I want to point out something about the photo of the six crankshaft:

You will notice that the crank key barely engages the cam gear on the crank. For any high RPM operation I recommend that an additional (Chevy) keyway be cut to secure the gear. As it is only the bolt tension holds the gear securely.

 

Thanks for the advice Flyer. To clarify, are you meaning cutting it deeper? Or cutting a second one? Do you have any pics? Or a link to the Chevy key to use?

 

Cut a second keyway in line with the first one on a milling machine. Use a standard shorter Chevy V8 key. It may seem trivial, but me and others have learned the hard way that it is needed for a high winding engine with a big cam. The end of the Ford key that engages the gear is actually standing proud of the crank surface, making it very vulnerable to shearing. When this happens the gear can twist on the snout, scoring up the crank and causing the valves to crash into the pistons.

 

Bronco, I like your trans. But if you're doing all this work, why use the smog head?

I'm old and dumb and need stuff 'splained to me more, Flyer. Since I haven't looked at one of these in a long time, is it a straight key and keyway, or Woodruff? And when you say the key is standing proud of the crank surface, I assume that is what we want (how else would a key work?) but that the issue is that only the tip of the key is engaging the cam gear, and that it mostly is being used to drive the pulley for the V-belts, right? And that you advise cutting a new keyway as an extension of the existing slot, so that it runs all the way under the cam gear, and that you end up with a Chevy key (Woodruff, right?) doing the driving of the cam gear, and the factory key still in place, driving the V-belt pulley as before. And that by doing it this way, we don't have to make a new keyway in the bore of the cam gear.

(I actually did that once, hand-filed a second keyway into a cam-drive sprocket for a 460, to raise the cam timing from 8 degrees retarded (emissions, 1976 engine) to straight-up timing. When I checked out my work with degree wheel and dial indicator, it somehow came out dead-on, and I was insufferably proud of myself for a few days (until whatever was my next screw-up).

 

Are you talking in general? I thought the 300 was a non-interference engine.

But still, good advice. I definitely want the crank and cam gears well secured.

 

As for the head, honestly, it's because it's what I have. I have 3 heads in the garage and they're all about the same. Searching out another when I have no idea where to begin looking seems like it would push my project way back. Our local junk yards don't hold on to much older than '80.
I also figured after a professional port and polish and head shaving, it wouldn't really matter which head I'm working with.

 

https://tse1.mm.bing.net/th?&id=OIP....d=1.9&rs=0&p=0

Yes, it is a woodruff key, not a straight keyway. When the woodruff key protrudes past the slot on each end there is very little strength in the sticky-outie part to keep it from shearing, so a smaller (curved) keyway under the cam gear is needed.

If you go with high compression pistons and a high lift camshaft the engine will definitely not be free-wheeling.

 

I did that one time. When I pulled the motor out I saw that piece and thought I would put it in a nice place so the kids wouldn't find it and use it for a deadly frisbee or bend it into a taco.....
fast forward a week or so.....stab the motor....then it dawns on me.... DOH!



okay I thought, I'll just pull the motor forward a little and slide it down. Uh..........NO. It has to go on before the flywheel and clutch and all that which I had painstakingly cleaned threads, RTV'd, going round torquing in sequence.......

 

the other stupid thing i did was never thought about replacing the THROWOUT BEARING!!!!!!!!!!!!!!!!!!!

 

Surely every one of us has done this once. Personally, I do this KIND of thing as general practice, the first time I rebuild ANYTHING. I could supply a thread on this subject with several painful stories.

Doesn't it matter that your open-chamber, no-squish head represents Detroit's first, unwanted, desperate attempt to slightly reduce unburned HCs to meet the new emissions regs, and required lowered compression (because of no squish to quell detonation) which led to a whole generation (the Seventies) of gutless engines? The EFI swirl head was the next-gen design specifically intended to fix the performance problems of the '70s. If you shave an open chamber smog head to gain compression, without squish you run into the problem that made the factory opt for low compression in the first place. I figure 1970s smog heads are only worth their scrap price.

 

OTOH, with a 240 or EFI head you need a piston with minimum 25cc dish at zero deck to keep the CR anywhere near 9.0:1. Most street cams close the intake valve at least 10° earlier than stock (Comp 252 closes the intake 18° earlier...) which pushes up the dynamic CR on top of that.

I'd still take a 240 head over a 300 head, but with porting, polishing, and bigger valves a 300 head will howl. You can always mill it down a bit to tighten up the chamber too.

 

I have a picture (that I unfortunately can't find at the moment) of my throwout bearing in a pile of crunched metal and ball bearings in the palm of my hand. I pulled into the parking lot at work, put my clutch in and heard a terrible crunch and the pedal snapped down to the floor. It didn't move again until I towed it home. There was nothing left of the throwout bearing when I pulled it all apart...

 

I understand what you guys are saying about the head.
However, in all 10 years I've been working on this engine, I've never seen a 240 head. I have no idea where I'd get one. I've also never heard good things about EFI heads, so maybe I'm mistaken on those. I thought they were prone to cracking, and the 'fast burn' was only beneficial to the computer.
Am I missing something? Yeah, there's a thermactor bump on my head from where the smog ports are, but what else?


In the end, I'm happy with the performance my Bronco gives right now, with nothing but bolt ons. Unless I do something that's detrimental to performance, I don't see how I'll have anything to complain about.

However, I really do appreciate all the feedback, information, and thoughts. I just don't have a expanse of optional parts and pieces sitting in front of me to pick from.

As far as squish, HC, etc. I still have to pass emissions. If I do something that reintroduces something, I might be in trouble. We're tested for HC and CO.

 

With my planned set up a zero decked 300 block, 22cc dished pistons, Fel-Pro 1024 head gasket and a 240 head with the chambers slightly opened up to unshroud the valves. I should be right around 9.0:1-9.25:1 area for compression.

I totally agree there is nothing wrong with using the 300 head. If you do the work to the 300 head it will haul! I'm using the 240 head because I've got a shelf full of them. If all I had was the 300 head I'd have no problem with using one.






The past few years I've been buying just about every 240 engine I've found for sale in my area. They are getting harder to find. Run the head you've got. Do whatever work you want to, and call it good. I would not choose the efi head over what you've got now! But if you really want a 240 head I'd be more then glad to sell you one of mine if you want to take a road trip to Minnesota!

Improving squish should actually improve the emissions not make them worse. But if your current set up passed the emissions test. Then any improvements made to your current head shouldn't change that.

 

Everyone forgets that Ford made a quick burn head for the 300 way before the efi head. It has the same ridges as the efi chamber, but mine is, and I'd have to ck the casting numbers to be sure, since it is so long since I looked, but I believe it is an 81 head. It has the round chamber of a normal 300 head, but with the quick burn ridges.