Pros & Cons of CIS vs CARBS

Carbs= performs better, requires frequent tuning, but less electronics to worry about.
CIS 84 and 85= Runs smoother, more reliable, and performs almost as good as the carb.
Just my personal opinion.

 

CIS pro: bullet proof reliability and fuel managment for excellent long term emission control

CIS con: poor airflow and sensitive fuel management requires low lift retarded camshafts creating drastic power loss.

Carb pro: individual thoats per cylinder, infinite and simple adjustability of fuel mixture across entire engine operating range, with airflow, performance and throttle response unmatched by all but the most complex and expensive multiport fuel injection systems. Carbs also have the adjustability to work with very radical engine modifications. Coupled with a chorus that cannot be duplicated, they are unmistakeably Ferrari.

Carb con: Because they operate solely by airflow mixing with fuel, one must study in detail the working characteristics and "art" of tuning them. Alter almost any one thing, and everything else changes with it. Just swapping mufflers or changing aircleaners throws the mixture off, they are that sensitive. And because so many are mystified by them, and because so many "mechanics" are far better at screwing them up than making them work right, they have earned a bad reputation of being troublesome. But its really not the carbs fault. The guys who take the time to tune them properly have virtually bulletproof cars that perform wonderfully.

 

If I had 10 grand or so to swap out the cams on my TR, I would lose that CIS so fast it would make your head spin.
The cam profile is absurd.

 

I agree...it's amazing that they got that much power out of a TR with those "sleepy" camshafts in place. I wonder what gains could be had with an aftermarket fuel management system combined with more agressive cams? I'm sure 450hp would be possible....

 

Since the vast majority of you guys have Ferraris with ancient FI systems, it's no wonder carbs seem better. They are. Those first systems were for emissions first and performance last. They had stupid cam timing, stupid ignition timing and low compression all in the name of emissions control.

Modern systems are very complex and give more power, more reliability and better fuel mileage than a carb could ever dream of. so we need to say pros and cons for a particular application. I might put carbs on a Mondial but you'd be an idiot to put them on a 360.

Ken

 

Good points, I would like to add that the CIS does gets better fuel economy and seems to dirty the oil less. and sense it is harder to get that pugged jet that goes undetected, less chance of a lean detonation damage. All in all the sound of Webers and aggresive cam makes me want them.

 

Anthony,
I owned a carb 78 308GTS and later a 87 328GTS (FI). I guess it all "depends"...the carb car sounded great and ran very well. The down side was that it always needed a bit more warm up time from cold start. Not a huge deal, but I hadn't owned a carb car in a long time...so it was an adjustment for me. Once I traded up to the 328, there was no looking back. I would say if this is a car you will only drive a little, then no biggie, but for me, I put 8,000 miles or more on each Ferrari I have owned, and I no longer want the fussiness of carbs.

 

All but two of my cars have CIS. I have used it my entire driving life with no problems. Jan 06 I got a really cool 74 MGB chrome bumper from the original owner. It is a sweet little car but it is the first carbs I have ever owned. My ONLY complaint is a cold start up. Anytime I take it somewhere I have to plan on leaving 5 minutes earlier just to get it warmed up so it will drive down the road. Once it's hot you wouldn't know if it was FI or not but cold... Drives me crazy.

My other CIS cars are just start and go. Summer or winter, doesn't matter. I never really appreciated it until I started sitting in the driveway playing with a choke lever and reading a newspaper

 

It's not just a question of the "two".

Leaving out the fiberglass versus steel bodies, there's the carb'd 308 (2 valves per cylinder), then the 2v CIS cars, and then the QV (quad valve : four valves per cylinder) CIS cars. By the 328 (3.2 litre QV), it was CIS with lambda. The QVs may have lambda too -- I'm not sure on this. Modern cars use electronic fuel injection.

As said, carbs give more ponies than the CIS machines, although the QV makes up for some of the difference.

But the carb cars require frequent (constant) fiddling.

The CIS systems are plug 'n play -- they're completely mechanical systems and almost never need adjustment. The big pie plate (air flow meter) in the intake makes the throttle response slower (although carbs need an "accelerator pump" to rev really well too).

Over the years, the CIS system got added support "gizmos" -- lambda, thermo-time switches, cold start injectors, etc, etc, etc. More parts = more things to go wrong.

And neither carbs nor CIS have on-board diagnostics.

You have to really know carbs to be able to tune (and sync) carbs.

CIS will almost never break, but when it does, even Jahwah can't fix them quickly: you have to test each and every part, one after another after another.

People on car forums often curse OBD systems for their "proprietary" reader devices and the way they protect the codes like the formulas for witches' brews. But the OBD feature of electronic injection does make it a lot faster to find and fix failed parts.

Of course, with the ability to add cheap sensors, EFI systems often also add enough parts to keep the failure rate up -- although the newer systems can not only detect failure, but work around them ("limp home" modes).

