[tjs72lemans]

Well, the '72 stock style exhaust double chrome splitter on the end only fits 2 1/4". The one side dual exhaust that came with the car was 2 1/4". Maybe the exhaust on a 350 was 2".

[dataway]

Tracked down the info .. 68 was a whacky year. Standard 400 (4 bbl) manual got a 2" headpipe, 2 1/4" tail pipe. Autos got a 2" headpipe and the funky resonator with a 2" tailpipe.

[Formulajones]

Originally Posted by SD455DJ

Formulajones is correct that a slightly taller air filter will lift the lid and allow better turning radius into the carb throats and a lot less turbulence. If you can't find a 1/2" taller filter of the same diameter you need to fit your air cleaner base, you can raise your stock air filter by coiling a min. 4' length of 3/8" windshield wiper jug hose under the filter. You can barely see that the lid is elevated and the 3/8" gap between it and the base. We do frown on 1" taller air filters since it is so obvious to the techs. We don't allow 4" tall open element air filters either, or aftermarket open air filters for that matter. The AC 212 air filter (14" x 3") will flow all the air the pure stock engines need. The A-body dual snorkle air cleaners are good flowing and the 3/8" raised lid helps more with smoothing the air flow.

Proper timing, jetting, and exhaust will net the largest gains, but a good dual snorkel air cleaner with a clean 212 filter will be 95% there for any additional power gains from the intake side.

P.S. I never did try 'with' and 'without' runs, but will the next time we head to the track...which is next year for us...bummer!

Dennis

Thanks for the clarification Dennis. Something else I've noticed a few are doing at some of the other stock races that I always thought was frowned upon, is taking the big 16" lid off and running a little 14" lid on top of the filter, basically exposing everything while keeping the dual snorkel in place. Noticed a couple of LT1 350 guys doing it which uses a similar type of air cleaner although on a smaller scale.

While I would frown on that at tech at a pure stock race, it's worth mentioning in this case if the OP wants to test something since we aren't playing by the rules. It's pretty easy at the track to remove the 16" lid and replace with a 14" lid to see how that affects the car. That might give you an idea of a direction to go.

[tjs72lemans]

Dataway, that's interesting, since the 68 models were supposed to be more hp than the 72.

[Formulajones]

A lot of the big HP muscle cars of the 60's had similar small exhaust.

The OEM system on our Z is just 2 1/4" head pipes, intermediate pipes, and the tail pipes are 2" That same system is what was used on the COPO camaro 427's and even the ZL1 camaros. Even if you opted for the Chamber exhaust the sizes were the same. Firebirds of that era would have been very similar. In fact I'm restoring a 68 400 Firebird now and it still has it's original system intact, and it's pretty small by the naked eye. It sounds nice and mellow, but I just cringe looking at it thinking of the HP that's soaking up LOL

Dad's GTO had small exhaust very similar, with little 2" resonators at the end of it.

There's a reason why these cars pick up so much with just the addition of a nice 2 1/2" mandrel bend system and some free flowing mufflers.

[1968GTO421]

Originally Posted by b-man

A short stub of 2-1/4” pipe mates up perfectly with the stock log exhaust manifolds. Flare the tubing before you cut it into a short piece, then install the stock flange onto it before attaching/welding the 2-1/2” down pipe to the stub.

I used a rat tail file on the inside of the flange to add some clearance so it would slip over the 2-1/4” pipe stub, it doesn’t take too much work to accomplish.

PYPES Exhaust offers custom down pipes already made this way so you can run 2-1/2” exhaust right off the factory log manifolds. Any muffler shop that halfway knows what they’re doing can fab some up as I have described.

It seals up fine. Most factory exhaust is 2” and some are 2-1/4”, both sizes will mate up to the manifold outlets. But you can’t just flare the end of a 2-1/2” pipe and expect it to seal, the tapered sealing surface on the manifold is too small so hence the need for the 2-1/4” stub to transition to the 2-1/2” pipe.

Thread with pictures detailing both the home built and PYPES down pipes:
https://forums.maxperformanceinc.com...d.php?t=630943

I checked out the Pypes website for GTO's and found several off-maifold pipes.
One was definitely for the Ram Air manifolds which I excluded for now.

