[Formulajones]

The only problem with flipping the lid is it now takes the crown of the lid and tapers it in toward the carb, this is usually a HP killer for a couple reasons. One is putting the lid closer to the air horn, the other is the direction of air.

Most likely the reason for a gain, and this gets back to why the pure stock guys are putting taller filters in, is because you've now exposed more filter area around the circumference of the base. The same thing is accomplished with a taller filter that simply lifts the lid up, and still keeps the lid in it's proper upright position. This still helps direct airflow properly, and also keeps the lid further away from the air horn. This method actually works better than the lid flip deal.

[tjs72lemans]

Thanks for the many responses. I built this car to be a nice street able cruiser with stock looks. I knew headers would possibly add to better flow, but stayed away due to many seemingly having issues with close proximity to starter. I stayed away from bigger exhaust, because there was talk of fitment to the stock exhaust manifolds. I wanted zero issues with fitments. The question I had was, because my common sense says an engine trying to suck air through two snout openings compared to everywhere around circumference of filter makes it work hard to breathe and perform. The dyno test runs no filter and short down pipes to dyno exhaust.
If I think about my stock 2011 Silverado, it has a similar hp (315 I believe) and it is very responsive and has good torque. Plus, it's heavy. If my Lemans ran similarly, I'd be more than pleased. I haven't wanted to flip the lid on filter housing to test, because it is restored and I don't want to mess up the finish. Plus, as mentioned, it seems it would cause less volume for air to carb. My thought was to get another cover with taller filter element, but not sure how much room I have so I don't hit bottom of hood. My Camaro has a 4" tall filter in Moroso housing, but the I cut a hole in hood to stick through with an L-88 style hood scoop to draw air from base of windshield. Works awesome.

[F ROCK]

The dual snorkle breathes plenty.
Have you checked your timing?
My 8.2:1 400 ran great with the dual snorkle and so does my 455

[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

[mrmark1957]

I have got a 73 Lemans with the stock low compression 400 with a quadrajet., stock dual exhaust and 3.23's. I ran it at the track with the stock big single snorkle air cleaner, then with the lid flipped, and then with no lid or filter, just the base. Flipping the lid made no difference. No lid and filter made it .1 sec and 1mph quicker.

[dataway]

When I put together my stock YS 400 auto I removed any casting nastiness from the head exhaust ports, gasket matched the log inlet ports, opened up the log exit as much as was safe. I used 2 1/4" mandrel bent pipes ( 2.25" offers a 26% increase in cross section over the OEM 2" ) and figure between those various changes I've got to be flowing reasonably more than an OEM 2" system. Engine is all stock except for the .040" over bore ... so while probably not optimum, has got to be better than OEM.

Still using the OEM single snorkel air cleaner though.

[Formulajones]

Originally Posted by mrmark1957

I have got a 73 Lemans with the stock low compression 400 with a quadrajet., stock dual exhaust and 3.23's. I ran it at the track with the stock big single snorkle air cleaner, then with the lid flipped, and then with no lid or filter, just the base. Flipping the lid made no difference. No lid and filter made it .1 sec and 1mph quicker.

Exactly what I was explaining above

[mgarblik]

My experience has been that the direction of the air flow and the "quality" of the air flow varies greatly by carburetor as far as performance. Seems Q-jets, AFB's are very sensitive to obstructions above the airhorns vs a Holley without air valves or velocity valves. Holley carbs are much more forgiving having a restriction near the airhorn. Engine Masters video seemed to verify this. The air cleaners that gave the clearest, straightest shot through the airhorn made the most power. Not always possible with a hood so close to the carburetor.

[GTOLou]

Originally Posted by mrmark1957

I have got a 73 Lemans with the stock low compression 400 with a quadrajet., stock dual exhaust and 3.23's. I ran it at the track with the stock big single snorkle air cleaner, then with the lid flipped, and then with no lid or filter, just the base. Flipping the lid made no difference. No lid and filter made it .1 sec and 1mph quicker.

I think you proved that low compression 400 didn't need much airflow to live off of.

[ta man]

I've had a few low compression 400's . What total timing was it at on the dyno and is it the same now? The reason I say this is they will tolerate and respond well to more timing. More total and a much quicker curve they need all the help they can get.

[NeighborsComplaint]

Originally Posted by NeighborsComplaint

my butt dunk says I lose 10 + hp

s/b butt dyno ... autocorrect on my phone got me.

[tjs72lemans]

I see there was mention of 2" pipe as stock. As far as I knew, my 400 dual exhaust came stock with 2 1/4" pipes, so that's what I ordered and installed. I just want to clarify that in case some think I have 2". I'm not sure if going another 1/4" to 2 1/2" solves much. But, I can only guess the stock type muffler that I got with the kit is more restrictive than an after market better flow design.
I wasn't involved too much with setting things up on the dyno or giving input, but my dyno sheet on timing just lists 10-35. Not sure if that means initial is 10 and max is 35 degrees. I was going to check timing after I installed in car, but it idled and ran so smooth, I haven't checked.

[Formulajones]

Originally Posted by tjs72lemans

I see there was mention of 2" pipe as stock. As far as I knew, my 400 dual exhaust came stock with 2 1/4" pipes, so that's what I ordered and installed. I just want to clarify that in case some think I have 2". I'm not sure if going another 1/4" to 2 1/2" solves much. But, I can only guess the stock type muffler that I got with the kit is more restrictive than an after market better flow design.
I wasn't involved too much with setting things up on the dyno or giving input, but my dyno sheet on timing just lists 10-35. Not sure if that means initial is 10 and max is 35 degrees. I was going to check timing after I installed in car, but it idled and ran so smooth, I haven't checked.

