Deck clearance?

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Re: Deck clearance?

Post by steve cowan »

408 Nova wrote: Sat May 15, 2021 3:01 am How much is enough at 8500 rpm? SBC, 4340 5.85" H-beams, 3.75" Crower 4340 crank, approximately a 440 gram piston and .927" x 2.75" straight wall pins (.150").
I was reading recently about NHRA pro stock from 2014 when they still running carbs,
With steel rod they were around 0.050"
Aluminium rods around 0.060"
They considered quench still a important tuning tool even at 16.1:1 compression or so.
I calculated at 9000 rpm your engine will have avg piston speed of approx 5625 fpm
This is where piston design,weight,wristpin quality and oiling of these areas is critical for longevity, seems drag racers can get away with alot of different things :D
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Re: Deck clearance?

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steve cowan wrote: Sun May 16, 2021 5:10 am
408 Nova wrote: Sat May 15, 2021 3:01 am How much is enough at 8500 rpm? SBC, 4340 5.85" H-beams, 3.75" Crower 4340 crank, approximately a 440 gram piston and .927" x 2.75" straight wall pins (.150").
I was reading recently about NHRA pro stock from 2014 when they still running carbs,
With steel rod they were around 0.050"
Aluminium rods around 0.060"
They considered quench still a important tuning tool even at 16.1:1 compression or so.
I calculated at 9000 rpm your engine will have avg piston speed of approx 5625 fpm
This is where piston design,weight,wristpin quality and oiling of these areas is critical for longevity, seems drag racers can get away with alot of different things :D
Yessir, hopefully these will be less than 5.50 or so second blasts in the eighth mile!
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Re: Deck clearance?

Post by Bill Chase »

MadBill wrote: Sun May 16, 2021 12:33 am I think there are guys here who would raise their hand for 0.030" on an iron block SBC. I'd say 0.035", closely verified in each cylinder, is safe for you. 0.040" and up is just giving away power.
How much power do you think is lost going from .030" to .041" recently put together a 385 with hypereutectic pistons zero decked and went with .041" gaskets. Am I leaving power on the table by not using a thinner gasket MadBill? Doubt I'll change it now, but if I end up tearing it down in 15-25k miles and everything looks good I will go to a thinner gasket. 638 oe roller block steel rods aluminum heads. Ended up using the afr recommend gaskets 1003 I believe. Also, this is a much lower rpm deal, pump gas. It will never see 6500 rpm, shift rpm is 6100-6200.
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Re: Deck clearance?

Post by MadBill »

As mentioned above, there are a number of variables that come into it, e.g. clearance need not be as tight if there is significant squish area. Also, it's not like the engine goes from hero to zero with 0.005" too much. Unless every last HP is critical I wouldn't change what you've got.
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Re: Deck clearance?

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steve cowan wrote: Sun May 16, 2021 5:10 am
408 Nova wrote: Sat May 15, 2021 3:01 am How much is enough at 8500 rpm? SBC, 4340 5.85" H-beams, 3.75" Crower 4340 crank, approximately a 440 gram piston and .927" x 2.75" straight wall pins (.150").
I was reading recently about NHRA pro stock from 2014 when they still running carbs,
With steel rod they were around 0.050"
Aluminium rods around 0.060"
They considered quench still a important tuning tool even at 16.1:1 compression or so.
I calculated at 9000 rpm your engine will have avg piston speed of approx 5625 fpm
This is where piston design,weight,wristpin quality and oiling of these areas is critical for longevity, seems drag racers can get away with alot of different things :D
I was reading recently about NHRA pro stock from 2014 when they still running carbs,
With steel rod they were around 0.050"
They were approaching 12,000 RPM in 2014, the OP won't need so much clearance for only 8500. ".035" to .040", minimum preferred." (S. Yunick)
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Re: Deck clearance?

Post by af2 »

Tuner wrote: Sun May 16, 2021 12:48 pm
steve cowan wrote: Sun May 16, 2021 5:10 am
408 Nova wrote: Sat May 15, 2021 3:01 am How much is enough at 8500 rpm? SBC, 4340 5.85" H-beams, 3.75" Crower 4340 crank, approximately a 440 gram piston and .927" x 2.75" straight wall pins (.150").
I was reading recently about NHRA pro stock from 2014 when they still running carbs,
With steel rod they were around 0.050"
Aluminium rods around 0.060"
They considered quench still a important tuning tool even at 16.1:1 compression or so.
I calculated at 9000 rpm your engine will have avg piston speed of approx 5625 fpm
This is where piston design,weight,wristpin quality and oiling of these areas is critical for longevity, seems drag racers can get away with alot of different things :D
I was reading recently about NHRA pro stock from 2014 when they still running carbs,
With steel rod they were around 0.050"
They were approaching 12,000 RPM in 2014, the OP won't need so much clearance for only 8500. ".035" to .040", minimum preferred." (S. Yunick)
Exactly .041 let it go at 9000! without hitting,,,
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Re: Deck clearance?

