I have a 6.0L iron block that has been bored .30 over. I purchased some sealed power flat top pistons for it but unsure if they will work since they are flat top. I have heard ls3 heads you have to watch for PTV clearance. All the other pistons I have seen have valve reliefs cut in them.

Thoughts?

Here are my thoughts on cams.

Comp cam part number 54-456-11
54-459-11
or 54-469-11 This one is the one comp recommended with the heads.

Thanks

 

My LS3 specs at 0.135"ptv on intake and 0.185"ptv on exhaust. We found that trying to run a cam with relativly small duration but tight (113) lobe seperation. Wouldn't fit due to valve clearance problems. If your going to run a wide lobe seperation like GM with short duration, you'll be fine, its when you try to modify, that will get you into major problems.

 

I'm posting from my phone, no editing allowed, I meant the ptv was with piston@TDC, sounds like your cam has a 111 degree seperation angle, depending on lift, I would predict you will have ptv clearance issues with a tight seperation. The GM ASA cam has duration like I wanted to run but, lift is only 0.525" to allow for proper ptv clearance.
Lots of experts here on this forum, I found out the hard way that all you read isn't always the truth. I suspect many of the pushrod and timing chain problems posted here on this forum are due to improper ptv clearances.

 

Not sure what good measuring this way is doing. PTV clearance is not just about the physical clearance, but piston to valve timing. At no time should any valve be at full lift with the piston at TDC. When checking for clearance you are ensuring that the piston and the valves are not out running each other.

In my experiences, you should have adequate PTV clearance with this camshaft.

I'd say from my experience, if you do not mill the heads you should have adequate PTV clearance with the specs for the cam listed.

For instance, the intake begin to open at 26 degrees before TDC on the cam you suggested. Full lift should occur at around 107 degrees BBDC. So in this movement the piston is moving down away from the valve as it opens and you do not want the ramp rate to out run the piston and kiss it.

The exhaust, on the other hand, is opening BBDC and is opening toward the piston as it accelerates up the bore. It will reach full lift, begin closing as the piston reaches TDC, and finally close ATDC. You don't want the piston to get there first.

 

BTW...The cam you mentioned should have adequate clearance if your heads have not been milled.

 

The first cam you listed (54-456-11) is the Comp 269LR HR12.
It's specs are: 607/.614 219/227 112�LSA+5°

That cam is nearly identical in specs to what Bortous is running in his LS3/LS2 engine.
~ (Bortous/Ed Curtis spec - 219/227 .625 .619 112LSA +4°)

He is also running flat top pistons and has reported no problems with PTV and his heads have been milled .030. +/-

Here is a link to the thread: https://ls1tech.com/forums/generatio...earned-23.html

 

OK I'll put this in the form so people who rode the "little bus" to school can understand: Comp Cams lists cam lobe lifts at TDC in their catalog on a couple of different lobe centerlines (very NICE of them to do this!) Because a LS3 head (uncut) has around 0.135"PTV clearance on an intake valve in a motor with no valve reliefs in the piston (stock GM), you should subtract the minimal valve clearance you want (I wouldn't try to run under 0.075"PTV on intake, 0.100"PTV on the exhaust because exhaust valve is opening as piston approaches TDC while intake is closing) Using the Comp Cams listed data figures, you can see if a cam lobe will fit your motor. Using the example of my LS3, we take the 0.135"PTV clearance, subtract 0.075" to come up with 0.060" total allowable ROCKER ARM LIFT. NOW and I'M REALLY TRYING TO GIVE EVERYONE GOOD INFORMATION, you need to DIVIDE this clearance figure by your rocker arm ratio to find allowable cam lobe lift (the figure Comp gives you in their data) So in my situation, we have 0.060" DIVIDED by 1.7 EQUALS 0.035" lobe lift @ TDC at the centerline closest to what you want to run.

The alternative is to go to the "Cam GURU" for their $500+ SUPER SECRET profiles (many of which are straight out of Comps catalog) and run what they deem is right for you. You could also use a GM HOT or ASA cam in your build. I can buy Comp rollers through the shop I work at for under $360, so I'll continue to spec my own cams you do what you want, either figure out what will fit or go the "little bus" route trusting someone to do the work for you.

My Comp profile, fit the LS3 with some advancing of the cam timing but, everything was pretty tight (0.040"PTV intake and 0.070"PTV exhaust) that wasn't what I wanted, I plan on beating the CR*P out of this LS3 doing drag racing and autocrossing. In hindsight, I made the mistake of reading postings on this forum and the GM High Tech Performance LS3 cam article and believing what I read before ordering ,my cam. Now it's Mahle piston time, no big deal. The bad: additional cost involved in the build, the good: new WAY STRONGER pistons/rods (going with Manley rods, they were on special last month), the VERY BEST thing is the rotating assembly will be lighter/stronger than stock for those 6800RPM shift points I plan on using.

 

Simple question here, but why not get flat tops with some valve reliefs cut into them already?

 

Or better yet, I have a set of L92 pistons that I am trying to sell that come with the valve reliefs already in them.

 

Dude, what the hell are you talking about that Comp lists their lift at TDC. Lift is lift no matter where the pistons is. The engine can be a t BDC and the lift is still the same no matter what. I just looked at a few Comp cams and it just says "lift" it doesn't say "lift @ TDC".

