Glad to hear you are back at it, and congrats on getting the degree.

I am in a very similar situation and I graduate next month with my BS degree. My block and head are at the machine shop getting cleaned and tested to see what the rebuild is going to take.

 

Nice going and congrats on the degree. Hope it works out great getting you where you want to go.

I think that's my first step on the engine is to take my block and crank down and have it all cleaned and prettied up. That'll tell me a lot of things like if I need to have it honed, what size pistons, work that needs to be done on the crank, etc.

So, crazy idea, and this stems from my poor experience with my last camshaft. Anyone ever thought about what it would take to convert a 300 to use roller lifters? It's probably a mistake, but when I looked up lifters on summit for the 300, a set of roller lifters was listed, and it got me thinking.

 

A fat wad of cash is all you need.

Were the roller lifters listed on Summit solid or hydraulic? On the old FSP site there were a few folks who ran/were running big solid roller cams in race engines. IIRC the lifter bores are the same as a 460 but spaced differently so requires some machining on the link bars.

Then all you've got to do is find someone with a steel 300 cam blank.

 

Heh, just curious. Didn't know if it was worth looking into.

 

My sister got a major in Computer Science and ended up being on the team that programmed the drilling operations software on the rigs I was working on.

Attachment 290851

 

That is really cool!!

 

So as far as a rebuild goes, I'm not looking to do standard "freshening up", but would like to work it up a bit.

I imagine my first step is to take the block and crank I have down and simply have it checked out, cleaned up, honed if necessary, etc. That'll be necessary for the usual stuff like main bearing, cam bearing, and piston sizes.

What do people recommend for pistons? Are there flat top pistons for these engines? Or ones from another engine that can be made to work? I'm mainly looking to boost up the compression a bit. Maybe to 9:1 or so.

What are the thoughts on compression? How much is good? How much is too much?

I'm thinking another Comp 260 cam, or one that's comparable. Metal cam gears, etc.

As for the headwork, what are the pros and cons of larger valves?

 

When I built my 300 (which will finally get swapped in this spring...) the pistons were dished late model hypereutectic with the narrow metric rings. I measured the dish at 25cc so at zero deck with a 240 head the CR came in ~9.4:1, IIRC.

There are 351W pistons with the right compression height for a 300 but you'd need to have the rods bushed, no biggie there. Speedpro, I think, makes a flat top with four valve reliefs that measures 12cc. At zero deck with a 300 head that would probably put the CR ~9.5:1.

Since the stock cam is retarded 10° the intake closes very late, at 70° IIRC. The Comp 268 cam I used closes at 60° - i.e. it raises the dynamic CR vs. the stock cam with the same advertised duration. The 260 cam closes 4° earlier than the 268. A dynamic CR of 8:1 is a good rule of thumb for a street engine and that's right about where mine ended up.

OTOH, a point of compression is only good for ~1% increase in HP so there's no need to push the envelope.

Replacement 300 pistons are heavy. I'd wager those 351 pistons are at least 100 grams lighter than the ones I used.

The ports and valves on a 300 wouldn't adequately feed a decent 302 and our engines would be 400 cubic inches if they had eight cylinders. I don't think there's any con to larger valves and I don't think there's enough metal in the head that you could port it too much. I may be proved wrong when I get the new engine in the Bronco but I opened up the bowls and ground down the valve bosses a ton and I don't expect to see much loss of velocity at low speeds.

 

Your piston options are dependent upon how much you want to spend. I used forged 302 pistons that weigh in at 385g a piece, but I paid money for them. It all kind of boils down to what your needs are. Baron posted some good info for you to start on.

Is there a source for this anywhere? I've never heard of a cam retarded that much from the factory. 4°, sure, but not 10°. I've actually been wondering this as my cam has 4° of advance built in and then I can go another 2° with my timing gears if I want to, but it's hard for me to make that decision without knowing where the baseline is. Although I'm assuming that the 4° of advance would be from zero, not from factory setting... haven't checked.

