Street motor camming difference between headers and manifolds

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travis
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Street motor camming difference between headers and manifolds

Post by travis »

On mild street V8 stuff, 250-350hp range or so, would you cam an engine differently with the only difference being iron manifolds vs small tube headers? If so, in general how would you do it?

A friend of mine has a ‘70 C10, 9.7-1 355 with lightly ported 416 heads (stock 1.84/1.50 valves), Perfomer intake, generic 214/224@.050 cam (Summit 1103), 1 5/8” full length headers, dual 2 1/4” exhaust, etc. 3.73’s and a stock torque converter in a turbo 350 trans. He swapped the leaky rusted headers for a set of chromed stock style small outlet ram horns, and it effectively neutered it. It went from being able to pull cleanly to 6k rpms in high gear to struggling to go past 5k now, even after timing and jetting changes. Before it would melt the tires from a dead stop, now it will do barely more than squeak the tires. Could any sort of cam change recover most of the loss of performance?
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Re: Street motor camming difference between headers and manifolds

Post by 427dart »

I wouldn't change the cam because of the restricted exhaust as it already has 10 more degree on the exhaust side.
There are or used to be better flowing factory type rams horn exhaust manifolds that had the larger 2 1/2 inch outlets.
Some years ago I used a pair on a SBC 415 in a heavy 72 Monte Carlo and it pulled hard thru the gears.
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Re: Street motor camming difference between headers and manifolds

Post by ptuomov »

The issue is 180-degree exhaust blowdown interference at low rpms and 90-degree exhaust blowdown interference at high rpms.


http://www.speedtalk.com/forum/viewtopi ... =1&t=51430

https://www.speed-talk.com/forum/viewtopic.php?f=15&t=42202

https://www.speed-talk.com/forum/viewtopic.php?t=29828
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Re: Street motor camming difference between headers and manifolds

Post by F-BIRD'88 »

Now you know the performance gain of bolt on tubular headers.
You lost about 12% torque and about 12% HP too.
Probabily more since the manifolds are "SMall"

You could replace with new long tube headers ( they do not last forever)
A set of tri Y design headers would be sweet.
On the 4416 305 heads you want to block the "twinned" center egr passages to stop the cross talk between the center 4 ex ports. You can do this with crimpeled up catering pie plate /baking pan thick aluminum foil stuffed down in the ext risers.
A set of the BIg corvette ram horn ex manifolds with 2.5" outlets is a alternative.
Join in a Y pipe merge .
Shorty headers are next best. ( again merged with a 2 into 1 Y pipe to max torque). If you file the new headers flanges with a bodyman's metal finish file to ensure it is true flat before install you will avoid a lot of the header gasket leaks problems.
tube Headers work. to the tune of about +12% more torque on engines like yours.
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Re: Street motor camming difference between headers and manifolds

Post by cjperformance »

travis wrote: Sun May 20, 2018 7:58 pm On mild street V8 stuff, 250-350hp range or so, would you cam an engine differently with the only difference being iron manifolds vs small tube headers? If so, in general how would you do it?

A friend of mine has a ‘70 C10, 9.7-1 355 with lightly ported 416 heads (stock 1.84/1.50 valves), Perfomer intake, generic 214/224@.050 cam (Summit 1103), 1 5/8” full length headers, dual 2 1/4” exhaust, etc. 3.73’s and a stock torque converter in a turbo 350 trans. He swapped the leaky rusted headers for a set of chromed stock style small outlet ram horns, and it effectively neutered it. It went from being able to pull cleanly to 6k rpms in high gear to struggling to go past 5k now, even after timing and jetting changes. Before it would melt the tires from a dead stop, now it will do barely more than squeak the tires. Could any sort of cam change recover most of the loss of performance?
Less exhaust duration , later exhaust opening(convert more cyl pressure into TQ), and earlier exhaust closing . For a shelf cam look for a single pattern cam, something with comparable lift or a little more if the hardware allows, around 268 to 272 adv dur, around 216 to 218 at .050" and on 111 to 113 LSA.
That will get all the TQ back and help out up top by 'shutting the door' on manifold pressure due to the now more restrictive exhaust.
The stock manifolds have their obvious limits, all you can do is make the most you can for the budget you have within these limits.
Downstream of the manifolds stepping the pipe size up sometimes helps out too, i have found in the past that stepping the pipe up about a foot or so after the flange works better than doing so right after the flange but that was on rear exit manifolds, the rams horns may respond differently.
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Re: Street motor camming difference between headers and manifolds

