Comments on my 340 plug under mag

340inabbody said

Thank you again for taking the time to explain this to me. I am digesting your response as well as others here. So I actually I AM running a colder 160° thermostat. I had thought bringing the temp down would help alleviate detonation. I get what your saying about colder temps making atomization more difficult. I will try a 190° T- Stat as well as what ever else I can try mechanically. I will also post my timing map.

I suppose I cannot retrofit annular boosters to a 4150 style Holley?

Here’s what the ceramic looks like on my Autolite 65.

View attachment 1716402101

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You are very fat at WOT. That big black carbon ring should be between .125 and .187 on pump gas.

Race gas can get down to about .080but if the weather changes quickly and you can’t make a jet change you’ll be into detonation.

Even I don’t like tuning that close to the edge.


You can change the booster in a 4150 Holley if you have the tool. I bought the tool because I just almost never use downlegs any more.

You are correct that 160 coolant temperature will reduce detonation but as you are finding you just can’t drop the temperature.

Todays pump fuel is is EFI formulated so it’s even tougher to get it vaporized without some heat or a good booster.

I forget is your intake a cold air manifold?