Hello! this is my first post so here goes...
I have a 1978 f250 4x4 that I just converted to a 460 (400 orig).
My question is, I have it set up with an Edelbrock performer 600cfm carb. Is this carb too small? the engine has been rebuilt (Ed Hale Performance) with an RV cam, Edelbrock performer intake, JBL headers, dual 2 1/2's (otherwise stock heads, etc original engine off a 1976 Tbird) the Truck pulls good towing a 28 ft trailer, but going up grades I have the pedal pegged to the floor ( checked WOT) and boy it sure feels like I could push it through the floor for a few more rpm.
Any thoughts?
Thanks!!

 

i see so many folks ask this ? after they spend the 250-300 bucks to relize that a 750 is better suited for a 429/460 then a 600. 600's should be left on small blocks and 750's on big blocks. my general rule of thumb,i know some big blocks run bigger but im talkin about mild street stuff

 

i agree. with those mods, go to a 750. 600 is too small for a 460. Ford used the same 600 carb on the 351 and 460, so tells you that either it was way too large for the 351 or way too small for the 460 ( i pick the latter).

also what gears do you have? if too low, might not let the motor rev to its torque peak.

rgds
Mike

 

also what gears do you have? if too low, might not let the motor rev to its torque peak.

rgds
Mike[/QUOTE]

I currently have 4:10's on 35" bfg's- however, a local gear shop suggested 4:56's or even 4:88's which was my next move- however, I agree going to a larger carb should be better. I have one from a 67 chevelle project (Chevy cars- FORD TRUCKS!) that I will put on for my next towing trip.
Thanks!!
ps: JBL headers??? I meant L&L headers... first post jitters...

 

I know from experiance a 600 is to small for any 460 really unless your just driving around town. My motor poped like it was running rich a lot at higher rpm, think the problem is you can get plenty of fuel but not enough air to mix with it. put a 750 holley on and brought it back to life untill the oil pressure started dropping out from bad bearings.

 

The 750 Holley works best on my 460

 

This'll draw some criticism, but I tell you what works absolutely phenominal, is a Quadrajet from Jet. Stage 2 Streetmaster...

http://www.jetchip.com/products.asp?pid=23033

The results are awe inspiring....especially at altitude.

 

Your total lack of carb understand is showing. Carb size is dependant on several things, not just CID, but RPM at which max horsepower is to be made, compression, cam, intake manifold and porting and exhaust system. Most true RV cams quit by 5000 rpm. Holley has a good formula to get you close for carb size.

http://www.holley.com/TechService/FA...ory=Carburetor

The first question is the info you need. It should also say that a street truck is too heavy for a double pumper regardless of transmission. Hell, a 428CJ only needed a 735 CFM carb to hit 6000.

 

Without a good exhaust and a cam change with head work your are full of lack of knowledge. But then you know everything, right? NOT! I've got more time sleeping in race cars than you have experience! You are sure quick to spend the other guys money on nonsense.

 

Very good Bear 45/70 (nice old caliber too!) You are correct. I have tried to explain to countless people the correct formula for Carb size. Most will not listen even though it is a very simple formula. displacement, rpm, volumetric efficiency, equals carb size. And carb size is usually MUCH smaller than people want to ever admit. I have referred lots of people to Holley's website to view this formula before they will listen, and even then, some still insist that they need a 1050 cfm carb on a stock small block. Hey bear do a search for the new military "Chey-tac" rifle, this may interest you.

 

Here's a short story to illustrate Bear's points: back in the mid-'90s I put a completely stock 100K-mile 460 out of a '74 F-250 I had wrecked into a '78 LTD II, and one of the first things I did in my relative ignorance of the time was to replace the 600 CFM Motorcraft with a 750 CFM Holley vac secondary. I noticed a low-end "laziness" immediately, but thought it was my imagination (telling myself there was no way a 460 should perform worse with the bigger carb) and went drag racing with the car. Generally, it would run 15.7s in the ¼-mile (I didn't think that was too bad for a stone-stock 460 in a 4500-lb car, but that's beside the point). Then one week I blew the power valve out of the Holley (before the days of the check ball) and I put the old Motorcraft back on, since it was a Friday and I didn't have time to change the PV before I went racing. Blew my mind when I ran a 15.29 with the smaller carb!

I reckon the moral of MY story is: until you go making wholesale changes to the volumetric efficiency of an engine (and I mean more than just an RV cam and headers), you're better off sticking with the smaller carburetor. Now my engine has 10:1 compression, slightly ported heads, 244º/.560" cam, and Weiand Stealth intake, and NOW the 750 Holley works just about perfectly! I have a feeling that I could bump up to an 850, but for now I think I'm gonna leave well-enough alone.

My 2¢...
Pat

 

If you are hell bent on running a 750, assuming it will be a vac 3310. I would get down leg boosters installed in it. They will improve throttle responce.

 

I'll have to decide between a 850 or 950HP for one of my builds...

 

And lower the CFM rating.

 

What down leg boosters would loose in cfm, if thats even true. Cause all holley 750 double pumpers have them, will far outweigh on the street in what you will get in throttle responce. I just had them put in my 750 vac 2nd Holley and I can tell you from "first hand" experience I will never go back. It's like this, Running the same roads I have for years, I come up to the r.r. trax or any other land mark I always have and I no longer have to put my foot in it like used to. I love them !!!