Ihave a tt 46 pro with a macs pretuned system on iy and ive only cut about 1/2 an inch off. when i get it to full rpm and run it for about 45 - 60 sec. and shut it off the thing smokes quite a bit, That normal ????? mind you im running a 10 x 8 master airscrew one her and im running it on a test stand. Any suggestions PLEASE HELP ME!!!!!!!!!!!!

Need more info. Like how you adjusted the pipe length etc. What were the rpms with just the header installed and how many rpms did the pipe add after it was installed. Is your engine fully broke in? A 10/8 prop is a lot of load on a 46 engine. You might try something with less pitch.

try an 8x8 or 9x6 to get the revs up. A piped engine needs to rev. Bog it = kill it.

Correction: a piped engine needs to rev in the rpm band the pipe is set for...

But yes, a 10x8 MA is quite a big prop.
You say you got a "pretuned" system... that leads me to think it is tuned for more rpm than you are getting on the 10x8. What are you getting on the 10x8 by the way?
A 9x7 - 9x8 - 10x6 prop should get you in the ballpark.

Watch out with the needle settings... don't go for the absolute peak like you can on a muffler. If the pipe is set correctly it will unload a lot more in the air than it does on a muffler... a very lean needle setting at this point will kill your engine.

If your engine is smoking after you shut it down it is WAY too hot... you may have already smoked the engine ... they really don't like getting that hot!

Is the engine coming on the pipe? It may never reach the optimum rpm's and fighting too much load. Too much load, too much heat.
Is the engine broken in? How much fuel have you run through it?

I agree with Rudeboy, it is possible that you have toasted the engine but the only thing in your favor is that you were not turning 25K where the engine can be destroyed in the blink of an eye. Keep your fingers crossed.

I have run 10X8, 10X9, 10X10, 11X7, and 11X8 on my YS45 but kept the pipe long. I tuned it for 11,500RPM static and never had any troubles with over heating. Tuning is the key. With proper tuning, fuel mixture and prop blast, you should not have any troubles with the 10X8 MA prop.

Kaos1

Jeff,

A tuned pipe cut too short, will require, after advancing the throttle to WOT, that you close the main needle, to get the RPM high enough, for the engine to get on-the-pipe. Then, immediately you will have to open the needle back to prevent a lean-run.

It would seem your shortened pipe is close to this point.

Pull the pipe back, even beyond the 1/2" that you cut off.
The prop you are using is larger than the 10x6 size intended for this engine/pipe combo.

You did not say what fuel you are using.
It must contain some Castor oil and 5-10% nitro. The pipe supercharges the engine and will make 15%, or more nitro, too much.


Too short a pipe will kill your engine, as will too much nitro with a pipe, on a standard (non-racing) engine.

The Mac 40 size pre-tuned system (if I recall correctly) comes tuned for performance with a 10x6 at about 15,500 rpm. The 10x8 is probably not letting the beast turn up high enough resulting in 'short pipe' performance... where the engine will tend to act goofy where its difficult to set the needle. If you cut the header more, its only making that situation worse.

As noted above, use a smaller prop to start with, and lengthen the pipe back to where it was (or longer). Try a 10x6 first.

Also of note........ once you find the peak rpm....... always set your high end mixture 500-800 rpm down from that point. The engine will unload in the air, if can go lean if you do not provide for some extra fuel.

Thank you guys i tried the 10 x 6 prop and it works great now thanks a lot guys

glad we were all of help