tmpusfugit

I would be more inclined to use the FI units that replace the Webers in VW land if I were to do the TBI approach. See http://www.cbperformance.com/SearchResults.asp?Cat=285 for some ideas along those lines. I also would not personally use the 44mm Webers, to do this much work I would go for the 48mm versions, either carbs or FI. One of my Spyder buddies is running the dual 48mm Webers on a 1720cc Porsche 356 engine, makes a lot of HP, so it is not too much air/fuel for a 928 engine to use 48mm.

RKD in OKC

Had a 71 Plymouth Satelite Sebring Plus. It had the small block 383 with factory installed Holley made six pack setup like the Charger 440 six pack of the day. It was 3 2bbl carbs on a special Edelbrock intake. Never had to mess with em at all. The only problem I had was keeping passenger side motor mounts in the thing.

danglerb

There was a track car forsale here in SoCal, maybe the guy still has it, that was converted to Webers. Owner told me it sounded like a pack of motorcycles.

My guess is maybe some gains on the top end, big losses on the low end, which might be fun to drive.

simos

Very nice build Åke, remains me about this street rod.

http://flatsixes.com/cars/for-sale-c...reet-rod-sale/

What's the tube in the middle of valley having filter on top, crankcase breather tube?

Strosek Ultra

The picture showing the linkage (post #29) is not my car. I don´t know about the tube. The street rod looks good, much more room for a custom intake under the hood.
Åke

dr bob

Someplace in my collection of things is a large briefcase/small suitcase of Weber tuning parts for IDA's and DCOE's. Keeping the carbs sync'd and tuned even for a street car was a huge chore. Weekly Saturday morning ritual was to run the valves, new plugs, sync the carbs. Autocross days got another set of plugs afterwards. Should I get lazy and miss a Sautrday, the car would be running like crap by Wednesday. Aircooled cars are a lot more fussy of course, and even with the best tuning technology available the carbs are amazingly sensitive to air density changes. As Doc Mirror says, there are so many adjustments that you can easily get them crossed up and end up having to start from scratch again. Primary venturies, four jet and emulsion tube options, chokes and throttles, plus basic idle screw that doesn't do much after the second port is exposed on throttle lift.

You'll need an air-density meter, or a barometer/thermometer/hygrometer setup and the charts that Doc and Wally know well.

Many folks seem to be able to tune for max horsepower, but getting them to be street-driveable in everyday traffic is at least as much art as science. Meanwhile, a good aftermarket EFI setup gets 'tuned' with a laptop and a wide-band oxy sensor. For less money amd certainly way less time and frustration.

mark kibort

just wish we had a bolt on intake manifold we could use with a single large inlet for a stock MAF.
I bet that BMW intake would work with some kind of adapters to the heads! shame we don't have something available by now! the CF intake for Anderson was nice, but a little more complicated with dual throttle bodies.... seems it would be pretty easy to put something on that Carl or Greg has made to fit the stock stuff with NO modifications but airbox.

The Fixer

I think it's as Wally states, steep learning curve.

I never had this much trouble with Webers and none with Dellortos.

To truly understand what happening inside Webers you need to be off the charts smart, but to get them to work right, not so much.

The most trouble i had were the vibration gaskets wearing out and causing vacuum leaks (side drafts)..

The power gain for me would be there doing this but for comparison (to a aftermarket FI system) cost for this setup Vs FI,

What's the aftermarket fuel injection of choice for our 928s and what does that system cost and how much fabrication is needed to get it installed?

danglerb

My understanding is some of the love for Carbs goes away in a high g turn as the mixture goes wild.

FBIII

Depends how the float system is designed.
Don't forget every Ferrari, Lamborghini, Maserati and Aston Martins ran Weber carbs from the 50's into the 80's and had a modicum of track success.

Gary Knox

I had a 1973 BMW 3.0 CS on which I replaced the OE dual downdraft Solex carburetors with a set of triple side draft Weber DCOE 40's. Also the european upgrade camshaft. Loved that car, and it was not difficult to get the carbs in tune, nor an issue keeping it in tune once it had been done.

Wish that combination/car was still in my garage - without the rust issues that prompted me to sell it in 1980!

tmpusfugit

Dr. Bob, your experience sounds a lot like mine on Webers. My buddy, I refer to him as Dr. Weber, is really good at tuning them, far far better than me. But, that said he spends more time tuning the Webers, cleaning jets, replacing plugs, changing jets, syncing them etc than he spends driving. When all is well the car is an absolute beast, but it goes from peak tune to something else in very short order and frequently unpredictable in that change....we are talking about a pretty small displacement engine,dual 48mm Webers, that has a cam set up specifically for the intake tube lengths, as well as a finely tuned exhaust. When the car comes up on the cam at about 4000 rpm, feels like a passing gear, then at 5000 rpm +/- it hits the exhaust resonate frequency, like another passing gear. But, if either Weber falls a bit out of tune it is the end of everything. I am thinking with larger displacements the cubic inches are more forgiving and the Weber tune is less critical? All my experience has been with the IDF/IDA series. I know nothing about DCOE and related Webers so I do not intend to direct any of my comments toward them.

