G8GT7

1.What is PTV Clearence
2.What is flycutting pistons
3.What is a meant by maximum gearbox torque
4.last question is when do I need to change my Rocker arms at what amount of power mine is 1.7 size

thanks

Bring the Noise

1. Piston To Valve (PTV) clearance = The amount of room between the valves and the piston when the piston is at the top of the exhaust stroke and starting the intake stroke.

2. Flycutting pistons = cutting valve relief's into the pistons so that the pistons do not contact the valves.
Some factory pistons come with valve reliefs some do not.

By measuring the PTV clearance a good mechanic can determine if the pistons need to be flycut for either intake and/or exhaust.

3. Not a clue (I'll leave that one for someone else to explain).

4. Increasing the rocker arm length from 1.7 to 1.75, 1.8 or 1.85 will affect the lift amount on the valve and the rate at which the valve opens/closes.

Simple answer: A cam with .550" lift on 1.7" rocker arm will have .582" lift on a 1.8" rocker arm and the valve will open and close faster.

If you go with longer rocker arms make sure you have the right shim's and push-rod lengths to keep the valve-train aligned.

I hope that helped you some.

G8GT7

thanks for you help

1.but is good that there is high amount of PTV clearence or the opposite is correct
2.So what is meant by a aftermarker cam with a tight PTV clearence
3.Do you know what is a 93 octane pump gas is it a 93 fuel octane
4.If the cam spec says 600" lift it means that with a stock rocker arm will reach this amount of lift

thanks agian

Bring the Noise

1. More room between the valve and piston is better.

2. Tight PTV means there is less space between the valves and the piston. This can be from larger lobe sizes, larger amounts of lift on the stock lobe size, running a smaller lobe sepperation (LSA), or having larger valves in the head.

3. Yes, 93 pump gas is just that gas you get at a pump station/gas station.

4. Double check with the cam company.
Usually if it is not listed most people would say that is true, but if you are looking at a cam for a different engine then it could be incorrect.
Example: LS7 cam lift numbers are based on a 1.8" rocker arm (as that is what comes in the motor from the factory). If you look at a ls7 cam to put into a L92/LS3/L76 then you would take the lift number (say .600") and divide by 1.8 then multiply by 1.7 to get the lift with stock rockers for a LS3/L92/L76 motor (which would be .567").

Piston to Valve clearance becomes an issue over the life of the motor (mainly due to the life of the valve springs).

Valve springs are designed to handle a certain level of ramp rate and max lift.
Pushing the springs to max lift and ramp rate (how fast the spring is compressed/how fast the valve opens) can shorten the running life of the springs.

Also some of the gm engines come with Active Fuel management (AFM). The L76 in the G8 GT, the L99 in the 2010 SS1/SS2 automatics, some of the L92 and L76 in the trucks/suv's, etc. The AFM system uses a special set of lifters on 4 of the piston (8 lifters total). Those lifters are not a performance part and can only handle a modest amount of lift and ramp rate. There are cam's on the market for AFM enabled engines but they are currently listed as specialty cams by most companies.

For a little reading look at the following page
http://books.google.com/books?id=Ro3...piston&f=false (simple google search "Kissing the piston").

G8GT7

tight PTV clearence aftermarker cams means large LSA=above 14 LSA correct??
and even lifts and duration ?
If I reduce the combustion chamber will it reduce my PTV clearence
thanks you

Bring the Noise

Tighter PTV does not always mean needing a larger LSA to correct it. Some cases it can help and some it can not.
Smaller lift can reduce PTV issues by increasing the space between the piston and valve.
Smaller duration can reduce PTV issues
Advancing the cam can reduced exhaust PTV issues a little but can cause intake PTV issues.
Retarding the cam can increase exhaust PTV issues a little but reduce intake PTV issues.

Reducing the combustion chamber for stock deck height heads will not increase or decrease the PTV clearance.

Example GM head castings 243 and 317. Both are based on the intake and exhaust designs of the LS6 head (243 is the ls6/ls2 head, 317 is the LQ9 head).
The 243 comes with a combustion chamber size of 64cc or 65cc (depending on LS6 or LS2) and the 317 comes with a chamber size of 72cc. Both heads have the same deck thickness and the stock valves have the same PTV clearance.

Now reducing the Combustion Chamber by shaving the heads .005" to .030" will actually create a tighter PTV clearance.
By shaving the heads the valves will set that much closer to the piston. Shaving the heads means removing material off of the bottom of the head which reduces the deck thickness.
Doing this can actually cause a PTV clearance issue with a cam that when matched to stock height heads does not have an issue.

Easiest answer to PTV still stands from the days of the 1st generation Small Block Chevy V8's.
Intake Valve to piston clearance should not go below .080" (if you are at .060" then machining valves reliefs is required).
Exhaust Valve to Piston clearance should not go below .100" (if you are at .090", .060", .075", etc then machining valve reliefs is required).

PTV clearance depends on the combination of parts that make up the motor in question.
How big is the cam (duration, lift, lsa, degree advanced in or not, etc).
Are the heads stock, shaved, aftermarket, or a combination (shaved stock, shaved aftermarket)?
Valves sizes stock or over sized?
Pistons stock or aftermarket?
Did the block need to be decked?

G8GT7

thanks alot

02_camaroz28

iTrader: (20)

Whats the max lift on Stock LS1 valve springs and also on Stock LS6 valve springs?