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Old November 10th, 2011, 02:52 PM   #1
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Dual exhaust horsepower

Hi All,

Can anybody throw a number on horsepower increase for a 68 cutlass stock 350 eng going from single exhaust to factory dual exhaust set up will yield?

Thanks, Joe
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Current: 1968 Cutlass S Convertible - 350 4bbl
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Old November 10th, 2011, 03:14 PM   #2
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10-15% increase, and with headers, possibly another 10-15%!
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Old November 10th, 2011, 08:06 PM   #3
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25 horsepower easily, plus better fuel mileage, its win win!
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Old November 10th, 2011, 09:26 PM   #4
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It could be from 20 on a 2-bbl carb to 50 on a 4-bbl, providing the distributor curve and jetting is optimized to the application.
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Old November 10th, 2011, 09:52 PM   #5
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Don't know if you want to keep the car all orginal or not, but I suggest "X" pipe duals. Gives a little bit more power over true duals and gives better equalization of both banks 1 and 2
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Old November 11th, 2011, 08:18 AM   #6
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Thanks all, it is a 4bbl carb. I know it was replaced and appears to be from a 1969 400 engine. Carb# 7029251.
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1969 Delta 88 4 Dr 455/2bbl
1977 Cutlass Supreme 2 Dr -3.8 Odd fire V6 converted to 74 Olds 350 4bbl - great project
1985 Cutlass Supreme 4 Dr - 3.8 V6 commuter car
1992 Cutlass Supreme 2 Dr - 3.4 DOHC V6
1994 Bravada - awd setup that was hard to beat

Current: 1968 Cutlass S Convertible - 350 4bbl
-who orders a posi 2.78 rear from the factory
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Old November 11th, 2011, 08:22 AM   #7
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Anyone know if i can use my stock manifolds if i want to convert to factory dual exhausts? (right now i have single exhausts with the crossover-under-engine setup.

I've been eyeing the setup from ILT.. It's 600 bucks for the setup i want (factory duals with turn down at the end for my bumper.

Anyone know what shipping would be like?
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Old November 11th, 2011, 08:31 AM   #8
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If your converting from a factory single to a dual system you can use the factory exhaust manifolds by installing a blockoff plate on the crossover. Why not just take your car to an exhaust shop and have an exhaust system fabricated? You can probably get one done for approx $3-400 dollars.
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2006 Mustang GT (Momma's)
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http://s1141.photobucket.com/albums/n587/oldcutlass/

http://s1141.photobucket.com/albums/...lass/plymouth/

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Old November 11th, 2011, 08:38 AM   #9
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Quote:
Originally Posted by Tony72Cutlass'S' View Post
Anyone know if i can use my stock manifolds if i want to convert to factory dual exhausts? (right now i have single exhausts with the crossover-under-engine setup.

I've been eyeing the setup from ILT.. It's 600 bucks for the setup i want (factory duals with turn down at the end for my bumper.

Anyone know what shipping would be like?
Tony, Yes you can use stock manifolds. You will need the cap for the passengers side crossover pipe opening. The drivers side front pipe is no longer made by walker but the rest are I believe if want to piece a system together and have the one pipe made. Another option you could try is http://www.thepartsplaceinc.com. Not sure on shipping but I think they have the whole system and the block off cap.
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Hx of Olds:
1969 Delta 88 4 Dr 455/2bbl
1977 Cutlass Supreme 2 Dr -3.8 Odd fire V6 converted to 74 Olds 350 4bbl - great project
1985 Cutlass Supreme 4 Dr - 3.8 V6 commuter car
1992 Cutlass Supreme 2 Dr - 3.4 DOHC V6
1994 Bravada - awd setup that was hard to beat

Current: 1968 Cutlass S Convertible - 350 4bbl
-who orders a posi 2.78 rear from the factory
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Old November 11th, 2011, 08:44 AM   #10
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First lets not confuse things. a performance exhaust system does not ADD horsepower, it free's horsepower that is being lost in a restrictive system.

The problem with that is, if the engine is not performing past the limits of the existing system, there is no real increase.

The word "STOCK" in your first post as in "stock 350" tells me you should not expect much difference.

