Model years & difference in handling?

[ttweed]

Originally posted by NeunElf
It might make sense to rejet carburetors, but I haven't heard of much of that going on. Even back in the '60s, American fuel had a different specific gravity than European fuel.

The biggest problem with the newer fuels in the early carb'ed cars is the volatility, not the lack of lead content. According to BA, the average Reid vapor pressure (RVP) has gone from 9 to over 11.5 psi since 1983. This has caused the float bowl percolation problems that some people have experienced, since the fuel essentially "boils" too easily with a hot engine.

Anti-percolation venting in the carb top cover and installing phenolic insulating spacers on the manifolds to keep carb body temps down can help this, as can running a looped fuel supply to the carbs with a return line to the tank (which the early cars did not have), insuring a constant supply of cool fuel to the engine.

TT

[Val]

TT, you wrote;

"According to BA, the average Reid vapor pressure (RVP) has gone from 9 to over 11.5 psi since 1983."

Who or what is "BA"?

"a return line to the tank (which the early cars did not have)"

By definition, does "early car" specifically mean 65-73?

Thanks, Val

[SprintStar]

Originally posted by Val
TT, you wrote;

"According to BA, the average Reid vapor pressure (RVP) has gone from 9 to over 11.5 psi since 1983."

Who or what is "BA"?

"a return line to the tank (which the early cars did not have)"

By definition, does "early car" specifically mean 65-73?

Thanks, Val

I believe BA is Bruce Anderson? It's a very well-known Porsche technical writer.

As for the return line. I'm interested to know more. I've just acquired a SC fuel tank which can accomodate a return line. But carbs don't need returns coz they got fuel bowls, right?

Looking to learn more too.

And yes, the Early cars are from 65-73. The 74-77 cars are the Middle years and then you have the SCs from 78-on....

Sprint.

[pwd72s]

"Val" are you stroking us? Regardless..."Marcel" goes fast because of the skill of it's driver, which is tremendous, (hell, I first saw this guy auto-x at the '75 pea-raid and he impressed me then!! I'm sure he's honed his skills way beyond that point by now.) and it's modifications, which I'm sure are numerous and possibly "secret"...If you like auto-X, and IF you can learn to handle the traits in handling of a short wheel base early 911, they may have an edge over the long wheelbase 911....for the same reason a go-kart would. But you know? The constant questions? They make me wonder about whether you are sincere, or whether you get your jollies making lots of guys spend lots of time on a keyboard. BTW, Tom T?....Porsche first used the 915 gearbox in '72...

[ttweed]

Originally posted by Val
By definition, does "early car" specifically mean 65-73?

In the discussion you quoted above, we were talking about the early cars with carbs, not a particular year range. When fuel injection came in, so did return lines to the tank due to the higher pressures involved.

TT

[ttweed]

Originally posted by pwd72s
BTW, Tom T?....Porsche first used the 915 gearbox in '72...

Ooops! Good catch, Paul. Edited my previous post to reflect reality. How did I do that? '72 is my favorite year!
TT