How far can you take a 2.2 911t with Zeniths

[dpetteng]

So, I have a 1971 911t with 35000 original miles and I would love to keep it on the original zenith carbs. I am wondering what updates I can do (barrels and pistons, cam etc) and still keep the zeniths. I know you can't go for big power with Zeniths but would love to know my limits?

I have seen lots of people go for bigger capacity, hotter cams (E or S) and even a counterbalanced crank but they all seem to go for PMO's or webers.

Any opinions welcomed

[Flat6pac]

Looks like SUpertec and Henry can enlarge the Zenith to any 40mm application.
Bruce

[Trackrash]

Agree, talk to Henry.

FWIW, when I increased my 2,2 to a SS2,5, using 90mm pistons, I could not get my Zeniths to cooperate. I increased the vents to 32mm, but had flat spots and not the power I expected until I changed to Webers.

Others claim to be able to get them to work, but I had no luck and gave in to Webers.

[Hi_Fi_Guy]

I had good luck rebuilding my Zeniths with larger venturi and re-jetting on a stock 2.2 and it was a significant improvement. That said if you are looking for a real performance boost I don’t think you would be satisfied. If I were going to keep the engine internals stock and keep the heat exchangers I think the my approach would be:
- upgrading the ignition system
- Weber or PMO carbs with appropriate fuel system mods
- adding an external oil cooler
- possibly switching from single exit to dual exit exhaust

Nothing wrong with the Zeniths and they can be made to perform better than in their stock configuration. So if you want the stock look with a subtle performance gain that would be the way to go. In my own experience they don’t offer the same response as a good pair of Webers but that has not stopped me from Zeniths on my Targa where performance is not my highest priority.

[dpetteng]

Like the sound of enlarging the zeniths. Would I need to do this to use an e cam and bigger barrels and pistons to 2.5?

[Trackrash]

Originally Posted by dpetteng

Like the sound of enlarging the zeniths. Would I need to do this to use an e cam and bigger barrels and pistons to 2.5?

Yes, if you want the motor to have more power than the original 2,2.

Those Zeniths are great carburetors on the original 2,2 Ts. Nice response, power and economy.

Problem is they are tuned for that motor and it's horsepower. For a larger motor with it's greater demand for air flow you have to enlarge the venturis to accommodate it. Zeniths came with 27.5mm venturis. An E cam 2.5 would like 32mm venturis.

Problem is those Zeniths, it has been my experience, don't respond well to that modification. There have been other opinions on this.

You will also have to enlarge the intake ports in the heads and manifolds to match the larger motor's requirements.

[Hi_Fi_Guy]

I agree with @Trackrash, if you are enlarging the engine size skip the Zeniths and go straight for the Webers or PMOs.

[dpetteng]

shame, I really want to keep the originality of the zeniths as the car is a single owner since new car. I will have a think... so I am guessing changing to e cams and euro pistons would not be possible on zeniths?

[Trackrash]

Totally possible. Give Henry a shout out and get his opinion. He may be able to work some magic on those Zentiths.

FWIW, Eruo and some US 2,2s came from the factory with Webers.....

[dpetteng]

Thanks! Who is Henry? LOL

[Trackrash]

Originally Posted by dpetteng

Thanks! Who is Henry? LOL

See post #2. And do an advanced search (user name) for Henry Schmidt

Henry Schmidt
SUPERTEC PERFORMANCE
Ph: 760-728-3062
Email: supertec1@earthlink.net

[30westrob]

For reference in MY 72 & 73 the euro 2.4 T used Zentiths. Were they the same as used on the 2.2
Rob