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#822117 - 09/07/10 05:14 AM The "CHIP" and it's secret revealed at last..  
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SS402 Offline
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Beaverton, Oregon
Ok, on carbureted engines the ECM (electronic control module) controls the timing curve, the M/C (mixture control) solenoid and the EGR (exhaust gas recirculation) valve. The timing has the greatest effect on performance since the since the ECM goes into Open loop at WOT and the main jets are supplying all the fuel, open loop means it's not accepting any inputs from the various sensors such as the MAP or Oxygen sensors. Instead it runs on a preprogrammed calibration chart that's stored in the ECM's ROM (read only memory).
This is where the CHIP comes in, it modifies the timing curve the same way we would do on a performance engine with a non-CCC distributor by changing the springs, weights, center plates and using adjustable canister to custom tailor the timing curve. Stock slow revving engines enjoy long and slow timing curves while fast revving performance engines enjoy short and quick timing curves.
A stock engine may have 8* initial timing, 23* centrifugal and 25* vacuum totalling 56* total timing whereas on a performance engine we would use more initial with less centrifugal and much less vacuum advance like this: 18* initial + 18* centrifugal + 10* vacuum thus totalling 46* total timing. Notice the timing curve for the performane engine is much shorter compared to the stock engine (56* vs 46*). Now all we have to do is adjust the spring rate in the centrifugal advance to be "all in" sooner or later, the stock engine is going to enjoy the heavier springs while the performance engine might enjoy the medium springs or a combination of heavy and medium or medium and light.
This is why there is usually Stage I, stage II and stage III chips. Each one has a more aggressive timing curve from mild to wild and unless the engine has been modified enough your not going to tell the difference, the preset timing curve in the SS ECM is fine for the engine in stock trim but as mods are made and the engine is built to rev faster the timing curve will have to be altered to follow suit.


George
Monte, Gone but not forgotten

The More I Learn About Dogs
The Less I Like About People
#822131 - 09/07/10 11:07 AM Re: The "CHIP" and it's secret revealed at last.. [Re: SS402]  
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Duts87SS Offline
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I wouldn't say that the timing curve gets "modified" as there is a timing table on the ROM/chip that the ECM uses regardless of open or closed loop.


Dustin
87 SS
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#822132 - 09/07/10 11:18 AM Re: The "CHIP" and it's secret revealed at last.. [Re: Duts87SS]  
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Duts87SS Offline
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And here it is:


Any RPM after 3600 uses the number in the corresponding 3600 cell. Ex: 4750 RPM & a MAP reading of 90 yields 27* of timing.

All of these numbers also assume that the physical initial timing of the engine is the same the initial timing on the "chip". Adding two degrees of initial timing to the engine without changing anything in the ECM will add two degrees to all the cells in the table above.


Dustin
87 SS
[Linked Image]
#822179 - 09/07/10 05:18 PM Re: The "CHIP" and it's secret revealed at last.. [Re: Duts87SS]  
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SS402 Offline
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Interesting.. i had never seen the actual map but had pretty good idea of it's layout, a mechanical advance would be hard pressed to operate as smoothly as the computer, it literally adds +/- 1* advance per 100rpm until it reaches 2400rpm then adds 4* @ 3000rpm and is "all in" by 3600rpm with almost 36* total timing.
I assume it's based on 10* inital..

I might add that the CHIP does not alter the operation of the EGR valve, it operates the same way as it would on a non-CCC engine. It opens the EGR valve during periods of high manifold vacuum and closes it during periods of low manifold vacuum, it opens the valve at idel speeds and cruise and closes it during acceleration and WOT, the ECM knows when to open and close the EGR valve VIA the MAP sensor. If the EGR valve opened during periods of high engoine load the spent exhaust gases would contaminate the air/fuel mixture and reduce power, that's the reason we close it when the gas is mashed.


George
Monte, Gone but not forgotten

The More I Learn About Dogs
The Less I Like About People
#822268 - 09/07/10 10:52 PM Re: The "CHIP" and it's secret revealed at last.. [Re: SS402]  
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Gruvin Offline
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Originally Posted By: SS402
Interesting.. i had never seen the actual map but had pretty good idea of it's layout, a mechanical advance would be hard pressed to operate as smoothly as the computer, it literally adds +/- 1* advance per 100rpm until it reaches 2400rpm then adds 4* @ 3000rpm and is "all in" by 3600rpm with almost 36* total timing.
I assume it's based on 10* inital...
the stock design is 6 degree initial


My first SS! Sold Jan 2004
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#822301 - 09/08/10 12:18 AM Re: The "CHIP" and it's secret revealed at last.. [Re: Gruvin]  
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BuzzLOL Offline
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.. Hopefully the newer tables keep on adding a tad of timing above 3600 RPMs... since dyno runs have shown benefit...


