hi all

i´m running a 396 with SP EFI, 234/238 112LSA .565lift cam...

i managed to tune out idle, WOT is fine...

my problem...when i cruise slowly with low throttle, like 35mph with 3rd or 4th gear with about 2000 rpm, the engine doesnt run smooth, exhaust gets a strange sounding note, with some gurgling, aso
BLM´s are fine...124 to 130

when i get on the throttle, the engine smoothes out...

is this just the nature of the beast, cam surge, or can i do more to minimize this?

thank you

 

Are you running closed loop? If so, try open loop and richen the mixture a tad.

In closed loop, low rpm & fairly large cams; the "switching" between lean/rich can cause that surging you are mentioning. This is why a number of guys SWEAR by open-loop and tune for the AF ratio they prefer.

In open loop, the ECM doesn't "swing" back & forth between rich & lean and usually runs much smoother.

 

This bin towards the bottom of the page here, http://www.bfranker.badz28.com/LT1Edit/LT1files.htm (Phil Tobins 401) was for a 401 that ran 10's. He had a MUCH bigger cam than you or I do. But he tuned it for closed loop. I dont know if you can read the bin, but it is a DA2.

 

Hi

i´m running closed loop, but maybe my 42# injectors are just too big for low cruise condititons..maybe i change them to 30#, but i hope it wont throw off the whole calibration...

at the other hand, i get stable idle with the 42#´s

thank you

 

Hi Steve!!

i have read the .bin, looks nothing special...

a few things...

its a 401, but the cylinder volume is set to 713cc´s
injectors look small at 23.4#/hr
volumetric efficiency seems to be low at the whole table...

interesting, isnt it?

 

Intersting it is only for a 5.7 litre and 24# injectors. Maybe this isnt the bin he used in his 401, and it was just his base LT1 when he had a ZZ9 cam.