Right now I have the 2.25" exhaust with with flowmaster mufflers. I've heard the flowmasters are restrictive and I know the 2.25" is too small for my combo but I'm not sure if I should go with 2.5" or 3". I have 049 heads and comp cam 274 solid. This is a street car (not daily driver) but I would to visit the track once in a while. Thanks.

For a milder street car, I'd probably stick with a 2 1/2" system. It's gonna be quieter than a 3" system. If your gonna spend more time racing and are looking for the most possible ET with a decent amount of HP (550 and above), then the 3" would be a wise choice.

..what Todd said.
A mandrel bent 2.5" system (including tailpipes) with either an H or X pipe and straight thru mufflers (non chambered type) would certainly suffice.

Get an X-pipe and Magnaflows with your 2.5-inch setup. You'll be happier, it'll be quieter, and it'll go faster.

SP~!

I swapped a 2.5 system / no cross over / raven mufflers, full tail pipes to a full 3" system with scavenger colletors, H pipe, Dynomax ultraflows, 3"tail pipes out the back. With the car's new exhaust it runs the same times with the old system disconnected on open headers, also swapped a T400 for the blown 350 trans at the same time, all in all was worth maybe .2 in the quater on my ride. New system sound different, but not really "louder".

Thanks for the replies. Is an X or H pipe going to make a big difference in performance?

I'd say yes. It'd be cool to track test it before and after...I bet you'll see a difference. It'll sure be quieter too.

Scott Parkhurst~!

Another option is a 3 inch x-pipe and mufflers then reduce it to 2.5 inch tailpipes.

i was looking up lots of exhaust info a while back and i found a chart on one of the exhaust guys pages.. they recommend that you run dual 3" when you hit around 450 hp from what i remember. ill try to find the chart again..

http://www.newcovenant.com/speedcrafter/tech/Power/exhaust.html

there is a good link..

I ran 11.78 with open exhaust and slicks, I ran a best of 11.84 thru 3" exhaust with drag radials and worn out valve springs. The 3" exhaust is perfect for a 454 if you plan on track time.

i thought i would throw this in from personal experience......i built a 396 a few years back for a friend to put in his camaro......the engine being very mild 8.8 to 1 comp. 284 crane cam,stock cast iron intake, with 3.42 gears and 3000 stall and 3800 lbs car. during my test and tune to dial in the car before he got it back i got the times down to 14.40 flat at 93 mph on street tires and thru the full exhaust...

ya the full exhaust was 2 1/4" pipes with 22" glass packs and tail pipes out the rear.....i knew this exhaust was hindering but i was doing what i could to get it dial in for what he had.......there was no extra money for nothing at this point it was what it was........

....just got done running the 14.40 at 93.xx....with the exhaust uncorked from the cheap summit style headers the car ran 14.000 at 99.xx mph.....wow what a jump.......6 mph which is about 60 hp was in the exhaust......

another example was a 396 bbc it ran 12.18 at 110 mph with a 1.72 60 ft time on regular 275 60 15 tires and thru 2 1/2" pipes off the headers to a pair of cal. turbo mufflers..with turn downs...about 15 bucks each the mufflers was.......with the car uncorked the car would run in the 12.20's and the mph was still 110.xx.....but i think since i had a pretty good size cam 263/273 @ .050 and heads was ported....i think this allowed the engine to breath more then it needed and the exhaust allowed some much needed back pressure....because the e.t feel off some and so did the 60 ft times....


i kinda think it depends on each engine on what exhaust is needed........i have a 396 now that runs thru 2 1/2" pipes from headers to full boar mufflers (stainless steel welded) and have 2 1/4" tail pipes out back......it's running over 107 mph thru the 1/4......never had tried to uncork it to see if im giving up anything......honestly i dont think im giving anything up....with the dual pattern cam and ported heads....and headers.........im sure its breathing very well........

My .02 cents, I have a 402 pushing 366 hp and I installed mandrel bent 3 in pipes from stock manifolds into flowmaster series 40's and 2.5's out the rear. Car runs very well and sounds great. Just the right amount of back-pressure!

