Exhaust help 2.5 vs 3"
 

So the time ol question of 2.5 vs 3". I have a 66 lemans and building a 461 stroker for it planning around 500 hp nothing crazy. I have kids and a wife who will be riding in the car also. I previously bought a flowmaster 1041 3" kit but I'm having second thoughts. I don't want obnoxiously loud and a lot of drone and think going to 2.5 might be the way to go. Fortunately I have a friend also building a 67 who will take the 3" kit off my hands if I choose to go with 2.5" so.i want be taking much loss. What are your thoughts.

500hp is fine with 2.5" pipe and some longer mufflers on there for the family. Forget the flowmasters. A 2.5" pypes pipe kit and their quieter option mufflers - or get mufflers then from dynomax or borla - for a good no drone sound.

I would go 2.5” not only to reduce the sound level but for ease of fitment as well as ground clearance.

Flowmaster mufflers never on a street car but their aluminized steel mandrel bent 2.5” exhaust kit is very nice. Get the Dynomax 17749 Super Turbo mufflers and you’ll have the performance you want and keep your family from hating your car. :)

Copy that. I was never considering running flowmaster mufflers after watching all the engine masters episodes and reading this forum. Looking at either the flowmaster 817412 and then selling mufflers for some money back as I like the side exit look or looking at the pypes sga40 kit with their turbo mufflers or flowmaster 17107 kit and getting some turbo mufflers. The problem.is I definitely want a good idle but I don't want obnoxiously loud just for the sake of being loud.

I have a 3" with X and Ultraflows and is is fairly quiet no drone and almost as much power as open headers on my 78. And that is even with the additional weight of the exhaust system. 525-550 HP. Having a 3" H 3" Flows and 2.5 mandrel tailpipes did hurt performance.

How much of a performance hit did you take?

I'm building a much healthier engine currently and I'm currently running a 2.5" mandrel bent pypes system with the pypes mufflers replaced with Magnaflows.

I have great ground clearance with this system, so if the performance hit isn't extreme, I'll likely stick with it.

Ok well I bought a flowmaster 817412 kit from their scratch and dent section on ebay for $600. Sold my 3" kit for $350 to my buddy and I'll sell the flowmaster super 40s from the kit for half price and probably gonna try out the cherry bomb salutes which are essentially a magnaflow knockoff and are $36 each.

Scratch the cherry bombs I just saw how much cheaper the 2.5 inch dynomax super turbos are. I wrote them off on the 3" because I didn't want to spend nearly $150 per muffler, the 2.5" ones P/N 17734 are only $60 each. Much more palatable.

The 17734 are only 14” long if I’m not mistaken, noticeably louder than the 20” 17749.

I had the 17734 mufflers on a ‘76 T/A and they were fine because that’s all I had room for under the floor pans but on a Le Mans I’d get the bigger quieter better flowing 17749s.

I bought a merged exhaust recently for one of my VWs and coincidentally it came with a 17734 muffler. :)

I picked up 2 17734s for $32 & $38 on the 'Other Sellers' discount tab. Not installed so no reviews.

Well my thought was that I dont want it super loud but I do want people to know its not stock. So I figured that the shorter ones would be a little louder but still reasonable. Do you really think the longer cases flow better?

The 17734 and 17749 were both tested in Jim Hand’s muffler shootout and the 17749 mufflers made more power. The bigger case was less of a flow restriction, bonus they’re quieter as well.

When I ran the 17734 mufflers on my T/A I had 2-1/2” pipes to the mufflers and 2-1/4” tailpipes. The car sounded powerful even with the 7.6:1 compression somewhat anemic 185 hp stock 400.

Pushing close to 500 hp they might be too annoying, that’s my take. The camshaft in a 500 horsepower 461 will provide the sound, overly loud mufflers will not be necessary

Copy that b-man. Sounds like I'll go with the 17749 ones.

Just curious as I'm driving my self crazy listening to sound clips. Does anyone a have a magnaflow style muffler and/or a dynomax super turbo sound clip or video on their car?

What mufflers?

That video is with super turbos 17770

Thank you

Can anyone confirm the newer super turbos are full size are the way through. Was looking at the 17749 and 17734 options and saw some reviews saying they neck down to 2" inside. Any body else know for sure?

Here is a dyno test I did on a mild, low compression (less than 8.0:1) 455 with stock heads, with headers.

First test had 2.5" pipes from the headers to a set of 3" FlowMasters, then to 2.25" tailpipes.

Second test is full 3" pipe, 3" 14" case Borlas ProXS mufflers, to mandrel bent 3" tailpipes. There is a 2.5" H-pipe ahead of the mufflers. First pull this combo made more power across the tested range, but the AFR leaned out big time. The test shown is after going several steps smaller on the primary metering rods (Qjet).

It would have been interesting to see the 3" system with 2.5 tailpipes. I initially wanted the full 3" on my own 73( 461 9.5CR 232 238 HR 260 SD CNC heads and 1 3/4" dougs but my other 2 cars with 3" are loud AF.

I was hoping to run 2.5 muffs and tailpipes after a 3" pypes X pipe.. just for sake of keeping the noise down and easier fitting tailpipes than the 3" .

I spray another 200 so the 3" tails may prove beneficial.

How do.you like the Borla XS and the 3" system .? How loud , drone? Etc..
The XS were my choice for 3" dur to their slim case design that gives good ground clearance for a 3" muffler.

