whall

Tom and anybody else...
Perhaps you can help me understand something re the X-pipe. I have my exhaust almost complete now - using 2-1/2's to a 2 in, 2 out Magnaflow where the cats were, then dual 2-1/2's to rear. I have opted to not consider the x-pipe as my Magnaflow shares the flows from each bank and the Magnaflow is going exactly where the cats were and x-pipe would be. My question is would I have been better off (hp wise) with a X and then the muffler.

Jim bailey - 928 International

The performance industry is very big but not unified and similar to the attacks on guns it is divide and conquer. By exempting all pre 1976 it keeps many of the hotrodders happy if their business is older cars. I do agree that California government has the ability to drive business out of California they have proven that over and over............ so 500 exemptions for what 25 million people ?? I better get my name in just in case I want to build a car in a hundred years or so........

Tom Cloutier

Warren,

Probably the most important aspect of the X and Y devices is that they promote scavenging of the exh gases in the inactive pipes. One exh valve opens on say the right side of the engine and that pressure and sound pulse transfers some kinetic energy to the slow moving gases in the pipes connected to the left side. That energy transfer helps to draw or scavenge the gases from those left-leaning pipes. When a valve on that side opens, the exh gases "see" a lower pressure region and so the engine doesen't have to waste so much energy pumping the gases out and down the exh pipe. The result is more power to propel the vehicle.

Unfortunately, a 2 in 2 out muffler will have little or no scavenging effect. If you want an unadorned X that you could have welded into the system you're putting together email me and I'll be glad to help.

Tom Cloutier
tomasc@thePowerBroker.net

Tom Cloutier

Hi Andy,

Not yet! I'm just one old guy, well not that old really. Still young at heart! i have virtually ignored those earlier cars because I don't own one and so it's difficult to test fit, etc. I'm not sure what to tell you. Are you coming to the People's Republic of CA any time soon?

Tom Cloutier

Tom Cloutier

Thanks, Pizza!

I can make a stainless version at any time. It's my metal of choice, but it's expensive.

On my car with Scavenger crossover headers and a 2 into 1 merge collector I located the bung in the outlet pipe of the collector where it sees flow from both sides of the engine. A sensor with longer wires was required. If I recall correctly, the O2 sensor for one of the 911s is the same as for the S4s, but has longer leads.

Tom Cloutier

Green Goblin

I would like to but I am unable to do so. I wish there was someone there with a 84 or older just so you could see how difficult or easy it would be. I will do some research, but if memory serves the stock manafolds are in the same position as the newer duel exhaust. Maybe Jim can shed some light and claify if a Y-pipe and the X pipe would have the same connections, it seems it would because I was going to put on 85-86 factory cats and was told that is a direct bolt on. We'll keep workin on it and figure it out.

Thanks Andy

Tom Cloutier

Ken,

MUCH easier! And cheaper, rather less expensive, too! I'll email you later.

Tom Cloutier

Tom Cloutier

Brendan,

If you're talking about flow in a single pipe versus duals, I haven't done a complete analysis yet. I want to model the stock pipes after the cats and the same configuration with 2.5" pipes, and a single 3.5" pipe. I know what the results will be, but don't have data yet.

I did a simple comparison a few weeks ago of a 2.5" U-bend and a straight pipe of the same diameter and length and have attached the files. These pipes are "perfectly" smooth (impossible in real pipes), so for this test the wall friction doesn't play a role. I'll do that test shortly--just change a parameter in the program. Easy!

Perhaps the main thing to notice is the difference in the mass of gas flowed through each pipe, about 0.063 lb/s. Anyone know offhand what the mass of a cubic foot of exh gas is? Anyway this may not seem like a lot, but remember that there are no friction loss effects included and as you add more bends, the loss increases (I suspect not linearly either).

Also notice the considerable pressure and velocity differences from one side of the U to the other, whereas the straight pipe has nearly equal velocity and pressure.

I hope you enjoy this as much as I do!

Stupid me. I can't upload an Excel file, so here's a couple of screen shots!

Tom Cloutier

Richard S

Warren, Magnaflow makes a 2in-2out muffler with an internal X configuration. Is this the one you are using? I think Tom was assuming there was no X in the 2in-2out muffler.

Andy, the manifold connections are in the same positions on all models, so the cats, X-pipe, etc will bolt to every year. Unless you mess around and put 32v manifolds on 16v heads. For example, I replaced the old, single cat with an S4 cat on my 1980 (84 Euro motor with stock manifolds). It's from the cat, X-pipe, etc, back that can get tricky.

mspiegle

So, does that mean you can locate the bung @ the merge on request? I have an aftermarket O2 system with very long wires.

Does stainless steel weigh more than other materials that you could use?

Tom Cloutier

Absolutely right, Richard. I never look at anything other than the straight through types. Good info. Thanks.

Tom Cloutier

Tom Cloutier

Yes, I'll weld the bung wherever you like (within reason)! Stainless is slightly heavier than mild steel, but I don't have hard numbers handy.

Tom Cloutier

MarkRobinson

The first black exhaust (pictured) has the X located way farther back than the factory. I just spent $ getting my X relocated to the stock cross-over point (as measured in the middle of the H on the factory Cat section) as the mis-match pulse drove me nuts. I drive a 928, not a camaro. Now, it's perfect. If the pulse drives you nuts, have a good exhaust place relocate the beginning of the X ala where the factory designed for the sides to mix....unless you have headers.

Robert_H

Tom,

So your Avenger setup is available again? Last time I spoke to you at Easy, if I remember correctly, you had said that you were not making them anymore. When I get my car up and running again, I would like to have one installed.

Rob

Fastest928

After many experinments to determing merge or corssover point, i concluded that the point needs to be further back for all 928, unfortunatley, no one point is optimum for all. I ended up picking a point that was the best compromise for all models.

The stock location is best for exhaust gas sampling, and allowing the cats to be as close to the engine as possible ... not for max power.