Anyone try the Edelbrock VRS-4250 Carb yet?
I don't know what I don't know regarding carbs. There have been comments that this carb might not be best for a street application because of tune difficulty and stability and I'm wondering what feature unique to the VRS (or other carb) would cause this? I can understand having more dials to twiddle causing you to get lost in the tune, but once optimized the engine combo, what would cause this one to fall out of tune while an older Holley wouldn't? It's not like the bleed orifices or jets change diameter over time. Is there a feature or circuit added that makes it susceptible to atmospheric changes?
IIRC the carb has at least 4 circuits. I can’t remember if Edelbrock doesn’t count one circuit so there is 5 the way I count. Either way, the Holley has 3 circuits.
Most guys get confused at the relationship between the main air bleed, emulsion and the main jet.
Then you have the idle circuit and the transfer slots. They have a relationship related to the idle feed restriction and the idle air bleed.
Then you have the transfer slots and its relationship to the idle feed restriction and the idle air bleed.
Then you have the transition slot width and length you have to deal with and most carbs benefit from restricting the transfer slots at least some amount.
And finally you have the power valve circuit. It has a relationship to engine load, manifold vacuum and the power valve channel restricters.
That’s just a rough outline of all the tuning for a Holley 3 circuit carb.
You can get a Dominator with what Holley calls the “intermediate” circuit. Very little use for that although some guys on line will fight you if you even broach the topic of not needing that circuit.
I forget how Edelbrock labeled their circuits and what they call the “intermediate” circuit but the way they laid out the emulsion it stack ends up another circuit.
I haven’t looked at this stuff in a while so I can’t recall how Edelbrock labeled each circuit. That’s the short of it.
As you can see, even with a Holley there is a bunch of tuning opportunities that can go sideways really quick.
It’s much easier to tune these things on an engine dyno where you can load the engine at any rpm and figure out the timing curve because that affects carb tuning.
I’m not sure that the extra tuning on that carb is worth it. Actually I’m not sure how many guys will even bother with it.