Adjusting VE table bigger cam/heads..values lower now at low rpm? Normal?
11-16-2007, 09:24 AM
#1
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Adjusting VE table bigger cam/heads..values lower now at low rpm? Normal? Had a TR224 cam on a 112LSA and now have a 228 cam on a 115LSA. Also had the stock LS1 heads swapped for Patriot LQ9 heads (72cc).
Car was previously tuned in MAF mode, but was running a rich AFR in the 20-60range at 1200RPM-3200RPM on the VE table. LTFT's were -5 to -10 on average. The tune was very safe, but left a lot of HP on the table. I am comfy w/ speed density, so swapped from MAF mode to SD and began tweaking the VE via fuel trims in closed loop (I'm too much of a puss to put it in open loop and use the AFR equivalence ratio in case I screw up
).
So......what I've noted is that the Ve table is shaping so that there is "less volume" at low throttle setting from idle to 3200RPM. Talking like 10% less than stock values in the cells. The upper end is a good 20% gain in flow. Also have a turbo, so the 100-105kPA numbers are higher still.
Seems odd to me that w/ 9.1 CR heads and a bigger cam I'd be telling the car that the VE is lower in the low RPM band. Seem right to ya'll? I'm asking in general. Will post logs, but wil not post the tune. Past exerience is that people take the tune.....and never leave feedback!
BTW, have MotoTron 60's and a return fuel system conversion. Injector duty cycle never peaks beyond 70%
Anyhow...seem normal? Opinions appreciated.
Car was previously tuned in MAF mode, but was running a rich AFR in the 20-60range at 1200RPM-3200RPM on the VE table. LTFT's were -5 to -10 on average. The tune was very safe, but left a lot of HP on the table. I am comfy w/ speed density, so swapped from MAF mode to SD and began tweaking the VE via fuel trims in closed loop (I'm too much of a puss to put it in open loop and use the AFR equivalence ratio in case I screw up
). So......what I've noted is that the Ve table is shaping so that there is "less volume" at low throttle setting from idle to 3200RPM. Talking like 10% less than stock values in the cells. The upper end is a good 20% gain in flow. Also have a turbo, so the 100-105kPA numbers are higher still.
Seems odd to me that w/ 9.1 CR heads and a bigger cam I'd be telling the car that the VE is lower in the low RPM band. Seem right to ya'll? I'm asking in general. Will post logs, but wil not post the tune. Past exerience is that people take the tune.....and never leave feedback!
BTW, have MotoTron 60's and a return fuel system conversion. Injector duty cycle never peaks beyond 70%
Anyhow...seem normal? Opinions appreciated.
11-16-2007, 10:56 AM
#3
Before doing VE tuning, when I'm getting a tune ready for a setup for first startup, depending on the cam size, I may pull as much as 40% out at 400 RPMs, 20-30% at 800, and 10-20% from 1200 from the VE to help them startup and idle without being blubbery rich.
11-16-2007, 07:35 PM
#4
Cams with positive overlap always reduce VE in the lower RPMs, and increase VE in the upper RPMs. ALWAYS. By nature, they decrease the VE of an engine until they get into their "zone" and then they increase VE. Its the trade off. Want the best of both worlds? Go get a Vtec!!
11-17-2007, 11:38 AM
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Cams with positive overlap always reduce VE in the lower RPMs, and increase VE in the upper RPMs. ALWAYS. By nature, they decrease the VE of an engine until they get into their "zone" and then they increase VE. Its the trade off. Want the best of both worlds? Go get a Vtec!!
This confirms what I've been seeing. Makes me feel better having a 2nd opinion
. Thanks. 