Thread: 2.8 MFI dyno
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356RS 356RS is offline
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Join Date: May 2003
Location: Bend, Oregon
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Originally Posted by Rusty911 View Post
Mark, is the difference in the MFI pump timing between the rsr pumps and the standard street pumps solely related to the space cams or is it a combination of things? In other words if someone puts an rsr space cam in an early 911s MFI injection pump like 1970, would that change the MFI pump timing from s to rsr or it more related to the cam in the engine.

It seems that it could get complicated if one modifies an S space cam or has a custom one made to match a GE-60. In that case is there a way to calculate the MFI timing or would you try standard S setting first?
The difference in pump timing is because of engine camshaft specs. The RSR's used factory RSR cams with close lobe centers. The MFI pump timing was advanced to better match the RSR cams specs. The engine builder sets the MFI pump timing when the pump is installed. The space cam itself does not change the MFI pump timing.

Custom space cams are a challenge. Knowing the MFI pump injection timing can play a big part when setting the engine's cam timing. Example:For a 3.0L high performance street engine with something like GE-60 cams there is no benefit in changing the MFI pump timing. For high lift and longer duration camshafts the MFI pump timing can be advanced to better match the camshafts specs.
I built a short stroke 3.1L (66 x 100) high butterfly, RSR Sprint cams and ended up setting my MFI pump timing to 5* BTDC after a few dyno runs to find the sweet spot for that engine.
Mark Jung
Bend, OR
Old 07-27-2020, 06:56 AM
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