weird results: octane matters?

[Piotrsko]

Funny, we usually thrashed #1 on a 72 super, dual port with 750,00 miles, generally overheated. Got about 75k per engine did 12 in total.

We also ran 135 main jets, (the engine would run well on 125) on generally 1 year old factory stock 33PDSIT carbs because that was the only way it would pass smog in Bakersfield due to 1st generation alky additive fuel. Made our own dual advance distributor using 009 weights and springs which made it 209 M distributor. Ran .017 gap to avoid gear change flat spot because aftermarket point conversion kits made everything worse.

All this and the pipes were still black. So it was either not burning everything or it was rich.

[Isaac Zackary]

Originally Posted by Piotrsko

Funny, we usually thrashed #1 on a 72 super, dual port with 750,00 miles, generally overheated. Got about 75k per engine did 12 in total.

We also ran 135 main jets, (the engine would run well on 125) on generally 1 year old factory stock 33PDSIT carbs because that was the only way it would pass smog in Bakersfield due to 1st generation alky additive fuel. Made our own dual advance distributor using 009 weights and springs which made it 209 M distributor. Ran .017 gap to avoid gear change flat spot because aftermarket point conversion kits made everything worse.

All this and the pipes were still black. So it was either not burning everything or it was rich.

The VW's may have been 10% richer, I'm not sure. But Super Beetles never came with dual carbs, nor did any of the T1 engines in the USA so I'm wondering how the 33PDSIT carbs were "stock" on a T1 engine, especially for that year. Aren't those T4 carbs? If so, there probably isn't a "stock" jetting on that engine for those carbs. I'm just saying... And that's my 2 cents.

[Piotrsko]

72 t4 in California was mandatory EFI, (Bob Bosch jetronic), so no carbs, single throttle body. Unique effect with CHP radios tactical frequency.

I said dual port, means 2 holes in head for intake not common runner port. Single carb.

[Isaac Zackary]

Originally Posted by Piotrsko

72 t4 in California was mandatory EFI, (Bob Bosch jetronic), so no carbs, single throttle body. Unique effect with CHP radios tactical frequency.

I said dual port, means 2 holes in head for intake not common runner port. Single carb.

Ok. Interesting, I didn't know that the T4 engine had mandatory EFI in '72 in California. But that makes sense seeing how EFI became standard on all air-cooled VW's in 1975.

I was just confused by the "33PDSIT carbs" on apparently a single engine you mentioned. As far as I know, The 1300, 1500 and 1600cc single port T1 engines got single 30 PICT carbs and the 1600cc dual port T1 engines got single 34 PICT carbs with the 1300cc dual port engines getting single 31 PICT carbs, which I'm guessing is what you meant. Of course the T3 also got the T1 engine but with a different cooling system and different carb configurations such as a side-draft carb as well as an EFI option as early as 1968(?). As far as I can google, the PDSIT carbs were used on non-EFI T4 engines and as only in a dual carb configuration.

But regardless I find the VW air-cooled engines to have started the greatest amount of myths in engine history. It was common for people to remove the thermostat, replace the distributor with a non-vacuum advance type distributor, lower the compression ratio and then jet it pig rich thinking that all that would make the car run better, and more importantly, cooler. And from what I've researched all those mods actually make the engine run hotter, not cooler.

In my personal experience I took a stock 1600 dual port T1 engine, with a stock 34 PICT-4 carb designed for a SVDA distributor but I disconnected the EGR. The engine had all OEM stock cooling except I modified it for a T4 oil cooler. I increased the CR from 7.5:1 to 9.5:1. I jetted it to run about 16.5:1 both idling and cruising and 13:1 at full throttle. I also increased the timing to as much as 50° advanced at max advance at part throttle with 35° max advance at full throttle via a digitally controlled timing map on my distributor setup. I never did find any signs of pinging even in hot weather and with the stock thermostat. In reality I had a hard time getting the heads up to 300°F, and a really hard time getting the oil up past 150°F. Of course the 5,000 to 10,000ft of operation that I drove the car at helped me pull it off. But on the other hand I could go up long mountain passes at full throttle with no problem, whereas I knew of other air-cooled VW engine builders that were doing the opposite, lowering the CR, retarding the timing and jetting them pig rich just so they could go up the mountain passes with no worries. Personally I was real pleased with the car. It felt really peppy, a whole lot more than my 1984 Golf diesel, and I never got less than 30mpg in it.