Play time?

[Red97]

I can weld that for you.

I'll need one to learn on... who knows maybe the crank/rod won't agree with +9mm more piston...

 

[huskihl]

I'll need one to learn on... who knows maybe the crank/rod won't agree with +9mm more piston...

What was it you said last night, a 14 pound 385? That should be cool if it’ll run it

 

[Red97]

What was it you said last night, a 14 pound 385? That should be cool if it’ll run it

Yes I believe it was something along those lines...

 

[Red97]

45 (stock) vs 54 (8611)

 

[RI Chevy]

Wow. Big difference there.

 

[Definitive Dave]

Cool project even if its an Echo

 

[Red97]

Cool project even if its an Echo

Might have a chance to be a pretty decent 5 cube sod cutter. For an Echo...

 

[Red97]

56mm fits...

 

[Red97]

Looks like 56mm can happen with the big bore jug...
.this would be the od of my 56mm sleeve.

While still leaving .055" wall ..

92.6cc

Just because

 

[drf256]

Joe,

It’s early, so maybe I read some things wrong, but:

I wouldn’t got through any effort to make the case capacity smaller, it needs to be larger to feed that cylinder.

The longer stroke saws have higher piston speed, so they move more distance with each degree of revolution, as you know. The 7900 is an anomaly with the high blowdown and large stroke. The 562XP illustrates the low blowdown generally needed with longer strokes.

I’d venture to say the saw you are building will need a physically high exhaust roof (~ 95) and 15-20* BD. My thoughts are that the case capacity won’t be enough to fill a lot of swept volume, even though the case pressure is high. You’ll have to reduce swept volume to compensate for the fact.

Where is your current 52mm hybrid timed and how happy are you with it?

 

[Red97]

Joe,

It’s early, so maybe I read some things wrong, but:

I wouldn’t got through any effort to make the case capacity smaller, it needs to be larger to feed that cylinder.

The longer stroke saws have higher piston speed, so they move more distance with each degree of revolution, as you know. The 7900 is an anomaly with the high blowdown and large stroke. The 562XP illustrates the low blowdown generally needed with longer strokes.

I’d venture to say the saw you are building will need a physically high exhaust roof (~ 95) and 15-20* BD. My thoughts are that the case capacity won’t be enough to fill a lot of swept volume, even though the case pressure is high. You’ll have to reduce swept volume to compensate for the fact.

Where is your current 52mm hybrid timed and how happy are you with it?

Not doing anything to reduce. Just had a bad spot that needed filled for sealing surface.

Current numbers
100
122s 129p
75

It is strong.... But feels a little tame.

Kind of like running a stock 80cc+ for the first time.. They are strong but lacking some of the wow/snap/aggressiveness..

 

[Czed]

Cool project even if its an Echo

You said my echo's were pieces of *s-word.

 

[srcarr52]

Joe,

It’s early, so maybe I read some things wrong, but:

I wouldn’t got through any effort to make the case capacity smaller, it needs to be larger to feed that cylinder.

The longer stroke saws have higher piston speed, so they move more distance with each degree of revolution, as you know. The 7900 is an anomaly with the high blowdown and large stroke. The 562XP illustrates the low blowdown generally needed with longer strokes.

I’d venture to say the saw you are building will need a physically high exhaust roof (~ 95) and 15-20* BD. My thoughts are that the case capacity won’t be enough to fill a lot of swept volume, even though the case pressure is high. You’ll have to reduce swept volume to compensate for the fact.

Where is your current 52mm hybrid timed and how happy are you with it?

The 562 is low blowdown because it’s a strato port design. More time with open transfers to flush out the exhaust with the back filled clean air.

 

[Red97]

The 562 is low blowdown because it’s a strato port design. More time with open transfers to flush out the exhaust with the back filled clean air.

Would love to hear your thoughts on any of these builds.

52,54,56 mm

 

[drf256]

The 562 is low blowdown because it’s a strato port design. More time with open transfers to flush out the exhaust with the back filled clean air.

True, but other strato designs don't do the same. Any thoughts on why?

 

[srcarr52]

True, but other strato designs don't do the same. Any thoughts on why?

550, 562, 572 all do. It's because they back fill the transfers with clean air. Other designs flush the exhaust with clean air and thus don't need the extra short blowdown.

 

[srcarr52]

Would love to hear your thoughts on any of these builds.

52,54,56 mm

Whats the original stroke and what stroke are the cylinders designed for? I've found it's easier to destroke a cylinder than go to a larger stroke. When going to a larger stroke the intake and exhaust durations can get out of hand quickly.

 

[Red97]

Whats the original stroke and what stroke are the cylinders designed for? I've found it's easier to destroke a cylinder than go to a larger stroke. When going to a larger stroke the intake and exhaust durations can get out of hand quickly.

Echo (saw) is 37.6 stroke

046 (cylinder) is 36mm stroke

The stock echo has a really tall piston for 45mm

After base cleanup I didn't have to take much out of the band.

As assembled
103
122s 129p
75
79.85cc

Which I was pretty happy with all but not having a lot of skirt to play with.

Would guess comp is still over 200psi

Have not timed the big bore jug yet, but should be in the same ball park.

 

[srcarr52]

Echo (saw) is 37.6 stroke

046 (cylinder) is 36mm stroke

The stock echo has a really tall piston for 45mm

After base cleanup I didn't have to take much out of the band.

As assembled
103
122s 129p
75
79.85cc

Which I was pretty happy with all but not having a lot of skirt to play with.

Would guess comp is still over 200psi

Have not timed the big bore jug yet, but should be in the same ball park.

The tall piston of the Echo is just packaging, the whole cylinder is likely stretched out. Most Stihl is always as tight as possible and that is why you run into free porting exhaust on them a lot. It's likely the Echo has a long rod which may work against you for dwell time at TDC. It probably won't like as much ignition timing as other saws but it will be more tolerant to low octane fuel and will probably run well on alcohol.

You are going up in stroke on the 046 cylinder so you see the intake and exhaust port timing is already looking at the higher end of what you'd want. You'll have to pay attention to where the bottom of the transfers are at BDC to make sure they are not shadowing over the piston.

I'd leave the intake as is, bump the exhaust up to 101, with about 18 blowdown, open the exhaust side of the transfers first by 1deg.

What is the 122s, 129p?

 

[Red97]

The tall piston of the Echo is just packaging, the whole cylinder is likely stretched out. Most Stihl is always as tight as possible and that is why you run into free porting exhaust on them a lot. It's likely the Echo has a long rod which may work against you for dwell time at TDC. It probably won't like as much ignition timing as other saws but it will be more tolerant to low octane fuel and will probably run well on alcohol.

You are going up in stroke on the 046 cylinder so you see the intake and exhaust port timing is already looking at the higher end of what you'd want. You'll have to pay attention to where the bottom of the transfers are at BDC to make sure they are not shadowing over the piston.

I'd leave the intake as is, bump the exhaust up to 101, with about 18 blowdown, open the exhaust side of the transfers first by 1deg.

What is the 122s, 129p?

Transfers open
122 on intake side then 129 ex side.

Primary/secondary

Factory coil is 39* btdc stock could try the more tame 590 coil, it is around 32* total

I'll look into the transfers.

I blend the lowers to match the windows. Didn't check the uppers at bdc..