MillerModSaws and the PS-7910

[shorthunter]

Thats exactly where this one is headed. Lmao. But if above 102 kills them I won't explore that option. Thank you.

I ported my 7900 and picked up roughly 12% on timed cuts in a 12" oak cant log. I ended up at 101 on the exhaust, 130 on the transfers and 80.5 on the intake but I also used a 460 piston with an aluminum base gasket/ spacer. It runs a 28" bar with an 8 pin sprocket and full comp chain really well. I am planning to raise the exhaust a little more and to replace the coil with an unlimited unit. Then I will do a build thread with a comparison to a stock 7900 with the slab sided piston

 

[MillerModSaws]

Think about this.........every grain of material you remove will lower case compression.

Ok. I see. I was thinking flow.

 

[MillerModSaws]

I ported my 7900 and picked up roughly 12% on timed cuts in a 12" oak cant log. I ended up at 101 on the exhaust, 130 on the transfers and 80.5 on the intake but I also used a 460 piston with an aluminum base gasket/ spacer. It runs a 28" bar with an 8 pin sprocket and full comp chain really well. I am planning to raise the exhaust a little more and to replace the coil with an unlimited unit. Then I will do a build thread with a comparison to a stock 7900 with the slab sided piston

What are you using for an unlimited coil?

 

[Mastermind]

Ok. I see. I was thinking flow.

One more tidbit......

Remember that transfer flow is forced........the piston displaces the mixture upward into the combustion area. Looking at scavenging into the jug might be more helpful than looking at the entrance.

 

[cuttinties]

I ported my 7900 and picked up roughly 12% on timed cuts in a 12" oak cant log. I ended up at 101 on the exhaust, 130 on the transfers and 80.5 on the intake but I also used a 460 piston with an aluminum base gasket/ spacer. It runs a 28" bar with an 8 pin sprocket and full comp chain really well. I am planning to raise the exhaust a little more and to replace the coil with an unlimited unit. Then I will do a build thread with a comparison to a stock 7900 with the slab sided piston

272xp coil.

Ok. I see. I was thinking flow.

Doesn't matter what you flow through if you don't use it efficiently. Don't put more in than you can transfer. Boils down to if you over fill the case it will spit back. That's wasted charge and not only that, it decreases transfer velocity. Same goes for the tunnels and upper transfers. Size does matter but more isn't always better. One thing I continue to see on Dolmar saws is the less is more approach yields the best gains. Mileage varies but don't feel like you need to change already good thing so much.

 

[shorthunter]

What are you using for an unlimited coil?

Husqvarna 50/51/55/262/272 coil

 

[Hedgerow]

What are you using for an unlimited coil?

You must re-index the flywheel when making this change over..

 

[SCHallenger]

 

[mdavlee]

You must re-index the flywheel when making this change over..

Ever get your 2 done?

 

[Hedgerow]

Ever get your 2 done?

Nope... Still procrastinating... And filing chains...
I think someone could port a saw faster than I can file a good chain..

 

[awol]

One of 'em may be done, just have to finish the rest of the saw to find out how it works!
On the subject of case volume in relation to trans duration, I think there is a lot of performance left untapped in these saws, simply because the right combination of duration, location, and size of the transfers has not been discovered.

 

[jar944]

I think there is a lot of performance left untapped in these saws, simply because the right combination of duration, location, and size of the transfers has not been discovered.

Cheaper than cutting and testing hundreds of possible combinations, and proven accurate by some top 2t tuners. Provided the inputs are correct.
http://www.vannik.co.za/EngMod2TDetails.htm

 

[fordf150]

 

[redfin]

If you're going after long bar torque leave it.

Think about this.........every grain of material you remove will lower case compression.

Thinking about this made me think of how Scott matches this piston to the lower opening of the transfers in I think it was a 385? Would that net a lower case compression?

 

[mdavlee]

Thinking about this made me think of how Scott matches this piston to the lower opening of the transfers in I think it was a 385? Would that net a lower case compression?

Yes. A 385 has a lot more case capacity over a 7900 also.

 

[Andyshine77]

You can go as high as 100° on the exhaust, especially with the added compression, I personally would stay around 101°-102° With the small intake and carb, extra intake duration works just fine on the 7900. Blowdown yes you want a lot of that 25° or more. You did the right thing with the intake side transfer, I've seen them ever larger.
You should have a pretty good running 7900 on your hands.

 

[MillerModSaws]

A little progress tonight. I hot the upper trans done. I went back in and squared them up a little compared to what I had roughed in then finished them with a diamond burr.

 

[Andyshine77]

Should work. What's final squish at?

 

[MillerModSaws]

Should work. What's final squish at?

.021"

 

[Mastermind]

You can go as high as 100° on the exhaust, especially with the added compression, I personally would stay around 101°-102° With the small intake and carb, extra intake duration works just fine on the 7900. Blowdown yes you want a lot of that 25° or more. You did the right thing with the intake side transfer, I've seen them ever larger.
You should have a pretty good running 7900 on your hands.

Keep in mind.......this is a 7910. The ring pin will end up in the transfer port if they are widened too much.