yeahbuddy

Is it possible to have a 3" dual exhaust setup without headers and keeping stock manifolds? Got a 68 Cutlass Supreme 4 door with 350 small block and 4bbl. I know the front pipes are going to be 4" longer than the coupe and convert. That being said, how can I get a 3" exhaust setup with stock manifolds? I believe someone on youtube had this going. My local muffler guy wanted to so a complete custom setup for $600. Trying to weigh my cheapest options here..if I have any. Trying to avoid headers. I recently heard friends Impala with 382 motors on 3" pipes and Flowmasters and it was ruthless! Id love for my car to sound like that.

MDchanic

I don't understand why you would want to put those pipes on that motor.

If you want it to make noise, just make a hole in the muffler.

- Eric

yeahbuddy

Mainly because there is a single exhaust on now and this video got my attention. Says he has stock manifolds with 3" and I think it sounds great

http://www.youtube.com/watch?v=sqKIp2Q6bSw

jozw30

Pretty sure you'll lose a bunch of power.......

2 1/2" might be a bit better with some louder mufflers?

You're car........good luck.

70olds455

A 3" inch exhaust is going to be too big for a 350 engine. You can get the sound you are looking for with a good 2 1/2" exhaust system. I put some race mufflers on my 1970 cutlass supreme and now it has a deep intimidating sound.

yeahbuddy

Is it going to be cheaper/safer to have a shop custom bend a 2.5" setup considering I have a 4 door and no headers?

redoldsman

Yes. Check with 2 or 3 muffler shops in your area if you have that many. 3" exhaust would be a pain and you would lose low end torque. These guys gave you good advice on the 2 1/2 inch pipes.

yeahbuddy

Thanks guys. I appreciate your advice and I will look for a 2.5" setup.

Rickman48

BTW - that 383 chevy motor probably sounds meaner because of a bigger cam and more compression, not the 3" exhaust!

MDchanic

Sort of what I was getting at, too.

Big exhaust pipes are probably the least important contributor to what he appears to be looking for.

- Eric

yeahbuddy

Just want to make it clear to a couple of you guys. I am going to be converting from a single 2" exhaust to duals. I am trying to get the best setup I can for my money so I am weighing out all my options. I insisted on the 3" because of the one I heard in person and the video I posted with a 350 using stock manifolds and 3" Flowmasters. 2.5" is a better choice for my 350, I get you. Some of you guys have had the privledge to grow up around these old cars but I am still in my twenties learning ON MY OWN based on what I read and ask and what breaks. So take it easy on me. haha

Got a question about down pipes. Pypes makes prebent mandel downpipes for 64-77 Cutlass/442. The thing is on their site it specfically says "1964-77 Cutlass & 442 (except 350 engines)" but every other site that carries the same set (Summit, Jegs, Ebay) says it will fit a 350. Im sure the manufacturer knows best but sometimes they dont. I emailed them but probably wont hear back for a bit with the holidays. If any of you are familiar with these downpipes? They seem like a quick solution for stock manifolds?

http://pypesexhaust.com/downpipes.html
http://www.summitracing.com/parts/PYE-DOF10S/

Merry Christmas

MDchanic

Look, YeahBuddy, the point we're (snarkily) making is a point that applies to ALL cars of ALL ages. It is basic point of engine design, and one missed by many modern "kids," who like to put pipes more appropriate to Cummins diesels on their Honda rice-whiners
(when I was young, the kids used to like raising the rear end way up, as though their car was a top-fuel dragster, thus wrecking U-joints, wearing out ball joints, and destroying their steering geometry).
Unless you are talking MASSIVE displacement or sustained, really high RPMs, the added diameter of pipes that size will kill your performance, and do nothing good whatsoever. They will also be much harder to fit, reduce your ground clearance (not a problem until you go over a driveway cut and "remove" your mufflers), and be more expensive - sort of a lose-lose-lose situation.

If you want to make a change to your car, just ask around here, and many very experienced people would be more than happy to tell you what will work best with your specific arrangement.
If you've got a stock 10.25:1 '68 350, you will probably see some power gain with dual exhausts, but possibly see a loss from going to larger-than-stock pipes. The reason is because your stock 350 with an automatic transmission probably shifts at about 4,500 RPM, and never even sees 5,000. You just aren't pumping that much air. Meanwhile, reducing the velocity of the air column in the pipes will reduce combustion chamber scavenging, and thus probably reduce power.

Others on the is board will be able to tell you their experiences with similar setups.

I would recommend reading some information on basic engine operation and design, which can be found all over the web, and scattered around on this site, then you will be able to ask higher-quality questions, and receive higher-quality answers.

Merry Christmas,

- Eric

yeahbuddy

Thanks MD. I understand basics like I said I am still learning something new everything. I got the idea the engine would breathe better with a larger pipe. As far as the RPM goes, yeah, I dont drive the car very hard as it is my daily driver...plus it has a 2 speed Jetaway that shifts at 70mph... But the duals and TH350 are coming close next on the list and I am doing my research. I talked to my local muffler guy a couple months ago and he quoted me $600 for front to back custom 2.5" setup with mufflers. He told me it will be better way to go than buying these pieced kits. The car is mostly stock from what I know as far as the motor goes. What I have done to the motor itself only includes Edelbrock Performer intake & 600CFM carb, electronic ignition, new wires/sparks/cap and rotor. I appreciate everything! This is how I learn!