Thanks
Peter

My plan is to use the 2.5" flowmaster kit I got with some free flowing turbos or cherry bomb salute and then also have 3" cutouts before niecking down the the 2.5 kit so I can uncork it for the strip while being reasonable on the street. Kinda the beat of both worlds

"How do.you like the Borla XS and the 3" system .? How loud , drone? Etc..
The XS were my choice for 3" dur to their slim case design that gives good ground clearance for a 3" muffler."

They are ok, not very loud. They drone at around 45-55mph in my car. Here is how they sound from the outside: https://youtu.be/H0UPbZH9wfY?si=dBuUTmfkvbjYXjFB

I have large case DynoMax Welded UltraFlows (3") on another car (making ~100rwhp more) and LOVE them. I had the large case 3" RacePros on the car, and HATED them with a passion - super-raspy at full throttle, just obnoxious to my ears - but surprisingly quiet at idle.

Photo of my exhaust system attached

"with some free flowing turbos or cherry bomb salute and then also have 3" cutouts before niecking down the the 2.5 kit so I can uncork it for the strip while being reasonable on the street. Kinda the beat of both worlds"

or the worst of both worlds. If you tune the car to run best with the mufflers, then it will be really lean and run like crap when you open the cutouts. If you tune it for open exhaust, then it will be pig-rich when you close the cutouts. IMHO, the "best of both worlds" is using a quality muffler (welded UltraFlow, AP Xlerator, MagnaFlow, etc.) with a straight through design - it will make virtually the same power as open exhaust, and you only have one tune to worry about.

Its really weird the sound of the 3" XS Borlas on your car, I have put em on BBC and high strung SBC, they sounded completely different. Do you have a h pipe or x pipe? Probably the cam make it sounds quite different too

When you say large case Ultra flows , we ve used em profusely on older builds when they first came out. MY experience with magnaflow is they dont age well , I mean they sound mellow and fantastic when you put em on. But the glassmat packing inside gets packed rather quick.

Large case like more than 14 inches? Thats the main issue on Second gens , very hard to fit more than 14" muffs under the cars. Some guys were able to fit 17" muffler bodies under a second gen...

I ran a bunch of transverse systems in the past with limited success ( customers not liking the sound compared to " true duals") but sure liked the ground clearance though.

Thrush /dynomax has a super cheap transverse system that sounds a little tinny for me but decent material for like 300$ complete. Its a great system for 1st gens .

What a dilemma , its not so much about the sound quality but quietness, no drone and not leaving too much on the table either.


Peter

Peter,

"Do you have a h pipe or x pipe?" it has a 2.5" H-pipe.

"Large case like more than 14 inches?" Yes, 20", on a '72 A-body, plenty of room. https://www.summitracing.com/parts/WLK-17547 Replaced MVR36 RacePros (no longer available, I believe, 18" case, 3").

"What a dilemma , its not so much about the sound quality but quietness, no drone and not leaving too much on the table either." Yes sir!! I've pestered Tom Hand with muffler questions for over 2 decades now! On my '67 Firebird I did an experiment with Tom - he sent me a pair of the 3" Xlerators (still Georlich back then), 18" long cases I believe they were. I actually cut notches into them, welding-closed the "wounds", to make the mufflers fit my floorboard a bit better. My muffler guy was able to get them to fit my '67 Firebird.

It HAD 3" FlowMasters on it. The reduction in noise was astonishing! E.T. dropped nearly a tenth, and trap speed was up over 1mph. It also had a Dr. Gas X, but that was used with both mufflers.

As Lee already posted, I too also found the go to muffler to be the Dynomax Ultraflow welded cases for me. Relatively mild sound that idles and cruises nice, no drone, they do get a little louder at WOT as you would expect but that's typical. They are a straight through design and from what I've seen on dyno's and my own track testing they really don't give up much of anything, and I have electric cutouts on just about every car here.

I have a pair on my 786hp Chevelle with a complete 3" system and Dr. Gas X and 3" torque tech tails. It's very mild at cruise, easy conversations with passengers. Same exact system I ran on the previous engine that made 608hp and the level of noise difference between the 2 engines has hardly changed if at all, and they both use the same headers.

I run Dynomax on 2 other cars as well and have been happy with those. Some other cars have different setups and different systems, some transverse, some pypes etc....

Either one of you have a sound clip? How do yo think the long case cherry bomb salutes would compare? Theire stainless straight through and half the cost

I'll have to shoot a video and post on my channel for a current sound clip. There are a bunch of older sound clips that are still current on most of the cars with descriptions on my channel I can link to when a get a computer.

I haven't known anyone that has run cherry bombs in decades since mufflers now have become more refined with better high flowing design and sound control. Used to run those things in the 60's and 70's and they are very cackly and obnoxious but we've also gotten older since then.

Hey Jones, I was able to find your channel through the link in your description.

The cherry bomb salutes aren't a regular glasspack they are essentially a magnaflow knockoff with an oval case and a straight through perforated tube and steel wool and fiberglass packing. They're also under 40 bucks each.

I'll look those up, ya have me curious now. When you said cherry bombs that's an old name from 50 years ago so I immediately thought of, well, you know, the old cherry bombs lol. Which are still made by the way.

Oh ya, I've ran those on my old skylark and my k5 and while cool and sound good they are loud. I may be getting old but I like to hear myself think while driving.