Holley 2300 350cfm vs 500cfm

[mcmillal]

Hi All,

I tried one last mod for the year this weekend. I installed a Holley 2300 500cfm two barrel carb on my mustang. Again, this was really just to see if any significant gains would be made. WOW! I could not believe the difference. After installing stronger valve springs two weekends ago and now the 500cfm carb the performance improvement is fantastic. We weren't sure how well the larger carb would work on the small log head. I expected a little loss on the bottom end and some gains at the top. It is simply better all around. It launches hard and pulls strong right through 5500rpm. Don't get me wrong, the 350cfm carb worked very well also. The test with the big carb was just to see performance gains. The thing I was most surprised about was that I didn't lose any drivability. My gas mileage is going out the window, but man it's fun to drive. I will try to get some GTech runs in tonight and post the results tomorrow.

..............Cheers, Alex

 

[Anonymous]

that sounds awesome. like to see the results

 

[CZLN6]

Howdy Alex:

Oh the Joy!!!!

How about some details? I've got a 1.08 Autolite on my 250 engine now and a Holley 500 on the bench. It's too dang cold to be messing with it right now, but your excitement over the improvement in performance almost motivated me.

I'd like to hear a before and after comparison with objective data, like a G-tech.

The drag strip and G-tech will give you good WOT data, but won't tell much about street driving. Do you do street driving? Do you still use a funnel adaptor, or are you mounting to a modified log?

What jets did you end up with in the 350? What are you starting with in the 500? What about squirter nozzles? Accelerator pump cam? Power valve #?

My 500 is stock at #78 mains, #28 squirter, and 5.0 PV. I'm guessing I'll need to jet down as I'm at 5,000' elevation, and move up on the squirter. I kinda hate to make changes til I try what Holley engineers throught appropriate. Even though they didn't have my engine in mind when they put the 500 together, it is a place to start.

Keeep it coming!

Adios, David

 

[Anonymous]

My gas mileage is going out the window, but man it's fun to drive.

Is the MPG loss due to the larger carb? Or due to you enjoying the new performance of it?


I'm curious as well... I'm still trying to decide on what carb to use when I get my 250 together....

 

[wsa111]

David, the stock main jet on the 4412-500 cfm carb is #73, with a .028 discharge nozzle & the 5.0 power valve.
Did someone make a swap or did the 3 look like an 8.
When my back heals, i'll get the modified head on with the 500 carb.
I plan to start with a 71 main jets, with a 6.5 power valve. But thats just for starters.
Alex glad you tried the 500 carb, as david said keep us informed.
I also have a 7448-350 carb also to try. they come from holley with a 61 main jet, i will try a 59 as a starting point. My past experience with holleys is that they are always rich unless you run them on a 454 or 460 cubic inch engine. William

 

[mcmillal]

Hi again,

David, one of the things I was most surprised with was the drivability of the car with the 500cfm carb. It works great both casual driving and WOT.
It is a stock rebuild, so the numbers William mentioned, 73 jet and 5.0 power valve, are what's in the carb right now. I'm not sure about the discharge nozzle. Believe it or not, I am using a funnel adapter. It has been hogged out to maximize the flow.

William, my 7448-350 originally had 61 main jets, but I bumped it up to 64s at the track. I pulled a couple of the plugs after one of my 1/4 mile runs and it looked a little lean. I increased the jet size and it did another plug test that looked better so I stuck with the 64s.

The loss in gas mileage is mainly due to my enjoyment of the new found performance.

Stay tuned, numbers coming.

.............Alex

 

[MandarinaRacing]

WOW! I could not believe the difference.

Wow, amazing, I can't believe it...that much improvement!?!?! We need to spread this around...hey Dean (Xe) you gotta take a look at this....

Keep us posted on more!!!!!

