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Thread: Speed density conversion tune
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02-12-2017, 03:46 PM #1
Speed density conversion tune
Hey guys, I have a new motor going together and I am curious how many of you guys switched to speed density. Pros and cons? How difficult was it to tune compared to mass air? Thanks guys
1995 formula a4,100,000mi, 10 bolt 3;73,tci 3000,hooker supercomp Lt's,100,000mi,n/w plate w/150 jets, mt/dr's.,a few more bolt ons. 12.70's/105. 11.60's/118
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02-12-2017, 05:20 PM #2Xtreme Member
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Supporting Member2021 Charger Scat 392
1994 Firebird Formula 381 stroker - Carrying the torch! - 9.90 @ 134.3mph on a 200 shot
The wrench/driver for LTConvert's 94 Z28- Ellwein 383/LE Trickflows/ D1SC / CPT Ultra Pro Race 4L60E
10.78 @ 125mph. Shooting for 9.99 for Frank Cahall!
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02-13-2017, 07:39 AM #3
I will be running nitrous but not much elevation change. Is there a performance difference between the 2 other than throttle response?
1995 formula a4,100,000mi, 10 bolt 3;73,tci 3000,hooker supercomp Lt's,100,000mi,n/w plate w/150 jets, mt/dr's.,a few more bolt ons. 12.70's/105. 11.60's/118
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02-13-2017, 08:52 AM #4Xtreme Member
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Supporting Member2021 Charger Scat 392
1994 Firebird Formula 381 stroker - Carrying the torch! - 9.90 @ 134.3mph on a 200 shot
The wrench/driver for LTConvert's 94 Z28- Ellwein 383/LE Trickflows/ D1SC / CPT Ultra Pro Race 4L60E
10.78 @ 125mph. Shooting for 9.99 for Frank Cahall!
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02-13-2017, 09:19 AM #5
I will be running nitrous but not much elevation change. Is there a performance difference between the 2 other than throttle response?
1995 formula a4,100,000mi, 10 bolt 3;73,tci 3000,hooker supercomp Lt's,100,000mi,n/w plate w/150 jets, mt/dr's.,a few more bolt ons. 12.70's/105. 11.60's/118
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02-13-2017, 10:48 AM #6LTx Guru
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The speed-density method is used to calculate the mass air flow. From that point on, the system works the same. That's why the PCM can keep the engine running even after the MAF sensor fails, and the system defaults to speed-density. The critical part of the speed-density calculation is the volumetric efficiency (VE). That's a table programmed in the PCM. If you change any part of the way the engine breathes... intake, exhaust, cam, etc..... you need to update VE tables. There is a utility available to help with that.
I'm not sure that elevation changes much. Elevation affects MAP, and MAP is part of the speed-density calculation, just like inlet air (absolute) temperature. That's how the density is calculated to convert volumetric flow (CFM) to mass flow (#/HR). Possibly an effect on VE???? Don't know.
As far as the nitrous, you tune the PCM to optimize for straight motor, then with wet nitrous you add the extra fuel and adjust the timing using external methods.... jetting the fuel to match the nitrous and retarding the timing with an external box. Since nitrous vaporization chills the incoming air, throwing off the speed-density calculation, you may (plate after IAT will not be as sensitive) have to carefully examine the plugs to insure your fuel/nitrous jetting is producing the correct results.Last edited by Injuneer; 02-13-2017 at 10:50 AM.
SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.
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02-13-2017, 12:58 PM #7
I always hear that SD has a better throttle response than a MAF, I asked someone either they had a bad MAF tune and when re tuned in SD the so called lag cleared up, his response was he could tell that the SD was a millisecond faster in throttle response, I didn't even ask...
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02-13-2017, 02:42 PM #8
Awesome info, thanks guys.
1995 formula a4,100,000mi, 10 bolt 3;73,tci 3000,hooker supercomp Lt's,100,000mi,n/w plate w/150 jets, mt/dr's.,a few more bolt ons. 12.70's/105. 11.60's/118
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03-17-2017, 01:25 AM #9
@MoeHorsePower, I know this thread is a little old, but do you do tunes in SD? Or only MAF?
1996 Camaro Z28-Built engine project car
1994 Camaro Z28-Bolt on project car
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03-17-2017, 06:49 AM #10
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