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When is a motor just a motor, just a motor?

When is a motor just a motor, just a motor?

(OP)
Dear Gentlemen,
I have another head scratcher that's really been squeezing my melon ever more and more.  Here's what I don't get...

Let us take, for example, two engines like the Ford 4.6 sohc and the Ford 4.6 dohc.  Both motors are fuel injected, metered by mass air amd O2 sensors, have identical stroke and identical bore yet a sohc computer will not run a dohc engine and visa versa.  Moreover, as long as you have the same number if pistons, it doesn't make sense (to me) why all computers aren't interchangeable because the built in feedback systems should compensate for any values unexpected by the computer.  I do understand that this isn't so.  You can't even get a 4.6 dohc to start with a sohc computer...  but I fail to understand exactly why.  I once read an article about some Ford engineers building a proto-type V12 and they used two computers from two in-line 6's to run it, so maybe a motor IS just a motor.  What kind of gamble would I take attempting to wire GM's 4.6 dohc Northstar to Ford's 4.6 dohc wiring loom and computer?  Please explain why that's just a boob-shooby idea.
Happy Holidays,Walter Carter
Palm Springs, California

RE: When is a motor just a motor, just a motor?

Just because things "could" be interchangeable "in theory", i.e. if a concerted effort were made in order to cause them to be interchangable, doesn't mean they "will" be interchangeable.

If there is no standard for the number of pin-outs on the ECU and what there assignments are, and the number of teeth on the crankshaft position sensor wheel, and the nature of the reference zero-position on that sensor wheel, and what the waveform of that sensor is, and how the cam position sensor signal and waveform is, and on and on and ON, there cannot be interchangeability because every designer will make their own choices.

And, don't forget the possibility that the parts are *deliberately* not interchangeable, for a wide multitude of possible rationales, rightly or wrongly.

RE: When is a motor just a motor, just a motor?

(OP)
Okay, that makes sense.  It sounds as though the major stumbling blocks would be the cam sensor and the crank sensor.  I would think the rest of the stuff could easily be swapped out.  To get a Ford computer to run a Northstar motor you would use the Ford mass air, the Ford O2 sensors, Ford temperature sensors and so on.  I cannot think of anything besides the crank and cam sensors that might present a real challenge. WC,Palm Springs, California

RE: When is a motor just a motor, just a motor?

I think knock sensors are engine specific in their signal to indicate knock.

If crank position sensors are out of phase, depending on how they are set up, it is not that much of a stretch to rephase them.

Regards
Pat
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RE: When is a motor just a motor, just a motor?

If you were to take /all/ the sensors (including pulsewheels) from the Ford, and stick them on the bare GM engine in roughly the right places, it would run.

Is there anything that makes you think otherwise?

 

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: When is a motor just a motor, just a motor?

(OP)
Mr. Locock:  No, I can see no reason why it would not run.  Even with a different bore, stroke and displacement...  I would still expect it to run.  However, is there any reason to suspect it might not run well?  WC,Palm Springs

RE: When is a motor just a motor, just a motor?

Yes. Common sense. It takes a fair while to calibrate a particular engine so that it runs well, with a diffferent engine you are starting from a baseline, that is all. Cam timing/profile, inertia, cooling, runner tuning, knock sensitivity etc etc.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: When is a motor just a motor, just a motor?

(OP)
Thanks to all who took the time to contribute to this discussion.  I've always found the discussions here to be insightful and, more importantly, consistently accurate.  I believe this forum is wonderfully unique in that respect.  I am forever grateful to those of you who so generously give your time to make this site possible.
Walter Carter, Palm Springs, California

RE: When is a motor just a motor, just a motor?

There's a Yahoo discussion group dedicated to DIY fuel injection.
It seems to have some pretty capable members. Not a lot of theory, but a lot of practical application.

Jay Maechtlen
http://www.laserpubs.com/techcomm

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