[Z Code 400]

This topic has been hashed and re-hashed a thousand times I am sure, but I wanted to pose this question with a specific engine combination in mind. When you decide to cast a vote for headers or manifolds, I would like you to be able to cite personal experience and not just a 'hunch.'

First of all, I think we can all agree that keeping exhaust gas velocity high is important and improved flow is meaningless unless an engine has the potential to use the added airflow.

Secondly, we know from a Dyno Test done in a 2000 issue of Muscle Car Review on a stock 370 horsepower 400 Pontiac with long branch manifolds, that the car only lost 10 HP when it was fitted with stock 'log' manifolds and that loss was at a very high 4800 rpm.

Lastly, we will examine this particular engine combination, intended purpose and expectations. Hopefully, these criterions will be adequate for those of you who choose to participate, to make a credible recommendation.

Here we go...

REQUIREMENTS for MODIFICATIONS:

Any changes to the car must allow me to retain all original features such as 4-speed back drive linkage. Changes must yield a considerable performance difference to be worthwhile.

VEHICLE:

The vehicle in question is a 42,000 original mile 1975 350 Formula. The 350 will be retained for the time being, but we will discuss the 413 that is sitting on the stand awaiting installation.

This is a Non-A/C Car with Manual Steering.

ENGINE:

The engine is based on a 1970 4-Bolt Main Block; it is zero-decked and bored .060" oversize. It is fitted with Speed-Pro L2262F Pistons that rest .005" 'out of the hole" at TDC.

Heads are 6X-4's port matched to Ram Air III Gaskets, with reworked bowls, multi-angle valve job and polished chambers. Heads and block modified for '421' cooling bypass opening.

Heads flowed a maximum of 220 cfm intake and 195 cfm exhaust @ .600" lift and 28 in/H20. They are fitted with new (stock) dual springs, ARP Studs and Comp Cams Roller Tip Rocker Arms.

Static compression is estimated at 8.90:1 overall.

Camshaft is one of my custom designs ground by Bullet. It is hydraulic (flat tappet) and features .461"/.461" lift (1.5 rockers) and 220°/226° @ .050" on a 111.5° LSA. Intake centerline is installed at 109.5° and the intake valve closes 39.5° ABDC.

Intake is a stock, yet port matched Edlebrock Performer with a 750 cfm Q-Jet and re-worked HEI.

DRIVETRAIN:

Transmission is a M-20 Muncie with 2.52:1 first gear driving a 1979 8.5" 10-Bolt Disc Brake Positraction with 3.23:1 gears.

Wheels are Corvette Rallye's (no trim rings or caps) 15" x 8" fitted with P-255/60/15's at all four corners.

PURPOSE:

Weekend pleasure car, driven to work from time to time, occasional trip to the drags for fun.

CURRENT EXHAUST SETUP:

Stock 1975 350 'Log' Manifolds with 'True Dual' exhaust constructed from 14 ga. 2.225" I.D Pipe. Dual head pipes flow into dual Magnaflow 'Center-Offset' Oval Mufflers mounted just behind the transmission cross member where the catalyst would normally reside.

Tailpipes are made from the same 2.225" I.D. material and follow the driveshaft tunnel. The bend up over the rear axle very gently and exit into the stock-style stainless steel dual tips.

These are not the 'dummy' tips that came on my car. Both sections of these tips are open.

This exhaust system is 100% brand new.

ADDITIONAL INFORMATION:

I would imagine this 413 will make around 335 HP in proper state of tune. I would consider adding headers if a considerable yield of at least 10 HP would be possible.

I would not invest the time, effort and money to modify a brand new exhaust system for a modest increase in performance, or to add flow the engine does not have the potential to use.

There you have it. I think I have provided all the information required to make sound recommendation. If you have questions or comments, please feel free to contact me at: 10851Man@gmail.com

Your time and attention is valued and appreciated...Robert

[Z Code 400]

Yesterday, I talked with Jim Butler for over an hour. During our conversation, I asked a lot of questions and learned a lot about Pontiacs.

As many of you will recall, I gave consideration to installing a 427 Chevrolet a few months ago after receiving numerous e-mails telling me how poorly set-up the 413 was. To say the least, it was discouraging. Although there were a number of forum members who have always been encouraging (Larry Navarro, Cliff Ruggles, Tom S, LloydTX, Geoff, Rocky Rotella and B-Man to name a few) all the negative comments really made me want to just abandon the project alltogether.

After talking with Jim and detailing all the planning and thought that went into the 413, I feel a lot better about it. He commented favorably on the flow differential on my 6X-4 heads (220 cfm Intake / 195 cfm Exhaust @ 28 in/H20) and the unique valve evnts of my custom camshaft. However, the most interesting part of our conversation related to exhaust headers.

