C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

MAF vs Speed Density?

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Old Sep 17, 2006 | 10:48 AM
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Default MAF vs Speed Density?

My dad has installed a complete '91 vette engine in his '89 vert. Just wondering what will have to be done to make this work.
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Old Sep 17, 2006 | 12:20 PM
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need the 89 knock sensor....remove the map sensor fro the the intake mfld and plug the hole .....if you're keeping the 89 MAF, -165 ecm, and wiring harness.

if you want to change to s/d, you will need a new ecm (-730) and rewire or replace harness.

is the new engine modded?
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Old Sep 17, 2006 | 12:35 PM
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Originally Posted by redrose
need the 89 knock sensor....remove the map sensor fro the the intake mfld and plug the hole .....if you're keeping the 89 MAF, -165 ecm, and wiring harness.

if you want to change to s/d, you will need a new ecm (-730) and rewire or replace harness.

is the new engine modded?
Thanks for the reply, redrose. The '91 engine came from a wrecked vette, don't have any idea if it was modded or not but looks stock to me unless some internals were swapped. I think he is wanting to go from speed density to MAF. He is keeping the 89 ECM. I was aware of doing away with the MAP sensor, but not aware of changing to a 89 knock sensor. The engine is already in the car and I doubt he will want to change the wiring harness for the 91 ECM. What benifits will be yeild by using the S/D rather than MAF? Thanks, this is the next step we needed.
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Old Sep 17, 2006 | 03:30 PM
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the first GM efi's were all s/d...millions (really) were sold in chevy, pont, caddy, pik-ups, etc for tBi and worked great (i owned several and power, gas mileage, and start-up were better than any carb ever)...then for untold reasons (NOBODY will EVER get the real skinny from gm) the l98 got MAF without MAP...then back to s/d 91-93...then both maf and s/d from then on, tho guesses are that maf is primary and s/d is back-up (i can't see in my ecm, i tried)...the controversy continues with each camp claiming superiority.

there is an f-body post that tried maf and s/d on the same car on the same day, same track and the maf was a tiny bit quicker...before chip burning reportedly made the s/d a bit quicker...tiny bits either way.

the MAF sensor is rumored (i haven't checked) to be flow limited in sensing ability (i'm gonna start my 468 big block on maf to see what happens.)

the MAF does report actual airflow to the ecm, maP ''calculates'' stored pressure/rpm to get reqd input...so maF MIGHT be more accurate...IF the programming AND the hardware are perfect..big ifs

street rods, jeep/chevy converts, pik-up tPi , prefer s/d due to space reqd for the maF, and they're getting rewired anyway
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Old Sep 17, 2006 | 05:03 PM
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Not to sure but i hear the map is more user friendly, and the maf is a little tougher with big modifed engines. I used Street & Performance they made me a harness for my set up . They also make add on harrness to make similar changes as you discussed. Give them a call they make a real nice product and will set you straight with what you want.
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Old Sep 17, 2006 | 06:17 PM
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Thanks guys, he is not into adding performance at this time. We have been working on it for some time now. Just to clarify, all that is needed to make the complete 91 engine work in a 89 vette with stock engine harness and ECM....we will need to change the knock sensor to a 89 and plug the MAP sensor and install the MAF??

BTW redrose, that is very good info.
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Old Sep 22, 2006 | 02:03 PM
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Originally Posted by bruced267
Not to sure but i hear the map is more user friendly, and the maf is a little tougher with big modifed engines. I used Street & Performance they made me a harness for my set up . They also make add on harrness to make similar changes as you discussed. Give them a call they make a real nice product and will set you straight with what you want.
I thought it was the other way around. I hear MAP is very picky about mods while the MAF can compensate better to mods.

Please correct me if I am wrong.
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Old Sep 23, 2006 | 02:42 PM
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Originally Posted by bowtie350_428
I thought it was the other way around. I hear MAP is very picky about mods while the MAF can compensate better to mods.

Please correct me if I am wrong.
You're right. It's the MAP system that is very sensitive to engine mods.

MAF systems have the ability to adapt to certain changes, within reason of course.

Jake
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Old Sep 23, 2006 | 04:22 PM
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Very interesting info guys, thanks. I haven't talked to dad in a few days but I think this will be just what he was looking for. More than likely, he will go with the MAF setup.
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