Hi, I'm a bit unsure about the system that's in my car at present. Mild pinto into 4-2-1 extractors, 2" outlet, 2" system with triflow muffler before the diff.
A guy I've dealt with at the muffler shop advised against anything bigger than 2 1/4 because I'll lose back pressure. He made a HUGE point about this but from what I see on the forums, bigger seems better. The triflow definitley keeps the car quiet, sounds fantastic at idle (crow cam), relatively quiet on throttle but makes popping ang gurgling noises when decelerating, the main reason I'm looking for other options.
I have a feeling the 2" system with straight through muffler after the diff will offer better performance. The engine is MUCH quiter than the xflow, so straight through might be ok. Otherwise chambered???

sounds like the guy at the muffler shop is an idiot. why would you want to restrict the exhaust from coming out of your engine?
i had a 2.5inch system with 1 muffler in it and i went back to a 2.25inch with 1 muffler before the diff because the 2.5 was too loud for my liking.
i didnt have the car dynoed to see the difference between the systems but it felt like i lost a little bit of performance from going back to the 2.25. i did gain the ability to hear things a lot clearer in the car though
 

The muffler shop guy may well be right concerning the exhaust size.
Sure you want minimal back pressure, which a larger pipe gives.
But the LARGER an exhaust, the SLOWER the gases travel.
The faster the exhaust pulse travels, the better it scavenges out the spent engine gases.
It's a compromise.
 
Cheers Gregg

ratta tat tat

Hi, I'm a bit unsure about the system that's in my car at present. Mild pinto into 4-2-1 extractors, 2" outlet, 2" system with triflow muffler before the diff.
A guy I've dealt with at the muffler shop advised against anything bigger than 2 1/4 because I'll lose back pressure. He made a HUGE point about this but from what I see on the forums, bigger seems better. The triflow definitley keeps the car quiet, sounds fantastic at idle (crow cam), relatively quiet on throttle but makes popping ang gurgling noises when decelerating, the main reason I'm looking for other options.
I have a feeling the 2" system with straight through muffler after the diff will offer better performance. The engine is MUCH quiter than the xflow, so straight through might be ok. Otherwise chambered???

 
2" done right is ample for a mild Pinto.  Not a fan of triflow mufflers though, they flow like crap.  I just use a basic straight through glass packed muffler and resonator (no step downs or baffles).  This keeps it quiet with a good note.
 
Woz

Woz, are you referring to the resonator when you say "no step downs or baffles?? This would just be a hollow hot dog, no glass or perforations?
And do you put the resonator before diff, muffler after diff? Or vica versa?
Thanks
 

ratta tat tat

Woz, are you referring to the resonator when you say "no step downs or baffles?? This would just be a hollow hot dog, no glass or perforations?
And do you put the resonator before diff, muffler after diff? Or vica versa?
Thanks

 
Some hotdogs step down in internal diameter, you dont want this.  I use the ones with no internal baffles or chambers, you can see straight through them and with no perforations (just holes, or perforations facing in, not out).
 
Muffler usually mounted in the OE place, resonator under boot floor at the rear.
 
Cheers
Woz
 

Ok. Thanks a lot

Wozzah Muffler usually mounted in the OE place, resonator under boot floor at the rear.

Cheers Woz

Hi Woz
I've been reading Scott D's MK1 build on RSM.
http://www.rsmotorsport.com.au/forums/viewtopic.php?f=27&t=3100&start=100
Danny recommends having the muffler under the boot floor, says it will go better. I like the look of it too, seems popular in europe.

Is there any reason not to do it this way?
Muffer under boot, resonator before diff.

This is the way I've done all my cars since the late 80s (teenager yrs ). For some reason running a back box(under boot) creates better sound and performance, tho my zetec mk1 has 2x boxes due to noise and both are same type and size. For a 1600 run a max of 2in zorst and 2.0 run a 2.25in. Fit a back box 1st try it for sound levels etc and if too loud(?) Fit a rezzy before the diff ..

Mounting mufflers and resonators as far back as possible gives the gases the opportunity to become more laminar in flow as opposed to turbulent. This is a major reason why cats and mounting right mufflers etc on the end of extractors is bad.

On the flip side some mufflers are actually designed to have a minimum pipe length after.

Laminar flow is not only more efficient but easier to noise suppress.

In theory the system needs to be optimised to work with the reduced back pressure of a larger pipe. In reality it just gets too noisy to suppress.

Please do not every use top fuel zoomies as an example. That is a totally different application with zero scavanging occurring in the design.