I want to build a new exhaust. What size do I "really" need?

Ain't that the truth! Dyno racing is the bench racer's best friend.

 

Ive seen several differant cars pick up a tenth and a couple mph or more by going to a straight through muffler from a flowmaster I dont dyno race and every car is differant and a muffler change could move the powerband (hooks better with less torque etc etc) changing how the car acts so ymmv



I only made a suggestion based on my opinion i know scooper is only changing his setup based on the drone he is getting and fwiw I personally like them (on my DD) and yes it has drone

 

If you decide to do a single 3'' here's a trick i used.Buy a tailpipe for a 1998 suburban 3/4 ton they are about $35 and have 5 or 6 mandrel bends just chop it up and get your welder out no need to run back and fourth to the exhaust shop.Useing the tailpipe trick and some 3" straight i did the whole exhaust on my pick up for $90.00.The best part no crimped pipe!

 

Joe, going PM...

Thanks for the good info derek!

 

Scott, if you really want to run a single muffler...Go 2.5" ID...2 pipes from headers to an X pipe. Then 2 pipes 2.5" ID to a single muffler with 2 inlets and one or two outlets after the rear axle (put the muffler where the original resonator was) You will like the sound and you should have no drone from it. I used to do this to the datsun Z cars when doing the SBC swap on em. They sounded good and ran well. I used to use a stock replacement walker muffler for early 70's fullsize chevy P.U. w 350 / 2 wheel drive. It was a 2 into 1 style.
OR Just put tail pipes on the dang thing!!! It will cure the drone 90 percent of the time.

 

check out the GEARZ website he did a segment about exhaust sizes. If i remember right according to what you have, it should be 2 1/2" duel or 3" single.

 

Going to a single is stupid. You're going to kill it. Ditch the Flows and go with two DynoMax mufflers.

 

I've said it before, just extend it over the axle and out the back or sides and the drone will disappear.... been there, done that. Much easier and cheaper than an whole new system.......

 

Ditto, on both counts. For proof of Flowmaster's restriction, check with the guys who were forced to throttle their engines with em in the Engine Masters competition. They're no better than Glasspacks. And to me they sound about as crappy.

 

I went from having dual 2 1/4 with an H pipe and flotec mufflers dumped at the rear end to having the same mufflers with 2 1/2 pipe H pipe and tail pipes and got rid of almost all the resonance .

 

I CAN'T!!!

I don't like exhaust exiting out the back and there isn't any room out the sides.

Here is what my under carriage real estate looks like (see pic)...No room for side exit pipes with all the caltracs and subframe connectors.

This is the main reason I originally asked about going into a single pipe. Then I could bring the one pipe out where the front of the subframe connector meets the subframe, which is the highest point on my frame, and I could run a sidepipe down the side and curved out just in front of the rear tire.

 

Finely! We get an honest answer! Now we really know why you don't want them out the back. You know they don't have to extend out the back.....you could run them over the axle, tuck them up close as possible to the body, and have them turn down before they get all the way to the rear. That way they will still be hidden from view, and the added length behind the mufflers should kill the drone. Try it, you will probably like it.

 

you can also run the tailpipes to the rear valence and turn them down Fox body Mustang GT style. I know that repeats somewhat, but the exhaust on those cars was invisible unless you lay down on the ground. Mine are 2.5" into the mufflers and 2.25" out duals in/out and tuck between the leafs and subframe aft axle. I have also considered cutting the pipes off and turning them down where they tuck between the quarter drop and spring.

I also have flowmasters with a full over the axle system and it drones, but we have discussed this at length previously.

For the record, I also ran a 2.5" into a single 3" RV type flowmaster Muffler(read big/long, and I don't remember the part #) mounted where the stock muffler was and it droned as well but I don't race the car so I don't have any gains or losses to report but the dreaded dyno numbers were about the same for the dual setup as the single but both systems used flows

 

Many branded Race series mufflers (fewer baffles), or any straight thru design mufflers (glasspack) will let the exhaust breath and help gain noticable HP. If you want the old school backfiring/rattle sound run 2", if you have a big block motor & want an aggressive breathing system run 3". I myself run 2 1/2" pipe on my cars because its not too opened up and I've seen the best gains with this size,

 

Just change the damn mufflers.