spi cly ports

getback Mon Dec 23, 2013 8:06 pm

Cox .049 Sub Induction Cylinder & Piston (SPI)

Cox .049 Sub Induction Cylinder & Piston (SPI)
I have both the cylinders on different engines and seems to me or its just me but I have trouble getting them to run , says it will fit baby bee s but the old cylinder's had open ports for the exhaust . Is it being closed off more cause a back pressure making the engine want to flood? why can you not run a tee dee piston/cly on a baby bee? just asking . Huh...

G.O. Stang Mon Dec 23, 2013 8:21 pm

I don't think the newer style exhaust ports change much. I think there is a small performance loss with that type since the tee dee cylinder sold at Cox Intl. comes with it milled out. But you theoretically should be able to install any cylinder from an 049/051 on any crankcase and it run. Unless you've got a a muffler on the spi cylinders. That doesn't work and will hurt performance from my understanding.

**RknRusty** Mon Dec 23, 2013 8:42 pm

Maybe you have a new type SPI piston installed in an old type SPI cylinder. That combo will run badly if at all. The method of creating SPI changed when the slit exhaust cylinders came out.

In the old open exhaust cylinders, an engine with SPI had a cylinder with exhaust ports ground low enough that the piston skirt would rise above the base of the port, opening the SPI gap at TDC. All pistons were the same, the cylinder exhausts were ground for SPI or non-SPI.

After the slit exhaust cylinders came out, the exhaust ports were all ground to the same height. An SPI engine with that type of cylinder had to have a piston with a short skirt. You can compare a regular piston with a short one and easily see the different skirt height. In this case, all cylinders(except special cases) were the same and the egnine had either an SPI piston or a non-SPI piston.

If you put a short new style SPI piston into an old style SPI cylinder, there will be WAY too much SPI to run well.

A Tee Dee P/C will run great on a Babe Bee. They are all interchangeable. Some have higher performance, some don't.

Rusty

getback Mon Dec 23, 2013 9:00 pm

RknRusty wrote:Maybe you have a new type SPI piston installed in an old type SPI cylinder. That combo will run badly if at all. The method of creating SPI changed when the slit exhaust cylinders came out.

In the old open exhaust cylinders, an engine with SPI had a cylinder with exhaust ports ground low enough that the piston skirt would rise above the base of the port, opening the SPI gap at TDC. All pistons were the same, the cylinder exhausts were ground for SPI or non-SPI.

After the slit exhaust cylinders came out, the exhaust ports were all ground to the same height. An SPI engine with that type of cylinder had to have a piston with a short skirt. You can compare a regular piston with a short one and easily see the different skirt height. In this case, all cylinders(except special cases) were the same and the egnine had either an SPI piston or a non-SPI piston.
Ok I got most of that understand the theory I always try and keep piston/cyl sets together .. I put a new SPI kit on an baby bee and a golden bee and have a super bee with that same cly kit on it and can,t get them to run? can I relplace the kit with tee dee piston/cyl kits?? THANKS ERIC
If you put a short new style SPI piston into an old style SPI cylinder, there will be WAY too much SPI to run well.

A Tee Dee P/C will run great on a Babe Bee. They are all interchangeable. Some have higher performance, some don't.

Rusty

getback Mon Dec 23, 2013 9:04 pm

getback wrote:
RknRusty wrote:Maybe you have a new type SPI piston installed in an old type SPI cylinder. That combo will run badly if at all. The method of creating SPI changed when the slit exhaust cylinders came out.

In the old open exhaust cylinders, an engine with SPI had a cylinder with exhaust ports ground low enough that the piston skirt would rise above the base of the port, opening the SPI gap at TDC. All pistons were the same, the cylinder exhausts were ground for SPI or non-SPI.

