1970 911 E engine rebuild
 

I am planning a rebuild of my 1970 2.2 911E engine. Have read Wayne's engine rebuild book and several others. Here is my question: Can I use 87.5mm bore cylinders with JE pistons w/ S profile without changing the E cam and E MFI? The new displacement will be 2,380 on a 2.2 crank. The compression ratio should be around 9.5. I want to preserve the E responsiveness at mid-range while adding HP/torque from the displacement increase. I am concerned that the E 2.2 MFI pump may not deliver sufficient gas across the RPM range. Thanks in advance. Rick

The volume was changed with each line of pump. Each application has its own Bosch number
Bruce

Rick,
You might want to contact Mark Jung. He recently built a flow bench to calibrate MFI pumps/systems. I expect that he has done quite a bit of research recently and may be able to answer your question. A friend of mine recently ran into him at the Emory Bros campout and gave me his contact info which is: www.356rs@peak.org.

Regards,

al

Rick, Your 2.2E pump should work fine with some minor adjustments. The increase in bore & compression will require a little more fuel than what the pump is now set at. You can keep the pump as is and do a A/F ratio test after the rebuild to see where you are or send the pump out for recalibration to meet your engine modifications. If your pump is in good condition and does not need any repairs, I can test and recalibrate it for you in one day. Let me know if I can help.

What P/Cs are you using? The only cylinder option you have without boring the spigots at 87.5mm will be Nickies.

BTW, any MFI pump can flow more fuel than any 911 motor can throw at it.

BTW, any MFI pump can flow more fuel than any 911 motor can throw at it.[/QUOTE]

Kenikh,
That's true, but where you want all that fuel to be is another problem that comes to play. The space cam has a different mapping, and part number, in each of the 10 production MFI pumps produced. Each model pump has it's own Bosch injection pump test procedure/flow spec. and each one is different. If all your concerned about is full throttle values on a, example: 3.0, then yes it can be done. But if you want the car to be street driven and have the proper A/F ratio at all throttle positions it's not going to be right. Example: You take a 2.4 T pump and put it on a 2.7RS engine. The RS spec calls for 57ml to 58ml of fuel delivery per 1000 strokes @ 3000 rpm and max throttle. The 2.4 T calls for 52ml to 54ml at those same settings. No big deal, turn the screws, richen it up right. Now at a nice cruising speed of 2000 rpm, mid throttle 29.5 degrees, where the 2.4T pump delivers 30.5ml of fuel in it's stock tuning, you have cranked up the fuel delivery for the 2.7RS but at that same throttle postion of 29.5 degrees, the 2.7RS spec sheet calls for 27.5ml, less fuel than the 2.4T pump. So now your good at high speeds but very rich at mid speeds. The space cam for the 2.7RS was tailored for less fuel at that mid range. On an engine dyno it would show up as a non-linear A/F ratio. Small changes with an engine can be re calibrated in the pump, but large changes will not be linear across the throttle range. Changing the space cam or using the correct pump is the best way. Full throttle track engines, race engines don't really care about the lower rpm's so maybe it's not a big problem for them. Street cars like the smooth throttle response at all loads.

Mark, thanks for articulating the shades of gray in my black and white "fact". A correct space cam really is important in controlling fueling. Also, the different pumps have different weights on the shaft that allow them to open at different points, so the various permutations needed to find tune the entire curve a numerous.

Can you make a T pump work on a 7500 RPM cammed 3 liter by turning screws? You bet (just take Jeff Higgins car for a spin). Will the AFRs be linear and perfect...nope. It will run great, but you will be barfing fuel at low RPM to keep the top end. It's a compromise regarding what you want to put into it. To really fine tune the fuelling you absolutely need the right space cam, weights, a dyno tune and AFR fine tune. Nonetheless, you can get there the ghetto way if you are content throwing up a smoke cloude of unleaded mist. :)

I agree. And Jeff did some time consuming tuning on his pump to get it right. Jeffs "dive right in" passion with his pump is what got me started with my MFI Dyno Project.
I also tuned a 2.2 S pump to work with my 2.7 short stroke (66 x 93), 10.6 comp, twin plug, GE-60 cammed engine. Same deal, don't get to close behind it when it's peddle-to-the-metal. You can tune them the right way, and you can tune them your way. It's all about getting where you want to be, and having fun doing it.

Thanks to all for the great information! I will proceed with the upgrade displacemnt using Nickies and keeping the same crank and pump. BTW, I bought this car in 1973 in Stuttgart and have had it ever since. probably about 150,000 miles on the engine now. Haven't had it on the street in years. I will post pictures as I progress through the rebuild and the body work. Thanks again for the advice on the MFI. Rick

Now THIS is the coolest bit of info yet. Right on!

Actually, for a race engine, part throttle response is absolutely critical. Remember Donohue's The Unfair Advantage where he goes to the Factory and the Germans don't have a fuel flow chart that goes below 4000 RPM? The 917 refuses to idle? He goes into detail about how critical part throttle response is to controlling the car.

Anyway, not to diminish an excellent and data-driven response to why you want to match the space cam to the engine cams. Which is what we always heard, but it helps a lot to know why.

If one wants perfect response and to squeeze every hp and Nm out of the engine, EFI is the way to go. Obviously not as cool as MFI, but much easier to set up and tune. In many cases, much cheaper also.

Lower rpm's
 

Your exactly right John. I should have though more about that statement before hitting the "submit" button. My point should have said "on a 2.4T tweaked pump on a big engine for racing you know your going to loose some low end space cam mapping but you got there without spending lots of $$$ on the correct RSR pump.