Piston wash patterns

[tree monkey]

So keep Exhaust port smaller to limit short circuiting?

If a motor is losing some charge via the Ex port, at what point of the cycle is it occurring at? Are we sure that we aren’t just doing a better job loop scavenging the entire volume? Do we know that the loss isn’t at least in part to a free flowing muffler?

There will have to be some loss for max power, just how it goes. There will be no way for charge dilution to be minimized without some losses.

So a tiny little ex port might make beautiful wash, but would be want that? A tight muffler would cause high pressure by the port opening and stall charge from exiting, effectively causing carbon deposits that would make the wash look better.

I’m just not sure that with the changes we make, a pattern on the crown can accurately predict all that’s going on in a cylinder.

I’m interested in max power at the expense of some fuel economy. Interestingly enough, most of the saws I do are only slightly less fuel efficient than a stock saw. For the life of me, I still am not sure why. I think it’s combustion efficiency.

you can't make power out of fuel lost out the muffler.
and for day to day use, unburned fuel burns the eyes and nose

 

[MustangMike]

Forgive my personal viewpoint, but this discussion seems to validate my findings that a particular Asian 660 (w/Cross MMWS P+C) ran stronger with a less aggressive muffler mod. If less unburned fuel is escaping, it will produce more power.

It ran strong with a Huztl muffler, with the only mod being a 1/2" hold drilled though the baffle. With a more opened up muffler w/o a baffle, it had good speed but seemed to lack torque. If you leaned on it, it just quit. Was noticeably stronger with the more restrictive muffler.

I know I took some heat for my comments at the time, but I did not imagine it, it really happened.

 

[RI Chevy]

Open it up Mike. Put headers on it and letter rip! LOL

 

[MustangMike]

I had headers on my current Mustang, and removed them. Same reason. Since the software limits RPMs in that engine to 6,250, the headers resulted in less drivability and low RPM torque and did not add anything to top RPM power. If the rev limiter were at 7,000, it likely would have been a different story.

Unfortunately, I can not make any mods to the tune w/o loosing the 50 State emissions legal certification.

I just learned to shift quickly my friend!

 

[RI Chevy]

Lol. [emoji106]

 

[Deets066]

you can't make power out of fuel lost out the muffler.
and for day to day use, unburned fuel burns the eyes and nose

Got any new, elusive riddles for us today?

 

[tree monkey]

yes

 

[drf256]

you can't make power out of fuel lost out the muffler.
and for day to day use, unburned fuel burns the eyes and nose

Understood.

But you also cant get the best scavenging without a little loss.

I've yet to make unburned fuel effect me from a saw. I guess the amounts may be negligible.

 

[bwalker]

you can't make power out of fuel lost out the muffler.
and for day to day use, unburned fuel burns the eyes and nose

This!

 

[Deets066]

Understood.

But you also cant get the best scavenging without a little loss.

I've yet to make unburned fuel effect me from a saw. I guess the amounts may be negligible.

This is what’s up right here.

 

[Deets066]

Use a little fuel to push the old charge out

 

[MustangMike]

Everything runs best when everything is in sync, and sometimes you just have to experiment to find out what helps to get it in sync.

 

[Bigmac]

I had headers on my current Mustang, and removed them. Same reason. Since the software limits RPMs in that engine to 6,250, the headers resulted in less drivability and low RPM torque and did not add anything to top RPM power. If the rev limiter were at 7,000, it likely would have been a different story.

Unfortunately, I can not make any mods to the tune w/o loosing the 50 State emissions legal certification.

I just learned to shift quickly my friend!

What length headers? Short, mid or long tubes?

 

[Bigmac]

Understood.

But you also cant get the best scavenging without a little loss.

I've yet to make unburned fuel effect me from a saw. I guess the amounts may be negligible.

Can you even call it scavenging with a can muffler?

 

[tree monkey]

Can you even call it scavenging with a can muffler?

scavenging is more important with a muffler then a pipe, so yes.

 

[drf256]

Can you even call it scavenging with a can muffler?

2 stroke engines run via scavenging. Different types exist (ie loop, cross, etc.), but without scavenging the engine wouldn’t run. Pipe or not.

 

[MustangMike]

What length headers? Short, mid or long tubes?

They were shorties, but top rated JBA Firecone. I was disappointed with the results and expected an improvement in torque.

Less restrictive mufflers, and less restrictive cats made nice improvements across the RPM range.

The failure of the headers still baffles me, but the car sounds and runs better w/o them. (the sound got a bit tinny).

 

[David Young]

Good bad ugly?

 

[huskyboy]

Good bad ugly?

What saw is that David?

 

[David Young]

A 361