Opening the 4 slit Cox Exhaust, Why/Why Not
03-25-2005, 09:44 AM
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Opening the 4 slit Cox Exhaust, Why/Why Not
Thought it would be easier to have a specific thread on this question asked by William Robinson ot Tim on the .049 thread. Looking for answers of how, other than a dremel cutting disk, and why not that Tim allueded to.
Clean
Clean
03-25-2005, 09:58 AM
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RE: Opening the 4 slit Cox Exhaust, Why/Why Not
Clean,
I just said no because for me it's easier to trim the piston skirt to bring SPI into these engines. Look at the Cox Killer Bee engines. It has the exhaust bridge. Granted the bottom opening is wider. Like I said in the other thread it's just easier for me to cut the piston plus I don't have to mess with cleaning up the inside of the cylinder plus I don't think you will see enough of a rpm difference in just removing the bridge to make it worth the trouble.
LAter,
Tim
I just said no because for me it's easier to trim the piston skirt to bring SPI into these engines. Look at the Cox Killer Bee engines. It has the exhaust bridge. Granted the bottom opening is wider. Like I said in the other thread it's just easier for me to cut the piston plus I don't have to mess with cleaning up the inside of the cylinder plus I don't think you will see enough of a rpm difference in just removing the bridge to make it worth the trouble.
LAter,
Tim
03-25-2005, 10:03 AM
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RE: Opening the 4 slit Cox Exhaust, Why/Why Not
Skirt trimming, now there is an interesting subject
The shorter the better. 
Tim, would you care to enlighten the ignorant among us what exactly you do and what effect it has.
TIA
Michael
The shorter the better. Tim, would you care to enlighten the ignorant among us what exactly you do and what effect it has.
TIA
Michael
03-25-2005, 12:55 PM
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RE: Opening the 4 slit Cox Exhaust, Why/Why Not
Michael,
I'm with you on the short skirts But anyways I shorten my pistons in my lathe. To be honest I don't know how much I trim. I just trim and test fit till I get about .012" to .015" of sub piston induction(the opening under the piston). I really like the bypass porting on these cylinders. I think DB does too. So from a performance standpoint adding SPI to them really makes them rock. The added bonus is it also lightens the piston too. But all of this piston/cylinder cutting aside if you want fast easy power get your hands on a Galbreath head and Nelson plug set up for www.kittingittogether.com and listen to the engine SING!!!
Later,
Tim
I'm with you on the short skirts
But anyways I shorten my pistons in my lathe. To be honest I don't know how much I trim. I just trim and test fit till I get about .012" to .015" of sub piston induction(the opening under the piston). I really like the bypass porting on these cylinders. I think DB does too. So from a performance standpoint adding SPI to them really makes them rock. The added bonus is it also lightens the piston too. But all of this piston/cylinder cutting aside if you want fast easy power get your hands on a Galbreath head and Nelson plug set up for www.kittingittogether.com and listen to the engine SING!!!Later,
Tim
03-25-2005, 02:12 PM
#6
RE: Opening the 4 slit Cox Exhaust, Why/Why Not
I bring the piston up to TDC and score a line where the bottom of the port is, then move that mark up .010. KUSTOM KRAFTSMANSHIP recommended .010 SPI. The TDs sometimes came with too much SPI, and he sold liner shims to correct that. While the piston is chucked up in the lathe, might as well thin the walls too. To remove the port divider [which I've never done] my guess would be to grind it out with a wheel. I would be interested to find out what this is worth after the other mods have been done?
STD or HD plug? It depends on nitro % and your personal experience against either a stop watch or a tach. For most COX applications the standard is OK.
STD or HD plug? It depends on nitro % and your personal experience against either a stop watch or a tach. For most COX applications the standard is OK.
