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Old 10-21-2019, 07:49 PM
PDC PDC is offline
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Default HP Loss with Flowmaster 40s?

I’ve run into a few threads that claim Flowmaster mufflers (and they make about a dozen different versions ...) literally CHOKE hp. I’ve also run into a few threads that suggest that suggest the ‘Original’ 40 series are worth ‘maybe’ 5-6 peak HP loss, if that.

So - I’m wondering: how bad are the original 40 Series Flowmaster mufflers - particularly the 3” version with full 3” dual exhaust (with an ‘H’ pipe) from the headers to the tailpipes?

I’ve got a mildly built 455, HFT cam, Box Stock Edelbrock D-Ports, Doug’s Headers, full length 3” exhaust with H pipe and Flowmaster 40s. Wondering if a 3” straight-thru design like the Magnaflow or the Pypes Race Pro would really be worth any measurable HP.

FWIW - I really like the sound of the 40s on this particular car. Lots of low-end, loud, smooth at higher RPMs. I don’t mind the interior drone. Just wondering if they really are choking off a ton of HP.

Thanks!

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Old 10-21-2019, 09:18 PM
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Might be useful as a reference:

http://www.pontiacstreetperformance....p/exhaust.html

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Old 10-22-2019, 02:48 AM
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I went from FM 40s to Pypes Race Pros and they sounded absolutely terrible. Then went to the FM 10s.

If you do choose to try something else, don't waste your time with the Pypes. I haven't tried the MF myself yet tho.

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Old 10-22-2019, 10:30 AM
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I've been around and back again with that on 2 different cars here and as far as track performance goes there was no discernable difference.

I've had my Chevelle over 30 years, raced it a ton, makes 600 hp and runs mid 11's with a complete 3" exhaust with a Dr. Gas X pipe. I've had various mufflers on that thing. Currently has an older set of super 40's on it. There wasn't a muffler that made any real change for the car other than sound level. Honestly I'm growing tired of the drone the 40's make, So I'll be going back to my favorite muffler of choice, a set of Dynomax Ultraflows.

I went through similar testing with my 70 Formula on the transverse systems. Started with an original Garner system on the car, switched to a Flowmaster Force II system which was not just a muffler change to their 40 series design transverse muffler, but an increase in pipe size to 2 1/2". Car picked up 4 tenths and more than 3 mph.
Wanting more I switched to a PYPES transverse system with there race pro designed straight through transverse muffler, and now an "X" cross over, but still the same 2 1/2" pipe. The car ran identical ET and MPH, no change what so ever.

With that said, you might see some change on a chassis dyno but from my experience with actual testing at the track, it hasn't been enough to see on a time slip, even on my 600 hp car. So I tend to choose the noise level I prefer to live with on the street, and if I want a performance gain at the track, I just flip the switch and open the cutouts. That DOES make a difference.

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Old 10-22-2019, 10:41 AM
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PDC,
""I’ve got a mildly built 455, HFT cam, Box Stock Edelbrock D-Ports, Doug’s Headers, full length 3” exhaust with H pipe and Flowmaster 40s. Wondering if a 3” straight-thru design like the Magnaflow or the Pypes Race Pro would really be worth any measurable HP.""

If it is a mild build and it's a streetcar this MotorTrend engine masters video shows going from 2.5" to 3" pipe and mufflers and losing 25hp 50 lb tq on the dyno. Even a (claimed) bad choking 3" would lose less than 1/2 of that loss maybe 12hp?
Unless you are racing your car at the track and hated the sound of the exhaust I might entertain other options, but if you like the sound of your exhaust and you aren't leaving 50hp on the table, enjoy your car as is. JMHO


https://www.youtube.com/watch?v=_PVXvHkr-Vs
"

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Old 10-22-2019, 01:52 PM
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Great video there. Yes, LOTS of misinformation floating around the internet, muffler shops, and bar stools. It appears as thought I'd see a bigger choke with the 40 series on a 2-1/2" system, and with the increase flow of the 3" system, differences in mufflers are not as pronounced.

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Old 10-23-2019, 12:14 AM
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2.5" mid pipes feeding into 3" Flowmasters (I think they were 40's, never checked), and into 2.25" tailpipes.

vs.

3" mid pipes into 3" Borla ProXS to 3" tailpipes.

Mild 455, stock huge-chamber 66 heads (about 7.8:1 with the pistons down .020"ish), low lift mild cam, tri-Y headers.


Second dyno is when a set of 19 year old FM 40's were replaced with Race Pros. Like 92GTA, I didn't like the sound of the RP's, but they ran a LOT better.
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'67 Firebird [sold], ; 11.27 @ 119.61, 7.167 @ 96.07, with UD 280/280 (108LSA/ 109 ICL)solid cam. [1.537, 7.233 @93.61, 11.46 @ 115.4 w/ old UD 288/296 108 hydraulic cam] Feb '05 HPP, home-ported "16" D-ports, dished pistons (pump gas only), 3.42 gears, 275/60 DR's, 750DP, T2, full exhaust

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Old 10-23-2019, 07:22 AM
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Lee, I know you have posted on this topic before, and I don’t doubt the dyno sheets. But I do wonder how much improvement was attributed to the move from 2-1/2” to 3” pipe. I also recall a different post of yours where (I believe) you said one of the Flowmasters was rattling - likely one of the deflectors loose and shifting out of place. This definitely helps, but it would be interesting to see the original 40 series (which I ‘think’ is one of FMs less restrictive designs) tested back to back against a Race Pro (for example) with both a full 2-1/2” and then a full 3” system to see how much change is attributable to the muffler design and how much the larger diameter makes up for that diff. The motor trend masters video that Jim posted suggests exhaust diameter plays a really big role here.

