Engine exhaust port larger than pipe connection

[RcAlchemy]

I have done a quick search and haven't been able to find the answerer I am looking for. Currently I have a stock Thor pipe from KM on my buggy and looking to change it out. My questions is...why is the Rovan (DDM copy) pipe flange connection a smaller bore than the exhaust port on my 30.5cc engine? Can you grind out the bore on the pipe to match the engine exhaust port? Hope I asked the question correctly. Thanks!

 

[Rep732]

Yea you can "port" match the exhaust flange as long as you have enough material and just be cautious how much of the weld you take off if the pipe flange is welded on the inside

 

[spents]

yes mate, as long as theres enough material ya can grind away to match the header to the exhaust port ,
easiest way is to just nut and bolt an exhaust gasket to the header and grind to the size of that,

 

[Rep732]

Take a dark marker and trace the inside of the gasket so you can see how much to grind as well

 

[RcAlchemy]

yes mate, as long as theres enough material ya can grind away to match the header to the exhaust port ,
easiest way is to just nut and bolt an exhaust gasket to the header and grind to the size of that,

but why is it smaller and why not just match each other? is there some kind of percentage of exit exhaust into a pipe for horsepower?

 

[Rep732]

Its just a low quality pipe as long as it looks the part that's all they care about. Any higher end pipe will most likely be port matched. My olimat and vrc pipes are the same size as the exhaust port

 

[spents]

but why is it smaller and why not just match each other? is there some kind of percentage of exit exhaust into a pipe for horsepower?

probably a mistake in measuring at the factory where the pipe was made,
seen a few of the chinese copies with small holes at the header

 

[Rep732]

May possibly crack since the metal is of lower quality also

 

[RcAlchemy]

May possibly crack since the metal is of lower quality also

i was thinking of that

Its just a low quality pipe as long as it looks the part that's all they care about. Any higher end pipe will most likely be port matched. My olimat and vrc pipes are the same size as the exhaust port

thanks for the reply

Its just a low quality pipe as long as it looks the part that's all they care about. Any higher end pipe will most likely be port matched. My olimat and vrc pipes are the same size as the exhaust port

true

 

[RcJunkie13]

I had the same problem, best advice was to get a real pipe, but if you can just get a Dremel and port to a regular gasket, if pipe diameter does not allow to go big enough use the dermel and taper it (make a funnel shape). Can you post what pipe you have?

 

[RcAlchemy]

I had the same problem, best advice was to get a real pipe, but if you can just get a Dremel and port to a regular gasket, if pipe diameter does not allow to go big enough use the dermel and taper it (make a funnel shape). Can you post what pipe you have?

its just a stock pipe. the Thor pipe from KM

https://www.kingmotorrc.com/product-km66056

 

[RcJunkie13]

got a pic of the port?

 

[RcAlchemy]

got a pic of the port?

no, i would need to remove the pipe. sorry

 

[RcJunkie13]

Look at this:
https://www.largescaleforums.com/threads/port-size.26366/

 

[RcAlchemy]

Look at this:
https://www.largescaleforums.com/threads/port-size.26366/

how did it work out for you? deff looks better rounded out.

 

[Polar_Bus]

Port matching weather it be on the intake or exhaust side is always advantageous. Your engine is simply an air pump. Obstructions cause flow problems. I have the DDM Dom pipe and i had to do a small amount if port work on the lower edge of my flange. I also had to machine the face of my flange as it was warped from welding and leaked oil. I also port matched my carb velocity stack and the carb manifold . Its the small details that make positive gains. The key to sucess is work in small light steps with a grinder. If you get too aggresive with a grinder you quickly end up with a junk part.

 

[RcJunkie13]

how did it work out for you? deff looks better rounded out.

I didnt really run it, it idled alright I guess, leaked a tad bit

 

[RcJunkie13]

As stated earlier, I highy suggest you get a real pipe, olimat, bart, vrc ect. It will give you soooo much better preformance, I reccomend a side pipe as it is well protected and as a bonus it looks sick. Check out the bartalone torpedo pipe

 

[Seandonato73]

but why is it smaller and why not just match each other? is there some kind of percentage of exit exhaust into a pipe for horsepower?

There actually is, but I don't want to get into it, and it refers more to the port area size, and pipe size, the outlet flange should be a seamless transition from port to exhaust.

 

[RcAlchemy]

There actually is, but I don't want to get into it, and it refers more to the port area size, and pipe size, the outlet flange should be a seamless transition from port to exhaust.

That’s what I understand is that it should be matching.