Looking to buy flowmaster header back kit.. Debating on the 2.5" kit or 3" there is a $200 difference. Planning on using the car to drive around and at the strip and am not planning on unhooking some pipes for the strip. Is 3" worth 500 bucks or is the 2.5" a better option? I have a 350 bored 30 over built up planning on having 450+ hp 3" pipes would be cool i have headers w/ 1 5/8 primaries and 3" collectors performance differences between the two? Thanks guys

-Tony

first off, if you have heard a 3" exaust in person you know how loud it is, I have a 3" back to the 3 chambered flows, then dumped at a 90\ , it is very loud, sounds great, but loud!!

I am thinking about putting a cross or X pipe in to quit it down a little but not sure,
also, if you run tailpipes it will quit it down.

you main gain some hp, but if you like the 2.5" go with it.

hope this helps a little!!!

Kevin
69 chevelle
350/ th350 combo

IF bigger and faster are in your future,I'd go with 3" pipes, I bought the mufflers and had a guy weld it up with an H pipe and dumps for 150.00 down here,mufflers were 65.00 a piece,500 seems kinda high :eek:

Take a look here.
http://www.pypesexhaust.com/

Jim

I have basically what you want on my car. I bought the car with the 1 5/8 headers/3"collector and 3" exhaust........but mine has the super turbo's on it. I would go with the 1.75" primaries at the very least on headers. I will be up grading soon. Mine is supposed to be 425 hp at the flywheel

Don't want to be negative, so don't take this wrong, but there is no way a 350 SBC or even most smaller big blocks need 3" exhausts. Exhaust gas cools down rapidly after it exits the header and loses a significant volume and pressure in the process. Any time you move a gas away from the power source, as the volume drops, you have to decrease the pipe diameter to keep the velocity up. Every dyno test and every drag race comparison I have ever seen has shown a 3" exhaust to be detrimental to overall performance for most vehicle / engine combos.

This is what I was wondering about. I am told it is good and it isnt. So, is it worth the money...is it even beneficial to have 3"? That one pypes site si awesome. Thank you. Whatever I decide I will prolly order from there. Any more info would be great Thanks

Tony

I have to agree with GRN69CHV. I have also read that a 3" exhaust is to big for most street motors, it would only be benifical if your motor has a big displacement and horsepower too like a 496bb with 550hp. Otherwise a 2 1/2" exhaust will make the engine perform better you can actually lose some horsepower with a 3" exhaust.

FYI,

I am running a 408BBC, 228/238@ .050 .578.578 lift Hydraulic roller, mild cleaned up oval ports, auto, 3.73 rear - 1-3/4" Hedmans into 2.5" pypes exhaust.

Ive got the 3" pypes on my car sounds great havent gotten to drive it yet bc i have a broken ankle...but it was only $445 with reducers mufflers x pipe etc and they are as cheap as $379 or something nice system definately like it....the 3" is too much it will kill any torque that your 350 is making down low. 450 isnt small but doesnt require 3" either read their page and they will recommend a 2 1/2 for you application and hp range good luck


good luck

quote from pypes page

We recommend 2½" up to around 475-500hp and 3" for over 500hp. For Extreme performance applications of 600 hp or more. 3½" or even 4" might yield the best performance.

3", flowmaster 3 chamber mufflers dumped before the diff. I had 2 1/2 before with a small block(warmed over 350) and switched to the 3" while the small block was still in. I did not loose any power. I have read and had many people tell me this would be the case. It was not. Don't know that I really gained any either though. The sound sure got better. I would run what makes the smile biggest on your mug smile.gif and not worry about power figures. On a dyno it might be a couple HP or LB of torque but I don't think you would feel it. I did not.

I agree I'm gladly given up some horses for the sound of the 3" and I have 2" headers too!! graemlins/beers.gif Mike

Brett,how do you know "it didn't lose any power" ? :confused:

..do you have a timeslip or a dyno to confirm that statement? Not trying to be sarcastic or harsh,just looking for facts.

