I have done a search on headers and seem to have located everything except tube size. I talked to Mondello and they said on the 455 to run 1 3/4 tubes for some back pressure with a 2.5 inch Flowmaster exhaust system. I will be putting Edelbrock heads on this engine and would have thought 1 7/8 would let the engine breath better. I'm going to purchase headers next weekend. Can anybody give me advice on where to go with this? Mike

 

I would go with 1 3/4 or 1 7/8ths, I'm not a fan of flowmasters but others like them.

 

On a stock 455 I would put 1/34.
If it's modified or you are planning on modifying go 1 7/8.

 

This is going to be a street car. .100 over, edelbrock heads and intake. Not sure about the cam size yet. I would also think the bigger the better!

 

Why so much?

Headers are designed to be more than just better flowing exhaust manifolds. Here's just one of many articles that show how headers really work;http://www.superchevy.com/technical/...0504sc_header/

 

Thanks DoubleV I can get over that, I am looking for low end torque and I Will go with the smaller tubes. Just found a set thats 1 3/4 at summit, great article. Thank you!

 

I wouldn't put less than a 1 7/8 on a 455 Olds. Even if it's otherwise bone stock. Your going with a larger bore and better heads, most likely a better cam. The ports will not be as big in the header as they are coming out of the head for one. I have yet to see a larger header cause loss of torque on an Olds. No way in purgatory would I put a 1 3/4 header on this build. Or any other 455 build for that matter.
Back pressure is just the opposite of what you want. Without knowing more specifics of what your building I can't say how big of an exhaust you'll need but don't rule out 3" to the mufflers and 2 1/2 over the axle.

 

Ok Smitty275, I just tested my engine man to get the specs for the cam. As soon as I get them I will post them. I have 2.5 inch climate system on it now, going to put the edelbrock heads on. I'm thinking about a performer intake because I done think I will have the clearance for the air gap. Thank you for the info. Mike

 

I'm only an hour away if you need help.

 

Cool, where do you live?

 

I live between Canton and Alliance in a little town called Louisville.

 

Cool, I was wondering if anybody was close to Cleveland. If you need anything let me know! I will post as soon as they know the cam size, I have a 1970 cutlass supreme.

 

Who's doing the build?

 

With all due respect I think you are wrong when it comes to stock engine. I don't know much about racing and I don't claim that I do but when it comes to stock I think you are giving wrong info. Remember not everybody is a racer here. Please I am not trying to start another argument so don't take it personal
I think on a stock or a mild engine that will never see above 5500rpm 1 3/4 will perform better.
The scavenging effect of a properly designed header can be a positive benefit to the induction system and to power output as a whole. The main thing to remember is that big headers do much more than reduce back pressure across the engine. Of course they are less restrictive, but that doesn't mean they make more power. To obtain the absolute benefit of the so-called "scavenging effect", header designers discovered that the length, diameter and shape of both the primary pipes and the collectors has a great deal to do with header effectiveness.
It's a fact that a good street header is going to use a small diameter primary pipes to help keep exhaust velocity high at slow engine speed. The collectors will generally be longer than those on a race header since the longer collector helps promote low-speed torque. On a stock type motor it is often possible for the header to actually over-scavenge the cylinder and create a power loss by drawing some of the incoming fuel charge right through the cylinder without ever being burned. the longer collector acts something like a buffer to slow down the pressure wave velocity as it leaves the primary pipe, thereby allowing the engine to utilize the fuel more efficiently.
That being said IMO on a stock or mild engine 1 7/8 is not only more expensive but also unnecessary and can result in a loss of power.

 

I understand now. Thank you, I have Powerlines Racing Engines doing the build. I was in auto class with 2 guys that started the company, go figure I went to a GM dealer and they started 1 beck of a business and there smoking busy. There builders seem to be very knowledgeable.