Turning it up a notch...

[Jon K]

Well my motor for my BMW is done. But, I am not excited about it - I mean I am, but its still 2.5L and using stock pistons (Ceramic coated, teflon coated) and stock (strong, forged) rods film lubed, but I dunno... I have a 76gts and all other supporting big boy parts, I figured I might as well do it right.


So, I bought another block and am prepping it for some fun. Boring it and stroking it - ~3.0L fully built. I also decided that in order to run 35 psi from my PT76GTS, I need to do some significant "fastener" work. The stock BMW blocks are provisioned for a 10mm bolt/stud. I had ARP studs for it, which actually taper thinner in the middle to about 8.5 - 9mm. They're only able to torque to about 60 - 65 ft lbs which is fine but when running super high boost, you can lift the head. So, I called ARP and ordered a custom stud in the same length as the off-the-shelf 10mm, except in 1/2" and a US thread 1/2-13 on the block and 1/2-20 on the stud end.

Not too many people have done this in a bmw engine - so, it took a significan amount of dedication to drill holes in the new block i just picked up. But, did that today and it all went well. I first plotted the stock head holes and numbers so I can make a torque plate, as the new 1/2" studs will be torqued to 95 - 105 ft lbs which might warp the block some.

Anyway, here are some pics as thats a hell of a lot more interesting than words. Thanks to my friend for teaching me how to use the mill and doing this **** myself.

Got my rods in, ordering pistons tomorrow



Manifold nearly done



Gathering data on existing holes:



About to mill it out!

[Jon K]

First hole is the scariest, the rest were only mildly disturbing



Running the tap through it



After all the holes were bored and tapped, I went back and counter bored it more to relieve the threads at the deck



Then went back around to open the tap again and now the fun part!

[Jon K]

Don't fear the block - just normal surface scale that will be blasted off. If you've seen my other engine, you know how much I pay attention to detail

Next up is boring the head out, the machining the torque plate and boring the block out. Then assembly when I get the pistons!

[Macv]

Wow, manifold is turning out great. Amazing skill

[Sam-Son]

Thats Crazy I can't wait to see how this ends up

[632 Regal]

way overkill on the fat studs man, distortion ediquite once torqued but might hold it all down nice. You talking alighn bore the heads with the torque plate torqued to spec with the fat studs? Might make for an interesting cross hatch pattern when opened and untorqued.

[Nick.Hay]

You are a , bastard Jon!!

Its going to be a work of art... That manifold already is!!

[Ferret]

Question!

Are you going to be using the B25 head?

If you are, how the heck are you going to stop the head from cracking? The general conspiracy theory shows that they're prone to cracking from studs to bore/compression chamber - there's not really enough metal there. Surely boring it out to take bigger studs is going to cause a problem?

You could torque it down *really* carefully I suppose to get an absoloute even torque down across the block, but following a 3 step procedure is likely to cause the dreaded crack?

You could use a B20 head to get extra compression I suppose, but you'd need a slight spacer in there - last time I did it the engine self destructed after the big ends started to wear - turning the zero piston-head clearance into an interference!

[Jon K]

Heads don't crack because they're torqued down, they crack when over heated. There's absolutely no reason clamping the head down will crack it. There are other guys who have done this as well. I am running a B25 head - not considering a B20 head because 1) they're not available easily 2) i've never dealt with one and 3) I can't afford to raise compression.

[Dave M]

Jon, we've got to find you another hobby, or a girlfriend (don't tell us you have one ).

Very, very, interesting. I won't toss my old M50 just yet. If you pull it off, I may have to try something next winter.

Good Luck,
Dave M