gx390 exhaust and intake

[ramairgtz]

Got the motor in my kart but when I bounce it the rear rack comes down and hits the exhaust and intake cover. Can I make a different pipe for this? How picky are they about back pressure? Also can I run the intake with just the filter and not the big black box? Here's a pic

[r97]

fix problem, custom header, k&n style air filter

[Russ2251]

How picky are they about back pressure?

Not picky at all. Back pressure is not a requirement and is not stated anywhere that it should be present.
By the time any damage is realized, engine will be worn out anyway.
However, too much back pressure will result in power loss.

[ramairgtz]

I've seen some headers for these that are just like a J bend about 10 inches long so I could easily make that only problem is I don't want it to be super loud. Do they make a k&n that fits the stock carb?

[KieranM]

try agk, they sell a uni filter for a 390 also a k&n style one.

http://www.affordablegokarts.com/mm5...gory_Code=AFC2

You could make up a muffler (see older threads, type in muffler in search) that attaches to the pipe. They would cut down on the noise.

But agk also sell a straight pipe with a muffler on the end and there very quite on a gx160 anyway.

[r97]

make a simple exhaust pipe then put your current muffler, or a different one (i.e lawn mower muffler, or home made one.) at the end of the pipe so your basically just re-locating the muffler.

[ramairgtz]

I noticed most of the aftermarket pipes are around 20 inches long is there any certain length it needs to be? If I can find some 1" id pipe in j and u bends I'll just make my own pipe.

[r97]

you could make the classic 90 degree sq tubing pipe, some one here prob has a pic

[KieranM]

a 90 degree bend on square tubing is going to be hard for the exhaust gases to escape

[Russ2251]

a 90 degree bend on square tubing is going to be hard for the exhaust gases to escape

Any loss of power will be so small ... it cannot be measured.

[r97]

if you got the cash get a 18 wheeler exuahst pipe (like the ones that come up behind the cab) and a peice of flexible pipe then rigg it up onto the cargo rack,lol

[ramairgtz]

I picked up 3 1"id 14" long 90 degree bends and I should be able to cut and weld those and make a pretty nice pipe. I've built exhaust for several cars header to tail pipe with misc 90 and 180 bend tubing and it's pretty easy.

[r97]

cool, post pics when your done!

[ramairgtz]

Here's what I have to work with

[r97]

those galvanized? cant quit tell from pic if so i suggest not welding them

[Russ2251]

Can be welded with proper ventilation.

[r97]

yea i know i'm just trying to avoid getting people killed!

[ramairgtz]

These don't look galvanized they have a kinda machined look to them but I'm sure they are.

[KieranM]

the whole welding galve thing is slightly overworked, wont kill you unless you plan to get high off it, just be sensible about it, anyways it just looks chrome plated, grind/sand it off if its galve

[r97]

sry if its a false-alarm but i cant tell using my computer, also i know its ok to do it, i know you can do it, and i know you prob wont die but whats the advantage here? grinding it off does work to grind off allllllll around where your gonna weld though