SC motor with Weber carbs?

[kalawao]

hey folks,

i am backdating my sc at the moment and i am also thinking about buying weber carbs and delete the electronic injection the 3.0 SC engine is equiped with .. i am right at the beginning with the engine - so .. which webers should do it or whats the best solution if i want to backdate the engine to a non-electronic injection .. ?!

thanks guys ..

martin

[VFR750]

There are a lot of threads and books on this. Having said that......

If your budget allows it, new PMO 40mm carbs would be the best. Rebuilt Webers less cost. Rebuilt Zeniths the "cheapest".

But, there is more!

Distributor needs to be recurved, or get a fresh 78-79; it is close enough.

Fuel pressure regulator, vacuum system for the brakes, throttle linkage adjustments

Want more power, add SSI exhaust; need new oil lines. (Nice regardless carb or cis)

Get a wide band AFR gage and O2 sensor for tuning. Plus synchronizer for air flow.

[Jack Stands]

If you have the original SC injection, it is a CIS system and not really an electronic system. Unless you replace the cams and do many other upgrades, you'll be disappointed with the results ( though the sound of the Webers sucking air is great).

[Ayles]

They look good too!

[flyn-hawn]

People say that you need to recurve the distributor, I did not and the car runs great. I have an 81 and took off the CIS because there was contamination in the fuel distributor (rust) and it kept plugging the injectors. I have 40 IDA that came off an SC do not know venturi or jetting sizes but I did have the carbs completely rebuilt. I did not do anything internally with the motor, I did add headers and dual exit muffler and an MSD6AL. The car ran harder than with the CIS and way more responsive, but fuel consumption is terrible probably 10 mpg. The sound was worth the switch to me. The engine compartment looked terrible hence the removal. It has been repainted, new wiring harness everything either bead blasted powder coated or yellow zinc plated and can't wait to get it back on the road.
That said the car is all apart now for a backdate and while the motor was out I sent the distributor to Aaron at Rennworks? for a rebuild and recurve with all new parts. I have not driven it yet so I don't know what the difference is other than it looks sweet!
These are before the backdate

[jmz]

Carbs are s complete waste of time if you dont also change cams in my opinion.

[Eagledriver]

228 RWHP was such a waste of time.

-Andy

[RSBob]

Have two 82 3.0s. One has new Webber IDAs and a recurved dizzy. The other has the original CIS in top shape. Pluses for CIS, car always starts right up with no muss. The car gets decent MPG the torque is ok but not sensational even with 175 lbs of weight taken out of the SC. Driveability of the CIS is just fine. Just not inspired. The Webbers suck major fuel, the plugs easily foul, it is a bit more difficult to start until you get the hang of it. The pluses is that they look cool, and seem to provide more torque, and sound cool - of course with the fuel they consume I would hope they are doing something other than looking pretty. If I had it to do over again, I wouldn't have gone to all the expense for the Webbers and just left the CIS. live and learn.

[banda]

Hello Martin

I have Weber 40's on my 78 3ltr SC motor with Webb cams and SSI's . I also bought PMO 46mm tall intake manifolds and it works great! Throttle response is unreal and it's a blast to drive. It feels like 50-75 additional HP as compared to CIS but I have not dyno'd it yet. I was able to use my distributor without modification.

My car starts easily without a choke and only needs a few seconds for the idle to smooth out. I am in a very warm climate though. I have never had a problem with fouled plugs. Gas mileage is average to bad. The key is getting them set up correctly which I had done by a reputable shop in San Diego.


Good luck with the conversion and if you get it set up correctly from the get go you wont be disappointed.

[haycait911]

just plunking webers on a 3.0 with stock internals is only good for fun noises, higher fuel consumption, and slightly better throttle response.

with cams and pistons it's a different story. my 3.0 with 9.5:1 JE, cams, and weber 40's dynoed at 250hp. stock distributor. bulletproof and fun.

[jmz]

Bingo!!!!!

just plunking webers on a 3.0 with stock internals is only good for fun noises, higher fuel consumption, and slightly better throttle response.



with cams and pistons it's a different story. My 3.0 with 9.5:1 je, cams, and weber 40's dynoed at 250hp. Stock distributor. Bulletproof and fun.

[jmz]

Stock 3.0 with simply carbs will NOT net you 228rwhp.
UNLESS YOU HAVE A VERY OPTIMISTIC DYNO!

228 RWHP was such a waste of time.



-Andy

[bcoats]

Hello, regarding guys running carbs on their 3.0, what type of plugs have you found to work well? I just fouled a plug last night, not sure what's in there now but will check, I believe the NGK BP7ES or something, if I recall from the receipts. I am wondering if I need to run a hotter plug with carbs? Thanks Bryce

[Eagledriver]

Originally Posted by haycait911

just plunking webers on a 3.0 with stock internals is only good for fun noises, higher fuel consumption, and slightly better throttle response.

with cams and pistons it's a different story. my 3.0 with 9.5:1 JE, cams, and weber 40's dynoed at 250hp. stock distributor. bulletproof and fun.

To get the most out of the carbs you do need to upgrade the exhaust. I race a spec 911 and our group has more than 30 cars, most of which have stock 3.0 engines. Just carbs and exhaust with a 78-79 distributor well tuned will get you at least 230 HP. Add in 9.8 Euro Pistons, 39mm ports and 46mm carbs gets you to an easy 245.

Keep in mind the big difference is the RPM that the power peaks at. The torque is similar between the CIS and carbs. But the engine will pull to 7400 RPM with peak power at 6800-7000 with carbs. That's the reason for the high HP numbers. For those driving on the street below 6500 RPM CIS is better. Our race motors,also use stiffer valve springs. With stock springs I'd limit my RPM to 6800.

-Andy

[wayner]

My 3.0 is just a lowly C, not an SC

It loves carbs
GT3s hate it

At 5 grand all hell brakes loose!
It has cams, and the carbs/intakes/ports/case have all been flowed

Here is a video if you want to hear how it breathes.
Video - Sending the 73 back to the crusher!

Here is the engine in question:

[dfhtrhjn]

I have a carb conversion on my RS clone, totally changes the engine in a fun way.

For the price of carbs you can get the Bitz EFI conversion. I've met a few people that have it; it sounds like they get a similar feel to carbs and still keep most of the fuel economy.

index

For the spark plug question, I run the hottest plugs NGK makes and adjust the air fuel ration/quantity to burn as much of everything as possible

[bcoats]

Thanks buddy I appreciate the info, this forum rocks!

[DonNewton]

For you guys here in San Diego running carbs: Where do you go for smog testing? I want to use them before CARB throws them in jail.

[NY65912]

My SC with DC-40 cams, SSI's, Monty, MSD, 10.5 CR pistons, fresh valve job and 46mm PMO's did 256rwhp.

[haycait911]

Originally Posted by bcoats

Hello, regarding guys running carbs on their 3.0, what type of plugs have you found to work well? I just fouled a plug last night, not sure what's in there now but will check, I believe the NGK BP7ES or something, if I recall from the receipts. I am wondering if I need to run a hotter plug with carbs? Thanks Bryce

depends on your carb adjustments. I use a Gunson Colortune. if I set them right, blue flame with orange streaks. BP7ES are fine. I tend to richen things a little, blue with maybe a third orange, then BP6ES.



when I built my 3.0 I wanted a drivable street engine. high peak hp at high rpm has no interest for me. I wanted a fat torque curve. I think I succeeded

small ports (34mm), JE 9.5:1, Dougherty special torque cams, webers and headers with a Bursch.