i believe a std head to be 139.2mm,

Need to know just for refernence really, as will be CC checking my head tomorrow, which is 138.2mm now.

 

up for the morning crew.

 

Anyone?

 

Measured my head just now,


1+4 = 44.5cc, 2 +3 = 45cc.


as my head is 1mm less than std, i have guestimated a std head to be 51.25 cc??????

 

bttt.

 

and again

 

Std head unskimmed measures 139 mm.

My head is 138.6 mm and the combustion chamber measures 46 cc.

Std 4 wd Piston Dome Volume is 19 cc, and my new pistons have 24 cc Piston Dome Volume.

For the record.....it's a 2wd head.



Can't say that for sure because the combustion chamber of the head isn't symmetric.


Why do you wanna know? You want to calculate the comp ratio?



Regards,


Bas

 

Hi,

Thats odd,
my 4wd head has 44.5-45cc across them @ 138.2mm,
and yours being a 2wd head has got more CC as std, but with 138.6mm its only 1-1.5cc more than mine.

i measured 2x std 4wd pistons @ 19.5cc, the ones in my engine are 20.25cc.


i want to know for reference and to know what my c/r was before and now.

 

139.15 to be precise.

 

You need the following specs to calculate comp ratio:

Cylinder Bore Size
Piston Stroke Length
Head Gasket Bore Diameter
Compressed Head Gasket Thickness
Combustion Chamber Volume In CCs
Piston Dome Volume (Negative For Dished Pistons)
Piston Deck Clearance (Negative If ABOVE Deck)



Regards,

Bas

 

Thanks, i do know all that.


its just easier to know the original head cc, then i can cross reference.

 

I don't suppose someone can measure the dimensions of a 4wd piston bowl - I need the diameter at the top, the bottom and the depth. If you could also measure the distance between the top of the crown and the compression ring that would be superb.

Does anyone know how much you can take of the top of the standard mahle piston?

Cheers

 

You dont want to skim the whole piston, you want to be opening up the bowl, to keep the engine's det characteristics.


from memory the crown thickness is 7mm at lowest point of bowl.



i just measured a new 4wd mahle +0.5mm piston.

top of 1st ring to top of crown = 8.3 mm,
bowl deepth = 6.1 mm,
top of bowl diameter = 73.3 -75.3 mm, matters on the part of radias is measured,
Bottom of bowl = 51.4 - 52.9 mm

 

Just measure the piston and block cc,

My C/R = ave of 8.27:1

Head ave 44.75cc
Block and piston = 16.6cc
H/G = 8.74cc.

 

Cheers mate,

Reason I ask is I'm trying to see if I can get away with using them on a nat asp application.

Target is a 8.5k rpm 200bhp pinto for under £600

I suppose the next question is how close to the compression ring can I bring the crown?

 

I've had it as low as 4mm on a turbo 1.8 cvh. running 200bhp, cast pistons, upto 6500 rpm


What C/R do you want?

Whats the cc of the head and gasket?

 

Heads going to be around 40cc

77.1 stroke, 91mm bore

0.75mm piston to head clearance

so with a 15cc piston bowl I make it 9.3:1, 10cc bowl 10.0:1, 8cc bowl 10.4:1

By machining the tops of the pistons A crown to 1st ring height of 7mm gives a bowl CC of ~13.8

6mm = ~10.2 CC

5mm = ~7.0 CC

So if its ok to take that much off the top of the piston and plane the block to give a sutable head / piston clearance then a CR of 10+ is feasable.


Any comments?

 

i wouldn't do it that way, not any lower than 4mm off the skirts of the piston crown.
then i would take 3 mm off the block

That will give you another 7cc, or if you take 4mm off the block = 13.6cc lost.


then how much can you remove off the head? as the piston would be just under flush with the block now (with 4 off piston, and 3mm off block),
then you got 1 - 1.3mm for head gasket.


also a std cossie bore is 90.82mm

 

Head would be at its limit already without going to spark plug inserts - 40cc is the numbers from the des hamil pinto book with a big skim and deshrouded valves.

The CR's I got, with 0.75mm piston head clearance - probably use a 1mm HG although it won't matter too much as I can take that into account when skimming pistons/ block.

If I skim the pistons to the following crown / ring heights I get the following CR - so from 8.3mm standard

8mm = ~8.7
7mm = ~9.3
6mm = ~9.9
5mm = ~10.5
4mm = ~11.1

So if taking 4mm or so off the piston crown is safe, then this looks like a winner :t-up:


Thanks for your help, been looking for those figures for ages.

 

Going off your Head cc, 498.5 engine cc, using a 82.5mm x 1mm H/G, std 4wd pistons,
4mm of piston skirt, and 3mm off block,
i worked out roughly 10.97:1.

or if you take 3.3mm off pistons, and 3mm off head = 11.38:1 c/r.


but you will still need to cc check it when you do it,