[tjs72lemans]

I restored my 72 Lemans vert and the original 400 engine was rebuilt mostly stock, except a 701 Voodoo cam and hei ignition. The dyno came in at 308 hp and 400 max ft lbs torque. I also put stock exhaust on. It has a 400 turbo auto. The real issue for me is it seems sluggish. I was expecting power similar to my 350 in my Camaro. Most of my present and past hot rods have sported open element air cleaners, because they seem to breathe better and less restricted. I'm considering either using my dual snorkel for car shows only and replacing with an open element or flipping the lid like in the old days to allow more air all around the dual snorkel. Would you agree the dual snorkel is a restricted type of filter? Anyone test any of this?

[ta man]

Either air cleaner will not make a huge difference in power. Stock exhaust will eat up horsepower. What is your gearing and carb?

[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

[Matt Meaney]

back in the day, i took the log manifolds and stock exhaust off my '72. replaced it with headers and 3" pipes. picked up a full second and almost 5 mph with no other changes. including leaving the dual snorkel air cleaner on. went from 13.8's to 12.7's.

[SRR]

Any head work? HEI re-curved?

[b-man]

You’ll see a big difference replacing the stock exhaust with a 2-1/2” mandrel bent exhaust and whatever free flowing mufflers you prefer.

The dual snorkel air cleaner isn’t restricting your engine’s breathing it’s your exhaust. The stock exhaust is always the first thing you upgrade from, even if you’re keeping the log manifolds.

Your Le Mans likely has a 2.78 rear gear which isn’t really going to help that 400 move a car that weighs close to 4000 pounds, convertibles are heavy.

[Schurkey]

NASCAR teams figured out that hot underhood air was detrimental to performance in the late '50s if not before.

Never understood why folks would put an open-element air cleaner on a vehicle, when the Treasure Yards are full of air cleaner housings already set-up for cold air intake from the radiator support, or nearby.

[tjs72lemans]

Since I did absolutely everything in my garage on this frame off, I didn't want to drive open exhaust downtown to a garage to do that. So, I wanted something that I knew would fit and have no interference (had no exhaust to go by when purchased in parts). Therefore I just bought a stock system with stock mufflers and installed myself on my back. It sounds quiet and the tips out the side have the sound I want. I figured if stock configuration was 250 hp and I'm now at 308 hp, there's not much difference to worry about with exhaust. Maybe I'm wrong.

No recurve to hei. Rear end is stock 3:23. Stock 4 bbl rebuilt by Cliff that runs and performs great. The motor was bored out .03 and stock rebuilt heads with no work and roller tip rockers. The sad point is the stock 8.2 compression ratio was whistled on the dyno at 7.8. I also have stock manifolds.

If I thought it would really make a difference, I would take it down to the local shop now and ask to replace with bigger tube exhaust. Not sure if that would also mean getting different mufflers than the stock style too. ?

[b-man]

The stock restrictive exhaust is the biggest thing hindering performance. New free flowing mufflers are needed along with it, my favorite for quiet and low restriction is the Walker Dynomax 17749 20” long muffler.

A recurve of the distributor would also be a big help.

You’d be surprised what having a more performance oriented ignition curve can do, coupled with a good exhaust it should feel like a different car.

[NeighborsComplaint]

I run a Stock dual snorkel and my butt dunk says I lose 10 + hp compared to no air cleaner or an open element air cleaner. I’ve tried a low restriction element and also no element in the dual snorkel and they run the same so it’s the dual snorkel housing that’s the restriction. With the dual snorkel, it spins the tires about 50’ from a 20 mph roll. With an open element or no air cleaner. It spins the tires as long as I’m on the throttle. Or hit the redline. I’ve found replacing the lid with a standard 14” lid works as well as an open element and keeps the OEM look

[NeighborsComplaint]

Originally Posted by NeighborsComplaint

my butt dunk says I lose 10 + hp

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

[leeklm]

Originally Posted by b-man

The stock restrictive exhaust is the biggest thing hindering performance. New free flowing mufflers are needed along with it, my favorite for quiet and low restriction is the Walker Dynomax 17749 20” long muffler.

A recurve of the distributor would also be a big help.

You’d be surprised what having a more performance oriented ignition curve can do, coupled with a good exhaust it should feel like a different car.

Just a personal observation on a recent project... I am a big fan of the dynomax turbo and ultraflow. Helping a buddy with his 389 stock 335hp dyno build and installed RA exhaust manifolds along with 2.5" pipes, H, and the long case 17749 mufflers. I like quiet, but this combo was a little too quiet for my liking. Would have been interesting to try this setup with no H pipe. Might have given it just a little muscle car sound.


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[b-man]

Originally Posted by leeklm

Just a personal observation on a recent project... I am a big fan of the dynomax turbo and ultraflow. Helping a buddy with his 389 stock 335hp dyno build and installed RA exhaust manifolds along with 2.5" pipes, H, and the long case 17749 mufflers. I like quiet, but this combo was a little too quiet for my liking. Would have been interesting to try this setup with no H pipe. Might have given it just a little muscle car sound.

You can replace the 20” 17749 mufflers with 14” 17734 mufflers for a more muscular sound. A little more restrictive muffler but probably not enough difference to be concerned with.

I bought a new exhaust for my VW project and it came with a 17734 muffler, go figure.

[Formulajones]

Originally Posted by b-man

You can replace the 20” 17749 mufflers with 14” 17734 mufflers for a more muscular sound. A little more restrictive muffler but probably not enough difference to be concerned with.

I bought a new exhaust for my VW project and it came with a 17734 muffler, go figure.

I'm running the A-1 Sidewinder setup on our bug with the hidden tailpipe and it uses the welded case Dynomax. Looks like the Ultraflow.

[ZeGermanHam]

Engine Masters season 2, episode 27 tested nineteen different filter combinations on a 760hp BBC. A factory style dual snorkel came out at 15th worst, killing 53hp compared to baseline. They estimated it would be suitable to run on something making up to around 390hp. An open 14x3" K&N filter with drop base killed 12.7hp compared to baseline. An open 14x3" paper filter with standard (i.e., non-drop) base killed 10.1hp relative to baseline.

A dyno cell is not the same thing as an engine bay, so it's not always apples to apples, but there are differences for sure. The Engine Masters episode is definitely worth a watch. There are some surprises in there.

[GTOLou]

Originally Posted by ZeGermanHam

Engine Masters season 2, episode 27 tested nineteen different filter combinations on a 760hp BBC. A factory style dual snorkel came out at 15th worst, killing 53hp compared to baseline. They estimated it would be suitable to run on something making up to around 390hp. An open 14x3" K&N filter with drop base killed 12.7hp compared to baseline. An open 14x3" paper filter with standard (i.e., non-drop) base killed 10.1hp relative to baseline.

A dyno cell is not the same thing as an engine bay, so it's not always apples to apples, but there are differences for sure. The Engine Masters episode is definitely worth a watch. There are some surprises in there.

They also flipped the top on the dual snorkle and it came out far better. Easy way is to run that dual snorkle w/ a taller filter element and it'll work out fine.

[GTOLou]

snorkel* lol.

[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.