s346k

iTrader: (4)

mods: cc503 cam, long tubes, crane gold 1.6 rrs on an otherwise stock 96 lt1 (impala ss motor).

how would this engine perform with only af adjustments, resulting in a fairly uniform 12.1 or so afr...? seems very rich to me, as all of my stuff was tuned 12.8 or so to max tq, then 13.1 to the limiter.

asking because we had the engine dynotuned and only the afr was addressed. the before and after was roughly a 15 whp gain...with regard to afr, the stock tune wasn't that far off, just a bit lean.

this tuner made 3 pulls with a total time investment of roughly 1 hour. i am very disappointed. we pulled the boat anchor 350 out of this thing and swapped in a cammed lt1 to gain power, mileage, and efi. it is noticeably more powerful than before, but gets terrible mileage and doesn't perform anywhere close to its potential.

My95Z

iTrader: (8)

If no timing adjustments or even just idle speed adjustments were made the car will perform sub par and get poor mileage as well as drive pretty bad. You would see great mpg and drivability gains with a proper tune where BLM cells, timing, idle speed, and other areas were properly addressed.

Is their a reason why they were shooting for the rich PE afr?

s346k

iTrader: (4)

no reason that i know of. what gets me is...this guy is a fairly well respected lt1 tuner around here. this wasn't his first rodeo.

it will surge and stall from time to time when coming to a stop. we purposely chose a small cam so it would be easy to drive.

i think i am going to purchase software and tune it myself. i can purchase software and a wb o2 for < or = to the price of another tune. then i'll know it's right. i'm not a perfectionist, but damn close...the way this thing runs now is unacceptable.

nitrous2fast

iTrader: (2)

Well when tuning the A/F is always addressed first. After that timing comes into play.

This is a simple way of thinking but bare with me...

Think of the A/F as the torque maker. if running the "optimum" A/F the engine will make generally "in the area of" the best torque.

Now think of Timing as the torque modifier. If less torque is required less timing is needed. Now if timing is a torque modifier it has to be a HP modifier because HP is ***tq/sec.

If the timing is never touched then the engine will never make the torque it should and also not make it as quickly(HP).

Something else to think about. say you need to make 120 lb/ft of torque to maintain 60 mph. now lets say that at 1800 rpms, A/F 14.7, 35* timing, and 200 gps of airflow the motor makes 120 lb/ft of torque. now you want to get better mileage. adding a few degrees of timing and now with 1800 rpms, a/f of 14.7, and 37* timing, and 180 gps of airflow the motor now makes 120 lb/ft of torque. The same torque is made but less air enters the motor. Thus giving better fuel economy but resulting in no power loss. This is generally done until the motor starts the go the other way and starts requiring more pedal/airflow to maintain the same rpms. This is generally very time consuming.

My95Z

iTrader: (8)

That is a pretty poor tune, I'd be upset too.

The cam isn't that small, if it were near stock cam size I could then see maybe skipping the timing tables (still not preferable) but this just makes no sense. Part throttle/cruising should always be addressed before any power tuning is done.

gregrob

iTrader: (8)

That person is not a tuner. A monkey could change WOT AFR. It's easy.

Getting a factory level calibration with a lot of added HP is not easy however and it takes some time. I hope you didnt pay him much.

Wicked94Z

iTrader: (26)

If this is just a cam only motor I'd go as lean as 15.5:1 at cruise and add timing until your manifold vacuum peaks (maximum depression rather). It's helpful to find a nice long stretch of flat highway, compare datalogs over the same stretch of road at different speeds to get your cruise A/F nailed down at different RPM and speeds. That cam isn't too big, you can really lean out the idle as well with no adverse affects on idle quality, plus the leaner you go off idle the less surge you'll tend to have in light throttle conditions.

s346k

iTrader: (4)

i agree with lean cruising. i've sat in on a few ls cars being tuned on the street. they did the same thing, more or less. i am just wondering how much power/mileage was left on the table due to the poor tuning. we will see, i guess. thanks for the responses, guys. i feel better about using an lt1 for the tuning guinea pig. maybe once i get somewhere with it i can fire up hptuners on my lsjuan.

Wicked94Z

iTrader: (26)

At small throttle openings, gasoline doesn't lose much power when you lean it out past 1.00 lambda.

(Desired A/F - Current A/F) / Desired A/F = Theoretical change in fuel consumption

One of the problems I'm having with E85 and mileage... If I go from .90 lambda to 1.05 I can feel a very noticeable loss of torque, granted I'm cruising at 50+kpa which isn't exactly a small throttle opening. I have the advantage of real-time tuning which really makes driveability tuning easier.