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Just wondering if there are any experienced guys who tuned tbi big blocks from the 90’s?
working on a 95k3500 dually. Its a 7427 with cam intake headers exhaust etc
curious as to what overall wot timing is being seen for these trucks? Stock bin i am using, and several others i found show fairly low timing at wot. 22-24 deg peak it seems give or take a few. From other bbc’s i have seen in carbed apps i thought they took alot of timing to make max power like 35-38 deg?
I havent done tbi stuff so just wondering does this seem normal? I assume its way low to account for tow loading. But alot of the lower kpa stuff is 39-48 deg or so. Seems odd but i understand towing may change this
i got air fuel in mid 12’s at the moment and during the pull i have 27-28 deg commanded but log seems to drop to 24-25 when in pe mode and doesnt seem to move much. I dont understand why or where this is coming from. I dont believe there were any subtracters in effect at the time. In the high 3000 to 4200 rpm range it did tickle the knock retard for split second, sub 1 deg but quickly disappeared. Other times it did nothing so didnt expect to see less timing than commanded. Perhaps these tbi heads really dont like alot of timing? I am debating on leaving wot timing closer to stock since the truck does pull a camper trailer. Everywhere else timing seems ok normally driving. Need to do another wot run but so far i am happy with it normal cruise driving
idle
also found it odd that i cant get good timing in at idle without it idling way high. Iac is 0 counts and i have to command 5-7 deg to idle 900-1000 rpm. Air screw in throttle body is adjusted to idle as low as possible. I thought maybe with cam and intake manifold its breathing, drawing hard on the induction system, and somehow the throttle is passing to much air somewhere and cant lower idle rpm. Maybe a leak but doesnt seem to be. Motor top end is all fresh and stock 454 tbi unit. Its happy tho but i would have liked to see 12-16 deg atleast. Oh well?
Have you checked idle with a dailback timing light? Your timing could be higher than what your're seeing. Also if you messed with the spark bias you could be at +/-9.8 degrees. Also high idle like that usually points to a vacuum leak. If you're using an adapter on the intake and TBI make sure the screws aren't going through the adapter and pushing it up.
There is a PE knock retard but it should only be at the start of PE. And you may just be at a higher map range giving you that lower timing. I'm going to say the usual - every engine needs something different. You should try out different timings and see what it likes...but you're probably in a safe range or maybe can add a few degrees before you get knock while towing.
Have you checked idle with a dailback timing light? Your timing could be higher than what your're seeing. Also if you messed with the spark bias you could be at +/-9.8 degrees. Also high idle like that usually points to a vacuum leak. If you're using an adapter on the intake and TBI make sure the screws aren't going through the adapter and pushing it up.
There is a PE knock retard but it should only be at the start of PE. And you may just be at a higher map range giving you that lower timing. I'm going to say the usual - every engine needs something different. You should try out different timings and see what it likes...but you're probably in a safe range or maybe can add a few degrees before you get knock while towing.
have not used a dial back light on this, guy only had a regular light. We went over timing 2 times. I did not change any spark bias so i dont think commanded would be different than actual. I can bring a dial light tho and see
engine top end was fresh assembled so i dont think any vacuum leaks are present but who knows. I personally didnt check but the guy assures me there are none. Truck seems very happy so thats good but just wish i had more references to go on
Thats pretty nice. I used my standalone wb to do initial tuning in open loop then enabled the narrowband for closed loop
truck has been running fine, needs a bit more cold weather tuning. Cold start idle was abit rough. Other than that everything else seems ok. Just curious on the timing for these things is all.
10-26-2018, 09:32 AM
