CIS to Webers Question... on a RoW 3.0SC
 

I am buying a set of 40IDA webers for my 1978 RoW 3.0SC.

The webers are being sold as "complete" and ready to install. The seller is also selling me a used Bendix (?) fuel pump for $100.

My questions:

- What else will I need for this conversion?
- Can I keep my A/C "as is" and run webers?
- I assume I will need a new gasket set for the conversion? Where can I get a gasket kit?
- Is the Bendix fuel pump the one to go with?
- What brand/model Electronic Ignition should I buy? MSD?
- From what I have read I should really change the cams to get the most out of the swap? Any recommendations? I already have SSI's and a dual out Monty
- Should I go with new wires?
- Anything else I should buy before I undertake the swap?

Thanks in advance!

Andrew

Also the webers I am buying have 36mm venturi's is this the correct size for a primarily "street" application?

whoops!
 

Not venturis!

I meant:36mm intake manifolds

Here are the details.

Weber 40IDA ( triple throat ) carbs in superb, virtually new condition with 36mm intake manifolds, K&N filters, Weathershields and throttle bar with linkage & ball joints.


Thanks again!

Andrew

search for a few threads on this...

there is no power gain, but it sounds and feels a lot better than CIS.

Get a rebuild kit and rebuild them and set them up carefully

jet them rich to compensate (partly) for the cams

for a few thou more you can do it right with new cams & pistons that are meant for carbs

Thanks.
 

What cams and pistons do you recommend for carbs?
Size/model/brand of both please. As you might have guessed I am new to all this.

not sure about the fuel pump, but it's also good to invest in quality (very fine) fuel filter. carbs like clean fuel otherwise they clog and sputter...

in the same vein, cleaning, sealing, and refreshing your gas tank is a good idea for the same reason...

another:

i've also been told that 36's might be a bit large-ish but good for top end. they are not inappropriate just that you may feel a bit sluggish below 3k rpm

Randy, et all:

Au contraire, dear sir. :) There most certainly IS a nice power gain converting from CIS to carbs! Further, the throttle response difference is astounding as long as the carburetors are correctly configured and setup. :)

Thats the whole trick, you see? Jetting, configuration and setup makes ALL the difference in the world and honestly, few people get it right since its time consuming, a bit expensive, and requires patience.

Rebuilding any used carb is always considered good practices.

Don't jet them rich! Jet them right! Excess fuel washes oil away from cylinder walls and costs you performance. Carbs (especially Webers) do run richer than CIS systems do and merely need to be jetted for the displacement, compression, and camshaft configuration of your SC motor.

Use an MSD ignition system with matching MSD coil. These make a big difference in the drivability of any carbureted or MFI'ed car. USe Magnecor wires and make sure your cap and rotor are new.

Don't use that Bendix fuel pump. Get the the Fuel Pressure Regulator that PMO sells so you keep your SC's original fuel pump and set FP to 3.5 psi before you begin the float level setup.

Hope this helps,

You'll want to get the insulators that go under the intake manifolds, these will come with longer studs. I double nutted the old studs and they came out easily.

When I did the conversion on my 2.7 I used my CIS fuel pump, new braided supply and return line, PMO regulator, a Russell fuel filter and the PMO fuel bars.

I didn't change the pistons or cams, I don't need a rebuild yet and while I left power on the table, it wasn't worth the expense at the time to do it. If the 3.0 is in otherwise good shape you don't need to be concerned about driveablility with carbs with the CIS pistons. If you need to rebuild anyway, then go for the whole deal.

Let me know if you need any help.

http://forums.pelicanparts.com/uploa...1144431529.jpg

Steve,

I am still using the stock ignition system with the Petronix Ignitor in place of points. Is there a big difference by switching to the MSD set up?

You are saying there is an increase in hp without changing the cams or pistons??

If so, how much is it?

Steve and Dean - Thanks!
 

Steve thanks for the advice especially on keeping the stock fuel pump, dean thanks for the information and offer to help me out.
I will take you up on it when I get to starting.
Dean did we meet at the Scituate, MA Porsche gathering 2 yrs ago? I had my 1988 Cab there and I thought we might have met there?

