HP Exhaust Manifolds on 65 383?

[mopar_4life]

Hello,

I'm going to be getting new exhaust on my 65 soon and I was wondering if it would be worth it to switch over to a set of HP Exhaust Manifolds? Or would it be better to keep with the Log manifolds that are currently on the car? I am not to fond of headers with the inherent problems that can occur with them, and the PITA that they can be.

Thanks

Eric

 

[tallhair]

Well there's been a bunch of threads that started out just like this and you'll get all 3 answers.

A. Leave the logs - it's a C body and should be quiet. What kind of a hat do you wear?
B. Go with the HP Magnums - Logs suck, Headers don't help that much and are too expensive. Magnums are the way to go - they look cool and that's what the factory did for the HP engines
C. Logs and HP Magnum manifolds both suck so if you want better performance go to headers or stay with the logs because Magnums are no better than logs.

 

[tallhair]

My preference is B. even if headers do improve exhaust flow A LOT I still like Magnum manifolds and the logs do suck.

 

[jct]

but i've heard the hp manifolds only yield 2 extra hp.

 

[tallhair]

but i've heard the hp manifolds only yield 2 extra hp.

me too

 

[Dobalovr]

but i've heard the hp manifolds only yield 2 extra hp.

You know that but the everyday Chebbie guy won't....especially if you go with some rumble

 

[mopar_4life]

So what y'all are saying, they basically just look cool. That isn't really a bad reason. I'm not looking for tons of power or really any gains at all. Its a heavy car...

And headers on a car like mine doesn't really make sense to me, unless I make a bunch of mods on the engine.

Might just see if I can find a set. Any recommendations on which years and such?

Thanks

Eric

 

[tallhair]

So what y'all are saying, they basically just look cool. That isn't really a bad reason.

That's what some say. I was just putting out the 3 sets of opinions that are pretty standard when this comes up.

They flow better than 2 HP but not a tremendous amount of effort has been put into definitely quantifying how much, at what RPM, and how much on various build levels of engines.

Mopar did things for a reason ... and they are definitely WAY cooler looking. I personally think the 67-70 or 71's are the best looking, but the later ones had more stiffening ribs to prevent stress cracks that could develop on the passenger side inner middle side if I recall.

 

[mopar_4life]

That's what some say. I was just putting out the 3 sets of opinions that are pretty standard when this comes up.

They flow better than 2 HP but not a tremendous amount of effort has been put into definitely quantifying how much, at what RPM, and how much on various build levels of engines.

Mopar did things for a reason ... and they are definitely WAY cooler looking. I personally think the 67-70 or 71's are the best looking, but the later ones had more stiffening ribs to prevent stress cracks that could develop on the passenger side inner middle side if I recall.

Thanks. I appreciate the information. I'll put up a wanted post and see if anything turns up.

Eric

 

[rexus31]

IMO, the time and money could be better spent on another area of the car.

 

[heyoldguy]

Well I dyno tested 1964 log manifolds against 1968 C-Body HP manifolds on a 1972 low compression 440.

RPM...........Logs TQ/HP...........HPs TQ/HP.........difference
2600...............402/199............405/200.........+3/+1
2800...............402/215............402/215.........+0/+0
3000...............403/230............402/230..........-1/+0
3200...............399/243............401/244.........+2/+1
3400...............391/253............394/255.........+2/+2
3600...............380/261............386/265.........+6/+4
3800...............365/264............372/269.........+7/+5
4000...............350/266............354/269.........+4/+3
4200...............336/268............344/275.........+8/+7
4400...............323/271............323/271.........+0/+0
4600...............304/266............301/264.........-3/-2
4800...............283/259............274/250.........-9/-9
5000...............260/248............250/238.......-10/-10
5200...............231/229............236/233.........+5/+4
5400...............214/220............210/216.........-4/-4

I'm not paying for HP manifolds if that is the only difference they make and I'm looking for a power gain.

 

[tallhair]

Well I dyno tested 1964 log manifolds against 1968 C-Body HP manifolds on a 1972 low compression 440.

RPM...........Logs TQ/HP...........HPs TQ/HP.........difference
2600...............402/199............405/200.........+3/+1
2800...............402/215............402/215.........+0/+0
3000...............403/230............402/230..........-1/+0
3200...............399/243............401/244.........+2/+1
3400...............391/253............394/255.........+2/+2
3600...............380/261............386/265.........+6/+4
3800...............365/264............372/269.........+7/+5
4000...............350/266............354/269.........+4/+3
4200...............336/268............344/275.........+8/+7
4400...............323/271............323/271.........+0/+0
4600...............304/266............301/264.........-3/-2
4800...............283/259............274/250.........-9/-9
5000...............260/248............250/238.......-10/-10
5200...............231/229............236/233.........+5/+4
5400...............214/220............210/216.........-4/-4

I'm not paying for HP manifolds if that is the only difference they make and I'm looking for a power gain.

I read that review thoroughly at FBBO and it was discussed here at some length also. I don't recall if you were in that the FCBO version or not.

I was actually thinking of that when I posted the comment above. I wished you had tested them against each other again once you did the power mods and asked you about that at the time ... because these runs were in it's low HP state. I understand that you have no interest in pursuing that then or probably now for your own purposes and told me so at the time.

That's why I said "not a tremendous amount of effort has been put into definitely quantifying how much, at what RPM, and how much on various build levels of engines."

I said above it's not much but is more than 2 HP, obviously on this specific low compression engine it's still not much. Magnum +8/+7 TQ/HP at 4200 (yes I know it's less than logs at higher RPM on this engine).

I would love to see, but will probably never see, tests of a 375 HP engine tested like you did with logs, HP manifolds, and headers with incremental changes from stock to about 450 HP range for nothing other than to know the actual difference in a stock 440 HP engine with some performance mods.

I think the difference on a 9.5 or 10.0 compression 375 HP Magnum would be more than that low compression motor you tested. Maybe 15+ TQ/HP, maybe more, still not a lot but still more.

Further I doubt bolting a set of headers on a stock 375 HP 440 or 335 HP engine moves the needle more than about 15 TQ/HP over Magnum manifolds ... just to put that in context.

A set of Magnum manifolds cost approx $250-300 ... how much are good fitting headers for a C body?

 

[e-440]

There is also a difference in the outlet flange size, 2 1/2 vs either 2 or 2 1/8 from Hp maifols vs non hp. If you are going with dual exhaust put the hp manifold on. If not leave what you got on as long as you are doing nothing with the motor. Log style manifolds are worthless. A good exhaust system will make a difference as long as you have a engine that runs well whether stock or not.

 

[heyoldguy]

Hey tallhair, no problem. The dyno is $550/day. I've got a 440 dyno mule here we have run at 400HP-658HP. I have headers, iron logs and iron HP manifolds. Just start sending money and I'll do tests at any power range you wish.

 

[65Fury440]

So if the dyno mule was higher compression, would the exhaust flow be more critical?

 

[heyoldguy]

Nope. Moot point anyway. Ye 'ol dyno mule is only 10.5:1 compression at 658HP and 8.9:1 compression @ 540 HP.

 

[tallhair]

Hey tallhair, no problem. The dyno is $550/day. I've got a 440 dyno mule here we have run at 400HP-658HP. I have headers, iron logs and iron HP manifolds. Just start sending money and I'll do tests at any power range you wish.

Nope. I'll pass. I think the results would show what I've already said and I'm happy with that so I'll still run Magnum manifolds over logs or headers on stock to stock plus engines.

 

[Zwap]

B-body HP's on my -66 Polara