How to jet an aftermarket cam, #91 Webcam |
|
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG.
This site is not affiliated with Porsche in any way. Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners. |
|
How to jet an aftermarket cam, #91 Webcam |
Kansas 914 |
May 21 2009, 05:23 PM
Post
#1
|
Advanced Member Group: Members Posts: 2,999 Joined: 1-March 03 From: Durango, Colorado Member No.: 373 Region Association: Rocky Mountains |
The symptoms (with 2 different sets of carbs Webers and EMPI same jettings) were the same. It will sit and idle at 1000 RPM with no problem (after a warm up) but is boggy on the low end under load - really have to keep the revs up to pull away from a stop light. Slight throttle increase after rolling creates a studder. Stomp it (WOT) and it runs great - pulls strong. It is like the throttle is an on/off switch, all or nothing - not much in between!!
I think I am close with the jetting but still not quite right. I wonder what the timing should be on a 1.8 with carbs and the webcam? The car also has electronic ignition (Crane Fireball). I read in depth the thread on jetting Zach's 2056 with 44 Webers. I also read a good bit on Harney's Carb Clinic (great read - printed it for reference). Using the formulas in the Harney Guide I am close based on the 28mm venturis. Idle jets should be 1.6 X 28mm = 44.8 (mine are 50) Main jets should be 4.1 X 28mm = 114.8 (mine are 115) I have 1.8L with a #91 Webcam (hydraulic cam & lifters) and Dual 40MM Webers. Here is my current Weber jetting: Vents = 28mm Emulsions = F11 Idles = 50 Mains = 115 Air Correction = 200 Here are the cam specs: LIFT = .430 DURATION = 265 DURATION @ .050 Degrees = 234 DESCRIPTION = Hydraulic grind for high performance street engines. Not recommended for engines with fuel-injection. TIMING CARD: As always your thoughts are appreciated. |
Jake Raby |
May 21 2009, 10:44 PM
Post
#2
|
Engine Surgeon Group: Members Posts: 9,394 Joined: 31-August 03 From: Lost Member No.: 1,095 Region Association: South East States |
The jetting sounds fine to me for a default..
Are these new carbs? Webers or HPMX Empis?? Have you re-set the float heights? Whats the fuel pressure? We have had to modify every carburetor we have used or sold for over two years now and each make has it's own challenges. Carbs don't like hydro cams and neither do I so we'll skip that topic all together :-) Just remember that you still need to adjust your valves and inspect the valvetrain every 8-10K even with them... I bet 50 bucks I know what your gripe is and its not in the jetting... People start swapping jets when they should be looking for other forms of faulty operation, like accelerator pump circuit issues.. |
Lo-Fi Version | Time is now: 3rd June 2024 - 12:33 AM |
All rights reserved 914World.com © since 2002 |
914World.com is the fastest growing online 914 community! We have it all, classifieds, events, forums, vendors, parts, autocross, racing, technical articles, events calendar, newsletter, restoration, gallery, archives, history and more for your Porsche 914 ... |