Lars and other timing Gurus.

big2bird

big2bird

Charter Member, Founder Bird-Run, Cruise-In Bird-R
Joined
Mar 5, 2008
Messages
5,719
Location
Anaheim, Ca.
A member would like to do the following:
Use 9.4-1 CR with 10lbs boost, for a (close guess) boosted CR of 15-1
AND, run on 91 octane pump gas.

CAN this be done by detuning to 28* max advance, or is it asking for trouble?
Is there a magic formula, or should we use exhaust gas temp to determine max advance.(The knock sensor already goes nuts at idle), OR,
Is it impossible, and higher octane with 34* advance the real answer.

Superchargers aren't my thing, although I am always willing to learn more.:D
 
big2bird said:
A member would like to do the following:
Use 9.4-1 CR with 10lbs boost, for a (close guess) boosted CR of 15-1
AND, run on 91 octane pump gas. Why the octane restriction? You can get higher than 91 octane at most stations. Higher octane is cheap insurance.CAN this be done by detuning to 28* max advance, or is it asking for trouble? I wouldn't use the word "detune". The whole idea of spark advance is to get the peak cylinder pressure point at 15* ATDC. When you boost it the pressure and temperature goes up, usually resulting in a faster flame front. You don't need as much advance. If you're giving the engine what it wants, you're not detuning it.Is there a magic formula, or should we use exhaust gas temp to determine max advance. It's been my experience that without a WBO2 system, it's real easy to misread EGT. I'd recommend getting one. It'll make life easier. (The knock sensor already goes nuts at idle), What did you do to the engine internals? The ESC system is custom calibrated for each engine configuration (internal noise signature and knock frequency). Excess piston slap against the cylinder walls creates the same noise frequencies as knock. And, seeing as the ESC system can only monitor cylinder noise, not cylinder pressure, it sounds like the ESC module is just being overwhelmed with mechanical noise. Which ESC system are you using? Perhaps a different calibration might give you some breathing room. OR,
Is it impossible, and higher octane with 34* advance the real answer. As I mentioned before, I'd definitely go with the higher octane while you're tuning and sorting this thing out.
Superchargers aren't my thing, although I am always willing to learn more.:D
Click to expand...

Once you get behind the wheel of something that's boosted, you'll be hooked!
 
Thanks Mike. You answered most all my questions, and gave me alot to digest.

91 Octane is the normal "ethyl" in Kalifornia now, with 10% ethanol and nitrogen enriched to boot.

The car is a street driver, and race fuel is a PITA.
 
Yup, 91 corn juice is all we got in CA!

Knock sensor is out of a C4 (because it had the roller cam and I have retro rollers) hooked up to a knock lite. Sensor sensitivity is down as far as it will go and the light flashes all the time, idle, cruising, might as well be hooked up to a turn signal flasher.
 
Well, the engine idles best at 18*, and it has been suggested to limit the timing to 24* under boost. I am going to have made three new stop bushings for his MSD pro billet. 8*, 10*, and 12*. He can play with that untill final boost pressure is decided.
 
enkeivette said:
Yup, 91 corn juice is all we got in CA!

Knock sensor is out of a C4 (because it had the roller cam and I have retro rollers) hooked up to a knock lite. Sensor sensitivity is down as far as it will go and the light flashes all the time, idle, cruising, might as well be hooked up to a turn signal flasher.
Click to expand...

What are you using for knock detection electronics?
 
enkeivette said:
Yup, 91 corn juice is all we got in CA!

Knock sensor is out of a C4 (because it had the roller cam and I have retro rollers) hooked up to a knock lite. Sensor sensitivity is down as far as it will go and the light flashes all the time, idle, cruising, might as well be hooked up to a turn signal flasher.
Click to expand...

I have HEARD that GM knock sensors do not like gear driven cams....gear noise....also wonder about those aftermarket toggles that way, must be in the freq range...??

that knock light is kinda strange, they talking of static sensitivity? almost like a open CMOS gate/output?? just seems odd seeing that these daze....

:drink:
 
BRUTAL64 said:
big2bird said:
Thanks Mike. You answered most all my questions, and gave me alot to digest.

91 Octane is the normal "ethyl" in Kalifornia now, with 10% ethanol and nitrogen enriched to boot.

The car is a street driver, and race fuel is a PITA.
Click to expand...

"nitrogen enriched" :rofl::rofl::rofl::rofl:
Click to expand...

Why not, shit, I"m stuck with Dihydrogen Oxide, at least he do is burn nitrogen....:banghead::ill::evil:
 
I looked at the link you listed. Without knowing more details of the knocklite circuitry filtering, I'm unclear how this thing is supposed to work very well.
What ECM are you running? Unless the engine is highly modified, I would expect the stock ESC unit to be more reliable (detection-wise) than this knock-lite.
 
