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Old 01-13-2008, 11:29 AM   #7 (permalink)
EcoModding Apprentice
Join Date: Jan 2008
Location: SF Bay Area
Posts: 150

Silver Bullet - '02 VW Golf TDi
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Originally Posted by Dane-ger View Post

I've played with the carbs on the engine quite a bit...and I also have a chart that give tuning specs (in terms of turns from closed of the main fuel jet) as a function of altitude and I have some baseline data that I can work from without leaning them out so much that it detonates. I also have a colortune device that I use when adjusting the carburetors.
Great...sounds like you have a handle on it!

(Hard to tell from your initial post how much you knew about the details of the car -- didn't mean to tell you stuff you already knew. )

As far as reducing HC's with an air injection/cat converter combo...I would be willing to bet that the cat was responsible for most of the actual reduction in emissions. If I did get a cat...I would use one of those high flow cats meant for modern high performance make absolutely sure restriction is minimized.
Yes, absolutely...the cat is doing virtually all of the work. Cats have to have have free oxygen to work efficiently, though, which is where the air injector comes in. By adding oxygen to the exhaust stream, the air injector system assures that the cat can work efficiently under all conditions. Summit Racing has a good selection of Universal Cats to choose from.

Of course, I offer this with the presumption that you are interested in maintaining the car emissions legal. I understand your next check is in 4 years, but I see little down side to maintaining low emissions while working to improve your car's FE.

It's obviously your choice, though...

Did you mean to say 6-2-1 headers (the L24 is an I6, not an I4). Actually, the stock manifold is a 6-2-1 design that works well with the engines firing order. The OEM manifold is actually a fairly good design...dyno tests have shown it to be comparable performance wise to many of the available aftermarket headers...using a 2.5" exhaust from the manifold back however has been proven to increase both power and gas mileage. I think the ultimate set-up would be an equal length 6-1 header with a 2.5" exhaust (equal length header combined with free flow exhaust is hard to beat).
Yep, my bad! I have a '72 Dime. For non-Nissan folks that's a Datsun 510. Its spare engine still has the cast iron header, which is, as you note, much better than the standard Detroit cast iron exhaust manifold. The header actually in my car is a long-tube 4-2-1 design that feeds into a 2.25" exhaust pipe. The L-24 in your car is the exact same engine with two cylinders added in the center, so I bet a 2.5" pipe would do the trick.

I actually already have one of the tallest geared diffs (3.36:1)...but I could convert to a 5-speed from a 280Z or 280ZX one of these days, which would do the same thing.
Sounds like you have all the easy stuff lined up and yes, a taller 5th gear would definitely help.

Still, you have chosen a car with a massive overbite and attendant drag 'shute front end. Good thing they're such handsome cars, eh?
Best tank ever: 72.1 mpg in February 2005, Seattle to S.F.
New personnal best 'all-city' tank June '08 ... 61.9 mpg!
Thanks to 'pulse-n-glide' technique.
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