2.8 MFI dyno

[r lane]

Don't know where this will get you and you may have done this. I would draw a line down center of a page, list the performance pieces of your first engine on the left side and in the same order, list your new motors pieces. Note your differences. I do think the pump, considering that your ignition is correctly working, is the first order of business at this point. No fuel up top, no HP. I have 3 MFI engines, never a dull moment.

[356RS]

Originally Posted by Neil Harvey

I don't have any real experience with these early mechanical injected engines. What work what doesn't. However, if we were to get involved with building one of these mechanical injected engines, I would want to know a few things about the pump. How many crank degrees is it on and how many off. I could calculate the start of the Injection, or the end or the middle. Then, I would look at the cam spec's the dome of the piston and consider if I needed to include a bowl in the piston dome then figuring out of the pistons are suitable without. Injection timing plays a huge role here too. I cannot see how you can consider a cam profile or its settings without first knowing the injection timing.

Great point Neil. These are the 2 standard MFI pump timing specs.
Stock MFI pump: Set @ 40 degrees after overlap. #1 plunger starts to rise @ 85* after #1 TDC.
@ 295* ATDC #1 plunger is at 50% of travel.
@ 115* after overlap #1 plunger is fully compressed. Total plunger travel is 6.90mm.

For the RSR's: Set @ 14* before overlap. #1 plunger starts to rise @ 34* ATDC.
@ 243* ATDC #1 plunger is at 50% of travel.
@ 55* after overlap #1 plunger is fully compressed. Total plunger travel 6.90mm.

Hope this helps.

[Rusty911]

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?

[356RS]

Originally Posted by Rusty911

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.

[faapgar]

Mark is correct.It only takes maybe 5 minutes for a pump change on the dyno.Good point Mark

[Mr Beau]

Originally Posted by 356RS

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.

Interesting. How much difference did it make on the dyno? I haven't seen any good articles for sequential EFI where changing the injection timing has any impact on power. I wonder if MFI is different.

[Neil Harvey]

Originally Posted by Mr Beau

Interesting. How much difference did it make on the dyno? I haven't seen any good articles for sequential EFI where changing the injection timing has any impact on power. I wonder if MFI is different.

I can tell it certainly does. However, if you are mapping for power or emissions, the timing points will be different.

Unfortunately, often, the mapping is done quickly to get a power result and all of the important part throttle stuff is never looked at. I have seem maps where the fuel timing has been left at one position all throughout the entire map. When done correctly, the fuel timing can be as different as the Ignition timing all over the entire map.

This is just one advantage the EF injection system has over a mechanical system. The mechanical system has set timing so you find the best position to make the best power over the whole RPM range.

This brings back memories of my time with the Turbo BMW engine. It had a mechanical pump that was controlled electronically. Until we got that system to work properly, we left many engine parts on race tracks all over the world.