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Topic: octane sensitivity vs advance curves (Read 1947 times) previous topic - next topic

octane sensitivity vs advance curves

motor

1976 351W
stock longblock
edelbrock RPM intake
600 vac secondary holley jetted for app.
stock duraspark ignition W/ blaster msd coil
taylor wires and NGK plugs (stock heat range)
long tube headers and 2" exhaust
Curve kit in the distributor

Now onto the topic this is in my truck that I drive daily I only run 87 octane fuel in it at any given time.All has been great till I put in the curve kit with the light springs test drive shown I had some severe detonation at part throttle.So tonight I went back into the distributor and swapped to the medium springs in the kit and restricted the mechanical advance to provide only 26* of mechanical advance v.s the 42* before set the base at 12* for a total of 38*at full advance.Now I still have this pesky light throttle ping.I really like the added pep of the faster curve Is the solution to this to drop the base timing more or try to tighten the curve up some more (full advance at 3,500-3,600) motor never see's above 5,100

Also this may not be related but our local stations recently switched to a 10% ethanol mix fuel.
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1974 maverick lsx powered turbo car SOLD
1973 maverick Tijuana Taxi Tribute
1957 chevy LSX Turbo project (race car)
Owner of Joe Dirt Fabrication

octane sensitivity vs advance curves

Reply #1 –
If you're running 87 octane, 12* is way to advanced. Try setting your base at 10.

octane sensitivity vs advance curves

Reply #2 –
a carbed motor needs more timing, due to the fact that fuel is sprayed into all cylinders at once. 12 degrees should be fine. 14 should be fine, too. but i dont have much experience in fine tuning a timing curve in the distributors. are you using the vacuum advance, too?
1979 Ford Fairmont
[/B]
5.0L/4R70W/8.8"/5-lug/3" Exhuast

octane sensitivity vs advance curves

Reply #3 –
Quote from: *MAYHEM*;201533
If you're running 87 octane, 12* is way to advanced. Try setting your base at 10.


Remember were talking about a 8:0:1 -8:5:1  compression motor.
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1974 maverick lsx powered turbo car SOLD
1973 maverick Tijuana Taxi Tribute
1957 chevy LSX Turbo project (race car)
Owner of Joe Dirt Fabrication

octane sensitivity vs advance curves

Reply #4 –
Quote from: 32VFoxBird;201536
but i dont have much experience in fine tuning a timing curve in the distributors. are you using the vacuum advance, too?


No vac advance.
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1974 maverick lsx powered turbo car SOLD
1973 maverick Tijuana Taxi Tribute
1957 chevy LSX Turbo project (race car)
Owner of Joe Dirt Fabrication

octane sensitivity vs advance curves

Reply #5 –
figured this would spark some good info...
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1974 maverick lsx powered turbo car SOLD
1973 maverick Tijuana Taxi Tribute
1957 chevy LSX Turbo project (race car)
Owner of Joe Dirt Fabrication

octane sensitivity vs advance curves

Reply #6 –
I would tighten up the curve.....The 12* base is fine....Any way to get total down to say 34*?
-- 05 Mustang GT-Whipplecharged !!
--87 5.0 Trick Flow Heads & Intake - Custom Cam - Many other goodies...3100Lbs...Low12's!

octane sensitivity vs advance curves

Reply #7 –
Quote from: V8Demon;201729
I would tighten up the curve.....The 12* base is fine....Any way to get total down to say 34*?



Not really without a distributor swap or welding the slot up some I dont have any audible detonation at wot.I myself though the total was a little high but considering the compression it probly needs the advance to help burn the mixture.I cannot see it needing 42* of mech advance as ford had it set up on top of the base timing.
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1974 maverick lsx powered turbo car SOLD
1973 maverick Tijuana Taxi Tribute
1957 chevy LSX Turbo project (race car)
Owner of Joe Dirt Fabrication

octane sensitivity vs advance curves

Reply #8 –
Most of those old distributors had a rubber sleeve on the pin, so travel probably was only about 30* originally...

Of course with heat and age it deteriorated and fell to the bottom in pieces(bet you were wonderin' what that junk was HUH?)

octane sensitivity vs advance curves

Reply #9 –
Quote from: TurboCoupe50;201770
Most of those old distributors had a rubber sleeve on the pin, so travel probably was only about 30* originally...

Of course with heat and age it deteriorated and fell to the bottom in pieces(bet you were wonderin' what that junk was HUH?)


rubber sleeve still on the tab :D  I wouldnt think it would make more then a couple of degree's differance.
[SIGPIC][/SIGPIC]
1974 maverick lsx powered turbo car SOLD
1973 maverick Tijuana Taxi Tribute
1957 chevy LSX Turbo project (race car)
Owner of Joe Dirt Fabrication

octane sensitivity vs advance curves

Reply #10 –
Does that dist have double slots??? Can't remember on those but the points type did... On those you pulled the rubbing block assembly rotated it 180* reinstalled... Of course you had to do the same for the main shaft or it was 180* out of time...

octane sensitivity vs advance curves

Reply #11 –
Quote from: TurboCoupe50;201787
Does that dist have double slots??? Can't remember on those but the points type did... On those you pulled the rubbing block assembly rotated it 180* reinstalled... Of course you had to do the same for the main shaft or it was 180* out of time...

yep Ive done rotated the shaft to limit the advance from the factory spec.
[SIGPIC][/SIGPIC]
1974 maverick lsx powered turbo car SOLD
1973 maverick Tijuana Taxi Tribute
1957 chevy LSX Turbo project (race car)
Owner of Joe Dirt Fabrication

octane sensitivity vs advance curves

Reply #12 –
Put a larger sleeve on the pin(old power cord), or add a couple layers of heat shrink to the one that's already on it... It will effect timing more than you think...

octane sensitivity vs advance curves

Reply #13 –
Quote from: TurboCoupe50;201795
Put a larger sleeve on the pin(old power cord), or add a couple layers of heat shrink to the one that's already on it... It will effect timing more than you think...


See im not experiancing a WOT/full advance ping just at a small range of part throttle at cruise.
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1974 maverick lsx powered turbo car SOLD
1973 maverick Tijuana Taxi Tribute
1957 chevy LSX Turbo project (race car)
Owner of Joe Dirt Fabrication

octane sensitivity vs advance curves

Reply #14 –
OK I see... I've seen recurve springs that tend to dump in a bunch of timing at low RPMs...These are generally a bit too long, so the weights pull in most of the advance at low RPMs... Have any old weights you could cut down a bit???

Course you could up the carb jets 4-5 sizes and drown out the ping... Won't do anything for your mileage though...:D