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Old 05-25-2020, 11:53 PM
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Default Exhaust pipe diameter Engine Masters VS Pypes

The Engine Masters episode that did the comprehensive study of exhaust diameter proved that pretty much there was no such thing as too big an exhaust. I was talking to the guy at the muffler shop and told him my Dougs headers had 3.5 inch outlets with necked down 3 inch collectors. I told him I was going to buy the pypes kit without mufflers and use the Dynomax mufflers that everyone says have no drone (canít remember part number). He started telling me that he knew cars running in the 10s with 2.5 and that he would have a hard time getting me ground clearance with the 3 inch and that my performance would suffer with the 3 inch (Before anyone says anything I am aware I mentioned this conversation in another post). The impression I took away from the conversation was not performance loss or gain but that he didnít want the pain in the ass of installing the 3 inch system. Anyway I was about to place the order for my header back kit on Summit and I noticed that Pypes themselves told a customer in the tech section that their performance would suffer if they went 3 inch over 2.5. This is in direct contrast to what Engine Masters proved on the dyno. I know that 2.5 inch would probably be quieter and that I am not making 800 HP or anything like that but how can bigger exhaust hurt the performance? Please enlighten me.

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Old 05-26-2020, 12:05 AM
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No one really commented in the exhaust section and I am about to pull the trigger. I want actual facts about lost performance because of too much exhaust. Plus I have bought the G Force crossmember now so hiding 3 inch pipe should be no problem

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Old 05-26-2020, 02:41 AM
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If additional restriction was needed (like a smaller exhaust pipe) then no one would be drag racing with open headers. I've experimented with adding sections of the same size pipe trying to tune the open exhaust, but have never seen any improvement from 12" to 48" extensions. The tuner pipe didn't slow me down but didn't help either. On the 525ci drag car at events requiring mufflers, I run a little more than a tenth slower with race mufflers the same size as the collectors. I have a bridge to sell you if you believe that I could bolt on a smaller pipe and smaller muffler and not loose a bunch more.

As far as I'm concerned the theory of having too large of an exhaust is a wife's tale.

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Old 05-26-2020, 08:43 AM
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Agree with Lust4speed. I think it's just more internet jibber jabber.

If you don't mind the increase in noise and can deal with the tight space, there is no real harm in it.

It is true there are some 10 second cars with 2 1/2" exhaust, just look at the FAST series where 2 1/2" is mandated. But also look at how much HP they make to push those cars into the 10's with small exhaust. Not your typical build with 500+ cubes and 700-800 hp.

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Old 05-26-2020, 10:01 AM
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FYI,I have been running Dynomax on my bird for awhile with 2 1/2 all the way back over the axles.They were 14in.When I put my 434 RA V in the car with custom headers life changed!At 2000 my 14in were 86 dec,changed to 18in and it dropped to 84 dec and then went to a non performance 18in muffler and it went to 81.Still too much for my taste.The past engine was a 455 with long branch exhaust.FWIW.Tom

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Old 05-26-2020, 10:08 AM
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Im not saying you cant run into the 10s with a 2.5 inch system, but why bother? Plus maybe that was a 2000 lb car. Or one with cutouts.

You will 100% give up power over a 3" system. I don't think anyone would argue that. Now with that said, if a 3" system is a nightmare to install maybe you consider cutouts. Or go to 2.5 at the back of the system, which would affect power much less I think.


Also FWIW I believe its been proven that the place you lose the most power is right behind the collector when you go from a 3.5 to a 3. Would be even worse with a 2.5. They make gradual reducers which help. Something I wish I had known when I had my system built.

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Old 05-26-2020, 10:11 AM
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I tested a theory a few years ago on my car. The exhaust at the time consisted of 3 inch X pipe, cone reducers to 2.5 ultraflows and 2.5 inch tailpipes. Just by removing the tailpipes the car picked just over one tenth and 1 mph in the quarter mile. This was on a well tuned and tested car. Many at the time who were aware of the test thought there would be zero gains. app 550 to 570hp engine at the time.

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Old 05-26-2020, 10:45 AM
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One thing about most of the Engine Masters shows (I've seen each one) is that whatever results they come up with is based around whatever engine combo they happen to have bolted to the dyno. In most of those episodes they'll tell you, your results may vary.........

