Benefits of switching to carburetors?

[thinkfloyd14]

First of all, please forgive me if this has been covered. I did do a search, but nothing came up. Feel free to point me to threads if need be.

I have a 3.0 SC engine which I purchased around 4-5 years ago from a member I found on these forums. The engine is still running great, no qualms or anything, however; I was curious to see what benefits I would gain (if any) by switching to carburetors (weber? PMO?.... sorry not an engine guy).

Why I ask? Because I wouldn't have to open her up if I'm not mistaken.

Sound? performance gains if any?

Cons if any? reliability?

Cost?

Background info...
My engine was rebuilt before I purchased it 4-5 years ago. At the time, the owner provided that it was rebuilt 8-10k miles before my purchase. The pistons, crank, rods all new forged, performance cams, new race studs, three angle valve job, Head work and balance work by Ross motorsports, carerra tensioners, comp clutch, pop off valve, lightweight flywheel, SSI headers-heaterboxes all new gaskets seals etc...

I added a M&K 2 in 1 out, but nothing besides that.

Thanks in advance.

-s

[Daves911L]

Probably no great advantage in switching a good running original CIS system to carbs.

Mechanical factors in your engine (camshaft/compression ratio) will limit performance gains to useful, but relatively modest increases. You can (assuming you like to tinker and tune) change the drive-ability/throttle response somewhat for the better. Or you can make it worse.

You will give up some convenience, like turning the key and having the car just start and idle. Your neighbors will appreciate the pops and chirps as you blip the throttle of your carbed 911 for several minutes early on Sunday mornings! And on hot afternoons you will crank on it for ages getting the boiled-off fuel out of the way and filling the bowls with fresh. Oh, and your garage will smell like gasoline all the time

You will gain simplicity with a nice, open engine bay where everthing can be easily reached. You will get a few pounds of weight savings where it counts (high and in the back!). There will be less things to troubleshoot when there is a problem. But the carbs may be less consistent (stuff always seems to get into jets, no matter how many filters are in the way).

You will gain wonderful intake sound. And you will gain terrible intake noise. The first time you run those carbs to redline in 3rd gear it will be the sexiest thing you have ever heard. The 15th time you come in after a 3 hour run home on the Interstate in bumper to bumper traffic and your ears are ringing.......well, you get the idea.

Water will get in your engine with carbs. It shouldn't, but it does. Even with the little water shields, sooner or later the car will sit out out in the rain and a drip will find exactly the worst spot. School of hard knocks speaking here! With CIS and that labrythine intake path, you'd have to drive it into the lake to get water. Oh, and related to the short vertical path that makes that glorious roar, throttle response, etc....you must learn to fish. Any time you happen to have a tiny nut slip through your fingers, it will always happen when you have just removed the air filter for a moment. If you drop that tiny nut on the other side of your shop, 30 feet away, and your air filters are off it will bounce 3 times and go straight down the intake. Never fails!

You will lose originality, should you decide to part with your car some day. Depending on where you live, you may lose your ability to meet emission tests. Usually a way around this, but it can be a headache.

Nothing wrong with carbs. They can and do work quite well. But really can't see exchanging a working injection system for them, assuming that's the only modification you intend. Thats my opinion, anyway.

[Tippy]

Throttle response would be light years better with carbs over CIS.

[uwanna]

The worst "benefit", your gas mileage will become unbelievable in a negative way!
My 3.6 964 motor gets about 8-10 more MPG at highway speed versus my old '68 911 2.0 liter motor with factory Webers. Of course gas in '68 was $.35 a gallon back then, so who cared!
I however agree, there's nothing like the sound of Porsche six in full howl with a set of Webers

[carrerarsr65]

i just did this swap to 40ida weber, gas mileage sukks haha, throttle respnse better,but no real hp gain on a stock motor,i put my weber on during a complete rebuild,je pistons twin plugged heads etc.from the cyl. heads up this is what you need,spacers(phenolic),weber style manifolds,pmo ones are best you can retain your power brake system with these as the come with a vacum port,then the carbs,40 with webers,pmo you can go to a 46 the pmos are more refined ,then the linkage,air filters,some jets to get it spot on , and maybe a afr meter to keep it running sweet any way keep us posted

[chrismorse]

If I recall Bruce Andersons comments correctly:

Mileage goes from something like 20-23 to 16
Power is up roughly20-25 HP
The conservative CIS cam timing and compression ratio limit the upside potential,
Unless you do an overhaul, but that is big bucks.
You loose a bit of reliability and smoothness but get better throttle response.
And as has been stated, there is "THE SOUND" and the gas aroma.
I doubt you will be able to pass the annual smog test required for registration renewal, (not required in some counties)

Spend another couple of bucks and get electronic TBI injection:

Better fuel mileage than CIS
Better throttle response than carbs
more power than carbs
no smell
smoother engine performance than either.
might pass the sniffer test, but I doubt it would pass annual smog, unless the manufacturer has a papal dispensation.

