Coffman exhaust info needed and Westcoast head

[curly]

Can anyone share with me or direct me to info on what Coffman pipe this is? Looking to know what model it is and what engine setup it would work best with. Only markings on it are “Coffman Exhaust System” and “550”.
Just bought a really clean 92 550SX and it had this setup and a Westcoast EP5500 head.

 

[TheBuzzard]

That's the coffman classic pipe. You rarely see it with the coffman manifold but cool that it's the complete coffman setup. It's the last ones they made since it's the Grey powder coated version. The others were polished chamber with orange head pipe. Supposedly according to coffman, that pipe created more HP than their half pipe. If you want all the info straight from the horses mouth, call coffmans an talk to Pam. 707 462 1887 is the shop number if I remember right off the top of my head. You can Google it. It's in Ukiah CA.
My bad it's 7881

 

[curly]

Thank you for the info. I'll give them a call this afternoon.

 

[Big Kahuna]

Was going to tag Buzzard but he already on it.

 

[kevbo]

Great find! Its old so a complete disassembly/inspection/reseal should be done before you put back into service. They are very easy to burn up unless everything is just right.

 

[curly]

Hello buzzard. A couple months back you directed me to Coffman regarding this Coffman 550 pipe I have. They supplied me with their instructions for it, thank you for directing me to them.

I’m curious on your thoughts about this detail in their instructions regarding modifying.

I just put together a 550SX motor, ported with a milled head and lightened flywheel, all machine work done by Harry Klemm. Also still using stock pump with bored nozzle with Solas 13/18 impeller. My goal for the motor/ski is to have nice bottom end power for just having fun free riding and hitting buoys. Top end is secondary to me.

What are your thoughts/experiences milling the exhaust pipe .1250 like their instructions say? I have NOT modified it or the cone yet, they are still as Coffman manufactured them.

 

[kevbo]

Back in 1992, mod class 550s were typically ported and propped for much higher rpm so shortening the pipe was necessary. Leave the pipe long for now and learn how to tune the carb. Then learn how to tune the impeller. I do not recommend turning up the RPM on a 550 anymore since they become so unreliable. Installing a 701 or 750 can equal the performance with perfect reliability.

 

[TheBuzzard]

Taking material off both ends of the head pipe shortens the system for less chamber volume. More chamber volume means more torque which is what it sounds like you want. Less makes the motor rev higher which gives you more hp in rpm but at the sacrifice of torque and bottom end punch. I don't remember the destructions saying that on the 550 pipe but I know that's in the 650 pipe. Their latest version called the rocket pipe, already had the ends cut and an additional water outlet for less pressure dumping water into the chamber. More hp

 

[fastgtfairlane]

With the sx pump, definitely do not cut the pipe. The mixed flow 550 pump puts a pretty hard load on the engine at lower rpms. That's why kawasaki developed the "breadbox" exhaust for that pump. The aftermarket half pipes are a longer tuned length designed for that pump. The full pipes like yours will make more top end power due to a shorter tuned length. Instead of cutting the pipe, there are other ways to fine tune your engine and pipe for max power with water routing. I'd recommend a running a 2nd cooling line and running it directly to the pipe separately. That will make the pipe run cooler which will essentially change the tuned length of the pipe. Cooler pipe will lengthen the tuned length and a hotter pipe will shorten the length and increase your rpms. That pipe will work well with the correct pump tuning and water tuning..the Solas impeller will work ok but a skat will give better acceleration. Skat impellers have a thinner blade and are quite a bit lighter than the Solas. Straight pitch impellers generally work best with the 550 pumps. A 15 to 16 pitch skat would be the ideal choice depending on your weight as well as the nozzle bore diameter. If you can find an ocean pro nozzle setup that would be the way to go. Your ski looks pretty clean! Set up properly the little 550 Reed engine can be a hard running and reliable engine. I'd recommend a 44sbn or dual 38 sbns. I ran dual 38 sbns on my 550 Reed engine. And now I believe zeeltronics is making an adjustable cdi so you can change timing curve and Rev limit. A ported 550 engine with a good pipe and porting can make 75+ hp without too much effort and still run pump gas. That's more than a stock 701 and considerably lighter.

 

[curly]

Thanks for the info, I'll leave it at it's length and see how it goes.