Stock PTV clearance/ clearance issue?
03-21-2012, 07:38 AM
#1
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Stock PTV clearance/ clearance issue? Does anyone know the factory piston to valve clearance on a 94 Z28? I was originally planning to shave the heads to bump compression, but read on a corvette forum that using the SS impala headgasket(part # 12553160) will bump compression .5. I'll be running a hotcam. The stock headgasket thickness is .049, And the SS impala gasket would be .029. Would that cause any clearance issues if used with a hotcam?
03-21-2012, 07:49 AM
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Would I still be in the safe range to take about .020 off the heads to bump it even more, or is that cutting it close. Better question is whats the most I can do without having to fly cut the pistons? lol
03-21-2012, 08:04 AM
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Since your piston is "in the hole" about .020-.025 and the head gasket is .028 you will always have the same PTV clearance no matter how much you shave off your head. The head surface is not involved. Since I only play with LTX engines with little bitty combustion chambers, I can't help you on how much material to remove. You'll probably wind up needing different pushrods also......but that's another thread.
03-21-2012, 08:20 AM
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Thanks to the 3 of you guys for your input. And I saw a chart for the LSX telling how much removed would change the compression. What would I expect for a compression ratio if I took off .020 from the heads and used the .029 thickness gasket? according to the vette forum I was on, the thinner gasket would add .5, meaning I would have 11;1. So is it safe to say I could get 12;1 by shaving .020 off the head surface?
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03-21-2012, 04:19 PM
#8
Keep in mind that stock LT1 pistons have valve reliefs cast into them which gives you ample clearance even with a fairly aggressive camshaft.
I ran a pretty big camshaft in my stock shortblock engine and it still has over .100" of clearance on int and ex.
I ran a pretty big camshaft in my stock shortblock engine and it still has over .100" of clearance on int and ex.
03-21-2012, 06:11 PM
#10
To calculate Compression Height:
block height - 1/2 stroke - rod length - deck clearance
9.025 - 1.740 - 5.700 - 0.17 = 1.568 for stock LT1
To calculate Piston "in the hole":
deck height - (rod length - piston compression height - 1/2 stroke)
9.025 / (5.700 - 1.568 - 1.740) = .265"
Shaving the head will bring the valves closer to the pistons. Thats like saying cutting off your foot doesn't make you shorter.
block height - 1/2 stroke - rod length - deck clearance
9.025 - 1.740 - 5.700 - 0.17 = 1.568 for stock LT1
To calculate Piston "in the hole":
deck height - (rod length - piston compression height - 1/2 stroke)
9.025 / (5.700 - 1.568 - 1.740) = .265"
Shaving the head will bring the valves closer to the pistons. Thats like saying cutting off your foot doesn't make you shorter.
03-21-2012, 07:29 PM
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so if I take .030 off the head and use the ss impala gasket, I drop .050 all together, and would still have optimum clearance with the hotcam? Originally I had planned to just use the gasket, but after realizing I have so much clearance with the thinner gasket, hell, why not shave .030 off
03-21-2012, 07:40 PM
#12
To calculate Compression Height:
block height - 1/2 stroke - rod length - deck clearance
9.025 - 1.740 - 5.700 - 0.17 = 1.568 for stock LT1
To calculate Piston "in the hole":
deck height - (rod length - piston compression height - 1/2 stroke)
9.025 / (5.700 - 1.568 - 1.740) = .265"
Shaving the head will bring the valves closer to the pistons. Thats like saying cutting off your foot doesn't make you shorter.
block height - 1/2 stroke - rod length - deck clearance
9.025 - 1.740 - 5.700 - 0.17 = 1.568 for stock LT1
To calculate Piston "in the hole":
deck height - (rod length - piston compression height - 1/2 stroke)
9.025 / (5.700 - 1.568 - 1.740) = .265"
Shaving the head will bring the valves closer to the pistons. Thats like saying cutting off your foot doesn't make you shorter.
03-21-2012, 09:57 PM
#16
I wouldn't go milling heads for compression without porting.
There is a .015 SBC gasket that can be modified to work on an LT1.
I only ever heard of one "stock shortblock" heads/cam motor having PTV clearance issues and needing flycutting but the guy who posted about it was less than honest so I suspect the block may have been decked and I know the guy who spec'd the cam was incompetent and cam timing has a LOT to do with PTV clearance.
There is a .015 SBC gasket that can be modified to work on an LT1.
I only ever heard of one "stock shortblock" heads/cam motor having PTV clearance issues and needing flycutting but the guy who posted about it was less than honest so I suspect the block may have been decked and I know the guy who spec'd the cam was incompetent and cam timing has a LOT to do with PTV clearance.
03-21-2012, 10:43 PM
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I plan to use the Mr G .026 gasket, i figure compression to 11:1...can someone tell me also how much could be expected from a .010 .020 and .030 mill over the 11:1. I would think 11.5 would be better for these motors.
03-22-2012, 06:07 AM
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03-22-2012, 08:49 AM
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I feel like a tard for forgetting about intake seating. lol. with that in mind, I'm back to saying I'll just use the thinner gasket. since I would be dropping close to .020-.030 there alone.