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Discussion Starter · #1 · (Edited)
Started to get annoyed by the oil consumption of my 2L engine, not sure yet if its a valve seal issue or a ring problem.
The engine has approximately 160,000km on it and I believe head was never removed.

I am traveling to Europe next month and I thought it will be a good idea to have a complete engine rebuild kit on hand just in case, I'm talking about piston, linears and all the related gaskets.

Spoke to a european vedor who offered me 2 type of Motronic pistons, one titled as Alfetta Motronic and is supposed to have a real compression ratio of 9.8 and the other titled 4th gen spider motronic with a compression ratio of 9.5.
See below a picture of both.

The spider is the one with arrow on the piston top to indicate gas flow direction, looks also as it have a smaller cut out for a smaller exhaust piston.

The Alfetta Motronic (Again slightly higher compression) is symmetrical.

Which one should I chose? Which are the genuine Motronic? Which will give real life better performance?

Thank You

Alfetta Motronic
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4th gen Spider Motronic
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Alfetta on top, 4th gen spider below
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Do you have full specs? What are the weights of each?
 

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Discussion Starter · #4 ·
Dont have spec, they weight more or less the same.

I/We know the CR is diffrent and that the Alfetta has the edge but i guess CR is not everything and I'm asking if any of you is familer with these particular shapes? the one used on the spider gen4 looks more modern.

In paralel to that my Alfetta is about to go through some modifications that includes switching to Weber carburetors, removing US emission camshafts and installing a mix of European camshafts 10548 03200 51 on inlet and 10548 03200 01 on exhaust (this is until I get a chance to acquire a better ones).

Thx.
 

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If you are aiming on wilder cams you need higher CR than still below 10. And you need enough valve/piston distance. You need to be sure the cams you want in the future will fit. Otherwise you do a lot of work (and spend money) double.
 

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Discussion Starter · #6 ·
If you are aiming on wilder cams you need higher CR than still below 10. And you need enough valve/piston distance. You need to be sure the cams you want in the future will fit. Otherwise you do a lot of work (and spend money) double.
Dont know yet the effects of Cam selection but i know that this is a fast road car not a racer.
fuel type is regular european 95 octane unleaded
plan is to improve tourq throughout the rpm range and be able to reach 6500rpm smoothly (today im at 5500).
 

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ok, so blueprint the engine. And do your preferred cam selection before pistonselection. I would prefer a bit higher CR , around 10.5. You do not want to put the now regular 95 octane, E10, in an old Alfa imho... Not with what you want to reach. Better 98 E5
 

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Discussion Starter · #8 ·
98 Octane is harder to find in Israel, but possible.
Goal is to get to ~160hp, assuming I'm using RJ camshaft, something that would work with standard head/valve and stronger valve springs what piston would be the ideal for that setup?
The vendor has 10.4 compression pistons but claims that they are "harder on the engine" plus from some reading I got the impression that Motronic pistons although Lower In compression provide better gas transfer and allow more ignition delay
 

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Do a compression test or a leak down test (Preferably a leak down test). Post your results here. We need some solid information to tell us the root cause of your oil consumption issues.

I hate to say but if you have told the guy who is trying to sell you 9.5 pistons your plans to build a 160 hp engine the guy is trying to move some old stock that he has on his shelves. RJ just finished an engine build and documented it in this section. Study it and develop a plan to build your engine. Talk to RJ about what he recommends for the cam that you intend to buy.

- Drew
 

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OKP told me these are 10.1. But as others have said. CR varies depending on pistons, combustion chamber and how much head has been shaved.

 

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Richard Jemison
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Go for the one "Sold" as higher compression. Neither makes 10 to 1. Shave the head .030" and get CR closer to 10.5 to 1. That will improve performance (Torque particularly)
A little seat with (no 3 angle seats) and top of the ports from the guide area straight into the open seats will add to whatever the piston/cam and compression would normally make.

Do it right if doing anything.




)
 

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Discussion Starter · #13 · (Edited)
Go for the one "Sold" as higher compression. Neither makes 10 to 1. Shave the head .030" and get CR closer to 10.5 to 1. That will improve performance (Torque particularly)
A little seat with (no 3 angle seats) and top of the ports from the guide area straight into the open seats will add to whatever the piston/cam and compression would normally make.

Do it right if doing anything.




)
Thank You Richard

In addition to the two types of Flat headed Motronic the vendor also has 10.4 High compression pistons but claims that they are "too heavy", see picture below these are not flat headed, what do you guys think of this option? (i'm not even mentioning their apple bite 11.5CR pistons which are probably race only option)

I think i will go based on your recommendation and choose the Alftetta 9.8CR Motronic pistons, I assume that once head is removed your suggested mods will not be a problem (although i don't fully understand the valve seating thing yet).

Again this is a weekend mostly mountains fast road car not a racer, the ability to reach higher RPM with more HP is great fun but not on the account of drivability.
Richard, With Carburetor, Euro Exhaust header and 123 Ignition what would be your ideal Camshaft for this setup and the changes you suggested above?

Br
Shmulik.


BTW should i use copper head gasket or regular one?


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