fuel injection,carbs,what to do?

[rfuerst911sc]

I know it's early to be planning next winters project but that's what I'm doing.I have a 83SC with CIS and while it works fine I want to change it,I want to "clean up" the engine compartment and maybe move to a more modern system.Having said that it appears to me the options are carbs either Weber or PMO,TBitz's CIS to EFI conversion or several aftermarket EFI systems.I am not looking to build a fire breathing beast but maintain a good street car.I am not planning to change cams or any internals at this time because the car is very healthy with 107,000 miles but want an induction system that would allow larger pistons/cylinders and more aggressive cams if I choose to do so in the future.Also I am keeping my AC if that matters.So what do you guys suggest?

[jpnovak]

I would suggest the EFI system. Tony's (tbitz) kit should be easy to install and cheaper than the carb alternative. It would also be emissions legal and give better gas mileage. It should support some hot cams depending on the lobe center (overlap). John (camgrinder) could make you a custom cam for EFI that fits well with a new displacement, CR and other concerns.

[randywebb]

The important questions are:

What emissions regs apply?

How much do you want to spend?

Do you want to be able to work on it and tune it yourself?

[Grady Clay]

I agree with Jamie.

Carburetors are an extension on 19th century technology. They are inexpensive, work well in many applications, can provide reasonably high performance, and are original to many 911s and Porsche race cars through the late ‘60s.

Mechanical Fuel Injection (MFI) is a product of Bosch’s fuel system for Rudolph Diesel’s engine in the early 20th century. In our application it is great in specific applications. It is original high performances stuff from the mid ‘60s and ‘70s. One of its primary advantages is the very high pressure (230 PSI) nozzles and the timed aspect of injection. The disadvantages are there is no feedback – it is a mechanical computer with very limited inputs. Pre-WWII technology but works great.

Continuous Injection System (CIS) is a product of the ‘70s emissions revolution. It provided reasonable performance with reduced exhaust emissions. The disadvantage is it is restricted in cam profile and other.

Electronic Fuel Injection (EFI) is the current hallmark. The advantage is the computer with feedback. The technique is the engine management (ignition and fuel delivery) is determined by ALL the conditions. Those are; throttle position, engine RPM, air temp, oil temp, detonation sensors, and much more. The sophisticated systems apply formulas and programs to translating the inputs to the outputs.


Randy asked some good questions. With a laptop, EFI, data logging, and appropriate software you can “fine tune” an EFI 911 engine. Remember, there is no substitute for all the machinery being correct.

Best,
Grady

[jmz]

I don't think I would change anything unitil I had a clearer picture of the end result. For instance, if you think you will put some wild cams in there at some point you will need individual thottle bodies. Port size also is a factor depending on displacement compression etc.

[rfuerst911sc]

Thanks guys keep it coming.Yes I plan to install and tune myself if possible.In Orlando I don't have emission testing.As far as future cam upgrades I don't see going any more radical then 964 or Webcam 20/21 cams.From a simplicity standpoint I like the TBitz kit but I see the advantages of ind. throttle bodies.I will continue my quest to gain knowledge on how to make the right decision.

[911nut]

I've heard some talk about using 993 SS cams in an SC motor and that they may be hotter than 20/21's. Does anyone know more about this?

[mede8er]

I'm going to PMO's on Bluebird just because I'm a hopeless romantic hardheaded oldschooler.......

[Formerly Steve Wilkinson]

I love my PMOs (3.4 twin-plug '83 SC), but to take advantage of them, you really need to also go to headers and an S cam. the "advantage" of the carbs, with such a setup, is that the air/fuel dumps straight down into the combustion chamber and straight out into the [relatively] straight exhaust, rather than going through the contorted path that CIS and a stock exhaust requires.

I also love being able to tune 'em, the instant response, and the sound. And yes, I realize they're old-fashioned, dirty and somewhat inefficient. I wouldn't have them on the car if it weren't that it's a 20-percent track/80-percent pure-fun street car that only does about 3,000 miles a year.