Like any big changes, It is always cheaper and faster to jump into a buddy's car that has already had the modification you are considering - Feel the difference and see if you can carry on a conversation at cruise.

Talk to the PMO guys and maybe one or two shops that specialize in installing/tuning TBI to get a better idea of costs.

I've got a 74 that still has the cis and if I trip over a bucket of money, I will go TBI in a new your minute.
I also have a 77 Ferrari 308 with 4 40mm webbers, (stock) and it has that aggressive howl beloved by all - but my wife, (always) and I, (occasionally) use ear plugs on anything but short hops.

I must be getting old,
chris

[wayner]

Cams + carbs = more fun

If you do carbs now you can use hotter cams

[acme911]

If yours is a '76 in California, Smog Test is your enemy.

[wayner]

Originally Posted by Daves911L

• Your neighbors will appreciate the pops and chirps as you blip the throttle of your carbed 911 for several minutes early on Sunday mornings!
  
• And on hot afternoons you will crank on it for ages getting the boiled-off fuel out of the way.
  
• your garage will smell like gasoline all the time
  
• You will gain simplicity with a nice, open engine bay
  
• stuff always seems to get into jets, no matter how many filters are in the way.
  
• You will gain wonderful intake sound. The first time you run those carbs to redline in 3rd gear it will be the sexiest thing you have ever heard.
  
• You will gain terrible intake noise. The 15th time you come in after a 3 hour run home on the Interstate in bumper to bumper traffic and your ears are ringing.....
  
• If you drop that tiny nut on the other side of your shop, 30 feet away, and your air filters are off, it will bounce 3 times and go straight down the intake. Never fails!
  

I turned this into a list. Love it

[VFR750]

After 5 years of carbs on a 3.0 I can say the list is 100% accurate.

Honestly, they are a love/dislike thing. (Hate is too strong a word here).

There is no doubt there is added power especially with a cam change. They look awesome and have a vintage look that make you smile and garners a lot of positive atention.

But the intake noise can be irritating of if the carbs are out of adjustment. I measured over 95db inside the car honking around. Full throttle is closer to 100db.

Fuel mileage is definately worse. But highway cruising can be ok. 20 mpg at 65+. Around town is where you suffer because you have to run them rich to handle throttle motion.

Throttle response? I guess they are better than CIS. But it only matters if you are stomping on it. An only if your acceleration jet can keep up with the throttle. Otherwise I'm not sure the difference is really great.

I will be going back to CIS in the future unless I go efi.

Changing to carbs is really expensive when you add in all of the changes that are needed. Plus alternate jets. While not as expensive as efi. I'm not sure if I haven't already spent the equivalent of a efi system with the tweaks, rebuild, manifold upgrade and recently a cam.

So should you do it. No.

Do you want to do it? It's a fun, wild ride! You learn a lot. Appreciate old school technology. Looks and sounds awesome.

If your car is your hobby, then you already know you can do anything you want to it.

[Steve@Rennsport]

Originally Posted by VFR750

After 5 years of carbs on a 3.0 I can say the list is 100% accurate.

Honestly, they are a love/dislike thing. (Hate is too strong a word here).

There is no doubt there is added power especially with a cam change. They look awesome and have a vintage look that make you smile and garners a lot of positive atention.

But the intake noise can be irritating of if the carbs are out of adjustment. I measured over 95db inside the car honking around. Full throttle is closer to 100db.

Fuel mileage is definately worse. But highway cruising can be ok. 20 mpg at 65+. Around town is where you suffer because you have to run them rich to handle throttle motion.

Spot-on right there!!!

Throttle response on any 6-throttle intake is light years better than the CIS system when properly set up. This applies to carbs, MFI and EFI.

Changing to carbs is really expensive when you add in all of the changes that are needed. Plus alternate jets. While not as expensive as efi. I'm not sure if I haven't already spent the equivalent of a efi system with the tweaks, rebuild, manifold upgrade and recently a cam.

EFI certainly delivers better fuel economy, however Engine Management is much more expensive when you factor all the hardware and the time needed to properly program it.

Carbs certainly aren't for everyone simply due to ideosyncrasies that few people now understand and are willing to deal with (cold starting is one). Plus, it takes patience to fine tune them for best drivability.