The gains found going from 2 1/4" crush bent factory exhaust to a 2 1/2' mandrel bent exhaust can be found in a post above where I mentioned my stock 400 picked up 4 tenths and a little over 3 mph. Those are gains that can also be seen on a chassis dyno to the tune of about 30-35hp. That's changing nothing else on the car at all. I'm not the only one that has seen gains like this with a factory stock car.
The funny part is that when I started experimenting with that test, I first used a 2 1/2" Flowmaster Force II kit with their transverse chamber muffler, which is said to be resitrictive. Comparing that to the Gardner reproduction 2 1/4" exhaust and still coming out with those gains is making a statement.
I found even more gains when I switched to the Pypes 2 1/2" transverse system and their race-pro transverse muffler.
There is a huge reason why everyone in Pure Stock is using the max allowed 2 1/2" mandrel systems on the cars. If it wasn't worth anything we'd all be running Gardner stuff. Most all those guys also see the same gains I found on all types of various cars with different HP levels.

Anyway,
One of the worst things you can do coming right off the exhaust manifolds is have a 90 degree crush bend. It's a HP killer! I've seen that comparison with 2 1/2' piping and it's been talked about numerous times on this forum and the difference is eye opening. When you use 2 1/4" pipe the difference is even worse.

There is a lot to be found here, but from the sound of it, and for what you're doing, I don't know if you want to go chasing this stuff. If it's just a cruiser you want to drive and enjoy, I wouldn't worry about it.

[b-man]

Close to a 20% increase in area going from 2.25” to 2.50” pipes. That little quarter inch increase in diameter adds a lot of area for needed gas flow. Also the quality of the bends in the 2-1/4” system are likely not that great, most if not all stock replacement systems are crush bent not mandrel bent. Makes a lot of difference. So your 2-1/4” system is choked down to maybe the equivalent of a 2” mandrel bent system, it’s just too small no matter how you slice it.

Coupled with going to better mufflers you’ll gain horsepower no doubt. Not going with headers is fully understandable as they’re more trouble than they’re worth in this application, the factory manifolds are more than fine for what you’re doing.

Sending the distributor or a spare one out for a professional recurve will pay dividends as well.

If you don’t like the sluggish performance you’re going to have do some work and spend some cash, changing your air cleaner won’t get you what you’re after.

[tjs72lemans]

Yes, this 2 1/4" system is crush bent and I can see your points of restriction. I will never run the car at the strip, so the last tenth I can get won't bother me. But, I was really hoping for something more performance wise out of this 400. Since it's actually built better than stock, I'm surprised I can't burn the tires from a stop though. Maybe these never did when new.? The torque converter is new, but just a stock replacement. I actually know nothing about it. I just told the trans rebuilder to order me a new one with no high stall for strictly a street cruiser.
So, I'm not sure if going to the expense of replacing my new 2 1/4" crush bent with 2 1/2" mandrel bent is worth the expense of what I'm lacking. But, as we all seek the best performance and fun in seat of the pants fun, I have to evaluate that.

[b-man]

You might be only a tune up away from spinning the tires, doing up the distributor curve might be something that noticeably improves performance. The stock ignition curves stink.

Spinning them longer will happen once you put a good exhaust on it.

The stock exhaust is always the first thing you change out, if you like it quiet and are happy with just cruising leave it be.

If not then you already know what to do.

[F ROCK]

I'm betting the timing is retarded. Give that dist a little clockwise twist...and see what happens

[mrmark1957]

I had a 73 Grand Am with the low compression 400 and 3.23's that unfortunately I never took to the track. I put a Summit 2800 cam into it. Butt meter said a SLIGHT performance increase over the stock 066 cam. The car had a tach and the difference was mostly between 3500 rpm and the 4500 rpm shift point. Just revved through that rpm area a little quicker. I then replaced the stock exhaust log manifolds with the Ram Air reproduction 2 1/2 inch outlet units, their 2 1/2 inch mandrel headpipes, #17749 Dynomax mufflers, and their 2 1/2 inch mandrel bent tailpipes. The car was noticeably faster full throttle, went through the 3500 to 4500 rpm zone much quicker, and felt ALMOST powerful accelerating full throttle from a dead stop. I would have guessed the cam added 10 horsepower over the stock rated 230 and the exhaust maybe 20 to 25 more.

[SD455DJ]

Originally Posted by Formulajones

The only problem with flipping the lid is it now takes the crown of the lid and tapers it in toward the carb, this is usually a HP killer for a couple reasons. One is putting the lid closer to the air horn, the other is the direction of air.

Most likely the reason for a gain, and this gets back to why the pure stock guys are putting taller filters in, is because you've now exposed more filter area around the circumference of the base. The same thing is accomplished with a taller filter that simply lifts the lid up, and still keeps the lid in it's proper upright position. This still helps direct airflow properly, and also keeps the lid further away from the air horn. This method actually works better than the lid flip deal.

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

[dataway]

Did they change the OEM pipe size between 68 and 72? I thought the OEM pipe size for a non-HO or RA, 400 (like the YS) with an auto was 2" OD (at the tail pipe).