I am looking to build my 4.9L and need some advice. Here is what I have planned so far.
Comp cams 260 extreme series cam with lifters, valve springs, retainers.
offy or clifford intake
EFI manifolds with single exhaust
ported and polished head
390 cfm holley carb.
If the bottom end is in good shape I plan to leave it at standard bore, but if it has some wear I will have it bored to .30 over.

Just wanted some critique on these plans and to see what you would do as far as rocker arms, and if the 390 cfm will be enough for this build.
The engine is an 85 model with the Duraspark II conversion and will have no emission stuff left with the build.
The plan is a nice low range torquey engine that will turn 35" tires with 4:10 gears with no issue, and occassonally tow a small boat/ 12 foot trailer with two quads.
So let me have your wisdom and advice please
The trans is a NP435 if that helps.

 

That should be just what you're looking for in terms of performance.

After '85 Ford used bolt-down rockers on the 300 heads, so unless you have it machined for screw-in studs there aren't a lot of options. Crane sell a stud conversion kit, but if the head is off anyway the kit would probably be a wash vs. machining and buying proper studs in terms of cost.

A 390 carb is fine, a 600 would be fine, whichever you can find cheaper. Any vacuum secondary carb is only going to let through as much air as the engine needs.

 

Thanks for the info BVA. If I were to go with an earlier head what year would be the best for the screw in studs, and with that head what would you use for as far as rockers? Or would machining my head be just as easy as replacing it?

 

I pretty much did to my engine what you're doing..cept with a 600.

 

After lots of reading it sounds like the 600 will work just fine and I have found them to be a good bit cheaper too. How do you like your set-up?

 

There's nothing wrong with the stock bolt-down rockers, machining for studs is only something that would have to be done if you wanted to use other rockers.

 

What BVA said X2. Stock rockers are just fine. You might consider re-curving the distributor. Duraspark_distributor_recurve_instructions_index

 

Okay thanks. I was unsure if the stock rockers would be good enough with the new cam. So the list I had would be pretty much all that will be required other than new bearings, rings, timing set, oil pump, seals and gaskets. And of course the machine work and a new throttle cable.

 

You don't even have to mess with anything with a Comp 260 cam. The 260 works with stock valve springs as well, so no messing with the head.

If you went up to a 268 cam, you'd need stiffer springs and preferably screw in studs, but it also wouldn't be a lower rpm motor anymore.

 

I wasn't aware that there was a difference in the bolt downs and the studs? I have bolt downs and wouldn't all I have to do is just fond studs and nuts to mount with? Just curious since I though both were the same

 

I went ahead and freshened my springs up. But like it was said..not necessary with the 260. The cam itself is a great all around perfomance grind with no emphasis on higher and lower ends. Just an overall increaser. I installed the kit with the timing set..cam..litters..springs..didn't do the guides or anything. Engine had been previously gone through. Clean as a whistle. I haven't dropped it in yet..that's for Friday now that I have no ice on the ground or any previous obligations. Should get her running soon though! Let ya know for sure

 

There are some kits available to convert bolt-down heads to studs, but standard studs have a different thread size than the head (head is 5/16, most studs are 7/16 or 3/8). Plus stud mount rocker heads have machined slots for the pushrods vs. round holes on the bolt-down heads (where the sled and rocker fulcrum keep everything aligned) so you would need some kind of guide plate.

 

I think you'd be better off with a Holley 390 or 465. You'll have better performance and throttle response with a smaller carb.

 

My origonal plan was the 390cfm, but was told above the 600 would work just as well and I can get one of those much cheaper. That is one reason I started the other thread in here, to get some feedback from others as I plan this out. I am a long way from the engine right now, but want to be as informed as I can before making the first parts purchase

 

If you go to Summit Racing site, and search under Summit Carburetors, then click on 'more info', down at the bottom of the page will be a 'cfm calculater.'
A 300, turning max 5500 rpm, needs a 290 cfm carb, iirc.

With carbs bigger is not better. Yes, you could run a 600 cfm, as many on the forum do, but you'll sacrifice bottom end. You will get better performance and throttle response with the proper size carb. Just as cam shafts have a power range, a specific rpm where they come into their power, you don't want a carb that is too large for your engine and means you don't feel it really responsive until you hit 2-3k rpm. That is what a 600 cfm carb will give you on your engine.

A 390 or 465 cfm holley would work great. The Autolite 4100, with the 1.08 venturi, a 480 cfm carb that ford installed on small v8's, would be in the upper end range of desirability. The good thing about Holley's is that parts are plentiful, and you can find a nice late model one to rebuild for a good price. The 600 is a dime-a-dozen because they work great on mid size v8's. The price is a strong lure.

When buying or considering any used carb, press it firmly to a solid surface so it can't move, and while holding it use the other hand to see if the throttle shaft wiggles up and down any. If you can wiggle the throttle shaft that usually means excessive wear and a vacuum leak, which means having to install a bushing on the carb body.

Good luck. k