M30 exhaust size....

[Zacm829]

I'm running a high flow cat from a Dodge Charger (the lame 80's ones lol), no resonator to a Brullen straight through muffler. It's fucking loud.

I was running my stock 325e exhaust with no muffler before, and I felt an actual difference switching to the 1/2" larger tubing. Low end is just about the same, but top end pulls harder. And my top end was good before.

Do you have a sound clip on this?

[yert315]

I've got a 3" single exhaust, albeit with a 2 1/2" muffler (just to get it going for now). There's a guy in town with a 3" single from the headers back and it pulls strong (m30 e30). Of course, I have no frame of reference, but I don't see a problem running a 3" exhaust, especially if you plan on going FI.

[E30SPDFRK]

Do you have a sound clip on this?

Unfortunately no. My engine shit the bed the day after I got it on.


I have some of the e exhaust though, which actually sounded pretty good.

http://s182.photobucket.com/albums/x96/e30spdfrk/?action=view&current=DSCI0041.flv

http://s182.photobucket.com/albums/x96/e30spdfrk/?action=view&current=DSCI0119.flv

[Zacm829]

Interesting, What numbers did you put down on that dyno?

Unfortunately no. My engine shit the bed the day after I got it on.


I have some of the e exhaust though, which actually sounded pretty good.

http://s182.photobucket.com/albums/x96/e30spdfrk/?action=view&current=DSCI0041.flv

http://s182.photobucket.com/albums/x...t=DSCI0119.flv

[E30SPDFRK]

182hp 187tq

[BDK]

couple of questions all concerning N/A motors...
1) How is two exhaust manifolds going into a single pipe more effecient than true duals?

2) If the size of the exhaust manifolds are say 1 5/8" ID, why go out to 3", the restriction is at the exhaust port, if you can't increase that, does it really help to go out to bigger pipes???...
FWIW, Hartge Headers are like 1 5/8" OD maybe 1 7/8" OD so going any bigger than 2"/2-1/4" seems abit ridiculous to me....

If air flows like water,
then going smaller to bigger would actually slow the flow,
The same size or close to it would equal the flow coming out,
going bigger to smaller would speed the flow as long as it is done gradually

[BDK]

Going up in diameter also moves the torque band up at the expense of low end torque . Stock M30's are lacking in acceleration off the line so I wouldn't change the sizing unless you increased the HP dramatically.

[Wh33lhop]

Going up in diameter also moves the torque band up at the expense of low end torque . Stock M30's are lacking in acceleration off the line so I wouldn't change the sizing unless you increased the HP dramatically.

Yeah, those M30s sure are torqueless.

[BDK]

I didn't say torqueless, but the torque range doesn't come on until like 3750 rpm,
abit high compared to modern cars,
so by increasing the tubing size you are now moving that to like 4250 simular to an S38.
fine if you know how to drive them, which I do, but a well tuned M30 will outrun an S38 stoplight to stoplight, it is the topend which puts the S38 over the top...

My point being,
most people here will not see 130mph,
so why not keep it "Quick" (more low end TQ) instead of "Fast" (more high end TQ)

[Wh33lhop]

couple of questions all concerning N/A motors...
1) How is two exhaust manifolds going into a single pipe more effecient than true duals?

Think of it in terms of cross section

You are going to have more cross sectional material (piping) for any given cross sectional area (exhaust gases) if you use two pipes, than one

This means
more surface area in contact with exhaust gases dragging the velocity down
more weight

In a single exhaust you need one more collector (2-1) than a dual configuration
But every properly designed dual exhaust has at least one H or X pipe and a single cat and muffler

2) If the size of the exhaust manifolds are say 1 5/8" ID, why go out to 3", the restriction is at the exhaust port, if you can't increase that, does it really help to go out to bigger pipes???...
FWIW, Hartge Headers are like 1 5/8" OD maybe 1 7/8" OD so going any bigger than 2"/2-1/4" seems abit ridiculous to me....

If air flows like water,
then going smaller to bigger would actually slow the flow,
The same size or close to it would equal the flow coming out,
going bigger to smaller would speed the flow as long as it is done gradually

Look at it this way

Higher exhaust velocity means higher exhaust pressure which means higher backpressure which, no, is never good.
Low exhaust velocity is not good either because you want a scavenging effect from the vacuum created by the inertia of the exhaust gases.
So you need a middle ground, an ideal exhaust velocity.

However, it looks like you've got a lot of misinformation

There are two stock exhaust manifolds and no one is talking about going to a dual 3" setup, that would be retarded. Already stated in this thread was that the maximum diameter you'd want for dual exhaust for an M30 would be about 2"

[Wh33lhop]

I didn't say torqueless, but the torque range doesn't come on until like 3750 rpm,
abit high compared to modern cars,
so by increasing the tubing size you are now moving that to like 4250 simular to an S38.
fine if you know how to drive them, which I do, but a well tuned M30 will outrun an S38 stoplight to stoplight, it is the topend which puts the S38 over the top...

My point being,
most people here will not see 130mph,
so why not keep it "Quick" (more low end TQ) instead of "Fast" (more high end TQ)

The torque peak doesn't arrive until later, but that doesn't mean they're lacking in low-end. In fact, as I recall they're setup similar to the M20, with the first resonance of the IM being lower RPM and the second resonance coming on higher (close to 3500-4000). But don't quote me on that.