Another chainsaw dyno...

[Terry Syd]

with that MOFO saw, I would really like to know how much is the carb and how much is the filter.

I'd bet the primary reason for the difference was the jetting of the low speed circuit. If you notice the graph, there is a big difference in power right off the bottom at 5,500. There isn't much demand for air at those low revs so a big filter (or removing the filter) shouldn't make much difference. - I also note that the power drops off earlier when it is at high revs, which is inconsistent with a high flow air filter. Perhaps as Joe said it may have been a bit rich on the high speed needle. This is where more testing on the dyno could tell what is actually going on.

 

[Red97]

Something definitely wrong with 501’s settings. It’s torque peaks at 6,5-7k and normally there isn’t sign of that dip, which looks rather typical for mis-set L/H mixture changeover. Box carb settings?

Bone stock with limiter. Little extra rich.

I don't feel it is missing much if any peak hp the dio is the extra rich condition.

Nah there's gotta be an anomaly with those runs. Or maybe the scale. If a mushroom type saw is four horse what I know about saws is *s-word. I mean, it IS literally *s-word. But that graph has something amiss. Joe'll finger it out.

Lol

I'd bet the primary reason for the difference was the jetting of the low speed circuit. If you notice the graph, there is a big difference in power right off the bottom at 5,500. There isn't much demand for air at those low revs so a big filter (or removing the filter) shouldn't make much difference. - I also note that the power drops off earlier when it is at high revs, which is inconsistent with a high flow air filter. Perhaps as Joe said it may have been a bit rich on the high speed needle. This is where more testing on the dyno could tell what is actually going on.

I'd guess close to 50/50 I've seen all of 1/2hp from pulling a filter.

 

[dustinwilt68]

Very interesting! I know 394's squish is pretty big and the reason the bgd helps it, what is the general consensus w/ the 95's? I felt the bgd and muff mod really woke up mine, wonder if it would sway that 95 graph a bunch?

Be interesting to see what some of the build off 395s make in comparison to each other.

 

[Red97]

How many have a "build off" 395 they would want to send in?

Could easily turn it into a dyno off... if people were interested

 

[dustinwilt68]

I will send mine, should have it back next week, loaned it to a logger customer to break it in. Just a work saw, stock carb.

 

[TreeLife]

How many have a "build off" 395 they would want to send in?

Could easily turn it into a dyno off... if people were interested

I don't have a build off saw, persay...but I do have a mmws 395xp that runs nicely

 

[Red97]

I'm thinking

Gas
Choke
Air filter

Work saw type stuff?

Idk just thinking out loud.

Packages seem to be moving much better now.

 

[dustinwilt68]

Send it Dom, I DNT own any race saws, just work saws that DNT get worked enough. I like it Joe!

 

[Red97]

Send it Dom, I DNT own any race saws, just work saws that DNT get worked enough. I like it Joe!

I don't mind 2 price heads, or crazy stuff inside the jug.

Needs to start good, run and idle. Make a few pulls

Not sure how "wild" others got with the builds.

 

[drf256]

Why do you feet the sharp drop off in power occurs at 11,700? Do you think the carb just can’t move enough air for the saw at that point?

This isn’t a dick measuring question at all. Like I said in the beginning, the interest in the dyno is seeing what changes are myth and what are reality.

Both Mike’s saw and mine are using Hemi chambers. Mine is only around 180psi (on purpose-a worksaw for a gentleman that lives in the warm south), but mine has fingers and a 272 slug and is still underperforming where it shouldn’t. It should be making more power at higher rpm because it has more transfer area than Mike’s. I’d assume the CFB saw to make more torque down low with dual ports and higher compression, but they are nearly identical. Mine has more case capacity because of the smaller piston-so mine is more like a 460 than a 440 in case volume, perhaps that’s how it keeps up with Mike’s on the low end.

Do the muffler outlets appear to be of the same approximate area?

