Holley 950 Street HP

Hi,

I looking for a new carb and have looked at Holley 950 Street HP (0-82951) for my weekend cruiser that see a track ounce or twice a year.
Is here anyone here that has try one of this carb?
Is it a "good" choice for a street car?
Has it 1.75 baseplate and Venturi 1.56 ?

https://www.holley.com/products/fuel_systems/carburetors/hp/street_hp/parts/0-82951

It is for my 512 with
10.4:1
TF 240 heads
Singleplane intake
Cam 251 at 0.50 and lift .594

Sitting in a 3860 lb car with 4200 flash stall and 4.10

Thanks in advance

Umm, well it might work. Those 1.56 venturi Holley carbs are a little "touchy". If you aren't a carb expert (and I assume you aren't since a carb expert wouldn't post a question on here) then I'd steer you towards a carb with a smaller venturi size. Especially for a weekend cruiser.

If you don't have much carb experience then I'd recommend starting with something like an old school 3310 or an Edelbrock 800. Carbs like that are good beginner carbs that will work on most anything and provide decent power.

Since you're in Sweden it might be tough to find a local Holley guy who can help with the tune so you should probably stay away from the exotic stuff. One problem with posting on this board is that you'll get a bunch of guys who tell you to put a Dominator on your engine or to buy a $1000 custom tuned carb. For what you are trying to do a used 3310 in good shape that you pick up at a swap meet for $50 would work almost as well as a $1000 tuner carb. But you kind of need to know your way around a carb to have a good chance of taking a $50 swap meet carb and making it work on your engine.

If you look thru the race parts for sale on this board you'll find a bunch of used carbs. For your engine I'd recommend something in the 750 or 850 range. Look over the carbs and maybe exchange PM's with the sellers. I'm sure you can find something that would work on your engine.

I bought that same carb for my 512 street car, the only parts of this carb that remain are the float bowls & the base plate, I had to change the metering blocks & the the main body for a AN booster with 1.590 large venturi, works great now, until the weather changes & then have to tune it again.

I would also consider a Quick Fuel 950 carb with a 1.45" venturi.

I haven't used that Holley Part # 950 HP but I have used and really like the Holley 950 HP #80496, even though it didn't really flow 950 CFM
I used that carb on a bunch of different BB Mopars for both street, strip and some engine dyno testing, I never had to change the jets, only the squirters(to smaller) due to living in the Mojave Desert in So CA. at 3500 Ft. elevation IHTHs

I have run it a couple of year with both an 4781 DP and a Pro form 850 DP and I also have an 3310 on the self... but no on that one.
It run cleaner and has more crisp throttle response with the P/F 850 but the 4781 was overall faster on the track, but it running pig rich on part throttle when is tuned for 12.5 A/F at wot.

P/F 850 is 1.75 X 1.40" If I remember correct and the 4781 is 1.75 x 1.56" venturi. I thinking it may want more cfm because it was faster with the "bigger" 4781? Well, do I need a bigger carb?

Okay, that extra information helps. Yes, the car would probably be faster with a bigger carb but your original post said it was a weekend cruiser and not a race car. So which is it?

For a weekend cruiser just rebuild the 3310 and go cruising. If you are looking for the faster carb at the track then get one of your other carbs tuned up and use them. I don't see any reason to buy another carb when you already have a few on the shelf.

If the 4781 was rich at part throttle when 12.5 at WOT then you probably made the very common mistake of using the main jets to tune for WOT. You should use the main jets to tune for cruise and then add extra fuel for WOT with the power valve circuit.

Or just sell the three carbs you have and use the money to buy a Super Sniper EFI kit. Then you'll have the correct air fuel ratio from idle to WOT and you'll have built in data logging and you'll be able to control your ignition timing with the computer.

I personally have no experience with that 950 Holley. But as suggested above, it is a good idea to compare specs on various 950s because they vary a lot. Some flowing more than others. It is a good idea to stay with a 'street oriented' carb like the 82951 as the tune is better for a street car.

Another thing to keep in mind regarding some other carb suggestions here; Holley describes their Double Pumpers as "hot street and race" carbs. As such, they are fat everywhere, especially on the cruise circuit. But I have found that to be true of most Holleys, including the 3310.

We have had a bunch of the 3310s over the years. It's a good carb, but is a universal, economy carb with no secondary metering block. So tuning is a bit more difficult. They are fat enough at cruise to usually need at least 4 steps smaller on the main jet to clean the cruise up. Then they need the PVCRs opened up to get the WOT back where it needs to be.

Similar steps would need to be taken on the Double Pumpers, too. I guess Holley figures it is better to be safe and too rich rather than closer to a 'clean' tune and risk a lean condition.

A BBM stroker needs/wants a lot of air, meaning bigger is better when it comes to carb selection. And properly tuned, there is no down side when it comes to drive-ability with the larger carbs.

IMHO, a 750 would be a HUGE cork in a 512. That is, if performance matters.

This.

I guess I can try to enlarge PVCRs on the 4781 and put smaller jets on it and see how it reacts. In which step do you in enlarge the PVCR channel. In .001" step?

You can get close if you keep the total area the same. For example, if you go down 4 jet sizes on the mains then you'll need to add that same amount of area to the PVCR restriction.

The total area stays the same so the same amount of fuel will flow at WOT, but the balance will be shifted so less fuel flows thru the mains and more thru the PVCR.

