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 Exhaust manifold compression question
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Civilian
Tribal Scout

19 Posts

Posted - 29 Jul 2015 :  12:48:37 AM  Show Profile  Reply with Quote
Can someone give me a ball park guess as to when I would NEED better flow from headers? I'm worried about back pressure, not so much about horsepower loss.

I have a 1962 Grand Prix and I'm trying to be economical, but don't want to screw myself either. I have a streetable performance 455 with 6X heads, so I shouldn't run higher than 9.5-10:1 compression. My options are as follows:

1. Put the stock manifolds on and have the muffler shop run the exhaust. I do plan on using an "X" pipe. Now the question is, will running a 3" exhaust from the manifold back decrease back pressure, or is it a waste if it's coming off a stock style manifold? Am I going to have problems blowing out intake gaskets and such because of increased back pressure with manifolds at this compression? Again, I am aware of horsepower loss vs headers.

2. Take is somewhere to have custom headers made. This option is what I'd like to do someday, but would really hurt my budget right now. Nobody seems to make a header specifically for my car. I could buy some inexpensive headers and beat them with a hammer to make them fit (like what I pulled off) but I'm not really excited about all the problems that can come with cheap headers anyway.

You can also email me at JPeters54@midwestern.edu. Any advice is much appreciated!

Jason

2barrelpower
Sitting Bull

USA
135 Posts

Posted - 29 Jul 2015 :  04:42:23 AM  Show Profile  Reply with Quote
When do you need headers?
When you want the full scavenging effect of headers. When you want to make the most power. When you want to be louder.
I don't think anyone "needs" headers.

Pontiacs had the best flowing manifolds back in the day as far as I know. A lot of guys on this forum swear by them.
This is where to buy them.
http://www.ramairrestoration.com/pontiac.html?cat=12&limit=15

If you believe what the magazines print, read this. The gist of it is that long tube headers are still the best, but the repro Ram Air manifolds aren't far behind (10-20 HP).
http://www.hotrod.com/how-to/engine/hppp-0312-headers-vs-manifolds/

Don't bend over for custom headers.

There was a conversation about X-Pipes recently on this forum.

I am at a loss as to why you think that you'll be blowing out intake gaskets.




69FB, 350P, 9 to 1, Comp 260H, Stock Valve Train, Performer Intake, 1406 Carb, Hooker Headers, Points Style, Crane XRI, Crane PS20, TH350, stock stall, 3.08 gear, and 235/60/15 Firestones.

Edited by - 2barrelpower on 29 Jul 2015 04:56:08 AM
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Admin
Ye Olde Webmaster

848 Posts

Posted - 29 Jul 2015 :  08:53:15 AM  Show Profile  Reply with Quote
Long tube headers are designed to optimize the flow of gases. As engines are built for higher horsepower, the log type manifolds which are durable and last forever become restrictive. Moving up to long tube headers allows the engine to expel the gases the best. Headers need to be matched with a decent dual exhaust system. So does one that has good free flowing iron or aluminum exhaust manifolds--not tube headers--but superior flow over stock log exhaust manifolds.

Where to start? 2barrel's recommendation on Ram Air Restoration is a good one.

Ram Air Restorations can set you up with cast iron or aluminum exhaust manifolds that will provide you with peace of mind. They will be superior to the log manifolds of that early 60s era.

Complement those exhaust manifolds with a true 2.5" dual exhaust system. (Your engine doesn't require 3" tubes, over kill.) Adding an H pipe or X pipe will balance the pulse between the firing cylinders. Adding free flowing mufflers will avoid constricting the flow of gases out the tail pipes.

You mention "intake" gaskets being blown out--a worry for you. You probably meant exhaust gaskets. Right? Anyway, your 455 should not blow out any gaskets with a good dual exhaust system in place with or without a balance tube.

My suggestion:

Contact Ram Air Restorations and confer with them about the right exhaust manifold for your 62 GP. Go from there....

Bill

"Dedicated to keeping the classic Pontiac engine alive."

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Civilian
Tribal Scout

19 Posts

Posted - 29 Jul 2015 :  10:53:36 PM  Show Profile  Reply with Quote
Thanks guys, for the education. Being new to this, I read what I can and listen to some of my car buddies. I was under the impression that too much restriction on a performance engine would cause all kinds of problems...including back pressure somehow blowing out intake gaskets.

I chose to do hipo manifolds on my '66 mustang instead of headers, and I couldn't be happier. I had seen the long branch manifolds on the ram air restoration website, but my dad (who gave me the car) seemed to think he had a pair at one point and they didn't fit. I called them today and they assured there would be no issues...so it looks like ill be ordering them.

Now, can I talk the Mrs. into splurging on the ceramic coating...?
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Blued and Painted
Chief PONTIAC

USA
3409 Posts

Posted - 29 Jul 2015 :  10:55:22 PM  Show Profile  Reply with Quote
Depends on the cam. Stock cams may show little or no power gain. Hot street/strip cams are designed to use the long tube scavenging effect.

-- http://www.sdperformance.com/moreTech.php?newsID=39 --


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 29 Jul 2015 10:58:57 PM
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Blued and Painted
Chief PONTIAC

USA
3409 Posts

Posted - 29 Jul 2015 :  11:02:19 PM  Show Profile  Reply with Quote
And this.

-- http://www.hotrod.com/how-to/engine/hppp-0312-headers-vs-manifolds/ --


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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2barrelpower
Sitting Bull

USA
135 Posts

Posted - 30 Jul 2015 :  04:08:55 AM  Show Profile  Reply with Quote
The sd performance article is good.

69FB, 350P, 9 to 1, Comp 260H, Stock Valve Train, Performer Intake, 1406 Carb, Hooker Headers, Points Style, Crane XRI, Crane PS20, TH350, stock stall, 3.08 gear, and 235/60/15 Firestones.
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