Thoughts on primary side jets dual 1850s

DanEC · #1 (**permalink**) 12-15-2018, 04:41 AM

I'm upgrading (sort of a loose term) my generic Holley 1850s with exterior adjustable fuel bowls and going through adjustments on them. The stock jetting was #65s and they have a #9 stamped secondary plates which I think equates to a .067" fuel orifice.

Motor is a stroked 428 with 427 LR dual quad intake, steel heads, medium flat tappet hydraulic cam.

Most of the Holley literature indicates #66 jets in many of the 1850 carbs. Since I run 93 Premium Ethanol and have a pretty free flowing exhaust system I was thinking it might be a good idea to go up to the #66 jets from the #65s. But - no real basis behind thinking of doing so.

Anyone play around with these 1850s on a dual quad FE at the strip or on a dyno to have an opinion or recommendation on this? Engine was built by KC and broke in on his dyno but they didn't try to do any real dyno tuning with it. Pretty sure carbs were not touched other than idle mixtures. Hard to figure A/F data on it as they only used a hood on one carb for air flow measurements.

moar_carbz · #2 (**permalink**) 12-17-2018, 04:30 PM

What things are occurring that make you think you should be using jets that are different than what you currently have?

How is it running?

How do your plugs look?

How does your tailpipe look?

What elevation are you at?

What's your manifold vacuum at idle?

DanEC · #3 (**permalink**) 12-19-2018, 03:09 PM

They are now buttoned back up with #66 jets mostly based on advice from the FE forum.

Gaz64 · #4 (**permalink**) 12-19-2018, 03:23 PM

You could notice some change in the middle to upper rpm range, but one step up might also be imperceptible.

The mains should be sized until the engine makes its peak hp.

Then the mains need to be sized until light throttle surge occurs, then come back up 2 steps.

Then the PVCRs should be increased in size and combined with the smaller main to give the total of the rich main and original PVCR in step 1.

You could play with the IFRs if you are keen.

Gary

moar_carbz · #5 (**permalink**) 01-23-2019, 07:42 PM

Dan, please hear my advice that one person's jetting working well from them does not mean it is optimal for you, and I haven't yet heard anything that makes me think your original jetting is not appropriate. Head flow, cam specs, and elevation make very real differences, and we haven't touched on that.