I have just had the air pump and precats removed and a new perfomance main cat installed. Rear mufflers are straight through supercat The inlet plenum and runner tubes have been ported and polished. Heads shaved with higher compression (98 Octane fuel). The air box has been opened up, K&N air filter installed, maf screens removed, IAT (MAT) relocated to the air box, power pipe and air foil installed. Also new temp switch installed in LH head in parallel with ECM to run the engine cooler (180 deg F, 82 deg C). Coolant has also been bypassed from the throttle body. Turbo 700r Trans is also now getting a stg2 shift kit and a 2500 histall.

I am wondering now whether retuning is worthwhile. Any extra performance to be gained? Appreciate any information.

 

Not really
The MAF on your car will adjust for any increased air flow which probably won't be a a lot until you put headers on to cure the weak L98 exhaust.
However
the factory tune is " mild" to accommodate a range of different driving styles.There are things that can be changed in the tune for someone who wants to drive more aggressively .
You can also change fan operating temp / delete VATS and EGR / change TCC lockup speed/etc when you get a custom tune

Read
http://temp.corvetteforum.net/c4/vader86/minormods.html

 

[QUOTE=rodj;1574571456]Not really
increased air flow which probably won't be a a lot until you put headers on to cure the weak L98 exhaust.
/QUOTE]

I thought by getting rid of the old cats and putting a single hi-flow cat that that should be enough. The rear mufflers are straight through supercats also. I can do the headers if it is worthwhile.

 

If the 87 BIN is anything like the 89, the timing curve really sucks. More mid range timing really wakes it up. Mine went from just chirping the tires on launch to smoking them.

 

I am not familiar with tuning terms. What does BIN mean? Is there a good chip or tuning package people use?

 

I guess bin is short for binary which is a string of bits which represents the code for programming the computer settings.

 

In simplest terms
The computer (ECM ) has a chip ( memcal ) in it and on the memcal is the tune ( the BIN ) which contains the info for running the engine.
With the right equipment any of these operating parameters written on the BIN can be changed as required

There are many different BIN's even (at least 17 for '87 Vette ) for the same engine/ model / years
They are identified from the factory by a 4 letter code (Prom BCC codes )
When talking ; guys refer to the tune they have by this code so they would say
" I have a ARAP BIN"

Some tuning reading
http://www.thirdgen.org/techboard/di...uide-book.html

 

Thanks.

Are there any recommended tunes for my vehicle here or is it a matter of every one does there own thing? Why are the preconfigured chips a waste of money?

 

Ultimately once you reach a certain point you get mods done to suit your car.
The off the shelf chips are too generic; one size fits all so all they tend to do is turn the fans on sooner and play around a little with fuel / spark settings
With a MAF car like yours you can go a long way with bolt on mods on a stock tune but as I noted above there may be some operating things like fan on temp you may want to change

 

Tuning is a very specialised thing though appears relatively cheap and simple to start playing with (bit like chess).

Is there a "soldiers 5" on getting started with tuning the L98? Even a list of parameters with a description and typical settings would be useful. Also a description on how the system works would be useful.

With the problems I am currently having with my transmission I discovered for instance that the gear changes are controlled hydraulically (not via the computer) in association with the TV cable from the throttlebody.

Is the spark advance / retard totally under the control of the computer?

My radiator fan is already initiated at a lower temperature (180 deg F, 82 deg C) from a newly installed temp switch in the LH head which is wired in parallel with the ECM.

 

The 4L60E ( same as T700 / 4L60 but electronic version) used in the later C4's has computer control of trans like Commodore

Your '87 has the main fan controlled by the computer and the Aux fan in front of radiator ( if fitted ) controlled by a switch in the LH head.
The computer gets engine temp from coolant temp sensor (CTS ) located at front of intake under TB.Not to be confused with the coolant gauge sender unit in RH head which only operates the gauge.
That is why when scanning a car it is possible to see a different temp on the scanner to what is shown on gauge because they are getting readings from different sources
There are many ways to bypass the computer control and have a mech temp switch control fans

Correct and totally adjustable in the tune

 

Computers are identified by the last 3 digits of the GM part #; yours is #1227165
These are guides for other GM computers but the system basics are similar to the "165" computer used in yours.
Note ;These are MAP systems that use a vac sensor so references to Kpa ( vac ) don't apply to yours which is MAF (mass airflow ) which measures airflow

http://www.diy-efi.org/gmecm/ecm_inf...730/qanda.html
http://www.diy-efi.org/gmecm/papers/tunetip.html
http://www.diy-efi.org/gmecm/papers/prog_101.html

165 specific stuff
http://www.thirdgen.org/techboard/po...148-post1.html

What is needed for tuning
http://forums.corvetteforum.com/c4-s...d-to-tune.html

 

Thanks a lot.

