New Dolmar 7900 piston

[Rudolf73]

Rudy, lighter's always nicer to have in terms of reciprocating mass and acceleration.

Here's the old piston, you can see how thick the webs are in comparison, as they probably need to be with windows.

1/2 Oz = 14g, 'spose it all adds up.....

Oh right, that makes sense yes. I just thought that windows would also play an important role with air flow and most modern pistons seem to have windows now.

 

[nmurph]

Naa, a 95-100cc lightweight monster with great AV and balance that makes the 660 and 390/395 look ordinary

The way the 7900's run, 88cc's would be all it would take.

 

[Rudolf73]

The way the 7900's run, 88cc's would be all it would take.

Yeah, I still want to see how much I can get out of my 85cc BB when I get around to it someday. I also wish there was a non-limited coil option...

 

[tdi-rick]

The way the 7900's run, 88cc's would be all it would take.

You see i'm looking at it from a racers perspective.

Here the classes run under 77cc (neatly knocks out the 7900/7901 @78.5cc but gives the 460 an advantage over the 371) and under 100cc, then open.

 

[tdi-rick]

Oh right, that makes sense yes. I just thought that windows would also play an important role with air flow and most modern pistons seem to have windows now.

A lot of saws need the windows to feed the transfers but the 64/73/7900 doesn't.

I asked why on earth they would have them and Romeo neatly answered crown cooling and little end lubrication and I slapped my forehead, duh

 

[nmurph]

Yeah, I still want to see how much I can get out of my 85cc BB when I get around to it someday. I also wish there was a non-limited coil option...

Yes, I wish Bailey's would have some made.

Has anyone here tried the 55 coil conversion? I saw where someone mentioned that they didn't think the saw made as much power with the UL 55 coil. Then again, that loss is off-set with the porting gains.

 

[Rudolf73]

Yes, I wish Bailey's would have some made.

Has anyone here tried the 55 coil conversion? I saw where someone mentioned that they didn't think the saw made as much power with the UL 55 coil. Then again, that loss is off-set with the porting gains.

I remember Brad put a husky (i think) coil into a solo 681/7900, but you need to play around with the flywheel and timing etc - no ideal. It would be nice if we could actually find the 'rev limiting' circuit and remove/bypass it. I'm sure someone on here knows about the inner functions of a limited coil...?

 

[blsnelling]

I'd take a heavier piston if it had wider skirts. It's easy to grind excess away, not so easy to add skirt width.

 

[WoodChuck'r]

Cut the top off of a tuna can and use that.

Gotta be innovative here....

Duct tape Brad. Duct tape.

 

[AUSSIE1]

Rudy, lighter's always nicer to have in terms of reciprocating mass and acceleration.

Here's the old piston, you can see how thick the webs are in comparison, as they probably need to be with windows.

1/2 Oz = 14g, 'spose it all adds up.....

Cheapskate Dolmar only give you one ring!

That's a heavy duty piston. It could loose some pounds there Rick!

 

[tdi-rick]

Cheapskate Dolmar only give you one ring!

That's a heavy duty piston. It could loose some pounds there Rick!

So did Husky on their good saws before the EPA became involved

 

[tdi-rick]

Yes, I wish Bailey's would have some made.

Has anyone here tried the 55 coil conversion? I saw where someone mentioned that they didn't think the saw made as much power with the UL 55 coil. Then again, that loss is off-set with the porting gains.

Pretty sure it was EC that said the OE coil made more power than the Husky conversion.

 

[WoodChuck'r]

Pretty sure it was EC that said the OE coil made more power than the Husky conversion.

From what I know, he believes that of all stock limited coils.....

 

[heimannm]

Well that's just great, I decide to buy a new saw and now it's obsolete before I even take possession of it...

Mark

 

[MCW]

Nothing wrong with limited coils. I know it may make tuning more difficult (if you don't have any wood to cut) but I believe the favouritism shown for unlimited coils is coming from the racers among us. From what I remember the increase in rpm's when entering a cant provides more inertia for that initial part of the cut. Approximately .01 of a second after the chain has hit the wood the unlimited coil makes no difference to cutting speed on a normal saw.
In the real world it doesn't make any difference unless somebody has a 7900 that is trying to pull 15,000rpm in the cut. If so I want one, actually make that two...

 

[tdi-rick]

Well that's just great, I decide to buy a new saw and now it's obsolete before I even take possession of it...

Mark

Could've been worse Mark, it could've been a computer, or a woman.......

 

[Justsaws]

Think I would stock up on the previous generation piston if I was a 7900 fan. The new one should make the EPA happier.

 

[mitch95100]

HUh I forgot Dolmar used a single ring piston I remember now that I seen that when I tore mine apart

 

[tdi-rick]

Think I would stock up on the previous generation piston if I was a 7900 fan. The new one should make the EPA happier.

 

[AUSSIE1]

So did Husky on their good saws before the EPA became involved

Yeah I know mate...just having a little fun. That was 15 years ago though!