Author Topic: 1.5 N/A exhaust size? (Read 6115 times)

watsongs · « **on:** April 27, 2005, 09:18:18 pm »

My cat converter has a large hole in the bottom, probably from sitting in tall wet grass for 3 years. I'd like to replace it with a straight piece of pipe - does anyone know the pipe diameter? Looks to be about 2", but I'm not sure, and I don't have the best way to jack up the car yet, so I only want to go under 1 time.

By the way, cherry bomb mufflers are kind of cheap; anyone ever put one in?

Thanks for the help

Greg

watsongs · « **Reply #1 on:** April 28, 2005, 09:56:18 am »

How about the size?

janb · « **Reply #2 on:** April 28, 2005, 12:20:30 pm »

Quote from: "watsongs"

How about the size?

for diesels... the bigger the better, tho I doubt if a 1.5l needs 4", 2-2.5 is likely optimum, since they do rev higher than the 1.6/1.9's

vwmike · « **Reply #3 on:** April 28, 2005, 02:14:45 pm »

Quote from: "janb"

Quote from: "watsongs"
How about the size?

for diesels... the bigger the better, tho I doubt if a 1.5l needs 4", 2-2.5 is likely optimum, since they do rev higher than the 1.6/1.9's

The bigger the better on turbo diesels. I don't think you're going to see much gain, possibly only torque loss on an NA diesel if you go much larger. 2" would probably be very generous.

racer_x · « **Reply #4 on:** April 29, 2005, 05:55:26 am »

The 1.5L diesels had either 1 1/2" or 1 5/8" exhaust. If you're replacing the whole system, go with 1 3/4" or maybe 1 7/8" on that engine. Anything bigger won't help power much, might hurt midrage torque and will just weigh more.

VWRacer · « **Reply #5 on:** April 29, 2005, 06:17:34 am »

No overlap on the cam means no scavenging effect from 'tuning' the exhaust. Therefore, no real downside to a bigger pipe. Two inch pipe is real cheap, but unless you plan to turbocharge the engine, going bigger than that won't help with only 50-60 hp on tap. If you do plan to boost it, then 2.5" would work great - and it's still cheap.

watsongs · « **Reply #6 on:** April 29, 2005, 08:06:23 am »

I'm just tring to replace the resonator for now -

greggearhead · « **Reply #7 on:** May 18, 2005, 12:23:41 pm »

Quote from: "VWRacer"

No overlap on the cam means no scavenging effect from 'tuning' the exhaust. Therefore, no real downside to a bigger pipe. Two inch pipe is real cheap, but unless you plan to turbocharge the engine, going bigger than that won't help with only 50-60 hp on tap. If you do plan to boost it, then 2.5" would work great - and it's still cheap.

Exhaust tuning doesn't come from overlap scavenging, it comes from the pulses that happen when the exhaust valve opens and shuts, so a diesel can benefit from that just like a gas engine. This is really only to do with the header or manifold and downpipe design, though.

The exhaust tubing diameter (after the header/downpipe) aren't dictated by scavenging, more from displacement and hp production potential. Oh, I have never seen/felt a loss in midrange or low-end response on a diesel from using a 2" exhaust. Fabricating a smaller mandrel bent one wouldn't be worth the cost over simply buying a Techtonics 2" setup off the shelf.