Dolkita 7900 vs ea7900 cylinder

[McKee bigcheif]

Do you fellas know if there is a difference between the two cylinders? I want to order a OEM cylinder kit for my makita dcs6421, but I see that they list the ps7900 and the ea7900 when I find an OEM kit. I'm not real sold on the big bore kits that's offered. I was watching dyno joe the other day, and I swear he said something was different at the exhaust port. I didn't know if makita went strato like everyone else has.

 

[EchoShindaiwaMakitaDolmar]

Send it to Dyno Joe/ @Red97 or Kevin/ @huskihl and be confident in the awesome saw they'll provide you.

 

[huskihl]

The EA kit has the enlarged exhaust flange to fit the slr tube into. PS7900 is the original. Personally I think the EA runs better

 

[ballisticdoughnut]

I have both styles of cylinder. One on a 6421 and the other on a 6401. 7910 cylinders have a larger exhaust port to accommodate the SLR tube as mentioned by Huskihl, the 7900 cylinder has a “normal” exhaust port. I really can’t tell much difference between the two but if I had to give the nod to one it would be the 7900 cylinder. The 6421 has right side decomp so your gonna want to order the 7910 top end. Left side decomp came on earlier saws.

 

[EchoShindaiwaMakitaDolmar]

I have both styles of cylinder. One on a 6421 and the other on a 6401. 7910 cylinders have a larger exhaust port to accommodate the SLR tube as mentioned by Huskihl, the 7900 cylinder has a “normal” exhaust port. I really can’t tell much difference between the two but if I had to give the nod to one it would be the 7900 cylinder. The 6421 has right side decomp so your gonna want to order the 7910 top end. Left side decomp came on earlier saws.

I thought I understood what @huskihl said about the ps7900 cylinder vs the "ea7900 with the bigger exhaust port"- but then I read your post and I'm confused because you didn't stick with the PS and EA designations of the 7900. What's a 7910? Thnx

 

[ballisticdoughnut]

PS7910 is the same saw as the EA7900. PS is Dolmar EA is Makita. If you have a 6421 and you want to turn it into a 79cc saw you want the PS7910/EA7900 top end. Both models use the exact same piston and cylinder with right side decomp valve.

 

[ballisticdoughnut]

https://www.sawagain.com/dolmar-ps-...linder-top-end-rebuild-kit-new-oem-038130071/

 

[McKee bigcheif]

this is the kit I was referring to...

 

[McKee bigcheif]

Ok, what exactly is the SLR tube if I may ask?

 

[huskihl]

Ok, what exactly is the SLR tube if I may ask?

Hard to explain and I don’t have a picture anymore. It is a tube with a small outlet that goes inside the exhaust flange and it is meant to burn off hydrocarbons to get the saw to pass EPA regulations. It is inside the muffler yet extends into the flange. Without removing the muffler, you wouldn’t know it was there

 

[McKee bigcheif]

So if my custom pipe blocks this off i shouldn't have any problems?

 

[huskihl]

If I were using a pipe on it, I would get the PS 7900 cylinder because the inside of the flange is smooth

 

[McKee bigcheif]

I have a harvy "ironhorse" style pipe on it now. It really woke this saw up! I may have to go with a bb 54mm kit,as OEM 7900 kits are like honest politicians!

 

[EchoShindaiwaMakitaDolmar]

PS7910 is the same saw as the EA7900. PS is Dolmar EA is Makita. If you have a 6421 and you want to turn it into a 79cc saw you want the PS7910/EA7900 top end. Both models use the exact same piston and cylinder with right side decomp valve.

Okay, the 7910 is synonymous with EA7900. PS7900 is the earlier version by Dolmar. Added that to my thin knowledge base, Thanks!

 

[huskihl]

I have a harvy "ironhorse" style pipe on it now. It really woke this saw up! I may have to go with a bb 54mm kit,as OEM 7900 kits are like honest politicians!

Did you gut the original muffler and try that and actually time them? Usually those type of pipes help the saw to rev but don’t produce nearly the torque

 

[huskihl]

And the big bore doesn’t run as good as either of the OEM options

 

[McKee bigcheif]

I gutted the oem muffler when I first got the saw. I will say that it was a huge improvement over the cat muffler. I built a ironhorse style pipe for the makita and one for my ms391. The pipe is amazing with both saws! That's what I like about this style pipe is the flat torque curve it makes. Dyno joe tested a few pipes and this one had the flatter torque curve. This style pipe pulls fuel! Harv said if a pipe doesn't go pig rich, you're just making noise. I would guess the pipe gives at least another .5 hp.

 

[Lightning Performance]

Hard to explain and I don’t have a picture anymore. It is a tube with a small outlet that goes inside the exhaust flange and it is meant to burn off hydrocarbons to get the saw to pass EPA regulations. It is inside the muffler yet extends into the flange. Without removing the muffler, you wouldn’t know it was there

I got one here cut in half to do a pic.

And the big bore doesn’t run as good as either of the OEM options

True. I have one on one of my Smurfs still stock not ported, yet. I do think the transfer port will lack volume so chasing the rest is chasing your tail after checking all the math against cross sections and total port areas. You give up some width there to fit in that package.

 

[Lightning Performance]

I think the better question is what piston should you be running with what setup? Log bar or short bar for different purposes will like a different piston most times.

 

[McKee bigcheif]

Long bar. My almost 50 year old back is tired of bending over to buck! As buckin Billy Ray says
Stand up and buck!