Smog compliance is a big obstacle for anyone living in CA with a '76 or newer car.

Carbs offer excellent performance, however I am very careful about recommending them to my clients, depending on the individual.

[chrismorse]

There are some counties, like Humboldt, that do not require annual smog testing for registration renewal.

However, Smog certification is still required for vehicle transfers, everywhere in the state. There is some wiggle room for cars registered as "Historic", but I would suggest you check to see what the Current interpretation is before you mod your car, or as some do, put the car back to stock every time a smog cert is required.

chris

[Farrell]

Originally Posted by VFR750

I will be going back to CIS in the future unless I go efi.

Changing to carbs is really expensive when you add in all of the changes that are needed. Plus alternate jets. While not as expensive as efi. I'm not sure if I haven't already spent the equivalent of a efi system with the tweaks, rebuild, manifold upgrade and recently a cam.

So should you do it. No.

Do you want to do it? It's a fun, wild ride! You learn a lot. Appreciate old school technology. Looks and sounds awesome.

This.

I agree, they are very expensive for what you get. I know EFI and MFI upgrades can get very pricey however, i haven't even finished my carbs yet and i wish i would've gone EFI, Ive spent almost as much as a full EFI system with engine management etc. My situation is a bit different then most, but boy they don't lie about the slippery slope. I know it would be a little bit more expensive with EFI, but totally worth it in the end.

[thinkfloyd14]

Originally Posted by chrismorse

.....Like any big changes, It is always cheaper and faster to jump into a buddy's car that has already had the modification you are considering - Feel the difference and see if you can carry on a conversation at cruise......
chris

Thanks chris, this is good advice, and I appreciate everyone's response. Seems to that that car sound I dream of may not be worth it in terms of practicality. But' that's not why any of us by these cars, is it?

seems to me the pros are better throttle response + 20hp roughly. Oh and THE SOUND!!!!! god i heard a carburetor ferrari the other day and it was orgasmic.

[thinkfloyd14]

Originally Posted by acme911

If yours is a '76 in California, Smog Test is your enemy.

True. Aren't they moving the cut off to 1980 soon??

[911pcars]

Do your homework first. Webers need cams to realize potential and any cam change worth the cost of installing is going to be too aggressive for the pistons in a stock CIS engine (iow, valves will interfere with pistons (and vice-versa).

And since you live in emissions-mandated CA, you'll have to contend with visual emission checks, so pick your inspection center carefully.

Sherwood

[Reiver]

Originally Posted by Steve@Rennsport

Spot-on right there!!!

Throttle response on any 6-throttle intake is light years better than the CIS system when properly set up. This applies to carbs, MFI and EFI.

EFI certainly delivers better fuel economy, however Engine Management is much more expensive when you factor all the hardware and the time needed to properly program it.

Carbs certainly aren't for everyone simply due to ideosyncrasies that few people now understand and are willing to deal with (cold starting is one). Plus, it takes patience to fine tune them for best drivability.

Smog compliance is a big obstacle for anyone living in CA with a '76 or newer car.

Carbs offer excellent performance, however I am very careful about recommending them to my clients, depending on the individual.

Steve,
A question about response with Euro CIS. vs. Carbs
I had a 930-16 US '83 CIS and it was nice but didn't jump when you hit it. A good push.
I've a 930-10 Euro '83 CIS with an onboard AFR (so I can tune it easily) and it does jump when stomped.
I know I have a HP/Torque increase but I think (?) that the different wur on the Euro that controls enrichment in the mid range specifically makes it more responsive.
The lambda on the US does this function where a simple vacuum does it on the Euro.
I see an AFR in the 12's when I hit it.
Am I nuts or is this a better system for performance? Would carbs be any better without a cam change?

[Bob Kontak]

Originally Posted by chrismorse

Power is up roughly20-25 HP

I don't think he said that. It's less.

[Bob Kontak]

Originally Posted by Daves911L

Probably no great advantage in switching a good running original CIS system to carbs.

Thorough and informed write up. Thank you.

[thinkfloyd14]

Originally Posted by thinkfloyd14

True. Aren't they moving the cut off to 1980 soon??

correction: the bill did not go through...

"The bill was proposed by Assembly Member Marie Waldron, a Republican from Southern California’s 75th district, and has the support of the SEMA Action Network. SEMA has attempted to do something similar in the past with a bill that would exempt all pre-1981 cars from emissions inspections in California. That failed, but maybe lining the pockets of the state with a couple of Benjamins means AB550 has a shot."

$200 Could Get You Out Of A Classic Car Smog Check In California