Alex

 

[wsa111]

Alex, when you had to increase jet size, did you make sure your float level was correct & the main thing did you have fuel starvation. These holleys love 7# of fuel pressure. I have richened many a carb up only to find fuel starvation the main culprit. On one vehicle i installed a complete new fuel line with a larger pickup in the tank & used an electric pump to a mechanical pump. After this i even leaned the carb from it previous jet sizes & dropped 3 tenths & picked up 3 mph in the quarter.
Run a fuel pressure chack before you start richening up the 4412-500 or the 7448-350 holley carb, or any 4 barrel holley. Hope this helps William

 

[CZLN6]

Howdy All:

Thanks for the clarifications. William- I'll definitely check the jet sizes before I install.

Adios, David

 

[MandarinaRacing]

These holleys love 7# of fuel pressure

Really?!?! That much??

Alex

 

[wsa111]

Anybody running a holley carb be it a 4412-7448 or even a 4 barrel on a v-8 application, definateley use the red electric holley fuel pump which punches out 7# to the fuel system. There is nothing like fuel starvation to lean out a potentally good fuel system.
If you are not running a holley 4412-500 cfm or a 7448-350 cfm carb or another holley 4barrel i cannot promise you a rich flooding problem with any other carbs but what i mentioned. If you are running these holleys its like breathing pure oxygen. no fuel no power.
Always check your fuel pressure with a guage. POWER,William

 

[Anonymous]

definateley use the red electric holley fuel pump which punches out 7# to the fuel system.

Now I know whats next on my list of things to do......

Doug

 

[addo]

Not sure I'd be in a hurry to install a Holley fuel pump. I've seen two fail in one year, on one vehicle. They just weren't very well made structurally; the motor wind connections all sheared at the commutator. :roll: Noisy mongrels, too!

Running a Facit diaphragm pump now on the Irrational truck; a little feeble but holds 6½lbs consistently and a new Carter waiting to go on. Hindsight has me sold on a return type regulator, too. Cooler fuel, less stressed pump.

 

[mcmillal]

William, at first I we did think it was a fuel starvation problem. I did a flow test and installed a fuel pressure gauge. All was good. The stock fuel pump works fine pushing out plenty of fuel at 7psi. As you said the Holleys do like that kind of pressure. No need for an electric pump. I think it was Falcon Fanatic that got me looking at the valve springs and that was where the problem was. I had stock springs that were too weak to spin up over 5100rpm. We installed stronger springs (rated about 100lbs) and that's where the biggest difference came. I can run it right up through 5500rpm pulling hard. So I figure if you've got some kind of cam installed be sure to use the right valve springs. I guess it really depends on how you're going to drive. If you drive it hard, high rpm, using stronger springs. If not, the stock springs are fine up to about 4700rpm.

................Cheers, Alex

 

[MandarinaRacing]

Noisy mongrels, too!

WHAT !?!?! WHAT !?!?!

Alex

 

[wsa111]

Alex, yes you do hear the pump running. the main thing to do is insulate the pump to the frame or mounting spot with the supplied rubber insulator.
Adam you must have gotten a bunch of defective pumps. I have used or installed a dozen in the past several years with no problems.
I should mention that the electric pump is only necessary on a modified engine. Anyone with an oz head using a holley 2300 series carb or on a modified log will this pump be necessary.
If you don't think you need one run a full throttle pass with a pressure guage that you can read under full power conditions. If you don't have at least 6# you best put on the electric pump.
I know many of you question my thoughts, but from past drag strip experience the constant 7# pressure lets you jet the carburetor accurately. William

 

[MandarinaRacing]

Alex, yes you do hear the pump running

I was just teasing Adam , I'm running a Holley Blue pump and inspite of my best efforts to dampen the mounting bracket I can still hear it....BTW were not doubting your advice, it's just that (for me anyway) 7# of pressure sounds like a lot, but don't worry I will try it. THX

Alex

 

[addo]

You can bolt the Holley pump's hoop bracket to a Ford trans mount rubber with a little hackery. That dampens noise a whole bunch (but adds weight). Cheap fix though.