Thread: Question on 3" setups

That question is retardedly vague to be answered accurately. If you want to know, why not do it for yourself?

EVERY engine responds to mods differently, there are almost infinite factors that affect the power, even down to the temperature and humidity during the test. In fact, anything less then a 5-10hp difference could be accounted for in dyno error.

On the question of the exhaust valves, running without an exhaust manifold can crack valves. This is because, if ran long enough, you can heat up the valves a decent amount, if you then shut off the motor, cool air can reach the valves, and possibly crack them due to rapid temperature change. The susceptibility comes down to port and head design, as well as valve placement.

The Power gains from the Exhaust size will be more related to camshaft design than anything else. Engines with more duration and overlap will be more susceptible to reversion from back pressure

Again, the question has been diverted by someone who has no answer. Gains were to be had on stock cams with basic bolt-ons. So , the question is what are the gains of a 3 inch over the traditional 2.5 or 60 mm catback? I know 3 inch makes the most power, but how much? I'm not trying to justify keeping a smaller exhausts, but want the information out there besides " go 3inch, it makes most power".

To be fair; These were Ronnie's 2 basic questions. You can go read dyno charts anywhere on the internet.

More on the "backpressure is good" myth.

I wouldn't say you are choking the setup. I am running a 2.5" SSAC and a 60mm Greddy catback/stockcams/popcharger/ss/prothanes/lightweight flywheel vs n1 cammed/b15 trans/pop charger(basically same setup minus cams and trans. Welll, we did a second gear roll and i got the jump and stayed ahead even in fourth gear. Either I have a freak motor or 60mm isnt choking it.

Its documented by the Honda guys. Go search honda-tech I've seen a few stock block h22s making low 200s test 2.5 vs 3 in and there are very clear gains.

Maybe I should have mentioned when I bumped this thread that it is 2.5 years old. =/
I was merely trying to keep historical theories (read: crap) I've posted up to date.

I'm about to go with a 3" system, my car at the moment is running a 2.5" mandrel bent system using 2 Magnaflow resonators to keep it quiet.

My header is a 2.5" SSAC and I will keep one of my current 2.5" resonators, then I'll go 3"

Since the diameter will be increasing I will be ok right? I just don't wanna ditch the 2 resonators and have a significantly louder system.

I will be going 3" just after the O2 sensor is bolted (shown in picture)





And this will be the tip, 75mm HKS Hi Power

not much point keeping the 2.5 reso, 3" all the way