Understanding High Compression Pistons for 1608

[smbaird37]

I am looking for a set of HC pistons for my 72 spider. I have found a few possibilities that say the pistons are high compression but give no specifics. HC pistons for the 1800 and 2L engines give a dome height in mm. What should I be looking for in 1608 pistons? Any info greatly appreciated as always...
~Steven

[fiat218]

I am looking for a set of HC pistons for my 72 spider. I have found a few possibilities that say the pistons are high compression but give no specifics. HC pistons for the 1800 and 2L engines give a dome height in mm. What should I be looking for in 1608 pistons? Any info greatly appreciated as always...
~Steven

Good question, I can get a answer too

[BEEK]

i have a set of 9.8-1 pistons for a 1608 in my shop, at least 3 of them, ill check the dome height tomorrow and post

[fiat218]

i have a set of 9.8-1 pistons for a 1608 in my shop, at least 3 of them, ill check the dome height tomorrow and post

What are the ones I bought..60mm

[smbaird37]

i have a set of 9.8-1 pistons for a 1608 in my shop, at least 3 of them, ill check the dome height tomorrow and post

What are the ones I bought..60mm

I think you might be mixing the overbore dimension with the dome height? The stock bore is 80mm - then the plus sizes .4, .6, .8, and 1. You bought the 80.6mm overbore pistons right? If I got my geometry right, this gives you slightly greater displacement but actually lower compression since you increase the size of the combustion chamber. Unless of course, the pistons have a high dome (i.e., high compression). I look forward to learning what Beek finds out....
~S

[djape1977]

all 1608 pistons i've seen so far have same height dome

[fiat218]

I bought a over size0.60mm
I was wondering if they would be ok,with the cam set up of 42/82. If not then I'd getting better pistons

[smbaird37]

Chris Obert has a set of 80 + .6 Mondial pistons for sale. He states that the dome is approximately 4.75 mm.

[FiatMac]

....... If I got my geometry right, this gives you slightly greater displacement but actually lower compression since you increase the size of the combustion chamber.
~S

Boring oversize and installing oversize pistons increases the displacement (swept volume) and leads to a slight increase in compression. The compressed volume is only minimally affected by the increase in bore. Compressed volume is the sum of the head combustion chamber volume, deck clearance volume(can be a positive or negative value base on whether the piston is below or above the deck at top dead center), piston land clearance volume, head gasket clearance volume, and piston dome volume(negative value). The only two affected by the bore diameter are the deck clearance and the piston land clearance volume, both of which are very small compared to the increase in swept volume.

Compression Ratio = (Swept volume + Compressed Volume)/Compressed Volume

In a stock 1608 engine going from stand bore to 0.6mm over would increase compression by about 0.1 units.

[smbaird37]

....... If I got my geometry right, this gives you slightly greater displacement but actually lower compression since you increase the size of the combustion chamber.
~S

Boring oversize and installing oversize pistons increases the displacement (swept volume) and leads to a slight increase in compression. The compressed volume is only minimally affected by the increase in bore. Compressed volume is the sum of the head combustion chamber volume, deck clearance volume(can be a positive or negative value base on whether the piston is below or above the deck at top dead center), piston land clearance volume, head gasket clearance volume, and piston dome volume(negative value). The only two affected by the bore diameter are the deck clearance and the piston land clearance volume, both of which are very small compared to the increase in swept volume.

Compression Ratio = (Swept volume + Compressed Volume)/Compressed Volume

In a stock 1608 engine going from stand bore to 0.6mm over would increase compression by about 0.1 units.

Thanks Stan! Great explanation! After I posted I began to think that I had not thought it out all the way..

The pistons from my donor engine are stamped RA2661 0.60 and TOP 0.04 UL. So also +.60 - anyone know what the second stamping means? Also, I measure the "dome" on those to be 3mm. Probably stock.

[BEEK]

the 1608 pistons are in my storage area, they are a higher dome than the us spec 1608. i just have to find them

[smbaird37]

OK found good info on Mirafiori and will paste here for everyone:

(1608 pistons) Are shorter in Length, a lot, than 1438cc Pistons.
When working with PBS Back in the Day, they "could" adapt/convert 1438cc
Pistons and make them workable for 1608cc Engines... with a Lot of Cost.
And... Vice Versa.
Yet, PBS advised against "Converting" 1438cc to 1608cc Pistons...
saying it was "pointless" and better to pay through the Nose to get Correct
Pistons... so, Imported all USA versions of 1438, 1608 (and 1592) Borgo Pistons

1608cc AE Borgo, SpA Pistons
*not mentioning AE, generic, cataloguing - it's consistently self-contradicting

Borgo# 66.6705 1608cc 125BC.040 (C/R 8.5:1)
124 Sport USA Spider Coupe
3mm Compression Height, 69.25 Total Piston Length

Borgo# 66.6523 1608cc (Coupe 125BC, Spider 125BS) ... C/R 9.9:1 (drool)
Works on USA 1608cc DOHC's with Clearance
4.8 Compression Height, 74.3 Total Piston Length

*** NOTE for SPOTTERS of DOHC 1438 or 1608 NOS OE Borgo Pistons ***

Repco, USA, Imported AE Borgo in the DOHC 1438 + 1608 with a "Private" Mark.
(AE Borgo in the Repco Box, white with Repco Label or Repco Corporate Colors)
Repco "Private" Production Pistons will O.N.L.Y be Stock Compression...
Marked as Follows...
1438cc ... RA 2664 (Borgo# 66.5946 Not on Piston or Boxing)
1608cc ... RA 2661 (Borgo# 66.6705 Not on Piston or Boxing)

[fiatfactory]

.

[Daniel]

Most of these options i'm sure are long gone by now, finding pistons is possible but having choices on brands
compression ratios will be very limited unless you go custom made. If you search the web you may find just
what your looking for as i did a few years ago for a 1608 build. I found an old New Stock set for sale online
someone must of been sitting on these for a long time then decided to sale them off.

[fiat218]

Most of these options i'm sure are long gone by now, finding pistons is possible but having choices on brands
compression ratios will be very limited unless you go custom made. If you search the web you may find just
what your looking for as i did a few years ago for a 1608 build. I found an old New Stock set for sale online
someone must of been sitting on these for a long time then decided to sale them off.

Daniel is still around ?