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Exhaust System Design?

736 views 13 replies 5 participants last post by  dave448 
#1 ·
Just wondering Bruce's... What is better interms of proformance:-

A. 50mm bore system with 3 boxes

or

B. 45mm bore system with 2 boxes
 
#5 ·
so in theroy silencers dont do much in restricting power or im i talking poo?

I always thought the boxes distrube air flow and slow the gas speed down so the less boxes a system has the better gas speed n flow, for example on the brothers GSi we changed his standard exhaust system(3boxes) for a standard 1.3SR system(2boxes) and guess what the car pulls much better though the rev range now!

So why did vaux slap 3boxes on the 1.6 non cat engines but only 2 on the carb models?
 
#9 ·
what do you want? .. quiet loud.. good mid range or all top end? ..if its a 1.4 a three box absorbtion arrangement is good. This free flow thing is deceptive ...you want the gasses in side to resonate ..cos the negative pressure waves travelling back to the engine can scavenge and help the incoming charge ..(valve overlap) .. you want gas speeds to be high ..so wrap the exhaust manifold ..and go for the smaller diameter pipe. The nearer the first silencer is to the engine the better top end you will have
 
#11 ·
Evil said:
But do you really need silencers at all (sorry to jump in uninvited ;) )???
Wouldn't a 2.5", no 'boxes, straight to back of the car be best??

Evil

im sure a exhaust system with no box works very well only on engines that rev to 20,000rpm like the F1 cars but street cars need to have the exhaust note low or you get fined or something (i almost did once with a peco) and a street car needs power n torque below 7,500
 
#12 ·
See.... I read a bit about exhausts and back-pressure and stuff. And I got the distinct impression that (even for a road car) no 'boxes is best.
Seeing as how all the back-pressure the engine needs is created in the headers, the rest of the system just needs to get the gases out as quick as possible.
I'm seriously hoping I understood (and remembered) this right....

On the Monza (as an example, it's all I have to 'run with'), I only have a straight through backbox (the internal pipe is straight and perforated) and I'd like it less restrictive and louder.
I've been told the backbox provides very little silencing, but the 2 pipes from the downpipes do go into a Y piece about 2ft before it.

So would no 'boxes lose me power by the bucketload?? and would it really be that much louder??

In your case I think I would be tempted to run 2" or 2.25" and 2 boxes. If you had to have 'boxes.
 
#13 ·
believe or not mate but u will lose alot of low end power n torque and the bigger in diameter the system the more slower gass speed is.

if u dont care about low-end power n torque go for it, "u lose abit down here but u make up here" and thats how it works, if im right?

its not the boxes that make the differences in N/A engine its the size (diameter) of the system but the box's do take away the stupid loud sound
 
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