Will this work ????

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cdownie3

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I'm building a 70 dart... I bought a pile of stuff from a buddy who is getting older and winding down his hobby. I got a 1978 440/727 , and a set of 915 heads . I figured I would bolt on the closed chamber heads to up the compression.After I pulled down the 440 I see that the piston stops about 1/8 inch from the top. Now for the question ... Is this going to give me a weird quench and cause detonation? I realize that I will ony have 9.5:1 compression at best.This is my first mopar build, still learning .. Thanks, Chris
 
Welcome to the site. That sounds like the pistons are way down there. What cc are those heads?
 
I dont see where you would get 9.5 since the 78 440s were only like 8.5ish. Are the closed chambers going to gain you a full point?
 
cdownie3 said:
I have not checked to see if the heads are milled ,but they are 73 cc stock.
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WRONG , thats NHRA SPEC , 915's are more like 80cc , maybe 82 ??

eaglesguy1981j said:
I dont see where you would get 9.5 since the 78 440s were only like 8.5ish. Are the closed chambers going to gain you a full point?
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Advertised might have been 8.5 but as delivered is lower . A 78 440 stock piston is more like .150 to .175 in the hole , there will be NO QUENCH whatsoever and putting on the 915s won't even raise the compression 1 point .
 
From a $$$$ standpoint, lowering the piston in the hole was the easiest way to lower the CR. I would calculate the piston comp. height I need to get your piston close to zero deck and invest in a new set of pistons.
 
Or simply bolt the closed chambers on and figure you're above 8:1 now. Mathematically it will compute to around 7.5:1 with the factory head and gasket. Less if it has Felpros in it. On the upside, you have a ton of piston to valve clearance and you wont need quench to stave off detonation.
 
moper said:
Or simply bolt the closed chambers on and figure you're above 8:1 now. Mathematically it will compute to around 7.5:1 with the factory head and gasket. Less if it has Felpros in it. On the upside, you have a ton of piston to valve clearance and you wont need quench to stave off detonation.
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Leave it a 8:1 and install a blower...you will have a kick *** motor then...8)
 
bremereric said:
Leave it a 8:1 and install a blower...you will have a kick *** motor then...8)
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I am going through the exact same thing right now - budget rebuild and I just want to make some compression. My '77 440 had been recently rebuilt and is .040 over - and the pistons were way down in the holes. I had .050 shaved off the block deck and hope to use a set of closed chamber large valve heads. I did the math and it works out to 9:1. The crappy thing is with this low compression you cant go too big on the cam (big cam = more overlap and duration) because it will kill the compression even more.

I will probably do a proper rebuild a year or two down the road and stroke it at that time - as long as my taking .050 off the deck hasn't limited my possibilities.
 
d55dave said:
I am going through the exact same thing right now - budget rebuild and I just want to make some compression. My '77 440 had been recently rebuilt and is .040 over - and the pistons were way down in the holes. I had .050 shaved off the block deck and hope to use a set of closed chamber large valve heads. I did the math and it works out to 9:1. The crappy thing is with this low compression you cant go too big on the cam (big cam = more overlap and duration) because it will kill the compression even more.

I will probably do a proper rebuild a year or two down the road and stroke it at that time - as long as my taking .050 off the deck hasn't limited my possibilities.
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IMO remember when you shave the deck the geometry changes for the valley pan and the intake manifold...please don't forget about that...
 
Yes, you are right. I am waiting until I get the heads on it so I can check - I may have to mill my intake some as well.

Thanks

David
 
Ok Plan B or is this plan RB... I bought another pile of motor parts off a guy named Bigfoot. One of the motors is a 1972 413, the block casting number is on the bellhousing area,kind of where a chevy would be.I pulled the crank and rods to use with a new set of pistons in the 440 with the 915 heads.The cranks is forged,but I can't find a casting # on it ,the rods are LYs,. Anybody have any idea's on pistons , Jegs has Ross pistons on sale,but I have never used them.
 
I can help here.
Recently been through it all myself.
My 440 is 30 over and the slugs were 100thou down the bore at tdc.The heads were 906s with 40thou gaskets.I cc'd and measured everthing and came up with 8.4:1

I replaced the 906s with 915s (measured them again)and used tin shim head gaskets and came up with 9.3:1

How does this translate to actul improvement?
I picked up 0.25 seconds on the eighth mile straight of.No other changes.
Haven't had it on the quarter since fitting the 915s but it looks promising.
 
d55dave said:
Yes, you are right. I am waiting until I get the heads on it so I can check - I may have to mill my intake some as well.

Thanks

David
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No doubt you will have to shave something , taking .050 off the deck is the same as taking it off the head surface , the intake side of something , the head or the intake , needs to be cut . Now you will have an intake or head that will only work on that specific block. The mistake you made was cutting the block, you should have gotten a different piston , but it's too late for that.

I see this too many times , non mopar versed shops ordering parts for the YEAR of the block they are redoing not realizing they are causing a nightmare for the guy paying the bill.
 
cdownie3 said:
Ok Plan B or is this plan RB... I bought another pile of motor parts off a guy named Bigfoot. One of the motors is a 1972 413, the block casting number is on the bellhousing area,kind of where a chevy would be.I pulled the crank and rods to use with a new set of pistons in the 440 with the 915 heads.The cranks is forged,but I can't find a casting # on it ,the rods are LYs,. Anybody have any idea's on pistons , Jegs has Ross pistons on sale,but I have never used them.
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You want to buy a piston with a 2.060 , or 2.065 ??, compression height, make sure the rods are rebuilt using ARP wavelock bolts , there will be no number on the crank .
 
I used the standard stroke rods..I had them shot peened and resized...they used the ARP wavelock bolts also...I used the KB237 pistons...Edelbrock 84cc heads..the Z1009 head gaskets and my CR is 10.14:1..my pistons are .010 below the deck...here is the site I used..

http://www.csgnetwork.com/compcalc.html
 
cdownie3 said:
Thanks , Is compression height measured from the center line of the pin to the top of the piston,not counting a dome?
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Get these books at Amazon and they will help alot....

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