so would 2.75 vs. 3 make a heap of a difference?

 

^^should ask a girl the same question

 

width isn't the only thing that will effect exhaust.
the twists and bends to a certain degree will also affect exhaust flow.
it's a bit more complex than most of you think.

 

I have a 3 inch single exhaust with a mugen header. huge increase in power above 6k rpm compared to same header with stock exhaust. At least that's what my butt tells me. It's pretty convincing too

 

lol wah wah....

What I am REALLY TRYING TO SAY, smart guy, is that without fi, 2.75-3.0 won't really mean much.

 

Sorry for my bastardo english. I'm in-hurry to do something and
didn't pay attention to the subject.

Ok....let me correct my question:
I have a very short exhaust system, no more than 5 feet from the exhaust port to the tip of the muffler. I don't have catalytic. I heard everyone using between 2.5 to 2.75 piping. I like to use 3" all the way. What can I expect from this modification?
I'm using a sidepipe sent by flomaster. The sidepipe is designed for cobra and seven cars. The round sidepipe still under research and sent to me with no charge in exchange for my feedback or information (power-noise) after install. The Hushpower II has inlet of 3" and outlet 3".

No! its not a turbo car. I don't need any turbo in 1,152lbs car.
Yes! i'm not looking for economy...simpy power I can harness.

Thanks

 

Are you using OEM ECU or aftermarket?

Here's my take, Ap1 and Ap2, header and length will make a difference.

OEM ECU = 70mm

Aftermarket = 3"

After saying that and knowing it's going in a lotus 7, I would opt for the 70mm.

#1 it's going to be quieter
#2 Your N/A and the difference won't be worth the increase of sound it will make
#3 There will be very little to no sound proofing, so it's going to be loud.

If you can take loud, 70mm. It sound is more important then power (or already @ 1,152 lbs, you're going to be fast even if you used a 2inch pipe) go with 2.5" (63mm)

 

Everything stock including ECU.
The problem is, the Hushpower II Flowmaster has 3" diam. I decided to use 3" all the way. My question, will I gain or lose power using 3" ???

 

you might gain some power at the tip top of your power band... but it is gonna be excessively loud and your gonna destroy low end.. If the motor really is in the Lotus then Im assuming the car is gonna be mainly for track, so killing low end torque like that would kill lap time.

 

Uhh, you use the top end at the track. Low end is irrelevant unless you race in a series, and then that's only for standing starts.