2” or 2 1/2”

[Nate S]

The engine is a 1970 383 HP block with factory flat tops, compression is 9.4/9.5 through 518 heads with oversized stainless steel valves and 0.20 shim steel head gaskets. Intake is a Edelbrock Performer with a Edelbrock 650 CFM carb, electronic ignition, voltage regulator and Engel cam just slightly hotter than what came in the road runners. As stated I am running HP manifolds through dual 2” exhaust with Flow masters. Thansmission is the original 3 speed automatic with valve body and push button shift. Gearing was just updated to 3.23 sure grip in a 68/70 8 3/4” rear end housing. I haven’t had a chance to drive the car since all the changes but I am hoping for the best. Thanks for the input!
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Ok, just have to ask, 518 or 516 heads? 518 are MW.

 

[Red63440]

Oops ,sorry…fixed!

 

[66Satellite47]

The 516 heads with larger valves and mild porting do well. The combination sounds like a winner for driving/cruising. Hopefully the available gas works OK.

 

[rumblefish360]

I think as i said before drive until he needs three inch. After the sun comes back out and he drives it he may want to up to a little more power. You and i both know its hard to leave a mopar alone. So for now i agree leave it alone.

Yup you did and then ridiculously suggested 3 inch.

 

[BSB67]

Exhaust pipes measure just a little over 2” OD so I am guessing they are 2” ID.

Tubing is measured and identified by outside diameter. You have either 2" OD, or 2 1/4" OD. Factory 383's had 2 1/4" OD compression bent exhaust to the muffler. The tail pipes could be smaller.

My Charger ran 12s at 109 mph. The Moroso calculator has it at about 450 hp. The car had 2 1/4" full body mufflers and compression bent exhaust.

 

[69 Sleeper Bee]

Looking at all the posts on this thread I still say leave the 2'' pipes that you say look to be new and when you have the new head pipes made to connect to the HP manifolds have an "H" pipe installed if at all possible like @Don Frelier said to balance out the system. I think this would offset the fact that the pipes are 2'' diameter. If you are 330 h/p or less this should be fine for your car IMHO.

 

[66Satellite47]

Tubing is measured and identified by outside diameter. You have either 2" OD, or 2 1/4" OD. Factory 383's had 2 1/4" OD compression bent exhaust to the muffler. The tail pipes could be smaller.

Darn, I should have caught that in post #1. 2 1/4" makes more sense.

 

[RJRENTON]

IMO....that the 2" O.D. tubes should perform better, depending on the runner lengths to the 4 into 1 collector and cam profile (longer exhaust duration) will support higher exit velocity and better scavenging of the cylinders. It has to deal with the resonant frequency of the exiting exhaust gases and the "tuning effect" similar to the Max Wedges' cross ram intake manifold, tuned to a specific RPM range. The same principle applies to the exhaust system. The reflected pressure wave actually reinforces the exiting exhaust pulse, pulling more spent gases from the cylinder, allowing more complete cylinder filling (more power developed). Larger diameter pipes or longer lengths or both will cause this effect to be diminished.
BTW....pipe is measured by the O.D. in inches X Schedule....2" pipe measures 2-3/8" O.D. x Schedule (Sch 5 or 10 or 40). Tubing is measured by the I.D. X wall thickness.....1-1/2" tubing measures 1.900" O.D. x 0.109" wall for Sch 10. Both pipe or tubing can be EITHER welded or seamless construction. Just a little information....
BOB RENTON

 

[rumblefish360]

It has to deal with the resonant frequency of the exiting exhaust gases and the "tuning effect" similar to the Max Wedges' cross ram intake manifold, tuned to a specific RPM range. The same principle applies to the exhaust system. The reflected pressure wave actually reinforces the exiting exhaust pulse, pulling more spent gases from the cylinder, allowing more complete cylinder filling (more power developed). Larger diameter pipes or longer lengths or both will cause this effect to be diminished.
BOB RENTON

This is true up until the pipe is ether to long or to short in which dyno testing is needed to know exactly where the best length per size pipe is. The effect of diameter change is t normally so drastic as to “Kill” the engine performance if the length is altered to suite the diameter.

Be it exhaust manifolds or headers, the length of the exhaust pipe should end in a pressure wave cancellation box so the negitive wave can travel up the pipe to help draw in more air and fuel into the cylinder. The amount difference can be huge.

