Changing the stock cams. What about the ECU?

[P10DET]

Originally posted by pche059
haha damn
well thx alot man... gosh you are quick too
hey is it worthwhile to get the cams done on an auto G20?
the kinda gear ratio you have on an auto requires a rather wide powerband to get the car really moving ....am i right?

Well, most of us Yanks like a wide power band anyway. We tend not to rev the engine as much (well, some of us). It's some strange thing with our general population. I guess they think the engine will explode if you rev it above 4k rpm or something.

I cannot comment on the cams for your car yet since they are still in testing. I would imagine JWT will come out with a set with a broad power band though. I think they would give the car a good bit more zip, but again, until the testing is done, I can't exactly say.

[pche059]

haha

Well, most of us Yanks like a wide power band anyway. We tend not to rev the engine as much (well, some of us). It's some strange thing with our general population. I guess they think the engine will explode if you rev it above 4k rpm or something.

this is not quite true...I used to drive a 2.2 DOHC VTEC...and man you will pick up a habbit of redline your car after owning one of those.....
the fact that there is still plenty of torque around the 7.2k rpm....

sad that with SR20DE s.... nothing much is left after 6000rpm.....

[P10DET]

Originally posted by pche059
sad that with SR20DE s.... nothing much is left after 6000rpm.....

Well.... most SR20DEs.

Actually, it's not that hard to make a SR20DE happy at higher revs. The older ones are certainly happier though. Keep working on the breathing....

CAI, cams, and header really bring it to life at higher rpms.

[pche059]

I have got my CAI done already....
am still thinking about the exhaust system...

how would the header and the big bore alter the power curve do you know?
would it extend the power band? to a high rev area or is it just more torque but power band remains?

[P10DET]

Originally posted by pche059
I have got my CAI done already....
am still thinking about the exhaust system...

how would the header and the big bore alter the power curve do you know?
would it extend the power band? to a high rev area or is it just more torque but power band remains?

The header (if it's a good one like Hotshot) will give you gains across the board. It should taper off far less at high rpm. Breathing is the issue at high rpm with the SR20. As long as it can breath, it will keep making power up there.

If you mean throttle body when you mention big bore, it will do nothing for power based upon dyno tests by others. It will improve throttle response due to the larger area.

[T4 Primera]

Originally posted by pche059
I have got my CAI done already....
am still thinking about the exhaust system...

how would the header and the big bore alter the power curve do you know?
would it extend the power band? to a high rev area or is it just more torque but power band remains?

I'll assume you mean a big bore exhaust. Be aware that if the exhaust piping is too large in a NA car you may lose power in the lower rpms. This is because the larger pipes can lower the exhaust gas velocity and screw around with the cylinder scavenging effect. Because volumetric flow is lower at lower engine speeds, the exhaust gas velocity can become too slow (if the pipe is too big) to help evacuate the cylinder at the end of the exhaust stroke. If you fit a header, then the critical part becomes the diameter and length of the primary pipes and the collector. I have a link at work that I'll post tomorrow which gives some rough guidelines.

[T4 Primera]

Here's the link for general exhaust pipe sizes.
http://www.isd.net/jhadfiel/exhaustsize.htm

A 2L engine is 122ci (which is off the bottom of the scale on this link) and lets say your gonna make 150-200hp at the flywheel, according to the chart, a 2 1/4" single pipe will be more than adequate. any larger and you'll likely lose bottom end torque, and in extreme cases, high end hp as well. Fitting a well designed header would make this a non issue as the header will bring things back (exhaust gas velocities) to where they should be. In this case you will get no gain from having pipes larger than the final collector on the header.

Also see this post for more cam info http://www.automotiveforums.com/vbulletin/t8026-2.html

[P10DET]

Originally posted by T4 Primera
I'll assume you mean a big bore exhaust. Be aware that if the exhaust piping is too large in a NA car you may lose power in the lower rpms. This is because the larger pipes can lower the exhaust gas velocity and screw around with the cylinder scavenging effect. Because volumetric flow is lower at lower engine speeds, the exhaust gas velocity can become too slow (if the pipe is too big) to help evacuate the cylinder at the end of the exhaust stroke.

BINGO!

So many people think that lower backpressure causes you to lose torque, but that's hogwash. Backpressure is never good. But, if you go too big you lose the velocity, just like T4 said. That is bad.

[P10DET]

Originally posted by T4 Primera
A 2L engine is 122ci (which is off the bottom of the scale on this link) and lets say your gonna make 150-200hp at the flywheel, according to the chart, a 2 1/4" single pipe will be more than adequate. any larger and you'll likely lose bottom end torque, and in extreme cases, high end hp as well. Fitting a well designed header would make this a non issue as the header will bring things back (exhaust gas velocities) to where they should be. In this case you will get no gain from having pipes larger than the final collector on the header.

Yep. I concur. Anything larger than 2.25" with anything but a fully built engine is not only overkill, but likely to cause a loss of performance. Mandrel bends though please.

As for collectors, Mike Kojima has done a fair amount of testing prototype headers for Hotshot and they found that any collector over 2" actually lost power - even on his built engine.

There is a large amount of misinformation about exhaust size still floating around and I think it comes from old school hot rodders of American domestics. On many of them the exhaust is so bad that they almost couldn't do anything to make it worse. That's really sad since most US cars have such a narrower operating range than most European and Japanese engines. IOW, the European and Japanese cars must have exhausts that work well from say 2000 rpm to as much as 8000 rpm and more. The US cars only need to flow from 1500 rpm to about 5000 rpm or even less since most US V-8s breath so poorly anyway near their redline.

[pche059]

hey...from the sound of this...
how about just changing the header and keeping the rest of the exhaust system?
am i still gonna get power gain?
save me money too

[P10DET]

Originally posted by pche059
hey...from the sound of this...
how about just changing the header and keeping the rest of the exhaust system?
am i still gonna get power gain?
save me money too

Yes, you will still gain power. In fact, you will still gain most of your power. The exhaust will only net you an addition 2-3 hp most likely.

I would say, bang for the buck, pound, frank, etc, exhaust is way down the list.