Single Carb vs Dual Carb vs FI

[toplessexpat]

Hey All -

It seems to be a while since this topic garnered much attention on here - but I thought I'd take a moment to chat about my recent experiences with the above.

While my FI set up is very satisfying, nice and easy driveability, I do like the sound that a well tuned carb can bring. On my 1800 I've got a 38ADL, which is a very large carb indeed. Very docile on the first barrel, and screams on the second.

However, I got the opportunity over the weekend to drive sptcoupe's eponymous vehicle. This has a very heavily modified 2ltr motor, and is complete with a pair of well set up 44 IDFs. He really does leave them well alone once they've been set up and they are a complete dream to drive. They open up smoothly and transition off of the idle circuit on to the mains so nicely that you really have to be looking out for the transition. They sound great at WOT, and really are very well behaved when just cruising gently around. What a phenomenal setup.

I know that some people have problems setting up multiple carbs. Jeff's approach really does seem to work well though, and I had a fabulous time. I've got two waffle top intakes in my garage. One for 44s and one for 40s. I suspect 44s will be going on soon...... which will just leave me wondering what to do with my 38ADL!

Andy

[narfire]

So, you're preferring the 44's over the 38?
Sometime in the future I'll be wanting to build another 2L for spirited street driving and was contemplating a 38 or twin 44's.
Chris

[vandor]

One would have to try both the single and the dual carbs on the same engine for a fair comparison.

Andy, you mean this is the first time you drove Jeff's Coupe??? Yes, once Jeff sets up those IDFs one could think the car had EFI

[toplessexpat]

Hey -

Yep, I think I prefer the 44s over the 38. While I love the kick that the 38 gives you when the second barrel opens, the smoothness of the 44s (when set up right) is just fantastic.

Csaba - well apart from the obligatory test drives to make sure that nothing is going to fall off, during which I'm normally listening out for something specific - I've not really had the chance to do a "spirited" drive in it. We took the Coupe and Scott's A500 over to Northside for the 4C, and then all three up to the Woodlands for Cars and Coffee....

... 6:15am: 4C and Coupe pull into gas station. Woman walks over... "sounds like you guys were having fun"

I'll dyno the 38 before I take it off, and then re-dyno with the 44s.

[seabeelt]

+1 on dual carbs. Haven't touched them since going up one on the idle jets a few months ago to get rid of some mild popping. They purr and then roar when you put you foot in it. I'll not be going back to a single carb.

[131]

From a 34 ADFA to a 34ADM is a big improvement, going to 40IDFs is a step up again, I'm really looking forward to the day I can crank it up with programmable injection.

[bradartigue]

I wouldn't call either a step up or down, they are quite different, just as different as L-Jetronic or EFI or CSI or whatever else you can slap on an engine to make it go. I will say that you drive anyone else's car then you tend to focus on the positives, so before you go through the ton of work required for duals to function or to swap to FI, drive them all around as much as you can.

FI is a whole different animal than carburetion, and if you can do it right the results simply blow carbs away in terms of reliability and performance. No dual carb setup will touch even L-Jetronic in terms of generating power across the widest band...and frankly your ADL has a better overall power curve than IDFs ever will (because ADLs are progressive and are more precise at low running speeds than the static, high flow IDFs). IDFs though, they've got raw power. Get a set of IDFs, DCNFs, DCOEs, whatever duals you want, on a four cylinder, and for some reason the thing just seems to go wild. It sounds fantastic, it has this power band from the middle to infinity... Sure you burn a few dozen spark plugs and your hand cramps from turning those screws all day long, but once it's done it is a lot of fun.

For me it's not just about driving. Which explains why I have no car here but a bunch of parts I'm tinkering with and a steering wheel nailed to the wall...silent reminders I guess. Anyway, I like to say if you like to tinker run IDFs. If you don't, then don't touch them. If you like to tinker and like electronics or just like wires, graft an L-Jet from a 2000 or build your own system (warning: most people who try this don't seem to finish the projects).

[toplessexpat]

Hey Brad -

So my clear take away from that was "drive them all around as much as you can." - which means Jeff, I'm going to be hankering to keep borrowing the Coupe for a while 'just to test drive them'

I'm definitely not planning on retro fitting FI here. I have a FI car (with HC), I don't need to spend time working that out - and I love wires .

Jeff certainly seems to have the dual IDF process cracked, and doesn't spend his time tinkering with their tuning. I may not dispose of the 38ADL quite yet, but the duals will be a lot of fun to get onboard.

A

[bradartigue]

Jeff certainly seems to have the dual IDF process cracked, and doesn't spend his time tinkering with their tuning. I may not dispose of the 38ADL quite yet, but the duals will be a lot of fun to get onboard.

One key to his configuration: Big IDFs on the 1800. 40 IDFs are too small for the larger engines if you ask me....sure you can tune them to run, but something never seemed quite right, sacrifice at the low or high end. I can usually tune a Weber of any type to some satisfaction, but 40IDFs on the 1800 and 2000 to me were always a struggle. I think they just don't let in enough air.

[carl]

It's the psychological effects of IDFs that push my buttons. With open stacks or sport filters they are incredibly anti social in their aural music....a single carb or FI can't come close. I don't do track days any more or attack highway ramps at 9/10s anymore but I do jump on the motor whenever I can just to hear the IDFs wail. Further, the IDFs only require 90 degrees of rotation whereas a progressive carb requires much more. As a result the IDFs give the impression of much quicker response as much less push on the gas pedal is needed. I recently converted one of my spiders back to a two barrel and could not figure out why the car had no power....I wasn't pushing the gas pedal far enough to get the secondary open all the way.

Kind of depends what you are looking for out of your spider. I went on a 20 minute ride on some local back roads a few weeks ago in my hooligan spider and had an absolute joyous time that kept a smile on my face for a week.

carl
79 spider with mild mods
74 spider cafe racer
76 128 wagon under construction (including intake manifold for dual 40 IDFs)

[bradartigue]

It's the psychological effects of IDFs that push my buttons.

Same here. Same with all of my cars, and why I've sold more Subarus and Toyotas than I care to imagine (they're boring as hell). Something very satisfying that sound...I can hear a TC coming a mile away.