Tuning a Holley using a wide band A/F gauge

[Stagdad]

Should be up and running tomorrow after much work including an A/F gauge .What would be the sequence for tuning ?.

I'm thinking get the primary cruse set up first then look at throttle pump jets.What am i after when you floor it ?Is it best to go rich on hard acceleration?

Cheers Steve

[GDPR]

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Not an expert on the Holley, but yes to rich (but not too much) on hard acceleration from a technical point of view - better charge cooling and knock resistance, plus less chance of the charge still burning on the exhaust stroke.

[V Mad]

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You might find this useful Steve

A well-tuned engine used in normal road conditions has an air/fuel ratio that is constantly varying. At light loads, lean air/fuel ratios are used, while when the engine is required to develop substantial power, richer (ie lower number) air/fuel ratios are used.

Bosch state that most spark ignition engines develop their maximum power at air/fuel ratios of 12.5:1 - 14:1, maximum fuel economy at 16.2:1 - 17.6:1, and good load transitions from about 11:1 - 12.5:1. However, in practical applications, engine air/fuel ratios at maximum power are often richer than the quoted 12.5:1, especially in forced induction engines where the excess fuel is used to cool combustion and so prevent detonation.

There is no one air/fuel ratio where all emissions are minimised. At an air/fuel ratio of 14.7:1 oxides of nitrogen peak, while hydrocarbons and carbon monoxide (CO) increase substantially as the air/fuel ratio richens.

[Stagdad]

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Thanks Guys ,Some usefull figures Chris.

Cheers Steve

[flying farmer]

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When I ran a holley (before efi) I set up the primary jets first to get the cruise mixture right. Hope you are using a source of cold air to the carb as optimum jet size will vary by at least three sizes if you are drawing ambient air from within the engine bay.

Pump jets are best set up next, and if you are using the pump cam selection box you need one that doesn't provide too much fuel as the standard cam is rather oversized for the stag engine.

For the secondary jets I would recommend using the strongest spring from the holley vaccume secondary kit, that seemed to let the secondaries open at about 5000 rpm, which could be felt as a slight bog down in 1st and second gear but was not noticeable in third or fourth. If you use a weaker spring it will put the bog into a lower part of the rev range and it will be more noticeable without any power gains.

I ended up using the same size primary and secondary jets with the strong spring, with weaker springs a richer jet is needed as there is not the gas velocity available to pull the fuel off the jet

If you suffer with a flat spot just off idle there is a usefull bodge to fix it. What is needed is a very fine hole drilling in each primary throttle plate, cannot remember which side unfortunately, but logically opposite the idle jets. This lets some air bypass the idle circuit, and the idle screws have to be opened to restore the idle mixture. This has the effect of making the idle circuit effective a few hundred revs further up the rev range by which time there is enough gas velocity to pull fuel off the main jets. This gets rid of the annoying flat spot just off idle, and was one of the most effective (and free) modifications I did to the holley

Neil

[V Mad]

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After all that palava Neil I am not surprised you ditched the Holley.

[Stagdad]

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I appreciate the time you put into that answer Neil,many thanks.

As it stands at the moment with 52 jets it goes quite well with no flatspot but cruses at about 14:1 so i guess if i hit the disired 16:1 -17:1 for economy i may start experiencing the flatspot.


And yes got a cold air shroud


Cheers Steve

[stagwingnut]

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stagdad .that is a very neat engine bay !!!i also run a holley and tubulars ,excellent !!!!!!

[Stagdad]

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stagwingnut wrote:

stagdad .that is a very neat engine bay !!!i also run a holley and tubulars ,excellent !!!!!!

And yours is White also