I was mounting a new filter and velocity stack on my .82 this morning and decided to do a before and after test. The fiter is a BruLine and the stack/carb gap was filled with a green automotive air conditioner o-ring that didn't protrude into the air flow hardly at all. The fuel is 15% Omega and the prop is an APC 14x4W. The tank was a 2 ouncer. No linkage was attached to the throttle and the spring held it full open. Here's the results:
No stack/filter: Peak 10,050 richened to 9,650 for the test run. Run time to empty was 2 min. 30 sec.
With stack/filter: Peak 9660, ran at 9360, and the run time was 3 min., 20 sec.
No spitting from the carb was observed before the stack/filter was added.

Wow! Awesome info, thanks!

Great thinking Tim to run this test. I wonder if there would have been that slight rpm loss without the airfilter and what the time factor would have been. Still have it set up for testing? Did you have the fine or coarse element in the filter?

Thanks,

Ernie

Tim:

Reinforces what I've been saying for a long time.

A one third increase in endurance with less than 4% rpm drop at peak.

I have to admit the rpm loss surprised me, that's not been my experience but at the same time I seldom set things up for full power operation.

Bill.

Ernie, I was using a fine mesh filter. I'm thinking it would have less effect on a smaller engine using the same sized stack and filter. I really need to repeat this test a few times to make sure the time is correct. I live in town and try to hold test running to a minimum. I'll be doing my .56 next and will run the same test with it. Let me pull the filter off and tach the peak.

The engine peaks at 10,170 with no filter and the stack. I didn't do a consumption test.

Great test Tim - thanks for sharing the info.

The power reduction equates to a little over 10% (according to prop power) - is it possible to run the stack without the filter?

Ahh - OK thanks! I was a little slow off the mark there!

Here's the result of the .56. 12x6APC and all other conditions the same:
No stack/filter: 10,290 peak and test run at 9,960= 4 min., 9 sec.
stack/filter installed: 10,020 peak and run at 9,760= 4 min., 47 sec.
Peak rpm with stack but no filter= 10,090 (no change)

I think the fine filter would tend to be more restrictive than the coarse one in general. If the 56 has a milder cam there would be less of a difference in fuel consumption due to less spitback. Now that brings up an interesting point. Most of the spitback is at lower or mid rpms I think. We usually don't run WOT for a whole tank of fuel. Therefore if you ran the same test, but at mid throttle, there might be even more of a fuel savings with the stack.

Ernie

This has probably been asked a bazillion times but "does anyone have the part numbers for the stacks? I have an 82 and a 91 that I would like to get the stacks for. Also does the 125 come with a stack? If not is there a stack that works for that?

[link=http://www.horizonhobby.com/Search/Default.aspx?SearchTerm=velocity+stack&CatId=]Velocity Stack[/link] Here's a link to the Horizon page that has the stack rclement. It's the top left one with part # SAI50GK93.

Hi Rob. I think the GK versions come with the stack and it is an optional accessory for all others. The smaller Saitos all use one stack, and large ones the other, probably both of your engines taking the smaller one. The part number for yours should be SAI50GK93. You'll still have to find an o-ring and I have a couple of spares which I bought at Tacoma Screw Products.
Ernie

Thanks Ernie and Tim. I just looked it up and it's out of stock for now. Due in soon though. Thanks again. Are we flying next week Ernie? [8D] [8D]

rclement, I just compared the part lists for both versions of the 1.25 and it looks like a velocity stack is not available for either engine. The carb looks like a new design just for the 1.25. I'm not sure on this info, it just looks this way.

The Saito 100 and 125 Golden Knights do not come with a velocity stack.

I have a couple 100's and the inside of the velocity stack which bolts right on, is almost the same size as the throttle hole in the barrel. They seem to run "OK".

I do not have a 125 but the screw spacing for the carb is the same because the 125 uses the 100 back plate.

Which velocity stack is for the 100? Part numbers appreciated. You know, you'd think that horizon would put the application for the part in their webpage....

thanks!

There's only one velocity these guys are talking about -- SAI50GK93.

You notice it has a Saito 50 part number. It is used by Saito from the factory on Golden Knights 50 through 91. But it will bolt right up to the 100 and 125 engines though it is on the small size in the venturi hole for the 100 annd 125.

The 100 and 125 golden knights do not come with a venturi.

Question: is the stack a tuned length, or just a length that looks good? The larger engines might need a little more length to contain the spitback. If it weren't for the horn on the end of the stack I would be tempted to clamp a piece of tubing onto the stack to make it a little longer and see how the test goes.

Ernie

Ernie:

"Velocity" stack is a misnomer; it implies a tuned length. What we have are more correctly just "Intake" stacks.

Nominal length is two to two and one half times the inside diameter. The longer it is the more efective it is in containing the back spray.

Bill.

Hi Ernie, Since the end is flared it might work to try a piece of copper tubing with a "flared end." I can't remember if I have a flaring tool or not.