Cylinder Pressure?

[baltobernie]

For those of you running high-compression pistons, what kind of cylinder pressures are you seeing? My new motor is measuring 190-200 psi, which seems quite high.

[vandor]

Cylinder pressure also depends on cams, but your pressure figures point to a bit over 10:1 CR.
Did you calculate the CR when the engine was built?
bye,

Csaba
'71 124 Spider, much modified
Auto Ricambi
http://www.autoricambi.us

[baltobernie]

The Vick pistons were advertised as 10:1, and I did not cc the heads, so I didn't bother to try and calculate the static or dynamic CR. My posted question was a solicitation for others to report their results, but if you say that I'm a little over 10:1, I don't think that's excessive or the cause of a blown gasket I've suffered after 3k on new engine. No engine damage; caught it before the engine even reached operating temp. Head and block are flat. Replaced with FelPro (Goetz) and will retorque this time after a dozen heating/cooling cycles. Let's hope the first one was a fluke.

[racydave]

Thats a bummer Bernie. Projects never seem to go as easy as what we expect, but the end results will be well earned!

[baltobernie]

Thanks, Dave.

With these cars, it's an easy, strightforward repair, and it did give me a chance to observe no pre-ignition or other damage in the head. I'll see our local Fiat mechanic next weekend at the car show, and will ask him what pressures he's seen in his Abarth.

At least we still have some decent weather to enjoy driving!

[BrianAz]

I rebuilt the engine in my 1980 2000 FI Spider earlier this year. In standard form before the rebuild the cylinder pressures were between 142 to 158 psi. After the rebuild using HC pistons from Vicks and Allison mild perf cams the pressures were at 250 psi before breaking in the engine. I don't know what they are now.

Hope this helps,
Brian.

[baltobernie]

Thanks, Brian, that puts my mind at ease.

[pope]

Brian,what compression of piston did you install? 8.9:1? Hows the engine been handling? Did you do anything to the fuel system? Any changes?

Thanks

[BrianAz]

Hi Pope,
The CR was 10.0:1 using Vicks HC pistons and keeping the standard 2.0L head. The engine pulls very well midrange. Idle is a little bit lumpy due to the cams (Allison mild perf cams, NOT the latest milder ones that Mark now has for FI 2.0L engines) . I polished the intake ports, kept the standard valves and fitted the Allison header and 2.25" exhaust system.
The ignition is set to 10 deg BTDC and I was running 91 octane fuel with no detonation problems. I never tried the 87 octane.
I left the fuel system standard. I checked out the A/F ratio at high RPM and high load using a wide range A/F meter and the engine was still plenty rich. The best way to do this of course, is with an oscilloscope and current probe on the injector wire so you know how much is left before the injector is fully open.

// Brian.