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Old 05-26-2020, 11:21 AM
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Quote:
Originally Posted by ta man View Post
I tested a theory a few years ago on my car. The exhaust at the time consisted of 3 inch X pipe, cone reducers to 2.5 ultraflows and 2.5 inch tailpipes. Just by removing the tailpipes the car picked just over one tenth and 1 mph in the quarter mile. This was on a well tuned and tested car. Many at the time who were aware of the test thought there would be zero gains. app 550 to 570hp engine at the time.
My JR Headers had 4 inch collectors and 2" equal length pipes before the collectors. The pipes were also positioned in a flat collector design. Maybe some remember that JR Flat Collector design.

From the 4" collectors I ran several feet of 4" tubing to custom reducers that fed the inlets of 3" Walker "long length" mufflers.

The pipes were retained on the vehicle using Marmon Flanges and Marmon Clamps. So in about 10 seconds I could swing the head pipes out of the way and have open collectors or drop the whole down pipe system (with the mufflers hanging still in place).

All that being said, I agree that even with 4" collectors and pipes to the mufflers, the car always was faster with the headers open.

Tom V.

I forgot to mention that I had down-turns immediately after the mufflers, no tailpipes.
So the difference in performance was not with the head pipe diameters or headers but totally in the Muffler
design from Walker. That is why the car has Tom Hand's VOE mufflers on the car today. I do stuff for reasons
as did Pontiac Engineers when they designed the VOE Mufflers many years ago. They work.

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Old 05-26-2020, 01:08 PM
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Quote:
Originally Posted by 64speed View Post
No one really commented in the exhaust section and I am about to pull the trigger. I want actual facts about lost performance because of too much exhaust. Plus I have bought the G Force crossmember now so hiding 3 inch pipe should be no problem
I posted my independent testing results about 6 weeks ago, on your other thread. Nothing new to add.

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Old 05-26-2020, 01:17 PM
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I posted my actual facts with a very good header system, 4" head pipes and Walker Mufflers.

Bigger head pipes buy you little when the cork is the mufflers.
When I was a National Tech Inspector for the SCCA we tuned for noise restrictions but still keeping as much performance as we could in the Muffler design.

Tom V.

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Old 05-26-2020, 01:28 PM
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I have Doug's 3 inch exhaust cutouts. So my headers run to a 3 inch extension, then the dumps...or, if the dumps are closed, it goes to a full 2.5 inch custom exhaust with an X pipe and dual 40 Series Flowmasters. Basically, I've either got the resistance of 3 inch (though much shorter and no mufflers) or the best 2.5 inch system you can buy.

My last dyno session, the most the car would make through the exhaust was 379.8RWHP.
With the 3 inch/dump, it made 407.33.

I like having a switch that can make the car go from civilized to outright insane. Passing a Prius with 469CID of open headers causes some pretty awesome facial expressions. I'd probably give up some of those 28hp if the 3 inch system went through mufflers, but not all of it. My experience confirms everything that Engine Masters already proved. Go with the big exhaust. Don't let a lazy guy at the shop talk you out of your top end performance.

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Old 05-26-2020, 03:02 PM
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Almost all bending machines used in a muffler shop don't come with 3 inch dies, that is the major reason they try to talk you out of 3 inch, is because they have no capacity to bend that size pipe.

The dies to go up to 3 inch used to be about $400 back in the 70s, so think currently they would be double that roughly. Factor in how many times they would be used to bend 3 inch pipe and it becomes pretty obvious why few muffler shops recommend 3 inch exhaust. The investment would never pay for the upgrade to the 3 inch dies, or if it ever did it would be quite far down the road.

Having worked at a muffler shop in the mid 70s I heard all the salesmanship excuses as to why your hot rod would do better with 2 1/4 or 2 1/2 inch pipes.

FWIW, The middle signature pic shows my 67 GTO dirt car, in the rules we were required to run cast iron exhaust on the cars. I substituted a set of RA III manifolds and ran the stock GTO head pipes, of course no mufflers. Engine was a 400 with an 068 camshaft in it.

In the middle of the season I wanted to see if opening up the exhaust would produce any more power. I was working at the muffler shop and we had no 3 inch pipe so instead I cut the ends off of 3 driveshafts to get 3 inch tubing. Because I couldn't bend it because of no dies I mitered all the corners, and welded the pipes back together to make the bends. 2, 90 degree off the manifolds and a slight kickout to go around the vacuum modulator. I terminated the exhaust just short of the rear axle. Even though I used short 2 inch sections of 2 1/4 inch pipe off of the manifolds into the 3 inch I was rewarded with feeling seat of the pants performance increases. 3 inch wasn't at all common back in those times, 2 1/2 was as big as anyone was using. 3 inch will help any engine, even a mostly stock 400 with a factory 068 camshaft and cast manifolds. I won 4 features that year after switching the exhaust to 3 inch.

