361 Shootout

[Trigger-Time]

I was 12 years old in 1972, dad was letting me pull our H Farmall tractor
at local pulls. At one of the pulls they dyno tested the tractors for HP
for each class. The dyno looked very old, it was nice looking just
the way it looked made you think of something made in the 40's or 50's.
Anyway the man running the dyno was old and moved slow. I ask him
if he would like some help. He grinned and said, son I sure would. So
I hooked up the dyno to the PTO on tractors most of the night.

The dyno was hooked up to a garden hose, dyno had a few valves
he would turn to put a load on the tractor's. When dyno test was
done for each tractor he would let the water out of dyno. That
water has hot hot hot, the old man said I can kill any tractor here
with this old dyno.

I never thought to ask what was going on in the dyno.
I guess where to many young girls my age running around at the time.

So was their a brake set up inside the dyno and the water
was just to keep brake cool?

TT

 

[timberwolf]

I thought about friction brake dynos and even to handle say a 10hp ported saw the heat produce would be about equal to a conventional kitchen stove with all the burners on max. Just seemed like it was going to be too difficult to keep the runs short enough and RPM stable enough to get good data. Way too much of a PITA to do RPM points one at a time and if using a computer then it is at least as complicated as an inertia dyno plus need to deal with the load arm and load cell.

I think it would be pushing RPM limit for a standard disk break, even using big saw chain sprockets the mass wheel can get going 5,000 RPM.

But the brake dyno would be more usefull than inertia for tuning a carb or pipe at fixed RPM.

I'm going to look over the data capture again tonight, should be getting an RPM update every 0.025 seconds but the way the data is exporting I get one every .1 seconds and groups of 4 or 5 in a row read the same value, plus there is some ossilation, one group is a little high then the next a little low and the ploted power curve ends up rough. Messing around filtering the data I can smooth it out, but have not tested that to see if the end result is repeatable.

Might try switching from optical to magnetic pickup and see if there is any difference.

I'd bet that tractor dyno was a waterbreak, kind of like two propellers pushing against each other to create a load.

 

[madhatte]

So was their a brake set up inside the dyno and the water was just to keep brake cool?

Called a water brake. What it is is a pair (or more) of counter-rotating fans inside a chamber with water pumped through. The water is both the fluid coupling medium (as in a torque converter) and the coolant. The two fans generate counteracting thrusts. The water has to be pumped in there at sufficient pressure to prevent cavitation or else the fans can free-wheel until the bubble collapses, which isn't good for any of the parts involved. I've seen some pretty big ones used as dummy loads for turbines. They seem to be pretty high-maintenance items.

 

[mtngun]

So was their a brake set up inside the dyno and the water was just to keep brake cool?

Most of the tractor dynos I've seen drove a big assed fan, but water pump dynos are common, too. Basically it's just a water pump, and you control the load with a valve on the pump output. Presumably he had some kind of load cell or spring scale to measure the torque applied to the pump. If you know the torque, and know the rpm, you can calculate the power.

One of the dynos that TW linked to used a water brake, prolly a scaled down version of your tractor dyno.

Pumps are expensive, though, and not necessarily designed to hold together at chainsaw RPMs. That's why I was thinking to use a disc brake, which can be had for not a lot of money. Yes, it would have to dissipate a tremendous amount of heat energy, but disc brakes do that all the time, and it wouldn't take that long to run a chainsaw through its paces. One of these days I oughta get off my butt and try it.

 

[timberwolf]

To do it with a disk break it would likely be best to run 2 sets of gears with something like a 12:1 to 15:1 reduction to get the RPM down under 1000 RPM on the disk break then could use a steering knuckel and caliper set up off a FWD car, a little work to a master break cylinder and that could be the bigger part of the mechanical systems. Just mount the saw on a swing arm and load cell.

 

[mtngun]

Ya, I dunno how many rpm's a disc brake could handle, so gear reduction would be desirable. I was thinking a motorcycle brake, maybe even a bicycle brake. Only way to know is try it -- from a safe distance. :hmm3grin2orange:

Entry level usb oscilloscope/data logger boxes start around $50. I've never used one of the cheapo units, but the specs make it look do-able.

If only I had time ........ may have to wait for retirement. As you once said, it helps if you don't sleep.

 

[Trigger-Time]

Ya, I dunno how many rpm's a disc brake could handle, so gear reduction would be desirable. I was thinking a motorcycle brake, maybe even a bicycle brake. Only way to know is try it -- from a safe distance. :hmm3grin2orange:

Entry level usb oscilloscope/data logger boxes start around $50. I've never used one of the cheapo units, but the specs make it look do-able.

If only I had time ........ may have to wait for retirement. As you once said, it helps if you don't sleep.

If my math is correct.

