GulleyGulley

I'm in the final stages of my engine rebuild (2.7). Any thoughts on converting from the CIS fuel injection set up to a carb. setup (Webers or Dellortos (sp?). I'm not sure of the condition of my injectors, so I may eventually need to buy new ones or possibly switch to carbs.

Steve Weiner-Rennsport Systems

Hi Jeff:

LOL,...You have asked a big question that has many ramifications. You should know know that emissions compliance is also a consideration, beyond the performance improvements.

Many people will have opinions on this and you should look through the archives to get a taste, but I'll tell you that a properly configured, setup, and adjusted carburetor package cannot be beaten. IMHO, the majority of people who have experienced bad luck with these things have had either worn-out carbs, improper fuel pressures & float settings, improperly adjusted and/or incorrect jetting. Its rarely a hardware issue.

Your only choices are PMO's (new) or Weber (used). Dellorto does not make a triple throat carb. I'd strongly,.........strongly suggest the PMO's.

Bill Gregory

Bruce Anderson also discusses this in his "Porsche 911 Performance Handbook"

GulleyGulley

Thanks for the replies. I was hoping I'd get a favorable response to using carbs over the CIS. I was leaning that way anyways. Just picked up a copy of Bruce's book this weekend - I check on the carb sections - thanks

Bill Gregory

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"><strong>Just picked up a copy of Bruce's book this weekend - I check on the carb sections - thanks</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Also check on modifications to the 3.0L/3.2L engines, as I believe that's where he talks about the CIS to carb conversion.

arknjl007

aloha from hawaii.... FUEL INJECTOR VS. CARBERATERS......i am searching for a similar path... i have removed my fuel injectors from a 82 911 porsche.... in storage 20 years....my questions are..#1. has anyone successfully taken a 6 cylider porsche and successfully ran a 4 barrell set up ... a new plentum....adapter plate for 4 barrell carb ????...... and question #2...has anyone sucessfully set up two- two barrell carbs.....on seperate plentum and adapter plates ...each carb here feeding 3 cylinders....what are the options here other than triple inline carbs or fuel injection.....wouldn't it be economical for a single 4 barrell or 2- 2 barrells.....and what size carbs ??? 500cfm for the two barrells ......i know the best of the best know exactly the do and do NOT here....so any help would be full of ALOHA... we are farmer mechanic kind...gotta build it somehow yeah ???? PEACE

Amber Gramps

Welcome to Rennlist. Please forget the idea of using Holly carbs. Please.

mfyoung1086

There is a shop in Indy putting 4 barrels on race motors

FI is the way to go IMO, MS 3.57 is a really really good update on the DIYer stand alones


buuuttt that being being sad, its prob easier to find a good p-car shop that can properly tune a set of PMO's compared to piecing together a stand alone. If your already leaning towards carbs go for it, both have pro's and con's and both will be better than the CIS your car is currently equipped with

arknjl007

ok ok...no holly carbs...i will be looking into pmo set up... more update when i learn alot more info.....thanks for the replies..aloha

spanky

I have CIS on my 75 911s and have never even thought about putting carbs on. I currently own 2 cars that have Webber carbs on them , my 240Z ( tripple side drafts) and a Fiat X1/9 (2 down drafts). I ve never had a problem with either of them after the car has warmed up but up until then it a bit of a PITA to drive them ( spitting and coughing)!! Either choice will have upsides and downsides. If you plan to run larger cams that are not stock then the CIS must go !! Enjoy!!!

RoninLB

Your "Location" is CNY. If NY there is no smog test for a 25+ yr old car, although NY may have recently removed smog tailpipe testing all together. If NYC give Rudtner's Racing a phone call in Freeport LI and just ask Bill for his thoughts after he gets a handle on you. Give him my sign in name

I have the cat's *** of a street 2.7 w/carbs

It's a toy. If it was a daily driver or if I had no idea of how to treat and take care of it I'd stick with CIS. Best Hy gas mileage is 17 mpg. Around town is 10 mpg if I'm lucky. You have to really want carbs or you'll soon be frustrated with it one way or another. For sure it's not street friendly. It's more of a wild dog on a leash.

carbs and E-cams in a 2.7 when dialed in properly with older 915 gearing pulls stronger than stock 3.2's


good luck

KNS

Is the guy still around? This thread is nine years old...

rusnak

yeah, old thread. One of the great things about carbs in the 911 is that you have one butterfly for each cylinder, instead of a plenum. I didn't understand the 4 barrel question at all. Another is that a carb will not be nearly as precise as the fuel injection system, so unless you are out of parameters due to extensive mods, why ditch the FI setup? I have a factory 914-6 with very old, very original Webers, and I have to tell you it's a major PITA to re-tune them every two years. No fun at all. I suspect an air leak somewhere in a bushing or something but the car is not a DD, so drivability problems are sort of ignored.

RoninLB

from what I understand FI precision is given as the differences in EGT between different cylinders. The idea is to have each combustion chamber delivering equal amounts of power. Combustion power is measured with EGT. Heat is power. The routine carb differences may be 100F-150F, which is noticable. A decent FI should get that EGT differetial down to 75F. A more precise FI should get that down to 50F. This is measured with the engine under load above 4K rpms. Of course engine condition is an issue.

Unfortunitly unless you're running expensive multi cylinder EGT probes and an aircraft computer gauge it's impossible to tune this issue. Aircraft Spruce seels a few of them. www.AircraftSpruce.com

All that bs said there is a guy around that tweaks his 911 w/carbs down to 50F-60F.

so your comment "a carb will not be nearly as precise as the fuel injection system" is valid for us.



and about your air leak..... if you went through the routine air leak finding and still haven't found it there is an electronic hand held air and exhaust leak finder around for about $100. The gizmo is the same and may be sold by various companies with their logo on it. The Snap-On truck may have one on board? Good luck.

RoninLB

Webers and PMOs for our cars are called Indivudal Runner. IR carbs have a barrel for each cylinder. IR is desirable from a performance stand point. Devaluing the car is another issue.