CIS vs. Webers

so i asked Roy at motormeister about the 915 transmission rebuild and also got some answers from DRD and warren.

this question is about my CIS system...after reading through bruce anderson's handbook and sorting through some other resources, i begin to think that the CIS system is really bad as far as throttle response and power goes...i am about to finish the job of changing from the stock ignition system to the Ignitor pointless and MSD setup...that will hopefully address some of the problems that i have benn having...

but when i go out to really make this thing scream, how far can i get with the CIS system? is it really as bad as people say, or can i still get a good 200HP and pretty quick throttle response out of it?

going to the 2.7 RSR rebuild will gain me how much?

how big is the difference between going with only the 2.7RSR rebuild with the Hillclimber Tranny (as warren calls it), as opposed to adding the SSI exhaust and Webers to it (which will add another 4K to the bill)?

what is the most bang for the buck update to the stock 2.7L 911S engine?

questions, questions...

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1976 911S Targa

A lot of what you are contemplating hinges on the smog requirements for your car. If you are constrained by this then gears may be your only way. As for the best bang for the buck - you first start with the exhaust, updated or SSI with a free flow muffler. Next go to Webers for improved throttle response, expect to loose several MPG. The final boost is cams and pistons. This wakes up everything to its full potential. When the tire smoke clears you have just spent about six grand on parts. You decide if it's worth all that. Check out the talk section of www.rennsportsystems.com and read up on Bruce Anderson - very helpfull info.
P.S. I'm getting about 200HP at the crank from my CIS 3.0L w/SSIs and 25MPG on the highway with low gears in the box.
P.P.S. One of my mechanics has a '76 with the 2.7RS setup (Webers), he gets 225HP at the crank, don't know about mileage.

[This message has been edited by RarlyL8 (edited 03-24-2000).]

rarlyL8...did u change the car to low gears and SSI? it appears to me that low gears and the RS setup without webers and SSI are my first (and maybe only) option...CA has pretty tough emissions laws, so you're probably right about being somewhat restricted by that...

the main question is (and you should know this, because you are still on a CIS): how worthwhile does the CIS feel with your enhancements? do you get what you would consider good throttle response? have you compared a car like yours to one with Webers, and was difference something that made you think "Wow, what a difference" or "Hmm, cool, but not worth the trouble?"

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1976 911S Targa

I did most of the mods that were listed on my last 911. My current car ('78SC 3.0L) has CIS, SSIs, and short gears. The gears came with the car. The less power a car makes the more you notice the gears. I put the SSIs on for about a 20HP gain. The reason that I will not go with Webers on this car is that on an SC a cam and piston change would also be needed to make the webers work in a significant (worth the $2000 that they cost) manner. I have removed all the smog crap and made a forced air induction system for the stock airbox that pushes outside air down its throat. Works real well. This in combination with the lower gears makes for good throttle response, but not quite as crisp as the Webers. Also, while doing a wide body conversion on the car I got rid of every once of extra weight not needed - including the A/C. The coupe weighs around 2500lb wet.
So to answer your question, yes the mods work well together and no Webers (to me) aren't worth the cost due to the other mods needed to make them work well. I like the gas mileage with the current prices being what they are.

Till, I have the exact same year and model car and have had the same contemplations about various upgrades. Not sure what you are setting the car up for, but here is my history. Started with a 1976 911S Targa, 2.7L CIS, with 75K miles. I have owned this car for two years. I read through Bruce Andersons book along with a few others and came to the realization that the 2.7L 1976 engine is not really one of the best engines out there. Many disadvantages and problems with all of the emissions equipment (Smog pump & complicated exhaust), chain tensioners, head studs pulling, etc. The first upgrade that I made was the removal of the smog pump and the installation of 1974 style heat exchangers and a sport pipe (B&B). This conversion made a big difference in the performance of the car and I would recommend it to anyone. The oil fed chain tensioners and raceware headstuds had already been installed. This would have been my next step if they were not already there. I next started to look into the webers vs. CIS and potential CAM upgrades. If I was going to do this much work to the engine I probably would have went ahead with a complete rebuild. I started to cost out all of these upgrades and the total was well above the cost of a rebuilt 3.0L or 3.2L. The conclusion that I came to, based on what I use the car for is that the CIS is fine. I am a weekend driver and I do not race. With webers installed, E or S cams, and some sort of higher compression performance P&C's the porsche handbook claims around 225 HP. To spend 6K-8K dollars "roughly" to get me from approx 185HP to 220HP was not worth it to me. The CIS starts easily and does not need much maintenance. If you are setting up a car for racing, maybe the upgrades are worth it to you, but I would evaluate spending the amount you are talking about on a 2.7L vs. a complete engine upgrade. Let me know how you make out and what you final decision is.

Good suggestions from both of you...two out o' two who got used to the CIS...makes sense, considering the maintenance, fuel efficiency, etc...

hey RarlyL8...how did you build that induction system? does it take air away from the engine causing a bit more heat, or do you draw the air from somewhere else?

BTW, John, i also had the chain tensioners put in during the last big visit to the garage...the headstuds are still stock, and since the engine only has about 40K miles on
it i also hope to still be fine with these until i decide for a full rebuild...how much did you spend for the heat exchangers/sport-muffler changes?

tomorrow hopefully Don (the mechanic) will put the MSD system in...the car's currently running on a blue coil only, and performs badly at high RPM's...

going on with trying to get everything to work in harmony...i'll post what comes of it...thanks until then.



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1976 911S Targa

Till, the location of the air inlet for a ram-air setup depends on the bodywork you have on your car. If you have a wing it's easy, just seal up the airbox and run a hose to the wing grill and seal it at that point (the added hose needed for when the engine lid is up will form a J pipe when the lid is down so water won't run into your engine when it rains). If not, take a look at the design of break cooling hardware. The flat air intake can be mounted about anywhere and the hose run to your airbox. A more involved method would be to run a hose from a cutout in the front vallance through the rockers and to the airbox. Racers use plexiglass opera windows with molded in air inlets (not a good thing for a street car though). Any way that you can harness fresh air that is forced in while you drive will work. In my case I have a 3.8GT wing, the one with the dual air inlets. I simply made them functional. None of these methods will take away from engine cooling. Use your creativity, It'll work.

Hey Guys,

I also have a 76 911S. I just want to remove the emissions equipment. Once I do this do I need to do anything special? Thanks.

Gonzo, the removal is pretty easy. Realize that you will not meet emisions though. You can remove the belt that drives the air pump and the system will be obsolete. There is a diagram of the entire air injection system on page 74 of the Haynes manual. If you want to get rid of all the air injection equipment, you can leave the air injectors right in the head. Remove the belt driven pump, the bracket and the all of the tubing running to the smog injectors. If you want to eventually upgrade the exhaust system to a 1974 sytle you may need to remove the injectors and plug the holes with bolts where the smog injectors go into the head. This is the only way that I could get the new heater box to fit on the car. I forgot what the actual bolt size is. Make sure that the bolt you use is not any longer than the smog injector. You will want to use bolts of the same material as your head so that you don't have two different rates of thermal expansion.