I should have put this preface in my previous posting. I'm actually an Alfa idiot.
I don't know anything about Alfas in general (or the model you are looking at in specific). The tiny bit of knowledge I've put together refers to my car specifically.
That said, no I don't have any reliable horsepower figuers of a 2.0L with carbs vs. injection. I've only ever heard the word of mouth stating "it's faster," but we all know how much word of mouth is worth. wink
I don't even know if people mean higher top speed or quicker acceleration at the low end. Personally, since I don't race, I don't care about top speed. On the flip side, I always appreciate quicker passing speeds.
Over the weekend I went on a drive with a group of Alfas. I know it's not empirical evidence, but my spider seemed to be running quicker than most of the rest -- particularly through the twisty bits of the road -- and most of the other cars have had the carb conversion.
While the cars ahead of me didn't ever seem to touch their brakes, I spent most of my time coasting with my foot off the accelerator, and I kept continually gaining on them. So the rest of the time my brakes were in use. It's not the way I prefer to drive, but I couldn't imagine the insurance implications if I caused a chain collision by rear-ending one classic Alfa into another. Of course, maybe everybody else was just a better driver than I was.
When I started restoring my car I didn't even bother looking into the carb issue because I didn't want to incur the time or the hassle or the big bill for fitting carbs. I don't believe in unnecessary fiddling for no reason. I don't need to take on extra problems or work. The Spider gives me quite enough to think about on a daily basis. wink
I specifically didn't buy a carbed car because I don't like to purchase other people's modifications (read headaches and mistakes). I don't have a lot of faith in most of the Alfa owners (in this area) who make their own modifications. My project had enough of the previous owners' "input" to repair before the car could be put on the road.
If I were you I'd e-mail Wes (from all reports he is supposed to be really friendly and helpful, although I have no personal experience to base this on) or call/e-mail the guys at international-auto.com They just recently started selling a repair manual for the SPICA (I wish they offered that a couple of years ago). They also sell all the carb bits and pieces, so I doubt they have a bias. They're always really friendly, and they know their subject material. They're all Alfa or Fiat owners, and they might be able to direct you towards some performance figures.
I know you're not looking for a spider (and I don't even know if the engines are the same in the spider and the GT AM), but I thought I would direct you to the Spider FAQ. (http://spiderfaq.home.att.net/). The following few paragraphs come from the series 2 section:
"In 1969 for the US market Alfa introduced the SPICA fuel-injection system for the first time. Created primarily for the famous Type 33 race car series, it was based on a diesel injection pump. This all-mechanical system provided precise fuel metering, allowing Alfa to squeak under the emissions laws of the US for several years without sacrificing power, driveability, or adding a catalyst. With the possible exception of Porsche, Alfa Romeo was the best adapted and most driveable car make available in the US at that time.
"Unfortunately the new SPICA system was kept a tight secret at Alfa (perhaps, because of the SPICA system’s relationship with Alfa’s racing division, this was not entirely as inexplicable as would at first appear), and enthusiasts in the US greeted it for the most part with great suspicion. In actuality, the system provides better fuel control than the dual-Weber setup, without sacrificing any power or driveability. It is very straightforward, if somewhat unique, and once the proper manuals and (relatively) inexpensive equipment are acquired, very simple to set up and maintain. In delivery, it is quite similar to the "tuned port" injection systems introduced in American cars in the mid ‘80s, but is not anywhere near as picky about fuel quality.
"None of this was clear to owners of Spiders in those days, so a sizable percentage were converted to Weber carburetors. Because today's emissions inspection requirements are becoming more exacting, and workings of the of the SPICA pump are becoming far better understood, an appreciable number of these Weber cars are being re-converted back to the SPICA setup. In Europe, where Spiders were nowhere near as popular and hence less common, people are actually beginning to import the cars back from the US, so they are now experiencing (some would say being afflicted by) the same troubles and joys of the SPICA system. A SPICA equipped car will probably have the only working example of a mechanical computer that you will ever see (except for maybe a slide rule). Once you understand the system, it’s really cool.
"For a more complete set of recommendations about what to look for and what to avoid when buying a SPICA equipped Alfa, I refer the reader to Pat Braden's Alfa Romeo Owner's Bible (available from Robert Bently publishers), at this writing obtainable at most major book stores....
"In 1971 Alfa introduced yet another enlargement of the twincam engine, the (now ubiquitous) 2 liter. Despite this fact, very, very few 2 liter Spiders seem to have been produced in 1971. In one book only 2 are listed as having been imported into the US. It wasn’t until 1972 that the 2 liter motor was produced in large numbers.
"While this motor, in its pre-emissions form, produced (depending on who you believe) 129 to 135 hp (one source claims 155 hp for the European version), it has always had problems with the head gasket. Unlike other motors from other manufacturers, failing Alfa 2 liter head gaskets don't leak coolant into the cylinders, but rather first leak oil into the coolant, and then coolant into the oil (with potential major damage to the engine). This problem has never been completely solved, although advances in gasket design and the introduction of roller-pin-and-square-cut-o-ring kits have helped a great deal. The model designation of the cars changed around this time as well, becoming "115.XX" Spiders (the XX being replaced by various numbers, depending on the trim level of the cars and their relationship to the rest of the Alfa Romeo line). They will be referred to as such through the rest of this document.
"In my own opinion, the Spider’s overall combination of performance, refinement, and desirability peaked during the 1970-1974 years (in the US, at any rate). Which year is mostly a matter of taste. The 1750 engines, while less powerful in raw numbers, are a bit "zippier" and smoother than their 2.0L counterparts. They also do not have the head gasket problems of the larger motors.
"However, 130ish horsepower out of a 117 cubic inch engine (the 2 liter) is quite impressive to your typical speed-shop crowd, and, again in my own experience, there are very, very few modern non-turbo cars with fewer than 8 cylinders that can keep up with a well-tuned ‘74 Spider. Unlike later years, these cars came hot from the factory."
For the record, I've never run into the head gasket problem yet -- knock on wood.
There seem to be quite a few people on alfabb.com who understand SPICAs and the issues surrounding them. You might want to post your question on that board. I seem to be the resident SPICA fan here, and I'm as far from an expert as you can get.
Good luck with your car hunting.