I'm looking over the 88 hack info from Moates files. Does 88 adjust the MAP according to what ever altitude the car is at... so even if you are in Denver the ecm will still use the MAP 100 column?

Anyone know why 88 has 4000 (main VE) or 4800 (others) as the rpm limit in many tables instead of higher like in 8D?

Thanks

 

MAP is MAP, elevation doesn't matter. Tables that are Vacuum referenced are elevation compensated.

RBob.

 

Hmmm. I just read a post talking about how you wouldn't be able to reach the high MAP values if you were driving at a high altitude. Was that for something else?

It makes sense though... that must be why the ecm does the Baro tests often?

 

There are no adjustments made to the MAP value. The reason the MAP doesn't go as high as the elevation increases is because the atmospheric pressure is lower.

The vacuum variable is elevation compensated as it is manifold vacuum. Take barometric pressure, sub off the MAP, and manifold vacuum is the result.

RBob.

 

I get it.

I wonder why the GM guys didn't make a method for altitude compensation? They certainly compensated for a bunch of other things. Some of which seem a little overboard.

Thanks

 

They did not need to compensate it for altitude. The VAC parts of the tables are referenced against BARO. BARO self corrects at certain TPS, MAP, RPM limits which are commonly hit during driving. Think OD pull at low RPM with moderate throttle. The MAP decreases as altitude increases, the MAP reading is tied to the fuel and spark tables which advances the timing and cuts fuel. It really doesn't matter whether the MAP reading drops due to altitude or throttle position.

 

hmmmm... Interesting....

In the area of performance tuning though, a big cam engine running in Denver isn't going to get much MAP table to tune, right?

 

The reason I'm trying so hard to fully understand how all this works is because I race all over the country. Although I haven't been to Denver yet there are some races there that I just might end up at some day.

 

The MAP readings will be lower @ WOT and and the VAC computation will end up being lower as well. That will narrow the MAP table somewhat, but with a big cam it is already jeoprodized anyway. I know on my BIG cammed 305 in my Van I used Alpha N and it ran fine through the west Texas mountains into New Mexicao and then onto Arizona pulling a Corvette on a trailer the whole way. Probably the first good road trip that the EBL setup had once released to the Beta's. I played with it for about 1 week trying to nail down the tune before heading out. I had it about 95% before heading out. I played with the tune at each stop until I got to Flagstaff. It was pretty darn near right, before heading back to DFW. Ran flawlessly on the return trip.

Performance will drop in Denver, but if you have a properly setup tune at sea level, it shouldn't be too far off at higher altitudes.