Have you verified your 9.2/1 pistons?

Dallarax19

Dallarax19

Builder -Dallara Replica
So I just bought some new pistons; Mondials for a Fiat/Lancia 1500. I wasn't sure what compression they would be but I guessed they would be 9.2/1. Looking at them I see the valve pockets are smaller than stock and the crown is 0.5mm lower as well.

Stock on the left and new on the right

Standard CC method

Measuring the Crown Difference


So when I do the math on these I get 8.7/1. If the crown was the same height between the two the math would work out to 9.3/1. I expect some measurement error but this is way off. I have seen thest pistons posted before on this site but did anyone measure them and what did your calcs turn out to be? I am curious what other folks have found.
 
What is the actual compression height of the pistons?

In pistons with a small flycut, I have come across 34.15mm, 34.45mm, 34.7mm and 34.9mm flat tops... it's the 34.7's that are the 9.2:1 in a 1300.

The euro 1500 is 9.2:1 because the head doesn't have the full circular decompression recess but it has large cast flycut pistons, 34.65mm CH, USA (?) has 34.45mm CH and I've seen 34.15CH pistons with a large machined flycut too.

Lots of pics and manufaturers specs in the 'ultimate sohc' thread.

SteveC
 
Re: Crown heights

Dallarax19 said:
Measuring the Crown Difference
Click to expand...

What exactly are you measuring in this photo, & how are you measuring it?

The skirt heights between these 2 pistons look different - just hope that's not what you're using as a reference here...:)
 
Not the skirts

Good question, I measured it a few ways but all relative to the wrist pin. I am using the dial indicator as the height gage and measured the high point of the wrist pin dimeter. The crowns are flat so it was the easiest. I also slipped both pistons together on one wrist pin and measured it with a straight edge and feeler gage but I had greater measurement error ( the height was greater).
 
Really interested in specific information

I looked at the SOHC post with lots of info but I gave up looking trying to find what I specifically needed. I would like to know this:

1) Combustion chamber volume for a Euro 1500 (9.2/1 CR engine) less head gasket
2) Combustion chamber volume for a US 1500 (8.5/1 CR engine) less head gasket

Compression Height - CH ( I assume this is the piston crown (flat top) to the center line of the wrist pin)

This is what I measured on my pistons
CH for US piston = 34.94mm
CH for new piston = 34.49mm
Again I expect a slight measurement error, this was done with a set of vernier calipers.

I have never really paid that much attention to the Lego approach of building a race motor so the mix and match side of it is new to me. With that said, am I getting it right where the 9.2/1 piston is really not reality. The 9.2/1 CR is really from the combustion chamber in the head (US 1500 head and a EU 1500 head are different castings)? Help me out on this one. So are the folks buying the 9.2/1 euro pistons for a US head really ending up with more like 8.7CR? Who had done this exact walk that I am looking at but has done it with actual measurement data? I would appreciate feedback
 
Whats the Mondial part number you purchased?

if it ends in 8289 then the pistons are 34.45CH small flycut (which others have used for 1600 strokers as they have a low CH)

if it ends in 7417 then the pistons are 34.7CH with a 0.6mm pimple (1300 pistons)

sounds like you have 8289's and want 7417's

SteveC
 
8289s but that is OK for me

They are the Mondial 8289s. Better for me actually but could be a disappointment for someone looking for a compression bump in a US engine. I was providing feedback to the seller as a heads up comparing them to the US pistons. I was surprised to find the CR would essentually be a wash but at a comprimise in the valve pocket relief. I have not checked the valve clearance yet at TDC but will get to that in time. Additional comments?
 
I would say (at a guess) that the manufacturer - Mondial - found it easier (and possibly cheaper) to use existing casting moulds to produce a 9.2:1 (with a no decompression recess head) piston for various models of 1500, including the euro 1500 X19. They simply use the same pattern as other sohc pistons and machine the crown to lower the compression height. It's only in the US where anyone is worried about interference / non interference engines anyway, and the casting pattern for the large cast in flycut piston is obviously different, and probably didnt fit in with their production run...