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Old 05-26-2020, 03:07 PM
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Quote:
Originally Posted by Navy Horn 16 View Post
I
Passing a Prius with 469CID of open headers causes some pretty awesome ...
Even better when said Prius floors it on a 2 lane road when you try to pass. My 3 inch exhaust goes to 2 1/2 to get over the rear end and exists behind each rear tire - pointed directly at whoever Iím passing. (No x pipe)

This topic has been beaten to death. No offense to the muffler shop guy, but I wouldnít take his word as the ultimate authority on performance.

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Old 05-26-2020, 03:18 PM
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I can give a Tinkers damn about loosing 25-30 HP on a street car!I just want to be able to drive it a highway speed and listen to my radio!80 plus dec on a street car SUCKS!JMHO,Tom

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Old 05-26-2020, 03:25 PM
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Quote:
Originally Posted by 64speed View Post
The Engine Masters episode that did the comprehensive study of exhaust diameter proved that pretty much there was no such thing as too big an exhaust. I was talking to the guy at the muffler shop and told him my Dougs headers had 3.5 inch outlets with necked down 3 inch collectors. I told him I was going to buy the pypes kit without mufflers and use the Dynomax mufflers that everyone says have no drone (canít remember part number). He started telling me that he knew cars running in the 10s with 2.5 and that he would have a hard time getting me ground clearance with the 3 inch and that my performance would suffer with the 3 inch (Before anyone says anything I am aware I mentioned this conversation in another post). The impression I took away from the conversation was not performance loss or gain but that he didnít want the pain in the ass of installing the 3 inch system. Anyway I was about to place the order for my header back kit on Summit and I noticed that Pypes themselves told a customer in the tech section that their performance would suffer if they went 3 inch over 2.5. This is in direct contrast to what Engine Masters proved on the dyno. I know that 2.5 inch would probably be quieter and that I am not making 800 HP or anything like that but how can bigger exhaust hurt the performance? Please enlighten me.
He's complaining about installing a kit from Pypes? That's just lazy IMHO. Are you going to run tail pipes? My 462cu Skylark has a 3" on it with dumps at the axle and it is loud not to mention it blows dust and dirt everywhere, it's going to get 2 1/2 mandrel bent tailpipes and Dynomax mufflers. I switched a truck I had from Flowmasters to Dynomaxs and was very pleased, no more drone and they sounded great. The lowest point is going to be the collector so pipe size really isn't an issue unless your lowering a car...
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Old 05-26-2020, 03:48 PM
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I am going to run full pipes. The muffler is the dynomax 17229. All the reviews say you can hear the radio and have a conversation. I don’t want it to be so quiet it sounds like a mouse fart but I don’t want it to rattle my brains either. I thought he just didn’t want to mess with trying to clear the crossmember but the Gforce crossmember gives you plenty of room to tuck anything reasonable up against the floor. Anybody got any feedback on these mufflers?

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Old 05-26-2020, 04:49 PM
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Quote:
Originally Posted by 64speed View Post
I thought he just didnít want to mess with trying to clear the crossmember but the Gforce crossmember gives you plenty of room to tuck anything reasonable up against the floor.
If you're fitting an exhaust, the area of greatest concern is over the axle. Gotta
clear the housing itself, the shocks, control arms, control arm braces, and even
the gas tank. Everything else being relative, the transmission crossmember is
really a walk in the park.

It really looks like you have three choices.

1) Learn to live with ground clearance issues
2) Lose some HP (and associated bragging rights)
3) Find someone else that meets your expectations

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Old 05-26-2020, 05:12 PM
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Quote:
Originally Posted by 242177P View Post
If you're fitting an exhaust, the area of greatest concern is over the axle. Gotta

clear the housing itself, the shocks, control arms, control arm braces, and even

the gas tank. Everything else being relative, the transmission crossmember is

really a walk in the park.



It really looks like you have three choices.



1) Learn to live with ground clearance issues

2) Lose some HP (and associated bragging rights)

3) Find someone else that meets your expectations
Clearing wide tires also.

One solution is 3" back to the mufflers, then 2.5 over the axle

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Old 05-26-2020, 05:38 PM
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A system with mandrel bends a big plus and many local shops don't have a mandrel bender.

http://www.bobsmuffler.com/muffler_myths.htm



.

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