Mike.

 

[Deets066]

Is this on a solo chassis?

Fruecrue is using a 058 solo gasket with a sock 014 dolmar gasket as far as I know. So that kinda lost me Mike.

Stroking a Dolmar 7900.....

 

[mettee]

Okay so what is making up the difference between Mike's numbers and Fruecrue numbers. Trying to "get it"

 

[mdavlee]

It was a Dolmar chassis. He’s using a stock piston and I used a 460 piston. That’s the difference. I never had a crank stroked or used a solo crank

 

[Fruecrue]

Just say it, it sounds sexy.

DUCATI!

 

[Fruecrue]

I’ll upload video soon.
Took 2 tenths off cut average.
About 3 seconds before, 2.8 after.