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Mastermind meets the Dolmar 7900

cbrduckdog

cbrduckdog

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TN&KY
How much improvement over stock????
Tough for me to answer this question. It has been over 4 years since I ran a stock 7900. Back then I compared the 7900 to a 460 but felt better mainly due to the anti vibe I guess. This one only had 140psi when I got it so it needed help in my opinion. I have never checked compression since the build but I guess I could.

Is it better than stock yes, how much better is hard to answer. If I wasn't milling my 660 would find a new home.
 
ptjeep

ptjeep

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This saw runs way better than a stock one. How much better, it made me consider selling my ported 660 to get one. Is that good enough?:hmm3grin2orange:
 
Mastermind

Mastermind

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This saw runs way better than a stock one. How much better, it made me consider selling my ported 660 to get one. Is that good enough?:hmm3grin2orange:
Hell my 395 was looking over it's shoulder......I think it's a little scared. :cool2:
 
SawTroll

SawTroll

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If I recall correctly the Walbro HD 12 carb that came on the 372 will bolt right in as well, not sure about the venturi size though.
The Walbro is actually a bit smaller than the Zama. Walbro is 16.67mm and Zama is 17mm.

......
A bit late - but the HD-12 is 17.46mm. 16.67 is the HD-6.

Likely, all those carbs really are too small, but that's another discussion....
 
Mastermind

Mastermind

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It's hard to top a good 79er...
:msp_wink:
You've got that right!!!:rock:
I never really put much thought into these saws anymore......I've done quite a few....but it seems like they don't show up for port work like they did a few years ago.

When Chuck fired that thing up and laid it to the wood.....to say my ears perked up would be a huge understatement. :cheers:
 
Hedgerow

Hedgerow

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I never really put much thought into these saws anymore......I've done quite a few....but it seems like they don't show up for port work like they did a few years ago.

When Chuck fired that thing up and laid it to the wood.....to say my ears perked up would be a huge understatement. :cheers:
I still have one that's bone stock..
It's a fantastic saw in stock form...
Since its an every day user, it would cause me great pain to be without it for a month...
I'm probably not alone.
 
Mastermind

Mastermind

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I still have one that's bone stock..
It's a fantastic saw in stock form...
Since its an every day user, it would cause me great pain to be without it for a month...
I'm probably not alone.
When I get back I'll only be a week behind or so. I've stop talking work so I could get caught back up to a reasonable amount.
 
Andyshine77

Andyshine77

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I never really put much thought into these saws anymore......I've done quite a few....but it seems like they don't show up for port work like they did a few years ago.

When Chuck fired that thing up and laid it to the wood.....to say my ears perked up would be a huge understatement. :cheers:
I think the 7910 is likely the cause. I know you ported a 7910, how did it run compared to the older 7900's?

I have a barely used stock 7900 as well, they run so good stock it's hard to breakdown and take the time to port it. The one I have has 190+psi of compression and squish set at .018 out of the box, what's not to like.
 
Hedgerow

Hedgerow

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I think the 7910 is likely the cause. I know you ported a 7910, how did it run compared to the older 7900's?

I have a barely used stock 7900 as well, they run so good stock it's hard to breakdown and take the time to port it. The one I have has 190+psi of compression and squish set at .018 out of the box, what's not to like.



Nothing...
Saw nirvana...
:msp_wink:
 
Mastermind

Mastermind

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I think the 7910 is likely the cause. I know you ported a 7910, how did it run compared to the older 7900's?

I have a barely used stock 7900 as well, they run so good stock it's hard to breakdown and take the time to port it. The one I have has 190+psi of compression and squish set at .018 out of the box, what's not to like.
I've done three 7910s in the last few months. I use the same numbers in them as the 7900.....but to be completely honest I can't say how they compare. I don't have enough trigger time on either to be a good one to ask. :msp_unsure:
 
Mastermind

Mastermind

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I'm curious to see how it works out for you. All of the good builders that I know say they can get more out of a 440 and a 372 than they can out of a 7900.
I'm building two 7900s today......thought I'd look at this thread again.

This 7900 that was the object of this thread holds more rpm in the cut than any 372 or 440 that I've ever built. With a 28" 8 pin it was holding 11,400......
 
Metals406

Metals406

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It would take some serious pencil time -- but I wouldn't mind seeing the ratio of port/trans area to crankcase volume and combustion chamber volume/shape between the 372 and 7900.

Might be telling why it's more beastly.
 
Hedgerow

Hedgerow

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It would take some serious pencil time -- but I wouldn't mind seeing the ratio of port/trans area to crankcase volume and combustion chamber volume/shape between the 372 and 7900.

Might be telling why it's more beastly.
The 372 should have a lot more crank case volume...
Both pretty badass...
Both quad ports...
Similarities end at this point?
 
nmurph

nmurph

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It might be the 8cc extra of the 7900:hmm3grin2orange::hmm3grin2orange::hmm3grin2orange:

I have an EC 7900 and a 460 from Randy. I am going to have to drag them out and drop them in the big oak chunck I have and see how they spin up.

Randy, I bought a Walbro for the saw. Do I just file away about half the key in the FW to advance the timing?
 
Mastermind

Mastermind

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It might be the 8cc extra of the 7900:hmm3grin2orange::hmm3grin2orange::hmm3grin2orange:

I have an EC 7900 and a 460 from Randy. I am going to have to drag them out and drop them in the big oak chunck I have and see how they spin up.

Randy, I bought a Walbro for the saw. Do I just file away about half the key in the FW to advance the timing?
Take .020 off the key. Then use a rope or stop to hold the engine while you clock the flywheel CCW against the cut edge of the key.....as you are holding the flywheel, snug the nut as tight as you can get it. Then rotate the engine CW to the stop to finish tightening the nut.
 
Andyshine77

Andyshine77

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No doubt the 7900's pull harder than the 372's where it counts.:popcorn:


This one was ported by EHP.
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