Post by PackardV8 »

Now you know the performance gain of bolt on tubular headers.
You lost about 12% torque and about 12% HP too.
Yes, No, Maybe. FWIW, the 12% figure given for SBC with and without headers doesn't hold true for all families of engines and all cams and not all SBCs. In mild street builds of obsolete engines where there were limited cam choices and similarly mild SBCs on limited budgets for cam and valve gear, I've done dyno tests where headers through mufflers and tailpipes showed zero power increase.
On mild street V8 stuff, 250-350hp range or so, would you cam an engine differently with the only difference being iron manifolds vs small tube headers? If so, in general how would you do it?
So yes, headers usually do require cam and compression adjustments to maximize the benefits. Previous posts had some good suggestions.

Since he liked the previous combination and since a cam change is so much more involved, why not go with some header suggestions?
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Re: Street motor camming difference between headers and manifolds

Post by andyf »

I did a cam test article for Popular Hot Rodding years ago with a big block Mopar that had cast iron manifolds. What we learned was that the engine was very sensitive to duration and overlap. If the cam was too big then power fell off. The cam had to be conservative to work with the manifolds. Best cam I tested was single pattern ground on 112. I'm sure with more testing that might have changed a little bit more. Cams that were too small worked better than ones that were too big. With the small cam you made good power down low but the engine gave up early. However, if the cam was too big then it lost power down low and never made up for it on top.
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Re: Street motor camming difference between headers and manifolds

Post by F-BIRD'88 »

Could any sort of cam change recover most of the loss of performance?

No, but supercharging it will. Tubular headers are very effective.
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Re: Street motor camming difference between headers and manifolds

Post by Monza355 »

That does sound like a whole bunch of powerloss :shock:
The ram horns are they the larger 2.5” outlet corvette style manifolds ?
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Re: Street motor camming difference between headers and manifolds

Post by travis »

Small outlet truck style ram horns...a bit different than the passenger car style afaik.

He said he is putting headers back on...can’t live with such a dramatic loss of performance he says 😂

I’ve never tried a small single pattern cam on a 112 lsa on something like this. I’ve had good results with small cams 110 lsa’s with manifolds...but never tried with that much compression
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Re: Street motor camming difference between headers and manifolds

Post by F-BIRD'88 »

While you have the car apart with headers off, exposing the exhaust ports then take the intake off and stuff the egr passages with thick foil and check from the ex side thru the ex ports that the 4 center ex ports EGR passages are plugged with the balled up thick aluminum foil.
Use a BIG single piece of the balled up THICK aluminum foil so it cannot come apart.

You want the foil to block off the 4 center egr ports but not extend into the actual exhaust port flow path. If nessessary reach into the exhaust ports to stuff the balled up foil in the egr ports tight. If it takes 2-3 tries to get it right so be it.
Now reinstall.. Move the current cam to a more advanced 104deg intake C/L. ( Do not guess or wing it to move the cam. Degree it properly and move it accurately to a new 104deg in C/L.
Recurve the distributor for a new short mechanical advance curve of 10deg mechanical advance travel. Now timing will be 24 base at idle and 34 total at higher rpm.
Button it all back up and go for a ride. Tell me it is not a LOT more torqey.

The current cams installed centerline should be about 107-108 deg in C/L
move it to a new 104deg position add new headers and the dis recurve.
Enjoy. Now from this you an decide on a new cam. ....or run it.
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Re: Street motor camming difference between headers and manifolds

Post by ptuomov »

Even things like bore spacing matter to how well manifolds work in a V8 and at what rpm ranges. Large bore spacing engines will suffer from 90-degree exhaust blowdown interference (with cast log manifolds) already at say 5800 rpm, while small bore spacing engines might go to 6200 rpm.
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Re: Street motor camming difference between headers and manifolds

Post by andyf »

There are a few people who know how to build engines to make power with manifolds. The guys who run in the FAST class have figured it out. Some of those guys are really hauling the mail with stock looking engines. They have cast manifolds and 2.5 inch exhaust and they still run 10's. Cam choice is critical.
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Re: Street motor camming difference between headers and manifolds

Post by BOOT »

I had a very sim combo to the op that works surprisingly well for what it is(headers not tried manifolds) and I have a combo like cjperformance stated with ramhorn manifolds that also worked well. Just found it funny too have two of my odd combos in this thread LOL
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Re: Street motor camming difference between headers and manifolds

Post by ptuomov »

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