Has anybody ever run the Holley 6425, 650 CFM 2 barrel carb on the street? How are they at part throttle? How about full throttle?
I have seen articles saying that they have good bottom almost as good as the 4412, 500 CFM. A Holley book that I have says not to use them below 4000 RPM under power. Anybody experienced or heard otherwise?
4 Jaw Chuck
07-25-2003 01:01 AM
Why run one if you can buy a four barrel for the same price? These things are for dirt track spec racers and thats reflected in their performance and construction.
07-25-2003 06:10 PM
I was thinking of using it for a couple reasons. There is better fuel metering through annular boosters in general, but maybe not with these. It is one less throttle shaft, therefore less vacuum leakage. I could have 650 CFMs with no secondary transition. Only having "primaries" and no "secondaries" to tune would be a lot easier, especially tuning by "the seat of your pants feel". There is less chance of fuel leaks with two barrels.
If they run half way decent I thought it would be worth a try running it. Other wise I'll stick with my current carb.
Oh yeah, and I have about ten different Holley four barrels in my garage, and I am trying to thin them out and only keep the ones I need.
4 Jaw Chuck
07-25-2003 07:22 PM
Let me try to answer your thoughts;
There is better fuel metering through annular boosters in general
Absolutely correct, except the reason why they put annular boosters on the two barrels is because they start "signalling" at lower velocities and with the big holes you need them. Any Holley booster can be retrofitted to any Holley carb by removing your old booster and "spinning" in the type you prefer (you slide hammer out the old ones). It is very involved to accomplish and for the street will likely have no effect on performance although metering will improve slightly. Their main benefit is better metering at low air velocities so mileage/economy would be the only gain you see.
It is one less throttle shaft, therefore less vacuum leakage.
Not even enough to worry about as long as the carb is in good condition.
Only having "primaries" and no "secondaries" to tune would be a lot easier, especially tuning by "the seat of your pants feel".
Having multiple stages to tune can seem a little harder but not compared to trying to get a big holed two barrel to meter efficiently at low speeds, tune with your stopwatch not your butt.:) Eliminating the secondaries means your foot becomes the bog sensor and you will have to drive it that way...much like a double pumper.
There is less chance of fuel leaks with two barrels.
Half as many bowls...can't argue with that. But if Holleys are rebuilt properly with the good gaskets they don't leak any more than an identical two barrel.
I have about ten different Holley four barrels in my garage, and I am trying to thin them out
Please send all unwanted 750 Double pumpers my way please, condition is unimportant.;) You can scrap the rest.:D ;) It sounds to me like what you want/need is a nice 3310 squarebore 750 double pumper, still the best carb they ever made if you ask me. The 780 vacuum secondary is good too but good luck finding one. Most guys here swear by the Demon carb, I have never had one so I cannot comment on them but from what I have heard/read they are the best Holley carb never made by Holley.
07-25-2003 07:47 PM
Yeah you are right 4 Jaw the 780 3310-1 is a nice carb. I have two of them. I put one on my Camaro, which is the car that I was thinking of putting the 2 bbl on. The Camaro has a 400 that is 10.5:1 and has stock 1.94 1.50 valves. It has a .480"lift and 230@ .50 duration. The 3310-1 was still a little too big. I put on a carb that worked much better. The Holley 4609. It is a replacement Shelby carb. It is rated at 730 CFMs and is like the 3310 only it has the high signal, bell shaped, truck primary boosters, and has downleg secondaries. It has better metering at cruise, and killer top end. Primary jetting is 66 and secondary is 79. It is like having a squarebore act like a spreadbore.
I just want to hear other people's experience with them and I might bolt it on and try it.
07-27-2003 09:37 AM
Anyone else had any experience with these carbs?
07-29-2003 02:36 PM
I noticed that there is a new member to this board. Tech@BG. Tried writing directly to you but it won't go through. Do you have any experience with these carbs?
07-29-2003 04:33 PM
Lots of budies of mine use them on circle trackers, but no one knows what they would be like on a street driver. My personal opinion, How can the 750 be too big for a 400ci? Especially with the mods you have already performed. I not sure you tuned the secondary springs correctly. I won't drive anything less than a 800 on the street. I almost always rework my 3310 to flow around 820-830 at 1.5". Never had too much drivability either. Unless the cam used pulled less than 8 inches at idle. You might need to tune the two barrels high speed air bleeds to prevent the rich condition carbs favor at high air speeds. But that would be all that you should need to do to get good fuel mileage from the two or four.
Tech @ BG
07-29-2003 04:34 PM
650 2bl Carb
The 650 2bl carburetor having the large venturi will not have the same type of drivability as a small 4bl carburetor would. Your engine is an air pump, so it will flow the same amount of air at any given point (unless it's restricted) using a smaller 4bl carburetor will increase the air velocity at lower RPM and engine load giving you better idle quality, throttle response, and drivability.
07-29-2003 06:20 PM
The carb that was too big was the 3310-1, rated at 780 CFM. I am pulling 16 in. of vacuum at idle. My idle speed is only 600 RPM and it runs smoothly believe it or not. The cam is the PAW 234o @.50, .488 lift with a 114o lobe seperation. The engine is a 10.5:1, Chevy 400. It has 1.94, 1.50 valves. Intake is the Performer RPM air gap.
Tech @ BG
07-30-2003 08:02 AM
If you ran a 650 Vacuum Secondary 4bl carburetor it will give you better acceleration and drivability than the 650 2bl since the air will be moving at a higher velocity. This will give you better atomization of the fuel.
07-31-2003 12:51 AM
The 4bbl will also flow quite a bit more air.
03-26-2010 09:52 AM
ran one on a Ford 360 stock motor the 6425 650 worked better than any 4 barrel and really made the motor come alive as well as got great fuel mileage
4 Jaw Chuck
03-26-2010 09:59 AM
6 1/2 year old thread!
01-28-2011 10:49 AM
650 holley 6425 2 barrel
hi does any one got a holley 2 barrel 6425 650 im looking for one please let me know