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Old 01-23-2013, 08:17 AM
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Predicting potential piston to valve clearance issues

There it is, Im trying to figure out if I should be worried, in advance. When do 350's generally run into p2v issues?
The block is getting keith black +18cc Dcup dish pistons. The heads have been milled from 64cc to 59cc.
The block will be decked to get a 1.561comp. height piston .10 in the hole.(Was even thinking of going .005)
The camshaft is advertised at .515/.530 with 1.5 rockers.
I suppose I would need the type of valve, all I know is they are stainless 1piece "competition series"

One of the machinests iv'e been talking with seems to be worried about the
p2v.

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Old 01-23-2013, 08:33 AM
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The primary factors are being overlooked here.
The max lift of the cam is irrelevent. When the valve are at peak opening the piston is more than half way down the bore. The valve opening at and near TDC overlap is the critical factor.
The more duration and overlap the more critical.
Piston valve relief depth and location--valve centerline locations. non stock geometry must always be checked.
larger than typical valves must be checked for radial clearance of the valve relief too.

need the Complete camshaft specs. or camshaft part number.

Why "worry" when you can check VTP clearance and not worry?

You or somebody is going to check-verify VTP clearance on hte assembled engine ,,,right....

Last edited by F-BIRD'88; 01-23-2013 at 08:54 AM.
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Old 01-23-2013, 09:22 AM
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Quote:
Originally Posted by F-BIRD'88 View Post
The primary factors are being overlooked here.
The max lift of the cam is irrelevent. When the valve are at peak opening the piston is more than half way down the bore. The valve opening at and near TDC overlap is the critical factor.
The more duration and overlap the more critical.
Piston valve relief depth and location--valve centerline locations. non stock geometry must always be checked.
larger than typical valves must be checked for radial clearance of the valve relief too.

need the Complete camshaft specs. or camshaft part number.

Why "worry" when you can check VTP clearance and not worry?

You or somebody is going to check-verify VTP clearance on hte assembled engine ,,,right....


Yes me or somebody will be checking clearance when ll is put together. The short block is at the mchine shop for a few weeks so im just brainstorming on stuff to keep my brain from exploding with anxiety.

The camshaft is voodoo- •Advertised Duration (Int/Exh): 270/278
•Duration @ .050 (Int/Exh): 221/229
•Gross Valve Lift (Int/Exh): .515/.530
•LSA/ICL: 112/106
•Valve Lash (Int/Exh): Hyd/Hyd
•RPM Range: 1800-5800
•Includes: Cam Only


Part Number: 20080721
Previoius Part Number: 60121
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Old 01-23-2013, 09:56 AM
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with that low lift and duration you shouldn't have any issues at all. you can very easily check with some clay but it shouldn't be an issue.
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Old 01-23-2013, 10:37 AM
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Quote:
Originally Posted by ap72 View Post
with that low lift and duration you shouldn't have any issues at all. you can very easily check with some clay but it shouldn't be an issue.
Okay very cool. I will still check for sure but good to hear from someone more experienced than myself.
The decking of the heads and block had me worried. Aparrantly I was worried about the wrong variables.
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Old 01-23-2013, 11:19 AM
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On hyd and solid flat tappet stuff with stock like 23 heads I start looking @ VTP clearance
potential issues when the cam gets bigger than 244@.050".
And then always check before running.

By you checking yours, you can get some idea of clearance relative to potential future cam swaps
with larger cams.

Rollers start looking when the cam duration gets to 238@.050" Always check actual VTP clearance.
Can be a world of expensive grief if you don't.
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Old 01-23-2013, 11:49 AM
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I have discussed this subject several times over the years with my engine builder in Dallas. He has been building drag race, circle track and high performance street engines since 1968. He told me that a SB Chevy with flat top pistons will have .100" clearance with 2.02" intake valves and a camshaft spec at 240 deg. duration @ .050", .550" valve lift, 112 deg. LCA if the valve action is kept under control.

In order to maintain control of the valv train, use appropriate valve spring pressure for the camshaft being used in order to prevent valve float. Valve lift from .500" to .550" should use short or reduced travel hydraulic lifters and valve springs with a minimum 130 lb. seat pressure and 340 lb. open pressure. That kind of spring pressure is a problem with flat tappet camshafts because of the lack of ZDDP in motor oils. Therefore, the use of a hydraulic roller cam should be considered. With any high performance camshaft, aftermarket short or reduced travel hydraulic roller or flat tappet lifters are preferred. Those lifters have a pre-load setting of .005" and cannot pump and float the valves because the lifters have nowhere to pump up to. Most cam companies have limited travel lifters for serious high performance engines using hydraulic camshafts.

Example:
Chevrolet V8 engines
Comp Cams 858 Pro-Magnum
Flat tappet hydraulic
.050" total travel
.005" pre-load.
Full roller rocker arms must be used.

Last edited by MouseFink; 01-23-2013 at 11:54 AM.
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Old 01-23-2013, 12:47 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
On hyd and solid flat tappet stuff with stock like 23 heads I start looking @ VTP clearance
potential issues when the cam gets bigger than 244@.050".
And then always check before running.