My Mighty Demon and my Billet MSD are magical, they need no stinkin computer to operate. :pprrtt::amused:

Engine mods:
383ci SBC
9:1
Forged Scat Crank
Forged Scat 6" Rods
Forged Aluminum SRP Pistons
AFR 195cc Aluminum Angle Plug Heads w/8032 Upgrade
Comp Hyd Roller Cam & Lifters .576 in .594 ex Lift 239in 245ex Duration @ .05
Comp Chromeoly Pushrods
Harland Sharp 1.65 Full Roller Rockers
Edelbrock Victor Jr
MSD Pro Billet HEI
Mighty Demon 750 Annular
Procharger D1SC 4" pulley, K&N filter
 
Okay, I had assumed this setup was a hopped up L98/LT1 with a supercharger. Well, given that, if this knocklite thing doesn't work out, there are several stand-alone GM ESC modules that you could easily hook up for testing purposes. I've got one on my '84, with a bright-ass LED mounted on the inside rear view mirror, which is easily seen while driving around the track. It lets me know when I've got the spark map over-advanced, and also when to take my foot out of the throttle until I get the opportunity to burn another chip. I believe TT has a somewhat similar knock display setup he's discussed at times.
 
69427 said:
Okay, I had assumed this setup was a hopped up L98/LT1 with a supercharger. Well, given that, if this knocklite thing doesn't work out, there are several stand-alone GM ESC modules that you could easily hook up for testing purposes. I've got one on my '84, with a bright-ass LED mounted on the inside rear view mirror, which is easily seen while driving around the track. It lets me know when I've got the spark map over-advanced, and also when to take my foot out of the throttle until I get the opportunity to burn another chip. I believe TT has a somewhat similar knock display setup he's discussed at times.
Click to expand...

MIKE< can you post/send me a schematic of how/where to wire that into my stockish Speed Density GM system?? or what you have at least, and I can figger it out maybe for mine???

:yahoo::friends:
 
mrvette said:
69427 said:
Okay, I had assumed this setup was a hopped up L98/LT1 with a supercharger. Well, given that, if this knocklite thing doesn't work out, there are several stand-alone GM ESC modules that you could easily hook up for testing purposes. I've got one on my '84, with a bright-ass LED mounted on the inside rear view mirror, which is easily seen while driving around the track. It lets me know when I've got the spark map over-advanced, and also when to take my foot out of the throttle until I get the opportunity to burn another chip. I believe TT has a somewhat similar knock display setup he's discussed at times.
Click to expand...

MIKE< can you post/send me a schematic of how/where to wire that into my stockish Speed Density GM system?? or what you have at least, and I can figger it out maybe for mine???

:yahoo::friends:
Click to expand...

Gene,

It's a pretty simple setup. I tapped into the ESC module RETARD output pin, and then connected that to a pulsewidth stretcher/LED driver circuit. The driver circuit then connected to a long two-wire harness that goes to a BA LED hung on the inside rear view mirror. I have the circuit contained in a breakout harness, explaining why it looks like there are two ESC units on the car. (I used to work in the group that designs/manufactures/calibrates the ESC systems on GM cars, hence the use of an empty ESC module housing. (Lower left corner of picture.)

IM000721.jpg

The ESC module pinout is available in most service manuals. The RETARD signal (Pin C) is a normally high, active low signal. The pulse stretcher is just a few transistors, caps, and resistors, tied to a slightly bigger transistor capable of sinking the current in the LED, which is bright enough to be seen out of the corner of my eye as I'm driving on the track. As long as you add enough input impedance onto your stretcher circuit input, the ECM won't know that you tapped into that RETARD line.
 
69427 said:
mrvette said:
69427 said:
Okay, I had assumed this setup was a hopped up L98/LT1 with a supercharger. Well, given that, if this knocklite thing doesn't work out, there are several stand-alone GM ESC modules that you could easily hook up for testing purposes. I've got one on my '84, with a bright-ass LED mounted on the inside rear view mirror, which is easily seen while driving around the track. It lets me know when I've got the spark map over-advanced, and also when to take my foot out of the throttle until I get the opportunity to burn another chip. I believe TT has a somewhat similar knock display setup he's discussed at times.
Click to expand...

MIKE< can you post/send me a schematic of how/where to wire that into my stockish Speed Density GM system?? or what you have at least, and I can figger it out maybe for mine???

:yahoo::friends:
Click to expand...

Gene,

It's a pretty simple setup. I tapped into the ESC module RETARD output pin, and then connected that to a pulsewidth stretcher/LED driver circuit. The driver circuit then connected to a long two-wire harness that goes to a BA LED hung on the inside rear view mirror. I have the circuit contained in a breakout harness, explaining why it looks like there are two ESC units on the car. (I used to work in the group that designs/manufactures/calibrates the ESC systems on GM cars, hence the use of an empty ESC module housing. (Lower left corner of picture.)

IM000721.jpg

The ESC module pinout is available in most service manuals. The RETARD signal (Pin C) is a normally high, active low signal. The pulse stretcher is just a few transistors, caps, and resistors, tied to a slightly bigger transistor capable of sinking the current in the LED, which is bright enough to be seen out of the corner of my eye as I'm driving on the track. As long as you add enough input impedance onto your stretcher circuit input, the ECM won't know that you tapped into that RETARD line.
Click to expand...

Well shoot, last fall I started a little breadboard with a quad op amp, and some pots for a comparator circuit....that input is high'rn a cat's back, so to just feed it as a straight op amp to a NPN and trigger a light and maybe a audible alarm....sort of my version of a Nader beeper, sonalert for maybe oil pressure, engine temp, Knock, tells me something is rong, and to check my gauges.....something useful....
I haven't done anyting with it in some time...other shit taking over....

and now the HSPeed blower quit working this morning, and of course in the garage, everyone is happy...:cussing::hissyfit::hunter:
 
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