Stephan

[Mike Bonkalski]

I sold my Webers carbs to go with IDA 3C throttle bodies with an integrated fuel rail. The money I got for the carbs was an even swap for the throttle bodies. Add a Megasquirt, TPS, fuel pump, fuel pressure regulator, injectors, a few fittings and a couple of cheap GM temp sensors and you are ready to roll.

[jmz]

Mike,
What have the results been like?

I am in a similar situation I am parts rich that could easily fund an EFI conversion, Mechanical inj or get me well on my way converting to a 3.6.

[KobaltBlau]

Originally posted by rfuerst911sc
I don't see going any more radical then 964 or Webcam 20/21 cams.

then stick with the tbitz kit, or even the CIS if it is working well. MFI or ITB EFI (or webers, for that matter) would be quite a bit more expensive, and it is only worth it if you have hot cams and all the associated parts to go with.

[rfuerst911sc]

In case it wasn't picked up in my posts I have upgraded to SSI heat exchangers and a M+K 2 in 2 out muffler.I think if I were to go with a 964 type cam profile and either TBitz EFI or Motomotions ind. throttle body injection it would be a very strong street engine.Add to that a upgrade to 3.2 litre and it gets even stronger.These are potential upgrades in the future.Like any other DIYer I am looking for the most "bang for the buck".

[Grady Clay]

The most “bang for the buck” comes from increased displacement, higher compression ratio, and induction/cam/exhaust systems to match your use.

Best,
Grady

[afterburn 549]

Yea what Grady said...and I know there are peo that would have nothing but carbs....but in this day compared to a stand alone sys (S.A.S). I would have to say Porche would not even put them on today, even it could be done ....Bet they would not do it. There is just so much more then a carb in my life,and good grief Cherly Brown when all done you could buy a very good S.A.S.

[randywebb]

Whatever happened to that el cheapo motorcycle throttle body thread? It seemed like such a good idea...

[Grady Clay]

Randy,

I’m not dismissing any throttle body. It is the concept of EFI that Porsche embraced with DME. Look at the gains achieved in performance while still meeting changing emissions standards. Today there are many choices for our “old” 911s. EFI is a good choice, depending on many factors.

Consider the comparison where you re-program an algorithm in EFI to changing emulsion tubes in a carb or changing the “space cam” in MFI.

As I said above, the big difference is the ability to use feedback. That is a HUGE difference. It let’s the engine run at the thermal and detonation limit without damage. With the tap of a few keys you can totally change the properties of the ignition and fuel systems. I suspect soon that will be true of valve operation.

Wouldn’t everyone like to have a 911 that with the tap of a few keys would be exceptionally drivable with great fuel consumption on the street, outrageous performance on track, and meet emissions standards? That is where this is heading IMHO.

Best,
Grady

[TonyG]

I've got an '82SC, rebuilt engine, bone stock with 20/21 cams, 40mm PMO's, SSI's. 200RWHP at 6000 rpms.

Idles perfect. Drives 100% as smooth and perfect as the CIS injection the PMO's replaced (with the exception that you need about 20 seconds to warm up the car since the PMO's have no warmup fuel enrichment setup).

I might be selling off the PMO's and the recurved/rebuilt distributor to go to an individual throttle body setup with a TEC3 in order to do a low boost turbo setup (Can't do that with the PMO's)... but that would be the only reason to part with my new PMO's (I love em).

TonyG

[Shuie]

What are your emissions standards for an '83? I havent lived in FL for a while, but Im going to assume they are at least as tough as mine are. Stick with the CIS or go to EFI. Thats right, I said it. EFI. Since Im a big fan of MFI that was hard to do. I feel better now

You could use the tbitz kit, or maybe even find an old Carrera setup w/DME on ebay. Or you could go to ITBs if you really feel like spending some money. If you want to run a mild-hot cam you probably want to get start saving for the ITBs.

good luck and keep us up to date. Im shopping DME motors right now and getting ready to start the same learning process.

[jpnovak]

Randy, I am still working on the MC TB thread. The parts are waiting for the new engine. I started the teardown last weekend. Updates are on the engine build threads...

Let's just say the new induction fits well with the new engine design. There will more updates in future posts.