After the slit exhaust cylinders came out, the exhaust ports were all ground to the same height. An SPI engine with that type of cylinder had to have a piston with a short skirt. You can compare a regular piston with a short one and easily see the different skirt height. In this case, all cylinders(except special cases) were the same and the egnine had either an SPI piston or a non-SPI piston.
Ok I got most of that understand the theory I always try and keep piston/cyl sets together .. I put a new SPI kit on an baby bee and a golden bee and have a super bee with that same cly kit on it and can,t get them to run? can I relplace the kit with tee dee piston/cyl kits?? THANKS ERIC
If you put a short new style SPI piston into an old style SPI cylinder, there will be WAY too much SPI to run well.

A Tee Dee P/C will run great on a Babe Bee. They are all interchangeable. Some have higher performance, some don't.

Rusty

USE hi COMMPRESSION GLOWS??

roddie Mon Dec 23, 2013 9:21 pm

I was also gonna ask that question... I wanted a new cylinder/piston for my speed contest entry.. and opted for the repro TeeDee set from Bernie. I do not have any high compression glow-heads though.. I've been wondering if it's that important on the reed-valve motor.. and while running a 4.75 x 4 prop.?

**RknRusty** Mon Dec 23, 2013 9:33 pm

getback wrote:
Ok I got most of that understand the theory I always try and keep piston/cyl sets together .. I put a new SPI kit on an baby bee and a golden bee and have a super bee with that same cly kit on it and can,t get them to run? can I relplace the kit with tee dee piston/cyl kits?? THANKS ERIC

If they won't run, it isn't the P/C that's causing the problem. Something else is wrong.

getback wrote: USE hi COMMPRESSION GLOWS??

You can, it will run well with regular or high compression. I use these, with between 3 and 5 head gaskets:
http://coxengines.ca/cox-.049-glow-plug-adapter-insert-style.html
Try regular and high compression and decide which runs best. But you have to figure out why it won't run first.

Just like souping up any type of engine, if you add performance to the business end, you have to be able to supply it with a higher fuel flow to get the full benefit, or it'll still be ordinary. That means boring the venturi and air inlets. .084" is about right. Some of those engines still have a smaller opening behind the reed, so you may still not have Black Widow performance, but still an improvement.

Rusty

Cox International Mon Dec 23, 2013 9:38 pm

SPI cylinder/piston sets are more difficult to start initially and it is recommended that one use a starter spring to facilitate this.

Any of our various sets can be used on Cox engines and the, open port, TD set (which is also SPI) will produce RPM results that are aprx. 200 RPM higher than the slit exhaust version with SPI.

Please keep in mind that a 5-10% difference in RPM between like sets is normal so that a "good" slit exhaust set may well perform better than a TD set.

HC glow heads (especially our insert-style version) should improve performance by aprx 500 RPM. But, here again, many variables affect performance and SPI performs best at high RPM's, i.e. smaller prop sizes.

batjac Tue Dec 24, 2013 12:26 am

Bernie, which of these two inserts would be the better choice for a red KB backplate feeding a TeeDee P/C set, running a stock Cox 5x3 prop? I'm not particularly interested in cutting down/tweaking different props to optimize.

Med Hot: http://coxengines.ca/insert-for-.049-head-adapter-3-5-fins-medium-hot.html

Hot: http://coxengines.ca/insert-for-conversion-a-and-texaco-head-hot.html

The Sub-Optimal Mark

**RknRusty** Tue Dec 24, 2013 12:36 am

I'm not Bernie, but my answer would be the medium hot. It'll never have a problem with getting wet and putting the fire out in a Tee Dee running full scream. Though the picture looks the same on the two, I think the hot plug actually has a smaller more fragile element. Hot plugs are for throttled engines that you want to idle, or run slow like the Texaco and stay lit with the reduced flow of methanol.

Cox International Tue Dec 24, 2013 12:47 am

Would love to answer but Rusty provided the exact ( and we mean exact ) answer that we would have provided Smile

Thanks Rusty and you helping out makes our job so much easier lol!

getback Tue Dec 24, 2013 12:11 pm

THANKS for all the good info. I have a new BW no. 150 I may just unleash the beast Babe Bee

not a beast but close enough

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