Is this site below, showing the downpipes to use for the log manifolds?

https://www.pypesexhaust.com/product...-409-stainless

Thanks for your help.

[b-man]

Originally Posted by 1968GTO421

I checked out the Pypes website for GTO's and found several off-maifold pipes.
One was definitely for the Ram Air manifolds which I excluded for now.

Is this site below, showing the downpipes to use for the log manifolds?

https://www.pypesexhaust.com/product...-409-stainless

Thanks for your help.

Yes.

Those are the ones I have on my own car using the standard log exhaust manifolds.

Probably getting them from Summit would be cheaper considering the shipping cost.

[tjs72lemans]

Thanks.

[Quad]

Originally Posted by Formulajones

A lot of the big HP muscle cars of the 60's had similar small exhaust.

The OEM system on our Z is just 2 1/4" head pipes, intermediate pipes, and the tail pipes are 2" That same system is what was used on the COPO camaro 427's and even the ZL1 camaros. Even if you opted for the Chamber exhaust the sizes were the same. Firebirds of that era would have been very similar. In fact I'm restoring a 68 400 Firebird now and it still has it's original system intact, and it's pretty small by the naked eye. It sounds nice and mellow, but I just cringe looking at it thinking of the HP that's soaking up LOL

Dad's GTO had small exhaust very similar, with little 2" resonators at the end of it.

There's a reason why these cars pick up so much with just the addition of a nice 2 1/2" mandrel bend system and some free flowing mufflers.

from Motor Trend Archives; Pure Stock Prep School Part 2- Pontiac Tech
Learn What Makes Them Really Run
Mark Weymouth writerDan Jensen photographer Aug 1, 2008

"ExhaustThe exhaust system is your last drivetrain issue to address. How important is the exhaust? Very! The Ram Air IV Judge in the lead shot of the last installment is a good example. The previous owner used it as a show car and we were going to use it as a race car. Its NOS exhaust system and factory-spec engine only allowed 13.90s at 105 mph. With a change to an X-type pipe system, the car went 13.13 at 111.8 mph.

To achieve the best results, you'll need to start with an all mandrel-bent 2.5-inch exhaust. Next, you need to decide whether to use an H-style pipe or an X-type pipe. Each has its own merit.

Most racers have adopted the X-type pipe system. It provides excellent scavenging in the low to upper midrange. At very high rpm, it's not as effective. Most PS cars run completely in the rpm range, where it does its best work. The one exception is the Ram Air IV, but even this motor, overall, is well served by the X-type, as it provides additional bottom end and midrange that the engine lacks on its own."

[Formulajones]

Originally Posted by Quad

from Motor Trend Archives; Pure Stock Prep School Part 2- Pontiac Tech
Learn What Makes Them Really Run
Mark Weymouth writerDan Jensen photographer Aug 1, 2008

"ExhaustThe exhaust system is your last drivetrain issue to address. How important is the exhaust? Very! The Ram Air IV Judge in the lead shot of the last installment is a good example. The previous owner used it as a show car and we were going to use it as a race car. Its NOS exhaust system and factory-spec engine only allowed 13.90s at 105 mph. With a change to an X-type pipe system, the car went 13.13 at 111.8 mph.

To achieve the best results, you'll need to start with an all mandrel-bent 2.5-inch exhaust. Next, you need to decide whether to use an H-style pipe or an X-type pipe. Each has its own merit.

Most racers have adopted the X-type pipe system. It provides excellent scavenging in the low to upper midrange. At very high rpm, it's not as effective. Most PS cars run completely in the rpm range, where it does its best work. The one exception is the Ram Air IV, but even this motor, overall, is well served by the X-type, as it provides additional bottom end and midrange that the engine lacks on its own."

I can attest to that with my own testing I did that I mentioned earlier on my RAIII. While not as powerful as a IV I still found substantial gains over the repo factory Gardner exhaust where the car was stuck at 14.10's and teens and 99 mph. An h-pipe flowmaster transverse kit picked it up to 13.70's at 102 with no other changes. I later changed to a pypes transverse setup with x-pipe and gained another couple tenths and similar mph.
I've since tuned and tweaked some more to run a best 13.10 @ 106 uncorrected in a bone stock RAIII.
I contribute a big part of getting there in just the exhaust system alone.

