Scaling Load vs Scaling Airflow

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Scaling Load vs Scaling Airflow

Post by decipha » Sun Nov 07, 2010 11:58 am

Recently, I've been getting PM's and email's where folks have been mistakenly confusing scaling load with scaling airflow, the two are completely different.

You would scale airflow to compensate for a large flowing maf. If you have a maf that flows over 2200 kg/hr you'll need to scale airflow.

in any calibration make sure the maf flow DOES NOT exceed 2200 kg/hr, (even lower at 1000kg/hr or 36#/min for v6 and 4 cyl calibrations) although you can put a higher value in there the ecu can not calculate it, so you would compensate by scaling airflow, to do so you'll need to cut sarchg in half, sarchg is the CID scalar that would normally have the value for your cubic inch displacement like ~301.xx, you'll have to cut that value in half so now you have a 151 cubic inch engine as far as the ecu's concerned. sarchg and maf flow is how load is calculated so skipping this step is going to cause engine damage when your at WOT still in closed loop :lol: next you'll need to cut the maf transfer flow values in half, well now your going to be very lean only getting half the fuel you need so you'll need to cut the injectors slopes and breakpoint in half to bring fueling back to where it was, if you have a newer ecu you may need to cut the manifold volume scalar in half, but first try so without adjusting the manifold volume scalar.

can you see what we did? we halved the engine size injectors and airflow, so mathematically we are still equivalent except now the ecu doesn't clip airflow and splits your v8 into two inline 4's.

now you may reach a point where your clipping load at 200, to compensate you would increase the sarchg value (CID scalar) so load is below 200, i typically never let load get above 180 on cars i tune that way you still have some cushion if they decided to turn the wick up. But keep in mind when doing this you'll need to adjust the fuel and spark tables so your not demanding a a bunch of timing and a lean mix under boost.

The only reason you would scale load is to get more control of fuel and spark. All scaling load means is that your rescaling the fuel and spark tables so you can demand a different value at high loads that the stock scaling doesn't need for a stock engine.

scaling load is done to control spark or fuel at higher load ranges that you can not access with the stock load scaling for the simple fact that the stock engine can't reach those loads. Typically a stock 302 only reaches ~75 load, even lower at 60 load below about 2k rpm.

here the scaling write up written by Chris Grey, gives you all the info you need

this may help also, scaling for boost

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Re: Scaling Load vs Scaling Airflow

Post by 87coupe50 » Thu Nov 25, 2010 2:04 pm

just wanted to say thanks for this write-up. I just had a 1000HP fuel system installed because I was running lean around 5300RPM with my new motor (SC'd). I had changed to a bigger pulley and was still running lean at 5600RPM. (MAF transfer at 4.1v was 4973Kg trying to richen it up)

First run with the new fuel system was still leaning out above 2500Kg. I made the changes in your write-up, then I was running super rich up top. So rich it was pegging my wideband at 9.6 (the lowest it would register). It took me 6 runs with changes to lean out the MAF enough to get me to the propper AFR. (MAF transfer at 4.1v was 1047Kg)

Dart SHP 363, 190 FAC, Victor 5.0 EFI, 70mm T/B, DBX-97, MSD 6AL, Glenn's 1000HP fuel system, S.D. 60lb'ers, V-2 S-trim - 3.7/6.87 8 rib, TKO 500, Alum D/S, Translock 31 spline, 3:73, S/F connectors, tubular K-member & A-arms, C/C Plates, Coilovers, Strange 10-way, adj. Baseline Susp. street launch, A/C : QH, BE/EA (A9P)


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