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I had those plans for when the CIS should gave "problems"... well, this weekend we had to abandon a regularity rally , engine became worse and worse , till i only could rev to 2000 rpm.
I suspect the fuel pump , as when i filled up (from 1/2 tank ) it was a bit better ... more static pressure on inlet pump i assume.
So , no , i won't mount a new pump to see if it is solved.... till another problem occurs. It remains a old school complex system , now 40 years old....
I estimated a complete new CIS ( from pump to injectors) in parts between 8k and 10k....no , thanks.
This time i will use 4 Webers IDF44 , and built everything "low" so that it can be under the hood.
What we need :
- 4 custom build manifolds , max height 50 mm
- 4 webers IDF44
- 4 trumpets 15 mm
- 4 filters 45 mm
- a custom gas command with 4 independant rods to the carbs
- 2 low pressure fuel pumps to replace oem pump and filter
- 2 filters/pressure regulators (in the engine bay )
- and of course some relais, hoses and clamps.
For tuning i already have the carb synchronising tools and will install a Innovate AFR gauge.
This , if i can get it running good, will be so much more reliable for about 3k in parts.... we will loose some torque , but for rally reliability is priority of course.... and it is a fun car , so MPG don't "really" count .
Design for the manifolds
and a presentation of the carbs...
not directly , no... i just want to try the Weber setup.
If it doesn't work , i can go back to the CIS and see what the problem is.
For that i will leave all oem fuel lines in place and work with new extra hoses. Later on i can remove all oem lines or reconnect for going back to CIS.... but sure hope the Webers will work !
i can agree CIS "was" reliable , but now all parts are 40 years old.... and expensive to renew if one wants it all done to be sure of a good fuel delivery.
So i think the Webers are worth a try. A lot cheaper, more simple , all new parts , and a proven reliability in so many cars , for so many years.
My instant thinking is sidedraft rather than downdraft, so you can add some runner length and gain usable midrange torque. My limited experience with Webers is that they tend to be sensitive to cornering load and vibration. Someplace I have a suitcase or two of IDA and DCOE tuning parts. Another smaller case with progressive version parts. It can be tedious to tune for eight separate chokes/Venturis.
A modern laptop-tunable injection package will be decades better the carburetors. Get a US version of the intake through the belly, use your S plenum and runners, with injector ports added.
Before any of that I’d check the pressures and fuel flow. Changing the whole intake for a tired fuel pump seems like a ton of work.
i can agree CIS "was" reliable , but now all parts are 40 years old.... and expensive to renew if one wants it all done to be sure of a good fuel delivery.
So i think the Webers are worth a try. A lot cheaper, more simple , all new parts , and a proven reliability in so many cars , for so many years.
Even the sound may be nicer
CIS is old and very complicated with a whole lot other weird stuff required to make it sort of run. Carburettors are not much simpler and getting really expensive. The problem with carburettors though it is getting hard to find an expert and also hard to find a dyno operator that will want to go near them. The cheapest and easiest solution is to go full EFI and get rid of that distributor at the same time.
My instant thinking is sidedraft rather than downdraft, so you can add some runner length and gain usable midrange torque. My limited experience with Webers is that they tend to be sensitive to cornering load and vibration. Someplace I have a suitcase or two of IDA and DCOE tuning parts. Another smaller case with progressive version parts. It can be tedious to tune for eight separate chokes/Venturis.
A modern laptop-tunable injection package will be decades better the carburetors. Get a US version of the intake through the belly, use your S plenum and runners, with injector ports added.
Before any of that I’d check the pressures and fuel flow. Changing the whole intake for a tired fuel pump seems like a ton of work.
Indeed dr bob , my first plan was sidedraft with DCOE's .... but then i need a crossflow manifold and realized how difficult it would become to reach the plugs.
We also worried that the fuel evaporation would be "far" away from the inlet valves ....with probably a bad idle , fuel condensing against the walls.
The downdrafts make the construction so much easier and keep the valley open for plugs. I decided to try that once i figured out i could keep everything under the hood.
Yes, we will loose some torque , but i want a reliable , "cheap" solution against CIS ... not the fastest 928 .
And yes, a lot of work for probably a tired fuel pump , but i had the plans , as you can see i already bought the carbs , coincidence CIS let me down this rally now.....