Post by af2 »

mag2555 wrote: Sat May 15, 2021 10:15 am Well first off to me the problem is spinning 8500 rpm with a H beam Rod, because to me your walking right on the edge even taking into account that weight piston!

For longevity at that rpm you should be into Bilet or Titainum, or if you can wallet the cost, then run Aluminum rods that you replace every 100 passes!

With steel rods that will work for that rpm you want a piston to Head clearance absolute minimum of whatever your piston to bore clearance is cold+.003, but the basic rule of Thumb for deck clearance is .032” to .037” and then the top ring groove to piston top needed to not have a melt down or picnched ring land is .200” for me.
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Re: Deck clearance?

Post by af2 »

mag2555 wrote: Sat May 15, 2021 10:15 am Well first off to me the problem is spinning 8500 rpm with a H beam Rod, because to me your walking right on the edge even taking into account that weight piston!

For longevity at that rpm you should be into Bilet or Titainum, or if you can wallet the cost, then run Aluminum rods that you replace every 100 passes!

With steel rods that will work for that rpm you want a piston to Head clearance absolute minimum of whatever your piston to bore clearance is cold+.003, but the basic rule of Thumb for deck clearance is .032” to .037” and then the top ring groove to piston top needed to not have a melt down or picnched ring land is .200” for me.
Really? I guess all the outlaw 410 are running ubotatanium>>> Not!! H beam works just fine..
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Re: Deck clearance?

Post by Alaskaracer »

Call me crazy, but I was running zero deck with my last engine, a 604" chevy. Set clearance with head gaskets at .040". No contact, running 8200-8300 rpm every pass. Steel rods, h-beam, iron block. New combo, aluminum block, aluminum rods, 5" stroke, 800-8200 rpm. .020" below the deck, plus .050" head gasket......only running that much because of nitrous......last engine was at 15.5:1, this one is at 16.5:1......
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Re: Deck clearance?

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MadBill wrote: Sat May 15, 2021 10:49 pm Block material is also a factor. The coefficient of thermal expansion is ~ 6 ppm for iron, ~13 for common aluminum alloys, so (assuming uniform engine temperature) heating it from 70°F. to 170°F., a 9" deck height aluminum block will expand (13-6) x 9" x 100 = 0.0063" more than an iron one.
You're saying I'll have 6.3 thousandths MORE clearance with an aluminum block versus an iron block, all things else being equal and at 170 degrees?
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Re: Deck clearance?

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That’s.0063 are sixty three ten thousand
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Re: Deck clearance?

Post by KnightEngines »

Set it at .040" & sleep easy.
Tighter is worth sfa power.
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Re: Deck clearance?

Post by MadBill »

408 Nova wrote: Mon May 17, 2021 12:40 am
MadBill wrote: Sat May 15, 2021 10:49 pm Block material is also a factor. The coefficient of thermal expansion is ~ 6 ppm for iron, ~13 for common aluminum alloys, so (assuming uniform engine temperature) heating it from 70°F. to 170°F., a 9" deck height aluminum block will expand (13-6) x 9" x 100 = 0.0063" more than an iron one.
You're saying I'll have 6.3 thousandths MORE clearance with an aluminum block versus an iron block, all things else being equal and at 170 degrees?
Yes.
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Re: Deck clearance?

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Re: Deck clearance?

Post by Super_Stock »

stealth wrote: Mon May 17, 2021 12:08 pm I agree with this...:

https://www.youtube.com/watch?v=lr86J9g0PWA
What? Drawing on your cylinder head?
So you either have virtually no gap between the head and piston top or you enlarge the gap so the flame front can get in there to stop pinging?
I don't know, but I think that's a real laugh...
Maybe if he showed a head that had the chamber "laid back" as he says, instead of the felt tip diagram, then it may make a little more sense, but he's sort of describing an open chamber style head to me..
Might as well run a small dish in the piston.
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