Carb conversion

[sixtwoeight]

I know a lot seem to be a bit offended at the thought of putting carbs on, and i know all the downfalls...!

I am searching for an M30 engine to do a carb conversion on. If i happen to find a motor with all its motronic gubbins intact, what is needed to do a carb conversion.

I have the fuelling side sorted, its just the spark.

I obvioulsy need a distributor. - From what?

Possibly a different cam to drive the distributor?? - Again from what?

Anything else that i havnt thought of?

Any help appreciated.

[dwcains]

Check out this site, which is appropriately named:

http://sidedraftsix.com/studio-time/

[sixtwoeight]

Thanks, nice site with interesting stuff - although im none the wiser with regards to my question.

[dwcains]

Looking at that car again, I realize it's not carb's, but rather has ITB's with injection. Nonetheless, the owner is a member here and he may be able answer some of your other questions. Wish I could recall his username, but perhaps he'll see your post.

[sixtwoeight]

No worries,thanks for your interest.

[raykoke]

Mayhaps this will help

https://en.wikipedia.org/wiki/BMW_M30

Cheers,

[GazM3]

A carb version sounds like a great way to go with triple webers to free up the restriction of the efi intake manifold. Some of the early m90 engines ran carbs with a distributor.

I'm not certain with a factory ecu but I can't see why u can't just disconnect the fuel side and use the ecu for ignition only. If building a hottie motor u will want an extended redline. Maybe something simple like a war chip where u can adjust timing only and let the carbs do the fuel only equation.

U can get very good drivability on Weber carbs but u need to have them tuned by someone experienced and with the aid of a wideband would help

Perhaps fill us in on the intention of the motors state of tune.

11.5:1 big cammed m30 on webers would sound delicious and easily capable of over 300bhp

[davem6]

I reckon Gaz is on the right track by retaining electronic control of the ignition system. Go for a Microsquirt module and run wasted spark with a six post coil or 3 dual post coils. This will give you fully programmable ignition curves and rev limiter and no need for a distibutor.

Personally I think staying injected is the way to go unless you already have carbies. Check out RHDEngineering they have some really good value ITB kits.

[GazM3]

Injection may be the sensible choice but if u setup some webers properly they would be awesome.

Triple dcoe45 carbs will work nice to about 50-55bhp per cylinder. Over this we would need dcoe48 which for memory don't have cold start manual choke.

The sound alone makes my man pussy wet (if I have one).

[Ralph in Socal]

Early M30s (pre 82) ran the standard distributor with centrifugal and vacuum advance modules. It's not hard to find the parts but getting them to work properly for the best end result will take lots of time best conducted on a dyno.

You may even find a spreadbore carb intake for the M30 as it was a factory setup in the late 70s. I know the factory dual 2 barrel Solex(?) intakes are also available.

Gaz - I don't want to know!!

Ralph

[Brucey]

carbs were used on the original E24 630CS model, but this was soon replaced by an injected version. L-jet was used on all euro E24s until ~6/80. Exceptions to that are;

- US-spec 633 until somewhat later (at least 1982 including some post 5/82 builds ) and
- 628 models which had LE-jetronic until the end

You can run an injection system (L-jet or motronic) to provide spark only, but there is a problem; the E24 systems all used a load signal of some kind to control the ignition timing. With motronic the ignition timing is all electronic and the load signal is taken from the injector duration (which is in turn derived from the AFM signal) and everything is sloped with temperatures etc too. If you tried to run motronic as spark only at the least you would lose the mapped ignition unless you replicated the load signals in some way.

With LE-jet things are different; the ignition system appears to be stand-alone (comprising distributor, amplifier and ignition ECU) and indeed it will both function and vary timing in the usual way (via centrifugal and vacuum systems built into the dizzy) to some extent. Indeed the ignition system provides the speed signal and primary timing signal to the fuelling ECU. However there are still complications; the fuelling ECU sends a load signal back to the ignition ECU and this in turn modifies the ignition timing map over and above what is achieved by centrifugal and vacuum advances. However if this feature is deleted, I think the main effect will be that the part throttle ignition mapping won't be optimised and this will affect fuel economy more than anything else.

Since fuel economy may not be a priority for you maybe this route will work OK; you can always fit a stand-alone mapped ignition later on if you decide you like the carbs.

FWIW with the right cam and the right (well set up) carbs, M30 engines can make 100bhp/litre, and they sound fantastic too. No fuel economy and no road manners, mind, whereas with TBs you can more or less have your cake and eat it too.

cheers