Carbs

[purplebomb302]

I know a CFI car can be swapped to a 2bbl carb. Not gonna lie I've thought about both a 4bbl swap and 2 bbl swap. I know a 2bbl would be easiest. I'm not saying I'm going to do a swap but I simply have questions.

Is there any advantage at all to swapping to a carb? If so, would anything be gained by going to 4bbl over 2bbl? What are the disadvantages other than tuning?

Fuel economy isn't a huge issue and I know if I did ever swap, 2bbl may be more fuel efficient over a 4bbl.

Also, would it be worth it on a lopo? Other than hurting the wallet, would it hurt to try out a carb?

Like I said, not looking to do a swap. Just curious only because I've seen many swap to EFI and I had an '86 CV with EFI and an '88 M7 H.O.

I've also been tossing around the idea of EFI too but not looking to swap. Thanks.

[1990Merc]

In my opinion, which isn't worth too much honestly, is that going to a carb would be a shortcut to fixing a troublesome fuel injection system. Like you said fuel economy is not going to be as good, power probably wont be as good either unless you start changing other things. The advantage is that its simple. If it were my car I'd probably want to switch to MAF EFI. If I had a 351 crate engine or something maybe I'd do a carb.

A 4bbl will give you more power if your engine can flow the air. Depending on the carb in particular it may or may not have a big effect on fuel economy. The magic of the General Motors quadrajet 4bbl was that it was basically a 2bbl carb with two massive extra barrels that would only open as much as the engine could flow, and only under close to full throttle where it matters. So you get nice high velocity air flow in your 2 small primaries giving you good mixture control and throttle response under part throttle and it really dumps the fuel in under full throttle. The other advantage is that in a low flowing engine like the Oldsmobile 307, the secondaries would barely open at all, just enough to max out what the heads and manifold could take. Fuel economy was actually fairly good. And they could use the same basic carb on any V8 from a 5.0 to a 7.5L.

Many of the more racey carbs out there have 4 equal barrels. Not great for fuel economy, and in my opinion not as good on the street in general.

[P72Ford]

On an otherwise stock '84 302 car, a 4bbl swap wouldn't be worth that extra money, in my opinion. To do it right requires a new intake (I'm assuming a CFI intake will work under a 2bbl), and when you swap intakes, you have to worry about emissions stuff (some areas require it), supporting the throttle cable, coolant port compatibility, etc. Its not a huge deal, but its all an extra expense; and if you're looking to do soemthing on the cheap, a 2 bbl is the way to.

Contrary to most people's beliefs, a properly tuned up carburetor (2 or 4 bbl) can knock down excellent fuel mileage. However, if you don't have the knowledge, it will take alot of tinkering, and experimenting.

An EFI swap is probably no more involved. In order to do a carb swap right, you have to knock the fuel system pressure way down. A Holley likes 5.5-7 psi. That requires either swapping to a mechanical pump, and modifying your associated lines, or, putting a regulator with a return set-up, on your car. A "deadhead" regulated system will not suffice. Its going to put too much back pressure on the pump. It might work for a while, but its a "hacked" solution in my opinion. A good return style regulator can run you close to $100 (the cheap ones never last). But if you want your car to be reliable, it would be the best way to retain the electric pump, and drop the pressure down where a carb would like it. A mechanical pump is probably only $20 (I bought a Carter high volume for my Dad's '90 P72 the other day for $20). However, you need to make sure you have a provision for the pump on the timing cover, and also make sure you have an eccentric on the cam.

Even still, you're probably going to modofy the pick-up in the tank, if you go this route. You'd remove the pump, and make sure the fuel will actually pick up in the bottom of the tank.

I'd remove any and all equipment you aren't going to use, lines, emissions junk, wiring, etc, and go from there. Once you've done a carb swap, if you want to go to a 4 bbl in the future, there are less nuances to worry about.

Either way, SEFI, or carb, theres work to do, if you want it right. I finished converting my '87 to carb. The previous owner had started it, and it was too far gone to go back to EFI. So I did the mechanical pump, new lines, and deleted every stitch of EFI from the car. I am familiar with carbs, and have experience tuning them, so thats the route I went. If you just want the car to run well "out of the box", and have limited knowledge of carburetors, I'd recommend fixing what you have, or looking into an SEFI swap.

