Tedd

1995 5.7 4WD auto E/OD GT4 Suburban:

I have replaced the original 5.7 motor with a 355 c.i. split rear oil seal short block, a Crane cam [part # 113931] with intake lift at valve .440" and advertised duration of 266° and exhaust lift at valve .454" and advertised duration of 272°, a pair of 23° twisted wedge Trick Flow heads and Flow Tech shorty headers with O2 sensor coupled to 2 1/2" dual exhaust with dual cats and mufflers and no crossover tube. The motor is topped off with some 8mm ignition wires. The rest of the motor and car is bone stock.

After chasing down a code 43 and correcting that problem, I timed the engine at 0° as stated on the fan cowling with the timing connector disconnected. The performance was nill and the poor thing would barely get around the block. I discovered your site and read about 1500 threads on timing and decided to try 6° BTDC. That was a big help but something is stil not quite right. The motor has instances of good power but seems hampered by something. It seemed like bad ignition wires[sometimes hitting, most of the time not] so I put on the 8mm afore mentioned, with not much change.

The motor makes more power than the stock motor but something is wrong, occasionally back fires in the intake manifold, but not consistantley. Its as if the computer is still searching for the correct settings? After I retime the motor I am resetting the ecm buy removing the ecm fuse at the fuseblock under the hood. As I understand the system, the motor warms up and needs twenty or thirty minutes of running time to build enough data to run the motor correctly, could this poor performance I'm experiencing be because there is not enough data stored to operate correctley?

This was originally a Summit Racing Tow motor, when I bought it from Summit [original lower end was bad in the summit motor so I aquired another short block and used their heads and cam and sent back to Summit the bad bottom end].

I am running the factory memcal at the moment but have a Jet stage 2 prom in the mail, I'm hoping this will cure the problem or at least help. I would also like someone to explain to me why the stock motor is timed at 0° but the new motor doesn't work at that setting, It seems as though the computer would compensate for the cam and the heads by advancing thr timing automaticley until pre-detonation is detected? But that is obviosley not the case! What is the highest timing setting I could use. As I said the motor is in a Suburban used mostly around town and for towing.
:hail:
All help and any replies will be greatley appreciated:

Happy memorial day to all: Remember our fighting men and all those who made the ultimate sacrifice so we could live in FREEDOM!!!

Regards,
Tedd Edmondson
tedd319@swbell.net

NJ SPEEDER

the stock motor was timed at 0 to deal with the small cam and an expectation of low octane fuel. also the stock motor had iron heads, which can not handle as much timing advance.
your new combo with a larger cam will need a little more ignition lead to get the entire fuel charge burned off properly and well as the aluminum heads you added allowing for a little more timing. 6 degrees of base is acceptable on a stock cam, with your cam i would think you could go to 8 or 10 degrees of base timing as long as you run good gas.
any dead spots you feel in the runnign of the engien are most likely lean spots in teh air/fuel mixture. with the increased air consumption of the motor the respective amounts of fuel must also be raised. if you look in the tech articles at teh ultimate tbi mods and the diy adjustable fuel pressure regulator you may be able to find your answers for the air/fuel nees of the motor.
the ultimate tbi mods will get more air in to allow those cam and heads to breath easier adn the diy afpr will help to balance out your new fuel needs when you raise the pressure a little.

later
tim

Pablo

iTrader: (1)

you need a custom chip it will never run right without one

Pablo

iTrader: (1)

oh and the computer never really "learns" a new combo. It makes attempts to adjust for part throttle operation but can only do so much and it also doesnt adjust timing unless it sees knock wehre it will just retard the timing at a preset amount just to save the engine.

It doesnt even try to do this at wide open throttle... Your engine is getting the same amount of fuel in the same curve and the same amount of advance at the same curve at wot as your stock engine maybe a little more fuel depending on some other things that im not gonna get into but rest assured its not running anywhere near right and a Jet "stage II" chip wont do it

Tedd

If the Jet stage 2 chip wont help what chip will? What do you mean buy custom chip

Also I've read a little about winalde (sp?) software. I'd be interested to know more about that.

NJ SPEEDER

ifyou wanna learn more about custom chips and chip tuning you will wanna check out the diy prom board. those guys have it down pretty good and can guide you in your process.
if you have a laptop and the wiun aldl software you can record the data as ytou drive around, then just make changes to the chip to compensate where teh ecm can't.

later
tim

RICH92RS350

If you don't want to burn your own chip for whatever reason,
(the best method if you're able) the next best thing IMO
is a custom chip from Ed Wright at Fastchip.com.
Very satisfied with mine.
About $350.
-Rich-