What size exhaust for 455 with w z manifolds
Thread Starter
Registered User
Joined: Dec 2010
Posts: 236
From: Newmarket, Ontario
What size exhaust for 455 with w z manifolds
I'm in the process of getting a new muffler system for my finished 455 swap. The muffler guy who comes highly recommended says that running 2.25 from the stock wz manifolds is the only way to do it right. He says that he can't really put the 2.50 in correctly using those manifolds....if I was using headers he could do anything at that point. He also says the trumpets are designed for 2.25 as well which I know. I'm confused since I've read in more than one post that 2.50 is the way to go with a 455 but most guys that say that are using headers. I want 2.50 now so that when i do get headers i don't have to redo the exhaust. The motor is not a racer but is using an edelbrock 04b manifold with a 40 bore and a quadrajet with an engle cam.
Is he correct telling me only 2.25 with stock wz manifolds or is there a way to get 2.50 to work correctly without affecting overall performance. Thanks.
Is he correct telling me only 2.25 with stock wz manifolds or is there a way to get 2.50 to work correctly without affecting overall performance. Thanks.
Registered User
Joined: Sep 2009
Posts: 2,444
From: mn
http://www.ramairrestoration.com/oldsmobile.html take a look at these.
I ran the pontiac ones on my 400 I liked them looked like a nice piece.
I ran the pontiac ones on my 400 I liked them looked like a nice piece.
Connoisseur d'Junque
Joined: Sep 2010
Posts: 21,183
From: The Hudson Valley
As discussed here:
How much flow will you need?
- Eric
HTML Code:
Pipe Diam Pipe Area Total CFM Max HP Max HP
(sq.in.) (estimated) Per Pipe Dual Pipes
______________________________________________________________
1½" 1.48 171 78 155
1⅝" 1.77 203 92 185
1¾" 2.07 239 108 217
2" 2.76 318 144 289
2¼" 3.55 408 185 371
2½" 4.43 509 232 463
2¾" 5.41 622 283 566
3" 6.49 747 339 679
3¼" 7.67 882 401 802
3½" 8.95 1029 468 935
- Eric
Registered User
Joined: Feb 2009
Posts: 2,257
Thread Starter
Registered User
Joined: Dec 2010
Posts: 236
From: Newmarket, Ontario
As discussed here:
How much flow will you need?
- Eric
HTML Code:
Pipe Diam Pipe Area Total CFM Max HP Max HP
(sq.in.) (estimated) Per Pipe Dual Pipes
______________________________________________________________
1½" 1.48 171 78 155
1⅝" 1.77 203 92 185
1¾" 2.07 239 108 217
2" 2.76 318 144 289
2¼" 3.55 408 185 371
2½" 4.43 509 232 463
2¾" 5.41 622 283 566
3" 6.49 747 339 679
3¼" 7.67 882 401 802
3½" 8.95 1029 468 935
- Eric
Milenko
Registered User
Joined: Feb 2009
Posts: 1,737
From: West Hartford, CT
Stick a 2 1/4" flange appx 1-2" long inside the 2 1/2" flange to act as sort of a bushing/adapter. I've done it a few times & never had a problem, not really even a hack move. You could put a little muffler cement between the two flanges, I've done some with it & some without, no leak either way.
I would go the 2 1/2" in case you add headers later. I would think you could cut a couple/few slots in a stock trumpet & expand it to fit the larger pipe but I can't remember if I ever actually have done that or not. I just use the Pypes 2 1/2" trumpets.
I would go the 2 1/2" in case you add headers later. I would think you could cut a couple/few slots in a stock trumpet & expand it to fit the larger pipe but I can't remember if I ever actually have done that or not. I just use the Pypes 2 1/2" trumpets.
Connoisseur d'Junque
Joined: Sep 2010
Posts: 21,183
From: The Hudson Valley
455ci ÷ 2 x 5,000 RPM x 0.8 ÷ 1,728ci/cf = 526 cfm
(455, requires 2 revolutions to cycle all cylinders, so divide by 2,
x max likely RPM of 5,000,
x 80% usual ballpark volumetric efficiency,
x 1,728 cubic inches per cubic foot
equals 526 cfm)
This is why these engines performed pretty well with their original 2¼" single exhaust systems, especially when shifting at about 4,500 RPM - that's a maximum of 475 cfm through a pipe that flows well to 408.
- Eric
Thread
Thread Starter
Forum
Replies
Last Post
