'74 2.7 Weber or CIS Pros & Cons.
01-27-2003, 02:19 PM
#1
6th Gear
Thread Starter
'74 2.7 Weber or CIS Pros & Cons.
Building a '74 2.7 and know that the CIS will be in need of repairs, wondering if I should scrap the heap and purchase some webers?
Questions:
Better performance?
More Reliable?
Compatibility with the 2.7?
What kind of modifications are required?
Do I need a choke, living in Hawaii?
And so on, and so on...
Looking for some real life experience other than my own.
Thank you.
Questions:
Better performance?
More Reliable?
Compatibility with the 2.7?
What kind of modifications are required?
Do I need a choke, living in Hawaii?
And so on, and so on...
Looking for some real life experience other than my own.
Thank you.
01-28-2003, 03:35 AM
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Check prices on rebuilt webers (with no core exchange) . . . app. $2500
Check prices on rebuilt CIS . . . app. $750
Now. . . .Weber = mucho grande power when mixed with the appropriate cam, valve size and pistons.
CIS = reliability and good service/mileage but if I understand correctly it has to use a less radical cam??
Anyway, Bruce Anderson has some good info on the internal differences of the carburated and CIS engines.
Check prices on rebuilt CIS . . . app. $750
Now. . . .Weber = mucho grande power when mixed with the appropriate cam, valve size and pistons.
CIS = reliability and good service/mileage but if I understand correctly it has to use a less radical cam??
Anyway, Bruce Anderson has some good info on the internal differences of the carburated and CIS engines.
01-29-2003, 10:05 AM
#3
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If considering webers, unless you have some already, PMO's would be the newer alternative (improved Webers). Also, as D.Autry indicated, read Bruce Anderson's "Porsche 911 Performance Handbook" as he has some good discussion on the CIS to weber conversion, what's involved, etc. Bruce also talks about it in a number of discussions in the Up-Fixin' series.
And D.Autry, you're right that CIS can't handle much change in the cam profile.
And D.Autry, you're right that CIS can't handle much change in the cam profile.
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Superdave312 (10-18-2020)
01-29-2003, 02:06 PM
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Pelican has a good article on CIS with cam mods. Seems that the 964 grind will work with CIS.
I'm going to tear into an old CIS in the next month or so. I wonder if there's any way to damper the vane without effecting response. Maybe if it were dampered somehow it wouldn't be as succeptable to pulsations.
ANYway, seems that pelican came up with a fairly good increase in HP (about 45 over stock) by going to higher compression (9.5 I think) and a 964 grind on the cam. They probably retrofited with and early model exhaust too, but the writer of the article claimed app. 230 - 240 at the fly (203 dyno'd at the wheels) on a '77 3.0 after the mods.
By the way. It looks like Vertex has rebuilt CIS units for app. 500.
Also, someone has listed a set of Webers on Ebay.
<a href="http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33550&item=2401143493&rd=1" target="_blank">http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33550&item=2401143493&rd=1</a>
It's low right now, but I still can't afford them so have at and good luck.
I'm going to tear into an old CIS in the next month or so. I wonder if there's any way to damper the vane without effecting response. Maybe if it were dampered somehow it wouldn't be as succeptable to pulsations.
ANYway, seems that pelican came up with a fairly good increase in HP (about 45 over stock) by going to higher compression (9.5 I think) and a 964 grind on the cam. They probably retrofited with and early model exhaust too, but the writer of the article claimed app. 230 - 240 at the fly (203 dyno'd at the wheels) on a '77 3.0 after the mods.
By the way. It looks like Vertex has rebuilt CIS units for app. 500.
Also, someone has listed a set of Webers on Ebay.
<a href="http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33550&item=2401143493&rd=1" target="_blank">http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33550&item=2401143493&rd=1</a>
It's low right now, but I still can't afford them so have at and good luck.
