mixing hp and non hp manifolds

swisherred

swisherred

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I recently saw a post asking if they could install a drivers side HP with passenger non HP manifold because thats what they had. They were told no...it could damage the engine?/? anyway, in my internet travels I cam across another post on an old site that spoke of a specific car that came factory that way....

"My date is hard to read but it says 12/28/67 (my car went out the door on 1/8/68). One oddity about my car that I believe is unique to the 68 383/2bbl/4spd Chargers is that the driver's side came with an HP manifold while the passenger's side came with a non-HP log manifold. I'm still trying to verify this though. Anyway, here's a pic:

yes, that is correct. '68 b-bodies 383-2bbl w/manual transmission used:
Passenger side is the "log" non-performance manifold, shared with the 350hp 440 in c-bodies.
Driver's side is the HP 383/440 b-body manifold.
Why?? Is it for "Z-bar" clearance, or did the car have dual exhaust because of the 4-speed?"

Im curious what the deal is here...could it have been 2843247 with the 2.25 outlet? Would this actually damage the engine if it was a 2.5"? Im curious because I have an HP exhaust system, but dont have the manifolds...trying to decide if I should buy the left manifold, both manifolds or just have a new left front pipe made to match my logs.
 
All 1970 383 2bbl B and E bodies came with a log RH and HP LH manifold. They didn’t seem to hurt anything.

I don’t know what size pipes they had bolted to them. They only had single exhaust on those engines so it was a Y pipe. Could have had a larger LH flange and pipe.
 
Not likely mismatched manifolds would cause damage other than less than ideal performance. The HP manifolds flow better above about 4000rpms. If the engine is a stock standard performance unit it will probably shift at about that point under full throttle. The 2 BBL cited will not have enough air/fuel going in to be a problem. You might notice a fall off in performance if the engine is a 4BBL HP unit above 4k rpms versus a unit with two HP manifolds. As the engine rpms increase, it would become more difficult to maintain a balanced air/fuel ratio on both banks of cylinders since the one with log manifold will have more turbulence/back pressure than the HP manifold.

Dave
 
The 1968 'Cuda 383 (factory car) was down-rated in horsepower (about 20 horsepower) due to the lh exhaust manifold having to clear the steering mechanism on that car. Something like 280 horsepower factory rating, I believe. Not sure what the rh exhaust manifold was.

With a full plenum divider in the intake manifold, it might affect how the carb needed to be jetted. The restrictive side would probably have a bit more residual "egr" than the better-flowing side would, with a notch richer jet to compensate for. But probably only at WOT or heavy loads. A shorter plenum divider or single-plane intake might lessen that situation, I suspect. In theory.

IF there was any real affect, might not be any worse than a free-flowing muffler on one side and a (generic) stock muffler on the other side.

Some people seem to be oriented toward "anything which differs from dead-bone factory stock can cause damage". Perhaps they had a friend or similar who did something "different" that then caused an engine failure (which might have been getting ready to happen, anyway)?

Enjoy!
CBODY67
 
I just read an older article, and be damned if I can remember where, about a guy using a low comp 440 to demonstrate how to use a Dyno to make changes and see results. This was all going on at a fairground. Anyway, the first change was from Logs to hipo's. No change in the output of the engine. I was a little tweeked at that since rumor said different. Maybe on a hiperf engine, but on a lot po stocker it evidently doesn't make a difference. Headers..jumped 15/15, that was the next change.
 
I suspect that a lot would depend upon the cam in the engine, which would relate to air flow at higher rpm, through the engine. If the logs are big enough in diameter, probably not a big difference at lower rpms. but 5000rpm would be a different situation, I suspect. LOTS of "unknowns" in the engine, I suspect, before a firm judgment might be made.

I suspect that the '74-era B/RB log manifolds (with their larger cross-section) flow better than the similar-design 1965 B/RB logs with their 2" outlet hole. A similar situation exists with the Chevy small block Ram's Horn manifolds. A few years in the early 1960s had 2.25" exits and larger cross-section than the "low-pro "normal" Ram's Horn manifolds that came on regular 283s, by observation.

The other thing is that unless it's a computerized-control dyno, a LOT of the results could relate to the operator's level of experience.

