[trd3146]

I am putting in a new exhaust systen in my '71 350. I am wondering what would be a good pipe diameter, and what the benefits are, if any, of installing a crossover pipe. Thanks for all the help.

 

[jholp]

TRD3146,

2, 2 1/4, 2 1/2 inch pipe will work fine. If your engine is a strong running 350 then tend towards the larger diameters above. If it is a low horsepower 350 then tend towards the smaller sizes.

You see if you put like a 3 inch pipe on a 175 horsepower 350 it will hurt the bottom end. If you put a 2 inch pipe on a strong 350 it will hurt the top end.

Now for the cross over pipe - you will get differing opinions here. Almost all will say it will quiet the exhaust system some. Most will also say install the cross over as soon as possible after the header flange.

Now the poo-poo fight will start over horsepower and torque. There are some well known header manufactures that indicate there is no real difference in horsepower or torque when using a cross over pipe! I have read magazine articles that claim increased power by using a cross over pipe but do not know who is right.

John

 

[Scooter]

I fully agree with what jholp posted, but would recommend a crossover pipe. It helps to equalize the exhaust. It has been recommended in articles in Hot Rod, Car Craft, Super Chevy, etc.

 

[Mike H]

I just installed a crossover pipe on my 454. It makes quite a difference in the sound and the bottom end torque. Read the article in Jan99 Popular Hot Rodding "Mondo Muffler Shootout", and form your own opinion. It wasn't cheap, but nothing worth while is.

 

[DZAUTO]

I can't respond to the diff in power or torque, but there is a noticeable smoothing out of the exhaust note.I DON'T LIKE IT. I like to hear the crisper exhaust note you get without a crossover. And one last thought. If you have a crossover and ever need to change tranny, clutch, etc., God will get you for the language you use!

------------------

 

[JWA]

I have a crossover with 3 inch to the rear bumper. I don't think my car is that much quieter. Mine is also far enough back that the tranny comes out easy so that maybe why. Hey DZ what do you do for the USAF? I'm an ex fulltimer now with the ANG(part time) as a avionics puke (F15).

------------------
Jeff A. ACES#841
68 SS396(454)
68 L78 Project
87 MC SS

[This message has been edited by ACE841 (edited 05-20-99).]

 

[DZAUTO]

I'm the military 747 structural technician. I work in the division that manages the Boeing military 747s (VC-25 at Andrews and E-4B at Offutt)in the Air Force.

------------------

 

[72CHEVELLE]

Flowmaster recommends that a crossover be used in conjuction with their exhaust system because it improves flow and yields more horsepower (according to them anyway). If you know what kind of exhaust system you're going to install, ask a customer rep at the company itself (Dynomax, FlowTech, Flowmaster, etc.) whether they recommend a crossover or not. I know a lot of people who who have 'em and I haven't heard any complaints yet.

 

[MIKE_D_67]

TRD3146,

I also agree that a crossover is a good thing. Not absolutely necessary, but it does have benifits.
As for positioning it, (distance behind the collector) I heard a good way to do this is to spray NON-high heat paint down the length of the exhaust (a couple-3 feet anyway), let it dry, run the engine enough to get it to full operating temp. and look at the pipe, where the paint stops melting/chipping off that's where to locate the crossover.
Never tried it myself, but it sounds logical.
Mike

 

[Buck Mustard]

I've heard the same trick that Mike described for locating the crossover pipe. Spraying some paint and checking where it quits blistering/chipping.

 

[Scooter]

I've also heard of what Mike said about how to locate it. Awhile back, I worked in a shop that did custom exhaust, and we would recommend crossovers, and used the same method Mike described. While I worked there, I modified my wife's Mustang exhaust where the crossover was, and added a bolt-in flange to each pipe behind the crossover so I could remove the trans by unbolting the collectors, then unbolting the flanges that I added, to remove the "H" pipe. This would eliminate the problems that DZ mentioned. I'm sure a good exhaust shop would do it if you requested, for a nominal fee, I'm sure.

 

[Guest]

Had a crossover installed on my 69 when I had the new exhaust done; glad I did it sounds real good! The method my shop used was to use a crayon and ran a line down the exhaust tubes and just before where the crayon stopped melting off was where he installed the crossover.-Rick