Your measurements are still on the physical of a cam and the measurements taken from the head. The piece you forgot in your whole "recipe" is head gasket thickness.

You say you can get any of these lobes out of Comps catalogs. Well, I want to see if they sell you LSG lobes and get back with us.

 

L92 pistons wouldn't fit a 6.0 bore without boring it out quite a bit. The L92 is a 4.065 bore vs. 4.000 for the 6.0s.

 

I know they are. The OP has an iron block so he can bore it out from the 4.030 he has even further and net him 376 cubes. It has been done many times already.

 

Here you go my "Small Bus Child" here is the Comp Cams lobe catalog with all their lobe offerings, when you look at the specs, in the top header, they have in the 5th column "Tappet Lift @ TDC" for 106degree lobe centerline and 110degree lobe centerline

Link: http://www.compcams.com/Technical/Ca...obeCatalog.pdf

Besides lift there is ACCELERATION of the lifter off of the base circle of the camshaft, most LS series lobes are pretty quick in getting with the program of getting that valve off the seat and into the air. I know its a lot of visualization and difficult stuff to envision but, there is LOTS of stuff going on in the operation of a valve train, I feel I'm wasting my time here trying to clarify what will fit and what wont. When looking at the lift figures going from a 106degree centerline to a 110centerline, you can see that retarding the camshaft gives you more room, if you want lots of room you retard it even further like GM does so they don't have to worry about high cost parts such a pistons with valve reliefs in them and those NASTY valve pockets probably increase Emissions output of the motor so in GM's mind it is best to do away with all of that nonsense and make one part fit everything from a Corvette to a 3/4ton pick-up truck.

While the piston to valve clearance can be roughly calculated using the TDC numbers there is almost always the case that the valves get tighter sometime before reaching TDC, but some data is better than none at all.

 

Gm does "waste" money on pistons with valve reliefs. The l92 has valve reliefs.

What you need to do is if your short block is together, bolt the heads on, find out where in the cycle max lift happens, set your degree wheel to that spec, And use the dial indicator method.

Or buy a cam and hope for The best.

 

I have the block already bored .30 over and pistons for it. I am not going to bore it any further if I do not have to or order different pistons. I have a brand new set of 821 ls3 heads and need to know if anyone thinks I will have PTV contact or issues with the cam I have which is a comp lsr 54-469-11 cam. Here are the specs.


Cam Style

Hydraulic roller tappet



Basic Operating RPM Range

2,000-7,000



Intake Duration at 050 inch Lift

231



Exhaust Duration at 050 inch Lift

247



Duration at 050 inch Lift

231 int./247 exh.



Advertised Intake Duration

281



Advertised Exhaust Duration

297



Advertised Duration

281 int./297 exh.



Intake Valve Lift with Factory Rocker Arm Ratio

0.617 in.



Exhaust Valve Lift with Factory Rocker Arm Ratio

0.624 in.



Valve Lift with Factory Rocker Arm Ratio

0.617 int./0.624 exh. lift



Lobe Separation (degrees)

113



Camshaft Gear Attachment

3-bolt



Intake Valve Lash

0.000 in.



Exhaust Valve Lash

0.000 in.



Computer-Controlled Compatible

Yes



Grind Number

281LRRHR13

 

Okay I'm going to beat the dead horse some more. Can you show me where in the Comp catalog there is a lobe with .035" lift tdc? According to your figures there is no lobe that will fit a LS3.

Then could you explain how this spec works with piston dwell and valve ramp rates?

This may be a pertinent spec for cam designers, but I have never found a practical use engine building.

 

I had three cams picked out. I finally decided on the

54-469-11 because it was the smallest one designed for the rectangular ls3 heads and this is the cam that the guy from Comp recommended for my application over the phone. The guy from Comp said he didnt think I would have any issues with ptv but I would like to double check since some people are on edge saying im chancing the engine. The specs are listed in my previous post.

You said it should have clearance, I just want to make sure you know which cam I plan on going with now.

Thanks


Oh and sorry I still ride the short bus as I figure this out. I figure its better to ask questions and learn than be the fool who turns the key and F*@(S the whole thing up.

 

In my opinion, asking for opinions on an internet forum where 99% of the people have no first hand experience with your particular setup is asking for trouble.

Also, keep in mind, gm's spec for deck square is .006 from end to end. So you could potentially lose that from one hole to the next.

Also, every engine is different. If your setup is borderline fitting or not without crashing valves, and you don't verify ptv for yourself, that is plain laziness. And you will have nobody to blame but yourself when your buying new valves, gaskets, bolts and whatever else if they do crash.

Asking questions is great, but this is not a question anyone on here can answer 100%. And it only takes 1% to turn you into the fool who turns the key and ***** everything up.

 

What you would do is OPEN the intake to exhaust lobe seperation and run the intake centerline more retarded like GM does, probably need to go to 116degree lobe separation which will take away some lower torque and add top end power. GM runs the LS7 cam at 120 degree lobe separation. Take a good look at the Comp Cams lift figures going from 106 intake centerline to 110 and see how the lobe lift decreases, you can roughly "guesstimate" the lower lobe lift for every 4 degrees of increase of retard by using the 106/110 figures.

 

427 zeo6. you seem like a knowledgeable guy, but you come off as a total ***. Try not to insult people, you wont earn your respect that way. If you dont care about "respect" why post?

Not everyone knows everything , thats why we post and discuss.
cheers bpatrol