Just some thoughts,
CBODY67
 
Here it is 24 hours later and I'm still asking myself, why? I guess I just don't get it?
 
swisherred said:
I recently saw a post asking if they could install a drivers side HP with passenger non HP manifold because thats what they had. They were told no...it could damage the engine?/? anyway, in my internet travels I cam across another post on an old site that spoke of a specific car that came factory that way....

"My date is hard to read but it says 12/28/67 (my car went out the door on 1/8/68). One oddity about my car that I believe is unique to the 68 383/2bbl/4spd Chargers is that the driver's side came with an HP manifold while the passenger's side came with a non-HP log manifold. I'm still trying to verify this though. Anyway, here's a pic:

yes, that is correct. '68 b-bodies 383-2bbl w/manual transmission used:
Passenger side is the "log" non-performance manifold, shared with the 350hp 440 in c-bodies.
Driver's side is the HP 383/440 b-body manifold.
Why?? Is it for "Z-bar" clearance, or did the car have dual exhaust because of the 4-speed?"

Im curious what the deal is here...could it have been 2843247 with the 2.25 outlet? Would this actually damage the engine if it was a 2.5"? Im curious because I have an HP exhaust system, but dont have the manifolds...trying to decide if I should buy the left manifold, both manifolds or just have a new left front pipe made to match my logs.
Click to expand...

I have asked myself that too. I bought a pair of HP manifolds for my 71 Polara. Ran the casting numbers after I purcased them and found that the passenger side is a 2.5 inch 2806900 HP manifold, while the driver side is the mentioned 2.25 inch 2843247 manifold. I did purchase a correct 2.5 inch C Body driver side manifold to keep the outlet sizes the same, but it has always struck me weird about it looking like an HP manifold but having the low performance outlet size.

By the way, that manifold is for sale if needed.
 
CBODY67 said:
...
I suspect that the '74-era B/RB log manifolds (with their larger cross-section) flow better than the similar-design 1965 B/RB logs with their 2" outlet hole. A similar situation exists with the Chevy small block Ram's Horn manifolds. A few years in the early 1960s had 2.25" exits and larger cross-section than the "low-pro "normal" Ram's Horn manifolds that came on regular 283s, by observation.
...
CBODY67
Click to expand...
Old thread, but something to respond to.
I had a similar thought years ago about the mid-70s log manifolds, as they are swoopier, larger outlets (2-1/8" IIRC) and ball-flanges to prevent gasket leaks. I presumed they'd give a cheap HP increase.

An oldtimer told me that they *don't* flow as well as the earlier LP logs in spite of the larger area. He pointed out that the #7 cylinder on the driverside dumps in with the other 3 on that side, and doesn't take advantage of the timing of pulses like the logs do. Looking at the earlier logs and HPs, the rearmost cylinder always dumps into the manifold 'collector' separately. The non-HP logs are on a '66 TNT rated at 365 hp.

However, the mid-60s B-body bigblock logs have all 4 cylinders aligned and then dump at the rear, and those engines are generally rated teh same as in a C-body.

So I dunno, but somethign I'd love to see some definitive info about...
 
There's a process, I forget the name of it? But the shop pushes this abrasive type mud through the manifold and it polishes more then it ports the manifold helping to increase flow. You can port the cylinder head, why not the manifolds??? Can be done on both intakes & exhausts.
Or you could go this road. Yeah, /6's are cool! Good Luck

Exhaust Manifold Mod
 
That process is called extrude-honing. Seems like lots of the stock-class / FAST guys use it.
I liked the story those guys told in that link, about opening up the outlets on the slant 6 manifolds, and the other simple improvements they made.

But I'll say this - they hogged this one out close to the corroded edge, I'd be worried it'll be a leaker.



upload_2021-1-23_18-11-56.png
 
I first heard of the extrude-hone process in a dirt track orientation. Where it was "stock parts only", but the level of competition usually demanded "non-stock parts" power to win in ce Mairtain classes. I believe the only thing it can do is enlarge/smooth what's already there, whereas what Brezenski did to intake manifolds and such was to hole-saw the runners so that flex-hones and grinder bits could be introduced to areas that were previously not accessible. When done, they'd weld the removed sections back into place and then refinish the manifold to look as if nothing had been done. I suspect that extrude-hone put a kink in Brezenski's business?

Generally, the "stock parts" rules in certain classes is to keep things on a more-level playing field, such that $$$$$ does not always win. Then there's the "claimer rule" where a competitor can "claim" the winner's engine by paying a fee (seems like it was $300.00 or so, back then?). Another reason to not put $15K into an engine that somebody could walk off with for a small fee to the track.