So CIS is in some ways even more reliable than modern EFI (longer MTBF), but in other ways is worse (atrocious MTTR). CIS was used for about a decade on Ferraris, and we're just now reaching the point where things are starting to go wrong. So you'll probably find more Ferrari shops familiar with Weber carbs than with CIS internals. (Of course, you could always get a VW, Audi, or Porsche mechanic for CIS. )

I've been on the fence for some time about converting my 328 from CIS to a custom designed EFI, just to add on-board diagnostics. (And to get rid of the AFM plate.)

(Actually, my CIS still works fine, but I think I've lost the vacuum sensor in the separate Marelli ignition computer, so the engineer in me is typically over-designing; starting from a replacement spark computer (using a modern processor) to converting to individual plug mounted coils, to going full bore to a multisensor (MAF + MP/T) ECU 'puter. -- Then there's the interface to cut off the aircon compressor at WOT ... and the chip could play mp3s in its spare time.
(There's that urge to add "just one more thing" that plagues most computer ECUs )
(I shudder to think what the bells/whistles list on the Microsloth ECU for F1 cars next year will look like.))
(But as long as my design stays on paper (or in the sim 'puter), it's harmless. )

Carbs, CIS, even EFI -- they all have trade-offs.

 

The only thing I will add is that I don't know what all this talk about 'fiddling' with carbs is about. Once they are set up, you just leave them alone and they are fine - damn reliable I'd say.
Now, that said, they are fun to 'fiddle' with, but it's just for fun mostly. And - no special tools required.
Everybody's different - I like Webers for the amazing personality they add, mechanical elegance, sound, simplicity and the reliability.

best to all.

 

Between tune-ups, sure. But compare CIS that you adjust once per solar eclipse.

 

I'd certainly agree with that WHEN THEY WERE NEW, but my K-jet and a growing number of K-jet are starting to have point failures as the units age to be as old - all very normal and also may happen with carbs.
I think that over the next few years that we will start seeing more and more K-jets have some trouble just from aging.
As far as DIY folks go, the carb is much easier to deal with as these natural life cycles progress.

best
rt

 

In many states, no emission checks are required once a car reaches a certain age.
Some states require a smog cert at sale.
Some states just require everything put on by the manufacturer is still in place.
Other states require bi-annual smog certification, like california in the major "air basins".
Maybe, in some states you might be able to get by with a tail pipe test??

My 77 required a cert on purchase but here in humboldt county, no bi annual smog cert - but if i want to sell the car in california i will need all the smog stuff intact and have it able to meet the tailpipe emission test.

Unfortunately, the Swartz killed the rolling 30 year exemption.

hth,chris

 

FYI, US Federal EPA and DOT laws require that all emissions and safety equipment put on a vehicle by the manufacture(OEM) not be removed or tampered with EVER...

 

In other words, after 30 years no one will check your car for that stuff anymore. Do what you want to.

 

My hang-up with carbs are the fuel dangers associated with carb fires, problems with the float bowls, stronger gasoline odors and fuel vapor leakage, etc. I really like the sound of a carb'ed car, but.....I like the startup-n-go reliability of CIS. I'd love to have a Daytona in my garage, but only when money is absolutely NO object and my mechanic is on speed-dial.

 

That is likely true...however, a few years ago at a local Atlanta area car show a CleanAir officer from the Georgia EPA impounded a car in the show that had had it's OEM emission equipment removed...is it really worth that risk...for what? The EPA is welcoming people to turn violators in too ... http://www.epa.gov/compliance/complaints/index.html ... yet another reason not to post on a open forum what EPA and/or DOT laws you plan to violate...

 

DGS, my experience with my carbed Ferraris (well, one of them is really a Dino) is that carb tuneups, WHEN DONE CORRECTLY AND NEVER TOUCHED AFTERWARDS, are quasi-eternal.

Those two conditions are absolute constraints. Tune it wrong and you will keep retuning for years, until you finally find somebody that does it right. Just look at one of the little screws and THINK OF TOUCHING IT (say if you plan to take the car above 3500 ft altitude), and you will be very, very sorry.

Cheers,

Julio

 

+1.

Modern racing cars are presumably smog-exempt, and they haven't gone back to carbs.

Not true in California.

 

One of the few pluses of living in Alabama; especially Birmingham. We don't even have an emissions program.

 

Would carbs offer a performance gain on a 308QV? Would you have to change cams to get the most bang out of your buck for that set-up? (Assuming no worries about emissions compliance.)

 

Yes. Just removing the CIS and installing carbs adds about 30hp, but changing on top of that adds almost nothing. Russ did both on his 328 and has a lot of dyno runs. Doing an EFI conversion adds about the same as a carb conversion, maybe a little more.

 

Whats an emissions program? Just kidding. We don't have one either. They phased it out about 1981.
Strangely, we aren't dying in the streets ...