Can somebody please confirm the combustion chamber volume of the EFI version of the 300 six? I have heard that the carb head is around 78cc and the EFI is around 68cc. Is this correct?

I ask because a friend and I seem to have a pretty serious problem. We are working with 300 six obviously that apparently has been blown up once if not twice before (long story). In any case we had a blown up motor and no machine shops around worth a darn. Doing a little bit of research we found a machine shop about an hour away that has experience with the 300 (the name of the shop shall be omitted until the situation is resolved). We talked to the shop and they said they could do it although he had about a 5 week backlog of work currently.

We took the block to the shop along with a bunch of parts. Knowing the factory compression to be about 8.8:1 we asked he if he could try to get this to around 9.8:1, with a forged piston if possible. He said he would see what he could do.

Five MONTHS later, the engine is supposedly ready, we went to pick it up Saturday. The delay was absurd but we figured it would be worth it as long as it was done correctly. We noticed that the piston actually came out of the hole slightly but he claimed it would be OK because it was significantly less than the thickness of the head gasket, which he said was 0.050"

Whatever, surely he did the math right, we loaded it up and headed for home. For the hour long trip home something about it just bugged me so we decided to check the math. We measured the piston at 0.026" out of the hole at TDC. If the compressed thickness of the head gasket is truly 0.050", that only leaves a quence of 0.024" That seems pretty tight but maybe it would be OK if everything else worked out.

The only trouble is, everything else does NOT seem to work out. When I run all the numbers, with a 78cc combustion chamber I come up with 10.4:1 compression. That's higher than we wanted but possibly still doable with premium gasoline. The problem is that if the EFI head is a 68cc chamber, the compression ratio jumps up to around 11.6:1. Since my friend doesn't exactly want to run race gas just to go to work, this could be a serious problem.

We are not equipped with the proper equipment to measure the combustion chamber personally. We tried to measure it given the difference in weight of a fluid and we came up with around 63cc but our margin of error is probably pretty high.

So you can see the problem! 5 months later we're just as dead in the water until we can get this resolved.

 

Carbed head combustion chamber cc is around 76cc.

The 240 and EFI heads combustion chambers are both around 68cc. The difference is the EFI are fast burn chambers.

If your pistons are above the deck surface I would find another machine shop and have the tops of the pistons milled down. Or replace them with some dished pistons.

 

Well my friend talked to the guy and he was supposedly "very nice about it." Since I didn't hear the phone call I don't know exactly what that means. It's going back for different pistons.

The question will be cost and time. Everybody makes mistakes, the difference is how they handle them. Is he gonna make it right and get it done quickly, or is he gonna charge extra labor and wait another 5 months?

 

I would be kind of concerned that the shop let the engine out the door like that in the first place. I am no engine guru, but can't imagine allowing the pistons to come up higher than the surface of the head.

 

It is not completely unheard of, especially in performance applications. That doesn't bother me so much as the fact that he didn't do the math to figure out if it would be a problem in THIS application.

 

Were the pistons he used domed, dished or flat tops? With the compression you are shooting for a zero decked piston with a fairly large dish should be all you need.

It was pretty common to use 352 pistons in the 300. But they required to mill down the piston tops. Maybe he just forgot to mill them. But it doesn't exactly instill confidence in his work.

Hopefully it works out for you.

 

I would not have more work done there.

It comes to mind that you might want to check the height from crank center to deck. A stock 300 should be 10 inches. Could it be your block has been milled in the past? Any machine shop can change out pistons.

At this point you and your friend might want to rent/buy some inexpensive tools and watch the video on power nation about how to build a 300, and put it together yourselves? It might be fun. I wish you the best.

Good luck.

 

They were 352 pistons, flat tops with valve reliefs, but he didn't mill them. This compounded by the fact that the block has apparently been milled before. He didn't forget to mill them, he just apparently didn't read that far.

We took the engine back and talked with the guy. He was very nice and told us that he was in a hurry trying to get it back and didn't run the numbers carefully like he should have, obviously. Although that in and of itself is not particularly confidence inspiring, the fact that he actually owned his mistake speaks volumes. So many people are completely unwilling to do that these days, that much at least was refreshing. We discussed the situation and started looking at different options.

We also took the cylinder head down there and had them CC it. We watched this process so we know it was done right. We found out that the chambers were actually 78cc! I'll explain that one further down. We crunched some more numbers and determined that with a 78cc chamber we were actually sitting around 10.5:1 compression. With the larger CC head, any of the proper 300 pistons would put us too low so the best bet would be to mill these pistons. We won't have to mill them the "standard" 0.050" that people usually do, rather just get them even with the block which should be about 0.026" and that'll get us in the range we want to with compression. With any luck he'll get this done fairly quickly and we can get this stupid truck running.



The question comes up, WHY does this thing have 78cc heads? Enter the tale of woe and BS that is this truck.

My father bought the truck around 1999 or 2000 with around 90k on the clock. He drove it until he upgraded in 2006, he passed the truck on to me with around 170k on it. I drove the truck for quite some time until it developed a ticking sound that sounded dead on like an exhaust leak. At this point it had about 199k miles on it. I took the manifolds off and actually found evidence of a leak, great, easy fix. I decided though that instead of trying to deal with the factory manifolds, I wanted to install a header. It took me a while but I finally got a header, had v-band clamps installed on the collector, had it ceramic coated, etc, etc. I got this installed and had a stainless y-pipe made up and everything. It looked great and ran great.