The first step is understanding what the acronyms for the parts, systems, transducers and the tuning parameters are:


General
CID - Cubic Inch Displacement
FSM - Factory Service Manual
GM - General Motors
GPS - Grams Per Second
KPA - Kilopascals
MPH - Miles Per Hour
PSI - Pounds Per Square Inch
RPM - Revs Per Minute
CWHP - Crank Wheel Horsepower
AWHP - At Wheel Horse Power
RWHP - Rear Wheel Horsepower
RPO - Regular Production Options
OEM - Original Equipment Manufacturer
ATDC - After Top Dead Centre
BTDC - Before Top Dead Centre
TDC - Top Dead Centre
VE - Volumetric Efficiency

Parts
CSV - Cold start valve
SBC - Small Block Chev
T700R / 4L60 - Turbo 700 automatic transmission
TB - Throttle Body
TCC - Torque Converter Clutch
D36 - Dana diff
L98 - C4 engine

Systems
EFI - Electronic Fuel Injection
TBI - Throttle Body Injection
TPI - Tuned Port Injection
VATS - Vehicle Antitheft System
EGR - Exhaust Gas Recirculation
TPI - Tuned Port Injection
ESC - Electronic Spark Control
EST - Electronic Spark Timing
FPR - Fuel Pressure Regulator
IAC - Idle Air Control
HEI - High Energy Ignition
HVAC - Heating Ventilation and Air Conditioning
OBD - On Board Diagnostics
PCV - Positive Crankcase Ventilation

Sensors
CSITTS - Cold start Injector Thermo Time Switch
CTS - Coolant Temp Sensor (also known as CST)
MAF - Mass Air Flow
MAP - Manifold Absolute Pressure
O2 - Oxygen Sensor
TPS - Throttle Position Sensor
IAT - Inlet Air Temp (same as MAT inlet manifold air temp)
VSS - Vehicle Speed Sensor
EOT - Engine Oil Temp

Settings & Parameters
AFR - Air Fuel Ratio
BLM - Block Learn Multiplier
HM - Highway Mode
INT - Integrator
WOT - Wide Open Throttle
PE - Program Enrichment

Computer stuff
ALCL - Assembly Line Communication Link
PROM - Programmable Read Only Memory
BCC - Broadcast Code
BIN - Binary
ECM - Electronic Control Module
PCM - Powertrain Control Module

Then I need to find out where the parts, systems, transducers and ecm are.
Then I need to understand what they do, how they do it and why.
Then I need to know what the normal settings are.
Then I need to get set up datalogging and facilitate reading/writing from the ECM
Then the hard part begins. What to change? On road testing.

Could be a while before the fun begins! By fun I mean improved performance.

 

What I have learnt so far for the 87 L98: 240 hp(179kw) @4000rpm, 340 ft-lb @ 3200 rpm('85-'90), 5737 cm3, 101.6 x 88.4 mm bore, 16 valves, compression 9.5, 0-60 mph : 6.3 sec, quarter mile 14.75 sec @95mph. It has aluminium 128 heads and a roller cam. Curb Weight : 3280-3320 lbs (1500kg).

It has a hydraulically operated 4 speed with overdrive turbo 700 auto trans (3.06, 1.63, 1.0, 0.7) with a lockup converter (soon to be stg2 with 2500 histall). The diff is a 7.875" dana model 36 (need to see if G92 is listed on RPO. If so it already has the desirable 3.07 diff gears vs std 2.59)

Roller Cam specs are CAM 87 L98 14093643 Dur In/Exh 294'/294' Dur@.050" 202'/206' Lift (w/1.5 rockers) .403"/.415" LobSep 114.5'.

My computer is identified by the last 3 digits of the GM part #; mine is #1227165. The "165" computer is used in the 87 vette.

There are many different BIN's even (at least 17 for '87 Vette ) for the same engine/ model / years. They are identified from the factory by a 4 letter code (Prom BCC codes ) eg ARAP

The MAF will adjust for any increased air flow which probably won't be a a lot until I put headers on as part of curing the weak L98 exhaust.

The timing is setup with a standing 6 deg BTDC and the ecm takes over from there. It may be worthwhile changing this to 8 deg BTDC.

The factory tune is " mild" to accommodate a range of different driving styles.There are things that can be changed in the tune for someone who wants to drive more aggressively . I can also change fan operating temp / delete VATS and EGR / change TCC lockup speed/etc if I get a custom tune

 

What exactly is TCC lockup speed? I thought we had concluded the ECM didn't control the auto transmission for my vehicle!