BLM question

[FUN-9C1]

On my LT1 Chevy Caprice 9C1 with 214k miles, BLMs are very low 120s in the low RPM/low TPS area, up around 140 in the 2600-3200 rpm/55-75 TPS range, and ~128-135 most other places. Is this indicative of something specific? Why so high in the midrange and so low in the low RPM/TPS range? If I use the BLM/128*VE formula to adjust the VE, I end up well over 100% in a lot of VE cells which tells me that something else needs to be taken care of first. The car is a daily driver and I've had it since 2000. I don't do anything special to it, just put gas in it and change the oil once in a while. The motor is stock, just has slightly freer flowing intake/exh. As far as programming, it's basically just shift points, timing, and speedo correction for the 4.10s. The car goes like a scalded cat and runs great, I am just being anal and enjoying trying to dial it right in. Thanks for any tips.

[dave w]

Changing the injector flow to lower number, for example 22lbs lowered to 20lbs will make the all the BLM's shift to a lower number. Likely the BLM's of about 120 will go to about 107 and BLM's of 140 will go to about 130.

dave w

[steveo]

On my LT1 Chevy Caprice 9C1 with 214k miles, BLMs are very low 120s in the low RPM/low TPS area, up around 140 in the 2600-3200 rpm/55-75 TPS range, and ~128-135 most other places. Is this indicative of something specific? Why so high in the midrange and so low in the low RPM/TPS range? If I use the BLM/128*VE formula to adjust the VE, I end up well over 100% in a lot of VE cells which tells me that something else needs to be taken care of first. The car is a daily driver and I've had it since 2000. I don't do anything special to it, just put gas in it and change the oil once in a while. The motor is stock, just has slightly freer flowing intake/exh. As far as programming, it's basically just shift points, timing, and speedo correction for the 4.10s. The car goes like a scalded cat and runs great, I am just being anal and enjoying trying to dial it right in. Thanks for any tips.

those trims are actually completely normal for that car right out of the box. GM often starts fueling out a bit rich or lean on purpose and lets the trims even things out. brand new cars often trimmed ~120 at low rpm. i dont know why you're hitting close to 140 in midrange, but i bet if you actually log an average (see my new tool?) the average trims in that area aren't so high, you're probably just seeing a peak.

is there a bit to gain by tuning it though? probably.

[FUN-9C1]

Thanks guys, glad to know this is pretty normal. I always wondered, if the car learns pretty quickly how much gas to squirt anyway, does it really matter what the BLMs are as long as they are not under or over the limit?

[steveo]

it will usually 'run a bit bette'r when trims aren't too far off and your base tune is closer, due to transitional fueling, wide open throttle, whatever. but yeah during cruise conditions it doesn't matter. in fact on my own closed loop cars i aim for ~120 trims, so it starts a hair richer and leans out during cruise on its own. i find it a bit more responsive that way.