Since I'm running an engine that has been converted to carbs from the '74 injection, I'm hoping that my current setup will work with the 3.0 with carbs. What do I look for, and where, to see how the current back pressure situation is handled?

Charlie

IMHO if you are looking for power doing cam and exhaust mods would get you more power than replacing the CIS with carbs.

Unless you are keeping your engine up around red line all the time you arn't even using enough air to where carbs will flow better than a cleaned up CIS.

Having jetted dozens of motorcyles and a few cars too boot I will also take CIS over carbs anyday when it comes to easily providing a good A/F curve over the full RPM range.

The only thing better than CIS is EFI.

Now if we were talking about what sounds better my opinion would be complete different though.

A lot of people's butt dynos are overly effected by noise and vibration.

Of course, you can't replace the cams if you don't get rid of the CIS.

And the word you want is "affected."

Superman did a nice up-grade cam install with his CIS.....Ron

- Ok, I guess I should say you can't replace the cams with an aggresive cam -- the 964 type will work.

We keep going around and around, tossing out information
that's been discussed, but not really focusing on the topic.

We know that improving cams, pistons and exhaust will improve just about any engine. But what can the guy in his garage with a mild budget do to improve his stock CIS engine?

We know that advancing the timing and dialing in a richer setting helps. I love the way me car runs with CIS and the tweaks to it. But the stock CIS engine has terrible efficiency.

So what can that guy with the mild budget do to improve his engine without dropping the engine and tearing into it to replace cams and pistons?

Replacing the induction and exhaust should open up the engine quite a bit, right? So carbs and an early or early-style exhaust will allow the engine to breath much better, even with the stock pistons and cams.

SO! Who's got a dyno chart for a stock 3.0 with SSI's or early exhaust AND (!) carbs?

I don't know about that. Late euro SCs had 68HP/litre, which is similar to a 2.4L 911E with MFI (68.7 hp/L), and almost as good as a 964 (69.4 hp/L). That is pretty efficent for a two-valve normally aspirated single plug engine without a computer. It is considerably more efficent than the EFI 4 valve 3.4 litre V6 in my truck. (55.9 hp/L)

Quote:

So what can that guy with the mild budget do to improve his engine without dropping the engine and tearing into it to replace cams and pistons?

Add lightness.

Quote:

Replacing the induction and exhaust should open up the engine quite a bit, right? So carbs and an early or early-style exhaust will allow the engine to breath much better, even with the stock pistons and cams.

No matter how efficent the induction/exhaust is, the engine will only pump as much air as the cams allow. CIS can handle a lot of power, (turbos, and Andial's stuff) but it doesn't tolerate cams with a lot of overlap. Carbs certainly have a shorter and cleaner induction path than CIS but if the engine can't pump any more air than CIS delivers, it won't help all that much, except for the somewhat subjective "throttle response".

Quote:

SO! Who's got a dyno chart for a stock 3.0 with SSI's or early exhaust AND (!) carbs?

Bruce Anderson's book says

" ..the conversion to carburetors is good for an additional 10 hp for a total increase of 20-30 hp-- but the greatly improved throttle response feels more like 50 hp."

The previous paragraph covers backdating the exhaust, so his 20-30 HP total is the combination. He also says that you need an 78-79 distributor to get enough advance once you junk the vac cannister.

Used Webers can be found for ~$1K, depending on what they come with, you will still need manafolds, air cleaners, some way of adapting the vac system for your brake booster, probably some other small stuff I haven't thought of.

If you have a "mild budget" I am not sure this is a lot of bang for your buck, especially with the downsides.

You pay your money and you take your chances.

Tom

Good points Tom and as this thread shows the prejudice against CIS is high and a lot of it is due more to opinion and rumor than fact.

Souk, How mild is your budget? First, I would do SSIs. Next Webers. Fianlly, pistons and cams. Some say the 964 type cams alone a worth it, but if I do an engine drop, I'd do the pistons also.

IF you are in a smog area, then you pretty much have to go to a newer engine (stock).

I agree with rocket person on one thing -- you want to separate fact from opinion. I do it with a dyno, with science and engineering principles, and with accel. times. The only way to get rid of the metal sensor plate in the air flow path is to get rid of the CIS. The system was the first try at FI not using MFI, and was designed for economy and lower pollution. EFI is much better.