I drove the truck for about 2 weeks until suddenly it got impossible to start hot, had absurd amounts of blowby, and started blowing blue smoke like you wouldn't believe. Very shortly thereafter it started losing oil pressure and you could hear at least one rod knocking. GREAT, just what I needed. Spun bearing and bad rings at a minimum. My options then were to rebuild, get a crate motor, or find a donor. Rebuilding wasn't really an option because as I have mentioned, I don't trust machine shops around here.

I was broke but my dad offered to get it taken care of and took it to his mechanic. After a little while he contacted my dad and told him he found a donor with only 70k miles on it. He quoted my dad an out the door price on this that would have been equal to the parts alone price on the crate motor. Beggars can't be choosers so I let dad go with whatever route he thought was best.

Not too far much later I got my truck back and was immediately NOT impressed. Despite having new gaskets, this engine leaked oil like crazy, the oil pressure gauge wasn't hooked up, the timing was 20° retarded, and finally he didn't even bother to do a basic tune up on it. I fixed the oil pressure sending unit, put new plugs, wires, cap, and rotor on it, set the timing, and replaced the lifter cover gasket and the truck ran OK. I won't say that it ran great, but it was certainly better than the old engine at this point, although I didn't fix the oil leak. Apparently some moron had overtorqued the cover and distorted it. I ordered a new cover and new gasket. The throwout bearing also started to go south.

Before I got around to replacing either my father upgraded trucks again and passed me his extended cab 4wd Chevy. My friend really needed a truck so I sold him my truck for a song. Before it left my driveway we replaced the lifter cover and the throwout bearing. Everything was good. I had a better truck, my friend had a truck, and it was out of my hair. About 3 days later the engine blew up, at least we though it did.

It started making a horrible racket, made no power, backfired like crazy, huge amounts of blowby, etc, etc. We ran a compression check on it and found that all cylinders were lower than we wanted to see. We started taking stuff apart and when we got the valvecover off we found that somehow one of the pushrods had jumped out of the rocker so it suddenly had a dead cylinder. That explains a lot, but doesn't explain the horrible compression. We decided to keep digging.

We pulled the engine and dropped the pan. It had thick metallic sludge in the oil pan a quarter inch thick. We also immediately saw that the rods had been marked TWICE where this engine had been previously rebuilt. 70k miles my butt. A quick check of the cylinders revealed they were already 30 over. So not only was my dad's mechanic completely incompetent when it came to getting it running properly (can't even set timing?) he also completely ignored the obvious fact that this "70k motor" had been rebuilt before. He either didn't notice (incompetent) or didn't care (dishonest) and just dropped it right in. That's how we got to the situation where we were having it rebuilt in the first place, but that still doesn't explain the cylinder head.

Obviously this motor had been rebuilt before. Obviously somebody must have put a carb head on it. The real kicker though is that all of the EFI provisions were put on the head. Somebody had to go through a lot of effort to modify the carb head to work with the EFI emissions, and for what? A way lower than factory compression ratio. Finally this explains why even when it just didn't feel good to me and never got the mileage it should have. No compression = no power and no fuel economy.

As you can well imagine we are very much interested in finally getting this stupid thing running properly. We are making every attempt to do it right this time using quality parts and upgrading where feasible.

When done it should have the following:

SpeedPro Pistons with Mahle Rings right at 10:1 compression
Factory Crank and Rods - Balanced
New Balancer and Flywheel - Balanced
ARP main studs
ARP rod bolts
Comp Cams 260H Camshaft
Comp Cams Lifters
Comp Cams Springs
Comp Cams Steel Timing Gear
Hedman Header
Mcleod Ceramic Clutch

 

Do you know what the casting # is off the head? It should be on the lower front edge of the cylinder head.

What kind of rocker arms does it have? Do the rockers bolt in or does it have rocker arm studs?

You might be working with a bit of a frankenstein engine.


78cc sounds like it's closer to a carbed head to me instead of a EFI head. I might be wrong about the EFI combustion chamber size. It's been over a decade since I cc'd one. But I could have sworn the efi head was the same or very close to the same size of the 240 chambers. I was just going off my memory and it's not always what it use to be. If I was wrong I apologize.

This is why it's a good idea to always check the chamber sizes when building an engine. And there's always a chance of minor differences in chamber sizes. You also never know if there has been previous work done to the heads.

 

I do not know the casting number at this time. When we get it back I'll try to find that to get to the bottom of it. As it is though I have no problem believing it is a Frankenstein motor. If you read my entire meandering story of the history of this piece of crap, you'll understand why.

As far as the rockers, they bolt down, no studs.

 

Are the Valves 'shrouded' in the combustion chamber?

I don't have any pics, and never sawed one, but imagine they are visible by looking at it. AFAIK, only the efi'd heads have this shroud for fast burn qualities.

 

Do I understand that you want to retain that 10.4:1 compression figure? That seems awfully high for a daily driver truck, especially if you are going for better cylinder filling at the same time, with the good manifolds, etc.. I'm guessing that's getting into premium gas plus water injection territory. Whatever, if you are shooting for high compression, that squish dimension should be tight to stave off detonation, although the figure you mentioned back a ways, .024", seems risky. I'd get nervous with squish any tighter than .035-.038". Double-check with the maker of the head gasket for the compressed thickness before you make any other decisions about milling piston crowns, etc..

 

I think he said he was shooting for around 9.8:1 compression.

 

Ah, now I see it. Well, in any case getting the squish right is a win-win in any engine rebuild.

 

Picked up everything this morning. Math now puts the compression at 9.95:1. That might put us in mid-grade or premium fuel territory but that's doable, much better than the race fuel it would have required at 11+

The goal is to hear this thing run Saturday. I work 2nd and he works 3rd. We're trying to get all our ducks in a row in the mornings this week so we can put it all back together easily on Saturday.