I have an E 30.

[Nader393]

Looks good; have you calculated the new CR?...

Yes, but it took some doing. I had all the necessary values to plug into a compression ratio calculator, except for piston dome volume for these new 85mm Mahle Powerpak pistons.

So, I called Ireland Engineering, because these pistons were made by Mahle for them. An older gentleman answered the main line, and told me he didn't have the dome volume, that it wasn't available. Strange. When you order custom pistons, the maker always includes a spec card with all the measurements.

Soo, I called MAHLE North America, got rerouted a couple times, and eventually connected with a helpful tech guy that was able to use the laser etching number on the piston to look up the specs. Long story short, the total dome volume on these pistons is only 0.9cc. Ostensibly, the deep valve pockets offset the piston dome volume.

Sooo, I plugged that into the CR calculator for the 2.9L stroker specs, and with a stock unshaved head (41.7cc), I get the expected 9.7:1. If I use the shaved head with the reduced combustion chamber volume (37.5cc), I get 10.4:1. Whew!

Soooo, anyone curious about component weights? Here's a comparo between stock 2.5L 84mm piston+pin+rings with m20 rod, versus Mahle 85mm piston+pin+rings with S52 rod:

[nbridgema]

Looks good; have you calculated the new CR?

I did this [decades] ago on a 1969 M30 2.5L, which BMW rated 9:1. It measured 10:1 :up:

Helps explain why it pinged so readily... ;)

[Nader393]

Just noticed, there's a divot in an unshaved stock head that disappears when it's been decked. See? It's under the exhaust side coolant passage for the first and sixth cylinders. #6 is shown here. So you can tell at a glance if a head's been shaved.

[Nader393]

Now, let's cc the head. To do so, you need a buret. It's that miserable tool you used in college when you were a pre-med student struggling through Organic Chemistry. Used to have horrible memories associated with it. But I last used this piece of scientific glassware to cc the head of my Alfa's race engine about 5 years ago. So, gradually changing the buret's association to better memories.

I used ATF because it's easy to read, runny enough but won't seep through potentially leaky valves. Close off the chamber with a plastic plate sealed with grease.

Looks like a 1mm shave results in a 4.2cc reduction of combustion chamber volume in an e30 head. This information may be useful to a handful of engine builders in this country.

[2mAn]

Oh Damn, you cleaned him out... well, I know he’s happy. Hopefully you are too

[Nader393]

So, Greg was selling, and I was buying. I cleared him out of the aforementioned crank, the Mahle 85mm 10.5:1 pistons, M52 connecting rods, Bimmerheads shaved 284 head (verified with stamping), and box full of bearings, seals, gaskets-n-stuff.

I now find myself buried in e30 parts, not that it's a bad thing. In fact, I'm tripping over heads. So I brought a couple back inside (sorry, wifey!) for further work. Like I said, the verified Bimmerheads unit is shaved. How does that affect the compression ratio? Let's measure heads! Stock is first, shaved Bimmerheads is second.

[rturbo 930]

A 2.9 stroker huh? I still have my worn out original engine, I'm seriously considering doing an ITB 2.9 stroker in the future, but I wanna know how drivable it's gonna be with a 284 cam (or similar). I'd probably just follow this: https://adamsautosport.com/informati...ine-checklist/

[Nader393]

oh dayum... Are you going to stroke the motor too? I plan to go balls deep 2.9 build. Same 85mm pistons and M52 84mm crank

Have you driven the car yet?

Yes, and yes.

I do indeed have the M52 crank. (Thanks, Greg!)



Car feels great since I fixed it, but I won't spew superlatives until it proves itself on the dyno. Not that it matters, because 2.9 (and stuff) is coming...

[2mAn]

oh dayum... Are you going to stroke the motor too? I plan to go balls deep 2.9 build. Same 85mm pistons and M52 84mm crank

Have you driven the car yet?

[Nader393]

The old lump is mostly stripped and on a stand. My plans will require a visit to the machine shop...

[Nader393]

Thanks again to Austin!, replacing the starter gave me back my power windows and HVAC blower. Who'da thunk that? (Missourah speak)

Then I drove the car for a week. And it was painful. Erratic, surging idle between 1500-2000 RPM. Bucking ride when transitioning from off throttle to on at low speeds. Disappointing, and super annoying. After all that work and high hopes, I thought "What have I done?!"

On the other hand, over 3K RPM, engine felt strong and angry, like this could be a contender after further sorting. But the replacement exhaust is also louder. More growl and snarl than rumble and roar like the prior one. I won't let the ear/mind/butt dyno fool me again into believing false gains. This needs to go to a real dyno for verification.

To fix the idle and bucking ride, I first replaced the ICV (idle control valve) with a spare I already had. Easy to do, low hanging fruit. That didn't do it. So next I replaced the TPS (throttle position switch). Had to order it, and it took a week to arrive. A full week of me driving this car in that condition, which kinda sucked.

When I finally got it, I felt like this $50 small plastic box would be the answer to my problems. The old one was full of oil, so I drilled a small hole in the new one to drain whatever oil vapor drips down the throttle shaft into the switch box. Sure enough, this new switch fixed the problem. Idles smoothly at 900 RPM. Well, smooth as a 284 cam in a relatively low compression engine can idle. Car is driveable again. I want to believe it's significantly more powerful, but like I said, it needs the dyno to show that. Stay tuned...

[e30austin]

Goddam! are you a pro?

I'll hang on to the exhaust for you as long as you need. It's sitting in my basement.

Done this once or twice, you know :)

Just glad you got it all going! little things can hang you up sometimes, but at least it was all easily solved.

[Nader393]

Awesome! Glad it runs. Perhaps I will make it up that way for the exhaust stuff soon. Appreciate it!

For your windows and blower motor, you need to check your starter connections (the small 4mm and 6mm ones). 99% of the time, that's the issue.

The K7 unloader relay grounds through the starter. If you have a bad solenoid, or tightened the connections too tight (pulling the thread out of the solenoid and ensuring no contact), the ground won't make a contact and will not activate the K7 relay. I can't remember which one it is, but I think it's the 4mm one. You can ground it to the engine block to test my theory.

Goddam! are you a pro?

I'll hang on to the exhaust for you as long as you need. It's sitting in my basement.

[Nader393]

Thinking about it some more, I kind of thankful that my screw up was big enough to not let the engine run. Can you imagine the headache if the distributor rotor was off only few degrees, and the engine ran, but shittily? That might have really delayed the diagnosis.

[e30austin]

Awesome! Glad it runs. Perhaps I will make it up that way for the exhaust stuff soon. Appreciate it!

For your windows and blower motor, you need to check your starter connections (the small 4mm and 6mm ones). 99% of the time, that's the issue.

The K7 unloader relay grounds through the starter. If you have a bad solenoid, or tightened the connections too tight (pulling the thread out of the solenoid and ensuring no contact), the ground won't make a contact and will not activate the K7 relay. I can't remember which one it is, but I think it's the 4mm one. You can ground it to the engine block to test my theory.