danglerb

What concerns me is that #9 piston.

Cute kids, my son at that age was fond of hammers and dropping small toys into holes like are all over that motor.

slate blue

Mark I thought we discussed the piston notching issue? I went and cut mine all the same, I figured that the exhaust valve reliefs were always going to face to the outside of the block.

Greg

slate blue

You are right that the bores get thicker as you go down, mine are thin too, I think as long as there is no detonation we should be right. My bores average about 6 mm but that is the average.

Greg

mark kibort

what do you mean? the cuts are extremely accurate, so im wondering if you are noticing the real note worthy issue in looking at the #6 vs #8 piston cuts.

walls do look thin, and they are. but then again, we only took 1.5mm off at each side.

Let me know more about what you see on the pistons.
mk

mark kibort

you mean the exhaust 4 valve cuts always facing downside?

you are getting warmer!

mk

mark kibort

why would they be tappered or oval??? that would be a neat trick at the machine shop

Thanks for the concern, but is that a valid one? what does concern me is the comment about the grain structure. however, there are many blocks in operation that are bored to 104mm from the stock 7-8mm thickness. (ending up at 5-6mm thickness) as long as they have not had issues, i should be ok. plus, im only seeing 40hp a hole vs the stroker 60hp a hole and less compression ratio too. (should work in our advantage)

thanks,

Mk

SharkSkin

Mark, that's what I meant. The #6 slug was oriented 180° opposite the others when cut.

SharkSkin

Also #6 has a dent at the 2:00 position(or so it seems).

mark kibort

Thats it, you win!

So, normally all the pistons will face with the exhaust cuts (the smaller cuts) facing down, right? right. However, there are piston offsets (the pin is closer to the exhaust side of the 4 valve piston, or the 2 valve cut side of the piston.
this means the offset is correct for the driver side bank and totally wrong for the passenger side. However, this obviousy wasnt a big problem, or porsche wouldnt have done it. Yet, on the S4, notice there is an arrow toward the front of the engine, and the valve cuts are the same , both intake and exhaust. SO, this means the S4 cured the problem and gives slightly more power. (in theory)

I was told that this gives a slightly better angle of the rod to piston during the power stroke.

so, the reason the #2 and #6 piston is different, is because now , they are the same!

the odd "dent" on the #6 piston is a shadow or jpeg artifact. Ill check! that surely would be a bummer if it had a dent like that!

Mk

Vilhuer

They can make all kinds of tricks without knowing they even did it. If they machine block when its too hot, do not have lower hald mounted in proper torque or do not use deck plate to simulate head when machining end result can be just about anything. See pages 58 and 72 for cone, trumpet, barrel, curved etc shapes:

http://www.msi-motor-service.com/dow...804-02_WEB.pdf

DK

Not sure how much you can shave off the block and heads before you start to affect the belt length and everything else involved - valve/piston clearance, cams, etc. I took 4 thou off the heads on my hybrid but nothing off the block, stock head gasket - and everything is fine.
www.eaglesledge.com/cars.htm

mark kibort

well, i think i have 10 thou off the block, but it could be less. the valve pockets are .175 based on a requirement of .150" so i have 25 thou to play with. i dont know how much we will have to take off the heads, but if it is like your 4-10 thou, im still ok as far as valve clearance. providing the .5" lift of the B1 cams doesnt hit the pistons. not too worried about the difference in cam timing, as we are only talking a few thou total on both sides equally.

im probably more worried about valve hit, but we will clay the pistons up and see what we got.
Mk

SharkSkin

Cutting both sides equally will affect valve timing. The only way you could change both sides without affecting valve timing would be if you removed material from one head/deck and added to the other!

danglerb

When you are ready to put this together will you "clay" the pistons first?

How does that work, just put it together with clay in the reliefs and turn it over by hand?

C.F.

Mark
You seem to have misunderstood the reason for the offsets , I dont think Porsche got it wrong.
Mopar V8 small & Big blocks all had piston offset ( I dont think Chevy or Ford ever did) , it was done to reduce piston slap & is to do with the thrust of the rod on the piston on the bore, the thrust face of the bore.
On mopars to gain a little power you would assemble the piston on the rod 180deg. out, eg with the arrow now pointing to the rear . If you cant reverse the piston on the rod because of a dome or valve cutouts you swap pistons bank for bank reversed which is what you should have done.
Yes it will improve rod angle which reduces friction which equals free power.