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Ignition Timing

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djl45

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Hi all.

What amount of advance are people using? Mine in on electronic [huh? - Mod.] and I have 23 deg at around 4500 RPM, but the car feels like it's holding back, like it's not getting enough fuel. It starts and ticks over OK, and its on twin SUs. It does pop back through exhaust on overrun.

TIA
 
thanks John I will ook at pushing mine up a bet to see if it improves this holding back? what octane do you call premium in the states? I use 98 (max you can get ) with a lead additive.
 
djl45 said:
thanks John I will ook at pushing mine up a bet to see if it improves this holding back? what octane do you call premium in the states? I use 98 (max you can get ) with a lead additive.
Click to expand...
We list octane differently in the US. IIRC, in the UK, "research octane" is used. In the US, "pump octane" is used, which is the average of research octane and motor octane. The spread between research octane and motor octane can be as much as 10 numbers, with the research octane being higher. Ours is typically 91, with 93 at higher altitudes. That could mean a research octane of 95 - 96. I have a Denis Welch head with the combustion chambers sized for premium, and a few other "goodies."

I don't think lead additives are allowed in the US, but other octane boosters are.
 
Manchester study on modern fuel burn rates: "The conventional, reformulated, and oxygenated unleaded gasoline of today has both a different burn rate during the combustion process and a different distillation profile than the leaded gasoline of the '50s, '60s, and '70s. These changes in the current gasoline formulation cause an engine that was tuned for leaded gasoline to need to have the initial timing, mechanical advance, and the vacuum advance systems tuned for the gasoline of today (requires more advance) if the engine is expected to perform its best."

Below are recommendations from Denis Welch (base curves 9-12 referenced are from the Denis Welch CSI distributor). I am using Denis Welch Curve 10 with the addition of 6 degrees initial timing. This resultant timing is the red curve in the graph.

"Denis Welch – The best starting point for installation of the CSI distributor in a BJ8 is one of our curves 9-12. We usually use 15 to 18 degrees static tuning to setup the CSI Distributor, not the 10 degrees mentioned in the installation manual. Make sure the vacuum advance is off when the strobe is used to check the timing as with the stock distributor. Check the timing at 1000 RPM (15 to 18 degrees) and then again at 3000 RPM (about 32 degrees). From 3000 RPM to 4500 RPM, we look for a timing advance of 32 degrees to 35 degrees respectively."
 

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  • BJ8 Timing Update.JPG
    BJ8 Timing Update.JPG
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  • DW CSI Advance Curves.JPG
    DW CSI Advance Curves.JPG
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WHT said:
Manchester study on modern fuel burn rates: "The conventional, reformulated, and oxygenated unleaded gasoline of today has both a different burn rate during the combustion process and a different distillation profile than the leaded gasoline of the '50s, '60s, and '70s. These changes in the current gasoline formulation cause an engine that was tuned for leaded gasoline to need to have the initial timing, mechanical advance, and the vacuum advance systems tuned for the gasoline of today (requires more advance) if the engine is expected to perform its best."

Below are recommendations from Denis Welch (base curves 9-12 referenced are from the Denis Welch CSI distributor). I am using Denis Welch Curve 10 with the addition of 6 degrees initial timing. This resultant timing is the red curve in the graph.

"Denis Welch – The best starting point for installation of the CSI distributor in a BJ8 is one of our curves 9-12. We usually use 15 to 18 degrees static tuning to setup the CSI Distributor, not the 10 degrees mentioned in the installation manual. Make sure the vacuum advance is off when the strobe is used to check the timing as with the stock distributor. Check the timing at 1000 RPM (15 to 18 degrees) and then again at 3000 RPM (about 32 degrees). From 3000 RPM to 4500 RPM, we look for a timing advance of 32 degrees to 35 degrees respectively."
Click to expand...
Thank you WHT for this valuable information, I will start to tinker around.
 
djl45,

Hopefully, you can get your car running better.

I just wanted to mention, when I say Curve 10 + 6, your are adding 6 degrees advance to the DW Curve 10. This adds 6 degrees to every value of the original curve as shown in the graph. I know you understand this, but it can be confusing sometimes. This gets you close to the DW recommended timing.

Regards, Bill
 
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