Carb to TPI on a 72 SBC 350 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-24-2004, 06:10 AM
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Carb to TPI on a 72 SBC 350

I just finished the final tuning of the TPI I installed on my Buds 72 350 Chevy powered pickup with a 700R4. Some back ground: it had a Carter Q jet, nice big valve heads, a 700R4 that used the Painless Wiring converter control, and Dual Flow Master Series 40 with an H pipe. We now have a easy starting, smooth running, more seat of the pants power and more fuel economy. One side benefit that I would like someone to explain is the very disturbing exhaust resonance we had with the carb set up is GONE!!! Go figure.

We canned the hard ware from an 88 Camaro, including the wiring harness for reference. I ordered the Painless wiring harness for the MAP so we could eliminate the Mass Air Flow sensory in the front. We pulled the MAP sensor and computer from a 93 Chevy V-6. I replaced the Coolant Temp sensor, O2 Sensor, oil pressure switch, and Knock Sensor and bought a Carter 5000 in line fuel pump. The other sensors appeared to be good and have checked out fine so far. I found the Painless Installation Instructions to be complete and straight forward. The biggest problem was X ing out all the stuff not needed since it was generic for Throttle body, MAF and MAP as well as with and with out polutition control. We had to mill a few parts to provide a "factory" look. It was very satisfying to have it fire right up one the first attempt. We had to shut down for a minor fuel leak because I had not applied enough torque to one of the high pressure fuel fittings. To regress, I had a local hacker reprogram the 93 chip to give about 4 more degrees of global spark advance and erase all the polution controll junk as well as the VATS portion. He smoothed out the fuel and spark curves also. It is about the same as the old "Hot Chip". Tomorrow, I will take about a 60 mile trip to see how much the fuel economy has improved.

We were able to get this done for less than $600. Now I am ready to tackle the 327 in my 36 Coupe!!!

Trees
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Old 10-01-2004, 11:41 PM
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quick question

this may seen like a wierd question but why did you trash the maf for a map..the reason i ask is due to the fact of preformance the vac can alter and make the ecm angree when the maf seened to be the choice i have had for that issue..i am courious due to the fact i may go to a tpi on my impala
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Old 10-02-2004, 02:19 AM
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I cant speak for trees but I can think of a few reasons. One being that replacing a MAP sensor can be significantly less than having to replace a MAF. Another reason is that you can rid of the ducting and the sensor itself for physical fitment as well as appearance (they look wicked with a nice big filter on the end of the throttle body).

When they switched to a MAP sensor they also did away with the ESC (Electronic Spark control) module as well, again simplifying things somewhat.

It is argued about which setup is better. MAF are more affected by vaccum leaks but less affected by overall engine vaccum. It sounds like a wierd concept but from my experience seems to be true. MAF systems are also a bit more accurate with the incoming air reading whereas the MAP system calculates air based on engine vaccum. I personally prefer a MAF setup as that is what I am most familiar with but Im sure someone should chime in with the reasons they like the MAP setup more.
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Old 10-02-2004, 05:39 AM
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Primary reason to get rid of the MAF was the room at the frunt (Ducting as mentioned above). Second reason is reliability of Speed Density system over Mass Air Flow system. The big boys changed over for a reason, maybe because of the big difference in cost of a MAF sensor and the MAP sensor.

Trees
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Old 10-02-2004, 01:36 PM
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Speed density is better than MAF because of the fact that air volume can better be calculated with MAT taken into account. MAF is older technology. I could be wrong, but I think that all the oems now use speed density.

Trees, that is great that you got it all together and running. I have thought about doing one of these on my 57 but with a Genboard so I can tune it myself. Sounds like your build went smooth.

Chris
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Old 10-02-2004, 03:15 PM
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Kevin, after what you have gone thru with your Turbo, this is a cake walk. Get after the 57 cause I am interested in how the Genboard turns out. I'm still looking for a easy, reliable system to put in the coupe. Right now I'm leaning toward the tune port with the small distributor. I want to feel comfortable doing it without pulling off the front end!!!

Trees
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Old 10-02-2004, 06:22 PM
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Actually many manufacturers nowdays use both a MAF and MAP sensor. I guess they figured it would be best to combine them and have the computer compare readings.

As far as I understand it, MAF more accurately read incoming air however since these systems dont calculate vaccum, leaks can cause them more problems than the MAP setup which will adjust fuel based on Manifold pressure.

I know later year Camaro's (1997 and up) as well as the Corvettes (and probably any of the later LT1/LT4 induction systesm) use both a MAF sensor and a MAP sensor.
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Old 10-03-2004, 07:42 AM
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I am not sure what the combination is used for, but it could vary well be a comparison. I would bet, however, that they are using a blend of the two for fuel calcs. A common practice on engines with fat cams is to use MAF for idle tuning and then transistion to speed density for power tuning, but I cant see why the oems would need this.

Chris
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