One of my other acquaintances had several vintage Ferrari's that he historic raced for a long time. One of his major reoccurring complaints was carb tuning.....and he had 10 Ferrari's and one Maserati, from as early as 1948 through 1967. All of them racers.....including 2 that were Phil Hill's cars that he raced in world championship races.... so it is not only us with Weber issues....

Strosek Ultra

There is one thing not being mentioned here. You cannot run an early 928 having the CIS K-Jetronic fuel injection system with a fairly large cam having a certain amount of overlap. The pressure pulses will upset the sensor plate making the engine behave badly, jerking or pulling unevenly at steady or low gas on flat road or slight downhill at low speed about 30-40 mph on higher gears.
First time I had this problem was in the early 80´s when we did modify a small BMW 2,3 liter six with a sports cam, high compression pistons, a well ported head with 3mm larger intake valves, headers and a free flowing exhaust.
The power was there but the car was difficult to drive in town at low speed. When the jerking started one had to push down the clutch pedal and downshift to get the rpm up in order to overcome the problem.
The car owner was not pleased so finally we installed three Dellorto DHLA45 twin choke carbs and it made all the difference. After some tuning the jerking was all gone, it was running as smooth as the stock engine but much more powerful. The idle was perfect, the engine pulled good over the entire rpm range but came good on the cam at 4000 all the way up to 8000. The carbs did make a huge difference in power compared to the K-Jetronic fuel injection system and the fuel consumption was almost unchanged. When we changed the carburetor main chokes from 35mm to 38mm the engine responded well with quite some further increase in power output.
Remember we tested the small BMW against a Porsche 928S rated at 310 hp and the Porsche was unable to outperform the BMW.
Åke

dr bob

So 48IDA's typically arrive with 44mm chokes installed. With small-displacement (under 500cc's per choke) they are seriously oversized for idling and casual street driving. Velocity is too low through the chokes (venturis) to draw the proper amount of fuel. Add in reversion pulses from a long-overlap cam and you end up with lean mixtures on top of the charge dilution from retained exhaust gasses. Changing to smaller chokes makes a huge difference in performance and driveability. Small-displacement engines love 38-40mm chokes or smaller for all but full-load high-rpm duty. Unless an educated eye looks down towards the throttle plate, you can't tell they aren't the Real Deal.

Strosek Ultra

Well said by Turbochad:
I have had Webers and Dellortos on both VWs and Porsches. I have not had to tune them on engines larger than 6 cylinders but I have the following thoughts to offer to those who are considering trying this mod.
1. The transition problem in 2 barrel IDA's has been solved by VW tuners. You can send your carbs to JayCee enterprises and they can add the extra holes to the idle circuit to solve this common problem. This was a design issue as these carbs were never considered for street use by their makers. With this mod the transition is silky smooth.
2. Phonelic spacers should be used between the manifold and the head to stop the transfer of heat into the carbs which caused fuel boiling. This is the result of modern fuels which have a much lower boiling point than older leaded fuels. This vastly improves the issue of fuel boil.
3. I find that the biggest mistake that people make in setting up a weber system is not properly setting the float levels and fuel pressure. Most of the issues of popping in corners and difficult tuning are caused by this or worn out shafts (air leaks). If you have the floats correct and the pressure within specs the rest is what is commonly thought of as tuning (synchronization, choke sizing and jets). With a little planning using the weber tuning manual by Bob Tomlinson you should be able to get the hardware settings within a tenth before every starting the motor. If you follow the air synchronization procedures the carbs are not hard to get to work correctly.
4. Set up properly (read item 3 above) IDAs are not that sensitive to air density changes and humidity. I live in Colorado and regularly run both my weber fitted cars in altitude variations of 4,000 feet without needing to change jets (my 911 runs great at 9,000 feet).

I rely on my carbs to determine the tune of my motor not the other way round. Remember carbs don't go out of tune unless they are worn out or improperly set up. If my car starts running poorly, I go to my ignition system or my valve train to see where the problem is. Carbs provide constant metering of fuel based on air velocity and don't feature wear items (fuel filter is the only exception) like other systems do. The key is the initial setup.

I would love to see a properly set up 928 with a four pack of IDA's. Cut holes in the hood and have a lexan cover made like the old ferraris with the air horns sticking through the hood plane. The horsepower would be far in excess of the stock FI system and would be close to an ITB FI system. It is far more unique than FI and the thrill of a weber at full song is second to none.