Slant Six Forum
https://slantsix.org/forum/

exhaust pipe constriction
https://slantsix.org/forum/viewtopic.php?t=31926		 Page 1 of 2
Author:  plymouthhillsidehemi225 [ Mon Oct 27, 2008 8:12 pm ]
Post subject:  exhaust pipe constriction
I just noticed on my volare, the previous owner must have replace quite a bit of the exhaust, and many of the bends make the already small pipe very constricted... how much would this affect my performance/mileage?
Author:  Eric W [ Mon Oct 27, 2008 10:27 pm ]
Post subject: 
I would say quite a bit. Example: I went from the stock 1 3/4" pipe on my Satellite to only a 2" system. My milage went up a couple of mpg's and my "seat of the pants" dyno could tell a difference. Not neck snapping, but there. The smoother the bends, the better the exhaust will flow out and the less the engine has to work to push it out.
Author:  Karasik87 [ Tue Oct 28, 2008 7:00 pm ]
Post subject: 
so changing the exhaust pipe does work. People always mention improving their exhaust to 2" or whatever they like, and I was always confused if they meant the manifold or the pipe.
Author:  66aCUDA [ Tue Oct 28, 2008 7:08 pm ]
Post subject: 
Changeing to 2 1/4 seems to be the best size for a street slant.
Frank
Author:  DusterIdiot [ Tue Oct 28, 2008 7:11 pm ]
Post subject:  The pipe...
One of the tricks mopar used first on the mileage getter 'Feather Duster' in 1976, then later on the super six cars and certain model 1 barrel units, was the introduction of a large diameter exhaust pipe with a larger muffler (as Dan would say the '318' muffler), then a pipe that was a bit smaller than the initial header pipe to keep the sound 'mellow'...
So 2 1/4" pipe from the manifold to the muffler then 1 7/8 or 2" after the muffler is usually the perscription. Just going to a 2 1/4" pipe on my old '74 duster from the 1 7/8" stock pipe was good for 1-2 mpg and a bit more in the lower torque band... it's money well spent... and there's more in there if you tune the carb and timing to match.

-D.idiot
Author:  Karasik87 [ Wed Oct 29, 2008 3:16 pm ]
Post subject: 
cool beans
Author:  plymouthhillsidehemi225 [ Wed Oct 29, 2008 6:00 pm ]
Post subject: 
well, what I am planning to do is get rid of everything from the catylitic converter on back and replace that with a thrush glasspack with dual outlets, the inlet size is 2 1/2 and both outlets are 2 1/4 but I will keep my stock exhaust from the manifold back to there... do you think that would let my engine "breath" fairly good?
Author:  Aggressive Ted [ Wed Oct 29, 2008 6:29 pm ]
Post subject: 
It may not help much at all.

I did mine in a couple of steps and never noticed much gain until I ported the exhaust manifold. I cleaned up the ridges in each individual port then, reamed out the exhaust pipe joint to 2.25" up about 4" or so into the manifold.
I had a 2.25" head pipe mandrel bent so there were no wrinkles, just a nice smooth bends. I used the Thrush Welded muffler for $29, similar to a Flow Master 40. I ran the 2.25" pipe all the way to the bumper with a slight turn down.
I had started at the rear and worked forward to the engine as money and time allowed.
When the system was completed it netted a full 2 mpg improvement and allot more instant torque and more overall power so I am not pushing the engine as hard as before. For reference: my average vacuum at cruise (60 mph @ 2500 rpm) with a 1920 Holley one barrel is 16 to 18".
Hope this helps! :D
Author:  dank10fenny [ Wed Oct 29, 2008 8:25 pm ]
Post subject: 
ted... what was your base timing? with what kind of dizzy mech. advance spring setup did you have?
Author:  66aCUDA [ Thu Oct 30, 2008 7:03 am ]
Post subject: 
Be careful using 2 1/2 or larger pipe as it has been reported that the gain of the 2 1/4 pipe was lost if you go bigger.
Frank
Author:  theslantingsix [ Thu Oct 30, 2008 2:01 pm ]
Post subject: 
could you do a 2.25 duel and still be fine just wonderin for when i drop in my headers
Author:  Aggressive Ted [ Thu Oct 30, 2008 2:40 pm ]
Post subject: 
Quote:
ted... what was your base timing? with what kind of dizzy mech. advance spring setup did you have?
dank10fenny,

Here is the setup I have been running the past two years. The only changes I have made have been with POD adjustments and re-jetting and tuning/modifying the 1920 carb.

Tuning: New 1974 electronic distributor re-curved with a red primary spring and extra long looped secondary spring from a 400 big block distributor. 340 distributors are good to rob springs from too. Using the 15R governor with a 11R V8 vacuum advance screwed out 3 turns, (VC-208 11R can $10.26 at www.rockauto.com ). CH-410X Blue Streak cap, MO-3000 Echlin rotor, Chrome Blaster 2 coil and MSD Blaster .85 ohm resistor in place of the stock MOPAR resistor which provides a full 10 volts to the coil at idle, Orange ECU and 8mm Blue Summit wires, NGK UR4/6630 plugs gapped at .040. Timing set at 16 degrees initial, 16 degrees mechanical and 22 degrees with the vacuum advance for a 54 degree total at 2500 rpm. The MSD Blaster coil and resistor provides good spark resulting in a smooth idle.

Cruise at 50 mph I am at 2000 rpm, 60 mph I am at 2500 rpm. On the freeway I am between 65 and 70 mph. Mileage to date for combined city and freeway is 25 mpg.
Author:  66aCUDA [ Fri Oct 31, 2008 6:08 am ]
Post subject: 
I would think at least an X pipe on duals. That being said I believe the data says that running true duals will negate most (if not all) the HP benifit from the headders,. You will not get the help of drawing the exhaust out for the other 3 cyls.
Frank
PS there was a really good article in one of the Hemmings rags last year on this.
Author:  SwingerDeluxe [ Mon Nov 03, 2008 8:07 am ]
Post subject: 
I'm a new member and have a similar question on this subject. I have to replace the cracked exhaust manifold on my '72 Swinger. I have received a used exhaust manifold in good shape and now will replace and will need a complete exhaust system. I would like to run the exhaust pipe to a glasspack muffler with single inlet and dual outs. Then run dual pipes to rear bumper with chrome exhaust tips. Can I purchase a 2.25" exhaust pipe for this slant six or will this have to be fabricated at the muffler shop? Also, do I want to stay with 2.25" from muffler back or can I run 2.5" without losing a mellow sound and performance? I do not want this sounding like a rice burner with the large chrome muffler hanging out the back like the kids are running now! There was a thread on here, that I cannot find now, with videos of several members' exhaust systems that sounded great! I believe they recommended MagnaFlow mufflers rather than Flowmasters or Cherrybombs. Thanks for any help and advice.
Author:  THOR [ Mon Nov 03, 2008 9:53 am ]
Post subject: 
You can still buy brand new a 2.25" manifold pipe for an Aspen/Volare that should fit right under the hood of your '72. They are pretty cheap from what I remember. Contact MiDi for more info... he is the one who showed it to me.

From there, use a magnaflow. I've run a 50 series flowmaster with 2.25" and it sounded nice, not loud by any means, however, all flowmasters and knock-offs can produce quite a drone around 60 mph.

Just watch out for MiDi's 64 GT, he's got a helluva fart can stashed under his rear bumper.

~THOR~
Page 1 of 2 All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/