Andrew

Yup we met at the Scituate meet and I think I spoke to you briefly at the Larz Anderson event last Sept.

The braided lines and associated fittings are overkill, but I only wanted to do it once and I wanted it to look clean. Rubber fuel line with clamps etc get the job done for far less $$.

Thanks Dean, I thought we met.
 

Dean,
I too am in the "do it once" camp and have no problem spending the extra to avoid future problems. Who installed your carbs and set them up?

You probably already know this but I feel compelled to say it again and again. Be sure to use a metal fuel filter - not plastic. Don't ask me how I know.

:(

Andrew - I am pretty strictly DIY, no mechanics for me unless I am short on time or completely stumped. I did the carbs and associated set up myself.

You probably already know this but I feel compelled to say it again and again. Be sure to use a metal fuel filter - not plastic. Don't ask me how I know. ...JanusCole

I've got a plastic filter in a Spitfire and would love to know what trouble I'm asking for if I leave it in...It's up against the firewall - 'away' from hot components....but - Murphy's law is a good way to keep ahead of problems and ask yourself, "what if...?"


Btw, can someone mention if any 911 can do 27 mpg w/Webers on the freeway at cruising speeds ?

Typically, it's mentioned that webers get 'half' of CIS...(15).

Believe me I understand how CIS differs from weber - but wonder
if in fact it "doubles" your economy over weber ? ?


Phil

my carbs & cams get around 2/3 of what I previously had with CIS. My carbs are very adjusted.

webers
 

no more webers for me lousy milage and drivability i just finished efi conversion and am delighted at difference check out bitz racing

Do a search. There was a thread about this last year, where someone posted the dynoed hp on their rebuilt stock 3.0 with PMO/Webers. TRE added some insight as well, which was quite enlightening.

Don't you have to readjust the distributor? Something about advancing...

Lessee, I average around 15 with my SC with CIS, so that would put it around 10.

Is it worth the extra 10 HP BA quotes? Torque figures not quoted...

Gas here just hit $3\gallon! Good luck!

ianc

10 hp? Yup that's what BA says & JW confirmed that to me a few years ago.

Above, SW said there would be a "nice power gain" iff... you set up the carb just right. So maybe it's more than 10 hp -- that's why I aksed him to respond.

Also, they changed intake port sizes on the SC's at some point didn't they? That might make a difference in power gain & prob. for mileage too.

ANyway, the induction noise & feel (engine response) I thought was worth it.

Yeah, I think the earlier SC had larger intake valves. Can't recall how much larger or what the cutoff was. Don't really know if this would contribute to more HP or not...

It seems to me that for a street-driven car, torque is much more important than HP anyway. You don't often run for extended periods at 5-6K RPM+ on the street. You'll want the torque for pulling away from stop lights, squirting in and out of traffic, etc., and the torque gains are less clear with carbs.

Even if the torque figures are slightly better with carbs (and we don't know this), the ease of troubleshooting, instant starts, ability to pass smog (for those of us in such states), and much better fuel economy are well worth it to keep the FI.

I don't honestly know about throttle response; never having driven a later model FI car converted to carbs. Compared to my Carrera, my SC's throttle response feels pretty much instant though...

ianc

All above is great replys. Then there appears to be two thoughts going on. I may be nuts so don't take me serious.

Carbs is like pouring gas into a hole connected to a combustion chamber. Guys who've run carbed engines by actually pouring gas out of a coke bottle know about this first hand. Either you like it or you don't.. and the cost of the gas is really insignificant to total cost of operation, unless its a commuter car.

The bottom line is to create combustion with power. The only monitoring of this power that I know of is EGT heat. You need the most efficient envelope for creating this desired EGT as the engine goes through all its gyrations that are constantly changing. With nice carbs a good tuner can create more power than the CIS and Motronic inductions imo. It's not a matter of pouring in more gas than necessary because this would only cool combustion and retard flame speed which leads to less power. It's the delivery of the correct amounts of air and fuel for power. So if you're into owning the greatest toy created use tuned carbs.

