[A Moller]

Hi,

I am building a Giulia 1600 Sprint (-62) according to FIA App K rules and hence need to stay with the standard Inlet+Exhaust manifold, which means breathing restriction even with a Weber DCD 36/36.

So, to get the most out of it I try to source as good high compression ratio pistons as possible, without getting too bad piston shape.

Question: Can anyone share experience and recommend any particular piston?

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I have found some decent alternatives. These are from Alfaholics (UK), Classic Alfa (UK) and OKP (D). All are on the low end on target CR and none have all the benefits combined in one piston - at least not as I see it in the perspective of maximum performance from a Normale engine.

 

[A Moller]

Hi again,

After some more research I found out that two of the bigger aftermarket suppliers do not make the forging (the un-machined raw aluminium piston) in a shape which allows higher compression than approximately 11:1. So, what we will do is to cast a "plug" after the combustion chamber and see if we can come up with a shape which is expected to give decent compression and offer a considerable gain in compression over the existing alternatives on the market. If so, we will custom make such pistons. Lets see how it goes, hopefully in January.

Do anyone know which high compression pistons are available to 1300, 1750 and 2000, while not to 1600?

 

[Gordon Raymond]

Check with Paul Spruell here in the USA. He has JE forged 1600 (78 mm bore) pistons in any ratio you might want.

 

[Andrew]

I got their 79mm pistons (.040" over) with matching liners for my 1600 vintage Super. Billed at about 10.5, came in at about 9.7. I'm running pump gas, so it's OK with me.
Andrew

 

[A Moller]

Thanks for the input. I checked with Paul Spruell and had a dialogue regarding the opportunities, but in the end there is 15 % lower peak output from 10,5:1 versus 12,5:1 and JE cannot offer more than 10,5:1 for the 1600 with that particular design. Hence I have to give my plan B a chance.

 

[Curtis]

Some thoughts from my experience with 1300 Solex race engines.

Any gains in power above 12:1 are going to be difficult to find in a downdraft race Alfa engine because the cams are so short in duration and timed with so little overlap as compared to the IR weber engines. Enough is enough.

At some point you are going to start losing more than you gain because no matter how well designed and fit the higher compression piston is, it is going to start having a more negative effect on the burn than it does positive effect on power.

Because of the cams and cam timing again, you will not need the deep valve pockets that will be part of an off the shelf piston, designed to also work in a IR weber race engine, and this will help you get some compression.

Lastly to make real power with a torqueless downdraft Nord you have to run some serious rpm so piston weight becomes really important.

In my 1600 weber race engine I am running a 1600 piston that makes good compression and allows a good burn (ignition 31-32 btdc). It has to be fit very, very carefully by someone who knows what they are doing. When first fit they measured 12.6:1. I machined them further to open the chamber up even more, and stopped at 12.25:1. PM me if you want to ask the guy who originally designed them for me, if he will have some made for you.

 

[A Moller]

Curtis, thanks for sharing your relevant and valuable race engine experiences.

What you say about the camshafts is probably the key to success, or the key obstacle to overcome - as I see it. We expect peak power at around 7500 rpm and about 12 mm valve lift with standard valve size. Since overlap wastes static compression and since the inlet cannot be acoustically tuned, I agree that the duration has to be limited as well as the overlap. But by applying a more aggressive lift (and blunt top section), unlike classic race-cams, the time-area can be sufficient with limited duration.

The concept is similar to restrictor aspirated race engines, such as Formula 3, where compression reaches 14:1.