for those of us

[Dark]

Originally Posted by Red Lion

Of course I think it's majorly excessive, but I'm an ass and I'm using an over-exaggeration to prove a point. Sure, you will get more horsepower with a 3" over a 2.5", no one can disprove that as Ice has already shown plenty of consistent dynos to prove it. But you do lose things in other areas, such as throttle response, noise, and even a broader powerband in some cases (you narrow your powerband, making the horsepower peaky).

My point is just because you make more power doesn't always mean it's the right thing to do for your car, but I guess it depends on what you're running and what you're using it for.



And to anyone mistaking back-pressure with flow, they aren't the same thing. Smaller exhausts have better air velocity, or in simpler terms, the air exits the exhaust at a higher rate of speed. This is because of the pressure difference between a smaller and larger exhaust and why smaller exhausts have better throttle response and better feel for torque at lower RPM's. H
However, larger exhausts flow more air (I wouldn't say they flow better, just more), but the air doesn't come out as quickly or speed up as quickly, which correlates to the decrease in throttle response and sometimes a lack of bottom end horsepower or torque. It's the same thing as the garden hose effect of putting your thumb on the end of a running garden hose; the pressure change makes the water come out harder/quicker, but not necessarily flowing MORE.

If I were to pick a perfect exhaust, it would have to be made with a flow bench to ensure it not only flowed more air but did so at an equal or better rate of speed, which I'm sure most cheap exhaust makers don't do.

honestly i believe that is exactly the point i was poorly attempting to make
thats why i suggested a header with a 2.5" dp leading into a 3" catback... should have plenty of speed as well as flow... altho i havent exactly flow benched one

[Red Lion]

maybe I'm just causing hell cause I'm trying to sell a 2.5" Greddy exhaust
http://www.nissanclub.com/forums/gen...ml#post3513457

[94sealtima]

Originally Posted by tomwito561

Increase you exhaust size if you need it, 3" is good to 500+ HP. You are not really going to notice any difference untill you have better cams.

so stage two cams and 3' exhaust would be about perfect?

[tomwito561]

I just know my car had JWT cams, Sheet Metal Intake w/75mm TB electromotive TEC3 stand alone running full sequential injection 10.5:1 pistons with a Hot Shot header. My exhaust during the dyno session was 3" with a resonator and a turn down (exhaust did not reach rear suspension). It made 182WHP and 149 torque.
I called Burns Stainless they can design you a header based on cams, compression, RPM, everything is noted then they run it through their program and it tells you how to build the header. So I cut apart the Hot Shot bought all the pieces from a different supplier (Burn's is super expensive) an built the header myself. 1.75" stepped to 2" with a close 2" to 2.25" merge and a 2.25" to 3" megaphone. Then I built a custom full length 3" exhaust went back to the dyno and made the EXACT same horsepower. The JWT cams do not have enough duration they are only 1 degree over stock 208 vs. 207. I was planning 13:1 and BC stage 3 cams but I will let who ever buys my head and cams see what they get out of it.
That is the combo the SCCA GT3 KA24DEs run and its good for 320 at the crank. They use custom cams though and will not give up the specs.

[allblackedout111]

Originally Posted by Red Lion

Except...NOT!

The debate was still over. The debate was about more power, not throttle response. There were about ten more posts after mine which said nothing more than what had already been proven and discussed. I completely agree with you about throttle response, which is why i still have a 2.5 inch. Can't be having no throttle response on the back roads can we?

Originally Posted by tomwito561

Sheet Metal Intake w/75mm TB electromotive TEC3 stand alone running full sequential injection 10.5:1 pistons

Can you elaborate on this? Pictures too maybe?

[Iceman00]

Dyno"s Please!!!

[tomwito561]

I don't have the dyno sheets but if I was lying I would have said I made 220 or 250. the photos I have are to big to post here but there are photos of all the stuff on Ebay the link is below.

Search results for altima racing parts in Racing Parts

[Iceman00]

Not calling you a lair, I really want to know.

What rp did you hit peak power at?

[pac99altima]

ice man u prove a good case but i still believe a 2.5 exhaust is ideal for an N/a altima

3inch's and we're talking bout the land of turbo and dats not what i have planned for my altima amongst others

worst case scenario : bolt up a 3inch get a dyno with proof and there goes undeniable fact =]

[tomwito561]

It peaked around 6,500-6,700 then fell off. I did the pull to 8,000, thats why I keep saying it's all about the cams. I increased the flow by building a cutom header, but after 6,700 the cams are moving to fast thus not keeping the valves open long enough to get enought fuel in to keep making power. Thats why Hot Shot can make a header that has a 2" diameter tube as a collector. Because the basic modded street engines will not flow enough to warrant a better design.

[Iceman00]

Originally Posted by tomwito561

It peaked around 6,500-6,700 then fell off. I did the pull to 8,000, thats why I keep saying it's all about the cams. I increased the flow by building a cutom header, but after 6,700 the cams are moving to fast thus not keeping the valves open long enough to get enought fuel in to keep making power. Thats why Hot Shot can make a header that has a 2" diameter tube as a collector. Because the basic modded street engines will not flow enough to warrant a better design.

6500RPM? How? Was it the manifold or the header? Normally with JWT cams, power peaks at 6000rpm. I was about to go with a Different cam setup, but now I think I might stick with JWT.

[tomwito561]

I think you are correct I dont have the print out anymore so I was guessing. My good friend owns the dyno and I could have him look it up if you really want to know.

[Iceman00]

Yes, I really want to know. If JWT's fall off is partly due to the manifold, by switching it to the Xcessive unit, I can extend the powerband without having to go with a more aggressive cam. Though PDM's Cams are looking quite nice...

[Asleep]

extend the powerband with turbo, yo.

[Iceman00]

Originally Posted by Asleep

extend the powerband with turbo, yo.

Lol, a turbo won't help my power from falling off at 6000rpm, I'll be just making so much power, I won't care.