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freakboy 12-19-2009 10:47 AM

Exhaust building 101....
Since there are so many people moding there engines with strait pipes but then someone brings up back pressure i am going to make a quick how to make a exhaust.. i got most of this information from

1.Make the pipe longer then you will think you need it then paint the pipe with normal paint.. Run the engine for a while untill the paint starts burning off. Then cut the pipe 1 inch away from were the paint is still on. This ensures your pipe isnt longer then it should be thus slowing the gasses down when they are leaving the pipe.

2. Make the inside of the pipe the same size as the exhaust port or a little larger. You dont want it smaller that will restrict flow and hurt performance..

3. The more bends in a pipe the slower the gasses will come out.... that should be a obvious one... in the bend one side will be crimped in a little(if you bent a pipe you know what im talking about) Which may hurt the exhaust gasses leaving.

Im probaly forgetting something so post below if you want.


r_chez_08 12-28-2009 03:56 PM

for no. 1, is that one inch of the burnt paint cut off, or 1 inch of ok paint.

freakboy 12-28-2009 04:06 PM

ok when the paint is burnt off chop it one inch into the burnt from the edge of the unburnt.

anderkart 12-28-2009 09:33 PM

Exhaust building 202 :

r_chez_08 12-29-2009 05:50 AM


Originally Posted by freakboy (Post 77368)
ok when the paint is burnt off chop it one inch into the burnt from the edge of the unburnt.

kk. thanks

1992suburban 12-29-2009 08:39 AM

ander thats a great chart.. if you have a cam card

anderkart 12-29-2009 10:10 AM

Yep good point suburban, for karts with stock cams I think freakboys strait pipe info is fine.

The down-loadable program I linked was only intended for those that have instaled a race cam and want to build their own 3-stage header to match their cams profile information.

1992suburban 12-29-2009 02:07 PM

i toyed around with mine, and the cam that I want looks like my lil .880 3 stage would be pretty close

Kaptain Krunch 12-29-2009 04:03 PM


but then someone brings up back pressure
Technically no engines need or want back pressure.

freakboy 12-29-2009 04:36 PM

exactly it reduces flow...

ericspants 05-12-2010 04:55 AM

cant Zero back pressure damage pistons/rings?

Russ2251 05-12-2010 07:28 AM

Why would it?
I once saw a post where a guy claimed that lack of back pressure would crack the block!!!
Where in the **** does this stuff come from???

psycho_builder 05-12-2010 01:28 PM

i dont kno about back pressure but i do kno that you dont wan cold air gettin to the hot valve when you shut it down, thats where freakboy's technique comes into play

devino246 05-12-2010 06:24 PM

Heres something to add. It seems kinda obvious but if the pipe is long or heavy, be sure to brace it.

Russ2251 05-12-2010 06:36 PM


but i do kno that you dont wan cold air gettin to the hot valve when you shut it down,
Tell me why and explain how you know this to be true.

devino246 05-12-2010 06:40 PM

And psycho, is it really that hard to add the extra letter to the end of your words?

robbie 05-14-2010 05:10 PM

I've heard that old warning a million times about cold air hitting the exhaust valve when you shut the engine down. Never gave it much thought, but here's something I found with a simple google search.

Russ2251 05-14-2010 06:26 PM

Link refers to high performance multi-cylinder engines and doesn't prove or disprove anything.
I've run engines with no exhaust whatsoever (just pouring out of the block) for many summers with no ill effect to engine in any way.
By the time any damage is realized...engine will be worn out anyway or will have been changed to something newer or more powerful. I have a garage full of low hour engines simply because I wanted something else. Virtually all of them have been badly abused and still run like factory new.
Don't go by what you heard on any subject. Use your own experiences. Don't ask your friends...they're dumber than you are.

snowman69 05-14-2010 09:22 PM

So if "no engine technically need back pressure" go and take the complete exhaust off a 2 stroke engine please. When you do that tell me how it runs.
2 stroke engines NEED back pressure to run properly.

robbie 05-14-2010 10:49 PM

I just want to point out that I wasn't trying to prove or disprove the theory about burning the exhaust valves. I thought the page I found was an interesting discussion, and I pretty much drew the same conclusion that you have, Russ.

I think it's also worth pointing out that the original post seems to be aimed at four stroke engines. 2 strokes don't behave the same way when it comes to exhaust pressure. But I'm pretty sure that's not what he was talking about.

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