You have this part slightly wrong;

The reflected pressure wave actually reinforces the exiting exhaust pulse,

Once the exhaust valve opens, the spent gasses and pressure wave leave the cylinder out the head and down the pipe. This positive pressure wave, the way I see it, is assisting the gasses out to a point but not the reflective wave going back up the exhaust pipe.

Going back up the pipe creating a negative pressure at the next timing event for the opening intake valve to a deeper depression to pull in more air and fuel.

Just like the cross ram induction system your reference earlier.

David Vizard has written about this. Engine masters did an episode on adding collector length. Both worth while to check out. But both, (IIRC) were in reference to header usage, not exhaust manifold use. With the headers, the effect was in the lower rpm range adding substantial torque.

 

[MelroseMopar]

Your 2 inch will be fine. I have a 512 Stroker that Dynode in the mid 500HP and close to 600FPT. I run a 2 1/2 in exhaust ( I do have headers though.) and have had zero problems. My headers are wrapped so I do have some improved flow with that, but they still feed 2 1/2 main pipes and magnaflow mufflers.

 

[66Satellite47]

This is true up until the pipe is ether to long or to short in which dyno testing is needed to know exactly where the best length per size pipe is. The effect of diameter change is t normally so drastic as to “Kill” the engine performance if the length is altered to suite the diameter.

Be it exhaust manifolds or headers, the length of the exhaust pipe should end in a pressure wave cancellation box so the negitive wave can travel up the pipe to help draw in more air and fuel into the cylinder. The amount difference can be huge.

You have this part slightly wrong;

Once the exhaust valve opens, the spent gasses and pressure wave leave the cylinder out the head and down the pipe. This positive pressure wave, the way I see it, is assisting the gasses out to a point but not the reflective wave going back up the exhaust pipe.

Going back up the pipe creating a negative pressure at the next timing event for the opening intake valve to a deeper depression to pull in more air and fuel.

Just like the cross ram induction system your reference earlier.

David Vizard has written about this. Engine masters did an episode on adding collector length. Both worth while to check out. But both, (IIRC) were in reference to header usage, not exhaust manifold use. With the headers, the effect was in the lower rpm range adding substantial torque.

Rumble & RJ, have you guys actually tried varying the tube length on the primary and collector with headers on a car at the drag strip? I was lucky enough to get the Hooker adjustable headers with my '65 Coronet. I played with both the primary length, and separately with collector length. Didn't make enough difference to worry about.
The stock style manifolds are a completely different deal. My bet is the pressure wave reflection has almost no effect at the exhaust valve due to the manifold design. IMHO.

 

[rumblefish360]

Rumble & RJ, have you guys actually tried varying the tube length on the primary and collector with headers on a car at the drag strip? I was lucky enough to get the Hooker adjustable headers with my '65 Coronet. I played with both the primary length, and separately with collector length. Didn't make enough difference to worry about.
The stock style manifolds are a completely different deal. My bet is the pressure wave reflection has almost no effect at the exhaust valve due to the manifold design. IMHO.

Primary pipe? No
Collector pipe? Yes
Reducer style? Yes
H vs D vs true dual? Yes
Exhaust stops at;
Axle - yes
Rear bumper - yes
With and without an H pipe ending at the axle - yes
Also tried 2-1/4 vs 2-1/2 vs 3 inch on small blocks.

Next experiment up?
David Vizard ideas in various pipe sizes on a moderate 340 in a lightened (not to drastically) ‘71 Duster/904

FWIW, the collector pipe effects (from what I have seen and been told by my older mentors) is the lower end of the torque scale. This is (or what I believe) a various RPM level totally dependent on the engine size and build spec of the engine.

On your Coronet, I am not surprised since it was track tested (am I correct?) or street tested. What size engine?

I have a question for you. How did you vary the primary pipe length?

 

[rumblefish360]

My headers are wrapped so I do have some improved flow with that, but they still feed 2 1/2 main pipes and magnaflow mufflers.

How do you figure that you have improved flow with wrapped headers?
What exact muffler are you running?

 

[33 IMP]

Primary pipe? No
Collector pipe? Yes
Reducer style? Yes
H vs D vs true dual? Yes
Exhaust stops at;
Axle - yes
Rear bumper - yes
With and without an H pipe ending at the axle - yes
Also tried 2-1/4 vs 2-1/2 vs 3 inch on small blocks.

Next experiment up?
David Vizard ideas in various pipe sizes on a moderate 340 in a lightened (not to drastically) ‘71 Duster/904

FWIW, the collector pipe effects (from what I have seen and been told by my older mentors) is the lower end of the torque scale. This is (or what I believe) a various RPM level totally dependent on the engine size and build spec of the engine.

