Vw engine emissions


I am considering building a Porsche speedster replica. I’m excited about this possibility but I also want to be responsible about how this may add more pollution to our planet. I will not use this vehicle as a daily driver. I’ll probably drive it 1,000-2,000 miles a year at most. I want to put a small 1600cc VW engine in the car but I am also aware that air cooled engines emit a lot more emissions then water cooled engines. The questions I have are how much more emissions does a small vw engine produce compared to newer cars and if I decide to build this car what tips would you suggest as ways to reduce the emissions as much as possible. Such as possible exhaust options or other ways to make the engine run as clean as possible.

Thanks in advance for any suggestions you may have about this topic.



A single (stock) carbed air cooled VW will want to run at 3.0 CO and 300ppm HC to idle nice. To give you an idea of how “fat” these figures are I will try to put it in contex, a car of today would not even move the needles on the analyzer that measured that 3.0 and 300ppm on the VW.

To put it another way ,if your 2009 car read 3.0CO and 300ppm HC BEFORE the cat there would be something very wrong with your 2009 car.

If you try and lean that 3.0CO out the HC will go up, just keep it from running any higher that 3.0CO and don’t drive with a dead miss (makes high HC) and your doing the best you can.

There were some half hearted attempts at NOX reduction on the air cooled engine and I don’t think they were very sucessful.

The best way to reduce pollution is to make sure the motor runs as smoothly as possible. Otherwise it is a huge polluter and there isn’t much you can do about it. Hence the reason these motors aren’t used anymore. Attempts to clean up the dirty motors of the past resulted in motors that ran lousy, got horrible gas mileage, and were unreliable. Honda lead the way when they introduced small efficient motors that actually ran smoothly from idle to redline, and from cold starts through warm up. Even these Honda motors had more vacuum lines than you could keep track of, but they worked and were reliable too.

You can have fun with your kit car, but if the pollution you are generating when you drive it spoils the fun, let the dream go and buy a Miata.

Another possibility is to put a FWD engine and transmission in the RWD position. You will effectively have a mid-engine car. I’s a replica, so faithful representation of the original car is only important if you want it to be. You could use the 2.5L I5 VW or the 2.4L I4 turbo. Be sure to measure the engines to see if they fit without modifying the rear bonnet. Or you could use any engine. Toyota built a 1.8L engine for the MR2 that might work. There should be turbo kits available to turn it into the Lotus configuration. But at 140 HP, it will run rings around an original 356 Speedster.

Conforming to emissions is the main thing that killed the air-cooled VWs. The air cools went from no emission devices to somewhat crude emission devices on the last of the carbed models. From there they went to AFC injection which was crude compared to what is used today.

Eventually the cost of making these cars coform to Federal regulations (along with crash testing, etc.) just did not make them financially viable anymore.

Oldschool is right; there’s a night and day difference in CO and HC even if you compare the later injected ones to a modern fuel injected car.

Your best bet is to build it, keep the engine in tip-top shape, keep it properly tuned/maintained, and live with it.
With a bit of time and ingenuity (and a wad of bills) I’m sure one could adapt a late model injection system to an older air cooled engine. Someone adapted a VW CIS injection system to a Subaru but the question I always had was; WHY?