I have a 96 lt-4 383 stroker, 6 speed, 345 gears, Hot Cam, Ram Air, BBK 58 mm TB, NOS 30# injectors, adjustable fuel pressure regulator, new NGK plugs, new Taylor wires, Magnaflow mufflers with custom 3 inch cat back exhaust (cats hollowed out), Custom PCM programing with LT1 edit and logging with auto tap. The problem I am having is in first gear at a 10mph punch at half throttle the 315 35 Eagles start to break lose but as soon as I hit full throttle the wheels seem to catch. The car seems to have more power at half throttle than full. It doesn't seem to bog down when I hit full throttle just not as powerful as at half. Any one ever had a similar problem? Any information would be appreciated.
Michael


[Modified by meyre1, 3:24 AM 3/22/2003]


[Modified by meyre1, 3:25 AM 3/22/2003]

 

Forgot to check reply e-mail. :banghead:

 

can you tell me what the O2 sensor voltages are at wot? how about knock sensor counts?

something you can do in order to eliminate a possible variable... make the whole timing table from 1/4 throttle onward the same as what you now have at wot. if it still feels really strong at part throttle in comparison, then you probably need to concentrate on the fueling.

something else to consider, a 58mm tb is a lot of area, even at part throttle. it effectively makes it wot well before you're actually at wot. this tends to make cars seem really powerful, since they squirt hard with not much throttle. then, when you finally mash it, it doesn't feel any stronger, so there's a sense of disappointment. (this effect is exacerbated by having more cubic inches.)

lastly, maybe you should have it dynoed (and do a wideband, while you're at it). this will give a clue as to how far off the power is. if it's in the ballpark, you can chalk it up to a faulty butt dyno.

 

:iagree: Get it dyno'd and take a look at the power band.

 

Very definitely. A 383 that makes peak power at 6500 RPM, assuming 110% volumetric efficiency, only need 792 CFM. A 58mm TB will flow 1025 CFM, which is WAY too much for your motor. A 52mm will flow 825 CFM, which would fit quite nicely.

 

two things-

1. the PCM does not use O2 or MAF sensors at WOT, it hops into closed loop.
I would suggest checking your closed loop tuning

I know my open loop tuning is iffy but my closed loop is nice.

if i go 90% throttle my car pulls ok
100% and its like the power trippled :steering:

 

Open loop is when it doesn't look at the O2 sensor...open loop means no feedback. In other words, when the engine goes WOT, it goes OPEN loop.

 

i'll never remember which one is which if my life depended on it :cuss

 

the MAF is most certainly used at WOT. it's used all the time.

secondly, WOT is only 50% throttle in the stock programming, so if you feel a difference between 90% and 100% throttle, you have other issues. (like maybe a faulty TPS.)

actually, i just checked my LT4 program, and it only takes 26% throttle to be "WOT" if over 4000rpm.



[Modified by MSR, 9:43 AM 3/23/2003]

 

doesn't the PCM run off preset tabels at WOT? I thought the PCM had 2 different modes-
WOT and non WOT
durring WOT it would use its own pre set tables to fuel and provide spark


Learn something new every day :cheers:


[Modified by TreyZ28, 2:25 PM 3/23/2003]

 

Yes, the ECM does use pre-set tables, but it has to have enough sensor data to know where it is. Normally the ECM looks at the TPS, RPM, MAF (or MAP, depending on whether its a MAP or SD system), coolant temp, and O2. All of the sensors I just listed, except for O2, are front-side inputs (what's coming into the engine), where the O2 is a feedback sensor (what's coming out of the engine). When the ECM is using the O2 sensor to adjust other parameters, it's running closed loop. When the engine is cold (i.e. low coolant temp), it does not run closed loop...it runs off of pre-set cold start tables. When the TPS hits a certain percentage, which MSR stated is 50% on the LT4 stock programming, until 4000 where it only takes 26%. Once the ECM enters WOT mode, it looks at ONLY the coolant temp, engine speed, and MAF/MAP values to figure out where it is and what it needs to do with fuel and spark....it doesn't use the O2 sensor to fine tune everything. Since it's not using feedback control, it's open loop.

When you hear about people running EFI systems with a WideBand O2, the reason for doing this is that they can use the O2 sensor to provide feedback at ALL throttle settings, all the time. Unfortunately, the stock O2 sensors are not capable of that kind of feedback. The one-wire O2 sensors used on the 165 ECMs act as a switch...the ECM sees the O2 input as either "rich of stoichiometric AFR" or "lean of stoich". The NTK L1H1 and the Bosch wideband O2 are the two most popular wideband O2 sensors (the NTK sensor is an OEM Honda unit). The main drawback to wideband sensors is that they require an external controller when the ECM isn't designed to use the WB sensor....the combined retail cost of the NTK sensor and it's control unit is $900. You can see how this gets expensive quickly, especially when you're doing research (we run one of these sensors on every cylinder when doing research).