Mastermind Meets The Dolmar 7910

[Mastermind]

I must of missed the numbers? Did you post them? I need to hollow out the muffler on mine still.

On this saw.....

Compression 190psi
Squish .022
EX: 102
TR: 128
IN: 84
Ignition timing advanced 6°

 

[parrisw]

On this saw.....

Compression 190psi
Squish .022
EX: 102
TR: 128
IN: 84
Ignition timing advanced 6°

Nice, a little less Blowdown then normal? A little more Conservative on the ex?

 

[Mastermind]

Nice, a little less Blowdown then normal? A little more Conservative on the ex?

That's a good number on the exhaust for torque IMHO.

I did a 7900 at the same time with 99, 128, 84 to do some R&D testing. The differences are small enough that most guys would never notice but we will see which is best for a true work saw.

 

[parrisw]

That's a good number on the exhaust for torque IMHO.

I did a 7900 at the same time with 99, 128, 84 to do some R&D testing. The differences are small enough that most guys would never notice but we will see which is best for a true work saw.

Right. I don't like going above 98 on ex, if you can keep comp up, I'm not afraid to go that high. Most of the huskies I've done are about 100, the last 372 was at 98, but it has big comp, so well see how it does.

 

[Wild Knight]

How much can you really change the shape and timing of the ports if you are rev limited?

 

[Mastermind]

How much can you really change the shape and timing of the ports if you are rev limited?

It being rev limited has nothing to do with porting the engine for more power and torque. This saw won't be on the limiter in the cut.........unless it's limbing.....and that would be a good thing.

 

[Wild Knight]

It being rev limited has nothing to do with porting the engine for more power and torque. This saw won't be on the limiter in the cut.........unless it's limbing.....and that would be a good thing.

Is there a rule of thumb for what changes in the ports create more torque with a broader power band, rather than creating peak power at max RPM?

 

[Mastermind]

Is there a rule of thumb for what changes in the ports create more torque with a broader power band, rather than creating peak power at max RPM?

Not any hard and fast rules that I'm aware of, but generally a higher exhaust port raises rpm at the expense of torque. I tend to run a lower exhaust along with more compression for a strong, torquey saw.

 

[Mastermind]

I must be the best thread killer on this site. This is the end of this thread,period,the end,adios,goodbye.

Your PM box hicky thing is full too. :msp_tongue:

 

[Trx250r180]

What was he really trying to say ?

 

[Mastermind]

What was he really trying to say ?

Su caja PM Hicky cosa está llena demasiado

 

[Mastermind]

الشيء الخاص بك PM hicky مربع مليء جدا

 

[B Harrison]

I really want this done now!

Why do I have to have a baby on the way and an unported 7910 at the same time.

 

[Mastermind]

I really want this done now!

Why do I have to have a baby on the way and an unported 7910 at the same time.

I've done two 7910s in the last month......

 

[7sleeper]

I really want this done now!

Why do I have to have a baby on the way and an unported 7910 at the same time.

No sure you have your priorities set correctly.

7

 

[bryanr2]

I really want this done now!

Why do I have to have a baby on the way and an unported 7910 at the same time.

Put "porting 7910" n the baby shower gift registry "as necessary to put food on the table" or "necessary stress relief"

 

[tdi-rick]

Have you tried Eutectic 1020 XFC "pink" brazing rod? It's the best I've used for steel and stainless.

I'll give that a try. I've got a mig but I would rather braze on a muffler.....

When I was in Tech school the old dude that taught welding insisted that we all start with a 00 torch without filler. I was one of the few that really took to torch welding and have always liked it.

Randy, I've had to do a lot of brazing over the years and with SS you need to treat the surface with 'pickling paste' (not sure what you'd call it over there, it's an acid gel) to get rid of the oxides in the stainless and use a high silver content rod, not brass.

I usually use a 45% Ag rod as that's what I have for steel/copper or steel/brass, but a higher silver content will wet out even better.

I absolutely lurve my little Harris 15-3 torch. Can do (almost) TIG quality welds with it. (when not brazing )

 

[Mastermind]

Randy, I've had to do a lot of brazing over the years and with SS you need to treat the surface with 'pickling paste' (not sure what you'd call it over there, it's an acid gel) to get rid of the oxides in the stainless and use a high silver content rod, not brass.

I usually use a 45% Ag rod as that's what I have for steel/copper or steel/brass, but a higher silver content will wet out even better.

I absolutely lurve my little Harris 15-3 torch. Can do (almost) TIG quality welds with it. (when not brazing )

I just started using silver solder........amazing how little it takes.

 

[barneyrb]

I just started using silver solder........amazing how little it takes.

Will silver solder take the heat generated? I'm asking because I honestly don't know, not trying to be a smart azz........

 

[tdi-rick]

I just started using silver solder........amazing how little it takes.

It's really easy to overheat and boil the silver, most blokes use too much flame directly on the solder so try and capillary the heat with something like steel that doesn't conduct heat away too quickly and lift the heat away quickly too.
When the heat is right it capillaries and follows the heat beautifully, leaving a really nice fillet, get it wrong and turns ugly really quickly.
Tip selection is important, just like fusion welding.

I've seen some shocking brazed joints by blokes that have been doing it for a long time, wrong tip, wrong heat and just don't care attitude I'd reckon.
I've often had the job of fixing the #### ups.