HELP! Dolmar 6800 porting ideas

[Shane¹]

I got a 6800 apart right now that the piston was starting to get some marks in it. Going to freshen it up with a new piston and rings. Should I port it or just put it back together they are pretty strong stock. What are some of your thoughts?

 

[Ketchup]

I think I’m jealous of all your Dolmars.

 

[Shane¹]

I think I’m jealous of all your Dolmars.

These are all my runners working on making about 4 or more runners from parts

 

[Shane¹]

I don't like the piston I have so I think I am going to order another one then see what I can do to port it up

 

[Ketchup]

Curious what the stock numbers are.

Do you have that bicycle just because it matches your saws?

 

[Shane¹]

Curious what the stock numbers are.

Do you have that bicycle just because it matches your saws?

Haha yup all dolmar colors here lol. I have not set it up because I was curious if anyone had done it see if it's even worth it

 

[Shane¹]

All righty going to start putting the 6800 back together been checking numbers on a few saws this is where I am at no base gasket. Exhaust 103 intake 73 transfers 126 squish .018". Think I might lower intake to 75 raise exhaust to 101 leave transfers. Too much blow down?

 

[Ketchup]

Just spitballing here. No experience with a 6800.

I can’t see the blowdown being a big problem at 25 degrees but you would probably get a larger bump in performance if you raise the transfers as well.

75/101/126 will probably run pretty close to stock with a tiny bit more grunt. How much you widen the exhaust will have additional gains. If you can widen exhaust to 65% of bore you may see enough rpm to warrant raising the intake a little farther. Raising the transfers to 123-4 would probably get you there as well.

There may be simple flow gains in other areas that are worth finding. Often air horns are restrictive, transfer lowers and tunnels have obstructions or rough surfaces, mufflers don’t match exhaust etc. I think that stuff is really important for a BG delete port job.

I have a feeling it will be a ripper, just because it’s an old Dolmar.

 

[Shane¹]

Just spitballing here. No experience with a 6800.

I can’t see the blowdown being a big problem at 25 degrees but you would probably get a larger bump in performance if you raise the transfers as well.

75/101/126 will probably run pretty close to stock with a tiny bit more grunt. How much you widen the exhaust will have additional gains. If you can widen exhaust to 65% of bore you may see enough rpm to warrant raising the intake a little farther. Raising the transfers to 123-4 would probably get you there as well.

There may be simple flow gains in other areas that are worth finding. Often air horns are restrictive, transfer lowers and tunnels have obstructions or rough surfaces, mufflers don’t match exhaust etc. I think that stuff is really important for a BG delete port job.

I have a feeling it will be a ripper, just because it’s an old Dolmar.

These saws run good stock only reason I even want to mess with it is there is a little damage to the cylinder near the exhaust port that I will grind out so figured might as well see what I can do with it

 

[Shane¹]

Widened exhaust and brought it up to 101, brought intake down to about 75 maybe slightly lower, matched muffler and gasket. Started putting it back together tonight hopefully finish it up tomorrow

 

[Shane¹]

After speaking with @Mastermind he suggested raising the transfers and lower the intake a touch more. Updates after I get time to work on it more