Conversion from CIS to Webers = more hp even with no add'l mods?

[Rufblackbird]

Hi everyone,
Recently I bought a set of Weber 40IDA carbs. I'm probably missing some parts of linkages and a bunch of stuff, plus it needs a rebuild, but I'd like to know, if I rip off all that CIS junk and put these carbs on, will I see an increase in hp? I don't have enough funds to be buying new pistons/cylinders and cams like B.A. suggested yet, so will Webers = more hp on an otherwise stock engine? Only mods I have is headers and exhaust. Thanks!

[hilandscott]

If you can get away with ditching the CIS due to a lack of smog rules, then yes, you will notice a HP increase.

I don't know the exact number of the boost in HP and torque (and it will be greater of course if you change the cams to non-CIS and increase CR of pistons), but the throttle response of carbs is supposed to feel like at least 50HP by the seat of the pants method.

[RarlyL8]

Dammit boy - haven't you been payin' attention?

Everybody sais 10hp for carbs over CIS with no other mods.
The 50hp feel is about right due to throttle responce. The pain in the ass running in the winter makes you wish you had the CIS back. 'Course this isn't a problem for you poor fellas livin' in the tropics.

[pwd72s]

OKay, Jeff...I was wrong...figure 10 HP and better throttle response? Geeze, I guess I never had a clue how sorry CIS must be. Pity all those SCWDP people....

[Rufblackbird]

Thanks guys. Actually, no...I haven't been paying attention. Before I got these carbs for a steal, I never paid any attention to them. Yeah yeah..I regret that now. I think this will be the way to go. Thanks!

[RarlyL8]

Seriously Jeff, before you spend a small fortune rebuilding those carbs think about how you will use your car. If your CIS works well you might not want to replace it just yet. You've got a ways to go on your car. The money could well be spent somewhere else, at least for now.

CIS gets a bad rap sometimes. For all its ugliness it is a pretty reliable component system.

[Rufblackbird]

Rarly, looking at Pelican's website, rebuild kits are about $50 per side. I bought the carbs for $350, and hopefully nothing is wrong with it when I crack 'em open. I think I still need to buy some additional linkages and the filter elements, but other than that, it shouldn't be that expensive...or will it?

Yeah..CIS does get a bad rep, but I do hate mine with all my heart. Ever since I've had it I've had a surging idle problem, which a rebuilt WUR didn't solve. I used to get 16mpg (I don't know what's wrong) and just got a best of 17mpg recently. I don't see how carbs wouldn't make a difference. CIS is supposed to give you 22-25 mpg, right?

Oh yeah...I've got quite a ways to go on my car, but I figure if I put the Webers on I could sell my CIS system to offset the cost. If I just let it sit, that's a pair of $350 paper weights. Any thoughts?

EDIT: The car is for street use (say 95%), with very few races, as we don't have much of a track here.

[emcon5]

Originally posted by Rufblackbird
I bought the carbs for $350,

That seems to me like a good deal.

I used to get 16mpg (I don't know what's wrong) and just got a best of 17mpg recently. I don't see how carbs wouldn't make a difference. CIS is supposed to give you 22-25 mpg, right?

My stock 82 will get 22-25 one a long freeway trip. Around town, I am lucky to get 15.

Tom

[speeder]

My milage is same as Tom's. CIS SC's get fantastic mpg at steady 80mph in 5th, not so great in stop and go. Reason I think is 80mph you are in peak rpm/engine efficiency. 2.7 should be about the same.

[Bobboloo]

Jeff,
As far as rebuilding those carbs its relatively easy and inexpensive as long as the throttle valve shafts aren't seized or wobbly. i.e. Needing to be re-machined. If they are a rebuild kit wont fix them. Sometimes depending on condition you may not even need a rebuild kit. They just may need a good cleaning.

Check the throttles before you do anything.

Bobby

[Wayne 962]

My suggestion would be to save the carbs for your engine rebuild. These are getting rare these days, and are probably a better investment than the stock market. Especially at the price that you picked them up for.

Yes, the carbs will probably be good for about 5% HP increase (10HP or so on your 3.0L), but as mentioned previously, the CIS cams will indeed hold you back considerably. To get all the response out of that 3.0L, you need to:

- run a more agressive cam
- replace the domed pistons so that you can run a more agressive cam and increase the comp ratio
- Back-date the exhaust
- Install the carbs

Depending upon your final compression ratio, you can achieve 50+ HP out of this combo.

