Cylinder Performance Figures

I had an email conversation with Bernie at Cox International about this some time ago.  He sent me this from Larry Renger, an engineer at Cox along with a follow up by Timothy D. Chapman.  I bench tested both cylinder types on the same crankcase on the same day and found that they were right, the cylinder with two boost ports out performed the four boost port version by 500 to 800 rpm using a Cox gray 5-3 and 35% Sig fuel.

From Larry Renger -

"I don’t recall the alloy, but the pistons were hardened and I think the cylinders were not.  We found the two boost port version ran higher rpm than four.  The reason is that it introduces a swirl to the mix that enhances combustion.  Four ports are too symmetrical.  This trick was used in the Killer Bee, Tee Dee and Venom.  I picked up the hint from the “Two Stroke Tuner’s Handbook”, a long out of print 2-stroke bible.

Larry Renger"

From Timothy D. Chapman -

"Hi,

I think I have it. The reason for the 4-boost port Tee Dees not making as much power as the 2-boost port Tee Dees is probably because the transfer ports expel out the air/fuel mix so close to the exhaust ports, so some of the un-burnt fuel goes straight out the exhaust. The Surestart has only 2 boost ports, AND the main port and the boost port is fairly centered. They (the transfer ports) have about .8 and 1mm on each side of the transfer ports before you run into the exhaust ports on either side. The Tee Dee has 4 boost ports, as well as the main port and it is perfectly centered between the exhaust port, leaving a very small amount of metal (about .4- .5mm) between the upper part of the boost port(s) and the exhaust port.

In the Two-Stroke Tuner's Handbook this is on page 118 and 119 (go by the number at the bottom of the page, not the PDF page numbers) and it is referred to as "short circuiting".

I hope this helps you.

Timothy D, Chapman"

Now we're getting somewhere. Must even be some more stats out there.
Thank you!
Ice

1/2A Nut wrote:Exhaust orientation makes a difference as they in turn positions the
bypass ports in their best arrangement.

If the exhaust ports are fore and aft the bypass ports line up with
the flywheel this helps to push / fling more fuel up thru the bypass
ports / past the piston with more force / flow.

Facing the front of the engine the port on the right gets the lions
share of the assisted flywheel driven fuel flow. If you have a single
bypass port cylinder if able have it on the right side to take advantage
of this secondary function of the flywheel.

Some may have seen enhanced competition car engine cranks have a
swepted channel milled into the flywheel to help guide the fuel / air flow
with more directive authority. With a dremel tool we could grind a bit of
a flow channel to a stock Cox TD crank.

Brad that theory makes a lot of sense..yet it is the one on the top with its exhaust ports almost sideways that runs 23k static/28k unloading while all others including the ones with exhaust at front and aft max out at 21k static.

Sure Brad I have also read that cylinder orientation is a means of ramping up power. I am still wondering what may make that marked performance difference in my engines. Near 10% difference in rpm means more than 30% shaft power difference.
.

Just a question. If you want to orient the ports front to back to hopefully achieve higher flow what washer or spacer works to lock the cylinder when another 1/4 to 1/2 turn remains on thtreads?
. thanks
Ice

Cox Int'l and Ex Model Engines used to sell "Timing Shims" specifically for raising the cylinder when a muffler was used in an SPI engine. They were a set of three different thickness copper shims. I can't seem to find them currently.

I cant find the cylinder shims anymore either Oldenginerod. wish I could. I have several engines I need to shim.
Bob

Basswood wrote:I cant find the cylinder shims anymore either Oldenginerod. wish I could. I have several engines I need to shim.
Bob

I bought some a while back, not for shimming cylinders, but they were the only source of the correct size copper gaskets I could find to use as Gilbert 7 head gaskets.

Basswood wrote:I cant find the cylinder shims anymore either Oldenginerod. wish I could. I have several engines I need to shim.
Bob

Kustom Kraftsmanship use to make a timing kit years ago. Along with the kit was an instruction sheet on how to use the kit.
I have one kit left that I keep (pristine) so that I can duplicate that same kit (when I need to).

If you look in the attached photo of the original KK kit, it has a brass ring to help installation of the shims onto the cylinder head.
The KK kit had two shims that were .003" thick, one .004" thick, and one .005" thick and were made from copper.

I make my own head shims from copper sheets and a purchased punch sets (english and metric.)
I don't know if I posted how I make my own here or not?
If I haven't, I should.

The punches (the good ones) cost about $200 a set. but you can use those punches to do more than head shims.
I have use then to make shims for the crankshaft to crank housing shims (copper).
Better to use the copper shims on my Tee Dee engines than the "steel" ones, or you can use the phenolic shims as well.
And other projects where I make my own shims for engines/ electric motors.

sosam117

Kustom Kraftsmanship Kit


Kuston Kraftsmanship Instructions


Punch and die for making cylinder head shims.


Punched out copper cylinder head shim


Punched out shim on Cylinder head.

Hi Gents,
Some guys in previous posts wished to time there cylinders. I did a posting on how to make your own.

Here is the posting:

https://www.coxengineforum.com/t13946-shimming-cox-cylinder-for-transfer-and-exhaust-timing?highlight=shimming+cylinder+head

Like you, I wish someone would make the cylinder head kits like Kustom Kraftsmanship did years ago.
In the mean time I'll have to make my own.

sosam117

This is really good information. The original timing kits used copper. Is there a way to use maybe neoprene or another material? Where are the .003 .004 and .005 thickness copper and possibly neoprene available? This is to correct incorrect deck height do to running and crowning the piston.

However we were saying even on a new motor the port position and timing might have substantial performance increase?

Thanks
Ice

Iceberg wrote:This is really good information. The original timing kits used copper. Is there a way to use maybe neoprene or another material? Where are the .003 .004 and .005 thickness copper and possibly neoprene available? This is to correct incorrect deck height do to running and crowning the piston.

However we were saying even on a new motor the port position and timing might have substantial performance increase?

Thanks
Ice

If you can't get the copper or brass or even aluminum (my Enya .049 / .06 / .08 and .10 use aluminum cylinder head shims).
You can cut them from heavy paper (gasket material).
Cutting the inside hole for the cylinder clearance. Then screw the cylinder onto the crank housing and cut the excess material off around the outside of the cylinder. I have done that as well. The down side is if you take it apart, you'll have to remake them with new ones.

I make my cylinder head shims out of .002", .003", .005", .010", .015", .020", and .025" from flat sheet of copper or brass.
The brass sheets I get at my local hobby shop. You can also get the flat aluminum sheets there as well.
The copper sheets I purchased off the internet.

sosam117

gtp reed valve engine is rated to 30 000 rpm just two boost port its exaust manifold is part of its performance just sayin cars engine spec ventury jet is capable of 22.000 with prop 6x3 on them no manifold direct exaust no test wit headers for now wil tes more stuf experiment wit cox cars engines