It will be slightly louder, and possibly a little more efficient- as in maybe at best 5-10hp, but i can guarantee you won't feel that in the seat of your pants- except your wallet paying for it.

To the folks saying 30-50hp free going from a exhaust manifold sngle pipe setup to true duals? Really, what planet are you living on? Not even close to reality.

X-Pipes, H-pipes, just as above, don't ADD power, they only free potential power, and on a bone stock 350 they really aren't going to do anything for you.

All that being said, everyone wants dual pipes, they look cool and sound cool- so go ahead and get em- Plus it is a good step to have done already in case you ever want to do other things that do add power (like a cam swap, or engine build)-

And if those things are in your future plans, then plan your exhaust upgrade carefully to match them. If you are going to do a performance engine build later- then don't spend good money running duals off restrictive factory manifolds, get a set of headers and do it right- but still don't expect to see major improvements until you have an engine that is going to take advantage of the system.

Last edited by RAMBOW; November 11th, 2011 at 08:53 AM.
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Old November 11th, 2011, 09:06 AM   #11
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Quote:
Originally Posted by RAMBOW View Post
First lets not confuse things. a performance exhaust system does not ADD horsepower, it free's horsepower that is being lost in a restrictive system.

The problem with that is, if the engine is not performing past the limits of the existing system, there is no real increase.

The word "STOCK" in your first post as in "stock 350" tells me you should not expect much difference.

It will be slightly louder, and possibly a little more efficient- as in maybe at best 5-10hp, but i can guarantee you won't feel that in the seat of your pants- except your wallet paying for it.

To the folks saying 30-50hp free going from a exhaust manifold sngle pipe setup to true duals? Really, what planet are you living on? Not even close to reality.

X-Pipes, H-pipes, just as above, don't ADD power, they only free potential power, and on a bone stock 350 they really aren't going to do anything for you.

All that being said, everyone wants dual pipes, they look cool and sound cool- so go ahead and get em- Plus it is a good step to have done already in case you ever want to do other things that do add power (like a cam swap, or engine build)-

And if those things are in your future plans, then plan your exhaust upgrade carefully to match them. If you are going to do a performance engine build later- then don't spend good money running duals off restrictive factory manifolds, get a set of headers and do it right- but still don't expect to see major improvements until you have an engine that is going to take advantage of the system.
Agree 100%. I dont think youll see much of a differnce at all with a 40 year old engine and stock manifolds
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Old November 11th, 2011, 09:50 AM   #12
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Quote:
Originally Posted by RAMBOW View Post
First lets not confuse things. a performance exhaust system does not ADD horsepower, it free's horsepower that is being lost in a restrictive system.

The word "STOCK" in your first post as in "stock 350" tells me you should not expect much difference.

It will be slightly louder, and possibly a little more efficient- as in maybe at best 5-10hp, but i can guarantee you won't feel that in the seat of your pants- except your wallet paying for it.
Ya know, I wish I had read that about 30 years ago when I was younger and didn't know better.

I converted my stock 350 to a dual system by blocking the crossover pipe and running pipes to the back. Only thing I did different back then was install a cross pipe (used to call them balancers back then; probably a pre-cursor of the X pipe?). You are so right, it is louder so I put in a set of resonators after the muffler. Toned it down and just added a little restriction I guess. But it sounds healthy too.

I changed my carb/intake from 2bbl to 4 bbl, and added HEI. With all these changes I notice the car doesn't really run different, but it gets better fuel mileage. And it doesn't give me mach 1 off the line either. It was always a good runner and fairly quick off the line. Still is. I think all I've done with adding the dual exhaust and 4bbl is put something on the car that I wished it had from the factory. It's a preference, and you're right there's no big difference in 'performance'. I'm not a racer, never will be. I just like my car for what it is and how I like to enjoy it.

I like the way you explained this issue. Thx
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Old November 11th, 2011, 10:57 AM   #13
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Funny -I seem to remember early 283's [195 hp] had an 220 hp option that was a 4gc carb and dual exhaust ONLY - no other difference! +25 hp!
Were there other changes [cam, heads] in the olds 350 [68-70] that brought the standard motor from 250 to 310 hp and added 60 hp?
And I think even the 330's had a 4-bbl upgrade with duals.
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Old November 11th, 2011, 10:57 AM
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