036/044 hybrid blow down advice

[Ronie]

I just finished up my 036 with a slant fin 044 cylinder that kevin was nice enough to send me, thanks @huskihl, and it runs good but I'd like to get it running a little better. At the moment the timing numbers are, EX 109, TR 128, IN 75 AND .030 squish. I'm going to raise the exhaust to 106 and I'm thinking about shorting about the blowdown to 16 or should I leave it at 19?

 

[JonCraig]

I’m not knowledgeable enough to offer any advice.

but I want pictures and a build thread!

 

[Ronie]

I’m not knowledgeable enough to offer any advice.

but I want pictures and a build thread!

It's already built but when I redo the cylinder I'll put some pics up.

 

[ZukiRyder440]

I just finished up my 036 with a slant fin 044 cylinder that kevin was nice enough to send me, thanks @huskihl, and it runs good but I'd like to get it running a little better. At the moment the timing numbers are, EX 109, TR 128, IN 75 AND .030 squish. I'm going to raise the exhaust to 106 and I'm thinking about shorting about the blowdown to 16 or should I leave it at 19?

Considering how short the stroke is on the 036 compared to the 044,(34mm vs 36mm), maybe it will be better with the lower exhaust and shorter Blowdown ?? . I’d say that 106 ex would be good, Shorter BD to bring the power up a little bit. Maybe not widen the intake at all and stay at about 78-79*? I could just be spewing out crap right now but I like to try and help any way possible

 

[ZukiRyder440]

How much are you cutting from the band and base?

 

[Ronie]

How much are you wanting to from the band and base?

I've cut the base as much as I dare and nothing from the band, .030 squish. This is how it looks now with just the exhaust widened and the intake lowered. In about a half hour I'm going start on it.

 

[AKJonsereds]

I know very little about hybrids but it seems in my limited experience, if you have enough compression to spare, a little more exhaust would be nice. As for transfers, I usually am on the side of slightly longer blow down but that seems like pretty low transfers….since the cutting of the cylinder was done to get fit and not add compression, might want to check that before going too high. Or find a popup?

 

[AKJonsereds]

Is there a [mention]drf256 [/mention] in the house?

 

[Ronie]

I went ahead an did it, numbers ended up being EX105, TR 122 and IN 80.

 

[AKJonsereds]

Looks good!

 

[cus_deluxe]

I went ahead an did it, numbers ended up being EX105, TR 122 and IN 80.

View attachment 318670 View attachment 318671 View attachment 318672 View attachment 318673

Lookin sweet! 'cept you forgot the mickey mouse ears at top of intake port dot dot dot

 

[Ronie]

Hopefully it's an improvement.

 

[Wonkydonkey]

Interesting thread, as 36 is a good saw but with a 44 top end it could be even better…

we want cutting vids as well a build thread.

 

[Ronie]

Interesting thread, as 36 is a good saw but with a 44 top end it could be even better…

we want cutting vids as well a build thread.

I've already built the saw so it's to late to do a build thread but I'll post a video of it in a day or two. Here's a video of it before I made the timing changes, When I first put it together I only widened the exhaust and lowered the intake to 75. J_M____ did a good write up on the one he did and I did mine the same way except I didn't cut the crankcase.

https://opeforum.com/threads/stihl-036-044-hybrid-build.12242/

Before timing changes

 

[ZukiRyder440]

I went ahead an did it, numbers ended up being EX105, TR 122 and IN 80.

View attachment 318670 View attachment 318671 View attachment 318672 View attachment 318673

That is some clean looking grinding right there! Nice job! And the saw looks pretty strong if ya ask me Ronie!

 

[Ronie]

That is some clean looking grinding right there! Nice job! And the saw looks pretty strong if ya ask me Ronie!

Thanks, I still haven't put the cylinder back on but I should have it ready in a couple of days and we'll see how it does.

 

[Mattyo]

when I did that hybrid case work it seemed to me that decking the crankcase was a big part of getting the head to fit. what a pain that was..... I ended up balancing between cutting the deck and cutting the base. Haven't heard from Jeremy in a while ...but he ended up with some funky throttle linkage that had to be customized to get it to work. lots of tinkering to do these

 

[drf256]

Unchartered territory in some ways.

What intake tract did you wind up using? The 036 boot has a pretty small bore.

From a purely theoretical standpoint, there are a few issues to bounce around.

The distance from the band to the ex roof will be physically shorter at the same degree reading with the currently shorter stroke.

The chamber volume of the 044 head is designed to make running compression with more swept volume statically.

The case volume is smaller and will cause mismatch alá an 044/46 hybrid, but you are also dealing with a shorter stroke.

So the way I see it (my opinion which is worth what you are paying for it), I’d want an exhaust roof around 103-105-not only does one need to consider the point at which to bleed off combustion pressure but also think about how much of that swept volume can be filled with charge during the case compression phase.

The case pressure should be high but there is less volume. I’d say 18-20* blowdown off the cuff.

Too low of an intake floor with only cause a lot of spitback. It can only fill so much.

It looks pretty damn good as in in your video.

What is your static compression in psi?

My gut would be 30 out of band, drop jug more to get squish near 20, and go 103/125/75. Just my gut on this one.

 

[Ronie]

What intake tract did you wind up using? The 036 boot has a pretty small bore.

In the video it has an 038 boot on it but has an044 one on it now.

What is your static compression in psi?

I haven't done a compression test on it.

My gut would be 30 out of band, drop jug more to get squish near 20, and go 103/125/75. Just my gut on this one.

Wish I could give them numbers a try but there was a little raised area on the roof, when I went to level it out I I caught the the roof edge and messed it up so buy the time I got it fixed it had raised the roof to 99. so I figured that I'd just put it on and see how it does. If runs like crap I'll see if there's a machine shop that will cut the case like Mattyo did.

 

[Mattyo]

The only real benefit to balancing cutting the case and the base is to avoid thinning out the base to the point of it being fragile enough to crack ears. That and cutting the cases gives a super flat surface