If you're going to all the trouble to replace it, I'd definitely get the 3.0". It doesn't necessarily have to be lounder. It depends on mufflers you choose. Use the biggest internal capacity ones you can find for less noise and low backpressure.

Not sure if you really need 3.0" right now...I've run extremely low 11's@123 with 2.5" and flowmasters on motor alone. On that 427 it didn't pick up much at all by uncapping, but as HP climbed with new motor combo it made huge difference. The 540" picked up literally 50 RWHP on the chassis dyno by uncapping the 3.0" Flowmasters!!! I had hoped the 3" pipes could handle it.

Pays to plan for upgrades! In fact I'm now trying to figure out how to get a 3.5"-or 4" oval setup under mine! Could save money by not doing it multiple times!


JIM

Hi Jim, I'll tell all of you if you're making a lot of power the 3" exhausts will definately help your power. My son's 540 is never uncapped, ran the same with 3" and 3 1/2" size exhaust and only lost 5 hundredths capped up with Borla XR-1 mufflers. These premium mufflers aren't that loud until the motor is opened up. The car runs low nines @ 147 MPH through the mufflers. Placement of these mufflers should be just forward of the rear wheels for best results. Cost a lot, work great, never wear out! The best working mufflers out there and they should work even better if you put a "X" pipe in them but it does change the exhaust note and my son didn't like the "X" pipe sound.

My freind and I both have pretty evenly matched 'Velles and he has the 3" and I have the 2.5" flowmasters with the same mufflers. Mine is fairly tame at idle, but louf when you get on it (sets off car alarms with the secondaries open). His is so loud you can't talk at idle. And when you get on it, its 2X as loud. His also sounds "hollow". Kind of like a new Mustang, even though its a 454. He can't even talk at a normal level inside the car. IMO, if its street go with 2.5". But, if you like loud, go 3". My $.02 worht.
Chris

Here is yet another example and my opinion. My combo (bottom of thread) originally had 2-1/2 duals with a H pipe, dynomax superturbo and tailpipes. By replacing that system with 3" duals, H pipe, 3" dynomax ultraflows with tailpies netted me an honest .15 seconds in the quarter and approx 2 mph. Now, when I compare todays system vs open headers, with open headers (1-3/4 X 3" no collector extension) my 60ft is actually .03-.04 sec slower, same at 660ft (.03 - .04 slower)and pretty much equal at the 1/4 mile, .01 sec either way. MPH is about 1 mph faster. BTW carb jetting/timing were optimized to achieve best ET's in both examples.

I think its important to look at the entire combo before jumping to any conclusion as follows;
With open headers the collector length on the headers are only about 5" past the 4 into 1 point. (short, where a extension may help).

Stall is only 2400 RPM, engine peak torque is a 4400 rpm,(I suspect a closed exhaust system helps the 60ft in this situation).Even after shifts the rpm's drop to 4100-4200rpm.

The second half (last 660ft) of the 1/4 mile the open headers definately pull better than the buttoned up exhaust system, but then again the rpm's are between 4500-6000.

For 2005 I will be running a 3200 stall with a shift drop to approx 4800 after shifts. Because of this mod and due to the fact now the launch RPM's/RPM after shift will be higher I believe I will see better benefits to open headers.


Test and tune to follow.

Sorry it's so long, just wanting to state all the facts.

Tailpipes can tone down a system quite abit including the interior especially at idle/slow speeds.

Originally posted by boldm:
Tailpipes can tone down a system quite abit including the interior especially at idle/slow speeds.
I definitely agree. Too many people dump their exhaust system in front of the rear axle and that makes for a lot of resonance. Tailpipes make a huge difference.

RedSS454, What kind of mufflers do you and your friend have? If they are flowmasters then i understand the noise. The 3" and 3 1/2" Borlas XR-1s aren't that loud if you place them near the rear.