So they are 9.2:1 pistons for a 1500, just not with a decompression recess head.

As I said a couple ofmembers have used /are going to use these exact pistons for a 1600 stroker build, and have machined / will machine more from the crown to give a low enough CH to work with the 67.4mm stroke crank.

SteveC
 
Good memory, wow!

I had forgotten about that site. I have the cc volume for the stock US 1500 head in my collection of data but it would take me a bit of time to find it, a bit lazy but easy to ask for, If I remember correctly it was 34ish as Lalo measured. If you have a lead on actual measured CC volume on the various heads, Euro etc (like Lalo did) that would be totally cool.

If I find a bit more data I will create a chart similar to my cam comparison chart that floats around this site now and again.
 
Here is the Wayback Machine link

I saved this off a few years ago. The "Internet Archive WaybackMachine" has links to old pages. Lalo's page is in there and it appears to be pretty complete. I don't think it has the info on the Euro head, but it's fun to look at anyway.

http://web.archive.org/web/20051217201959/www.lalosgarage.com/

The good old days of the World Wide Web.
 
good info here...

http://www.xwebforums.com/forum/index.php?posts/182697&page=6

when Hussien did some measuring of his Tipo head (same combustion chamber as the euro 1300/1500) and a few caculations on the variation you can get with different head gasket thicknesses and valve depths in the head.

One absolute number is difficult to come up with for any of the particular heads, as simple (and very small) differences can make a half a cc (or more) difference in the final measurement, which is why you always need to measure your head, on your engine to verify your static CR.

SteveC
 
So if you use the 7417 pistons in a 1500 with the euro head, compression should be higher than 9.2:1 and would there be any issues with interference under normal circumstances? Unless the belt pops

Ive been reading all the piston threads and If i wanted to get compression closer to 9.5 im trying to figure out what pistons to use, and ill be using a euro head so i should be guaranteed a 9.2:1

Mark
 
7417 are 34.7CH with a 0.6 pimple dome, thiscalculation uses a 34.9CH piston with 0.1mm skimmed offthe block to get the piston at zero. Same applies to the 34.7CH pistons with 0.3mm skimmed off... but you could not skim the block and get a lower CR if that's what you want.

IMO these engines begin to light up at 10:1 and over and with a SQ of 1.0mm.

You want euro head, euro 1500 intake manifold and euro cam (either 1300 or 1500 type) but you want to verify the cam is the correct one... easy to buy the wrong one as many people have.

*******************************************************************************
The euro spec 128 / X19 1300 uses a piston that has a 34.7mm compression height, and it has a 0.6mm dome (it's really more like a pimple) and have the small valve flycuts. With no skimming of the block / head, with these pistons your up around 9.6:1 in a 1500 (depending on gasket thickness , chamber volume etc etc as this all varies with production tolerances) and the piston is still around 0.25mm down from zero.

If you use pistons from an Uno 70 (this is a 1301cc engine which stock has a CR or 9.35:1) these have again the small flycuts, are flat on top,small flycut and a 34.9mmCH. They are just 0.1mm down from zero deck.

So with 34.9CH pistons in a 1500 using a thin re-torque type h/gasket (1.2mm crushed) bored to 87.00 mm with the std stroke and 0.1mm block skim to set the pistons at zero

swept volume = 380.00cc
head gasket volume = 5.95cc
volume of reliefs = 0.70cc
volume in cylinder head = 33.5cc
total * BDC = 420.15cc
total * TDC = 40.15cc

Static CR = 10.46:1

And this is without using any sort of dome piston and having all the advantages of a flat top piston (better flame propagation and faster burn, able to use less total ignition advance, high squish / quench etc etc) and not removing any block or head deck thickness.
***********************************************************************************

SteveC
 
Got it, pistons with 34.9 CH small flycuts and a thin head gasket it should be around 10.1. Now with crappy California gas I think thats probably the limit for compression to avoid detination
 
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