Anyone try the Edelbrock VRS-4250 Carb yet?

[Newbomb Turk]

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.

 

[cpearce]

Any new information on these, dyno results perhaps? Ive not seen one other than in shops. The little I have heard is they are absolutely bad *** carburetor.

 

[Newbomb Turk]

Any new information on these, dyno results perhaps? Ive not seen one other than in shops. The little I have heard is they are absolutely bad *** carburetor.

I’d love to get one (or TWO on a TR) on the pump to actually tune them, but I’m not buying one (or two) to do it.

Eventually someone will come by with one of them.

I watched a guy put one on a vehicle (I don’t want to say who it is because this isn’t a thrash on him) and it did exactly what he said it would (confirmation bias) but even he didn’t attempt to tune it. And he’s got a pretty big YouTube following.

I watched all of it, and I know what I would have done to tune it but he didn’t attempt any of it. I may have been wrong, but a wrong tuning decision is better than no tuning decision because it gives you a direction to go.

The issue I see with the carb is guys claiming they bolt it on and the carb makes so much more power you can rotate the earth, I (being a skeptic) have a hard time swallowing that.

With a split emulsion and with that 5 potential bleeds you can get crossed up very quickly.

I can also say driving around with a digital O2 sensor and trying to actually make tuning decisions with it is near impossible.

You really need to data log the O2 sensor because your eye and a digital device doesn’t have the resolution to see the changed in A/F ratio.

The first thing I look for when looking at A/F ratio on the dyno is the shape of the curve. That tells you a lot. I see many graphs of A/F ratio that look saw toothed. That’s a big indicator that at the very least the emulsion stack is off.

It’s hard to see that without data logging it.

 

[mbaird]

I would think these would be a hit with big cammed street / strip engines . They come standard with so many thoughtfull upgrades.

 

[RustyRatRod]

I think Shane has tried or is going to try one on a slant 6.

 

[PRH]

There was a time when I woulda really wanted one…….but the last time I felt like that about a carb was when the King Demons came out.
That thing was a QC nightmare.
I finally got some replacement parts from BG to make it usable, and ended up getting it to work as well as my tweaked 9375HP……but no better. So it went down the road.

Nowadays, I feel like I already have too many carbs, and def don’t feel like I need one of these new Ede carbs.
But, it would be fun to try one on the dyno and see how my old junk compares.

 

[MOPARMAGA]

Yes, id like to see what 2-850s would do on my tunnel ram.
I have nice blp 850s but just to try them id give them a shot.

 

[MOPARMAGA]

I thought they were originally marketing a "950" too but I see only 650, 750, 850.
If I ever get really good at making my life harder than it needs to be I'll try and modify some baseplates for the biggest blades that will fit,
Homemade twin blades would be cool.