3 inch exhaust with manifolds??

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Princess Valiant

Princess Valiant

A.K.A. Rainy Day Auto
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I have a 68 coronet and since its a bigger car than a dart I was thinking of using a 3 inch exhaust kit instead of the 2.5"

is this a good idea with stock HP manifolds?

Its a 440 HP from 67 with 915 heads and the goodies but to stock 67 GTX specs. Nothing wild, just a badass street car is the goal.

Someone told me the sound is different between 2.5 and 3 inch exhaust. ......???

The 3 inch costs a bit more so I am wondering if its worth it or just a waste of $$ considering the other factors of the driveline combo and intended use.
 
Dunno Rani ! I'm gonna use the stock ex manifolds on my 68 big block GTS. I did use a better intake and carburetor. And I'm using a Howards cam with More ex lift and ex duration to help the exhaust get out better. It should be an ok cam since it has a 112 deg lsa. I too would like to hear some opinions on this.
 
Nothing wrong with that at all. The stock high performance manifolds have 2.5" outlets, so stepping up to 3" shouldn't be difficult in that body. I would do it. As mentioned, "about" all you would gain is in sound......but that's a BIG difference. I've done it with manifolds and a mild Chevy 350 and it really woke the sound up. I plan on running a 3" system on my Ford truck when I put the headers on it.
 
I went with 3" on my Polara, but I also installed headers at the same time, so any gain just from the pipes wasn't measured. Go big or go home!
 
I have also considered headers ....I just like the look of the manifolds better but headers are not bad bad.
 
There's a big permanence with manifolds. Unless you spend big bucks on ceramic coated headers, they do not last forever. Manifolds do.
 
RustyRatRod said:
There's a big permanence with manifolds. Unless you spend big bucks on ceramic coated headers, they do not last forever. Manifolds do.
Click to expand...

I have some hedmann headers now with the ball socket thingy on the back.

if I used them I would keep the manifolds stored somewhere for sure
 
I put 3" exhaust on a street driver once and will not do it again.
Wasn't worth the expense for me since I'd didn't make the car any faster
than the 2 1/2" pipes.
I was using headers. And the pipes exit in front of the rear wheels. Very loud
with the 3" . the 2 1/2" weren't exactly quiet.
If I was running a supercharger 3" would be a go for sure.
 
I had a 71 Camaro with a SB 400, M22 4 speed, and a 3.73 geared 12 bolt. It had the second design "offroad special" GM solid lifter cam. It's not real tame. I had 2" primary tube hookers on it with 3" exhaust and 2 chamber flowmasters to the rear end with turn downs. I was working at the local Toyota dealer then. They would have to reset car alarms everyday after I pulled in for work and left. That thing was loud. But it sounded badass.
 
stock exhaust manifolds --> 3" head pipes --> 3" x-pipe --> 3" muffler'd exhaust --> 3" tail pipes = definitely a good setup according to Andy Finkbeiners "How to build max performance Mopar big blocks"

hes got a little section specifically on making power with stock exhaust manifolds (HP manifolds of course) because he did a bunch of intake/exhaust/cam combo testing because he likes the sleeper look too.

i thoroughly enjoyed it because after im "done" with my Duster i wanna put together a nice daily driver with heat/ac and power steering with overdrive that can drive at a comfortable rpm on the hwy to the track, nail down a low 13/high 12 second timeslip with a quick swap to slicks then drive home and have it be a total sleeper so exhaust manifolds, "stock looking" intake, conservative paint job, etc etc etc.

when i get home ill look up exactly what he said and report back.
 
ok so heres what his results were:

470 cu" 400 stroker
didnt specify what he used for an intake
Eddy Performer RPM heads (no details given with regards to porting/modifications if any)
Mopar Performance .528 solid flat tappet cam
B-Body HP manifolds
3" head pipes - custom fabbed (no bolt-on sets available)
full 3" TTI H-pipe exhaust system with Dynomax mufflers

this combination gave him 550hp on the engine dyno / 475hp on the chassis dyno

* special notes on cams:
1. the MP .528 is indeed a pretty mild cam - it only has 243 degrees of duration at .050 lift and also calls for quite a bit of lash which lessens the duration even more.

2. when testing various cam profiles...
* all cams with MORE duration than the MP .528 lost a bunch of power below the torque peak and didnt make much more power, if at all, above the torque peak due to reversion

* all cams with LESS duration than the MP .528 made a tiny bit more power on the bottom end and WAY less power on the top end = these cams are just too mild


So there you have it bud - ima use his findings as a "general guide" for my combo:
10:1 500 cu" shortblock
440 Source Stealth heads (the cnc ported version)
Sonoramic Long Rams (15" runner version)
twin 1000 cfm EFI throttle bodies on an SDS EFI system
MP .528 cam (or possibly the hydraulic roller equivalent)
B-Body HP manifolds
full 3" exhaust with an x-pipe instead of an h-pipe
A518 OD tranny, 8-3/4 resr with a spooled 3.23 gear, etc etc etc

id like the platform to be one of the following:
1955 ChryCo 300
1960 ChryCo 300
Any year Sweptline
1966 Coronet like the one i STILL regret selling lol!

AAAAAAAANYWHO, enough with the rambling - i got my hands full enough with my 440 Duster so all this other stuff is just a pipe dream at this point lol

Hope the info was somehwat useful and best of luck with your ride man!!!!!!
 
RustyRatRod said:
I had a 71 Camaro with a SB 400, M22 4 speed, and a 3.73 geared 12 bolt. It had the second design "offroad special" GM solid lifter cam. It's not real tame. I had 2" primary tube hookers on it with 3" exhaust and 2 chamber flowmasters to the rear end with turn downs. I was working at the local Toyota dealer then. They would have to reset car alarms everyday after I pulled in for work and left. That thing was loud. But it sounded badass.
Click to expand...

Rob ,that's a BIG CAM.. 260- ish at .050,320 old school advertised... 2" inch primary ,on a SBC?!?!?! Louder than the call you advertising, lol...
 
Rainy Day Auto said:
I have a 68 coronet and since its a bigger car than a dart I was thinking of using a 3 inch exhaust kit instead of the 2.5"

is this a good idea with stock HP manifolds?

Its a 440 HP from 67 with 915 heads and the goodies but to stock 67 GTX specs. Nothing wild, just a badass street car is the goal.

Someone told me the sound is different between 2.5 and 3 inch exhaust. ......???

The 3 inch costs a bit more so I am wondering if its worth it or just a waste of $$ considering the other factors of the driveline combo and intended use.
Click to expand...

It's truthfully louder ,Rani.. You want that "60's muscle car sound" , stay with 2.5 " pipes, good mufflers ( not flowmaster/magnaflow,thinking Walker Ultra Flo long case..,worth every damn penny..) tailpipes out the bumper , add a sweet Mopar raspy B body exhaust tip.( was thinking '71 B body tips. Just personal weird thoughts...
 
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