I have been chasing a low mile Napa rebuild 300 that came out of a '81. I'd like to "kick it up a notch" and want to run it by the esteemed straight six crowd here. Specific questions in bold. Of course, feel free to comment with other thoughts.

I don't want to do a full rebuild as the engine is basically in good shape, so if I can leave the short block alone that would sure help the budget. I know the CR of a stock early 80s 300 should be 8.0, correct?

I do have a 240 head still sitting on a complete 240 I picked up last yr, so the plan is this:

Have the 240 head rebuilt with Chebby 1.94/1.60 valves, deck it enough to clean up, and do some home porting (with sanding rolls only for my amateur porting skills). Should I do screw in studs?

Unknown spec better but not too radical cam.

I have an Offy C intake craigslist find, and a 2 barrel 2150 1.14.

EFI exhaust mainifolds to a free-er flowing exhaust. I already have the Walker "Y" pipe 45166 (I think that's the right p/n), but am open to something else especially if it's an off the shelf solution. I do not want headers; I like the ruggedness of manifolds. I've read that these manifolds can be ported for better flow; is that something that can be done fairly well at home? or is there someplace these can be sent to?

The head should bump compression to ~8.5 or so, yes? I believe most recommend the Fel Pro 1024 head gasket?:

Fel-Pro Performance Head Gaskets 1024 - Free Shipping on Orders Over $99 at Summit Racing

My '85 F150 engine is very tired with lots of blow by, but as you all know, it's hard to kill a 300. The new engine would hook up to a NP435/4x4 combo.

 

Can't answer all of your questions, but since I've been calculating compression ratios lately, I can weigh in on that. Skip to the bottom if you don't care about all the math. But if you do, here it is, and explains how it works.

The 300 stock:

3.98" stroke, which is a 1.99" crank throw.
Connecting rods are 6.207".
Piston height is 1.778".

This brings the piston up to 1.99 + 6.207 + 1.778 = 9.975".
The deck is 10", so you have 0.025" of space from the top of the piston to the top of the deck/block.

cylinder volume = (diameter / 2) ^ 2 * pi * height

volume (piston) = (4.00 / 2) ^ 2 * 3.14159 * 0.025" = 0.314 cu. in. (or 5.15cc)

Head chambers are roughly 76cc stock. (or 4.64 cu. in)

Your head gasket takes up some volume and is normally 4.17" across and 0.048" thick.
Head gasket volume = 0.6555 cu. in. or 10.74cc.

The piston dish is 25cc (or 1.526 cu. in.)

Then there's a small area around the piston since it doesn't have perfectly 90° edges, has some space between it and the cylinder walls, etc. that is usually 1 - 1.5ccs. (Let's go with 1.25cc)

Add those up. 5.15 + 76 + 10.74 + 25 + 1.25 = 118.14cc

Stock cylinders are 50.01 cu. in. or 819.56cc.


Total volume = 819.56 + 118.14 = 937.7cc
Compression = total / compressed
Compression = 937.7 / 118.14 = 7.93

So yeah, around 8:1, give or take a few.



This changes when you bore it out, since your cylinders become bigger. A 4.03" bored cylinder is now: 831.93 ccs. The head and block are usually shaved a little, but overbored pistons are also a little shorter to make up for this. Usually around 1.767 in height. So, let's say the volume doesn't change in the head.

831.93 + 118.14 = 950.07cc
Compression = 8.04

So you almost get a 0.1 compression bump just by boring it.


If you straight up put the 240 head on it. It's usually 68ccs. So your head volume is reduced by 8ccs. This brings it to 110.14cc.

831.93 + 110.14 = 942.07
942.07 / 110.14 = 8.55:1


So yes, about a 0.5 bump in compression just by using the 240 head.


Going from the regular to the Fel Pro 1024 reduces the gasket volume by almost 2 whole ccs, for a total of about 108ccs.

This'll make it about 8.69:1


Not too shabby, huh?


I know that's a bit of math, but I know I prefer it when things are explained to me instead of just "yes or no".

 

Ab covered your compression question.

Here's my feelings on the screw in studs. You are already going to have a bunch of work done to your head. So why not have the screw in studs done at the same time? I consider it to be fairly cheap insurance. Because it would suck to get the engine finished and then have one of the stock studs pull out of the head. If you have the screw in studs installed it's one less thing to worry about.


As far as porting the EFI exhaust manifolds, yes you can do it at home. The outlets are where you want to remove the most material. Enlarging the outlet hole size is what is going to gain you the most performance. You want to enlarge the outlets as much as possible but still leave the cone for the exhaust to seal to. On the head side of the manifolds you mainly want to clean them up and smooth things out. And depending on how far you want to go with things. You can actually polish the inside. But be warned once you start polishing stuff it can get addictive.

 

My machinist quoted me $125 to convert to screw in studs.

 

Your head had pedestal mount rockers didn't it? His 240 would have studs. So the price may differ slightly for his.

I did say "fairly" cheap insurance. The higher the cam lift or the higher the rocker ratio is, the more of a good idea it becomes. But I have seen rocker studs pull out with a stock cam. It's not real common but it does happen.

 

I'm using my pressed in studs head since my pedestal mounted one is currently getting my Bronco from A to Z.

Honestly, I thought $125 was a lot less than I was expecting, and thought it was not only cheap insurance, but allows me a lot better control over my valve adjustment.

 

My bad. It's hard enough for me, keeping up with my own projects.

 

No worries, I try to do the same, but lose track from time to time.

 

FWIW, my engine builder routinely installs screw-in studs without asking when they do a head. I suspect that experience (they had a UPS contract for overhauls) may have had something to do with this...

 

Da-yam AB, I'm impressed! Yes, just the answer I was looking for. Not quite the magic 9.1ish for best CR on reg fuel, but good enough.

 

Thanks for the info Fordman. It confirms my thoughts on screw in studs. As long as I'm right there, why not?

Good to know too about the efi manifolds. I much prefer to use them over headers. If I was looking for more power then headers would make sense, but they flow well I think for street use, and if I can make them better with some home porting, then I'll go that way. I have two sets so when I get time will start playing with one set.

 

Bronco, by your figures (.025" piston crown below deck, and .048" gasket thickness) the engine has .073" squish height, almost twice what you'd want, and nearly useless for the squishband to do its job (and the opportunity to have some squish area is a major reason to replace a smogger head with a 240 head in the first place). The more static compression he builds into the engine, and the more dynamic compression he gets from upgrading manifolds, cam, port cleanup, etc., the more important it is to deck the block to get maximum squish action. (Oh I know YOU know all that, Bronco, but guess that you forgot to include it in your figuring).

(Is that the compressed gasket height?)

 

Those are the stock numbers, at least for my '81. Certainly nothing to get excited about, huh? And yeah, that's the stock gasket thickness.
Kinda why it does some good to overwork them and make'm right.

Just shaving the block down to 0 deck and using the FelPro 1024 gasket will bring your squish height from 0.073" to 0.039". All of that height is just the gasket, so not much more you can do about that.

 

Yeah, about the only way you're going to get up past that is to either have the block shaved down and/or shave the head. Or, more extensively, start swapping out pistons (but that's beyond the scope of your project I imagine).

If you shaved the head from 68cc to 64cc, you'd hit 9:1, but that depends on how much material you'd want to take off.

 

Didn't understand that part.

Anyway, looks to me like if you shave the deck and/or change to a thinner gasket enough to get the squish height around .038-.042", you pick up something near to ANOTHER half a point of static compression . . . which however might not require higher octane fuel because now your squish is squishing good.