[KSZR]

Originally Posted by Formulajones

I can attest to that with my own testing I did that I mentioned earlier on my RAIII. While not as powerful as a IV I still found substantial gains over the repo factory Gardner exhaust where the car was stuck at 14.10's and teens and 99 mph. An h-pipe flowmaster transverse kit picked it up to 13.70's at 102 with no other changes. I later changed to a pypes transverse setup with x-pipe and gained another couple tenths and similar mph.
I've since tuned and tweaked some more to run a best 13.10 @ 106 uncorrected in a bone stock RAIII.
I contribute a big part of getting there in just the exhaust system alone.

Interesting, my 72 Lemans with 400, #16 heads, 068 cam, logs, crush bent quiet system and 3.55s is stuck at 14.6 at 95.

Looking to go to a mandrel pypes system.

What would the ram air manifolds bring for improvement? Worth the effort if I can find them?

[Formulajones]

Originally Posted by KSZR

Interesting, my 72 Lemans with 400, #16 heads, 068 cam, logs, crush bent quiet system and 3.55s is stuck at 14.6 at 95.

Looking to go to a mandrel pypes system.

What would the ram air manifolds bring for improvement? Worth the effort if I can find them?

I've never tested between log manifolds and RA manifolds but I know some people have. Dennis would be a good one to ask.

From the dyno stuff I've seen these guys post like Dennis, I don't recall a huge difference between logs and RA manifolds as surprising as that may sound. I think the HP differences were in the single digits if I remember correctly.

[b-man]

From what I’ve read the RA manifolds are good for around 8 to 10 horsepower at the most over the logs on near stock applications.

Not much bang for the buck when you consider the cost to do the changeover.

The biggest gain is from freeing up the exhaust by going to the 2-1/2” mandrel bent system and good mufflers, probably gaining 25 hp over the restrictive 2-1/4” crush bent exhaust.

[mrmark1957]

My 71 Olds 442 came from the factory with 2 1/4 headpipes and 2 inch tailpipes.I had changed the cam in the motor with a Kenne-Bell Mark 2. The best I could get out of the car with stock exhaust was 13.9 at 103 mph. I took a long extension with a 9/16 socket and loosened the headpipes off the exhaust manifolds about 1/4 inch to relieve some backpressure and ran it down the 1/4 mile. The car went 13.4 at 107 mph, backfiring out of the carb at higher rpm from being too lean. If I would have had richer secondary rods for the Q-Jet to put in, I'm sure it would have improved even more.

[scott70]

This what I run. I use a common 14" lid with a wix 46926R "racing" filter. Stock filter measures about 2 7/8" high and the wix is 3 3/16" so I get a little more height and gets the lid a little further from the carb.

[Formulajones]

Originally Posted by scott70

This what I run. I use a common 14" lid with a wix 46926R "racing" filter. Stock filter measures about 2 7/8" high and the wix is 3 3/16" so I get a little more height and gets the lid a little further from the carb.

That's the same thing I mentioned earlier that I've seen some of the Factory Stock guys doing at a few of the other stock races, which is, or should be, frowned upon at the Pure Stock Drags that Dennis is involved in.

But it works

[tjs72lemans]

Thanks for the info. I sold about three after market chrome (not great) air cleaners at my garage sale last year, as I was clearing stuff out I thought I'd never use. Now I wish I had one of those back. I used them on Chevies!

[NeighborsComplaint]

Originally Posted by Formulajones

That's the same thing I mentioned earlier that I've seen some of the Factory Stock guys doing at a few of the other stock races, which is, or should be, frowned upon at the Pure Stock Drags that Dennis is involved in.

But it works

.. and the same thing I stated in Post #9 but I guess I'm not the authority the rest of you all seem to be.

[scott70]

Originally Posted by NeighborsComplaint

.. and the same thing I stated in Post #9 but I guess I'm not the authority the rest of you all seem to be.

Just showing what I've used for many years now.

[KSZR]

Originally Posted by NeighborsComplaint

.. and the same thing I stated in Post #9 but I guess I'm not the authority the rest of you all seem to be.

I read post 9 and took note of it, interesting. Thanks