30" dia tire at 70mph turn's 784rpm's

20" dia = 1176rmp's


TT

 

[timberwolf]

Yep, I had about the same math, figured they should easy be good for 100mph and took a 30" tire and got just over 1000 rpm.

Would be more than a bicycle brake could handle, motorcycle maybe, but I would think it would be better to have something more substantial just for heat disipation.

You don't want to brake or accelerate too fast with the break dyno or you measurments become affected as the whole thing starts to work like an inertia dyno. Also would have to take gear and friction losses into the driveline in. For a friction dyno that would need to be estimated. On the inertia dyno you can do a coastdown and measure how quickly the wheel slows, get a negative HP or torque figure for that then add it to the accelerations to take friction and windage losses out of the system.

 

[Woodman 460]

Great post T.W. I am happy to see that you are displaying such usefull knowledge here for us all. I hope to carryout some port work on my 361 this winter!

 

[parrisw]

I thought about friction brake dynos and even to handle say a 10hp ported saw the heat produce would be about equal to a conventional kitchen stove with all the burners on max. Just seemed like it was going to be too difficult to keep the runs short enough and RPM stable enough to get good data. Way too much of a PITA to do RPM points one at a time and if using a computer then it is at least as complicated as an inertia dyno plus need to deal with the load arm and load cell.

I think it would be pushing RPM limit for a standard disk break, even using big saw chain sprockets the mass wheel can get going 5,000 RPM.

But the brake dyno would be more usefull than inertia for tuning a carb or pipe at fixed RPM.

I'm going to look over the data capture again tonight, should be getting an RPM update every 0.025 seconds but the way the data is exporting I get one every .1 seconds and groups of 4 or 5 in a row read the same value, plus there is some ossilation, one group is a little high then the next a little low and the ploted power curve ends up rough. Messing around filtering the data I can smooth it out, but have not tested that to see if the end result is repeatable.

Might try switching from optical to magnetic pickup and see if there is any difference.

I'd bet that tractor dyno was a waterbreak, kind of like two propellers pushing against each other to create a load.

Hey, What kind of pickup are you using? You said optical, when I first saw the pics of your dyno it reminded me of the governors I used for my RC Heli's, you could use an optical or mag pickup for them, the optical pickup was very easily messed up with indoor lighting, had to be out in sunlight to work properly, and even then I had a hard time with it. I went to a magnetic pickup and all was good.

 

[timberwolf]

I wasted the evening trying different pickup sensors, different numbers of triggers, about every setting I could and it just looks like the data logger is a POS as far as what I am trying to do.

Sent an email to see what it is going to set me back to get the right electronics... GRRRRRRR!

 

[timberwolf]

Here are a few carb pics, 044 and 361 carbs. both were taken out about 1.5mm in the venturi increasing the venturi area by about 20%. 044 and 361 carbs share the same 20.5mm throttle plate diamiter, but 361 is a lot tighter than 044 in venturi at 15mm vs 17mm and choke 18.8mm vs 22mm.

There is very little room to take out 044 carb as there is a fuel passage on the left hand side that runs very close to the bore. I ended up sleaving the passage with a brass tube to gain more space.

 

[Tzed250]

Thank you for the pics and info!!!


.

 

[mtngun]

How do you know how much metal can be removed from the carb before running into trouble ? Is that a trial and error thing ?

I'm thinking I best have a spare carb on hand before I attempt this.

Thank you for sharing your knowledge, TW, you are too generous.

 

[timberwolf]

It can be some trial and error, but looking the carbs over closely it is not too hard to pick out where the internal passages are and avoid the errors as much as possible.

 

[parrisw]

Here are a few carb pics, 044 and 361 carbs. both were taken out about 1.5mm in the venturi increasing the venturi area by about 20%. 044 and 361 carbs share the same 20.5mm throttle plate diamiter, but 361 is a lot tighter than 044 in venturi at 15mm vs 17mm and choke 18.8mm vs 22mm.

There is very little room to take out 044 carb as there is a fuel passage on the left hand side that runs very close to the bore. I ended up sleaving the passage with a brass tube to gain more space.

Awesome stuff!!! I like the carb holder! I see you always have 3jaw chucks in your pics, do you ever use a 4Jaw?

 

[timberwolf]

I do use 4 jaw chuck for turning offset parts and square stock, that about the only time it gets used.

 

[parrisw]

I do use 4 jaw chuck for turning offset parts and square stock, that about the only time it gets used.

Cool, I try to use my 3Jaw most of the time, it just doesn't hold parts as good as I like, maybe a new one is in order, I find if I tighten it loosely then indicate it and tap the stock to get the best runout I can, it seems to work ok.

 

[parrisw]

Anything special for boring? Or just a regular ol boring bar?

 

[timberwolf]

Yep, used a boring bar, but sometimes have ground a small 1/4 HSS tool with a profile to do the edges of the venturi when removing choke plate and reworking the entry for a race carb.