exhaust primaries

[nike 5]

Exhaust primaries
The measurement that people generally suggest either 1 3/4 or 1 7/8

Dumb question (but want to make sure I get it right).
I assume that this is inside diameter that everyone is refering to (not the exterior diameter)

[MadMaxHSV]

Correct, internal diameter

[stevieturbo]

Actually...you'll find most exhausts are measured on the OD, not ID


1 3/4 will be more than fine, even if you do start to make a lot of power.

[ringram]

Some would argue that 1-7/8 are better than the 1-3/4 even on a stock engine.

http://www.ls1tech.com/forums/dynamometer-results-...

Ive also seen a test by Texas speed showing the same and some engine builders like Bret Bauer state the same.
Id say go the 1-7/8 unless you already have 1-3/4

[EssexVXR8]

Go for 1 7/8" and make sure you get a reputable make, think difillipo are about the best , i certainly think they greatly helped my output, if your going FI they are a must have

[stevieturbo]

I made well over 700rwhp on 1 3/4's 2-3 years ago....I didnt see them as a problem. Fitment is also easier, as is plug access.


But if you can easily get the larger version, at sensible money...then by all means do.

Dont go thinking its essential though.

[ringram]

Ah but Stevie what about all that horsepower you left on the table!

[stevieturbo]

ringram said:

Ah but Stevie what about all that horsepower you left on the table!

I think its still on the table !!

[MadMaxHSV]

stevieturbo said:

Actually...you'll find most exhausts are measured on the OD, not ID

hmmmmm mine measured larger on the outside diameter so assumed the other way. Apologies for bad info.

I can second the quality of the DiFilippo headers. Went for 1-7/8 ceramic coated. No issues with installation although you need to drop the steering rack (no clearance problems seen on other brands) and plug access is fine still with this size. Delivery and tax from Oz was the biggest pain.

You'll need a re-map to get the most out of them. Potentially more important with the larger diameter.

[nike 5]

Many thanks for the replies - glad I asked, I would have been wrong.

Have gone for 1 7/8 with an equal length of 30inches.

Next question will be the the pipe from the collector (four into one)to the silencer.
What size would you suggest. 2 1/2 or 3inch.
Is there a rule of thumb ratio between primary size (1 7/8) and the outlet from collector.

While I do want a nice sound, and not to restrict flow, I need to be able to pass track day noise restrictions, so not planning on going too large.

[MadMaxHSV]

If you've gone 1-7/8 go for 3" (My 1-7/8 DiFilippo's are 3" out)

[ringram]

Same here.
2.5" is ok up to around 550fwhp thereafter you will start to lose a % of power
3" is ok for around 730fwhp IIRC

No point paying more for the 3" unless you need it. But marginal cost probably isnt too much.