Re: Do Killer Bee back Plates sold onlne give better perf?

aspeed Thu Aug 20, 2020 4:17 pm

You can approximate it. TI R2. will get you the area of the .082" venturi. For the KB backplate, you can take the bigger diameter area, and then subtract the width x length of the spray bar. It will have to be guestimated for the length because of the radius' at the ends. I just filed mine more oval with a 1/8" round file for a few strokes. There is not a lot of material there anyway. I only have one white nylon backplate of that type. All the rest are tank mount or TD. I guess the Medallians can be calculated that way too.

davidll1984 Thu Aug 20, 2020 6:04 pm

my thinking is kb back plate is not giving power of black widow it seat for the reed valve is larger look inside reed valve seat diferance is spray bar not inside ventury is best look at the venom back plate Huh...

GallopingGhostler Fri Aug 21, 2020 7:34 am

SkyStreak wrote:They say not to go over .082 ventury on a tanked engine. How do you calculate the intake size on a horseshoe bake plate. The spray bar divides the intake.

Good question. I've noticed on venturis such as on some K&B, the venturi hole is smaller for a side bleed than for a spray bar centered in the venturi hole. Appears to be related to the amount of exposed cross sectional area at bleed hole / spray bar.

Somewhere there is a guide, how to on the largest permissible diameter on the horseshoe ventuir before a pressurized fuel system is required.

SkyStreak Fri Aug 21, 2020 9:54 pm

GallopingGhostler wrote:
SkyStreak wrote:They say not to go over .082 ventury on a tanked engine. How do you calculate the intake size on a horseshoe bake plate. The spray bar divides the intake.

Somewhere there is a guide, how to on the largest permissible diameter on the horseshoe ventuir before a pressurized fuel system is required.

I'd like to see that guide if anybody has.a link.

SkyStreak Fri Aug 28, 2020 12:58 pm

Was able to get out and run my subject engine. Two years ago this engine ran 16 - 17,000 w/ 15%, 5.5x4 prop and what looks like a standard beige back plate. Now I only got 14.700.

Looks like I need to do some maintenance and try again.

SkyStreak Sun Aug 30, 2020 3:14 pm

Does anyone have the width measurement for the Cox oval shaped Mylar reed?

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