38/38 Carb to FI Conversion

[iconoclast6]

I hope are well and staying healthy. And driving, rather than steering.

A valued e9 colleague and whisperer has extolled the virtues of converting my well running (fingers crossed) carbed 3.5 CS to FI.

I will be following up with him, but figured it can't hurt to bring this question to the community as well.
Thoughts on process, modifications, tuning, parts/links, expectations and performance will be appreciated.

Alas, just when I imagined the never ending e9 restoration/upgrades and tweaking had come to a pause...I am tempted anew.

 

[OCCoupe]

KISS don’t go fancy, go with what works and is easy. As the ever so knowledge Ron Popiel once said, “set it and forget it”!

That said collect the parts for an L-Jet manifold and for a motronic 1.3 setup from a 1988-89 635csi or late e34 535i. Some time, $$$, and profanity and you’ll have a virtually flawless carefree 3.5 fuel injected delight!

 

[rsporsche]

I have to agree with Mike ... if you ever think you want to do this, get the L-Jet manifold and e21 'C' tubes while you can still find them at a quasi reasonable cost. the motronic 1.3 is relatively easy to find. i have a question for you, how stock is the 3.5, or more importantly ... how non-stock is it? a person on this forum that i trust convinced me to go with megasquirt as my 3.5 is not stock.

 

[Stan]

SFDon is King of the Megasquirt

 

[OCCoupe]

SFDon is King of the Megasquirt

If I were to go megasquirt, I would reach out to Don. However I don’t think Chuck needs to go that route with a stock 3.5. @HB Chris has a b35 with a mild cam and he used the 1.3 motronic setup with the 179 ecu and it is perfect and worry free. I’d you are trying so maximize every hoof of hp out of your engine then megasquirt is the way to go.

 

[Stan]

I really like the look of the @HB Chris engine.

 

[Stevehose]

Take the 2 carbs off and replace with 3 for 50% more sound and fury

 

[Stan]

Take the 2 carbs off and replace with 3 for 50% more sound and fury

And of course, eye candy

 

[OCCoupe]

And of course, eye candy

Stan, who tunes your carbs? This to me will determine triple carbs vs a newer factory fuel injection system.

 

[Stan]

Stan, who tunes your carbs? This to me will determine triple carbs vs a newer factory fuel injection system.

My car has weber 38/38 downdraft.
Tuned by Vintage Sports & Restoration in NH.
I like the look of triple side draft but my engine is perfect for me.

 

[OCCoupe]

@Stan my point is that once the fuel injection is set up you’re not so dependent on someone tuning your carbs if or when they go out of sink or need tuning.

 

[Mike Goble]

A valued e9 colleague and whisperer has extolled the virtues of converting my well running (fingers crossed) carbed 3.5 CS to FI.

If it ain't broke - don't fix it.

 

[iconoclast6]

I have to agree with Mike ... if you ever think you want to do this, get the L-Jet manifold and e21 'C' tubes while you can still find them at a quasi reasonable cost. the motronic 1.3 is relatively easy to find. i have a question for you, how stock is the 3.5, or more importantly ... how non-stock is it? a person on this forum that i trust convinced me to go with megasquirt as my 3.5 is not stock.

It's pretty much stock. The only upgrade has been to remove the points to add a 1-2-3 ignition from VSR in N.H.

 

[OCCoupe]

If it ain't broke - don't fix it.

Also great advise.

 

[iconoclast6]

If I were to go megasquirt, I would reach out to Don. However I don’t think Chuck needs to go that route with a stock 3.5. @HB Chris has a b35 with a mild cam and he used the 1.3 motronic setup with the 179 ecu and it is perfect and worry free. I’d you are trying so maximize every hoof of hp out of your engine then megasquirt is the way to go.

Correct. Not doing megasquirt. Dont have the $$ or technical resources here.

 

[Stan]

Correct. Not doing megasquirt. Dont have the $$ or technical resources here.

Drive out to CA, drive the Targa California, then drive over to @sfdon and leave the car for MegaSquirt, borrow or rent a car, to to wine country, The French Laundry, & see the sights...

 

[Ohmess]

Chuck - I'm a fan of carbs. Once you get the jetting set up, I don't find keeping my carbs in sync to be difficult.

Fuel injection will give you better fuel economy, slightly more power and somewhat better reliability. For many people, concern about who is going to fix their carbs if they have problems is a major reason to change. I determined to learn to do my own carb tuning to avoid this.

If you decide to go to fuel injection, I have a bunch of L Jet parts that I pulled from a Euro 633 CSi when buying three diffs from a guy in Maryland.

Note too if you go in this direction, you not only are changing your intake, but also your fuel delivery system. You need to install a higher pressure pump and a return fuel line.

 

[Dales]

A related question. My 1970 2800cs needs new carbureters. What are the pros and cons of replacing the existing rebuilt dual Webers with new 38/38 dual Webers vs replacing them with triple side draft Webers? The mechanic who works on my car says he can not do anything more to improve the existing carbs and advises me to not spend anymore money on them. He does the mechanical work on BMWs for Alex McCulloch, works exclusively on older BMWs, and is very reliable. I would appreciate any opinions regarding dual vs triple Weber carbs. Dale.

 

[shanon]

Just my 2 cents: if your motor is stock (ie: OE cam & headers) it doesnt make any sense to go beyond a dual 38/38, The synchronized 38s should give you a little more grunt/snap off the line if tuned/jetted properly. A dyno session will determine optimum results.

If the motor is 'hot rodded/built', then an FI or Triple conversion can be truly taken advantage of.

Again, just my .02

 

[Mike Goble]

A related question. My 1970 2800cs needs new carbureters. What are the pros and cons of replacing the existing rebuilt dual Webers with new 38/38 dual Webers vs replacing them with triple side draft Webers? The mechanic who works on my car says he can not do anything more to improve the existing carbs and advises me to not spend anymore money on them. He does the mechanical work on BMWs for Alex McCulloch, works exclusively on older BMWs, and is very reliable. I would appreciate any opinions regarding dual vs triple Weber carbs. Dale.

If two carbs are trouble, three carbs are more trouble, which is one reason why I went with one carb.
There's not much to wear out in a carburetor that isn't part of a standard rebuild kit except the throttle shaft bushings. You can get replacement bushings from places like Pegasus.

Throttle Shaft Bearing Kit, Weber 32/36 DGV Carburetor - Pegasus Auto Racing Supplies

Eliminate friction, wear and vacuum leaks in your Weber 32/36 DGV carburetor! The double-sealed bearings in our Throttle Shaft Bearing Kit install easily with no machining necessary.

www.pegasusautoracing.com