PRE and POST VTEC torque drop. please help
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PRE and POST VTEC torque drop. please help
ive got a B18C and there is the infamous torque drop right before VTEC, then it VTEC engages for about 500rpm then ANOTHER torque drop for about 1K rpm. I'm running the stock p72 but i have a skunk2 IM. could the second drop be caused by the ecu wanting to open the butterflies??? at what RPM's do the butterflies open??
also does anyone have any recomendations for settings for adjustable cam gears?
thnx for the help.
also does anyone have any recomendations for settings for adjustable cam gears?
thnx for the help.
Joined: Nov 2001
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From: DE, USA
Re: PRE and POST VTEC torque drop. please help (1slowcivic)
Basically, GSR have 2 Torque peaks.
1st one is at 3,000 rpm then slowly goes down.
2nd one is @ 6,200 then slowly goes down.
The GSR engages vtec at a low 4,400 rpm but compensates this with the longer intake runners to retain air velocity. @ 6000rpm secondaries open and air has direct shot @ the cylinders.
If you swap out the 2 stage manifold, you will have to raise the vtec engagement because there is not enough air velocity at lower rpms when vtec kicks in.
@3500-4000 rpms the "small lobe" cams runs out of breath which explains the torque dip and there is not much you can do about it. But you get it all back when it switches over to the big cam plus a little more.
[Modified by JD_B18CDX, 11:30 AM 12/19/2002]
1st one is at 3,000 rpm then slowly goes down.
2nd one is @ 6,200 then slowly goes down.
The GSR engages vtec at a low 4,400 rpm but compensates this with the longer intake runners to retain air velocity. @ 6000rpm secondaries open and air has direct shot @ the cylinders.
If you swap out the 2 stage manifold, you will have to raise the vtec engagement because there is not enough air velocity at lower rpms when vtec kicks in.
@3500-4000 rpms the "small lobe" cams runs out of breath which explains the torque dip and there is not much you can do about it. But you get it all back when it switches over to the big cam plus a little more.
[Modified by JD_B18CDX, 11:30 AM 12/19/2002]
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Re: PRE and POST VTEC torque drop. please help (JD_B18CDX)
thnx for the quick response. that makes perfectly good sense. i have the JUN program sitting right in front of me. i need to solder it in. i also have my old VAFC in front of me which i need to install so now that i know the motor is healthy im gonna put em in. thnx again.
oh yeah, do you know some good settings for the cam gears??? i know every engine is different, but usually there is a small adjustment that works for everyone.
oh yeah, do you know some good settings for the cam gears??? i know every engine is different, but usually there is a small adjustment that works for everyone.
Joined: Nov 2001
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From: DE, USA
Re: PRE and POST VTEC torque drop. please help (1slowcivic)
oh yeah, do you know some good settings for the cam gears.
If you dont have access to a Dyno, leave it @ stock settings.
I have skunk2 stage1 cams and +1 +1 works best for my setup.
If you really want to mess with it.........
In theory, if you advance both intake and exhaust cams @ the same rate, you shift the powerband in a lower rpm. This might work for you because the "Dips" will be less pronounced but might not get the most out of your IM. Just hope that the IM flows a whole lot better to compensate.
Advacing or retarding either one of the cams only will affect duration and you definitely need a dyno to do this.
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