ok, i have always understood that ign. timing should be set so that max bmep comes some specifice number of degrees(cannot remember off hand) after tdc. so then, the timing should be different for different engines with different burn rates and such. i would assume in the interest of emissions that a newer engine should have a faster burn(faster burn is a good thing right?). then i go working on some old cars(relatively) and find that some E16's called for like 2*BTDC, some older engines actually called for 2*ATDC, and then cars like an A32 max calls for 15*BTDC. i am recalling all of these from memory so they may not be exact, but you get the point. why would the newer engines need more advance? is it that they can handle more advance? were the other engines set up for something other than power(duh)? is a slower burn a better thing? any ideas guys.
and here is just a rant since i have gone and started a thread. i hate when people trash good cars. since i have been reading this particular forum i have gained a lot of respect for the Q. the other day a ragged old '92 Q straggles in for a state inspection. i had to reject it for like everything in the book. yeah it had 200k on the odo but there is no excuse for a nice car to be leaking everything from everywhere. it was running like crap. my old B12 with the "hopeless chokeless" carb runs better. the same goes for some max's and Z's.
ign. timing
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s13sr20chris
- Posts: 4148
- Joined: Tue Jun 10, 2003 9:32 am
- Car: '89 Nissan S13 w/redtop running 13psi and not leaking fuel anymore
- Contact:
What you're not seeing with the idle timing is what happens at cruise or under load.
On no car is timing static, obviously with new ECU driven timing have large 3 or 4D maps (engine speed, throttle position, gear selected, engine temp, airflow) the timing will be all over the place.
On very primative systems the engine vacum controlled timing - vacum advance.
On 70's cars a hybrid of electronic ignition was used, no lookup tables but a bit better than vacum accuated coil.
On these cars, the idle timing was partly determined by where the timing needed to be at 70 MPH, not what made for the best idle. (A friend used to time his 50's car by checking the top speed possible at different settings)
The speed of a burn is not function of spark timing, but chamber geometry, compression ratio, fuel properties, fuel atomization, and distribustion of fuel droplets.
with ECU driven timing, the idle timing is whatever happens to be best for emissions and smooth idle. On some cars, which use a "timing adjustment connector" the adjustment of the CAS with an timing light is only to calibrate the CAS so the ECU knows the exact position of the pistons.
with ECU's and wildly different chamber designs you're not really comparing apples to apples in looking at different idle timings.
So in VA cars need to be leak-free to pass safety? Is this an annual check, or just done when cars pass ownership?
The only thing more mind-boggling than how much some people spend on cars, is how much some people won't.
On no car is timing static, obviously with new ECU driven timing have large 3 or 4D maps (engine speed, throttle position, gear selected, engine temp, airflow) the timing will be all over the place.
On very primative systems the engine vacum controlled timing - vacum advance.
On 70's cars a hybrid of electronic ignition was used, no lookup tables but a bit better than vacum accuated coil.
On these cars, the idle timing was partly determined by where the timing needed to be at 70 MPH, not what made for the best idle. (A friend used to time his 50's car by checking the top speed possible at different settings)
The speed of a burn is not function of spark timing, but chamber geometry, compression ratio, fuel properties, fuel atomization, and distribustion of fuel droplets.
with ECU driven timing, the idle timing is whatever happens to be best for emissions and smooth idle. On some cars, which use a "timing adjustment connector" the adjustment of the CAS with an timing light is only to calibrate the CAS so the ECU knows the exact position of the pistons.
with ECU's and wildly different chamber designs you're not really comparing apples to apples in looking at different idle timings.
So in VA cars need to be leak-free to pass safety? Is this an annual check, or just done when cars pass ownership?
The only thing more mind-boggling than how much some people spend on cars, is how much some people won't.
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s13sr20chris
- Posts: 4148
- Joined: Tue Jun 10, 2003 9:32 am
- Car: '89 Nissan S13 w/redtop running 13psi and not leaking fuel anymore
- Contact:
yes you are right about not all being apples. no i did not fail it for the leaks; i just noticed them and was completely discusted. it failed for both front side marker bulbs, both rack boots, and drivers upper control arm. thats just normal stuff, but the guy would not pay for it. ok by me. he just wants the prestige of a Q i guess. thanks for bringing up the ecu vs. distributor thing. dont know why i was thinking i could compare those two completely different systems.
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
The Q at low load cruise might have 40 degrees of total advance whereas the moment you accelerate it might drop to 20 degrees......the max full load timing at 4,000 rpm is around 20-22 increasing to around 26-28 at WOT 6,500 rpm.
Idle in park is 15 degrees but idle in drive is 20 degrees......the ecu juggles the timing a lot to maintain idle speed also.
I wished all states had excellant inspection programs.
Idle in park is 15 degrees but idle in drive is 20 degrees......the ecu juggles the timing a lot to maintain idle speed also.
I wished all states had excellant inspection programs.