What I think I am seeing is that the hybrids are undercarbed. The stock (and possibly problematic) carb on the RDM did the worst. The CFB carb did better with thinned shafts for more airflow. The Deet’s carb did the best with no choke at all and a V-stack. Again, not to discredit the two builds that did better than mine. Don’t care if I lose everytime, but I thirst for knowing why.

 

[Moparmyway]

Easy to say now, everyone is the best “Monday morning” coach ........

It would be great to see the carb from Deeters swapped around on the other hybrids. I do realize that the saws are probably on different sides of the ConUS, but it’s still nice to think about.

 

[mgr1]

Think that the bigger case capacity kills hp.
If you could make some crank stuffers and test it again...

 

[Terry Syd]

the bigger case capacity kills hp.

The crankcase compression determines when there is maximum delivery flow. Maximum delivery to the cylinder occurs when the flow into the cylinder through the transfers is coming to a halt and at that exact moment the rising piston closes off the transfer ports.

Above that RPM the piston closes off the transfer port too early while the port is still flowing. That's why you increase the time/area of the transfers so that the Maximum delivery can occur at a higher RPM.

Conversely, below the RPM for maximum delivery the rising piston reverses the flow and starts sucking the mixture back out of the cylinder.

Here's something that I still find surprising, changing the compression ratio does NOT change the maximum charge. It is still the same amount of mixture, it just becomes a timing issue.

Another issue about crankcase compression is that the higher the compression, the shorter the powerband. In other words, you can make more horsepower at the higher RPM, but the powerband won't be as long. Thus, we usually see fairly low crankcase compression ratios in saws as we want a broad powerband.

I've read chainsaw racers say that a full circle crank will push maximum delivery ratio up about 400 RPMs and of course, they don't worry about having a broad powerband.

I can't sleep, so thought I'd write some stuff...

 

[MustangMike]

Al, I think Joe said the tune was a bit rich, and this could account for it, plus having the greater case capacity … smaller case capacity (similar to crank stuffers) generally give higher RPMs.

Since the drop off was well outside your broad and very impressive power band (8,000 - 11,750 RPMs), I would not be concerned about it at all.

You and CFB both did very well, and maybe it also shows there is more than one way to skin a cat! The two saws look like twins in their effective range.

Both extremely impressive for a 14 lb powerhead.

 

[Red97]

View attachment 252628

Why do you feet the sharp drop off in power occurs at 11,700? Do you think the carb just can’t move enough air for the saw at that point?

This isn’t a dick measuring question at all. Like I said in the beginning, the interest in the dyno is seeing what changes are myth and what are reality.

Both Mike’s saw and mine are using Hemi chambers. Mine is only around 180psi (on purpose-a worksaw for a gentleman that lives in the warm south), but mine has fingers and a 272 slug and is still underperforming where it shouldn’t. It should be making more power at higher rpm because it has more transfer area than Mike’s. I’d assume the CFB saw to make more torque down low with dual ports and higher compression, but they are nearly identical. Mine has more case capacity because of the smaller piston-so mine is more like a 460 than a 440 in case volume, perhaps that’s how it keeps up with Mike’s on the low end.

Do the muffler outlets appear to be of the same approximate area?

What I think I am seeing is that the hybrids are undercarbed. The stock (and possibly problematic) carb on the RDM did the worst. The CFB carb did better with thinned shafts for more airflow. The Deet’s carb did the best with no choke at all and a V-stack. Again, not to discredit the two builds that did better than mine. Don’t care if I lose everytime, but I thirst for knowing why.

The dip is because yours was still extra rich. Both saws were tuned at 14k ish

Ranchdad was prolly around the 13.8k cfb was prolly 14.3k

More of a gradual quick "clean up" with the leaner tunes. Where the ranchdad still had a hard 4 stroke until clean up. The dip means nothing other than it was still rich at those rpm.

I cannot "see" what the curve will look like. Looking at the raw data scrolling across the screen. Just any crazy anomalies, or missing chunks of data. As long as I don't see those, and have a smooth run. I take it home and graph it.

My thoughts are as long as I have a couple thousand rpm of down slope from peak hp it shows the "powerband". No matter how lean/rich it is tuned those peak numbers don't seem to change.

