MFI and Compression Ratio Changes

[NevenM]

Wayne

In your book you suggest that altering the compression ratio of an engine would require an MFI Recalibration, Why? The MFI space cams are matched to the volumetric efficiency of an engine, I cannot see how altering the compression ratio would affect this

I'm rebuilding my '73E and are hoping to get the Comp Ration as close to 9 as possible (std is 8.0). Also from what I've seen I'd be surprised if factory engines were very close the the spec comp ratio, If I set my deck height to 1mm, my comp ratio will be 8.97
To get it down to 8 i'd have to have a deck height of 2.2mm which
is nothing like it was when I tore it down

Comments?

Neven
73 911E
70 914/6

[Wayne 962]

I just read through the section on MFI (pg 96-98) and I couldn't find that?

No, you're right - changing the compression ratio by itself shouldn't require the pump to be altered. However, if you change the cams or the displacement, then you should modify the pump to match.

There is lots of debate on this subject - the only way to calculate the compression ratio accurately is to perform a cc measurement of the heads and piston dome...

-Wayne

[NevenM]

Wayne

I have CC'd my heads and pistons, and connot see how they built it to 8 to 1

Page 112 "Waynes top engine picks", "Stock 2.4S with 2.2 Pistons",
"You will need to have your MFI pump recalibrated or your carburetor jets changed to accomodate the change in compression"

Neven