Exaust on a 1.5i

lex86 · Post by **lex86** » Mon Nov 21, 2005 3:35 am

Hey people its been a while eh

Just an update, have got a new cd player in my car now (fully sic! - has full colour screen and sound changing side leds)

Anyhow

Was just gonna throw ya's a question about exausts on a 1.5i.

I went to my local exhaust place (after much thinkin and looking elsewhere) and they gave me a quote of $200 from the Cat back. Sports exaust btw, 2.5inch piping.

Pretty good guys, nice reputation

"Speedy's Exaust" do an Australian search

Lemme know what ya think, post some piccies for me!

lanos2001 · Post by **lanos2001** » Mon Nov 21, 2005 3:41 am

i think 2.5" is a bit big for a 1.5l i only got 2.25" on my 1.6l and some people think thats too big for mine as well. i'm not seeing a problem with it though. i say go at the most 2.25"

nick

Post by **PrecisionBoost** » Mon Nov 21, 2005 3:43 am

My stainless 2.5" piping cost me $7.50 Canadian per foot.

Mandrel bends were about $50.00 CDN

I made the stainless flange myself.... but a standard flange set is probably in the range of $10 to $15

$200 sounds about normal for crush bent mild steel.... I'd guess double that for stainless steel (depending on how cheap stainless is down under)

Given your going to 2.5" you should be fine with crush bends.... I would perhaps consider 2.5" on the large side for your engine displacement.

Personally I'd go with Stainless 2.25" X 0.065" wall thickness to increase exhaust velocity.

Post by **PrecisionBoost** » Mon Nov 21, 2005 4:02 am

I have a 2.0L that will have a turbo..... based upon various information I chose to go with 2.5"

I would say that a naturally aspirate 2.0L would be fine with 2.5" as well.

What you have to keep in mind is cross sectional area.... increasing the diameter from 1.5" to 3" ( double ) results in four times the cross sectinoal area

1.5" = 1.767 square inches
1.75" = 2.045 square inches
2.0" = 3.1415 square inches
2.25" = 3.976 square inches
2.5" = 4.909 square inches
2.75" = 5.939 square inches
3.0" = 7.086 square inches

Why is cross sectional area important?

Because it determines the flow rate of the exhaust gas.... the slower the velocity (flow rate) the more the exhaust cools off.

So jumpin from 1.5" up to 2.5" is an increase in cross sectional area by a factor of 2.78

If you were running 12psi of boost on your 1.5L this change in diameter would make sense..... but if it's a Naturally aspirated engine your not going to see much in the way of gains.

I don't want to get into it now.... but there is a way to figure out the optimal exhaust size based upon several factors.... it's a real excersize in mathmatics but I found an engineer who did his masters on the problem.

Unfortunatly I have missplaced the link..... I can't find it.... I have six different computers I have links on..... so it could be on one of the computers at work ( 4 ) or it could be on one of my two computers at home.

Hmmm.... actually.... I have two or three other hard drives that are "spares" so it could be there as well.

I wish I had the link.... it was a great tool.... it was a web based calculator.... just fill in the info and seconds later it gave you the exact optimum size for your vehicle.

lex86 · Post by **lex86** » Mon Nov 21, 2005 11:10 am

Thanks fer the quick responses and info!

I did i little looking on the net and found the following

1. http://www.wallaceracing.com/exhaust_valve.php
Seems quite similar to what you were talking about.
2. http://www.btinternet.com/~mezporting/e ... ength.html
Quite extensive and adds more information

As it is doubtful that I'll put a turbo into my woo (i'd be seriously laughed at & in general i dont think i'd put one in :P) what size piping would you reccommend? 2.25"

... On second thoughts, 2.5" piping is huge lol. I might go for the 2" Instead and get a phat exhaust tip to make it look snazzy

Yeah i'll go for the 2" pipe, nothing too drastic a change, just makes the car sound as good as the stereo.

Next on the list is respraying, rims, lowering then decals :P

Ahh i can dream cant i.

-Lex

woo · Post by **woo** » Mon Nov 21, 2005 11:51 am

ive been told by a few exhaust shops that the general rule of thumb with exhausts on stock motors is that you get best results with pipes that are 1/4 to 1/2 an inch bigger then stock.
As a sife note, my brother wants to make a gonzo pipe to put in place of my resonator..... any imput?

Post by **PrecisionBoost** » Mon Nov 21, 2005 11:59 pm

2" should be good.

Hmmm.... that first link had a link to a book from Amazon.... it looks like a great book for techogeeks (like me)

http://www.amazon.com/exec/obidos/ASIN/ ... 93-9317540

Audacity Racing · Post by **Audacity Racing** » Tue Nov 22, 2005 12:15 am

i have that book... very handy... you'd like it erf. i dunno that some people would get it first time through cause there is some pretty heavy subject matter on pulse seperation and backflow thrusting caused by pressure changes across bends and "devices"

i reccomend to anyone who wants to know some good exhaust info (and wants to make their own)

hey efrain... you ought to read about the intake manifold design

daftmajin · Post by **daftmajin** » Thu Nov 24, 2005 10:40 am

1.5L + 2.5 inch exhaust = bye bye torque