Engine Rebuild Question

I am having my 73.5 Targa 2.4 engine rebuilt (rings,valves,guides,bearings,etc). I also had the CIS system removed and Webers installed as well as oil fed tensioners. My mechanic also sent the cam to Webb Cam to be tuned for the Webers. My questions are, what exactily was done to the cam and how will what was done improve the performance of the engine? What can I expect as far as changes in performance from the original CIS to the new rebuilt Weber version?
Thanks for your help, Paul

You need to ask your mechanic. And of course if the cam is "hotter" you have suficient valve to piston clearance.

[This message has been edited by mackgoo (edited 10-24-2000).]

Mackgoo, Thanks for your response. My cam was made "HOTTER" but, that's my question. What is physically done to the cam to make it hotter and how does this translate to more HP (performance)with the Webers vs CIS? Thanks,Paul

I believe that when a cam is made "hotter," it is generally given higher lift and longer duration (i.e. the valves are kept open longer). I believe that one of the drawbacks of CIS is that it cannot use high lift cams, because for reasons that are not entirely clear to me, the high lift upsets the air flow monitoring. Something to do with pulses in the intake, the CIS needs smooth intake to accurately meter fuel.

Higher lift means that the valves are lifted off of their seats higher. This, of course, opens up the air flow, its just like a hose and water, the more open a water valve is, the more water flow you get. Internal combustion engines are basically air pumps, and the more air you can pump in and out of cylinders, the more power is generated.

Cam timing over lap is the problem with CIS. The intake valve opens before the piston reaches TOP DEAD CENTER, well not all of the exhaust gas goes out the exhaust valve some of it goes back up the intake runner causing the stream of intake mixture to pulse. Cam preformance can be incresed without adding lift. Web cam is very good at there job and offer cams that do not need new pistons to work.

With CIS as in my 83 SC motor I had a smooth throttle responce form idle to red line. I could idle the car down to 35 MPH in fifth gear without lugging the motor and then stand on it and it would pull out smoothly. With the Webers or PMO's it won't be so smooth maybe a little burble if you mash it at low RPM's. You are probably going to lose some of your low end torque but gain high end torque.

I'll make a suggestion. Ask the motor wizard what grind he ordered and call Web Cam and talk to them, they are very friendly and helpful.

Randy Jones
1971 911

Since you are into the engine at this time for big $$$, anyway, I think it would be wise to consider different pistons, as your stock CIS pistons are only 8.0:1 compression, and machining them for additional valve clearance makes little sense.

After you find out what cam grind your mechanic ordered ... and I hope it wasn't constrained by your stock 'T' CIS pistons, discuss with your mechanic (or here) what pistons are available, sucjh as a J&E set for 'S' cams and 9.5:1 compression ratio. Also, used, but within spec, sets of 2.4E and 'S' piston and cylinder sets are available and would be suitable for your Weber set-up. If Web-Cam has not already started work on your cams, a grind that matches the Garretson Enterprises GE-60 profile grind, or the factory 'S' profile, matched to a set of 'S' or J&E pistons will provide maximum power out of your Weber-equipped engine for the street!

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Warren Hall
1973 911S Targa