 

Thanks for the info, guys. Much appreciated.

Why are the pistons dished? Is this to lower compression?
Also, are valve reliefs in them to make them non-interference? If the are, and I get flat top pistons, would I be removing this safety feature and have to be concerned with engine damage should something ever happen to the timing gears? (Not that I ever see that happening, but still...)

 

A factory 300 piston has a large ~22cc D-shaped dish in the piston. The bigger the dish, the lower the compression so I guess you could answer that question with a yes.

Ehh, sort of. Each piston is different and some of us have shaved decks/heads and others don't. It's more to stop the valves from hitting the piston in the sense that you now have a flat top piston which is much higher and much closer to the cylinder head. I'm not actually sure whether or not the 300 is interference or not (I think it is) but the valves themselves sit 0.3" in the head and then when you add your deck clearance and piston dish/valve reliefs, you'd have to have some totally FUBAR'd camshaft timing to ever make a valve contact a piston.

 

I don't believe it has interference, since I've heard of guys shredding their phenolic cam gears and just straight up dying on the side of the road. Tow it home, clean out the oil pan, put new gears on, and fire it back up. Just curious if that would change with some aftermarket mods.

I've also heard that 360/390 pistons work well, but automatically means you have to bore it out to at least a 4.040".

Is it just easier to get stock 300 pistons and then shave the head/block?

 

Easier? Sure, if it matches your goals. Ideally you'd want to zero deck and then use a 0.040" thick head gasket for good quench. Ford made a lot of 4" bore engines. You can pretty well adapt any piston over as long as it has a compression height you're happy with and the proper pin size. If the pin size is smaller than the rod, a simple bushing can be made to make it work.

 

This is the first time I've ever rebuilt an engine, so I'm mostly going from things I've heard/discussed. I know what I'd like to accomplish, but not necessarily sure what the best methods of getting there are.
I know plenty of people raise their compression, how is it normally done? With different pistons? How do you know which pistons to go with or how much they'll change the dynamics of the engine?

 

It's all math in the planning stage, and you're soon to find out why building an engine is completely different than a simple rebuild.

Compression depends a lot on what fuel octane you want to use. It has also been proven that compression alone will hardly do anything to improve performance but it will however significantly help you when you build the rest of the engine to match. If you want to stay on 87 octane you should definitely keep it under 9:1 compression, I'd say, but others might disagree and explain why. The 300 is funky though and anything above 10 pretty well calls for race fuel, so if you're in that middle range you'll need higher octane. A lot of people seem satisfied with the compression ratio that the 240 head offers, so let's do some math.

Attachment 290813

The above is a factory 300 engine's dimensions. Knowing this, and knowing that a 240 head has a 68cc combustion chamber, we can work out through online compression ratio calculators that this 300 would have a compression of about 8.7:1, rounded up, assuming the piston dish is 22cc and the head gasket compressed thickness is .040".

The easiest way by far to raise compression is to shave the head, and since you're using a 300 head (I think) with 76cc combustion chambers, and that each .010" shaven off a head on a 300 is equivalent to 2cc in combustion chamber thickness, you would need to shave off 0.040" from your head to be at the equivalent compression of a 240 head. Do you want to stop there? I'm not sure. I don't know what your goals are.

Now, a smart man who says, "Hey, I want higher compression but the last thing I want is autodetonation" would figure that he needs to make sure that quench is on his side, and since this smart man knows that .040" is considered the best quench distance and that an aftermarket head gasket for the 300 compresses to 0.039", he would need to zero deck the block, which removes 0.043" from the block. This is roughly the equivalent to shaving the head 0.040" and he has the added benefit of having better quench and therefore a smaller chance of autodetonation. The obvious problem with this though is that his man will need to take his entire engine apart and give the machinist a bare block.

I would personally zero deck the block no matter what, and if you wanted more you'd be left with two options: 1) If you're on a budget, shave the head or 2) If you have some money, buy some fancy pistons.

It all depends on what you want to do, and the more of what we know your goals are the better we can help you.