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Discussion Starter · #1 ·
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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Discussion Starter · #2 ·
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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Discussion Starter · #4 ·
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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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.
 

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Discussion Starter · #6 ·
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 [email protected]".
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 [email protected]" 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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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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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
 

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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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I was told by a local dealership parts department that the AC Delco HL-124 (GM 12499425) LSx lifters are the service replacement for the AC Delco HL-123 LT1, LT4 and L30, L31 Vortec lifters.

However, the original AC Delco HL-123 (GM 17120735) Vortec lifters are still available over the counter.
 

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Discussion Starter · #16 ·
Can you explain the differance to me between the lifters I purchased and the comp 875 lifters?
I was under the impression the GMs were a nicer quality peice.

The comp 875's are the same price I payed for the GM kit so it wouldnt be a big deal to return the GMs to jegs.
 

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The Comp Cams 875 lifters, for all practical purposes, are solid lifters. They only have a 0 to .005" pre-load only to keep the valve train quiet and as a safety margin to keep from popping out the push rod cups. You could set them at zero pre-load but it is not advisable. You must use full roller rocker arms and fully adjustable rocker studs with CC 875 and 15850 lifters. Since they are restricted oiling lifters, you must use full roller rocker arms to prevent burning out and seizing the pivot ball in stock or roller tip rocker arms. Restricted lifter oiling is necessary at high RPM to keep the rod and main bearings fully pressurized with oil.

If it was not for the extra cost of full roller rocker arms and the difficulty in setting the pre-load, more people would use Comp Cams 875 and 15850 lifters with high lift camshafts.
 

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Discussion Starter · #18 ·
Dish pistons with d cups or not usally dont have tpv issues at all. There is always that remote chance but being .010 in the hole and dish and small cam you are way good.

Probably with dished you could run 1:6 or even 1:7 rockers without issue.

Never had a dish piston small block chevy With tpv issues. Flat tops zero decked with big vales and large roller cam maybe.

Why use dish pistons and mill the head why not use flat tops. They are cheaper and should be right where you need to be without cutting the heads.



Already have the heads. Short block is paid for but not built yet
 

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Discussion Starter · #19 ·
Got ya.

I ran the numbers and it looks like with a .010 deck and felpro 1094 .015 head gasket will leave you with 9.4:1 cr should be pretty good with 64 cc heads. About the same with 59cc and .041 head gasket. 9.3:1 But with 0.041 head gasket and deck of .010 will be close to the point where the gap is too high. But at .050 it should be usable. .060 is the limit for quech distance any more and its not going to be right. .040 is ideal.

If you have not gotten the block decked yet zero deck it or .010 or less. With zero deck and 0.041 i come up with right around 9.2:1.

I wanted to use a gm .028 gasket with. 010 deck and 9.5 compression. I was going to call today and see if the block has been decked. If it hasn't, I was thinking of going .005
 
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