3" or 3.5" exh

Okay, 69 bee total restoration happening here. Let me explain my ideas and ill hopefully snag one of the other guys running a big hammer that can give me a bit of advise. So im running a 505 indy headed EZ-1 295s. 11:1 COMP Fairly large flat tappet cam everything was spec'd out by porter racing heads, cam heads being ported etc... Ill assume im 675 700 hp range. Im running a dana 60 BUT no fuel tank. Ill have a fuel cell mounted in the trunk. My issue is the exhaust size. Ive always used 3inch. But this time im kicking around 3.5 due to power level. id assume but not sure if 3 inch is big enough or if it would be a bit restrictive, or if 3.5" is over kill. Not concerned about price. It is what it is.


Origional plan was since my collector is 3.5 inch i was going to run a granatelli 3.5" elec cutout then from that down to a 3" X-PIPE and run 3" all the way out.



2nd idea was stay with 3.5 the whole way through a 3.5 " Xpipe 3.5 out the tail end.


3rd was to stay 3.5" from Collector thro the cutout 3.5" Xpipe, then possibly step down to 3" out the rear.

Mufflers are chosen i plan on running the round dynomax ultraflows whatever size i decide on pipes. Id love to hear some 3.5 inch exhausts if anyone has vids. Anyone think for 700ish HP the 3.5 is over kill???? I think it would have a nice sound.

My old pump gas BB stroker motor in my street Duster ran 7;00 in the 1/8 mile locally with the 3.0 inch exhaust system on it, it had a set of MganFlow 14 inch oval x 7 .0inch high side inlet with center exit straight through pipes mounted behind the rear end between the rear subframes and the rear 1/4 panel.
I remove the complete exhaust system, it had a set of Hedman fenderwell race headers on the 505 C.I. stroker motor with 3.0 inch pipes back to the muffs behind the rear end with the muffs exiting at the rear bumpers and it ran 6:98 in the 1/8 mile. Not enough gain for me to worry about. I thought it was probably the loss of weight that affected the ET and MPH
It would run 9.993 in the 1/4 mile at 134.6 mph corked up with the air cleaner on weighing 3450 Lb. with me in it running on 91 octane non ethanol Oregon swill it was a real hoot to drive on the street and sometimes at the track

Run 3" - use my mufflers!!

Holy hell thats flying, and with the full 3 inch exhaust being used. How much Power were you putting out?

Whats ur mufflers?? Have any vids?? Im curious what you have. Im kinda fussy about exhaust sound. I like more of a deep roar or even the scream of the X-pipe. I try to avoid anything that will make the exhaust cackle on acceleration.

Once that exh gases cool around the rear end, you can decrease the size of the tailpipes with little effect on HP. It will also quieten the car some and the further rearwards and the bigger the mufflers are the quieter it will be as well.

My 572 Hemi, runs 3.5" collector into a 3.5" in/out X pipe, after the X it tapers nicely to 3" at the rear end and 3" out the back with into large case 3" Magnaflows at the very rear of the car. Fuel tank is in the trunk so have the space.

Car is pretty quiet with 11:1 CR and over .700" lift roller.

I think that motor, it was a longtime ago that I built and dyno that motor (it made 727 HP in Klamath Falls, OR at 4300 Ft above sea level) that 9.99 run was with a set of CNC ported 440-1 heads with an Indy 400-3 intake with Wilson 2.0 inch tall anti reversion space with a stock Holley 9375 non HP 1050 CFM Dominator.
That car and motor exceeded my wildest hopes regularly

We've been 10.01 @ 133 mph at 3,700 lbs. with 3" exhaust.

Dynomax Ultraflow mufflers.

So im assuming the 3.5" isnt necessary at all. So, im thinking then 3.5" collector through 3.5" cutouts, then into a 3" X-pipe and out the rear with the round 17223 round ultraflow placed where? I was going to place them where the factory fuel tank was supposed to be. So they are closer to the rear end of the car, UNLESS they would sound better placed just after the X pipe.

on my charger, i'm going 3 1/2 into a 3" xpipe, then couple to the existing 3" over the axle pipe, 3" rearward from there into a race bullet of some kind, then a fabricated [by me] turndown 6" or so, wide.
if i don't like the sound, i will install something where the factory mufflers were [possibly another race bullet ?].
after it's all done, i'll send the total system out for coating.
and believe it or not, i have run a strait 4" pipe [adapted from the 3" over the axle pipe] to the bumper along side of the factory gas tank. it fit fine with no clearance issues.

When will u have this done? Ill come over and check it out

www.classicchambered.com . Or, search YouTube for many videos my customers post. If you go to my website, go to the "Sights & Sounds" page & enjoy.

I have 3" on two cars. One dumped at the axle on the Roached Runner and one all the way back to the stock tips on the red Charger. I have 3-1/2" on my Challenger with bullet mufflers. It is load is and understatement....

Any sound clips or videos of the 3.5. And is the 3.5 worth the effort over 3inch @ roughly 700ish hp?

No, I don't have any sound clips that I get to post on here. At 700 I would say yes. You would want to go up to 3-1/2".

Sweet, so 3.5 through x pipe and then the tail pipes out the back with mufflers are ok to be 3inch? Or best to make it 3.5 the whole way out?

one thing to remember, the farther away from the head port, the colder the exhaust gasses are, and the slower they become.
that's why a smaller tail pipe works. it has a tendency to keep the gas flow up.
however, i have no idea how much hp my engine will make, maybe 475 ?
above a certain hp amount, you need to keep pipe size constant.
let me know when you want to come over and bs.

My old pump gas 517 C.I. Street motor made 727 HP at 4300 Ft. in Klamath Falls Oregon on a fairly new, less than one year old, DTS engine. I posted on how that motor responded to removing the 3.0 inch stem from the car at the track, .02 ET and .2 MPH in the 1/8 mile gain with it off.
My message is I really don't think switching from a 3.0 inch system to a 3.5 inch exhaust system will make a noticeable gain on the street or at the track: work:

i remember that Cab.
i think you figured the gain was just the removal of the weight of the pipes.
now with that said, every 2" header i have seen has a very short collector.
would any low rpm gain be seen by adding an extension, say 12-18" of 3 1/2" [the collector size] before transitioning/reducing to 3" pipe ?

Every BB and 426 Street Hemi car I've raced with 727 and 833 NP 4 speed liked the 3.5 inch collector extensions
I would start with the 18 inch long extensions usually and never trim them any shorter
I did try a set of 3.5x 12 inch long extension on my old M.W. stocker and I can't remember now if they were faster or slower than the 18 inch ones were: confused: