AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 25,809
- Reaction score
- 13,117
OP @Chadderbox70
The engine does not care how much or how little idle timing it has, so long as;
1) the T-slots are synced up and
2) the setting you choose does not cause a tip-in sag, and
3) the sunshell doesn't rattle too harshly when you put it into gear.
4) and the plugs stay clean.
The Idle-timing window will usually fall between 8 and 18 degrees. More Idle-timing just means more Idle-Power.
A high cylinder-pressure engine will make more power at idle so will fall to the low end, whereas a low-pressure engine may like to run towards the higher end.
Typically, it will fall between 12 to 14 degrees, to satisfy the T-slot synchronization.
Big cams with late-closing intakes idle at low cylinder pressure, and so like lots of idle-timing, to get the power up.
Short period cams with early closing intake valves, make lots of idle-pressure, and with too much Idle-timing, will make too much Idle-power, and will really smack the sunshell, unless you you limit the idle-timing or modify the Forward clutch.
The difference between the ICA(Intake Closing Angle) events, varys from about 55* with a really small performance cam to maybe 75* with a really big street cam. Typically we install cams with Ica's in the range of 58 to 68. That's a range of 10 degrees. And the idle-timing has a similar range of 8 to 18. So this is how easy it is;
just take 50 off your Ica spec, and that can be your Idle-timing starting point. If you intake closes at 68*, then it will like 18 degrees. If your intake valve closes at 58 degrees, it will like 8 degrees. This assumes it has a decent Scr, compatible with the cam that is installed . In your case, the 703 cam, in per the card, has an Ica of 60 degrees, so 60 less 50=10* is the starting point. At a true 10.5 Scr, this will be close.
Of course, once the Idle-timing is bugged out, all your other timing systems will need to be reworked, this is just part of HotRodding.
Here's a challenge;
set it up like I preach, and after you get it idling in it's happy place........... go back and reset the Idle-timing to 18*, leave it there, and I don't care how you set your carb, try to find another happy place of;
no tip-in sag,
smooth transition,
no popping or stalling on decel,
no clanging into gear, and above-all, where
the plugs stay clean........
BTW,
The plugs in my HotRod, were installed in 1999, and they have over 125,000 miles on them. I pulled them out in 2004, thinking to replace them, for an upcoming Test-N-Tune, but they looked so good, I just put them right back in. A few days later, at the track, these same old plugs, ripped off a 93 mph in the Eighth....... and those same plugs were still in there, until last year, when, I had the idea to sell the car, and gave it a tune-up. That was the first time I looked at them since back in 2004, and they looked just fine. I only swapped them out cuz, the buyer was coming for the car.
Sadly the schmuck was a no-show.
So in frustration, I did a few victory laps around town at up to 7200rpm. Everything seemed normal, lol.
Here's the deal;
this engine cranks close to 180/185 psi.
The Ica is 63*, and the Idle-timing is, get ready for this;
13*, plus/minus 1 degree.
I'm leaving now, do whatever seems good to you.
The engine does not care how much or how little idle timing it has, so long as;
1) the T-slots are synced up and
2) the setting you choose does not cause a tip-in sag, and
3) the sunshell doesn't rattle too harshly when you put it into gear.
4) and the plugs stay clean.
The Idle-timing window will usually fall between 8 and 18 degrees. More Idle-timing just means more Idle-Power.
A high cylinder-pressure engine will make more power at idle so will fall to the low end, whereas a low-pressure engine may like to run towards the higher end.
Typically, it will fall between 12 to 14 degrees, to satisfy the T-slot synchronization.
Big cams with late-closing intakes idle at low cylinder pressure, and so like lots of idle-timing, to get the power up.
Short period cams with early closing intake valves, make lots of idle-pressure, and with too much Idle-timing, will make too much Idle-power, and will really smack the sunshell, unless you you limit the idle-timing or modify the Forward clutch.
The difference between the ICA(Intake Closing Angle) events, varys from about 55* with a really small performance cam to maybe 75* with a really big street cam. Typically we install cams with Ica's in the range of 58 to 68. That's a range of 10 degrees. And the idle-timing has a similar range of 8 to 18. So this is how easy it is;
just take 50 off your Ica spec, and that can be your Idle-timing starting point. If you intake closes at 68*, then it will like 18 degrees. If your intake valve closes at 58 degrees, it will like 8 degrees. This assumes it has a decent Scr, compatible with the cam that is installed . In your case, the 703 cam, in per the card, has an Ica of 60 degrees, so 60 less 50=10* is the starting point. At a true 10.5 Scr, this will be close.
Of course, once the Idle-timing is bugged out, all your other timing systems will need to be reworked, this is just part of HotRodding.
Here's a challenge;
set it up like I preach, and after you get it idling in it's happy place........... go back and reset the Idle-timing to 18*, leave it there, and I don't care how you set your carb, try to find another happy place of;
no tip-in sag,
smooth transition,
no popping or stalling on decel,
no clanging into gear, and above-all, where
the plugs stay clean........
BTW,
The plugs in my HotRod, were installed in 1999, and they have over 125,000 miles on them. I pulled them out in 2004, thinking to replace them, for an upcoming Test-N-Tune, but they looked so good, I just put them right back in. A few days later, at the track, these same old plugs, ripped off a 93 mph in the Eighth....... and those same plugs were still in there, until last year, when, I had the idea to sell the car, and gave it a tune-up. That was the first time I looked at them since back in 2004, and they looked just fine. I only swapped them out cuz, the buyer was coming for the car.
Sadly the schmuck was a no-show.
So in frustration, I did a few victory laps around town at up to 7200rpm. Everything seemed normal, lol.
Here's the deal;
this engine cranks close to 180/185 psi.
The Ica is 63*, and the Idle-timing is, get ready for this;
13*, plus/minus 1 degree.
I'm leaving now, do whatever seems good to you.
Last edited:
