Being a "Hot Rodder" I'd vote for the larger diameter and let it drone. What good is a quiet Y Block anyhow. We've been quiet for too long now.

If the engine's stock, keep it smaller.  If you've done some work to it or plan to do some work to it, go a little larger.  Consider that if you go a little larger now, future modifications will be less likely to be restricted by the exhaust system.

I now have a 2 1/2" system with an X crossover with the new engine and the torque is great.  They seem to work well with the combination.  It is loud when I get on it.  I'll be trying some Hooker Aeroflows to quiet it down some.  The glass packs sound nice but I know that I'll be seeing the blue lights if I leave them on.  Plus I plan to start driving it regularly again and I don't want to annoy the neighbors.

The referenced site deals with header design.  How do you apply it to tailpipe diameter?   I'm trying to optimize tailpipe diameter for low rpm torque and am interested, and have been thinking about 1 7/8 inch also.  Currently the pipes are 1 3/4.  Your idea of mismatched mufflers is interesting.  Had not heard that before but it makes some sense.  The glasspacks on my truck side exit 1 foot behind my cab, and at a certain constant rpm on the interstate the sound gets doubly loud.

Mike

Guys that wanted torque band improvements in street cars have tended toward small tube "Tri-Y" designs and I've seen some dyno proofs that show that approach works too. But after the exhaust comes out of the header - low back pressure rules - how much noise can you tolerate for how low a pressure.

The most interesting example I can remember was a big block Cuda with some funny little caps over the "boom tubes" sticking out the back. The caps had holes about 1-1/8 ...1-1/4 diameter, clipped on with a single bolt - and made the nasty big block much more tolerable for the drive-in circuit (and soon disappeared when the money came out). There is a street exhaust system sold for my daily driver Camaro (by SLP) that actually gets tuned for sound by inserting washers in the tailpipe joint - its just a matter of what you are willing to trade ... noise or backpressure.

The exhaust crossovers and "X" pipes are both devices that have been invented to aid the mufflers and quell noise while keeping down the backpressure. The "X" pipe seems to work well on my big block Olds - but I don't have any frame of reference - didn't try anything else on the way. There is a young man that hangs out at a shop I frequent that put one (an "X") on his late model Mustang - and hates it because of a particular reasonant frequency on the freeway. My hearing isn't that sensitive and it didn't sound that bad to me.

     46, aim the pipes back away from the cab, helps a ton. pc, it's more the length of the primaries that affects the "Timing "of the negative wave, and you lose that when the rpm changes. size affects gas velocity, has very little to do with the wave timing.

Using a 90° turn-down at the outlet helps - and I once saw a couple of big washers welded onto the side of the muffler cans to stiffen the tin and ease some of the "ting ting ting" stuff..................

In my opinion, bigger is better as long as it fits.  That's why we ran dumps in the 60's.  Honest officer I don't know why those things are behind my front wheels, the car was like that when I bought it.

TC

Regardless of the firing order on an American V8, there will inherently be two cylinders on each bank that fires consecutively with each other.  As a result there is a high pressure wave created in each tailpipe that can be reduced by installing a crossover or X-pipe that’s the same size as the exhaust system.  When installing one of these in the exhaust, it’s typically recommended that it's done as close as possible to the engine for the most advantage.  The further downstream it’s placed, the less effective it becomes.

Some of the older 180° header designs actually took two tubes from each bank and criss-crossed them under the engine so that a true 180° firing took place within the collectors to eliminate the same intermittent high pressure pulse within the collector.  Headers built on this particular design can actually use a collector size that’s much smaller as a result.  Most vehicle chassis layouts do not accommodate this so you don’t hear much about it today but this particular style of header would not see as much advantage from the use of an X-pipe by lieu of not having to balance out a non-existent intermittent higher pressure wave.

Just all food for thought and an excellent thread.

          You got it, Harley did too. Ever notice the XR's ran a 2 into one into 2 setup?

     The flattrack bikes after about 1970, (Aluminum XR's) made more torque that way, came of the corners harder. Guys tried to duplicate the older drag pipe style and managed to slow the bikes down. Went back to the factory setup immediately. The only form of racing that does not use some type of collector style exhaust to promote cylinder ehaust extraction by the engines firing order is the fuel cars. With 6000 hp and close to that in torque, I guess they feel they don't need a lot more low end! 

 The X pipe or crossover steup has it's greatest benefit on the bottom end thru midrange, with mufflers. It reduces the peak pressure of the pulses by splitting them between two mufflers. Works. 

            See, you heard more than you really wanted to know. This is the problem of dealing with a bunch of old "know it alls" with too much time on their hands. Author included. Sorry, im sure you'll be totally happy with the 2" and glass packs, should sound neater tha H...!

maybe next time I should ask a technical question. Thanks to everyone who participated.

          Might be a resonance in your tailpipes, maybe some thing silly like an extra bend or longer pipe will stop it. Also the higher end mufflers, like a three chamber Flowmaster or the Edelbrocks are a little better. But not perfect, My Flowmasters drone big time at 2000. 2 1/2" tailpipes and mufflers don't help. Better than the Pro street Ranger I have with 3" turn outs in front of the rear wheels and a 408 Windsor though.

Outlaw 56 F-100