Now with the screamers, 15k+ those shoe real well on the top end of the graph, as they already have a good load by 14k (where the graph starts) they look good. But the peaks are still the same. Long as the tune isn't so rich to be under peak hp rpm.

I would fully expect your saw to start pulling away at the 12k+ mark. Still going to need around 15k+ to show the top end well.

It would be fair to use the cfb curve and replace your "dip" from the 11.5k to the 14k where yours is pulling a bit harder.
If that makes sense.

 

[Bigmac]

View attachment 252628

Why do you feet the sharp drop off in power occurs at 11,700? Do you think the carb just can’t move enough air for the saw at that point?

This isn’t a dick measuring question at all. Like I said in the beginning, the interest in the dyno is seeing what changes are myth and what are reality.

Both Mike’s saw and mine are using Hemi chambers. Mine is only around 180psi (on purpose-a worksaw for a gentleman that lives in the warm south), but mine has fingers and a 272 slug and is still underperforming where it shouldn’t. It should be making more power at higher rpm because it has more transfer area than Mike’s. I’d assume the CFB saw to make more torque down low with dual ports and higher compression, but they are nearly identical. Mine has more case capacity because of the smaller piston-so mine is more like a 460 than a 440 in case volume, perhaps that’s how it keeps up with Mike’s on the low end.

Do the muffler outlets appear to be of the same approximate area?

What I think I am seeing is that the hybrids are undercarbed. The stock (and possibly problematic) carb on the RDM did the worst. The CFB carb did better with thinned shafts for more airflow. The Deet’s carb did the best with no choke at all and a V-stack. Again, not to discredit the two builds that did better than mine. Don’t care if I lose everytime, but I thirst for knowing why.

Just looking at the info, I agree it’s a rich tune causing the drop off. What seems to be a reoccurring theme is the case volumes effect on peek power and contrary to mosts believe is the two port transfers make great power on the dyno. Not sure if it’s case volume related but deets saw had stock transfers, with a filled lower lip(if I remember correctly) meaning more transfer area isn’t as crucial on these crude saws, I am coming to the conclusion that with these box mufflers the higher case compression is really need for scavenging, because the mufflers are not efficient. Even the 395’s aren’t out preforming the 066’s both stock and ported on the dyno...yet most feel the 395 is the king. The last stock dyno of the 395 it didn’t even get into the 7 hp Mark

 

[Dieselshawn]

Putting a larger carb onto a MS260 made a world of a difference.

It was hilarious to see jaws dropping from friends with chainsaws when they saw the tach four stroke at 17,200 rpms for my ms260.

A buddy of mine with the same saw machined his carb out. Used race gas and a custom head.

Racing against each other with 18 inch bars and .325 chain, he beats me every time. Even when we swap bars and chains.

I then put on my 24 inch bar with 3/8 chain, he puts on his 20 inch with 3/8 chain.

Mine starts winning possibly due to a better torquier power band. I used regular gas. (This saw hates premium gas)

 

[MustangMike]

The burn time on the premium is likely too long, especially mixed with the oil.

 

[Terry Syd]

Back in the '60s I worked at Long Beach Honda in SoCal. We got access to a twin cylinder 50cc road racer and ran it at Lions Drag Strip.

You couldn't tell the RPM from sound, you had to watch the tach (we're talking 22,000 RPM redline here). The 87 octane gas clearly made more power in the high compression engine than the premium high octane.

 

[Bigmac]

Back in the '60s I worked at Long Beach Honda in SoCal. We got access to a twin cylinder 50cc road racer and ran it at Lions Drag Strip.

You couldn't tell the RPM from sound, you had to watch the tach (we're talking 22,000 RPM redline here). The 87 octane gas clearly made more power in the high compression engine than the premium high octane.

That’s cool, Honda did a bunch of research in the 80-90 on octane and rpm, and they were able to find Pre-detonation cant occur somewhere in the 12k-12.5k range meaning regardless of fuel grade the dreaded ping could not occur above that rpm, and like you are saying the faster the burn the better, pretty cool