Flowmaster 40's. I am thinking to swap to something a little louder , but at idleing I can still talk at a reasonable tone over. They would also need to bolt inplace of the old flow's. I like the flowmasters. Good throaty tone and not annoying. My freinds is annoying on the other hand. I don't get how the tone is different being that they are the same series. Could his exhaust (3") be too big? How do those Boralas sound? There is a guy with a SVT Mustang thats really hot-rodded and sounds pretty good (for a mustang) and i was thinking what it would do for a BB.
Chris

Hey All,

I felt like I was home when I saw this thread! Have of the topics is/has been stuff that I've been going through. My 70'454 Chevelle had a stock exhaust system that was recently changed to
a /header/3inch/2chamber flow system/dumps by rear axle (sadly). The bugger is LOUD, sets off parked car alarms all the time. The thing pops like crazy slowing down too.

I personally think its neat to see the exhaust dump underneath, but having that bugger reverberate off the ground gets old quick (I feel like I need ear plugs when I drive). I stopped by a friends shop today about adding an x-pipe (still in debate or x or h, h would be alot cheaper and easier.. but if x performs betta.. wait this feels like a math equation), and maybe changing the exhaust from the flows to DynoMaxs or something (still in debate) and having it dump out the rear / up high hiddin by bumper.

If you do plan to beef up the engine alot more, it would be wise to plan ahead and just do the exhaust once, so Id say go for the 3' as well. If you don't plan on packing in the hp, having to big of pipes will do more damage then good for your block.

One big advantage of going to a 3" system is that it will allow for future improvements. Should you decide to mod the engine, you will be "exhaust ready".
If you are concerned with noise, make it an X-pipe setup, with 3" Dynomax turbos and 3" tail pipes.
As my engine guy has always said....if it can't *****, it can's git!
BTW...a DR. Gas X-kit, with the DynoMax muffs and tail pipes fro Torque tech will set you back $600+ bucks, but in my estimation, worth it.
Ron

I may be wrong, but I believe the Dynomax 3" turbos have a necked down inside tube of 2.5". I think the Summit Turbos also have necked down inside pipes. Kind of makes the 3" tails useless, unless future muffler updates are expected. Even then, I think the gases will be cooled enough for 2.5" tails.

Bill

I have used the Dynomax 3" turbos in the past, and they were 3" all the way through.
These are the BIG ones, not the ones that are the same size as the regular turbo muffs.
Like turbos on steriods! Huge on the outside.
Ron

For what it's worth, I've never seen an engine lose power with exhaust pipes and mufflers that were too large a diameter. I've also never seen a case where open-header power was not improved with collector extensions.

DF

Ron,

My guess is you are talking the Dynomax 3" offset/offset 17792's with a 16" body and 23 overall length? These will have a 3" internal tube.

Bill

Yes Bill,
Those are the ones!
BTW, in HRM's test, the 3" is too big for a rat motor myth was dispelled.
Ron

Some of our Dyno testing did show a loss of hp with pipe that was too big and mufflers that were straight thru. However, that was the exception. Most high performance vehicles benefited from the extra volume. I would say your combination would not be hurt by 3" but 2.5" mandrel bent would certainly be enough for your current combination. The 3" X to 2.5" combination has become quite popular and should be considered. It also gives you more options for using oem looking chrome tips.

That being said the difference in price is not a big issue. Example; Pypes 2.5" system with X,tails and hardware List price $319 3" X, tails and hardware $379 A 3"X with 2.5" tails system would be somewhere in the middle. Depending on where you purchase them the difference may be even less.

I left out the mufflers because the prices can vary greatly on various brand mufflers.

I ordered a pipes 3.00" with "X" and Gorlich 3" mufflers. Delivered to my door in L.A. the total was $506.

Great discussion.

boldm, your observation on the extension mimicks the advice given by Dr. Gas, " torque tube" as he put it. Seems to hold true.

I did what Bill refers to, necked the thing down from 3.5 off the headers to 2.5" tails. Frankly, 3" tails would be tight. There is a slightly different 'rap' to the exhaust note through the smaller tails to be sure, but I'm of the opinion a system like that could see another 100 ( 600 total ) hp and not give up much, if anything, over open headers.

Plus the engine seems to enjoy the scavenging/harmonics of the x crossover.

A well engineered exhaust should match or exceed open header performance in most of our 'mid range' power rides.(400-600hp) I wouldn't infer much above that.

To Frieburger, You are right on the target with the collector extensions. On a 481" with an Turbo 400 transmission , 18" collector extensions were worth two tenths and two MPH.