628csi vs 635csi (Differences?)

The 628 is a sweet motor, but an upgrade...  ooh, this would be a big job....

basically the 628 shares most of the parts with the 635 BUT there are a few crucial differences....

Bodywork- the 628 usually came with a different front spoiler and bumper arrangement (more like the original '76 model year 6ers). To many it is uglier and less aerodynamic than the 635 version; this is a matter of opinion (although many have been changed...). However it is a matter of fact that it weighs a lot. A 635 (late '82 to mid '87) bumper/spoiler assy is a lot lighter, plus your car won't want to take off at speed...

Running gear; suspension, brakes, transmission etc are all the same as base model 635s, BUT you will be far less likely to find a 628 with a limited slip diff or other options fitted from new; the list price of the 628 was about 2/3rds that of the 635 so they were often bought on a budget and not specced up in the same way as 635s often were. 628 wheels are 14" items, which are very lightweight, an at least you can get tyres for them (unlike the stock metrics found on 635s). But they are not going necessarily to cope with 635 power very well, so should be changed for 15" wheels or bigger. If retained with 635 power, 14" tyres would have to be checked for increased speed rating.

Engine; this is where the big differences are. Basically the 628 used the E28 528's engine, complete with Bosch L-jet engine management. 635's all use motronic except for a few early cars (79, 80) which were fitted with a slightly larger 3.5 engine with L-jet. This proved to have an appetite for head gaskets owing to the large bore size, so was replaced by a slightly smaller (~3450cc) Motronic engine PDQ. I think that the L-jet camshaft is different to the motronic one at the distributor end (someone else will know for sure) and would make engine swaps kind of tricky, although not impossible. Running the L-jet on a 3.5 engine may be possible, but as well as the possible dizzy drive worries you would have to fit bigger injectors, a different AFM, and a bunch of other stuff.

Ripping out the L-jet is also an option, BUT the L-jet loom isn't entirely separate from the service indicator, computer (if fitted) etc. on the 628. If going down this route I would recommend that you look for an early motronic 635 (say an '81 car with E12 chassis and -002 ECU for example) as an engine donor; these have an engine loom that is almost entirely separate from the rest of the car; although extracting the old one from the 628 will be difficult fitting the new one would be relatively easy.

hope this helps

cheers

 

The advantage of the 628CSi is that they're pretty
much unwanted so they're very cheap. £1500 will buy
a really clean one or a scrapyard 635CSi unless
you're lucky. I bought a 1983 628CSi Auto about 5
years ago - Henna red with black leather, the basic
bumpers with 14 inch Bottle top wheels and
FBMWSH for £1100. It was a very clean thing with
new wings. I had the devil of a job to sell it again
though and got £1300 after a struggle.
The 2.8 does respond very well to a spikey camshaft
- around 15 bhp and they rev really sweetly. I wouldn't
want another 628CSi Auto though - it's got to be a
manual.

Oh, one mistake above- although the 628 diff is the same type as a 635, the standard ratios in 628s and 635s were usually different, with 628s having lower overall gearing.

628s, (sweet though they are),  are sluggish, no doubt about it, especially auto ones (and they never got the 'EH' switchable auto, just the bog standard 4-speed with mechanical kickdown). 9+ seconds 0-60 is the province of shopping trolleys these days. Tuned, you can get 220+bhp out of the 2.8, but why bother when you can get a 635?

-oh, BTW, as well as my late chrome bumper 635, I did buy a 628 basket case as a project car.

'WHY??' you all ask??

Well, simply because it has L-jet on it, (and does have ABS, but not so many toys like computers, air con etc). I plan to install a supercharged 635 engine, which will probably need a custom ECU eventually. But I reckon with a bit of pigging about I should be able to get it to run safely on L-jet because you can adjust the ignition timing without difficulty. You simply can't do that with Motronic, only the very late ones fitted to highlines can you burn a new eprom, and this is a dark and clumsy art (in my hands anyway).

So the plan is to iron out the mechanical gremlins on L-jet before going for the full monty ECU swap...

Watch this space... at the current rate of progress it'll be about two years....

cheers

not that far really, steps backward include buying the wrong type of supercharger (d'oh!) and a few other things.....

Steps forward include snazzy wheels, right gearbox (not yet fitted), black leather recaros, and a few other tasty bits.... like I say at the current rate of progress about two years...

never thought of a V8 for long- not a 6er then, is it??

I'll keep you posted....

cheers