How much drivability would I lose?

thrown_hammer · 07-23-2003, 09:04 AM

Am thinking about PMO carbs for my 3.2 And some '74 Heat exchangers with a Dansk sport pipe. How fussy are carbs? Am I insane? I just think the carbs look "better" in an early car. But I do like to walk out and hit the key and go...Every time.

rdane · rdane's Garage

I have the SSIs and am thinking about the PMOs on my '79, 3.0. I would like to know what we'll loose and again from adding the carbs to a typical 3.0 SC engine.

I am thinking it is a good chunk of change that could be paid up front and used in a more extensive rebuild (read a bigger, better motor) in the future.

Phoenix · Phoenix's Garage

Funny how it goes.
I have PMO's and often wish I had MFI.
The grass is always greener...

masraum · 07-23-2003, 09:36 AM

I'm no expert, but if you have to drive your car in the cold I think that could be a pain in the @$$ with carbs compared to the FI. You'll likely loose some fuel efficiency, but then again that's probably not a big deal if you are considering doing this change. Otherwise I have read that the earier carbed cars feel like they have better throttle response.

The fuel injection is really easy to live with!

IROC · IROC's Garage

I'd go with the exhaust first and then think long and hard about the carbs. IMHO, if you really start looking into the realities of switching to carbs, it is a daunting task on a Motronic car. For instance, you're going to need an ignition system in addition to the carbs. Plus, while you're at it, you really ought to change the cams and pistons to really take advantage of the carbs. It goes on and on.

I'd put a neat exhaust on the 3.2 and be happy. You could do something really neat like headers and Supertrapps. That would be hard core. :>)

Mike

Formerly Steve Wilkinson · 07-23-2003, 10:28 AM

I have SSIs and a Fabspeed muffler on the bottom and PMOs on top of an '83 SC track-and-street engine, and I put the carbs on at least in part because I simply thought it would be fun to play with them, and the clean in/out mixture path sure makes power. (I dynoed at just over 275 at the flywheel a couple of weeks ago, the engine being 3.4 liters now and twin plugs.)

Upside: Great power and responsiveness. Once you get the carbs set up right, they stay there--no fussiness there. And yeah, I enjoyed setting them up.

Downside: 12 mpg. If you get a microscopic piece of dirt anywhere in the carbs, you'll be running on five cylinders, at least when you're on the idle circuit. It's happened to me once, and I have an expensive diesel-engine fuel filter plus an in-line filter on each carb bank. Risk of fire when you start, because the PMOs have no choke, and you need to pump-pump-pump-pump to get them going. In warm New York weather, it'll take maybe two catch-and-die cycles, in the winter maybe five.

If you simply want the power, the carbs are great. If it's a daily driver (I drive mine maybe once a week) and you live where it goes below 60 degrees, you'll soon be cursing 'em.

Stephan

thrown_hammer · 07-23-2003, 11:11 AM

I think I will stick with the FI and change the exhaust side. I can always chip the DME to get more power from the intake side of things.

plain fan · 07-23-2003, 11:14 AM

A local guy had a 3.2 Carrera that had headers and supertrap exhaust on it. Sounded great! Some people thought it was loud, but you didn't hear that from anyone in our PCA group.

07-23-2003, 11:24 AM

MAF Kit & SSI's.

jmz · jmz's Garage

mass flow, better exhaust and a chip will do WONDERS

Glasgow 911SC · Glasgow 911SC's Garage

This was posted on the Porsche Club GB site by guy called Richard Bernau;

"Just relaying some info from Titanic List regarding horsepower gains from mass air flow conversion and SSI exhaust backdate. Rob Van der Poel was testing an FVD mass air flow kit and he has SSI backdate exhaust on his 3.2 Clubsport. He reported:

"By the way, after my questions to and answers from you all, I,ve tested the FVD air mass meter on the dyno and despite the huge power gain promise, it only gave 8 BHP and 2 NM of torque. I could hardly notice any difference on the road. The air mass meter will be returned to FVD. The clubsport engine (mine std was dynoed on 238 bhp and 285 NM) gave with the SSI exhaust system 248 BHP and 290 NM. This combined with the lighweight car is enough to outrun 964's (except RS !) so no need for the mass meter for me. This car is the most rewarding sportscar I have ever driven."

As you can see Rob's Clubsport engine was in a good state of health to start with. The SSIs were worth 10hp and 5nm and the mass air flow 8hp and 2nm.

Richard "

david914 · 07-23-2003, 01:17 PM

Not exactly the same, but I have Weber 40IDF's on my 914 (4 cyl). The upside is they are fun to play with. The downside is they're fun to play with. Like Stephen said, they're REAL finicky about dirt and misadjustments. The position of the moon and stars seems to have an effect on how they'll respond on any given day. Not that I would switch back to FI on the 914. It's just that the FI on 911's works so much better than carbs unless you're building an all out beast, AND THEN there are alternative FI systems that are available for those applications. For a daily or semi-daily driver, FI is definitely the way to go unless you enjoy playing with the carbs fairly regularly (which some of us do and there's nothing wrong with that!).

jhugh · 07-23-2003, 02:19 PM

Or you could go the zany route of some Motec frickin supercomputer, crankfire ignition and those gorgeous sliding FI intake stacks. It would sure look right.

masraum · 07-23-2003, 02:37 PM

Actually you can disable the fuel side of the DME and leave the ignition side when going to carbs.

724doorE · 07-23-2003, 03:38 PM

I have three letters for you....MFI

CamB · CamB's Garage

I had carbs on my '69T (before I messed with it).

Cold start was pretty good (never below 50 deg here though). Warm start SUCKED. Foot flat to the floor and crank it. Scary.

Mileage was actually pretty good, but it was only 125hp from 2 litres...

Steve W · Steve W's Garage

The 3.2's Motronic system is capable of a lot of response, enough so you don't even want to think about carbs or PMOs - but not in the engine's stock form. The difference in response and power between my car, and a stock one is night and day. The Motronic system is capable of leaping when you step on the throttle, whereas in stock form, it's kind of like 'ok, hold on, alright I'm coming'. Modify the exhaust or backdate it, and chip it for the best results. If you want even more response, put in a cone air filter with the proper adapter, have the throttle body bored and ported, and ExtrudeHone your intake manifolds. MAF sensor would be the last bit if you wanted to spend the bank, but it's not necessary. A couple of weeks ago I took off my MAF sensor and put back in my stock air flow sensor with cone filter to road test a chip I have been working on, and to my surprise, noticed no loss in response or power. I only spent 30 minutes driving it, but it sure has me wondering about the benefit of the sensor. I'm gonna have to put in some more seat time to verify this.

Randy Webb · 07-23-2003, 09:06 PM

I haven't had to adjust my Wevbers in 3 years...

GAINs: induction howl, engine responsiveness, power (over CIS), no MFI pump noise, looks, easy to repair & diagnose

LOSE: PITA to start in cold weather -- so where do you live?

thrown_hammer · 07-24-2003, 03:48 AM

I guess I will stick with the DME set up and get some headers and a good dual in dual out muffler.Then have Steve burn me a chip. I was thinkin last night. I live in northern IN. I like to drive more than dink around with adjustments.

cegerer · cegerer's Garage

I love my carbs. Of course, I'm currently trying to cure a problem in the idle circuit that's causing a miss at 3500RPM's ..... sometimes love hurts.

-- Curt