[ekancler]

I grabbed the exhaust manifold casting numbers off my 1977 W72 400 TA yesterday:

Exhaust Manifold LH 499624E L136 – December 13 1976
Exhaust Manifold RH 496002H K196 – November 19 1976

Although John Witzke lists the correct castings for 1977 W72s as 499623 LH and 495986 RH (and for 1978-79 as 10002755 LH and 495986 RH) some W72 owners report that they have 499624 LH, 496002 RH as I do. For example https://forums.maxperformanceinc.com...d.php?t=855059

Although I can't find any info to verify this, I'm gonna guess that my manifolds are correct for my car and given that my (numbers matching) engine is stamped December 16 1976 that they are likely original too. But I'm more curious about whether they would be considered high performance manifolds. And I can't find info on that either. Wallace Racing lists the Firebird 1975 455 SD 495624 LH and 496002 RH exhaust manifolds as high performance manifolds. The RH casting is the same as my 1977 400 W72 and the LH casting is only one number different – 495624 vs 499624. (http://www.wallaceracing.com/exhaust1.htm)

So does my 1977 W72 TA have effectively the same manifolds as the 1975 455 SD? If it does, I guess that would mean I have high performance manifolds.

(I am curious what the E and H signify too. )

[highway star]

I don't think the exhaust manifolds are a "high performance" model. I have in my notes for my '78 W72: L/H 10002755a R/H 49598610002754c. Can't confirm 100% as I tossed the oem exhaust manifolds for headers back in the 1980's. I regret that as those are the only oem items I don't have for this car. Surely someone with their oem's will confirm.

['ol Pinion head]

All that Ive recognized W72 oriented is specific use of a certain EFE valve for manual trans applications & another for auto applications.

Need to pull out & reaquaint myself w the late '76-78 dated 400 manifolds that I have. The first thing that comes to mind in quickly identifying them is the long strengthening rib design of the casting of these later 70's ex manifolds. This design was prevent cracking, there is no larger diam outlet from what I've seen.

[jerry455]

I don't believe there was a 455SD in 1975. The W72 manifolds were the same as the other 400 engines. The 455SD had Ram Air style manifolds that look completely different than the stock manifolds.

[ekancler]

Apologies, I should have written 455HO not 455SD.

[ekancler]

Also as I wrote below "John Witzke lists the correct castings for 1977 W72s as 499623 LH and 495986 RH (and for 1978-79 as 10002755 LH and 495986 RH)"

My 1976-81 Pontiac Parts guide shows that 1977-79 W72s had 10002755 and 495986. It doesn't list 499623 nor does it list either of my manifolds (499624 LH and 496002 RH) at all. Seems strange to me especially as both my manifolds have late 1976 casting dates.

[78w72]

Originally Posted by ekancler

Apologies, I should have written 455HO not 455SD.

75/76 455HO wasnt anything special like the true HO engines in earlier years, same ex manifolds etc as a standard mid 70s 400/455

['ol Pinion head]

Originally Posted by ekancler

Also as I wrote below "John Witzke lists the correct castings for 1977 W72s as 499623 LH and 495986 RH (and for 1978-79 as 10002755 LH and 495986 RH)"

My 1976-81 Pontiac Parts guide shows that 1977-79 W72s had 10002755 and 495986. It doesn't list 499623 nor does it list either of my manifolds (499624 LH and 496002 RH) at all. Seems strange to me especially as both my manifolds have late 1976 casting dates.

The letter after the casting number identifies what casting box the manifold was poured, nothing more.
The mid 75 455 4spd offering w/ 455 HO sticker on the hood scoop was little more than an emissions certified 4sod 200net hp 455 big car engine. A 455 block to build up on, if one chooses, but the engine was no where near the performance league of the '71-72 455 HO engine. For '76 model Birds, Pontiac marketing came to their senses & dropped the HO moniker off the decal.

In referencing cast iron engine parts & factory cast alum intakes, I always go by the actual casting number. Similar deal with original alts, distributors, starters, will go by the roll stamped number on the housing. Master Parts Books often have parts numbers that are off a digit from casting numbers, or have nothing to do with the original casting number, or use a superceded later part number.

Following are a few original W72 400 usage manifolds have stored in the shop, 3 of them awaiting installation. Fortunately they are easy to get to. Have many clean dated original manifolds, that are not pulled out of long term storage & hung up yet. As pull out more, will hang them up.

499624 D J216 LH (from current Feb '77 mfg Y82 4spd project car)
499624 B D096 LH
1000275 A C148 LH (from curent Nov '78 built 4spd T/A)

496002 D E097 RH
this last one am not 100% sure on it. Will have to view '79 W72 car disassembly pictures /notes as well as ck notes on '78 X7 & WC engines I've owned over the years. Hope this helps.

[ekancler]

Seems like I have correct and quite likely original manifolds. And that they're not anything special from a performance perspective.

I appreciate all the responses.

[ekancler]

Originally Posted by 'ol Pinion head

499624 D J216 LH (from current Feb '77 mfg Y82 4spd project car)
499624 B D096 LH
1000275 A C148 LH (from curent Nov '78 built 4spd T/A)

Are the 499624 and 1000275 basically the same design or did Pontiac use two different but very similar manifolds for the W72s?

[Trevor78]

Probably not so much High Performance, just not the regular low performance, still the preferred option!

[ekancler]

So in light of them being, seemingly, non-performance manifolds, I'm wondering if there is a high performance D-port manifold that would be a good drop-in replacement - in that no exhaust mods would be needed to mate the manifold to the pipe. Although I may go to headers.