Even in a log manifold, there will be positive and negative pressure pulses as each cyl exhausts and others are in overlap. Even the first-gen Hemi had to work against such things! But I suspect that such designs were more about just getting the exhaust out of the combustion chamber and past the narrower-width frames of the time, more than anything else. Which made the Chevy Ram's Horn exhasut manifolds such a big departure and aid to performance, back then. Then, later with the "big exit diameter" in the earlier 1960s 327s.

Consider, too, that the cam timing and carb flow levels of the earlier V-8s was not nearly what came to be standard by the middle '60s. So what we had back then was probably pretty adequate with the stock engines of smaller displacements.

IF you try to compare the Chrysler factory power ratings of the pre-'66 V-8s with those of the post-'65 engines, there can be some similarities with the 2bbl motors, but in the case of the normal 4bbls, it seems to go a bit flaky AND appear that advertising might have been an influence?

For example, the normal cam for many years, beginning with the 350 2x4bbl Plymouth Fury motor had specs of 252/252/.390", with the same specs being on 383 2bbls until 1967 when the "new standard cam" 256/260/.425" cam replaced it. Same 270 horsepower rating, but in '68, when the 1.74" exhaust valves were added with the 906 heads, suddenly it went to 290 horsepower. All with similar single exhaust systems.

On the 383/325 in '68, it had the "standard cam" with the HP manifolds. Same rating as the prior year with the normal manifolds. The 383HP in the Road Runners had the 1967 440/375 cam and HP manifolds, with only 10 more horsepower and a few hundred rpm higher torque peak?

Possibly, the cams in the 413 4bbls and 426W engines were credible for their time (spec-wise), but was the later 256/260 "standard cam" that much better? Just by looking at the cam specs? Or was it the smaller-cfm AFBs on those motors, compared to the later engines? End result, it's hard to really compare motors from back then on only one aspect of their design and specs.

BUT, as the air flow through the motors had to increase for more horsepower, components started to change to accomodate such. 4bbl intake manifolds seemed to change yearly, until about '73 or so, when emissions orientations were more important (but also meant the engines had to be more efficient, which should have also equated into more "power", too, all things being equal). Generally-larger diameter under-car exhaust systems were in that mix, too. Which appeared about the same time as the visually-larger log B/RB exhaust manifolds.

Perhaps "Uncle Nick" might have some free time to do some dyno tests on exhaust manifolds ('66, '75, and HP)? Perhaps on a '70-spec 383 with the 256/260 cam and then with the 268/284 HP cam? Then cap it off with a Performer 383 (or the prior DP4B Chrysler-part numbered) Edelbrock manifold for good measure? Which should give us some reliable figures to deal with, hopefully. Or perhaps this might be an article in one of the Mopar magazines, but I'd tend to trust Nick a bit more than them, myself.

Just some thoughts,
CBODY67
 
CBODY67 said:
....
BUT, as the air flow through the motors had to increase for more horsepower, components started to change to accomodate such. 4bbl intake manifolds seemed to change yearly, until about '73 or so, when emissions orientations were more important (but also meant the engines had to be more efficient, which should have also equated into more "power", too, all things being equal). Generally-larger diameter under-car exhaust systems were in that mix, too. Which appeared about the same time as the visually-larger log B/RB exhaust manifolds.

Perhaps "Uncle Nick" might have some free time to do some dyno tests on exhaust manifolds ('66, '75, and HP)? Perhaps on a '70-spec 383 with the 256/260 cam and then with the 268/284 HP cam? Then cap it off with a Performer 383 (or the prior DP4B Chrysler-part numbered) Edelbrock manifold for good measure? Which should give us some reliable figures to deal with, hopefully. Or perhaps this might be an article in one of the Mopar magazines, but I'd tend to trust Nick a bit more than them, myself.

Just some thoughts,
CBODY67
Click to expand...
Looking at a low priced 1968 #2806900 got me looking for some cost-benefit data on whether To buy, or Not to Buy... I run a 1965 engine in that car w 915 heads, and having the asymmetric manifolds bugs me slightly, though I RARELY push the engine over 3000 rpm. BUT, I have nice dual pipes to put on, and maybe the HP manifold on the right might be worth doing.... Any more thoughts?

Sorry about digging stuff out of the boneyard, but this subject doesn't quite die off.
 
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