Just wondering whats the best size exhaust for a NA

currently im running 2.5 inch pipes from block to about where the Y pipe would be and then its 2.25 to a single exhaust outlet

should i upgrade to 2.5 inch pipes leadint to 3inch and outlet ?

any opinions would be great

 

i read in a mazda rotary preformace magazine that making the exhaust bigger as it goes will creat more power but if you still have cats i wouldnt worry about it

 

I have 3 inch pipe from the header to RB cat back, not cats at all, and my only other bod is a cone filter and I ran a 15.2 on bald tires, so i'm a fan of 3 inch pipe

 

hmmm

right now its going to be a straight pipe
and i just got a cone filter too no port job or anything

so 3inch would be ok ?
not alot of low end torque loss ?
is it really sluggish before 3k ?

 

i wouldnt up grade to three unless i had a turbo. but three would probably be good about half way back

 

yea thats what i was thinking ..

if i make it 3 inch all the way it'll lose alot low end power ...
ok so 2.5 and then 3inch is what im going to do unless someone can defend 3inch piping all the way

 

If you want to keep some low end.. I'd go with 2.5" You need a little bit of back pressure in your exaust (and for S4 cars, for your 5/6th ports to work as well).

All I have is a bonez cat, with 2.5" custom cat-back. When I get the RB header, I'm going with 2.5" all the way.

 

For a non-ported non-turbo engine, you want to keep the primary tubes small, around 1.75" inside diameter. If you like, you can then gradually increase the inside diameter as you increase distance from the engine. The Racing Beat catalog (paper catalog, not online catalog) has an entire tech section that covers exhaust design.
http://www.racingbeat.com/

 

racing beat sells a book called mazda rx-7 preformance handbook and in that they have a rally race rx7 that goes from 2.5 to about three they go over the pros and cons of each kind of exhaust up grade for what mods you have done

 

so im guessing 2.5 to 3 would be a safe bet ?

 

im shur it would be ok and some day when you decide to port your intake and engine having that exhaust would help alot

 

i think i got away with 3 because of the rb cat back its dual 2.25 i think 2.5 is the bigest you'd want straight tho otherwise you might notice it alot in the low end, although i'm not really concerned with it since i never drop to low rmps when racing

 

Really? Got a time slip, or a turbo?

 

There's the slip, I only wish I had a turbo

 

thats pretty good

 

can anyone suggest a size for piping on a true dual set up i was gonna go 2.25 what u think?

 

I would suggest not going any bigger than the exhaust sleeve size... (2in?).