Following this conversation, I went out into the shop and installed the Hedman #28150 Headers on my 1975 Formula.

I explained to Jim how adding headers to our 440 Chryslers made no measureable difference at the track or on the Dynojet. Jim explained that some engines have such an efficient port design, that little if any benefit can be realized from the addition of headers, except in very, very high horsepower, racing applications.

Jim described the 'Achille's Heel' of the Pontiac head is the 'squashed' center exhaust ports, which hamper exhaust flow substantially. Based on this design principla, Jim believes that a Pontiac will respond more favorablly to headers than most other engines. In fact, Jim told me he has dyno'd thousands of Pontiac's over the years and has seen the addition of headers yield 30 to 60 horsepower, depending on individual application.

That was all the encouragement I needed...:-)

Jim also described back-to-back comparisons of Log Manifolds, Long Branch Manifolds, Ram Air Manifolds and Tubular Headers. The Long Branch Manifolds made the higest HP and TQ of any ofther cast iron manifold and the tube headers made as much as 20 to 30 HP over both of the performance manifolds.

Jim is a very polite and patient individual. He was a huge help to me with respect to this project.

Just wanted to share this information with all of you.

Have a great week...Robert

[WARPed]

Jim is a good guy and has helped our Pontiac industry dramatically. Follow is guidelines and you will be very happy with the results.

[sixt8bird]

He is one of the biggest class acts that any car enthusiast can ask for. He will talk forever and share his experience for free even if it eats up his whole day. He actully told me that it was people like me that makes his day when I said I was honored to speak to him in person for over an hour over my combo and what would work best!! One class act!!!!

[JohnnyC]

Z Code,
This is a good post, and such a hot topic to decide. I'm in the same boat as you are, in a few weeks I will be finishing up my 463 I've been working on since last August, and (aside from cam debates) my exhaust is one the final, and hardest decisions I've been wrestling with. Where will your car be driven the most? If 90% street, and just a few trips to the track, like mine will be, I'd say think strongly about the after market Ram Air and long branch manifolds. I know that headers will make more power, there are many other variables to consider. First of all, 75% of headers will start leak at some point or another. I know this will be debated heavily by some, by from my experiences its true. They are simply harder to maintain, and require much more attention. I've tried some many things/types of headers on my 400, numerous gaskets and install methods, pro exhaust shop installs, etc. and they always ended up leaking at some point, and with a mostly street driven vehicle, its no fun taking a drive somewhere, and get out smelling like exhaust to all those around you. There are so many things that can go wrong from poor production, warping, etc. you really have to be lucky for it be positive. On a primarily track driven car, this is much less an issue to worry about. The second issue that I feel is important to consider, is that headers are going to produce much more heat, and feeling excess heat from headers warming your legs in the cabin is no fun on a 90 degree day with No A/C. I know that some people have been able to master these difficulties, and therefore enjoy the great benefits in power and sound that headers produce, however, its never as easy as some make it sound. Believe me, I've tried ! Therefore, unless some new technique/promise of no problems with a header arises, I'm going to use the Ram Air manifolds and enjoy driving my car instread constatly fusing with them. So Just wanted to give some more "food for thought". Thanks

[form406]

i say ram air restos for convenience, coolness, and actually performance it looks as well...they will fit in with the rest of your clean stock looking car...classy...

[Will]

That engine doesn't look like a bad setup to me. What do people think is wrong with it? The only thing I see that I'd change would be the installed intake centerline, I'd advance it another couple of degrees.

The headers vs. manifold debate really comes down to what YOU want and what you're willing to deal with. Headers are more of a pain, they cause ground clearance problems, will eventually rust, and often leak, but they do make more power. If ultimate power is not your concern, get the RA manifolds and stop worrying about it.

[David Jones]

"People" don't think anything is wrong with it. The owner was nearly convinced that Pontiacs were slugs because one guy had a poorly conceived and/or executed 455 and that 427 Chevy's all would turn 7000+ rpm right from the junkyard.

[form406]

if you lived in hawaii this could be your police car...they give the officer a budget for their own police car...any model, any build if im not mistaken...

[tom s]

if the body could use long brach manifolds I would stay with cast manifolds,BUT since you cant I would vote for headers if you are trying to squeeze every last HP.JMO,Tom

[Z Code 400]

Went with the #28150 Hedman Headres...NO ground clearance issues...installed the Flowmaster #17104 Kit and nothing can be seen hanging down. It was the best combination I have ever seen on an F Body.

I am very glad I went this route...Robert

P.S. Thanks to all who posted..and special thanks to Jim Butler for setting me straight....