high or low compression engine?

[tannercore]

1. how can you tell whether or not you have a high or low compression engine?

1986 535i (euro)

2. is high or low compression better?

...if so, how/is it difficult to convert it over?

thank you

-tanner!

[John In Valdosta]

1. The engines are identical in every way except the ecu and the pistons. Check the ECU if the last three digits of the ecu are 061 it's probably a High Compression, if the last three digits are 059 it's probably low compression. There are exceptions but this is a good indication.

Check your VIN in a BMW VIN Decoder. There are several, a google search turned up this one http://www.bmw-z1.com/VIN/VINdecode-e.cgi

2. A high compression (Euro or dirty) motor is rated at 218hp stock, the Low Compression motor is rated at 182Hp, this make the euro motor very desirable. BUT the euro motor needs premium gas or it will ping, this makes it less desirable.

If you have a high compression motor keep it and be happy.
If you have a low compression motor chip it and be happy.

[Madhungarian]

Hi Private Tannecore!
Sounds like you need to do some more research in this matter!
The easiest way to confirm what you have is by VIN. There is a number on the block behind the starter too, but near impossible to get to!
M30b34 is a high comp. euro motor, I am not sure if there was a B35 eurospec one, but the US B35 is low compression.
You do not want to convert, one or the other. Like I said, do a little more research, than we can help better!

[Rich in Tupelo]

Quote:

M30b34 is a high comp. euro motor, I am not sure if there was a B35 eurospec one, but the US B35 is low compression.


Mad... does this mean the 86 euro motors are high compression? I know otherwise, so just checking your comment.

The euro motors came in both High and low compression. The best way to tell is to look it up on the VIN sheet. If it comes up as non-cat, most likely it is the high compression motor or dirty motor and not what is referred to as the green euro motor or low compression one.

Rich

[Madhungarian]

Sorry, I do not know about 86, my 85 is a high comp. motor.
However if you use the vin decoder posted and plug in the number you will get a read out on your motor M30B34 is a high comp motor.
Model year 85 / 86 gets touchy because the manufacturing date that matters.


[Edit by Madhungarian on [TIME]1113499039[/TIME]]

[Azure]

My understanding was that the M30B34 came in two flavors - high comp (10:1) and low comp (8:1 kat/clean). Only the low comp was officially available in the states (both high and low comp were available in Europe). These were the engines used in the E28.

The later M30B35 came, essentially in one, kat-using clean 9:1 flavor, and was designed to be used worldwide and meet emissions worldwide, to allow BMW to only have to use the one engine for the E34 instead of having to produce two M30 variants, like they'd done with the E28. The only differences between markets for this engine (US and Euro) were some minor ECU programming equivalent to about a 5hp difference.

Someone correct me if I'm mistaken - but this was my understanding having read the history of the 5-series, and it sounds like we had some conflicting responses above.

[John]

This got me interested, so I hit the link. I have an '85 M535i, definately a gray market, German car. Acording to linked page I have a cat, ture. Page says I have the B34, perhaps. Says I have the 260/6. False, I have the 265. Gives production date as 5/85, but the mfg tag on the car is 6/85. Just like an old BMW, there is no telling exactly what it will have. I had a few New Class cars (2000tilux, 2000ti, 1800, 1800ti) and not a one of them was exactly alike.

[RobertRO]

[QUOTE="Azure[/I]The later M30B35 came, essentially in one, kat-using clean 9:1 flavor, and was designed to be used worldwide and meet emissions worldwide[/QUOTE]
Well, according to my information, the M30B35 came in two versions:
- 9.2:1 compression and 220 HP (DIN), used only on 1986-1988 E32 7 Series 735i
- 9.0:1 compression and 211 HP (DIN), used on all E32 7 Series 735i and E34 5 Series 535i from 1988 on.
It seems (I don't have clear information here) that the 220 HP version was non-cat, while the 211HP version was cat.

Anyone can confirm / comment this info?

[dworthy]

You are correct, there was two different motors used during the 86-90 E-32 m30 b-30 thru b-35, one with cat and one without cat. That is the major difference, also there were different ECU's between the two. In the 90's BMW deceided that playing with two different motors was crazy and got tired of making different parts, that is why with MY 91 they phased out the M-30 for the M-50 to replace the 3.0 ect and the M-60 for the 3.5 and 4.0 etc. It was also the same time that the M-20 motors were phased out, so the only thing with a rubber timing belt was the euro 316i M-40 until MY 92 when the M-44 was changed over.
Well of course the best way to find compression is to do the test..

[Shawn D.]

[QUOTE="RobertRO"]Well, according to my information, the M30B35 came in two versions:
- 9.2:1 compression and 220 HP (DIN), used only on 1986-1988 E32 7 Series 735i
- 9.0:1 compression and 211 HP (DIN), used on all E32 7 Series 735i and E34 5 Series 535i from 1988 on.[/QUOTE]

The M30B35 also came in the '88-'89 E24s.



[Edit by Shawn D. on [TIME]1113620027[/TIME]]

[Azure]

The later M30B35 came, essentially in one, kat-using clean 9:1 flavor, and was designed to be used worldwide and meet emissions worldwide

Well, according to my information, the M30B35 came in two versions:
- 9.2:1 compression and 220 HP (DIN), used only on 1986-1988 E32 7 Series 735i
- 9.0:1 compression and 211 HP (DIN), used on all E32 7 Series 735i and E34 5 Series 535i from 1988 on.
It seems (I don't have clear information here) that the 220 HP version was non-cat, while the 211HP version was cat.

Anyone can confirm / comment this info?

As I mentioned, I was quoting what I'd read in the history of the 5 series.. I didn't see anything of a 9.2:1 variant of the B35 in there, only the E34 535i 9.0:1 variant.

So I think we're both right.. seeing as you were reasoning there was more than one version of the B35, and me, as I was basing my statement that there was only one version of the B35 used in the 5-series.

Both of which are true.

In the 90's BMW deceided that playing with two different motors was crazy and got tired of making different parts, that is why with MY 91 they phased out the M-30 for the M-50 to replace the 3.0 ect and the M-60 for the 3.5 and 4.0 etc. It was also the same time that the M-20 motors were phased out, so the only thing with a rubber timing belt was the euro 316i M-40 until MY 92 when the M-44 was changed over.

As a secondary consideration, as I understand, the next series of engines were also designed to utilise certain newer technologies, such as self-adjusting valves, as BMW was coming under pressure technology-wise at the time from their Japanese competition who were already producing engines with these innovations (my twin-cam '90 240SX for example, which doesn't require valve adjustments).

[Edit by Azure on [TIME]1113674939[/TIME]]

[dworthy]

Well that and also, the M-30 has been around since the 60's and that is a long run for an engine. BMW had to update the motor to keep up with compition out there. Plus BMW has to keep with the solid performer and long last motor that will power these cars for the next 30 years. Now I am sure that in the first 10 years there will be alot of changes to "fine" tune these motors.