DIY Weber Conversion?

[Wrecked944]

I've been looking at the MotorMiester website and they offer a carb conversion "kit" for less than 2G. I've been thinking about replacing the CIS system on my 1980 911SC with Webers. Is this a "plug 'n' play" install that a backyard mechanic can do? Or is this somewhich which requires an experienced mechanic?


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Janus Cole
1980 911SC & 1987 944

[9eleven]

Its a fairly easy DIY job, but if you are planning on spending anywhere near $2000, I'd go ahead and spend $500 or so more and get the PMO conversion kit, brand new.

They are better, and PMO is a well respected, less, ummm, "controversial" vendor.

Unless you have SSIs and/or plan on changing the cams, however, you will not realize the full potential of carbs. IMO, unless you change the cams to take advantage of the carbs, its not worth switching to carbs.

[This message has been edited by 9eleven (edited 08-02-2001).]

[iustasail]

Unless you split the case, change the cam, and go early exhaust /SSI's, carbs will give you no performance gains at the cost of a lot of noise, bad emissions, pore gas mileage and annoying cold start behavior.

I love the carbs, port/polish, Solex cams, and 914-6 OME/Dansk exhaust on my six with 175hp out of 2.3L; but its a package deal and quite loud with lower gas mileage compared to a stock 3L CIS engine.

[Jim T]

you don't need to split the case to change the cams.

[cds72911]

Ummmmm, guys, not speaking from personal experience but Bruce Anderson says that carbs add about 10 hp to the 3.0 vs CIS and it feels more like 50 hp.

While a cam upgrade and SSIs may be nice, it seems like carbs are reasonable upgrade.

Personally, I'd go for the low-hanging-fruit first: 15-20 hp from a set of early heat exchangers or SSIs and an early muffler. Then carbs after that and cams when the budget allows.

That is basically what I'm doing to my 3.0 - actually SSIs and carbs first, hotter cams later. Maybe not the fastest way to extract horsepower, but it works with my budget.

Charlie

[Wrecked944]

Thanks very much for the info. I definitely intend to have the cams changed. Maybe even a 3.2L p/c upgrade and *maybe* an exhaust change as well. But those are in the distant future when I have the $$ to pay a pro. I was figuring that in the meantime, I'd do as much as possible on the cheap and present my pricey mechanic with as little to do as possible. This carb thing may be do-able. Thanks again,

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Janus Cole
1980 911SC & 1987 944

[Wayne 962]

I'm not a big fan of the carb conversion. You may get a bit more HP at some RPMs, but the motor won't run as well under most conditions. Plus they are crap for the environment (open fuel system), and you can never get the mixture absolutely right with carbs for all operating conditions.

Also, upgrading to a 3.2 with carbs will not be as good as running a 3.2 with the Motronic. If you're going to go for a better setup, I would in general hold out for the 3.2 motor with motronic. One of the primary advantages of carbs is that you can tune and balance them to the displacement of your motor (if you are using non-standard displacement or cams).

In general, it sounds like you are headed down an expensive path that will only net you a couple more HP...

-Wayne

[mjc76]

Read Steve Weiner's articles on his website they are very good. He recommends the carb upgrade over the CIS for performance minded individuals on a budget. His articles are very informative and well written.
http://www.rennsportsystems.com/~porsche/2.html

[RoninLB]

Carbs are another toy to play with. If you are not a " weekend wrench " your in for a wild ride. I woulden't expect a shop mechanic to put in the time that is necessary, unless you are a big spender.........Also, for all those with carbs reading this, I found a fuel filter that uses an efficent "venturi effect" in its 1st stage, then filters to 2 microns. It has a gauge to read the amount of filter loading of this replacable filter, which is also available in 10 microns. A "high water" alarm light is an option. $200-$350 depending on options. I'm into overkill........Ron

[Formerly Steve Wilkinson]

Steve Weiner got me to switch to carbs (PMOs) on the SC engine I rebuild and upgraded to 3.3+ liters (100mm barrels) plus twin plugs, S cams, headers, etc. The CIS intake path is very convoluted, as is the stock exhaust path on an SC. With the carbs and headers, straight in comes the good air and straight out goes the bad air. I love the PMOs; they're fairly simple to set up and tune, using PMO's extensive directions, and they really snap when you stand on 'em, particularly with an aluminum flywheel and clutch. Yeah, they're dirty (no inspection here in Upstate New York), but probably put out about as much pollution in a year of my driving as a Winston Cup car does in one morning of practice.

Stephan

[Wrecked944]

Has anyone ever attempted to improve on the CIS? Such a low-tech system almost begs to be tinkered with. In my ignorance, I can imagine dual throttle bodies and air sensors, each controlling three fuel lines...maybe a mass flow sensor to replace the "barn door" air sensor...modified air box to simplify the air flow path...

Probably a million reasons why those wouldn't work...I'm just surprised there hasn't been some attempt to improve the design short of total replacement...


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Janus Cole
1980 911SC & 1987 944

[wckrause]

The only improvements I've seen or heard of is going to a larger throttle body. This was mentioned in a Bosch book that I have. The author claims that an increase of less than 5 hp was the result.

Also, some people drill holes in the air filter cover and report a difference.