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**JasonC** · 03-06-2007, 09:46 PM

X pipes and H pipes are sapost to equal out the pressure in the exhaust system and create more power somehow. I know alot of muscle cars from the 60's and 70's had H pipes on them from the factory. And they knew what they was doing with horse power back then.

**matt** · 03-06-2007, 09:53 PM

Originally posted by MrK View Post

I was running the stock (bent to shit) dual 1.75" exhaust on my m30, and I figured it was time for a change, so I had the stock system ripped out, and I installed a full dual 2" exhaust instead, using the same rear muffler and a very similar resonator, only with 2" inlets/outlets. One thing I did NOT install (which was on there before) was some sort of cross-over/x-pipe.

Did I lose power? I definitely lost sound quality at high rpm. The butt-dyno says that I may have lost 5-10lbs/ft of torque down low. How important is this x-pipe?

Comments? Advise?

Very important.

Also important: sizing exhaust pipes properly for motors. A single 2" is plenty for most stockish e30s. (No FI)

**trent** · 03-06-2007, 10:10 PM

Originally posted by matt View Post

Very important.

Also important: sizing exhaust pipes properly for motors. A single 2" is plenty for most stockish e30s. (No FI)

Why did the late factory E36 m3 exhausts not run an X?

**matt** · 03-06-2007, 11:50 PM

Originally posted by trent View Post

Why did the late factory E36 m3 exhausts not run an X?

I have never seen one that doesn't... Got a pic? They may cross in the cat or resonator.

**MrK** · 03-07-2007, 12:42 AM

Originally posted by matt View Post

Very important.

Thx for your input.

Originally posted by matt View Post

Also important: sizing exhaust pipes properly for motors. A single 2" is plenty for most stockish e30s. (No FI)

Clearly stated above that my e30 is not stockish :) look for it.

**matt** · 03-07-2007, 09:17 AM

I don't see anything about your car in your sig or in your post... How much HP do you have? The fact that you lost torque means your exhaust is too big.

**JasonC** · 03-07-2007, 11:07 AM

2" exhaust to big??? Seems a bit on the small side to me.

**matt** · 03-07-2007, 11:09 AM

Dual 2" is too big.

**matt** · 03-07-2007, 11:11 AM

Doh, M30 motor. My bad.

Still... single 2.5 is plenty up to 250whp +

**MrK** · 03-08-2007, 01:29 AM

matt:

I agree with you on that, but I plan to modify the m30... past 250whp hopefully.

I'll be installing an x-pipe in the next couple of days and I'll post pics as well as seat-of-the-pants impressions and sound difference if any are interested.

**MrK** · 03-10-2007, 11:07 AM

Well gentlemen, the verdict is in:

I fabbed and installed an x-pipe, and I notice NO difference in power seat-of-the-pants. The sound improved on high rpm, but there is a slightly annoyying drone on the low range :(

All in all, not an improvement at all IMO.

I'll tune the m30 with the SMT7 and dyno it, to see what kind of gains I can get.

**winstontj** · 03-12-2007, 11:55 AM

Check out www.e30m3performance.com. I'm blocked at work or I'd link the article but there's a ton of info on that site! You can really learn about x pipes & exhaust flow as well as how to tune appropriately for your motor.

The x pipe both balances and equalizes pressure as well as allows for exhaust gas pulses to draw on each other and increase flow. H pipes are used on many V-8's to link the sides. On older carbed v8's you have seperate intake carbs and if the exhaust is kept seperate (dual exhaust situation) you essentially have two 4-cyl motors sharing the same block. This can cause balance issues which decrease performance and longevity. The H pipe links the both equalizing the exhaust and allows the motor to be tuned as a unit rather than two seperate entities.

Because we have common plenum manifolds the x pipe does not need to serve this function. It does however allow the exhaust pulses to feed off the other cylinders and aid to draw excess gasses out of the other side. For example firing order 1-5-3-6-2-4 keeps each consecutive exhaust pulse switching between the forward manifold and the aft. This means that when #1's exhaust pulse flows out it draws out #5 which is next to pulse. The X pipe allows the previous cylinder to draw the next cylinder's gas out early when the piston nearer the bottom of the stroke. Its called exhaust gas scavenging. When the #5 exhaust valve opens there is already a pull on that runner sucking the exhaust out as the valve opens which gets a little jump on the piston pushing the gas up the bore.

Hope that makes sense. It's legit and combined with an appropriate length runner and proper dia. tubing you should notice an increase on the dyno with the X pipe rather than without.