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Compression ratio concerns

I'm having a serious engine shop work on my crank and install new cam bearings on monday.
I'm thinking of asking them to grind the decks on the block as well. Maybe ask them to cut 0.050" leaving me a piston-to-deck-clearance of 0.030"

Do you think I'm wasting money?
 
MOPOWER871 said:
yes, but will he ship them?
Click to expand...
I could ask him, but I hardly dare to think of the shipping cost...

But the message here is: if I want to make the big difference, go for new heads instead of waste money carving some iron of the deck?
 
If it were me I'd deck the block. Are you absolutely sure your .080 in the hole? Was this measurement taken with the new pistons?
 
65-440 said:
If it were me I'd deck the block. Are you absolutely sure your .080 in the hole? Was this measurement taken with the new pistons?
Click to expand...
Don't have any new pistons. I have the SP 366 flathead pistons that sat there when I pulled it apart.. I'm quite sure I got the measurement right. Used a clock to find TDC and used feeler gauges and also a caliper to be sure...
 
RRSweden said:
I'm having a serious engine shop work on my crank and install new cam bearings on monday.
I'm thinking of asking them to grind the decks on the block as well. Maybe ask them to cut 0.050" leaving me a piston-to-deck-clearance of 0.030"

Do you think I'm wasting money?
Click to expand...

I think you will raise the compression about 3/4 of a point. Then, if your engine was making 340 HP it might go all the way to 350 HP. And I think you'll have to mill the intake surface of the heads or the intake manifold .062" so the ports and bolt holes will line up.
 
You can always get your deck clearance reduced by changing pistons. The KB 400 has a compression height of 1.908. This gets you to about .027" below deck. Even then you will still be at 8.9 to 1 with 88 cc heads. If you can reduce head cc s by going to a closed chamber head of say 75 cc, and use a .020" head gasket, then you will be up to about 10.1 to 1. For me, I prefer the higher C Ratios at my altitude of 5200 feet. It has made a big difference in the engines I have built. That piston and head gasket will also get you about .047" of quench, which will help reduce the chance of pinging.
 
A guy in sweden is selling a pair of closed chamber heads, but pre-67 (I think they're from 61).
It's the 67 heads I want, not these, right?

I also found that the -67 915 heads came with both 1.60" and 1.74" ex-valves.
Do you think I should buy a set of 1.60" if I find a pair?
 
If you can find a pair of 2780-915 heads, yes buy them! Even if they have the 1.60 ex valves. That's the 67 440 head. I believe most, if not all, the 1967 440s came with the 915 heads. But the Plymouth GTX and the Dodge R/T with the 440 had the 915 heads with the larger (1.74) ex valves. As far as a 1961 big block head goes, the closed chamber is good, but port flow is going to be less than the 67 head. You can always install larger valves and do some porting. If done right, this will improve the flow. The 61 heads also have a different rocker arm shaft mount, and only have 4 valve cover bolts. A friend had a 63 Chrysler 300 (413 engine) that would keep up with my 68 Roadrunner, in which I had installed a 413 motor with the 906 heads. The 300 had closed chamber heads, and the RR had open chamber. So the early heads aren't all that bad. What is the casting # on the 61 heads? The 60s heads ending in 516 can make good power if done right.
 
I'm not a big fan of decking the block more than just doing a clean up unless you can prof it's thick. I have a 440 with pistons that are .050 down, .020 gaskets and closed chamber heads and it equates to 10.3 to 1 if I did my calculation right. My heads are the 516's but I installed the 1.74 valves and pocket ported them. The valve pockets suck from the factory and just doing them only makes a very noticeable difference. If you do deck the block, mock up the parts to see how they fit. Sometimes they fit better than before. It all has to do with core shift during the casting process. Mom's quality control wasn't always on the money. I mock up all my builds no matter if I cut block or head surfaces. You could take maybe .025-.030 off the block and .025 off the heads? It's not always easy to bring up the CR when you have open chamber heads and pistons that are .080 in the hole. You might check into how much new pistons cost vs doing all that machine work....
 