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Old 10-23-2019, 09:59 AM
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Quote:
Originally Posted by PDC View Post
Lee, I know you have posted on this topic before, and I don’t doubt the dyno sheets. But I do wonder how much improvement was attributed to the move from 2-1/2” to 3” pipe. I also recall a different post of yours where (I believe) you said one of the Flowmasters was rattling - likely one of the deflectors loose and shifting out of place. This definitely helps, but it would be interesting to see the original 40 series (which I ‘think’ is one of FMs less restrictive designs) tested back to back against a Race Pro (for example) with both a full 2-1/2” and then a full 3” system to see how much change is attributable to the muffler design and how much the larger diameter makes up for that diff. The motor trend masters video that Jim posted suggests exhaust diameter plays a really big role here.


PDC, Have you looked at this.
http://www.pontiacstreetperformance....p/exhaust.html

Lots of interesting stuff. I used the largest DynoMax I could fit.

Murf



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Old 10-23-2019, 10:01 AM
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PDC, my previous comment was that the old FMs were NOT rattling. No rattles, no change in sound (tone or loudness), no rust holes. I had long suspected that the topend power was lower than it should of been, as the car was a beast off the line but seemed to go flat at upper rpm. It wasn't until I saw the dyno results that I decided to try different mufflers.

This also a few years after I replaced the FM's (3", not sure what series, but rather loud) with 3" Goerlichs on my '67 Firebird. If you don't remember, that car basically ran a tenth quicker and 1mph faster after the change.

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'67 Firebird [sold], ; 11.27 @ 119.61, 7.167 @ 96.07, with UD 280/280 (108LSA/ 109 ICL)solid cam. [1.537, 7.233 @93.61, 11.46 @ 115.4 w/ old UD 288/296 108 hydraulic cam] Feb '05 HPP, home-ported "16" D-ports, dished pistons (pump gas only), 3.42 gears, 275/60 DR's, 750DP, T2, full exhaust

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Old 10-23-2019, 10:12 AM
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I may try those Goerlich - I’ve heard nothing but good things about them.

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Old 10-23-2019, 10:14 AM
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Murf - Yes - that’s a great article and God knows Jim Hand has the experience. But I believe his comparison testing was with 2-1/2” pipes and mufflers. I was wondering how much of that one might get back with a 3” system feeding 3” mufflers.

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Old 10-23-2019, 10:15 AM
78w72 78w72 is online now
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yes thats the same article as jim hand tested a bunch of mufflers in his book & the flowmasters were basically the worst flowing mufflers he tested. they sound good on lots of cars/engine combos if you like the chambered sound. i have a set of 2.5" on a 9:1 mild cam 400 78 t/a with full tails & i like the sound but they do have some drone.

race pros are the same basic design as the ultra flo's, both are a straight through muffler with a perforated pipe & the case packed with sound absorber. the race pros cost less & are about .25-.50 thinner so they can tuck up to the floor a little better. for those few that say they sound "terrible" there are a lot of people that like them. but again sound is all just subjective opinion, so you cant really go by a few that didnt like them on their specific engine combo.

i have the 3" race pros & a full 3" pypes kit with X & full tail pipes on a 500+hp 1972 firebird with a 10.75:1 old faithful roller cam & personally i love the sound. they are rather mellow at idle but still have a nice "pop," but when you get on it they really come alive & have an almost exotic car sound.

heres a vid of a short low rpm burnout & i will try to post another one of the car at the track... i don't hear anything remotely "terrible" about them. & you can hear the 78 t/a flowmasters on another vid i have on that youtube account but thats before tail pipes were installed.

https://www.youtube.com/watch?v=INO3b_DKQcs


Last edited by 78w72; 10-23-2019 at 10:51 AM.
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Old 10-23-2019, 10:49 AM
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Quote:
Originally Posted by PDC View Post
Murf - Yes - that’s a great article and God knows Jim Hand has the experience. But I believe his comparison testing was with 2-1/2” pipes and mufflers. I was wondering how much of that one might get back with a 3” system feeding 3” mufflers.


Hey, I never really noticed that he tested 2.5” instead of 3”.
Note though, that the difference in actual performance was less than .20 in the quarter from best to worst. That is with a 2.5 “ single exhaust. I can’t think that with 3” dual exhaust the FM’s could be too hard on performance.

Good luck in your quest!
Murf


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Old 10-23-2019, 11:33 AM
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Pipe diameter as eluded to plays a big roll, as I found out with track testing I posted above.

Going from crush bent 2 1/4" Garner exhaust, to 2 1/2" mandrel bent Flowmaster exhaust, both transverse systems, picked up my Firebird 4 tenths and over 3 mph. I touched absolutely nothing else on the car. The ole' track calculator shows that's at least a 30 hp gain, that's substantial.

When I switched to PYPES with their race pro transverse muffler that blows straight through, same pipe sizes, it did nothing for the car. Ran identical. Raced the car for about 6-7 years now with that Pypes system and have not been able to better it's best times.

Granted now this is a car that makes a smidge over 300hp at the wheels so it's not a power house, but I've tried all kinds of tricks to find that extra tenth to run that magic number I've been looking for without breaking the PS rules, so it's pretty well sorted out.

https://youtu.be/er1z7PpqsnY

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Old 10-23-2019, 12:17 PM
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That’s a good point. An exhaust that bottlenecks a 500+ hp car probably isn’t a problem for a 300 hp car.


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