On your Coronet, I am not surprised since it was track tested (am I correct?) or street tested. What size engine?

I have a question for you. How did you vary the primary pipe length?

Hooker adjustables come with a slip-on bolt secured collector, and indidual head pipe extensions, to enable the racer to add primary pipe length. I got mine used, at the orange county raceway swap meet, and I didn't get the primary extension pieces with mine. The collectors did not have a flange for a street exhaust system, so i made a set of flanges and welded them onto mine.

 

[66Satellite47]

My Hooker adjustables were as 33IMP said. I did have all the primary extensions and tried them. I did have a couple pairs of the collector extensions. The suggested method at the time was to use a thin coat of paint on the collector extension and see where it burned off to. Then cut at the point where the paint stayed. I track tested for my 426W and my 440+.030 both liked either no primary or maybe 1-2" extension. The collector extension made no performance difference so I just used the stock collector. With my 400/452 motor no primary or collector extensions. The 426W and 440 was an actual 12.0 CR. In the 440 I used a .585 lift 308* solid and later a .635/645 mushroom cam and both a .720 274* and a .660 280* roller.

 

[MelroseMopar]

How do you figure that you have improved flow with wrapped headers?
What exact muffler are you running?

I have the TTI 1 7/8 headers and TTI complete xpipe exhaust. mufflers are the magnaflow super turbo. Wrapping any type of exhaust piping is a crucial and important step when controlling exhaust temperatures and reducing radiant under-hood heat. Keeping exhaust gases hotter within the exhaust system helps in decreasing density and increasing the flow of exhaust gases. This improves exhaust scavenging which, in turn, adds power. Also, limiting the radiant heat inside the engine bay can decrease temperatures up to 50%. This reduces heat absorption for electronics, air intakes and through the fire wall, keeping dash components and cabin temperatures to an absolute minimum. Hotter gasses flow faster than cold gasses. SCIENCE!!!

 

[rumblefish360]

Hooker adjustables come with a slip-on bolt secured collector, and indidual head pipe extensions, to enable the racer to add primary pipe length. I got mine used, at the orange county raceway swap meet, and I didn't get the primary extension pieces with mine. The collectors did not have a flange for a street exhaust system, so i made a set of flanges and welded them onto mine.

I did t know that, thanks, very cool IMO.

I have the TTI 1 7/8 headers and TTI complete xpipe exhaust. mufflers are the magnaflow super turbo. Wrapping any type of exhaust piping is a crucial and important step when controlling exhaust temperatures and reducing radiant under-hood heat. Keeping exhaust gases hotter within the exhaust system helps in decreasing density and increasing the flow of exhaust gases. This improves exhaust scavenging which, in turn, adds power. Also, limiting the radiant heat inside the engine bay can decrease temperatures up to 50%. This reduces heat absorption for electronics, air intakes and through the fire wall, keeping dash components and cabin temperatures to an absolute minimum. Hotter gasses flow faster than cold gasses. SCIENCE!!!

View attachment 1201217

I think that should have been added to your post!

 

[MelroseMopar]

I did t know that, thanks, very cool IMO.

I think that should have been added to your post!

Your Probably right. I was just thinking of the 2 1/2 exhaust pipe part when I wrote it. The main reason i wrapped was the engine bay temp decrease because I am running the Holley sniper EFI system as well and was worrying about street use temps.. the exhaust scavenge/and(Slight ) power increase was just a bonus..

 

[Pat Mercadante]

My 64 Fury was upgraded to a 383 this past summer. Before I could finish the exhaust I ran out of warm weather. The dual exhaust that came with the car is just about new with Flow Masters, all nice and shiny. The car isn’t going to be raced and will just be used for cruising. Exhaust pipes measure just a little over 2” OD so I am guessing they are 2” ID. Question is, is it worth upgrading to 2 1/2” pipes for a cruiser from new 2” pipes off of HP manifolds.

 

[Jeremiah]

2.5" minimum if you have a cam with a good amount of overlap. I can kill my 451 by closing the electric cutouts when it is cold (no choke) just from the change in back pressure. If that happens a 950 RPM think of the restriction at 5500 or more. Just food for thought.

Also, I picked up 25rwhp with the cutouts open. I think you could do better with something other than turbo or glass packed mufflers at the expense of some extra db's for the neighbors.