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Re: [T3] Dual carb versus EFI ?

On 14 Nov 2001, at 21:02, James Wallace wrote:

> Would someone please provide a "rookie" explanation of the trade offs between a
> EFI engine versus a dual carb set-up?

EFI was introduced on the type 3s in 68. It was introduced in order to meet 
the increasingly tight emissions requirements. The 68 VW type 3 was the 
world's first mass produced EFI car, and, as such, provided a test bed for 
every EFI car produced over the last 30+ years.

In addition to reducing emissions, the EFI gives easier cold weather starting 
and more even power than the carbureted engines. It does not require 
rejetting for high altitude as it is automatically compensated for air pressure. 
It has few moving parts, and if not abused it is extremely trouble free. There 
are few adjustments and these adjustments are stable over decades, so the 
only adjustment that might need periodic attention is the idle speed. 

While repair parts can be expensive, it is generally possible to get perfectly 
good used parts at good prices and replace any EFI part that has failed. 
Thus repair can be cheap, but only if you figure out exactly what is wrong. If 
you, or your mechanic, just start replacing parts randomly the cost can 
quickly skyrocket. 

OTOH, the EFI is a "black box" which is pretty much obscured from our 
inspection, so those who feel the need to tinker with it will be frustrated. It 
does not have internal adjustments that one can easily change to override 
the emissions controls in favor of higher power. I don't think any of us know 
how well it can be made to work with larger displacement engines, as this 
just really hasn't been tried. Its one real weakness is the wiring harness 
which is fragile and easily damaged by careless mechanics and owners. A 
second problem for people who don't work on their own cars is in finding 
mechanics who can be trusted to work on our old Bosch D-Jetronic EFI 
systems; they are pretty rare these days, so doing your own work is MUCH 
better (also cheaper, faster, & reliable.)

Carbs allow for infinite tinkering for higher power, and this is both a strength 
and weakness. Many owners are seduced into a carb conversion by the 
claim that carbs are simple and anyone can install one, but then they 
discover the multitude of jets that every carb has and the fact that the set 
they bought did not work quite right with their engine. The learning curve for 
figuring out the right jetting combination for your engine is just as hard as 
learning how your EFI works. It is also true that the carb parts you may need 
(jets, gasket kits, electromagnetic pilot valves) are also getting hard to find. I 
suspect that most people with carb conversions never get it quite right, and 
just manage to produce a car that runs pretty much okay, but pollutes like 
crazy. Probably the best way around this problem is to search out an original 
67 dual carb set of parts.

The whole pollution issue is a hot potato, but my personal opinion is that 
pollution is something that we all have to share a concern about. It's not just 
the other guy's problem, and it's certainly not true that we can continue to 
pollute at the same rate that our parents and grandparents did. Same thing 
with gas consumption, which brings on a dilemma: In general, cars which 
pollute less, use more gas.

In the end it is a matter of personal choice, but it is a mistake to assume 
that a switch to carbs will be either cheap, simple, or quick.

Jim Adney
Madison, WI 53711-3054

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