holley 750 too small?

[poprocks440]

448
10.4.1 compression
eddy 84 heads
eddy gasket matched rpm manifold
JE pistons
stock forged rods w MP nut bolt kit
stock forged crank
10 inch converter
3.91
727
28x9x15 slicks
750 DP holley
.564 com cams hydraulic cam
all in a factory looking all steel all interior 67 gtx 12.00 to 11.90s shifting at 6000. i feel like it should do more?

 

[BCBOUND]

750 too small ??

...sounds like you should have close to a 900 CFM carb and a regulated fuel supply of 5 psi min at idle....:headbang:

 

[Revhendo]

What RPM are you rolling through the traps at? 60ft. times? Street car? Strip car?

 

[67 coronet]

a regular 448 running upto 6000rpm's should have a 778 cfm requirement at minimum.(by the math)so a hotter set up should go alot bigger.i would consider a 950 cfm hp carb depending on what the car is used for.

 

['67Satellite]

I'm no expert, but you have to take efficiency into consideration. Not even the most extreme race engines are 100% efficient. As per the equation below, 6000rpm at the trap, and 95% efficiency (which i think would be well above what it actually is). You're at about 699 cfm.

That number is the most air that can be pumped through that engine at that rpm. But going on the big side is probably a good idea, I just don't think going too big is going to help you out at all.

Anyone have any comments on my math/reasoning? I'm always looking to learn something new.

 

[Cranky]

It's always worked for me to go bigger than that equation suggests.....only one was to find out imo is to get it a try. I have a 950 HP laying around and a buddy tried it out on his 360 powered Duster and it picked it up a lot and to the point where he didn't want to give it back!

 

['67Satellite]

http://www.carcraft.com/techarticles/selecting_right_carb/index.html

Read this after i posted my previous comment. As i figured, there is more than one thing in an engine working to make math completely useless. Some good information in that article (secondary choices, etc.).

I guess in the end it's either trial and error, or someone's hot rodding experience. I too have a 750 carb on my 440, so i'm interested to see what everyone has to say.

 

[70rr-brian]

I bet a 850cfm would get you down to around 11.5 or maybe a tick lower. But that is just a guess. If you know anyone that has one give it a try...Just give it back. LOL

 

[lewtot184]

if your using a dual plane intake go 125% above the "equation"; single plane 110%.

 

[67 coronet]

I'm no expert, but you have to take efficiency into consideration. Not even the most extreme race engines are 100% efficient. As per the equation below, 6000rpm at the trap, and 95% efficiency (which i think would be well above what it actually is). You're at about 699 cfm.

That number is the most air that can be pumped through that engine at that rpm. But going on the big side is probably a good idea, I just don't think going too big is going to help you out at all.

Anyone have any comments on my math/reasoning? I'm always looking to learn something new.

the equation i have always used is:
(cubic inches x max rpm)divided by 3456=aprox cfm baseline for nonmodified eng.
about the same as yours,but you remove volumetric eff from the equasion.same stuff used by old school tuners like grumpy jenkins,smokey and many others.the hotter the eng,bigger you go up in cfm.most of it is a test and tune or guessing game anyhow.

 

[mattsmopars]

I ran a 850 Holley DP with the choke horn milled off in my 72 charger.
The engine was a 68 440 HP .040 over six pack TRW forged piston, 509 purple shaft cam, M1 intake, MSD ignition,906 heads,and headers with a 3.55 gear and it always did absolutly great.
Matt

 

[Meep-Meep]

The bigger carb will provide more top end power (to a point) but give up on the low end. If your engine has a power band up high and you have deep gears then try a bigger carb. Only way to know what carb is right is to try several and let the trap speed and ET decide.

 

[67 B-body]

My setup has an 850 with choke milled down "gone"..... Too small for my engine!! I would love to try a 1050cfm 4500 Holley and a 1" 4150 adapter plate!

 

[ykf7b0]

Put that 850 on there and watch that Mopar come alive!!!!

 

[Photon440]

I'm no expert, but you have to take efficiency into consideration. Not even the most extreme race engines are 100% efficient. ...edit...
Anyone have any comments on my math/reasoning? I'm always looking to learn something new.

I would have thought that some of those hyper tuned race cars would be 100% efficient. Chrysler claimed 104% efficiency on the 413 cross ram, and that was 50 years ago...

 

[poprocks440]

this is my street strip car. with the 3.91s i shoot the traps at 6000. my 60 foots are 1.66 to like a 1.72. im affraid to spend the money on the 850 to not pick up any. by the way. i had to jet up a lot on that 750 before i got good color on the plugs. im talking like stock jets were in the low 70s and im now in the low to mid 80s w jets. how many sizes can u go up before you need a bigger carb?

 

[poprocks440]

and does the 850 DP have the same diameter venturies? as a 750DP? i know the 850 will give more fuel but will it give more air also

 

[MoparLife]

Carb selection can be tricky. I have tried many combo's on my car and I found that flow testings tells the real story. The last 850DP I built for a customer flowed 930CFM on the flow bench. Based on all the information you have noted, I would run a 850 Holley HP Ultra. You get better tuning with adjustable air bleeds, better flowing metering blocks, billet throttle plate and adjustable idle bypass valve (no need to drill holes in primary throttle plates). You get alot of carb for the money! If you have any more questions feel free to PM me.