For this guy's (my71) application,I think a 2.5" system is plenty.My 454 gets by with a 2.5" system,and it weighs 4000 lbs. and runs high 12's/low 13's with 2.73's

My71,if you don't want an H or X pipe system,Jeg's sells a complete 2.5" system w/mufflers for $169 http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=118272&prmenbr=361

Please also keep in mind the difference between the 21/2 and 3 is bigger than you think not only will you loose torque but you might also have clearance problems..thats what they told me when I bought the system..doesn;t exactly matter to me bc my car isnt exactly stock

Does anyone have a sound clip of their 3" exhaust

If you go to my website below you will find a link to my 3" exhaust sound from the main page. Engine is a slightly worked L78 with aluminum heads. Another link has some specs and pics of the system. It was on car when I bought it and I can't say anything relative to power differences over a 2 1/2", but the sound says it all. Enjoy :D

No time slip, no dyno report. Just seat of the pants and grin factor. Not everyone is concerned about a couple horses or a hundreth less ET. I do not have a dyno or drag strip close by. Wish I did have the strip. Does anyone have any proof other than what they have hurd or read in a mag that it makes that much difference. Keep in mind I said that much. I hope this does not come across as taking it personal. I am not. I like a good debate :D . I would actually like to see a test with all being equall 2.5 vers. 3". Good talking to ya 4 Speed graemlins/beers.gif .
P.S. If you could try a 3" system and show me a lot of difference I would be happy to eat some crow. I would still keep the 3" pipes though :D .

ok live dont have any slips online or anything..but what it comes down to is that it depends on a particular combo...bigger exhaust you will loose lower end torque if mismatched....head to head testing isnt relavent bc its combo specific...a 307 doesnt need a 3" exhaust and the ricers dont need a 4" tailpipe but they like how it sounds

My .02 worth. I have a complete 3" system with X pipe and Dyno Max welded mufflers on my '67 GTO with a 462. (I got the system from the Buick GS Club, very nice and lightweight).
Anyway, before the 462 went in I had the 3" system installed behind the mostly stock 360 hp 400 HO engine with the stock Pontiac HO manifolds. Seat of the pants feel was no power/torque loss from the old 2.5 into 2.25 system. With the manifolds, new system was as quiet as the old.
With the new 462 and Doug's Headers, it was quite a bit louder, but not objectionable. Car is a 4 speed with 3:23's, worked Q-jet, ported 6X heads, RPM intake, Crower 221/229 cam, HEI. I can lug down in 4th at low speeds with no problems and can easily pass at freeway speeds, no downshifting. Kicking in the secondaries is just like hitting passing gear in an automatic.
Point is I have experienced no noticeable loss of torque with the 3" system in either the stock 400 or the modified 462. Could be the legendary Pontiac torque is just hard to kill.
But when the time comes, I intend to use the same setup on my project '67 SS with mild 454. (headers, street cam, RPM, custom Q-jet).

Brett,no problem man..again,not trying to offend you.This is a good thread..info is flowing as usual,and thats a good thing.Thats what this website is all about. graemlins/thumbsup.gif
Sixties Guy,your GTO and its combo sound like a lot of fun! :cool:
I've been tossing the 3" system idea around for my car..I just want 3" leads and stick with my 2.5 tailpipes.

My best e.t. with 2.5" pipes and street tires is/was 1.86 60ft and 12.69...best ever e.t. is 1.66 60ft and 11.78 w/slicks and open headers,,,best e.t. on drag radials with 3" pipes is 1.64 60ft. and 11.85...so the only close comparison is the street tires and drag radials,but 2 tenths off the 60ft. will not take .84 off the e.t....both my bests are comparable to the point that,they were at two different tracks with about 600 ft difference in elevation with the quicker e.t. at the lower elevation track. I would also venture to say that 3" pipes are very close to the same performance vs. open headers only much quieter. Can you make any sense of this? :D

Bob,what was the difference in mph?

Something to keep in mind. The thread started out looking into 3" exhaust for a 355CI small block. On a 450+ CI big block, there should be a definite benefit to a 3" exhaust over a 2-1/2" for a motor that is ran flat out. What's the point of diminishing returns - who knows for sure? But I would bet a 350CI small block at 7000 RPM or a 450 CI big block at 6000 RPM may be a probable cross over point to justify going from 2-1/2" to 3". Also, keep in mind that the first 4 feet of exhaust after the collector is where the exhaust temp is still really high, after that point the temp drops considerably and the exhaust gas condenses, therefore requiring less volume.

