Changing from FI to dual carbs

[henry]

What type of improvements can you expect, with this change, FI to dual carbs? (40MDF).

[So Cal Mark]

great sound when you open the throttle, the potential for more top end power

[MIGHTY 8]

You ever driven a Ferrari Daytona?

Or a Lamborghini Miura?


I haven't............but with the butterflies fully open on these dual Webers, I certainly feel like I am!

[henry]

So............mainly..........good sound.....????? The potential for more top end power...???

[wmausbach]

Henry,
I hate to burst your bubble but you are looking at a 10% (DCOE) to 15 % (IDF) DECREASE in power. Carbs will give a slight perception of low end hp and the sound is great but the reality is F.I. is the ultimate. On modified engines carbs are easier to tune which is why so many choose that route. I always quote the BMW 2002 as baseline the 2000cc Ti with DCOE's put out 120hp, the Tii put out 130hp with F.I. with the same spec's on the engine( CR, Cam, etc). The IDF's that every body loves on the 124 engine has a 90 degree bend in the manifold which causes less than optimum flow.
By the way I'm an old carb guy and I still have my DCOE's to prove it.
Ciao
Wayne in Houston

[124ADDHE]

Yeah, im sure that there is the potential for more peak power with the FI but that is not all that is important, the overall powerband is superior with the isolated intake per cylinder with better torque; also as you mentioned, the sound is phenominal!

I would really love to see equal cars do a drag race with the two systems though

[wmausbach]

I hate to burst your bubble but F,I is superior in peak HP, overall power band, startability, and altitude adjustment. The sound is truelly the only asset other than the ability to dial in quicker. This is the reason most modified engines done by non-professionals use carbs. F.I. requires a lot of very knowledgable dyno tuning and is usually way beyond the normal budget. The last modern OEM engine using carbs (DCOE) was the Abarth Strada in 1985. There is a reason for this.

American sportscar racers found this out in about 1965 when EVERY top contendor switched to FI from the ultimate carb the Weber DCOE. Even the much cussed original Hilborn injection was superior. Ask vintage Corvette racers which produces more power.

I still have my DCOE's and I'll use them because I understand them and can dial them in.....and I like to hear the sound. I just have no dillusions that they produce more power anywhere.

Ciao
Wayne

[124ADDHE]

Ok Wayne, so lets see your Dyno numbers, I would love to see real proof! There are many reasons that carbs were eliminated in north america but im pretty sure that the initial reason was for emissions reasons, not power. I have to disagree about the starting, my carbed fiat starts as soon as the button is pushed, much faster than my many other vehicles, maybe your carb wasnt tuned correctly? Yes, I agree, more "potential" for peak power, I sure dont think the seriously archaic FI on the fiat is up to the performance and certainly not the tuneability of the dual carbs! I know that the isolated runner "in theory" will provide low-mid gains, I would love to see a back-back dyno of the FI vs dual carbs.

you really cant tout the stock FI too much with its seperate igntion, flapper-style metering, no ability to reprogram; its really nothing like a modern setup. There would be absolutely no comparison if we were talking about modern systems or even some of the exotic racing setups being used, as you mentioned, in the 80's with individual intakes, slide-throttles and mapped ignition.

[124ADDHE]

I couldnt find much to make my point but here is one fellow with a ducati bike whom did a back-back and he admits that he could have a bit more carb on there:

http://www.bikeboy.org/900fuelvscarb.html

Looks like more torque with the carb, dont get me wrong though, I know FI is better, just the EFI in OUR cars is NOT better than the carbs throughout the powerband.

I do have a full EFI system for sale, $350, everything included, been trying to sell it for 6 years since I put the sidedraughts on the car.....no one wants to buy it, I did sell all my carbs though.

[wmausbach]

You can always find the "Bike boys" doing comparsions on ill tuned FI vs carbs. As I said carbs are much easier to tune for the non-professionals. Look to the professional racers and see how many carbs you see on F-1, Indy, or even the GT cars. They have free choice and the carbs were abondoned in the mid 60's.

As far as the Bosch system goes even with a Flapper it is still superior than carbs up to about 150hp. See Jim Fierst (Whoa Brake fame) or Gary Baucum (Mechanic for 3 national SCCA wins with 124 engine) who both have told me this face to face and have the creditials to back it up.

The reason modern system were changed was for cost which is the driving force for modern car makers. Foe example look at the Mega Squirt setup and compare it with the AFM. Crank fired igntions system are cheaper to produce that a distributor. Electronic sensors are far cheaper that hardware like a AFM.
Both operating properly will keep the correct air/fuel ratio which is why carbs can not pass emmisions testing. They can not meter the precision that any type of FI can.

Sound s like you have had a bad experience with FI. The one advantage you did not mention was cost. AFter initial purchase the carbs are a lot cheaper to run and maintain. This is why it makes sense for the FIY like us.
Ciao
Wayne