Staggered uppers on 357?

[Ketchup]

Hi guys!

I’m porting my first 357. Target numbers are 106/124/80. Maybe a bit higher on the exhaust. My question is has anyone left the secondaries low and just brought up the primaries? @huskihl, @Stump Shot, @Mastermind , @drf256, @srcarr52, @Red97, and anyone else! Open to any advice. Thanks everyone.

 

[farminkarman]

Hi guys!

I’m porting my first 357. Target numbers are 106/124/80. Maybe a bit higher on the exhaust. My question is has anyone left the secondaries low and just brought up the primaries? @huskihl, @Stump Shot, @Mastermind , @drf256, @srcarr52, @Red97, and anyone else! Open to any advice. Thanks everyone.

If it were my saw, I would open the secondaries 3 degrees after the primaries and blow them upward.

 

[srcarr52]

I’d shorten up the intake duration if you can.
I normally open the intake side 1-2 deg after the primaries and leave more upward angle in them.

 

[Stump Shot]

Hi guys!

I’m porting my first 357. Target numbers are 106/124/80. Maybe a bit higher on the exhaust. My question is has anyone left the secondaries low and just brought up the primaries? @huskihl, @Stump Shot, @Mastermind , @drf256, @srcarr52, @Red97, and anyone else! Open to any advice. Thanks everyone.

You will need about 4° to 6° lead time for the primaries to have the proper effect.
I usually think about the piston diameter here with a small one needing less than a large diameter piston.

 

[Ketchup]

You will need about 4° to 6° lead time for the primaries to have the proper effect.
I usually think about the piston diameter here with a small one needing less than a large diameter piston.

I think I understand…
4-6 between the primary and secondary?

You’re saying staggering something like a 395 would want more like 6 degrees and a 346 would want 4ish?

 

[farminkarman]

I think I understand…
4-6 between the primary and secondary?

You’re saying staggering something like a 395 would want more like 6 degrees and a 346 would want 4ish?

You are going to find differing opinions on how much stagger is required for each saw. Some of it depends on how you did the rest of the port work and and timing. For smaller saws (50cc and less) I stagger them 2 degrees. On a 395 I have used 4 and worked great…maybe more would be better, but I haven’t tried, so not sure.

 

[Stump Shot]

I think I understand…
4-6 between the primary and secondary?

You’re saying staggering something like a 395 would want more like 6 degrees and a 346 would want 4ish?

Yes and yes.
When you think about it, imagine the primary clearing the top of the piston, so the secondary doesn't trap a pocket of burned fuel there at the intake wall, a larger piston needs more time for that to happen. Aiming is critical for it all to work together picture the secondary just sliding over the top and merging with the primary at the wall like a shotgun blast pattern and keep the primary's down to revert back slightly to the exhaust port, that is if they hit the wall correctly just next to one another.

 

[Mastermind]

Sound advice.

 

[Stump Shot]

You are going to find differing opinions on how much stagger is required for each saw. Some of it depends on how you did the rest of the port work and and timing. For smaller saws (50cc and less) I stagger them 2 degrees. On a 395 I have used 4 and worked great…maybe more would be better, but I haven’t tried, so not sure.

There's no two people that port alike and everyone needs to adjust things to work for themselves and their own style.

 

[Ketchup]

Thanks gentlemen. First go is x105, t124/128, i78. We’ll see…

 

[Mastermind]

Thanks gentlemen. First go is x105, t124/128, i78. We’ll see…View attachment 370019View attachment 370020

I predict that will run very well.

 

[huskihl]

105
120/123
78

Yee haw

 

[pbillyi69]

is it done yet?

 

[drf256]

I’d say 76-78 on the intake.

You got great advice here. I’ve only done one of them, and my first call was to the man w fingers of franks in the Mitten state.

FWIW, numerically high exhausts can generally tolerate less BD. Raising them uppers more will make it hotter but peaky.

 

[Ketchup]

is it done yet?

Headed for the wood pile this morning. Might have other build issues that show up but I’m gunna light it.

 

[pbillyi69]

right on.....light it up!

 

[Ketchup]

Ripped pretty hard once I realized the metering plate on the carb wasn’t tightened down. Got halfway through some noodling and it started to run away. Definitely an air leak. Back to the bench…

 

[pbillyi69]

nice

 

[pbillyi69]

did you advance the timing as well?

 

[Red97]

Flat, get the charge moving, it's gonna do something right or wrong.

Have not done extensive testing to prove/disprove anything on staggagered transfers.

BUT.... What I have noticed from my builds and others is any that "felt" "torquier" "more Torq" "torqué" were simply lacking power to other versions of the same build.

98% of the time is was a lack in power over the whole range.

But I hope to do further testing on the matter sometime.