Weber 40s on a 3.2?

[rstanley87]

I,m rebuilding my 3.2 from the bottom up and keeping it stock except for arp rod bolts and changing the delavar studs to steel. I've read Waynes book on rebuilds and Bruce Anderson's Performance handbook. My question is, is it possible to use weber 40s with a stock 3.2 internals to improve throttle response. I would be using the motronics for ignition only with a remapped chip.Ive looked up the threads and most go with 46s but the formulas I've seen seem to show that 40's would work. What are the pros and cons of these two sizes for a 3.2 . I'm looking for a fun street car not a track monster so torque and throttle response are what I'm looking for.Ive read the cons of carbs ( poorer gas mileage,cost, maintenance,etc) and I know just rechipping and staying with the fuel injection is the practical way but carbs are just too sexy to not consider them. Thanks Ron

[snbush67]

40's will work perfect, but you should consider at the minimum a cam regrind to work better with the carbs. Also some SSI's to let your motor breath.

If you go with larger ports and other work then you should consider 46's.

Shane

[1QuickS]

There is another option to consider, 42mm throttle bores created from 40mm throttle bodies. The 42mm bore conversion helps fill the void between 40mm and 46mm throttle bodies for the mid-displacement engines.

[1976 TN Porsche]

Ron. I am running a 3.2L in a 1976 911S with Weber 40 IDA3C carburetors. They run "GREAT" Very torquey and fun to drive on the street. My engine is a stock 3.2L Weber 40 IDA3C carburetors with 38 venturis / F26 emulsion tubes / 160 air correctors / 55 idle jets / 160 main jets. I had the carburetors re-bushed by Paul Abbott at Performance Oriented. I am running MSD 6A Ignition box with a Pertronix igniter in 2.7L Distibutor Re-bushed By Barry Hernson. I think you enjoy them. Craig.

[rstanley87]

Thanks guys.

[911st]

My understanding is they are on the small side. Even with the stock cam.

Does not mean you will not be happy with them.

I think there is good info on this in Bruce Anderson's book.

Think about it. The intake port is something like 40mm and you are probably going to be running a 36mm venturi.

[avendlerdp]

What's wrong with EFI? It's not a bottle neck on the 3.2.

[rstanley87]

Like I said EFI is the easiest most practical way but webers seem to offer better throttle response and look and sound so cool. I guess my original question was, is it better to run at the high end of a carbs range or the low end of its range? Maybe just putting it in the middle with 42s would work best.

[lindy 911]

For street use running at the low end (40 mm) is a much better choice. You will see better torque on the low end and easier set-up. The only down side is top end performance, say 4500 rpm and higher. If you plan to spin your motor I'd opt for the 46 but then you have a bunch of other things to think about like compression, cams, piston tops, exhaust... the list is endless.

I have a 3.0 with 46s and it's a beast but I rev it to close to 8,000 and the motors built for that. It feels stock until you get to 4500 or so and then it feels like it has nitrous all the way to 8,000.

Maybe that helps. Paul Abbott knows his stuff when it comes to Webers. Give him a call.

Lindy

[911st]

A chipped and tuned exhaust 3.2 stuffed into an earlier car is a great set up.

Yes carbs are sharper when you blip them at the stop light and they look way cool and vintage if you open the hood.

However, a chipped, stock EFI is probably going to out perform carbs a lot of the time and over more of the power band with a lot better manners.

The EFI adjusts fuel and timing with changes in environmental conditions like altitude and temperature. No leaning on a cold day or when making a run up in the hills. On a hot day on the track it can pull timing to protect the motor. On the freeway it self adjusts to maintain ideal AFR's. With EFI the timing and AFR values can be set over a wider range and better fit to ideals like bending the timing curve around peak TQ where we are most sensitive to detonation or running over 40 deg of timing at cruse for best fuel range.

On top of that, Carbs are not always "plug and play". They benefit from some effort on a dyno with someone that knows what they are doing and or running a wide band. Same with the ignition settings.

With EFI and the quality tunning chips we now have, it is pretty much a "plug and play" but also a "set it and forget it".

Both systems have there advantages.

[RWebb]

the carbs need to be matched to the engine displ. and the cam - 40 should be fine unless you get real wild with your 3L motor

SSIs will be 'needed'

an EFI system can always outperform carbs, but how many $5,000 bills are you willing to throw at EFI?

[gtc]

If you're going to bother with carbs, why not skip the SSIs and get some headers properly sized for a 3.2?

I don't see the appeal of sacrificing top-end for throttle response. I would buy a mass air conversion kit and have both, with the added bonus of good fuel mileage.

[snbush67]

I recommended SSIs because of heat and cost as an acceptable performance increase over stock exhaust. Headers are the best performance option and maybe actually cheaper if you do not have to backdate oil lines.

[RWebb]

SSIs are headers - they have a box for heat wrapped around them

if you will never need heat, you can save a few lbs. w/ just headers - engine performance will not change

[1976 TN Porsche]

Talk to Paul abbott at Performance Oriented.com And he will help you set up a good carb combination. Give him a call. He is a good man.

[1QuickS]

The most typical complaint about Webers is that they are finicky: this is true if they are old (defying adjustment due to wear issues) or are not adjusted properly (a surprisingly large percentage.) Certainly new PMOs or remanufactured MFIs provide more performance or EFIs are easier to live with (penalized with a softer throttle response); choose your poison: you live with an enthusiast car with their associated demands; embrace the challenges of your fuel delivery system selection and enjoy the uniqueness provided by each.

Weber forever!

[1976 TN Porsche]

Weber Fever Its Great. You only have to hear it once. They Talk To you.

[justinp71]

I know this is an old post, but I figured I'll add my experience.

I have a 3.2 with DC40 Cams, 38mm intake ports, 1 5/8" headers, Magnaflow exhaust, 9.55:1 compression running on 40mm IDA webers ...and... it maxs out on power at 5k. Revs from 3800-5000 fast and then 5000-6500 is about the same amount of power. Cam maxs out at 7k, so 46's are in my future, just not in my budget...

BTW I love the motor!!!

[1QuickS]

46PMOs will require the intake manifolds so best to get a kit. Alternately I know of a service provider that can modify your Webers from 40 to anything up to 46mm. You will still need intake manifolds to match the bottom bore of the Webers. I'd recommend 38mm main venturis in 46mm throttle bores to suit your 3.2 with DC40 cams for a street performance setup.