PS we rally in "Historic" class , so we may not use modern injection ...
I have worked mostly with Dellorto carbs which unfortunately are NLA. Genuine Weber is quite expensive. Has anyone tried the low cost Fajs carbs, Chinese copies of Weber? Have no personal experience but people say that Fajs works as well as genuine Webers.
Åke https://www.ebay.com/itm/Carb-CARBUR...UAAOSwcUBYMa1e
Last edited by Strosek Ultra; 09-22-2020 at 05:27 AM.
no idea Ake, they look exactly the same as Weber IDF44....but i wouldn't use those cheap copies . It's already a job to get them tuned , so starting with a lower ? quality isn't good already from the start .
I would fear lower quality bearings and seals... with problems later on ?
I don't see how that mocked up setup is going to fit under the hood unless you're planning to have the inlet filters above the hood like a hot rod.
With carbs, the fuel system needs to be kept really clean by the time the fuel gets to the carbs or you'll be clogging jets.
I have dual 45mm Dellortos on my 914 and getting 2 synced and running well is enough fun. Can't imagine how much fun twice as many barrels will be with jet choices, emulsion tubes, velocity stack lengths, float levels, accelerator pump settings, adjustments for temperature changes, etc.
Interested to follow along but seems like replacing a fuel pump is a heck of a lot easier. A properly running and tuned K-Jet system tends to stay that way as long as the car is used regularly.
I'll share that I've had good results from IDA's and IDF's, and never had a car that wouldn't run at least decently with the carbs right out of the box. Getting the last bit of performance is an art as much as a science, but with books of notes I could go to almost any track with an air density number and temperature, and do pretty darn well. Perhaps the biggest challenge is anticipating during morning practice what conditions would be for an afternoon race session. The basics (choke size, primary Venturi size and stack heights) are established based on altitude before the car goes in the trailer. Pump nozzles might get changed but mostly not. After that, the tuning parts are all in a stacked assembly that bottoms in the float bowl, so actually changing stuff is a couple screws for an access cover, then the jets and emulsion tube comes out for each hole. Deciding what to change is where there's some voodoo science, since so much is interactive.
Fuel injection was a godsend for tuners. Even the mechanical, like Kugelfischer then its derivative CIS, are much better than carburetors. CIS with altitude correction works amazingly well for performance. Not so much for CO emissions or fuel economy, but the addition of real-time control pressure correction for measured exhaust gas oxygen (CO) sensing helped a lot with both. U.S. 928's never saw those improvements, moving instead to the analog/digital hybrid L-Jet injection after just a couple years of CIS. Probably driven by the need for better fuel consumption numbers, plus the need for having catalytic converters that would survive the duty. With a national highway speed limit at 55MPH and lines for fuel still in the memories of most drivers, not much worry about extended high-load driving anyway.
we live in a "flat" country , near sea level. So no problems with altitude.
I know , probably a new pump is the solution ... but i have that "itch" to try the Webers ...as it was planned to do once.
If i can get it running "decent" , for me that's enough as i use that car only for rallies... so simple reliability is most important , there is no rally every day....entry fee, preparation etc...
I rallied my BMW CS '70 for 5 years without any problem ... on triple DCOE45 ...
I think about 90% of the historic rally cars use Webers....
I agree a CIS can work perfect , but once problems i see here many "horrible" threads..... desperate seeking through a complex system.
I love the idea of the Webber’s on that motor. Especially for a rally or race car, might be different we’re it for road use. As I understand the Webber’s are usually pretty rich at idle and then lean out as butterflys are opened. Has anyone had issues with that phenomenon? I have a friend with four 48s on a domestic v8 and that is the condition he faces.
good remark Oldshark , that's what i have seen also on my other 928 which i build with 4 Webers IDA48. Car runs but not yet tuned (dyno) as it's not finished by now... soon as winter gives more time to spend in the garage. But as i tried to lean it out at idle , it only idle's with a AFR +/- 12 or richer , leaner it stalls. I sure couldn't get it around 14. But i must experiment further....
I wonder if i will see that same rich idle occur with the IDF44's....or if i can get it leaner... 13.. 14 ??
09-21-2020, 07:19 AM
From CIS to Webers on a '82 s