70olds455

The pypes downpipes fit the 350 engine. I have a 2.5" pypes exhaust system with the street pro mufflers and downpipes on my 1971 cutlass. The pypes exhaust is good performance exhaust system and sounds pretty loud too.

yeahbuddy

Did you get the x pipe setup or the straight?

MDchanic

To make this more concrete, here are some illustrative numbers.
I'm lazy, so I'm using someone else's data, rather than sitting with my calculator and creating the numbers myself, based on 115 CFM flow per square inch, and an assumed requirement of 2.2 CFM per HP:


As you can see, a pair of 2¼" pipes should flow about 816 CFM, which is well over your 600 CFM carb capacity (exhaust gasses contain fuel in addition to air, at a ratio of 1 part fuel to 14.7 parts air, if I recall, and are hotter, so take up more volume), while a pair of 2½" pipes will flow over 1,000 CFM.
A pair of 3" pipes will flow about 1,500 CFM, which is WAY more than your engine needs.

- Eric

70olds455

I have the straight pipes on mine.

getawaycar

If you want to talk with a muffler guy who really knows his business call Ed Hanson in spring valley. I have had a lot of stuff built by him for work and it has all been amazing quality at exceptional prices. Like Eric has made very clear it is important to know what flow characteristics the exhaust system you construct would function with the rest of your performance parts. Every conversation I have ever had with Ed he has asked those kind of questions before making recommendations. He has also talked about using an X pipe the ties dual exhaust systems together to improve scavenging although I am not clear on how it works. I do know he is the exhaust guy in San Diego that all the other exhaust guys call when they need help. Ask your muffler guy if he knows him or give him a call yourself. Even if you don't have him do your work it would be worth the conversation.

Eric, people put ridiculously large exhaust on Cummins engines too. I had one guy bring in a truck with dual eight inch stacks behind the cab of his pickup! The turbocharger outlet is only three inches...

Chris

gearheads78

Use 2 1/4" pipe and some 2 chamber flowmasters. You will get the sound you want without the power and torque loss.

carluvr60616

hey guys i have a 77 cutlass salon rocket 350 edelbrock performer intake 600 cfm carb, im doing longtube headers and have an existing y piped 2 1/2 inch dual exhaust that came with the car when i bought it. I already have a dual hump trans cross member to accomidate true duals, should i try to salvage the 2 1/2 inch exhaust to save some $$ at the cost of performance? Would it be a big performance difference and worth the extra green if i tried a new exhaust kit with a smaller diameter pipe?

thanks hope everyone had a Happy New Year,

Steve

MDchanic

I'd say use what you've got since it's already there.

You can't beat "Free" at any price!

- Eric

z11375ss

Flowmaster kit from Summit. Headers, H pipe. Take a listen at the link.

DENT

Thats a cool video.

Tony72Cutlass'S'

Here's a twist,

i've got a single exhaust system on my olds 350 (stock). Everyone compliments the sound and thinks it's dual exhaust. Shows how much kids my age know these days, eh'?

I say get a sexy exhaust from inline tube, supposedly they make a great 'stock' exhaust that'll look factory for a decent price. I would get a shop to bend me one, but people in montreal seem to think that since you own an old car, you're made of money.

I digress, best of luck.

-Tony

Olds64

I agree that you wouldn't want to go to 3" pipes on a 350. Keep it at or under 2.5" and you will be fine. I suggest you use your local exhaust shop. I found a local shop that does excellent work for great prices. Plus, a local shop will probably offer you some type of warranty that you wouldn't get with a mail order setup.

coppercutlass

I would use 2.5 with headers on a moderately built engine. Here is where i stand on the whole issue we stuck my old 350 sbo in my dads 77 pontiac bonneville originally 403 and i ran it with headers and i had it all dialed in. My dad wanted to use the manifolds and true dual. I went ahead set it all up once we had it running it idled rich ran like a pig. To run an exhaust that big you would have to re jet the carb which is what i did. Im in the reagion of roughly 400 hp and i run 2.5 in. exhaust with hooker aero chmabers and it sounds tough. My old engine in my dads car even with restrictive exhaust and 2.25 exhaust still sounds good. imo use the 2.25 exhaust with some flowmasters or muffler of choice and you will be happy .

Erinyes

This particular combination, 2 1/4" head pipes and 2" tailpipes makes me ask why, since I'm on the verge of ordering tailpipes from Thornton for my 53. I've got the B body issues as well, since the front was subframed with a 65 Delta 88 425. I already have the proper dual manifold setup, and the outlet is 2 1/4".

What would be the benefit to dropping to 2" tailpipes? Purely for sound issues? Better scavenging? (Which seems unlikely, purely instinctively, since the tailpipes are such a long distance from the head pipes, and the mufflers have already enabled the gases to expand...) It won't affect flow materially, but is cheaper and easier to fit?

From the chart, it would seem as if the 2 1/4" dual exhaust would be the best fit overall, but if there is a benefit to dropping the diameter at the tailpipe, I'm right at the point where it would be best to find out -- before I spend my money!