Mastermind Revisits the MS661

[Mastermind]

Yup, you nailed it. Now that I know more, I have so much more to learn.

But lets get back to your question Sir ....... Do YOU think case volume plays a role in higher exhaust or blowdown duration ?
Please elaborate what you know and what more you have learned

I've been trying for several years to get the 681 to really come alive. I'd tried everything under the sun.......more intake, less intake, more blowdown, less.....

Finally, I said F it and raised the hell out for the exhaust. My thinking was that if I had 81 on the intake, maybe rather than fight that, I'd embrace it and lengthen all the durations. It worked pretty well.

But what's that got to do with the 661?

 

[junkman]

Is that how you lowered the compression ? by raising the exhaust more ? I know in dirt bikes it raises the rpms doing that .

 

[Mastermind]

Is that how you lowered the compression ? by raising the exhaust more ? I know in dirt bikes it raises the rpms doing that .

I took less out of the squish, and went much higher on the exhaust.

 

[junkman]

I took less out of the squish, and went much higher on the exhaust.

Will that hurt long bar tourque ?

 

[MustangMike]

Now, is this a trend, we gonna start porting everything like this??? They seem to run very strong!

 

[jmssaws]

Now, is this a trend, we gonna start porting everything like this??? They seem to run very strong!

I cut very little from the chamber and run a high exhaust most times

 

[Mastermind]

Will that hurt long bar tourque ?

Not that I can tell with the 28".

Now, is this a trend, we gonna start porting everything like this??? They seem to run very strong!

Every configuration has to be done differently. There is no "everything" that can be done "like this". I'll be honest, I think I was swimming against the current on the 661. Everything I've learned tells me that it has too much intake, and too much exhaust. But, when you think about the case volume, the small size of the transfer ports (not at the upper end, but thru the passages), and the M-Tronic tuning system, this saw is far from a "normal" animal.

 

[Mastermind]

Like on the Solo 681, rather than worry that I had far too much intake, I thought that if I have that much intake timing, maybe I need to take all the other numbers higher.

Well......I did that a few years ago, but I made a turd. This time I decided to increase all the durations......except the transfer duration. Instead of increasing transfer duration, I increased blowdown.

 

[mdavlee]

Will that hurt long bar tourque ?

One of the strongest 7900/681'ive run has a high exhaust and low compression. Runs a 9 pin and 28" pretty easily.

I like higher exhaust. Most of my stuff was 2-8 degrees higher than what Randy has been doing.

Case capacity is easy to test with some fluids. Just have to level the case off. Put the crank at bdc. The other thing is the stuffer doohickey.

Keeping transfers smaller by whatever means will help velocity. Might be a pop up or even trimming the piston there. You just have to play with this stuff. Madsens gets 12-15% on a dyno over a stock 661. They cut the piston for their changes.

 

[junkman]

Like on the Solo 681, rather than worry that I had far too much intake, I thought that if I have that much intake timing, maybe I need to take all the other numbers higher.

Well......I did that a few years ago, but I made a turd. This time I decided to increase all the durations......except the transfer duration. Instead of increasing transfer duration, I increased blowdown.

This sounds like my jug Simon did ,it has 180 psi also ,transfers were not touched ,just intake and exhaust work done .

 

[VinceGU05]

I agree with your sig.

"Its what you learn, after you already know it all, that counts"

And here's another.

Now that I know more.......I have so much more to learn.

ignorance is bliss

 

[Red97]

Anyone have a pic looking into the case?

Can't say I've paid much attention to the 661's yet....

The's saws all look plenty strong, nice work to all of ya.

 

[Miller Mod Saws]

Anyone have a pic looking into the case?

Can't say I've paid much attention to the 661's yet....

The's saws all look plenty strong, nice work to all of ya.

 

[Red97]

View attachment 21292

Thank you

Yeh that is tight..

I can see these liking the bit more bd and can handle the higher ex.

Maybe one day I will get my hands on one.

 

[mdavlee]

Might try 7900 like numbers

 

[Cigmaker]

Don't listen to Randy I got a saw from him today that's only twice as fast as before I sent it to him. Plus he likes cows

 

[bryanr2]

You might be surprised Mike. I'm chatting with Brad Snelling about it right now. I'm not good at keeping this stuff to myself. I want to see us all build great saws.

I sorta wanna see how the thinking in this thread goes before I let the cat out of the bag......

 

[Dieselshawn]

Watching the porter's food throwing movie....

 

[Deets066]

I like what ya did here Randy, 661 looks good. I have a little different look on porting now than I did a year ago.

I used to want to drop jug as far as possible to get compression. But now I'd rather get my machining closer to my desired port timing numbers so there is less grinding

 

[Moparmyway]

I like what ya did here Randy, 661 looks good. I have a little different look on porting now than I did a year ago.

I used to want to drop jug as far as possible to get compression. But now I'd rather get my machining closer to my desired port timing numbers so there is less grinding

I agree 100% !!!
Great post !!