Cranky said:
I'm not a big fan of decking the block more than just doing a clean up unless you can prof it's thick. I have a 440 with pistons that are .050 down, .020 gaskets and closed chamber heads and it equates to 10.3 to 1 if I did my calculation right. My heads are the 516's but I installed the 1.74 valves and pocket ported them. The valve pockets suck from the factory and just doing them only makes a very noticeable difference. If you do deck the block, mock up the parts to see how they fit. Sometimes they fit better than before. It all has to do with core shift during the casting process. Mom's quality control wasn't always on the money. I mock up all my builds no matter if I cut block or head surfaces. You could take maybe .025-.030 off the block and .025 off the heads? It's not always easy to bring up the CR when you have open chamber heads and pistons that are .080 in the hole. You might check into how much new pistons cost vs doing all that machine work....
Click to expand...
Yes.. The more I think about it, the more I reallice I need to replace parts somwhere... The best option, as I see it is to look for a set of 915's for a resonable price..
 
RRSweden said:
Yes.. The more I think about it, the more I reallice I need to replace parts somwhere... The best option, as I see it is to look for a set of 915's for a resonable price..
Click to expand...
Yes, that's a good place to start. Check all the salvage yards for a 1967 440 motor. And Don't rule out a set of good used alum heads, such as the Stealth, Performer RPM, or other good aftermarket head. Edelbrock also has an E Street version with smaller 75cc chambers. Those would get you to almost 9 to 1 C/Ratio. Get your deck clearance to .030 along with using a .020 head gasket, then your at 10.03 to 1. Also keep in mind that the 915 heads have closer to 79 or 80 cc chambers.
 
I plan to build my 440 at 12.5 to 1 C/Ratio. You lose about 25% of cyl pressure at a mile high of elevation. So 12.0 here is like 9.5 or 10 to 1 at sea level. Somewhere between 10.5 and 11 to 1 is the point I start to get pinging up here, with the 91 octane premium. Read 64 posts #9 post on fuel blend for Hi Compression engines. He explains it pretty good. But lots of factors have an effect on pinging, not just C/R. What elevation are you at in Gothenberg?
 
Garys1969RR said:
I plan to build my 440 at 12.5 to 1 C/Ratio. You lose about 25% of cyl pressure at a mile high of elevation. So 12.0 here is like 9.5 or 10 to 1 at sea level. Somewhere between 10.5 and 11 to 1 is the point I start to get pinging up here, with the 91 octane premium. Read 64 posts #9 post on fuel blend for Hi Compression engines. He explains it pretty good. But lots of factors have an effect on pinging, not just C/R. What elevation are you at in Gothenberg?
Click to expand...
About 10-20 meters
 
Another issue that striked me... If I would buy pistons with taller compression height, is there gonna be trouble if they'll reach up above the beveled edge where the cylinder meets the deck?
 
RRSweden said:
Another issue that striked me... If I would buy pistons with taller compression height, is there gonna be trouble if they'll reach up above the beveled edge where the cylinder meets the deck?
Click to expand...
The highest compression height I saw was 1.908. To get to zero deck you would need 1.935 compression distance. Even then, you would have no problem as the top piston ring is still below that. So this KB 400 piston is going to wind up .027" below deck. Then if you were to cut down the block by .010", it would be at .017 below the deck.
This would get you a C/R of 10.36 to 1 with 75 cc heads and a .020 head gasket. 80 cc will get you to 9.8.
 
Garys1969RR said:
The highest compression height I saw was 1.908. To get to zero deck you would need 1.935 compression distance. Even then, you would have no problem as the top piston ring is still below that. So this KB 400 piston is going to wind up .027" below deck. Then if you were to cut down the block by .010", it would be at .017 below the deck.
This would get you a C/R of 10.36 to 1 with 75 cc heads and a .020 head gasket. 80 cc will get you to 9.8.
Click to expand...
I've found a set of nice used pistons with 1.900 compression distance. That takes me up to 0.028 deck clearance!
The hunt for a set of 915's keeps going. A guy in Norway said he had a couple, I will hear from him soon..
 
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