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Discussion Starter #1
Hey fellas I need some help, fast.

Im RE-building a 468 Gen IV BBC for my 70 Nova. Heres what is going into to:

70 454 block, bored .030 over
Reground factory crank
World Merlin II Rec. Port (119cc) cast heads.
Comp Cam Hyraulic roller (11-430-8) (280/280)(224/224) .566/.566 110°

I was going to keep the flat tops (with two valve reliefs in it) but after finding problems with the pistons Ive decided to replace them too.

I had a closed chamber 101cc head on it before, and now going to a semi/open open chamber Merlin Head Im thinking Im going to loose a lot of CR. What is the best choice (and best on my wallet) for this build. Trying to stay at 10:1 or lower.

Do I have to run a flat top with a valve relief? Can I run a mild dome piston w/o a relief? Thank you in advance!!

Rob
 

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468= .060 over bore
461=.030 over bore

Ft pistons and 119 chambers will yield around 8.5:1 or less depending on deck, and gasket thickness and swept volume.

Go with the 1970 LS6 replacement piston.. its set up for closed chamber heads with 11.25:1 on a .020 gasket.... with the 119cc head it should come out to 10.0:1.to 10.5:1 depending... but this is a press pin if that makes a difference to you.. also Probe has this piston in a factory spec.. in the FPS line of pistons

the OLD TRW pt # was L2349F.. which I spose is still the speedpro number...

SRP actually has the best piston choice with a 23cc dome.. it will yield round. 10 to 10.5 depending on deck and gasket..

look for a dome volume of around 23cc.. up or down a 1 or 2 cc will be livable
 

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First off....what kind of pistons do you want? Cast, hypereutectic or forged?

Full floating pins or press fit?

Stock replacement or with deeper valve reliefs for added cam choice possibilities?

Any nitrous or boost?

Does the ring pack matter to you? Definitely makes a difference in power output and on the wallet.:yes:

The more we know the more accurate we can be with our suggestions.:yes:
 

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Discussion Starter #5
Looking to get Forged, but will settle with hyper. No cast

I would like to go floating pin, ease of assembly, etc

I am already swapping in a new cam, that probly wont change ( i put the specs above) So yes a not-so-stock-piston.

No power adder

Yes Im looking for good performance, without blowing my entire wallet.

I found some KB pistons (kb257-060), check specs on summit. Im thinking about these, what do you guys think?

thank you!
 

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Look at SRP #212137

these will be a great buy and quality and your compression requirements.

Al
 

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if your going to go Kb look at these then....

Keith Black/KB Pistons 9919-060
with a 119cc head yields 9.6 according to KB


http://www.summitracing.com/parts/UEM-9919-060?part=UEM-9919-060&autoview=sku

Pistons, Forged, Dome, 4.310 in. Bore, 5/64 in., 5/64 in., 3/16 in. Ring, Chevy, Big Block, Set of 8

Summit Racing Part Number UEM-9919-060
Bore (in) 4.310 in.
Bore (mm) 109.474mm
Piston Style Dome, with single valve relief
Piston Material Forged aluminum
Compression Distance (in) 1.645 in.
Dome Height (in) 0.200 in.
Piston Head Volume (cc) -18.30cc
Wrist Pin Style Press-fit or floating
Pin Diameter (in) 0.990 in.
Piston Ring Thickness 5/64 in. x 5/64 in. x 3/16 in.
Quantity Sold as a set of 8.
Notes Solid dome design.
 

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I have the SRP 212136 for my 468 and ended up with 9.98-1 static compression ratio with a 110cc head and .038 gasket, zero decked block. With 118cc heads I bet you'd end up around 9.6?-1 which would work good with your cam. These are the 4032 alloy forged so they can run with a tighter bore clearance. SRP says not to use them with much nitrous but I know of one motor that's been sprayed many times with a 300 hit and no problems.

There isn't a whole bunch of options if you're looking for 10ish-1 compression ratios on a 454 based build.
 

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Look at SRP #212137

these will be a great buy and quality and your compression requirements.

Al
I have the SRP 212136 for my 468 and ended up with 9.98-1 static compression ratio with a 110cc head and .038 gasket, zero decked block. With 118cc heads I bet you'd end up around 9.6?-1 which would work good with your cam. These are the 4032 alloy forged so they can run with a tighter bore clearance. SRP says not to use them with much nitrous but I know of one motor that's been sprayed many times with a 300 hit and no problems.

There isn't a whole bunch of options if you're looking for 10ish-1 compression ratios on a 454 based build.
Good thing you posted that part # 212136

The 212137 I posted would be .070 over!
:eek:!:eek:


 

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I have the SRP 212136 for my 468 and ended up with 9.98-1 static compression ratio with a 110cc head and .038 gasket, zero decked block. With 118cc heads I bet you'd end up around 9.6?-1 which would work good with your cam. These are the 4032 alloy forged so they can run with a tighter bore clearance. SRP says not to use them with much nitrous but I know of one motor that's been sprayed many times with a 300 hit and no problems.

There isn't a whole bunch of options if you're looking for 10ish-1 compression ratios on a 454 based build.
If your information is correct.
Your compression calculation is not!

 

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Discussion Starter #13
One more question, Im trying to get this engine finished soon...

A lot of the pistons are weeks away,

I would like to get the KB257-60, but can I physically run them (clearance wise)

done hieght is .250 , volume is -25.50, I know this will bump cr up, but I think it should have clearance with the open chamber world heads, right?

The L2349's have a Dome height of .210 and they dont have problems, right?

Thank you guys!
 

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Big Al, My 9.98-1 ratio with a 110 chamber was calculated on a program that took all variables into consideration including the area around the piston above the top ring and also the actual head gasket volume-not just a round circle volume calculation as these gaskets are combustion chamber shaped and have more open area. I found out things change real fast when you get into the nitty gritty when calculating this stuff!

Haustkraft, make sure the .250 domes would work with that small cam you have-it might be a little high on compression. But with the KB solid domes you could always mill some off if needed.
 

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Discussion Starter #15
Haustkraft, make sure the .250 domes would work with that small cam you have-it might be a little high on compression. But with the KB solid domes you could always mill some off if needed.
Is that a typo? You mean they will work, with the exception of the high CR?
 

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They should work just fine with your open chamber heads but may be high on compression for the cam you have. You need to do the math and figure out the exact ratio with those pistons, using your deck height, gasket volume, dome volume, and chamber size. Then run your specs through a dynamic compression ratio calculator to see where it ends up and if it'll be compatible with the fuel you want to burn.

A friend of mine ran a 468 for years with the .250 domed TRW pistons and 781 heads on pump gas with a hydraulic 292 magnum cam and it worked well. But your cam has an earlier intake closing point with the shorter duration so the dynamic compression ratio would be much higher.
 

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Discussion Starter #17
I see I see, I did some math with the KB piston Calc, and on the Stan Weiss site. I thank you VERY much for your help!
 

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A friend of mine ran a 468 for years with the .250 domed TRW pistons and 781 heads on pump gas with a hydraulic 292 magnum cam and it worked well. But your cam has an earlier intake closing point with the shorter duration so the dynamic compression ratio would be much higher.

The cam can reduce the amount of static compression. It can not create more compression than the sealed chamber cam make.

Al
 

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Yeah, it all boils down to when the intake valve closes for your dynamic compression ratio vs. static compression ratio. 8-1 dynamic seems to work well for most iron headed 92/93 octane pump gas motors from what I've seen.
 
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