Real Fiero Tech

Not sure I can identify with keeping the beat up car and letting the nice one go instead of the other way around...


Anyway, at 258,000 miles, my M30 needs a head gasket. It had been seeping coolant onto the back of the block for a while. I couldn't figure out where it was coming from because I couldn't find any leaks on the hoses back there, but coolant showed up on the bellhousing. I found that the waterpump shaft seal was seeping, so I replaced the waterpump and figured that the coolant had been carried to the back of the engine by the air stream. I had been periodically topping off the coolant.

The car was fine for a 2 hour drive Sunday night, but overheated on the way to work Monday. On the way back Monday evening it overheated again. I popped the hood and there was steam around the back end of the engine. After a little playing with my flashlight, I was able to find a small jet of steam coming out between the block and head.

So obviously, if I tear it down far enough to replace the head gasket, I am *NOT* going to put it back stock. The stock gasket is .070 thick. Cometic makes a gasket for it, so I can get said gasket in any of Cometic's standard thicknesses... with a two week lead time. There is also an ARP stud kit for this engine and I'll just have to use that instead of the stock one-time-use head bolts.

So this weekend I'll tear the head off and measure the piston deck. Nobody knows what the factory piston deck on this engine is, despite the fact that it's been extensively hot-rodded around the world for 40 years. I'll order the gasket thickness that will get my quench clearance down to about 0.040. That will probably bump my compression up by 0.1 or so, but with the better quench clearance, that should actually be *better* for eventual turbo use.

OTOH, there's a '97 M3 S52B32US not far away for $1500... It's a 3.2 with 240 HP and 235 ftlbs. It could bolt into my car using M50 525i engine mount brackets and oil pan and give me a 30 HP boost while actually gaining a little torque vs. the 3.5 litre.

I can see a tuned 3.2 giving more peak TQ than a 3.5, but for more average torque in the lesser-RPM ranges where 95% of all real-world driving is done, displacement ALWAYS wins, even with less-efficient combustion.

The M30 3.5 is a 9:1 engine with 2 canted valves per cylinder. The head doesn't flow very well and the chamber shape is a mess.

The S52 3.2 is a 10.5:1 engine with a 4 valve pent roof chamber and variable cam phasing on the intake cam. I have no doubt it produces a torque curve that's superior to the 3.5's at pretty much every point.

I'm not going to use that engine, however. I was mostly joking in that sick gearhead way about it.

After spending a day and a half cleaning my dad's garage, it took me 6 hours to pull the head.
It would have taken 4, but the damned wire clips in the injector connectors *underneath* the wiring trough on top of the engine were... well... not easy to remove. You can bet they'll be in the pile of leftover parts when this bad boy goes back together.

Preliminary measurement puts the #1 piston at .018 out of the hole (?!?!?1eleven).

Holy smokeroonies!

No joke... I've never even heard of that before.

Good grief, Will. ALL of the LSx engines have the pistons 0.010" out of the hole. Not a big deal. This came about because at the time, ( '96 ) GM was locked into composite head gaskets, 0.051"-thick, for aluminum-head V8s, whether traditional, LTx or LSx. So the only way to fix the quench was by letting the pistons have a positive deck measurement at top center.

The Dark Side of Will wrote:The M30 3.5 is a 9:1 engine with 2 canted valves per cylinder. The head doesn't flow very well and the chamber shape is a mess.

The S52 3.2 is a 10.5:1 engine with a 4 valve pent roof chamber and variable cam phasing on the intake cam. I have no doubt it produces a torque curve that's superior to the 3.5's at pretty much every point.

I'm not going to use that engine, however. I was mostly joking in that sick gearhead way about it.

Consider the LT5 against the LO3, which made more torque from 600-2400 RPM? NOT the LT5.

Yes, .010 out of the hole is nothing new. This is nearly twice that.

Atilla the Fun wrote:

The Dark Side of Will wrote:The M30 3.5 is a 9:1 engine with 2 canted valves per cylinder. The head doesn't flow very well and the chamber shape is a mess.

The S52 3.2 is a 10.5:1 engine with a 4 valve pent roof chamber and variable cam phasing on the intake cam. I have no doubt it produces a torque curve that's superior to the 3.5's at pretty much every point.

