hi all
just a thought - I've read constantly that a 3" cat back exhaust is too large for a naturally aspirated 3.5 L engine. I can understand this, as the gains up top would be overshadowed by the crappy low rev power.

but

I've also read lots that large exhausts shine when computer mods come into play.

so therefore would it make sense to get a 3 inch cat/muffler and 3inch exhaust (along with extractors and intake) just before doing computer mods to gain even more power than the 2.5inch system without crappy low end?? has anybody done this?

IMO it would be a waste on an NA. i recently changed my 3" cannon MUFFLER to a regular 2.25" inlet muffler and you can really tell the difference!! isnt backpressure amazing?? :bowrofl:

I'm sure that an ECU upgrade will improve low RPM torque. Chipping isn't just for top end power, it will effect he whole rev range. Exhaust diameter will also be the case. A chip may partially fix row RPM torque loss but I wouldn't stuff up drivability just for a top end power figure for a power run. Even the Commo and Falcon guys steer clear of a 3' with their larger engines.

That said, you can only try and let us know how you go. You just might prove us wrong. How about 2.75? .25 larger than 2.75 is worth more than .25 large than 2.5.

I thought backpressure was a myth! Like, it was just a concept someguy made up while he was drunk in a bar one day... :nuts:

The concept of Backpressure is really simple, The Idea is to maintain still a good positive pressure inside the cylinders when the exhaust gasses escape, so when the inlet stroke opens fully, you don't have to fill a vacuum. Basically you're giving yourself slightly denser mix.

Another thing with back pressure, if it is the right amount, it will help the extraction of exhaust gasses from other cylinders.

Does this make sense?

mmmmmmmmmmmmmmmmmmmmmmm................yeh, I've read all that stuff before...not 100% convinced on it though...


still, 3" system on a magna NA....u could go to 14year olds and go i have a 3"! :nuts:
meh, max i would go myself is 2.5", but like redav said, dunno if there's really any point going 0.25" larger.

The concept of Backpressure is really simple, The Idea is to maintain still a good positive pressure inside the cylinders when the exhaust gasses escape, so when the inlet stroke opens fully, you don't have to fill a vacuum. Basically you're giving yourself slightly denser mix.

Another thing with back pressure, if it is the right amount, it will help the extraction of exhaust gasses from other cylinders.

Does this make sense?

Well, if that was correct, then we're wasting our time buying headers. Headers give an increase in performance as they scavenge more exhaust gas from the cylinders and I'd almost say well enough to lower pressure enough to cause a little more air to be sucked it. That give's a little more air to burn with the rich mix therefore more bang. It's quite possible to fit headers and cause a car to come closer to leaning out.

I'm not sure how back bressure fits with this but if you have an amount of air flowing at a certain speed which enters a larger space, it slows down. This is why low RPM torque is lost. It's like looking at a river. It's fastest at it's narrowest point. That's not to say the better exhaust needs to be narrow but a river don't move much relatively at it's widest point.

i thought the reason for 3" systems not being suited is solely to do with turbulance.

I'm running a 3" cannon muffler on my car. With dyno tuning to back it up.. Have to say that the only loss from the mod is a greater loss of traction lol

I'm running a 3" cannon muffler on my car. With dyno tuning to back it up.. Have to say that the only loss from the mod is a greater loss of traction lol

Is it just the muffler or the rest of the piping? Wouldn't matter what size the muffler is at it's outlet as long as it's equal to or greater than the piping. It's the rest of the piping that counts.

i was considering going a larger exhaust if i kept my car - but that was only after bolting on just about EVERY bolt on mod RPW has to offer and making a shy flick under 200FWHP - on a stock engine - i don't think it is worth it - it is the bottle neck of the power in your system so there is much better efficient methods of power available - and a ECU tune won't completely help with a 3" system

muffler - meh - debatable over the good of a 3" cannon over a 2.5" lukey - either way - it is more free flowing - but i don't think a 3" system is worth it unless you are putting out some impressive figures - or you are forced induced.

Manual

Lil off the subject,

i got a 2.6L elante .......... i got a 2.5 inch exhaust and as everyone says 2.5 inch is to big for a 4 cylinder .... when we were on the elante cruise i found that i didnt have the same low rev power that the others had ( this was minimal....) but when it got to mid to high revs it flew though the extractors helped i ges ........

anyways what im sayingis for us 4 bangers dont get a 2.5inch exhaust if ur looking for performance.. the only reason why i got it was it was the guy at midas knocked some $$ off for me and said it would sound good ... so being only a 1st gen , power and performance isnt something i was after anyways.

just thought that might help some of the first gen guys cos i know a few are doing some serious mos now

If you want a good article then try this page.

web.tampabay.rr.com/redroby/3liter/

I believe he is even talking about our genus of engine.

Very good explanation of why you should do what mods at what time and why a 3" just wont work properly.