exhaust and cold air intake advice

[EUR003act]

2L motors should only ever go 3inch if theyre charged (whether turbo or super). you dont get any gain above a 2.5 in small n/a motors, you can even loose power by going to big. this is what ive been told by multiple exhaust guys that have been doing custom setups all theyre life

[blk05gli]

it will be interesting to see the dyno results - nice work though

[ginganggooly]

2L motors should only ever go 3inch if theyre charged (whether turbo or super). you dont get any gain above a 2.5 in small n/a motors, you can even loose power by going to big. this is what ive been told by multiple exhaust guys that have been doing custom setups all theyre life

I doubt these exhaust folks would have had much experience with k-series race cars... The results speak for themselves really. In fact, all the sub 13 second k-series hondas i know of are running 3" exhausts.

[EG5]

I doubt these exhaust folks would have had much experience with k-series race cars... The results speak for themselves really. In fact, all the sub 13 second k-series hondas i know of are running 3" exhausts.

3 inch FTW , As Slim said - results speaks for themselves
Tried 2.5 and 3 inch on our k20a eg already. We dont lose power at all running 3 inch

[Omotesando]

You don't lose power but do you lose low-mid rpm torque?

One would assume the 3 inch is great for high end power at the sacrifice of low rpm grunt. If you'll be revving to 9500-100k rpm I guess 3 inch is better.

?

[BiLL|z0r]

100k rpm, wow that's a high reving engine

[EUR003act]

I doubt these exhaust folks would have had much experience with k-series race cars... The results speak for themselves really. In fact, all the sub 13 second k-series hondas i know of are running 3" exhausts.

excellent point there... and as said later on, im guessing you lose alot of low end power/ torgue? and as for noise, im guessing constant drone while cruising?

[Omotesando]

100k rpm, wow that's a high reving engine

Yeah sorry I couldnt count lol. Should have read 10K RPM you cheeky boy :P

[ginganggooly]

excellent point there... and as said later on, im guessing you lose alot of low end power/ torgue? and as for noise, im guessing constant drone while cruising?

I don't know for sure as i've never seen the two graphs overlaid. I would assume that you would sacrifice some low end power. Sometimes the drop is quite small- I went from a 2.25" to a 2.5" on my b18c and had solid gains from 3k rpm onwards with a negligible drop below that point...

In terms of noise- not really, I've been in a few vehicles with 3" systems that have been reasonable, and i've been in a few cars with 2" systems that were absolute barry crockers... I think the choice of mufflers, resonators, lengths etc have a huge bearing on this.

[Omotesando]

But pls remember 2.25 inch to 2.5 inch is a much less significant jump compared to 2.5 inch to 3 inch piping.

The piping area of 2.25 is only 4 square inches smaller than 2.5 inch.
The 2.5 inch jump to 3 inch piping is 8.8 square inches more, or 12.8 squre inches more than a 2.25 diameter piping.

In other words, the jump from 2.5 to 3 inch has increase the pipe area by more than 200% than the jump from 2.25 to 2.5 inch. and that's not taking into consideration the difference between 2.25 to 3 inch!

So there is most probably going to be a much more significant loss in low-mid-range power going from 2.5 to 3 inch than 2.25 to 2.5 inch!

[ginganggooly]

But pls remember 2.25 inch to 2.5 inch is a much less significant jump compared to 2.5 inch to 3 inch piping.

You need to take into consideration that I'm comparing a 1.8L b-series to a 2.4L k-series. The k-series heads have much better flow, and the bottom end has an additional 600cc...

If i were to fit an aftermarket exhaust to the euro, i'd fit a 3". I imagine you'd need to be going a little further than just bolt-ons to really get a decent benefit from a 3" exhaust.

[EUR003act]

all good points, and as i said at the start, i wanted a very quiet exhaust when not driving hard (i do alot of 3+ hour driving). and yes i definately agree, if you went 3" you'd definately have to do more than cat-back (extractors would be a must) if you wanted high power gains...

i suppose my questions will be answered on sunday when i see my dyno results!