Custom Exhaust Diameter

I have a Custom ITR and a Custom Jeep Cherokee in the planning stages right now. I want to put a dual exhaust on both with custom tips. I have the tubing for the tips/mufflers, but I need to know what diameter to use for the pipes the are going to be running back from the engine. TIA

It depends how thick they would be on the real car. depending on the scale, you would devide the actual thickness by the scale.
For example, say the real pipe was 10cms from one side to the other, and the scale was 1/24, you would devide 10 by 24 and you would get 0.41666, so the scale exhaust would be about 4.16mm .

Hope this helps, if you don't understand what I am saying, just speak out and I will try to help you.

I understand what you're saying Junno. Now all I need to know is what size the 1:1 exhaust would be. I'd say about 2" on the ITR and 2.5" on the Cherokee. If my calculations are correct, that's 5.08cm on the ITR and 6.35cm on the Cherokee. Divide the ITR by 25 and get .254, so I will need 2.54mm tubing. For the Cherokee, divide 6.35 by 24 and get about .264, so I need 2.64mm tubing for it. Not much difference, so I'll go with the closest one I can find, which is 3/32" (2.4mm) tubing. Is this correct, Jonno??

Stock piping on the ITR is about 2.5-2.75, the exhaust on my civic is about 2.25, I believe the cherokee is about 3, or maybe a tad more.

still yet, the closest I'll be able to get is the 3/32" tubing, which I already have (need more) since I'm also using that for roll cages.

Stock piping on the ITR is about 2.5-2.75, the exhaust on my civic is about 2.25

nope...
factory piping on most civics is lucky to break 2 inches...

aftermarket, yes, stock no.

the stock exh on a teg would not be any bigger than 2.25 inches, as most aftermarket systems are 2.25...
and that's upgraded from stock... sooo...

2.5 or 2.75 would be used on something with a turbo... and not stock that way, especially not from honda...

that's a bit nit picky, but if people want to be accurate... hey...

I was actually gonna try to make a turbo or find one, so that's even better. either way, I picked up 4 more pieces of 3/32" from the hobby shop. Thanks for the input...now all I gotta do is figure out how to fit the pipe into the tips... Do you thing putting bondo over the end to fill it in and then carefully drilling it out would work?? The inside of the tip is 1/4" aluminum tubing I think. Not sure.