![]() |
|
|
|
Registered
Join Date: Sep 2007
Posts: 56
|
Poor low speed driveability
I have an 83 sc with 120/104 camshafts, tec3, twin plugs, ssi, sport muffler, 98 Mahle p&c 10.2 compression ratio, Magnecore wires, gt3 fuel pump, carrera intake, wide band o2 sensor.
It runs well above 3000 rpm. It surges below that. Do you think more tuning would smoothen it out below 3000 rpm? |
||
![]() |
|
Registered
Join Date: Jul 2001
Location: Portland Oregon
Posts: 7,007
|
Hi,
If you are using a Carrera intake manifold & throttle setup with 120/104 cams, this combination will never run properly under 3K due to intake reversion. The solution is either less camshaft or another intake system such as ITB's or carburetors.
__________________
Steve Weiner Rennsport Systems Portland Oregon (503) 244-0990 porsche@rennsportsystems.com www.rennsportsystems.com |
||
![]() |
|
3 restos WIP = psycho
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,665
|
Quote:
![]()
__________________
- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 |
||
![]() |
|
Try not, Do or Do not
|
Steve is absolutely correct. The cam is entirely too aggressive for most EFI systems. Excessive overlap seems to be the culprit. The lobe center on a 120-104 is 100. I would think that any lobe center less than 108 would create intake pulses that would be difficult for your EFI system to overcome.
If your system can substitute idle vacuum with some other data perhaps you can cheat the system. I am not by any stretch of the imagination an EFI expert so with a cam this aggressive you may be fighting an losing battle.
__________________
Henry Schmidt SUPERTEC PERFORMANCE Ph: 760-728-3062 Email: supertec1@earthlink.net Last edited by Henry Schmidt; 08-19-2008 at 09:40 AM.. |
||
![]() |
|