Heads and cams for 10.4 pistons

[ward00]

I have just secured a fresh 84.6 overbore 10.4:1, 2 liter shortblock built up with Venolias, balanced crank, and Carrillo rods! and have some questions from the pros.

Would a thicker .080 Allison performance gasket reduce the compression with a 2 liter head (the head I have is mated with FI)? If so how much? Alternatively, would the 1.8 head with the .080 at least keep the compression at 10.4. I really dont want the compression higher than 10.4.

I plan to use a ported bigger valve head, dual IDFs, header, and lightened flywheel. What cams (I currently use 40/80-80/40 ) would you suggest for this engine so that it performs to its potential but is still street driveable like the 40/80-80/40's I currently have use.

If I stayed with the 40/80-80/40's, what kind of cam timing would you suggest?

Last question, would the stock 2 FI work with the 10.4 compression? Not planning to do it, but curious.

[joelittel]

I’ve been told the 2L Head has better flow than the 1.8 so I’d keep the 2L if it were my car.

There have been a few post where forum members adjusted their cams at a dyno shop, and if I remember correctly, the optimal cam position ended up being exactly what the manufacturer specified on the cam sheet.

Subscribed and looking forward to reading your progress.

[fiatfactory]

.

[ward00]

May I ask how you have concluded the pistons will provide a 10.4:1 static compression ratio? That's kind of impossible to do without knowing head gasket thickness and combustion chamber volume.... both of which are still the be determined.

SteveC

10:4 comes from the manufacturer. I know what you are getting at, but if a piston is sold for a particular stock application (in this case for a 2 liter head), one has to assume some baseline, in this case what its sold as. My question has to do not with the particular compression I will have but how to lower it using a particular FIAT head. My understanding is that the 1.8 liter head would raise the compression over that provided by a 2 liter head, is that true? Another question is whether one head is superior over the others in terms of installing bigger valves and porting?

Thanks

[AndyVAS]

The 1800 head has a smaller combustion chamber but not by a lot. The area that the 2L heads have removed can also be removed from an 1800 head making the combustion chambers equal. Shaping the combustion chamber for max flame travel is worth it even if you drop the compression slightly doing so.

Flow numbers on an 1800 or 2L are only slightly off due to casting and casting difference is what will make one better than the other for porting and bigger valves should you go big enough to require extra large seats. If you have several heads, look them over closely for what seems to be the best casting and use that head.

[ward00]

Flow numbers on an 1800 or 2L are only slightly off due to casting and casting difference is what will make one better than the other for porting and bigger valves should you go big enough to require extra large seats. If you have several heads, look them over closely for what seems to be the best casting and use that head.[/quote]

Ok, I have both heads and when I remove them I will look at them. Is one head better than the other for installing bigger than stock valves?

[Nut124]

Ok, I have both heads and when I remove them I will look at them. Is one head better than the other for installing bigger than stock valves?

When you remove the valves, look at where the seat contact is on the valve and how much margin is there in the seat steel inserts. No use putting in bigger valves if you cannot cut the seat larger.

[fiatfactory]

.

[kenncarp]

10:4 comes from the manufacturer. I know what you are getting at, but if a piston is sold for a particular stock application (in this case for a 2 liter head), one has to assume some baseline, in this case what its sold as. My question has to do not with the particular compression I will have but how to lower it using a particular FIAT head. My understanding is that the 1.8 liter head would raise the compression over that provided by a 2 liter head, is that true? Another question is whether one head is superior over the others in terms of installing bigger valves and porting?

yes 10.4:1 compression ratio from the manufacturer, and that is simply a guess on their part as they have no idea is the pistons were to be used in a 1756 or a 1995 engine As the same piston will fit both engines was it 10.4 when fitted to an 1800 or 10.4 when fitted to a 2 litre?

And that is my point, there is no point to ask "how do I raise / lower my compression ratio" when you actually have ZERO idea what it actually is right now.

The one and only way to determine this is thru DIRECT MEASUREMENT of your particular engine/head/piston/gasket scenario. If anyone tells you any different they have no clue.

SteveC

Ward is correct, I have a similar setup in my car, and have actually checked compression ratio and it is accurate. I have a set of Venolia pistons, advertised as 10.5:1 CR by my machine shop. I was skeptical as well, but the proof was in the pudding. They were dome top forged aluminum pistons that with the stock head and head gasket would make close to 11:1, but we dummed it down by deepening the valve seats, and opening the head up a little. We also used a oversized head gasket. I checked CR when assembling the motor, made deck clearance measurements, tried to be as accurate as I could, and it came out at about 10.4:1, so I was stoked!! She's running strong on dual 40 idf's off of a 1600 sport coupe, and I couldn't be happier with the high compression setup!

[ward00]

SteveC[/quote]

Ward is correct, I have a similar setup in my car, and have actually checked compression ratio and it is accurate. I have a set of Venolia pistons, advertised as 10.5:1 CR by my machine shop. I was skeptical as well, but the proof was in the pudding. They were dome top forged aluminum pistons that with the stock head and head gasket would make close to 11:1, but we dummed it down by deepening the valve seats, and opening the head up a little. We also used a oversized head gasket. I checked CR when assembling the motor, made deck clearance measurements, tried to be as accurate as I could, and it came out at about 10.4:1, so I was stoked!! She's running strong on dual 40 idf's off of a 1600 sport coupe, and I couldn't be happier with the high compression setup![/quote]

My pistons are Venolia as well. If they are more or less than 10:4 is not my question, the question was how much can the compression be reduced doings simple stuff like putting in a thicker gasket. Your gave me the info I needed.

[Nut124]

10.4 CR? What fuel are you running? Are there any signs of pinging, detonation?

Your observation about valve seating depth and head gaskets choice affecting CR are on spot. Many folks do not factor these in. How did you actually measure your CR?

I'm working on a rad build and have yet to select pistons.

[kenncarp]

10.4 CR? What fuel are you running? Are there any signs of pinging, detonation?

Your observation about valve seating depth and head gaskets choice affecting CR are on spot. Many folks do not factor these in. How did you actually measure your CR?

I'm working on a rad build and have yet to select pistons.

Only 93, and 0 pinging up to 7000 rpm. I made flat wooden boards to fit on bottom of head with a hole in it, filled with water til full to get deck volume, measured how much piston was sticking above block for deck height, factored in my bore size and viola, there are formulas online.