EXHAUST PIPE SIZE?

[jpriest26]

does anyone know what size the factory exhaust pipe would be. i have a couple holes in mine an plan to modify it myself but i dont know what size the pipe is. i need new pipe fot the thing. :?:

[IdealSociety]

ive had multiple different sizes on mine range from 1" OD to 1.5" ID

best thing you can do is honestly almost cut into it and measure the spots you need to repair since it may have been replaced before, that and so many of our exhausts have been redone at some point in our poor cars' lives who knows what factory was anymore :shock:

[FestYboy]

factory is metric equivalent of 1.5" ID with 1/16" wall thickness

[jpriest26]

ah ic thanks. i may wind up flaring it out a lil anyway when i redo it so about 2" for better flow and better sound. im cuttin the muffler off since its about shot anyway and "Y" the pipe just after the axel and put dual resonators on it and run it straight out the back. ill have to notch the bumper before i do it but it should look an sound pretty dam good. i already have one resonator tip on it now and with the muffler on it sounds ok but it should sound much deeper and throatier with two tips and no muffler. and it should breathe a lot better as well

[jpriest26]

im just glad that my state doesnt require exhaust gas inspections causemine wouldnt pass now as it is. i had to remove the cat and knock the ceramic out of it cause it was broke and annoying the hell out of me. so when i take the muffler off ill basically have a straight pipe on it

[oxbrain]

Going up to 2" exhaust on a stock engine will really hurt low end torque. It's bad enough on the 1.6L.

[TominMO]

Going up to 2" exhaust on a stock engine will really hurt low end torque. It's bad enough on the 1.6L.

Does anyone know what diameter the FMS performance exhaust is? 2" does seem like a lot for a 1.3 motor, so maybe it's 1.75?

[jpriest26]

yeah thanks i didnt think about that

[jpriest26]

i think i will go with 1.5 or 1.75 then since im goin to "Y" it out and put resonator tips on it for extra tone

[funky technician]

Going up to 2" exhaust on a stock engine will really hurt low end torque. It's bad enough on the 1.6L.

actually, thats a myth with fuel injected engines, it only applies to carbed engines, and has to do with the double loading effect backpressure creates, anyhow, hears a good link that explains it.

http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

just match the size of the down pipe and you'll be fine :wink:

[GenevaDirt]

^^not to argue...but I did match the size of the down pipe and my car really did change in the way it ran....I have since had things happen that have made the exhaust more restricted and it changed back to running like it used to...I will be putting it back to the way it was....ran much better. My car is a 91 fi

[oxbrain]

actually, thats a myth with fuel injected engines, it only applies to carbed engines, and has to do with the double loading effect backpressure creates, anyhow, hears a good link that explains it.

http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

just match the size of the down pipe and you'll be fine :wink:

No, backpressure is a false term. It also has absolutely nothing to do with burned valves. Carburetors don't use the exhaust to meter fuel, so I don't see why changing the exhaust could affect them in any way.

Changing the size of the exhaust pipe changes the exhaust velocity, and can ruin any scavenging effect of the exhaust manifold. Matching the downpipe is usually best, and the festiva downpipe is nowhere near 2".

[funky technician]

Carburetors don't use the exhaust to meter fuel, so I don't see why changing the exhaust could affect them in any way.

it explains that in the writeup, right hear actually, you have to read it all
"cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition."

[oxbrain]

I read that page, it's wrong.

How is the air being pushed back through the carb? Why is it that this effect isn't happening on race engines with tons of overlap?

Back pressure is just resistance, it isn't going to reverse the flow of air back through the cylinder. The effect of this resistance is that the piston has to work a bit harder to push the air out. Scavenging is using the venturi effect to create negative pressure behind the exhaust valve, making it easier for the piston to move the air. Going to too large of a size exhaust pipe reduces the velocity of the exhaust, reducing the scavenging. It's a very simple concept.

[funky technician]

ya, I understand your poind of exhaust scavange being based on the venturi effect of the slightly reduced tubing, but I was talking about the "torque loss" you mentioned, thats were the misconception is