[P72Crazy]

Interesting topic, a lot of opinion and info in multiple threads. I like P72Fords post. I don't have any 5.0 CVs or GMs but owning a "pile of 5.8s" I have had to deal with the 7200 VV. Many folks hate this carb and it can be challenging, but it's a carb. If the stepper motor/actuator and the diaphragms are working properly, the only "bad" is see with it is that Ford did a poor job filtering the fuel. I have gotten as much as 24 mpg highway to an average of 20 mpg with these cars. AND, its funny about the octane requirements from year to year. Some cars I've owned will only perform on premium fuel, others were perfectly fine with 89 octane. I have had a couple that would run on anything that would go down the "neck". I have proven to my brother that it's all in the carb! Move one over to another car and it's like doing a "performance transplant". I have never had a holley that would give decent fuel mileage, but I've never had more than 3 or 4 of them. Also remember, "there's no substitute for Cubic Inches", especially in a big sedan.

[fmansfield444]

I've had CFI, SEFI, and a carb on my 85 Vic's lopo and so far I can tell you that the only one I haven't had problems with is the carb. All except the CFI had decent power and I think the only thing I noticed from carb to EFI is that EFI has a better throttle response.

I like EFI and I definitely prefer it to a carb on a car that is a daily driver. But I only drive my 85 a handful of days so the carb made sense. It has had no trouble running when cold or anything. And it's 55 years old. Yeah I had to get it tuned but honestly that's not all that hard and took maybe a couple tries for me. But I had an experienced carb guy show me.

I set mine up with a low pressure electric pump to depressurize the fuel, when I went from CFI to EFI that swap was a little more challenging but the carb swap wasn't just plug and play either.

I have noticed poorer mpg with my carb but I don't really care. Mine is a 2 barrel for now but I am building up a roller block that will be 4 barrel as long as I can find one with an aod TV hookup.

[purplebomb302]

Wow lots of ecxellent replies. So far the CFI on my car isn't giving me any problems. I was just curious as to what everyone thinks of going carb. My '88 H.O. ran pretty well and I enjoyed the power in it. I'm going to run the CFI until I find a roller block, extra time and money, which probably won't be for a few years yet.

[P72Ford]

I have a Holley 600 DP (thats a mechanical secondary carb) on my '87 Coupe. Its "light" as these cars go, with a 3600 stall torque converter, non lock up transmission, a Silverfox valvebody, and 3.73s. If I mash it from a stand still, it is the definition of throttle response. It snaps right up, no stumble, no hesitation, flashes the converter, and I pull away sideways. The car has a fresh 304, GT40Ps, air gap intake, and stock HO grind, with 1.7 RRs. Nothing crazy.

I've changed the accelerator pump, pump the carb retains the stock jetting. It may be a little rich, but I'm going to work the tune out this spring with a vacuum gauge and a wideband.

You have to fiddle with them. And just because they run good, doesn't mean they're running right.

[Piece-it pete]

Someone here added a 2nd CFI.

Pete

[fmansfield444]

It all depends on what you want out of the car. If I relied on it to get to work everyday then I would go with SEFI all day long.

But in my opinion and the reason why my 85 is staying carbed with my new motor is that you can make more power for a lot less money with a carb setup. I had to completely rewire my car too so that's another reason for it being carbed now. My 85 will be a street strip car not something I need to always be able to go so that's why it's staying carbed.

If I had to choose and I had unlimited money to spend then I would go with fuel injection anytime.

[fmansfield444]

Someone here added a 2nd CFI.

Pete

Lol I read this and imagine a 2 carb intake with 2 CFI units on there. I bet that's almost as much power as SEFI.

[purplebomb302]

All this is good info. For now it'll be CFI until I decide I want more out of it. I'm definitely glad I asked.

[Mr.Blue]

Lol I read this and imagine a 2 carb intake with 2 CFI units on there. I bet that's almost as much power as SEFI.

Guy said it was still a total dog........sefi stomped it.......this is on a ltd II lx...looks kinda cool though.......

[gadget73]

GM did this in the 80s, they called it CrossFire. It sucked for them too, and their TBI system by and large worked pretty good.

[turbo2256b]

A guy in another forum has a 3 2 bbl cfi set up on a FE motor and is working great

[fmansfield444]

A guy in another forum has a 3 2 bbl cfi set up on a FE motor and is working great

Why? Just why?