2 months ago I rebuilt my 1980 Carbed 300 with stock pistons and bore, Comp 268 cam kit, Offenhauser Dual Plane intake, Heddman Headers, and a Summit Racing 650 cfm Carb. I also had 3/8 ARP screw in rocker studs installed. I haved searched just short of a year for a 240 head to bump the compression and low and behold I found one in the great state of Texas just down the road from me. Mr. Motzingg was nice enough to let me have his 240 head in a swap for my stock manifolds and even let me use his tools to pull it while he wasn't there! Thanks again sir!
On to my build I plan to have the 240 head refreshed with a 3 angle vavle job with 30 degree back cut. Im going to use 3/8 ARP studs again along with some 1.7 cbb roller rockers from F-250 Restorer. A big thank you to you also! The 268 was a good cam with great power but too small for me. Im going back with a Crower performance level 4 cam (http://www.crower.com/camshafts/ford-240-300-6-cyl-hi-draulic-hauler-cam-284-hdp.html). Should wake it up really nicely running pump gas on 9.1:1 compression instead of the 8.7:1 i have now. Stay tuned for updates and pictures if I ever figure that part out lol.

Thanks, John

 

 

Why are you doing 1.7 rockers if you're swapping in an already large camshaft? - One that is also designed for 1.6 rockers.

 

What troezi said X2......

 

I didnt figure they would do anything but good considering they were rollers. I understand that they add even more lift to the already huge cam but wouldnt it be worth it with the added life to the vavle train?

 

The usual recommendation is to build the lift into the cam and avoid possible geometry problems.

 

The 1.7 rockers will add both lift and duration, completely changing how the camshaft performs. It will also completely change the valvetrain geometry and add a lot more stress to everything. Roller or not, the 1.7 rockers will not give any added life to the valvetrain. You're already going to be stressing things with the large cam and stiff springs. Adding 1.7 rockers will not help. I highly suggest upgrading to 3/8" pushrods.

 

Is there a way I could calculate the changes it would do to the cam specs? Im not trying to be hard headed but i just dropped 150 dollars on these rocker which I know is a good deal but its hard to buy something like that and then have them sit on a shelf. Also I completely over looked the pushrods. What brand do you recomend and will milling the slots in the head be required for the size increase?

Thanks, John

 

Using those rockers won't hurt anything but it's just not really necessary with a new cam. People *obviously* use them with aftermarket cams all the time - run different ratio rockers on the intake and exhaust side to compensate for head flow, etc. Don't sweat it.

The specs sheet on that cam says CR of 10.25:1 or higher. It may feel lazy below 2,000 rpm at 9:1. It's funny you say the Comp 268 is too small for you because everyone is always worried they will lose "low end" if they swap to it.

 

Chromemoly pushrods, maybe, but 3/8" is total overkill unless you're planning to turn 6,000+ rpm.

 

Alright how about this, Ill start off by running the roller rockers and if I dont like it Ill take them off and run the stock ones.

 

I have used 1.75 roller rockers on a cam with .600 lift. I highly recommend using the 3/8 pushrods tho. The slots should be milled out to .385", by taking an equal amount off both sides of the slot. I use an extra long 4-flute end mill on my mill to do this.

 

Ill keep that in mind.
Quick question, I was having problems with my summit carb and I had a holley four barrel with vac secondarys from a camaro laying around so i slapped it on. I had to lean it out quit a bit with the mixture screws to get it to idle smooth. Once i did that it crisp throttle response...excep...... When i mash the gas realy hard and really fast it kinda jerks and then falls on its face then slowly climbs back up the rpms. I revved it and when the two lil nozzles spray down into the carb is when it bogs. How do i tune this down or fix the problem? I searched everywhere but couldnt find any other adjustment screws.

Thanks, John

 

You didn't say how big the 4V was. You have one of two conditions - it is either too lean (my guess) or too rich on tip-ins. The accellerator pump circuit needs to be adjusted for your engine. Search a Holley website for the details. This can be tuned in one of five ways:

bigger or smaller squirters
change the pump cam
change the cam orientation on the throttle shaft
50 cc pump vs 30 cc pump
rebuild the carb

If the carb is way too big you will never eliminate the problem completely. That is why I recommend a carb in the 350 - 450 cfm range. Good luck.

 

I am new to Holley carbs how do I identify it? Is the size stamped into it somewhere?

Thanks, John