Weird (to me) Cylinder/Piston Relationship

Kim Wed Apr 21, 2021 5:32 pm

OK...if this is something that has been covered in some thread I haven't seen, or is so common, nobody even thinks about it...I'll take my lumps and go to my corner. Very Happy

At "!/2A Day" Leo showed me this engine he'd acquired with some others.

It looks like a normal double-slitted cylinder (to me), but uses only the top slot for exhaust, and the bottom for a goodly portion of SPI. I don't think he's run it yet, so no performance reports, but we wanted to see what you guys thought about it.

I don't know the piston length, but will check it and maybe do a run to see what happens, depending on what you guys think.

Top Dead Center, with a bunch of SPI from the bottom slot:

Weird (to me) Cylinder/Piston Relationship 54_15

Bottom Dead Center, with only the top slot providing exhaust:

Weird (to me) Cylinder/Piston Relationship 5510

Mike1484 Wed Apr 21, 2021 6:20 pm

Hi Kim ,

Looks like a Killer Bee cylinder but it look like excessive sub piston induction to me . Could be a modified piston .

Mike1484

roddie Wed Apr 21, 2021 6:25 pm

Hi ya' Kim. Yea.. that lower port/slit looks about 50% larger than the upper. I looked at several of my slit-exhaust cylinders.. and both upper/lower slits look the same to me. Maybe someone ground them lower? Still.. that doesn't explain the exhaust only exiting the upper slots.. Huh...

I'm curious of the internal porting.. and whether there's single or dual bypass and possibly boost-ports?

**Admin** Wed Apr 21, 2021 6:58 pm

That's a Killer Bee cylinder. All real Killer Bees use a slit cylinder with the lower slit wider to allow for SPI. I'll have to go dig out a Killer Bee to see how much SPI it has.

Some years back, Bernie sold pistons with shortened skirts to lighten the piston and allow for SPI with a Sure Start cylinder. Using one of those shortened skirt pistons with a Killer Bee cylinder would give excessive SPI.

Kim Wed Apr 21, 2021 9:20 pm

Admin wrote:That's a Killer Bee cylinder. All real Killer Bees use a slit cylinder with the lower slit wider to allow for SPI. I'll have to go dig out a Killer Bee to see how much SPI it has.

Some years back, Bernie sold pistons with shortened skirts to lighten the piston and allow for SPI with a Sure Start cylinder. Using one of those shortened skirt pistons with a Killer Bee cylinder would give excessive SPI.

Well, OK...but wouldn't the bottom port still serve as exhaust at bottom center in that case?

1/2A Nut Thu Apr 22, 2021 12:48 am

Killer Bee cylinder but the sliver case is not, should be gold.

Compared to a 1996 KB:
SPI on your engine is indeed showing more gap.
KB SPI opens up exactly half of the port at TDC.

At BDC the piston does not go down far enough to
break the lower port opening.

Does it have a KB piston and crank?

Small Cox Logo

ledler Thu Apr 22, 2021 12:00 pm

1/2A Nut wrote:Killer Bee cylinder but the sliver case is not, should be gold.

Compared to a 1996 KB:
SPI on your engine is indeed showing more gap.
KB SPI opens up exactly half of the port at TDC.

At BDC the piston does not go down far enough to
break the lower port opening.

Does it have a KB piston and crank?

Don't know about the piston but has a regular crank. This is my engine, Kim was kind enough to post photos for me.

Bought a grab box of seven product or sure start engines and the KB was among them. All of the engines have excess SPI of from .020 to .024. I think the Admin answered that question as they may be the short pistons that were offered by Bernie.

Tried the KB cyl/pis on a Medallion and saw a great improvement. 10%N, 6-3 prop and low compression head around 17000. The same fuel and prop with high comp head on a TD yielded the same RPM.

Thanks everyone for your replies, you've answered my question about what I have.

roddie Thu Apr 22, 2021 6:43 pm

Hi ledler, Good to know of you and your Cox engine interests. Kim S. would certainly join me in telling you that CEF is a great community. Best of luck to you! These engines are a lot of fun.. even running them up on a test-stand. Small Cox Logo

ledler Sat Apr 24, 2021 12:55 pm

roddie wrote:Hi ledler, Good to know of you and your Cox engine interests. Kim S. would certainly join me in telling you that CEF is a great community. Best of luck to you! These engines are a lot of fun.. even running them up on a test-stand.

Sorry I didn't answer your questions about timing and ports. I'll try now. It has dual transfer ports and a boost port on each side. Looks like one boost port opens when the exhaust is about half open and the other boost opens just as the exhaust port is fully open.

balogh Sun Apr 25, 2021 6:53 am

That assimetrically timed single booster design gives a swirl to the fuel+air charge and is said to be as efficient as, or more efficient than the double boost design in old TeeDee cylinders.

ledler Tue Apr 27, 2021 10:15 am

balogh wrote:That assimetrically timed single booster design gives a swirl to the fuel+air charge and is said to be as efficient as, or more efficient than the double boost design in old TeeDee cylinders.

Thanks balogh, I learn somthing new on this site everyday. I wondered if that was by design or a production tolerance/error.

balogh Tue Apr 27, 2021 10:54 am

I think it was simple by recognition that by asymmetrically positioning the boosters relative to the by-pass ports a spinning motion can be added to the fuel charge that will improve the flushing of spent gases from the cylinder on the one hand, and help reach a more uniform mix of fuel and air on the other, hence accelerating the burning process. Let alone the slightly shortened production time for the cylinder that may have been the underlying primary object of changing from 2 to only 1 booster ports per side.

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Weird (to me) Cylinder/Piston Relationship

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