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8v pistons, 16v pistons.

2K views 37 replies 11 participants last post by  tomstickland 
#1 ·
I took my recently acquired 8v engine apart tonight to look at the pistons. Just like the 16v engine they stick out above the block by about 0.5mm at TDC. The 8v pistons are flat topped but with a bowl where the spark plugs would stick through. So I guess this is all to do with squish and flame front propogation.

The 16v pistons have a very shallow bowl on them.

Ideally I could have the 16v pistons machined so that they are similar to the 8v pistons. This would involve machining a pocket about 4mm deep. Are this pistons thick enough to tolerate this?
 
#3 ·
hum. Thought they only added another 2mm to the pockets that are already there?!? Are you saying a pocket 4mm deep in the centre (i.e. the already lower part) of the 16v piston?

I've got some forged pistons you can have for a few £'s Tom you're worried about strength.
 
#4 ·
The 8v pockets are about 4mm deep,25mm diameter and off centre so that they line up with the centre of the 8v spark plugs.
The 16v pistons have a very shallow pocket.
I was advocating machining an 8v style pocket into the 16v pistons.
I'll take some photos when I get the camera back.
 
#9 ·
16v bottom end, different con roads. Fully floating gudgeon pins. I don't think the 8v pistons will fit to the 16v conrods?

Well my options are:
-skim the 16v pistons flat (need to remove about 1mm of material to do that)
-make a pocket in the 16v pistons to roughly match the 8v ones and to get the overall compression ratio correct.

I can't take any pictures until Friday.
 
#11 ·
Well whole pistons would be nice, seen the top down for the 16V and remember seeing an 8v piston yonks ago btu can't remember clearly.

Tom you can make the pistons fit. You can either retain them as interference fit or get them machined to acdeopt the circlip as used in the full floaters.

Andy the 16V piston is machined for the 4 valves. The 8V piston will have valve cut outs to, might even have 4 so you can fit the piston either either way.

Chris
 
#13 ·
Yes I am a pillock. The 8V head ain't a hemi, its the crap old twisted bath tub chamber. The hemi's have the cut outs on 8v's. Which doesn't consist of vaux engines. To long playing with v8's for me!

The 8V head has vertical valves, hemis have them angled, pent roofs (16V's) have them at a shallower angle than hemis.

Chris
 
#17 ·
Hmm fair diff there then!

8V pistons on the 16V rods I would say.

Unless you can measure the thicknesses of the pistons. The 16V piston may have a thicker crwon than the 8V due to the higher CR so you might be able to machine the bowl a bit.

Chris
 
#22 ·
if you get some new 8v pistons i recomend you get genuine mahle pistons,thats what i have and they do them in 87mm form these are alot better than the AE and acosiated companies replacements as they dont tend to crack near the oil control ring and at £200 all in including carriage from germany.autosprint ordered mine
 
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