I just got my Mahle Mondial pistons of ebay.
84.8 with a 4.5 mm dome and suppose to give me 9.8:1 compression in my 2.0l motor (should be 9.8:1 in a 1.8l motor)
I measured them and I believe the dome is even 4.9 mm tall. (3.5 year Tool and dye maker apprenticeship)
According to an old Mirafiori Archive post I found this should give me around 10.4:1 I guess the machine shop wants to shave the head a little so it could be even more than 10.4:1
http://archive.mirafiori.com/show.php?f ... 9#2_117979 (about 40% down on the page by Steve Cecchele)
I only have access to 93 octane, what am I going to do?
The top of the piston has about 9mm of meat on the top. Shaving 1mm off is not going to weaken it to much, is it?
By how much would a 2mm head gasket reduce the compression?
I think the standard gasket is 1.3 mm and if I did the math right it should be 3.95 cc per cylinder!?
Shaving of a mm of the piston should give another 1.7cc.
Help please!
Another piston post
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Tobi
Another piston post
Last edited by Tobi on Mon Aug 12, 2013 10:42 am, edited 1 time in total.
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131lover
- Posts: 42
- Joined: Thu Aug 16, 2012 5:14 pm
- Your car is a: 131 supermirafiori
Re: Another piston post
Hi Tobi!
Just buy marks 2mm MLS gasket and tell the machine shop just to take as little as possible on the head and you will havs ni problems!
One thing that is to recommend is an extractor exhaust,it gets rid of the extra heat from the extra compression.
Alf
Just buy marks 2mm MLS gasket and tell the machine shop just to take as little as possible on the head and you will havs ni problems!
One thing that is to recommend is an extractor exhaust,it gets rid of the extra heat from the extra compression.
Alf
Last edited by 131lover on Mon Aug 12, 2013 12:02 pm, edited 2 times in total.
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focodave
- Patron 2018
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- Your car is a: 1980 Spider 2000 F.I.
- Location: Fort Collins, CO
Re: Another piston post
Tobi,
I am running a 2-litre, bored 0.8mm over, with 10.2-to-1 static compression.
I run it on 91 octane.
I've got the timing set at 7 degrees BTDC and I am running plugs that are 2 steps cooler than stock.
No ping. None at all!
And I drive it hard, up some pretty steep grades to the mountains.
My gut feeling is that if you can get 93 octane fuel (I wish I had access to that), and you set the timing back a few degrees and run cooler plugs -- you will be fine.
Dave
I am running a 2-litre, bored 0.8mm over, with 10.2-to-1 static compression.
I run it on 91 octane.
I've got the timing set at 7 degrees BTDC and I am running plugs that are 2 steps cooler than stock.
No ping. None at all!
And I drive it hard, up some pretty steep grades to the mountains.
My gut feeling is that if you can get 93 octane fuel (I wish I had access to that), and you set the timing back a few degrees and run cooler plugs -- you will be fine.
Dave
1980 Spider 2000 F.I. (my hobby)
1970 MGB GT (my other hobby)
2008 Ford Expedition (daily driver)
2019 Harley-Davidson Electra Glide Standard
2019 Harley-Davidson Iron 883 Sportster
1970 MGB GT (my other hobby)
2008 Ford Expedition (daily driver)
2019 Harley-Davidson Electra Glide Standard
2019 Harley-Davidson Iron 883 Sportster
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Tobi
Re: Another piston post
Thank you Dave and Alf.
I measured the pistons again (Calipers are not a perfect tool for measuring certain things) and it turns out i have the 5.2 mm dome pistons as described by Steve Cecchele (link in original post).
So, that gets me up to 10.5:1 compression plus what the head shaving and the 0.8 mm oversize is going to do.
I will have to bite the bullet and spend more money on a 2mm head gasket, get the colder spark plugs and set the timing accordingly.
I am sure the guy I bought the pistons from was honest and did not know.
I believe he was just another victim of
"VICK AUTO SPORT" by being lied to and given the wrong facts.
I measured the pistons again (Calipers are not a perfect tool for measuring certain things) and it turns out i have the 5.2 mm dome pistons as described by Steve Cecchele (link in original post).
So, that gets me up to 10.5:1 compression plus what the head shaving and the 0.8 mm oversize is going to do.
I will have to bite the bullet and spend more money on a 2mm head gasket, get the colder spark plugs and set the timing accordingly.
I am sure the guy I bought the pistons from was honest and did not know.
I believe he was just another victim of
"VICK AUTO SPORT" by being lied to and given the wrong facts.-
131lover
- Posts: 42
- Joined: Thu Aug 16, 2012 5:14 pm
- Your car is a: 131 supermirafiori
Re: Another piston post
There was 2 different pistons for the 1800 124 SC the 4,5mm and the 5,2mm cant remember from wich years but they where the so called 9,8-1 in comp, i think that they had different gaskets because i havent seen any difference in comp from different years !
With the 2l block and head you will get (give and take) 10,2-1 in comp according to Mr Crofts book, i Think this was measured with 1,27mm gasket that was for the 124, I would recomend you to use Marks mls 2,0mm it will last for ever and your comp will be just fine!!
One thing to have in mind is if you have your head done, the valves should be machined down in the seat to get the maximum of the valve size, that will increase the flow and slightly reduce the comp, not by much but Everything Counts!
Relax and build your Engine..
Alf
With the 2l block and head you will get (give and take) 10,2-1 in comp according to Mr Crofts book, i Think this was measured with 1,27mm gasket that was for the 124, I would recomend you to use Marks mls 2,0mm it will last for ever and your comp will be just fine!!
One thing to have in mind is if you have your head done, the valves should be machined down in the seat to get the maximum of the valve size, that will increase the flow and slightly reduce the comp, not by much but Everything Counts!
Relax and build your Engine..
Alf
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fiatfactory
- Posts: 506
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- Your car is a: 1970 128
Re: Another piston post
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Last edited by fiatfactory on Tue Jul 02, 2019 10:41 am, edited 1 time in total.
nothing to see here... move along.
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Tobi
Re: Another piston post
Well, I ended up using the 2mm head gasket and got 1300 miles on the motor so far. I am using 93 octane gas and did not hear a knock yet.
I will keep your advice in mind and make things right when I have to take the motor apart and that could be sooner than expected.
The motor runs great and pulls hard but it also burns oil when I go over 4k rpm. The guy at the machine chop told me that it can take up to 2000 miles for chrome rings to brake in but I am not sure the rings are chrome rings. They also told me they honed the walls with 800 grit, sounds very fine to me. "After" honing they put quiet a few scratches in the walls when they fitted the rings and he told me that would be normal and is not a problem.
Anyway, the very next thing I have to do is put the car on blocks and store the battery in the basement because it is starting to get pretty cold here in Minnesota.
I will keep your advice in mind and make things right when I have to take the motor apart and that could be sooner than expected.
The motor runs great and pulls hard but it also burns oil when I go over 4k rpm. The guy at the machine chop told me that it can take up to 2000 miles for chrome rings to brake in but I am not sure the rings are chrome rings. They also told me they honed the walls with 800 grit, sounds very fine to me. "After" honing they put quiet a few scratches in the walls when they fitted the rings and he told me that would be normal and is not a problem.
Anyway, the very next thing I have to do is put the car on blocks and store the battery in the basement because it is starting to get pretty cold here in Minnesota.