'86 Monte LS (total'd Fall '2013), '87 GTA TransAm TPI350 TH700-R4, '85 Fiero 5-speed, '75 MG Midget Buick Alum.V8 BW 5-speed manual, '77 Pontiac Astre Formula wagon 5-speed posi, '78 F150 4WD 351"M ==> 400" C6, '79 Caddy Seville Olds EFI 350" TH400, 19' Slickcraft 425HP 351W MerCruiser I/O
#822406 - 09/08/10 11:03 AM Re: The "CHIP" and it's secret revealed at last.. [Re: BuzzLOL]  
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Duts87SS Offline
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Spanish Fort, AL USA
I doubt there are any .bins for the CCC setups that have a table for anything above 3600 (unless someone modifies the code, of course). The TPI .bins only read to 4500 or 4600 (again, unless using modified code).

Also, just to elaborate, the columns to the right are for high load or WOT. The far left column will probably only be used for deceleration. My car with a 383, AFR180s, and Comp 268XFI roller cam idles at around 55-60kPA. Stockish would probably be 45-50.


Dustin
87 SS
[Linked Image]
#822506 - 09/08/10 08:41 PM Re: The "CHIP" and it's secret revealed at last.. [Re: Duts87SS]  
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PA
I was lost after reading the very first post think

It's too bad really since I'd love to learn the basics of tuning. I've tried reading about it over at TGO, but 95% of the posts are from people with as much knowledge as me (none) and it's way too hard to weed out the BS from fact to even get started.
Too bad they want so much for a basic tuning CD through Summit/etc frown

#822513 - 09/08/10 09:10 PM Re: The "CHIP" and it's secret revealed at last.. [Re: rons87mcss]  
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200kSS Offline
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Quote: "I might add that the CHIP does not alter the operation of the EGR valve."

I gotta disagree there. I have a GMPP "ZZ4" CHIP in my 88 ecm and there is no egr valve within 20 feet of the car. After installing said chip, the infamous code 53 went away, hopefully forever.


88 SS Black/Oxblood. Power Tour car
80 Malibu 2dr. Drag Week car
#822568 - 09/09/10 12:49 AM Re: The "CHIP" and it's secret revealed at last.. [Re: 200kSS]  
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86ttop Offline
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Just an FYI, there is no vacuum advance at WOT.


Leo Paugh
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#822612 - 09/09/10 03:50 AM Re: The "CHIP" and it's secret revealed at last.. [Re: 86ttop]  
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85_SS Offline
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EGR duty cycle is controlled by the ECM through a solenoid mounted on a bracket next to the distributer.


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#824039 - 09/14/10 11:43 PM Re: The "CHIP" and it's secret revealed at last.. [Re: 85_SS]  
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I could re-write the table.. (.bin) file..If its not copyrighted of course. Anyone have the ability to get into there stock computer?


1986 Monte Carlo SS, White/Maroon, SBC 350 w/ Patriot Vortec Heads, True Duals, MSD HEI Digital Ignition, Edelbrock Cam & Carb, Electric Fan, TH350 w/ Street Shift Kit w/Cooler, Shaved Doors, Sunroof,HUD Speedo...
#824113 - 09/15/10 04:23 AM Re: The "CHIP" and it's secret revealed at last.. [Re: WorkinprogreSS]  
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Gruvin Offline
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Originally Posted By: 32v_dohc
Ok guys lets clear up some misconceptions.

First the CCC carb ECM handles spark by going to a VAC X RPM table and selecting the right main advance. This advance is then modified for coolant temp, the difference between the cold start temp and present CTS, a barometer vs map term and a highway mode term. Then it trims to max spark if the sum of all exceed the max allowable spark. That is what goes to the distributor if there is no knock. Nothing more, nothing less. If it senses knock there are tables for the attack rate, recovery rate and max retard for both WOT and Non-WOT. Go to moates.net filemanager and download $40.zip. It is the CCC carb ECM Hack. It has my name at the top wink

GM created several knock sensors to help zero in on the characteristics of the different combonations of bore size and head material type. They did this exclusively to sense the tiniest bit of knock so that they could be right on top of it for controlling NOX emmisions. ANY knock sensor will do an acceptable job of protecting the engine assuming you are in the right ball park on the fuel side. NOS and crazy rich make sounds no knock sensor can hear.

Sorry Chris but EGR doesn't do anything but reduce NOX. Every case I have played with EGR has reduced mileage and torque. For a stock engine I would probably keep it but for an engine with a non stock cam I would let it go if I could.

Bigger engines need nothing in the way of changes to perform well. Changes to ignition timing to match the cam are helpful with long cams that don't have appropriate compression. One thing that can bite you on the carb is bigger engine bog less. This means air valve tension can be dailed back. The tension on the carb controlls vacuum under the valve and has an effect on secondary fuel flow. Less tension equal less fuel. Richer rods may be required on max effort 400's. For the most part a stock carb from a 305 will bolt right on a 400 with no other changes and perform well.

HTH

John
originally posted here on this site in 2006


My first SS! Sold Jan 2004
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87 SS bought 9-5-04: Sold 6-18-2010 - project 87 finds a new home with another undisclosed MonteCarloSS.com member!

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