Doggy, I think head to head is relavent. It goes with out saying that different combos will favor different size exhaust. All I was saying when responding to the original thread was, that the 3 " worked good for me with a small block. I did try it with 2.5 before. Switched to the 3" It ran real good. Not loosing anything (that I could feel) anywhere. On a dyno it probably did. Possibly at the track also. Just think it would be cool to see what the diff. really is.
4 Speed, you could be the true, real life tester here. With the same combo and no changes except diameter of exhaust :D . I think your wife should agree to spring for the exhaust in the name of science graemlins/thumbsup.gif .

imo 3" is way too big unless your puttin out 450< Hp. You need some backpressure to get some good torque numbers, i guarantee if you like to race from light to light you WILL be disappointed get 2 and a half"

I get what you are saying live...but I meant is specific examples dont matter It matters what it would do on his car...you might need a 3" on a 327 that winds to 9k and puts out 700hp but not on a 402 that sticks to 5k the exhaust that is required and what is lost depends specifically on the combo and power level and motor size..playing with dd2k I was loosing about 80hp to my old exhaust sounds rediculous but hey it was a pos 20yo rusted kinked system with crappy mufflers that my motor actually blew out the baffles on and they would clink at idle...now sounds better drives harder and doesnt fall off at higher revs :D

There is a 9 second SBC powered Nova in this months issue of Hot Rod..guess what it runs for exhaust...
2.5"

I get ya dog. Nice chatten with you all graemlins/beers.gif .

I have 3 inch on my 406sb and love the sound and the car seems to run good. I am planning on dyno running it in the next few weeks. It is a 406sb 10.1 compression, afr 195's 64cc chamber, 1.6 rockers, 292 244@50 cam with 535 int/exh lift. Performer rpm manifold and a 750dbl pumper. Hooker super comps with 3" collectors and torque tech 3" prebent pipes that all plug into flowmaster mufflers. I bought mine in a 3" size due to the expected hp the car would make. The pipes cam pre fab to fit my 66 chevelle with no issues. The headers caused more issues than the exhaust. I guess I'll see what the dyno says but I expect it will be decent.

Originally posted by mr 4 speed:
There is a 9 second SBC powered Nova in this months issue of Hot Rod..guess what it runs for exhaust...
2.5" yep 2.5 the way to go

Hey guys...

haha I didn't realize this was such a hot topic amungst us. I hope no enemies were created here. Souded like it got a little personal for one small fraction of time. I'm sure everything is kosher. I decided I am gonna go with 2.5". Just seems as though it'll be enough, or better, than 3". I know some say its cooler to have it, but I think the car kicking people's a**es will be enough talk on my part. ha Thanks for all your input though. It helped a lot! Keep ya posted on how the car is comin along.

Tony

So based on what you guys have been saying... For a smaller HP Smallblock motor(say 250hp stockish motor)- Would there be a BENIFIT to running 2 1/4 pipes instead of the 2 1/2?

IE: Would there be more bottom end torque than if you ran the bigger 2 1/2" pipes on the same engine?

Ben,IMHO and experience,a small block under 325 HP will be fine with 2.25" pipes,especially if they're mandrel bent,and headers are a plus.

You don't need backpressure in a exhaust system, exhaust is a science and to really find out any real help you would have to talk to some pros. there is a lot more too it. Personally i would go with a 3" system into the X or H pipe and then step down to a 2.5 into mufflers and out. Most small block headers have a 3" collector, using a 3" pipe after the headers extends the collector and will create MORE torque. Don't believe all this mumbo jumbo; 3" on a mild 350 IS overkill, but if you are making about 425 or more horse i think the 3 into 2.5 system is the best you could get. My friend has a 71 camaro with a mild 396(almost stock) and he put on a 3 inch system, it was loud but it made more torque and made the car much smoother. If you only have an honest 350-375 horse i think just a 2.5 system would be more than adequete. BUt remember be honest with yourself on your horsepower ratings. We are puttin this system on my friends 68 camaro with a 355
10-1 compression
AFR 195CC
air gap
1 5/8 super comp headers
Ultradyne solid flat tappet 276 cam
We expect about 425 horse
we are running
1 5/8 with 3" collecter super comp hookers headers
3" into Dr. Gas X pipe
2.5" out of X pipe into
2.5 Ultraflow mufflers
and 2.5 over the axle.