[b-man]

Any swap to the high performance exhaust manifolds that unfortunately are experiencing spotty availability as of late, would most definitely require the replacement of the down pipes that connect to the manifolds.

Don’t be too quick to replace your stock manifolds, the high performance exhaust manifolds are good for maybe 8 to 10 hp at best on a stock engine. Not much return on investment for that small and almost imperceptible power increase.

There are plenty of fast cars still running the factory log style manifolds. Headers unfortunately reduce ground clearance and can be troublesome leakers so be aware of that before you go that route.

Here’s one example of a very fast car using almost all stock pieces and the stock log exhaust manifolds, read some of the last few posts to see what kind of surprising performance they were able to achieve:https://forums.maxperformanceinc.com...d.php?t=834245

Keep in mind that these guys are the top of the heap and are no strangers in their ability to wring power out of well-blueprinted and detailed factory combinations. The performance of mostly stock Pontiacs might surprise you if you’re willing to just try to make everything as right as you can with little if any aftermarket parts.

Pontiac 400 engines were great performers in their day. Stock GTOs and Firebirds were definitely no slouch right off the showroom floor and the vast majority were equipped with the standard log manifolds. Every single Tri-Power 389 GTO had log manifolds, none of them were factory equipped with the higher flowing HO or Ram Air manifolds that were introduced in 1967 on the 400 GTO and Firebird HO and Ram Air engines.

The standard exhaust manifolds are not necessarily badly restricted low performance pieces, they did their job quite well for the majority of Pontiac performance cars.

[SD455DJ]

Well said B-man! 375 hp is fairly easy with stock exhaust log manifolds, so don't throw them away.

Dennis

[ekancler]

Originally Posted by b-man

Any swap to the high performance exhaust manifolds that unfortunately are experiencing spotty availability as of late, would most definitely require the replacement of the down pipes that connect to the manifolds.

Don’t be too quick to replace your stock manifolds, the high performance exhaust manifolds are good for maybe 8 to 10 hp at best on a stock engine. Not much return on investment for that small and almost imperceptible power increase.

There are plenty of fast cars still running the factory log style manifolds. Headers unfortunately reduce ground clearance and can be troublesome leakers so be aware of that before you go that route.

Here’s one example of a very fast car using almost all stock pieces and the stock log exhaust manifolds, read some of the last few posts to see what kind of surprising performance they were able to achieve:https://forums.maxperformanceinc.com...d.php?t=834245

Keep in mind that these guys are the top of the heap and are no strangers in their ability to wring power out of well-blueprinted and detailed factory combinations. The performance of mostly stock Pontiacs might surprise you if you’re willing to just try to make everything as right as you can with little if any aftermarket parts.

Pontiac 400 engines were great performers in their day. Stock GTOs and Firebirds were definitely no slouch right off the showroom floor and the vast majority were equipped with the standard log manifolds. Every single Tri-Power 389 GTO had log manifolds, none of them were factory equipped with the higher flowing HO or Ram Air manifolds that were introduced in 1967 on the 400 GTO and Firebird HO and Ram Air engines.

The standard exhaust manifolds are not necessarily badly restricted low performance pieces, they did their job quite well for the majority of Pontiac performance cars.

Wow thank you for that! Very helpful to hear. Especially as I'm not out to make a super high power engine. This is a project with my daughter. We don't need 500hp here

So here's a follow-up: If I stick with the standard exhaust manifolds should I also stick with the standard exhaust? I live in a rural part of Oregon so no smog. I could ditch the cat and go to high flow mufflers...

[b-man]

You’re going to benefit from both a performance and muscular exhaust note standpoint by replacing the exhaust with a nice free flowing mandrel bent 2-1/2” dual exhaust and a quality crossflow muffler. A good low restriction exhaust makes a noticeable difference and is worth the money even with the stock log style manifolds.

The crossflow muffler behind the rear axle (like the factory used) provides the best solution as far as packaging is concerned, there really isn’t adequate room under the floors to stuff twin mufflers under there like you can on a GTO or other A-body car.

There are very nice reproduction factory exhaust systems available and I’m sure for those who are into originality they’re awesome. But freeing up the power that’s waiting to be unleashed on an otherwise stock Pontiac 400 by using an upgraded exhaust system is a great feeling.

[ekancler]

Originally Posted by b-man

You’re going to benefit from both a performance and muscular exhaust note standpoint by replacing the exhaust with a nice free flowing mandrel bent 2-1/2” dual exhaust and a quality crossflow muffler. A good low restriction exhaust makes a noticeable difference and is worth the money even with the stock log style manifolds.

The crossflow muffler behind the rear axle (like the factory used) provides the best solution as far as packaging is concerned, there really isn’t adequate room under the floors to stuff twin mufflers under there like you can on a GTO or other A-body car.

That's good to know. I've been on the fence about going to true dual with the stock manifolds.

[TAKerry]

I was talking to Pypes at a show and much to my surprise the guy said that the transverse muffle provided a bit more hp than the dual mufflers. I have duals on my 77 and will go with the single transverse on my 79, curious to see the diff. in sound as well.

[ekancler]

I only found one factory repro exhaust system. Looks nice but not mandrel bent...

https://www.gardnerexhaust.com/exhau...xhaust-system/

I'm thinking that this is the way to go:

https://pypesexhaust.com/i-23437340-...m-sgf911e.html