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#1
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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 (can’t 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 didn’t 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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468/TKO600 Ford thru bolt equipped 64 Tempest Custom. Custom Nocturne Blue with black interior. |
#2
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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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468/TKO600 Ford thru bolt equipped 64 Tempest Custom. Custom Nocturne Blue with black interior. |
#3
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I posted my independent testing results about 6 weeks ago, on your other thread. Nothing new to add.
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'73 T/A (clone). Low budget stock headed 8.3:1 455, 222/242 116lsa .443/.435 cam. FAST Sportsman EFI, 315rwhp/385rwtq on 87 octane. 13.12 @103.2, 1.91 60'. '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 |
#4
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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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Mick Batson 1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon. |
#5
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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. |
#6
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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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#7
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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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1967 Firebird 462 580hp/590ftlbs 1962 Pontiac Catalina Safari Swapped in Turd of an Olds 455 Owner/Creator Catfish Motorsports https://www.youtube.com/@CatfishMotorsports |
#8
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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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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
#9
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Quote:
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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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. Last edited by Tom Vaught; 05-26-2020 at 12:08 PM. |
#10
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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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frittering and wasting the hours in an off hand way.... 1969 GTO, 455ci, 230/236 Pontiac Dude's "Butcher Special" Comp hyd roller cam with Crower HIPPO solid roller lifters, Q-jet, Edelbrock P4B-QJ, Doug's headers, ported 6X-8 (97cc) heads, TKO600, 3.73 geared Eaton Tru-Trac 8.5", hydroboost, rear disc brakes......and my greatest mechanical feat....a new heater core. |
#11
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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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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#12
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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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77 Trans Am, 469 w/ported E-Heads via Kauffman, matched HSD intake, Butler Performance forged rotating assembly, Comp custom hyd roller, Q-jet, Art Carr 200 4R, 3.42s, 3 inch exhaust w/Doug's cutouts, D.U.I. Ignition. 7.40 in the 8th, 11.61@116.07 in the quarter...still tuning. |
#13
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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. |
#14
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Quote:
This topic has been beaten to death. No offense to the muffler shop guy, but I wouldn’t take his word as the ultimate authority on performance.
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1965 Pontiac LeMans. M21, 3.73 in a 12 bolt, Kauffman 461. |
#15
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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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#16
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My car is pretty quiet inside with full 3 inch exhaust..I have a video somewhere on this site.
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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
#17
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Well..
Quote:
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“Nothing in the world can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent. The slogan Press On! has solved and always will solve the problems of the human race.” ― Calvin Coolidge |
#18
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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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468/TKO600 Ford thru bolt equipped 64 Tempest Custom. Custom Nocturne Blue with black interior. |
#19
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Quote:
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 |
#20
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Quote:
One solution is 3" back to the mufflers, then 2.5 over the axle Sent from my SM-T817V using Tapatalk |
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