When jetting a carb you should not think in jet sizes. Jet sizes are meaningless. Use the difference in area. So think of it in terms of adding 2% area, which adds 2% fuel. If you learn to convert everything to area and work in percentages it makes more sense.

https://www.mathsisfun.com/geometry/circle-area.html

The inside diameter of the main jets can be found on line or in several different books. The diameter of the PVCRs can be found by measuring with drill bits.

The decimal points can make calculations more difficult. So just eliminate them. As long as you remain consistent with the position of the decimal points throughout the calculations, they don't affect the outcome for this.

Let's say you have #75 main jets and .068 PVCRs.

#75 main jets have a listed diameter of.082. Eliminate the decimal point and take half of .082........041 and then multiply it by 3.14 and then by that number again.

So, 41 x 3.14 = 128.74 Then multiply 128.74 by itself (squared) = 16,574

Do the same for the PVCRs, half of .068 is .034.
So 34 x 3.14 = 106.76 x 106.76 = 11,398.

Whatever area (flow) you take away from the mains (16,573), add that much to the PVCRs (11,398) so that the total of the 2 stays about the same. Most Holleys seem to be fat on the cruise, but are usually close on the WOT. So you usually need to step down on the mains and then go larger on the PVCRs.

You do not need to include both both mains jets and both PVCRs in your calculations. Although you make the same changes to each pair, you only need to calculate the volume of one of each.

Don't worry that this procedure isn't perfect. It will get you close enough on the balance so that the final tune will be easier to achieve.

Oh, and one last thing. Make sure that your car is actually cruising on the mains. I have encountered more than one big engine with a big carb and low gears that actually cruise on the idle circuit due to the small throttle blade opening. As a good rule of thumb, the farther over 2,000RPM that you're cruising, the more likely you are to be on the mains.

IHTH Trying to keep this simple.

That last bit there is super important- I’ve only found success with hollys on the street after reducing the idle feed restrictions until the idle mixture screws gave a good idle at 1.5 turns out. I’ve found that at least in my congested neck of the woods most situations in traffic end up mostly cruising with such small throttle opening that you mostly feed the carb with the transfer slot and idle discharge port. The idle discharge ports are restricted by the corner idle screws but the slots use the IFRs as jets.

When you get best idle vacuum with the idle screws 1/2 or 3/4 turns out you’ll know what you have to do. I’m a fan of sticking guitar strings in the ifr but you can make jets out of brass set screws or buy fancy metering blocks. A wideband and a vacuum gauge makes it much easier to tune especially when you get around to using the power valve for wot- which can get tricky too if you race and the vacuum increases on the big end...

The idle mixture screws control the volume of a mix of fuel and air that goes to the idle discharge ports. The IFRs and IABs control the balance of fuel to air in that volume.

Each slot typically has it's own restrictor in the carb body.

I used my LM1 with the dual O2 conversion to learn on how to fix Holley double pumpers for light part throttle cruise AFR
AndyF had indicated to me that the idle circuit mixture would affect the total AFR from idle to WOT, which they do. I took it to the next level on one of my old Holley # 9375 non HP Dominator carbs to help lean out the light part throttle cruise by drilling and tapping the main body for a #6 brass set screw to reduce the transition fuel feed and idle fuel feed circuits, that flat helped a bunch on the idle and part throttle cruise AFRs up to around 2300 RPM
Every circuit on most carbs. are tuneable

This is very helpful an more easy to understand for me
I gone dig deeper in this subject, perfect little project to have on the kitchen table when it is winter outside now.

Thanks for all respons to you all

Square the diameter, or radius before you multiply by pi.

You don't ever need to use pi. Just square the diameter and compare. Pi is on both sides of the equation so you can ignore it.

For example if you're going from an 0.060 jet to a 0.065 jet and you want to know the percent change you compare 60 square to 65 squared. Ignore the decimal points and ignore pi.

Of course.

Dropping pi is good to know. I had never tried it without pi. But when using pi for this calculation, it doesn't matter whether you squared before pi or not.

And percentages can help, but aren't necessary to this. Whatever number you take away from the mains should be put into the PVCRs. You just need to do the math to see what balance of numbers on the mains and the PVCRs keep coming back close to the original total.

i did an excel spreadsheet to compare area, it's super quick copy and paste or ctrl down, even do quick formulas to divide jet areas into each other to see how much percentage you are adding or dropping...unless my diameters are wrong, that 72 to 73 jet jump is larger than most...

i did #8 brass screws in the transition slots and drilled that as large as i could without killing the hex, around .081" or so...
it's lean enough now that if i hold the rpm's steady at ~1800 rpm when the motor is cold it will start to get really unhappy after about 5 seconds.
it's good once it's warm.

lots of people say the transition restrictor isn't necessary with the older holley carbs because the transition slot in the baseplate is sized correctly, unlike the newer biller stuff.

i dropped way down on the main jet and went for an easy cruise, got it up on the mains and just barely crowded the throttle, nice and lean and unhappy...added more jet until it was nice and smooth and the plugs were clean.
i started looking at main jet area plus PVCR area at that point, it's pretty close to equal area as the secondary side. that's good enough for now.

If I'm remembering correctly the numbers on all Holley jets are flow numbers, not the inside diameter I had a chart that showed several of the upper 70s jets, 75,76,77 maybe, that had the same I.D. but different tapers on the fuel outlet sides of those jets which changed the flow number results
As far as jetting I do most of my tuning in two jet numbers up at first until the car slows down and then down one jet size at a time until it slows down again in the 1/4 mile MPH while watching the spark plugs for color and spotting on the insulator