Of course, that wasn't your original question. I question the carburetors when you really don't get all you can out of them. Plus your gas mileage will go south of the border as well.

Save them for a rainy rebuild day, is my opinion...

-Wayne

[epbrown]

Jeff's already gone to headers, so the 10hp everyone's talking about isn't counting the 20 hp he likely got from that already, right? He'd be around 30hp total over a stick 3.0 now.

Why not throw 'em on there until he's due for a rebuild anyway - what's the "against" argument? He'd get better results with a different cam and pistons, but it won't hurt anything now, or would it? It certainly cleans up the engine bay...

Last question: how bad are carbs in cold climates? I've got SU's in the RR and it's only slightly tougher to start than my SC. What makes Webers more difficult? I mean, 30 years ago pretty much everyone was using carburetors in IL and they got by okay...

Emanuel

[911_Dude]

I have Webers and headers on my 2.7. Its a fair weather car since it has no heat or AC. But I cant help but drive in occasionaly in the winter. I live in Kentucky where we get a few days of cold. If its below 32F it really doesnt like to roll from a complete stop as I come out of the driveway. Alot of gas pedal pumping to keep it going. After a few blocks its ok, with just some lean popping from the carbs. But its very hard to get it up to normal operating temp in the winter (above 180). So it never feels as strong as a good summer day. It starts fine, it just takes several attempts and it needs to warm up for a few minutes (in winter).

Gas milage is 26 on highway, 15-16 in city.

You'll need to get a low pressure fuel pump for the carbs. Webers like about 3.5-4 psi and (I think) the CIS pump is about 70 psi. And fuel pressure regulators for the same reason. You can get linkage kits, and you will need an air flow meter (cant think of the brand name) to properly set up the carbs. There is a helpful book on tuneing Weber carbs that I found useful called "Haynes Weber Carb Manual."

If you switch to carbs I know you will like the driving experience. But as a daily driver it will be a bit more effort to get up and go than the CIS.

[Wayne 962]

From my new book:

While they have a great reputation for performance and adaptability, these carburetors are not without their own set of problems. They must be used with extremely clean fuel, as the jets and passages tend to get clogged very, very easily if there is any debris in the fuel. I actually recommend running four fuel filters on your car if you’re running a set of Webers. One filter back by the pump, one in the usual spot in the engine compartment, and two small tiny filters directly in front of the fuel inlet to each carburetor. This seems to give the best protection against clogging in the inside passages. The float levels must be carefully set when rebuilding the carbs. Throttle response and drivability suffer if attention isn’t paid to the proper setting of the floats. For more information, see Project 28, Carburetor Rebuild, in my other book, “101 Projects for Your Porsche 911.”
You also don’t want to over-pressurize your carburetors. The Weber float valves can be sensitive to too much fuel pressure. Make sure that you use a fuel pressure regulator and set it between 3.5 and 4.0 psi. Don’t let your pump run directly into the carburetors – this is a common mistake that can stress the float valves, and possibly make them leak.


-Wayne

[Rufblackbird]

Tom & Dennis - Geez...I dunno. The 17mpg figure is for ~300 miles, 85% of which is freeway at 60mph (speed limit here is a lousy 50mph). I don't see why a 2.7 should use more gas than a 3.0. Maybe I have a hotrod motor but just don't know it?

Bobby - the valves aren't stuck open. It's the first thing I checked when I went to look at it (that's about the extent of my knowledge of carbs). One one carb the shaft doesn't move a bit, but on the other there is very little play. What is the exactly procedure to checking the shaft for play?

Wayne - My 2.7 (don't have a 3.0...I wish!) has or should have ~117K miles on it. At least that's what the odometer shows. It isn't economically feasible for me to do an engine rebuild right now. Besides, my parents will kick my ass if I take up any more space of their garage, as the car just came out of a 1 year 5 month hibernation. I'm sure they're a better investment than the stock market, but I more or less have to recoup some of the expenses. If I can tear out the CIS system and get some $ for it and all the linkages and filters don't cost a whole lot, I'd rather live with the Webers. If I can get no hp boost whatsoever but a big increase in throttle response, great. As long as my mpg doesn't go into single digits I don't have too big of a problem with it.

Emanuel - Exactly! I'd like to know too if it'll harm the engine. I don't see why it should, though. They sure would clean up the engine bay...IMHO they look much cooler than CIS!

Thanks for everyone's replies. Our weather here usually stays in the mid 70s to mid 80s range, and our all time low is I believe 55 (on Oahu anyway). I don't think I'm gonna have too big of a problem with carbs.