By you checking yours, you can get some idea of clearance relative to potential future cam swaps
with larger cams.

Rollers start looking when the cam duration gets to 238@.050" Always check actual VTP clearance.
Can be a world of expensive grief if you don't.
Okay thanks for the specs, My cam is 229 @.050 and it is a roller.
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Old 01-23-2013, 12:54 PM
How fast is fast enough?
 
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Quote:
Originally Posted by MouseFink View Post
I have discussed this subject several times over the years with my engine builder in Dallas. He has been building drag race, circle track and high performance street engines since 1968. He told me that a SB Chevy with flat top pistons will have .100" clearance with 2.02" intake valves and a camshaft spec at 240 deg. duration @ .050", .550" valve lift, 112 deg. LCA if the valve action is kept under control.

In order to maintain control of the valv train, use appropriate valve spring pressure for the camshaft being used in order to prevent valve float. Valve lift from .500" to .550" should use short or reduced travel hydraulic lifters and valve springs with a minimum 130 lb. seat pressure and 340 lb. open pressure. That kind of spring pressure is a problem with flat tappet camshafts because of the lack of ZDDP in motor oils. Therefore, the use of a hydraulic roller cam should be considered. With any high performance camshaft, aftermarket short or reduced travel hydraulic roller or flat tappet lifters are preferred. Those lifters have a pre-load setting of .005" and cannot pump and float the valves because the lifters have nowhere to pump up to. Most cam companies have limited travel lifters for serious high performance engines using hydraulic camshafts.

Example:
Chevrolet V8 engines
Comp Cams 858 Pro-Magnum
Flat tappet hydraulic
.050" total travel
.005" pre-load.
Full roller rocker arms must be used.
While thats a good rule of thumb, if you're getting close to that mark it's real easy to check. a more square lobe will have problems with less lift and duration than a gentle one will have. You don't even need to intstall a gasket to check, just bolt on a head, 2 or three head bolts snugged up, and check both valves on one cylinder. You can add your gasket thickness to the result if you're cutting it close but for most street applications its not an issue.
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Old 01-23-2013, 12:59 PM
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MouseFink- I purchased LS7 roller lifters so I hope they will suffice...
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Old 01-23-2013, 01:09 PM
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While you have some time, get your head wrapped around this tutorial from Isky.....
ISKY Racing Cams - Do It Right. Race with the Legend. Camshafts, Connecting Rods, Valve Springs, Lifters
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Old 01-23-2013, 01:16 PM
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Roller camshafts with similar spec and valve springs with similar pressure need short or reduced travel lifters to maintain valve control at high RPM.

Never use hydraulic roller lifters that were used in Chevrolet engines with a net-lash (non-adjustable) valve train. The lifters in those engines are AC Delco HL-105 (GM 5234670) . Those lifters have .237" total travel and will loft over the return flank of the cam lobes, collapse and reduce valve lift by .119", pump up and float the valves between 4300 - 4800 RPM, with disastrous results.

The best hydraulic roller lifters to use with a camshaft with more than .500" valve lift is:
Comp Cams 875 Pro-Magnum - Reduced Travel - restricted oiling
Comp Cams 15850 Race - Short travel - restricted oiling - REM coated - HD retainer clip
.005" pre-load
.050" total travel
Must use full roller rocker arms.

LS7 lifters
AC Delco HL-124 (GM 12499425)
.166" total travel
.082" pre-load
I do not know how those react with high lift camshafts and high load valve springs

How much valve lift doe a LS7 engine have? I think it is .561" I / .557" E with 1.7 rockers
LS7 valve spring pressure:
108 lb. seat pressure at 1.750" assembled height
296 lb. open pressure at .500" valve lift

Last edited by MouseFink; 01-23-2013 at 01:38 PM.
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Old 01-23-2013, 01:49 PM
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Well thats a real shame isent it?
Thought they would be fine.
Chevrolet Performance 12371042 Chevrolet Performance Roller Lifter Kit

These are the ones I bought. Those are the ones your talking about?
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Old 01-23-2013, 02:16 PM
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Latest specifications for LS 7 beehive valve springs:
AC Delco HL-124
GM-12499425
2.313" free length
1.960" installed height
101 lb. @ 1.960" seat pressure
310 lb. @ 1.370" open pressure
1.085" coil bind
354 lb/in. rate
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Old 01-23-2013, 02:32 PM
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Quote:
Originally Posted by 0trbo4myCHEVUICK View Post
Well thats a real shame isent it?
Thought they would be fine.
Chevrolet Performance 12371042 Chevrolet Performance Roller Lifter Kit

These are the ones I bought. Those are the ones your talking about?
Those are not LS7 lifters. The GM 12371042 part number is a kit containing the retainer and 16 lifters. The lifters used in the kit are:

AC Delco HL-123 (GM-17120735)
LT1, LT4 engines
L30, L31 Vortec truck engines
.060" pre-load
.120" total travel
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