I've noticed a few folk here who have the same problem as me-living at altitude. It gets old driving down the hill to double check my changes. Does anyone have an estimate of how much 7,000ft alt. will change my int. after I lock the blm at 128???? If I had a # to shoot for up here it would make it so much easier... I do drive down the hill a fair amount so would like to make sure I don't run it lean down there, I'd rather have it a little on the rich side up here. Already tuned a two-stroke motorcycle perfect for home;then went down the hill and ran it hard-the results were ugly......

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86 406

 

I am taking a guess here, but here it is. @ Sea level the Baro is about 29.9 (here in San Diego). as a general rule we say that you will loose about an inch for every 1000 feet of elevation change. this being said @ 7K you are going to have 22.9". that being said you are loosing 23.4% cyl filling efficiency & I would expect that the motor is going to have a cow trying to pull that much fuel out (or Vice versa for your app)

Here is the catch. I dont know if this is going to be a linear thing or not (I think that it ought to be, 'cause the VE table compensates for the non linearity). if that is the case then I would think that multiplying or deviding the VE table by that value would get you close enough.

BUT, I thought that the SD code (I dont know what you have I am assuming SD as I would expect the MAF to be pretty close on its own), did some BARO/MAP learning on key on, engine off. I thought that it took a map sensor reading & then used that as a similar multiplyer, in which case all this ought not matter any.

I suppose that as a test you could go from one alt to the other & tune in one or two spots on the VE table, & then see how this number compares to my guess.

How about a comment from the Big Dogs?

BW

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Bobalos
aka Bob W.
www.r71camaro.homestead.com
r71chevy@earthlink.net
<><

 

86 406?
MAF with a 165, right.

The MAF should be rather accurate at various altitudes, BUT I've never worked on a 7K elevation calibration, It would seem to be you'd want the 128s at the lower altitudes, and let it self correct for the "normal" high altitude.

depending on what this 406 you might want to reevaluate the injector sizing, you'll need a large dynamic range for being in extremes like you have.

You'd have to double check the code, but if there is an exhuast back pressure cal., and you have a real low back pressure system that may come into play.

Sorry for the vaque and generic answers but best quess I can come up with

 

[QUOTE]Originally posted by Grumpy:
[B] 86 406?
MAF with a 165, right.
Yes it is a 165 with maf-and fms 24lb. inj.
Just went down the hill today, elev. ranging about 2000ft. Without the blm locked up here I'd gotten it reading 120 to 128 across the different cells. After driving for the day down below the blms were low 140's! So I'm definitely going to have to compensate substantially even with the maf; I didn't think it'd be that much. As for speed dens. it must be significant too. Thanks for all the input.



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86 406