I happen to love my CIS engine, but....

If I have to choose between building an engine versus removing the CIS and installing carbs with a better flowing exhaust, I would choose carbs and exhaust.

Even with just a top end "rebuild", I would need time (mine is free to me, a wrench's is not), P's & C's (or just P's), cams, seals and gaskets to built a 230HP+/- engine. (notice I left off exhaust). I'd send my heads off for a refresh too. All of that takes a lot more time and money than removing CIS and installing carbs (and ancilliary equipment). AND I still have to buy carbs and and exhaust.

To get 20-30 HP more, I can spend a weekend of my home hobbiest time to pull the CIS and swap in carbs. In the same weekend I can swap exhaust.

Distributor? Well, I have a 78 distributor. If I had an 80-83 SC, I'd send the distributor out for recal., but that wouldn't require my car being disabled for a week or more. A week if I really budget my time and worked in the garage every night after work...late into the night!

To get my CIS engine to Euro spec, I'd have to spend time and money too. How much will it cost to get my engine up to Euro spec...for 204 HP!

So, keeping bigger picture in mind, how would I rather spend my time and money? How much of that do I have? And is a 230HP+/- engine going to be worth that time and money (compared to a 210HP engine carbed stock 3.0)?

The 230+/- and 210 HP are just guess (I'd love to see test data of the two "case" engines), but the point is the exponential cost of HP.

If it were someone else's money, and I could dream of a "potent" engine, you can bet I'd be dreaming big.

As for opinions and rumors..no one here has presented test data of one or the other (specific to the two "case engines"). I'll debate the value of the work until the data is available.

Exactly my point...progression as dollars are available.

ahh yes! science and engineering principles...and DATA! That would be a good start...then we can debate the value of the data :D

Well, if you HAVE to scrap the CIS why not just buy an old carrera intake and a nice aftermarket EFI computer and do it right.

It will still be way cheaper than a new set of carbs or about the same as a nice used set.

Then your induction limitations will cease to exist and you can do anything with the engine that you like.

Rocket man, I hate to sound so contradictory..but EFI would open up another messy can of worms in this discussion. :)

But I like messy cans of worms. ;)

My argument is that if you have to bastardize the car then why switch to an inferior technology?

Carbs may look and sound neat as hell but switching from any FI to carbs makes as much sense as going from electronic ignition to points.

If someone wants to have it all then go with individual throttles and velocity stacks with injectors.

When it comes to low restriction, tuning and power NOTHING beats EFI. I just view CIS and MFI as EFI's low tech predecessors.

As long as we are talking getting rid of intake restrictions, don't forget that the low pressure the carb uses to suck fuel into the air flow is created by restricting air flow at the throttle and/or venturis.

Sounds like a risky anti-carb scheme to me.

http://forums.pelicanparts.com/uploa...1062955910.jpg

As I recall the original poster has a mid year911 and an SC motor. My vote would be to install the 3.0 motor with carbs and early exhaust in the 911. I suspect the car would be very quick....EFI or not!

Ditch the CIS, install the webers and have fun!

Rick Deman just tuned, re-jettted and dynoed my 3.35-liter, twin-plug, PMO-carbed, SSIed, S-cammed 911SC and got the equivalent of 290 hp at the crank, assuming a 15-percent power loss to the rear wheels. Lightened somewhat, it's a monster for its streeability and age. Throttle response is like one of those Japanese cars where they give you 80 percent of the throttle effectiveness in the first half inch, to make them feel stronger than they really are...

Stephan

Yes! And my similarly modified but very mildlly cammed 3.2 turns 250 hp on the engine dyno -- with a ruler flat torque curve.

But these type of engines cost $$. Souk wants to do it in bit-sized pieces.

I'm not sure if that's a "complete" impression of Souk.. I think adding that he'd rather do a slow perfect install rather than a quick big bucks wallop is clearer. That kinda style usually goes with the mechanically obsessed wrench guy IMO. His replys reflect that /whatever .............Ron

Hey do not forget what I forgot, that you need to make provissions to get vacume for your brakes. There are two places on the manifolds where you can drill in bosses for this. But you may need to add a vacume tank as well. I have tried not using the tank and 85% of the time the brakes are fine, but they are not as good as before. I can not figure out why since the place I am getting my vacume is closer to the vacume source than with the cis set up.