4 BBL manifold to replace K-jetronics? Blaspemy?

[coachkadis]

After finally getting my jetronics issues ironed out, there were several times I hunted for a company that maybe fabricated a replacement intake manifold that could run maybe a Holley 4 Barrel carb or such. I think one could sell. Yep, I said it. Looking at the costs for a rebuilt fuel distributor or the WUR makes me wonder why no one has at least attempted this. Or maybe they have and I missed the advertisement or the thread covering this idea. Why not Webbers you say? Some of us cant afford the price of the carbs and manifolds if that is what is needed to replace the jetronics. Many years ago I fabbed a dual quad manifold for a Buick all aluminum V8. I had swapped the engine into my Chevy Vega. A little too much carb for 215 cubic inches but it did look sweet. Anyhow, just wondering if anyone has tried.

Thanks
Coach

[A930Rocket]

I recall they did something similar for the 240-260Z’s way back when. I don’t know how well it drove though.

[HarryD]

I would think it would be easier to do a PMO conversion to dual 3 throat carbs. All the hard work is already done.

But given the cost, you might just want to rebuild what you have. Bear in mind that CIS was used by many car makers in the 70’s and 80’s. Once setup, they just work with minimal fuss.

[jrwilson]

The CIS runners can be run "wet" and a number of people have made airboxes with a Holley 4-bbl pattern on the top to run a carb. Runs well from what I hear.

[76FJ55]

there is this thread.

[GH85Carrera]

As a 49 year member in PCA, I have seen many guys put carbs on a 911, from factory Webbers, PMS or a 4 barrel. Not a single one drove for beans. Carbs work OK at wide open throttle. That is about it.

In corners (was al love corners) they exhibit fuel starvation, the run really bad at idle, and even worse when the temps are cold. Long ago I did the opposite for my El Camino, I happily disposed of my factory carburetor, and put on fuel injection from a home made setup using throttle body components from 90s C10 pickup. It runs like a modern car, in zero degree or 100+ it starts instantly, and never hesitates.

The biggest reason that pushed me to go to fuel injection was sitting in a freezing cold car waiting for it to warm up enough to idle at all. That and trying to pull out onto a road with traffic. Hit the gas and it just coughed, and sputtered before it ever got moving slowly.

Just find a competent mechanic for the CIS. When working right, it is a good system. Most issues are vacuum leaks.

[Jeff Higgins]

Originally Posted by GH85Carrera

As a 49 year member in PCA, I have seen many guys put carbs on a 911, from factory Webbers, PMS or a 4 barrel. Not a single one drove for beans. Carbs work OK at wide open throttle. That is about it.

I'm sorry Glen, but that's just nonsense. I cannot believe that in your 49 years around these cars that you have never met anyone who could make carbs work. When set up properly few systems work as well. I know a number of people who, as a matter of fact, gave up on modern EFI systems and substituted carbs. Their cars never ran better and they were never happier. I've lost track of the number of cars and motorcycles I've owned that rely on carburetors (I still own three motorcycles that do). They all ran superbly under all conditions, varying weather conditions, altitudes, from idle to part throttle to full throttle, hard acceleration and cornering - everywhere. They are a damn good intake system, very well proven, extremely flexible and adaptable.

But, well, putting a Holly four barrel on one of our motors, while it no doubt could be made to work, is right up there with an LS or Subaru motor swap. Definitely considered blasphemy in our circles. I bet a used set of Webers and manifolds would prove to be cheaper anyway.

[reclino]

It's.been done a few times, I just did a quick dirty forum search and these came up
Preventing icing may be required.
I would think a 4 barrel is to large for a 911 engine.
https://forums.pelicanparts.com/porsche-911-technical-forum/357313-oh-yeah-buddy-kill-newbie.html

And this one
https://forums.pelicanparts.com/porsche-911-technical-forum/452264-911-american-carburetor-swap-3.html

There was someone else recently who made his own manifold, and I think he was somewhat local to me in eastern North Carolina... Can't remember who it was.

Found it

https://forums.pelicanparts.com/porsche-911-technical-forum/1085924-now-something-completely-different-part-1-a-2.html#post12342294

https://forums.pelicanparts.com/porsche-911-technical-forum/1163636-now-something-completely-different-part-2-a.html#post12277210

[mikedsilva]

I bench tested this.. haven't had time to try it on the road yet.

[Hi_Fi_Guy]

I watched the Hoovie/Car Wizard series where they put the Holley system on a Ferrari 308 and the engine made more power on the dyno than Ferrari advertised when new and supposedly the drive-ability was improved at all revs/speeds. So I guess anything is possible.

I’ll be sticking with my PMO carburetors for the foreseeable future though!

[Jay Laifman]

While carbs may solve some problems - and I have had an extended problem with CIS that I think is now solved - do note that the cams on CIS cars are way detuned from carbed 911s. So while you may solve some problems, and people may be better than their incorrectly running CIS was before, at the end of the day, it will absolutely and always be slower than a well running CIS car.

[PeteKz]

Let's see if Tom (OldH2S) rings in. He has done this too.

[Steam Driver]

I think bad-mouthing carburetors is a bit short-sighted. Porsches of all varieties ran beautifully for years with carburetors. A properly set-up set of Webers runs great.

The 914-6 I had for years (now departed and I miss it) had modified (larger venturii, and idle jets, main jets, emulsion tubes) set-up by someone who knew what he was doing and it ran great in all regimes. The key here the set up, that requires the knowledge, and experience, not to mention drawers full of little brass Weber parts to get it right. Unfortunately all that stuff is getting thin on the ground.

In the mid-seventies when emissions rules were getting hot and heavy a friend of mine had a portable exhaust gas analyzer that we used on one day, driving, to check my car’s mixture. Except when initially accelerating when it briefly went rich (as it should) it was amazing how steady and consistent the mixture was. We were amazed; didn’t expect that.

Once a Weber (and probably everything else) is properly done it should be fine until it gets dirty and needs disassembly and cleaning at some point. Yes multi-card set-ups occasionally get out of synch but that’s easily remedied, and maybe the idle mixture will need tweaking but other than that carbs are trouble-free. Practically no moving (wearing) parts, no sensors, and no computers needed.

As you can tell, I like carburetors. To me the only real advantage to EFI is that it’s more readily tunable, and generally gets better fuel economy because of overrun fuel cutoff.

[Jay Laifman]

Note that I did not bad mouth Webers. I bad mouthed Webers together with CIS cams.

Webers with correct cams can be wonderful. But Webers with CIS cams will never be equal to a correct CIS car or an earlier Weber car that already comes with a correct cam.

As is, a 1973 US CIS car had 140 hp. A 1973 ROW car with carbs had 130 hp - and that is with a cam designed to work with the carbs. So the HP of a CIS car with Webers added will be south of 130 for sure - which is less than even the most base early 2.0 911. (Note, I believe the same impact is widely understood in the 914 world where injection is removed and replaced with carbs).