I'm not going to use that engine, however. I was mostly joking in that sick gearhead way about it.

Consider the LT5 against the LO3, which made more torque from 600-2400 RPM? NOT the LT5.

http://web.archive.org/web/200212201217 ... 090LT5.PDF

http://en.wikipedia.org/wiki/Chevrolet_ ... engine#305

305 TBI peaks at 255-275 ftlbs, LT5 makes 300 ftlbs at 1200 RPM.
Don't quote "specific torque" to me or I'll make fun of you for being a Honda fanboy.

BMW gears the hell out of their cars anyway. With a 3.82 first and 3.46 final, torque below 2K is almost irrelevant.

According to GM Powertrain, the LS3 makes less than 300 ftlbs at 1000 RPM. The L9H VVT 6.2 for trucks is a little better, but not much. Clearly torque below 2000 RPM isn't a huge priority for GM... and I tend to agree. As long as you have "enough" below 2000 RPM, then you can put your effort into finding "more" elsewhere.

The LT5 does not make anywhere near 300 ft-lbs at anywhere near 1200 RPM. Spreading that BS just to try to win an argument is truly wrong.

Did you look at the .pdf I linked?

Can you find *anything* on the internet to support your contention that the LT5 is gutless on the low end?

I had my dad use his dial indicator setup to find TDC exactly... it was .0005 different than what I had measured. So I'm using .019 as the nominal dimension for piston deck. Cometic has a .056 thick gasket, which would get me .037 quench clearance. I'm inclined to go with that, since this engine shouldn't ever see more than its stock 6200 redline without the head coming off again.

However, they *ALSO* have a .051 gasket, which would give me .032 quench clearance... that's getting pretty slim, however.

My dad went ahead and bought the 3.2 for my mom's E30. It has a cracked cam cover, but that's not a big deal. Dimensionally interchangeable ones are cheap, even if they don't say "BMW ///M Power" on top

Ordered .051 in lieu of .070 standard thickness, with 92.5mm gasket bore in lieu of 93mm.

The block bore measured at 3.621x... Damned straight. *Exactly* the stock bore spec. The block is basically *pristine* with 258,000 miles on the clock. BMW builds some good shit.

The Dark Side of Will wrote:I had my dad use his dial indicator setup to find TDC exactly... it was .0005 different than what I had measured. So I'm using .019 as the nominal dimension for piston deck. Cometic has a .056 thick gasket, which would get me .037 quench clearance. I'm inclined to go with that, since this engine shouldn't ever see more than its stock 6200 redline without the head coming off again.

What are the rod and main oil journal clearances for that motor?

pretty snug... .0008 to .002 (give or take for Metric)

The Dark Side of Will wrote:Ordered .051 in lieu of .070 standard thickness, with 92.5mm gasket bore in lieu of 93mm.

The block bore measured at 3.621x... Damned straight. *Exactly* the stock bore spec. The block is basically *pristine* with 258,000 miles on the clock. BMW builds some good shit.

Zee Germans do good work. A few friends who rebuilt old Benz diesels and the bores have measured stock at 300-400k. Germans don't mess around.

That's a rather blanket statement, Paul. Every manufacturer has its quirks.

http://www.youtube.com/watch?v=r6RDVBHsCfg

http://www.youtube.com/watch?v=Mco77TK94GU

And VW is German, but they do some genuinely strange things. The throw out bearing on my friend's MkII Golf is NOT INSIDE THE BELLHOUSING. I shit you not. He said he thought he needed a new throw out bearing, so I told him I'd help him change it. He gets the new unit and hands it to me. It's the size of an inch-tall stack of quarters. My reaction: "Da fuq izis?"

I know my BMW's pretty easy to work on, and I've heard that Mercs are pretty easy to work on. I've never heard anyone say that VAG's are easy to work on. In fact I've heard people go out of their way to talk about how hard those cars are to work on.

Case in point: http://www.corner-carvers.com/forums/sh ... php?t=8643

I love that guy's sense of humor. Three hundred and seventy four point two heat shields, ... haha.