FI is great for its purpose. Don't buy carbs unless you really really want them.

I think that carbs can actually do a good job, but they are inherently less versatile than FI. If the car is a track car, you spend most of your time at high RPM's and temperature\throttle variations are not that great. Carbs can shine in this application.

For a street car that needs to (possibly) sit for a few days, start easily, idle well, pull smoothly no matter what the temperature, pass smog, and hold resale value, FI can't be beat.

ITB FI would be best, but barring that, the application should determine the method of induction,

ianc

I read a few of Tyson's replys awhile ago. Is this what you mean?

Originally posted by ianc


I think that carbs can actually do a good job, but they are inherently less versatile than FI. If the car is a track car, you spend most of your time at high RPM's and temperature\throttle variations are not that great. Carbs can shine in this application.
------ Good point. It's a package deal. If you have a high rpm cam you adjust for high rpms. If it's a street cam you tune for the street. If your cam is a little of both you tune for a little of both. My act is waiting for speed racer bear bait to come up so he can escort me and my V-1. My carbs are tuned to pull 4th gear between 65-100mph quickly. He passes and I'm pacing the mother almost instantly. My brother's stock '88 911 took noticeably longer which meant that the '88 had to finally reach very high speeds before I could pace him. I've spent weeks living in his car traveling solo so I know how much power it has. Can you imagine if I had a carbed 3.2 and compared it my bro's car? There is a gearing issue between the cars when viewing the total package though.

And for bonus coupons my engine combustion runs about 25-50 deg cooler at 4.5-5k than at 3.5k in 5th so no way is it even close to detonation the higher the rpms become.. up to a point I figure humbly as I haven't pushed the edge yet.

I can go on forever about this.


ITB FI would be best, but barring that, the application should determine the method of induction,
-------- if you can tune the ignition and fuel flow on the fly it'd be a nice FI. You can apply nice FI or carbs to anything you want. It's what do you want and what do you want to play with?

all above is a prejudicial rant

distributor curves can be adjusted.

He helped me dial in my carbs.

God bless America.

3.2 and larger do this,

ianc

in a simplistic way. You can't be dialing the flow and curve to your liking. If you want more injection for a particular reason you're stuck with other consequences afaik.

No, there is a basic fuel-air map. This is modified according to 'weighting factors', which are signals received from various sensors. These increase or decrease injection time (pulse width) according to temperature, load, etc. As the FI gets more sophisticated, the better it is able to make these decisions.

Timing is also adjusted as necessary by the ECU, with knock-sensing available in later iterations.

So you really can dial the curve; if not to your liking, then at least to prevailing conditions. ;)

ianc

IIRC, 220-230 hp was what someone at TRE quoted as the gain with Webers on a stock 3.0. I don't know who at TRE made this comment, but those numbers are what I recall. As well, I cannot recall if this increase was in conjunction with SSIs and other exhaust changes.

The person who had his rebuilt stock 3.0 with PMOs dynoed, made close to 240 hp; again to my recollection.

As for intakes, in '81, Porsche changed intake sizes for at least the US 3.0s, lessening their diameter from 39mm to 34mm, yet raised compression .8 pts. The horsepower from a late 3.0 is the same, however the engine develops a bit more torque.

To be certain, it must be considered that not all 180, 200, 220 or even 250 hp is alike on different engines. Sure, I believe 240 hp is obtainable with Webers on a stock 3.0. I believe 240 hp is obtainable with a CIS 3.0. The caveat is how efficiently is that power coming on, and where.

The other caveat about 3.0 engines and Webers is to just throw them on is fairly much a waste of effort, money and engineering, particularly when it is considered that when built in a rather radical street/race form, a 3.0 with Webers that has had its pistons and cams changed, can develop over 300 hp.

Since you are in MA, you might want to send the Webers over to Matt at Eurometrix. He can make sure that there is no hidden damage like a crack in a bloat bowl, refurbish them so they look and act new, and he can rejet them for your exact engine setup. Not cheap, but it might be worth it in the long haul.