Just degreed my cam and checked PTV clearance and I have a problem. My minimum clearance on the intake is .040" with the crank 10 degrees ATDC. Even after reading that some people have run with it that low, I am not comfortable with it. Now I need to decide whether I want to fly cut the pistons approximately .060" or go with a smaller cam. Here are the specs on the build

1999 LS-1 60,000 miles on the stock short block
Texas Speed PRC Stage 2.5 5.3L CNC ported heads 2.02/1.575 valves, .017" mill on the deck, PRC .650" dual valve springs.
GM Multi Layer Steel Head Gaskets
Comp Cams LSr Cathedral Port 54-457-11 cam 223/231 @.050" .610"/.617" lift, 107 deg intake centerline.
LS-2 Timing Chain

I measured using stock lifters that were disassembled and shimmed to make them solid, installed checker springs and adjusted the pushrod checker for zero lash. Then I used a dial indicator on the valve retainer to check PTV.

When I measured intake centerline using the degree wheel , I got 105 degree intake centerline, but I feel that is within the +/- error I would expect using the tools I was. Exhaust PTV was fine, I saw a minimum of .150" between 5 and 10 degrees BTDC.

In helping to make the decision whether to fly cut or go more conservative with the cam, I will have an LS-6 Intake, Long Tube Headers and a T56. It is going in a 68 Camaro with 3.73 gears and it is a weekend toy. My gut feeling is to fly cut and keep the cam. The only thing bothering me is that it seems like these are pretty aggressive ramps and I am worried about valve train control. I probably can't return the cam now so I would take a hit on it, although I probably could resell it on here. What are your thoughts?

 

If you had an adjustable timing set, you could retard the cam which would give you more intake PTV at the cost of some exhaust PTV.

 

I thought about that KCS, but I don't think that will make up .060" of clearance. Maybe 0.010 " at the most.

 

Flycut. It isn't hard at all.

 

I'm surprised you have that little clearance with that setup

 

I am too, so I did it twice to make sure. I also checked that the 0.006 reading for the intake lobe was correct and it was spot on.

 

They must be very aggressive ramps.

 

Depends on how much you retard it.

FYI, I ran my engine with .060" clearance checked with light springs. With the real springs, you gain even more due to deflection.

 

0.017 milled off the deck ? If your pistons are out of the bore 0.006 thats giving you 0.028 quench, much tighter than the .035 to .045 most people run.
Going to .060 cometics would put you in the safe zone.
Retarding 3* could give you another .020 turning your .040 into .070 or there abouts. You lose a bit of compression but that cam sounds like it would have a lot of dynamic compression anyway.
I like your choice of cam, I would try to keep it but something does not add up. Have you CC'd the chambers ?

 

Because the minimum is after TDC of the piston, the valve will be chasing the piston. Valve float would be an issue but in theory it can't hit. The clearance will also increase while running due to pushrod, rocker, etc. deflections.

Not sure I would feel comfortable either, but just providing some additional thoughts.

 

Since I already ordered pushrods, I am not sure I want to change head gaskets now. I have calculated that my pushrods will have .070" preload, so I guess I could go up to 0.020" thicker in head gasket to give 0.060" clearance. That might work. Does anyone know the compressed thickness of the GM MLS gasket? I used the GM 12499217 head installation kit.

 

I checked and that kit comes with the 12589226 head gasket which has a .051" compressed thickness. SO with the piston out of the hole .006 as discussed ( I didn't check) the quench is .045".
The .060 Cometics would give .009" extra
As asked before, the chamber size is 61cc with the .017 mill

 

One more thing to consider is that you have a VERY early IVC with that duration and ICL. Most cams are usually around 40-45 degrees ABDC (@.050") and you're at about 37-39 degrees. Retarding the cam 2-4 degrees might not be a bad idea regardless of the PTV issue.

 

I think I didn't understand what you were telling us, sorry. Are you saying the heads were milled .017 or the block was decked .017 ?
Also, the cam has 107 intake centerline, what is the LSA ?

I agree with dr_whigham, flycutting would let you keep everything you have and keep compression.

 

Squalor, block is untouched, heads are milled .017.
LSA on the cam is 112 deg.
As KCS states, that IVC is fairly early. I really don't want to get into adjustable timing sprockets since I bought brand new stock sprockets, but it may be worth it.

 

I did some more research and my cam is advanced 5 degree from Comp Cams 107 IVC at 112 LSA. I think KCS is right that I should retard the cam regardless. I wonder how much a 4 degree retard would help my PTV. Here are a few more of the readings I got
10 BTDC .140" PTVC
5 BTDC .100" PTVC
0 TDC .067" PTVC
5 ATDC .048" PTVC
10 ATDC .040" PTVC
15 ATDC .058" PTVC
20 ATDC .087" PTVC

 

OK, that makes more sense. Your chambers are 58.5 cc so that's what happened to some of your PtV but you get around 11.5 to 1 static compression ratio. Your quench is as you said, I was wrong.
Since you have a degree wheel I wonder what would happen if you installed one tooth retarded from dot to dot ?

 

Texas Speed told me the chambers were 61 cc.

 

I have to agree with KCS. If this were my car, the solution would be as simple as an adjustable timing gear. It is rather odd for an LS1 cam with duration of 223/231 @.050" to have a 107 deg intake centerline. If you look at the valve events on your current 105 ICL:

IVO is 6.5 ° BTDC ( - indicates ATDC)
IVC is 36.5 ° ABDC
EVO is 54.5 ° BBDC
EVC is -3.5 ° ATDC ( - indicates BTDC)
Overlap is 3 °

As KCS said, this is a very early intake valve close. And, the is a very early exhaust valve open for this cam size and power level.

A much more common intake centerline for a cam this size in a LS engine with factory style long runner intake would be a 109 degree centerline. On a 109 degree centerline your valve events would look like this:

IVO is 2.5 ° BTDC ( - indicates ATDC)
IVC is 40.5 ° ABDC
EVO is 50.5 ° ATDC ( - indicates BTDC)
EVC is 0.5 ° BBDC
Overlap is 3 °

In my opinion this brings everything into line nicely. The valve events still look pretty good to me on a 108 degree intake centerline too:

IVO is 3.5 ° BTDC ( - indicates ATDC)
IVC is 39.5 ° ABDC
EVO is 51.5 ° ATDC ( - indicates BTDC)
EVC is -0.5 ° BBDC
Overlap is 3 °

In general I think you should find that every degree you retard the cam should get you about 6 thousands or .006". So, if you were to install it on 108 degrees your .040" + .018" would get you .058" and on a 109 degree ICL current .040 + .024" would get your .064"

If it were my car, I would run it on a 108 to 109 degree ICL if it gave me around .060" and call it good.

 

Speedtigger and KCS, you guys are making alot of sense, thank you very much for your input and everybody else who has commented. It does seem odd that this cam is so advanced. After reading what other people have done, I think I would be fine with .060" PTV clearance on the intake. If the same change in clearance applies to the exhaust, I would still have .126" on the Exhaust PTV if I retard 4 degrees.
Another advantage of retarding 4 degrees is I would decrease the dynamic compression slightly. I am afraid that I might be prone to detonation with the current cam phasing.