I'm comfused

StephenW · Post by **StephenW** » Sat Jul 27, 2013 1:23 pm

So here I am googling about and thinking about my options for improving the performance from my '88 635CSi. I'm confused as to which engine I actually have.

My engine bay decals and rego paper state the engine is a 3430 cc catalyst engine which means it should be an M30B35 engine right? My owner's manual states power as 136kw and compression ratio of 8.0:1 which is indicative of am M30B34 engine but also says 3430cc.

Wikipedia says B34= 3453cc and B35= 3430cc

My engine has 3.2/3.5 on the intake manifold and the BMW roundel on the valve cover which according to a thread on Mye28.com indicates a B34 engine

I would have thought I would have an M30B34 since my '88 has a July '86 build date plate. If so then why does my engine bay decal and manual say 3430 instead of 3453?

TrevorB · Post by **TrevorB** » Sun Jul 28, 2013 5:41 am

Should be a B35, can you post a photo?

StephenW · Post by **StephenW** » Sun Jul 28, 2013 6:59 am

I should note this is an Australian delivered car

Here's a couple pics.

Ozibimmer · Post by **Ozibimmer** » Sun Jul 28, 2013 7:15 am

Hi Stephen
You may have to post the pictures up on photobucket
I just bought a bunch of Chips for the Later Motor 3.5 to help to improve performance but they will only work in the later motors such as the ones in the Very last E24 and the E34 3.5

StephenW · Post by **StephenW** » Sun Jul 28, 2013 8:35 am

Photos re-upped

GazM3 · Post by **GazM3** » Sun Jul 28, 2013 11:24 am

Hey Steven.
The engines are abit confusing around this time. Prob easiest way to tell would be see I it has cat converters and a "unleaded fuel only" sticker over the fuel guage. If so then most likely its the low comp.
if it has no sticker no cats and big dia fuel filler then its most likely the high comp. the high comp are orsome and have a very pronounced surge after 3500rpm where the low comp is more linear.

If u are based in Melbourne we have the mechanic to get best out this engine. Most if the ones Matt has worked on they fly with only some basic mods to exhaust, modern fuel injectors and adjustable cam timing Its not uncommon to have similar power at the rear wheels with the basic mods than it originally came with at the flywheel

Mark E · Post by **Mark E** » Sun Jul 28, 2013 11:31 am

Hey GazM3... is that mechanic you're referring to any good with the M90 short stroke motors (no cat / early Bosch Motronic)?

I'm trying to find someone over here in Adelaide who can tweek mine along those lines.

Cheers...

StephenW · Post by **StephenW** » Sun Jul 28, 2013 11:45 am

Thanks for the offer Gaz but I'm in Sydney. My car has the unleaded filler neck but this would have been a requirement as the car was built/delivered/whatever after February 1986. If it is as is now evident. a low comp engine, the next mod I'll be doing is to put pistons in it. Either that or an M62 conversion.

Shipper 01 · Post by **Shipper 01** » Sun Jul 28, 2013 11:41 pm

Stephen,

Normally the manifold on the B35 just has 3.5 written on it. Your manifold has 3.2/3.5 written on it which is the standard manifold for the B34. Normally, an 88 build would have a B35 in it but, if you have a build date earlier than 88 and your compliance plate has 88 on it then you may have an earlier build car with the B34.

Additionally, get your engine number and go here. http://www.bmw-z1.com/VIN/VINdecode-e.cgi

The vin decoder is your friend. The engine number sits to the top rear left of the block on the top of a blade of steel perpendicular to the main alignment of the engine.

The only other way I would work it all out is to take of your manifold and check the size of the inlet port. This is a dead give away. See attached pic. The B35 has way bigger ports. In the pic the perspex cutout is a B35 inlet port held against a B34 manifold. Take off your manifold, post the width and height dimensions, I'll check my heads and wallll-ah, we know what you really have.

GazM3 · Post by **GazM3** » Mon Jul 29, 2013 1:46 am

If u want to upgrade if seriously think about turboing the low comp m30

StephenW · Post by **StephenW** » Mon Jul 29, 2013 8:54 am

VIN decoder says B34. Thanks Gaz

Yes at 8.0:1 comp, I'm going to seriously consider a turbo. Maybe one of those rear mount jobbies seeing as I already have a set of stainless extractors on it.

Thanks for the help

Shipper 01 · Post by **Shipper 01** » Mon Jul 29, 2013 11:24 pm

must have been an earlier build and just complianced in 88 or, engine swapped for the lower hp engine. If you are doing a turbo build, start a thread so we can follow it.

StephenW · Post by **StephenW** » Tue Jul 30, 2013 12:01 am

Earlier build. Tag in the engine bay says Build Date Jul 86.

I'll definitely start a thread if I do the turbo. It's a fair way down the priorities list though.