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heretic
09-21-2007, 02:31 PM
Who out there is running a aftermarket Cam?

If you are at what lift do the stock pistons need to fly cut for valve clearance?

Will .480? or .500" lift clear without having to fly cut the pistons?

white95v6
09-21-2007, 04:39 PM
i have run up to .580 lift and 226 deg duration and no issues with a 96-up pistons and those are almost flat tops.

fturner
09-21-2007, 06:25 PM
i have run up to .580 lift and 226 deg duration and no issues with a 96-up pistons and those are almost flat tops.

Our pistons are not flat tops and have a fly cut in them.

white95v6
09-21-2007, 08:26 PM
Our pistons are not flat tops and have a fly cut in them.

i am aware of that. ;) i was just saying with a piston that has almost a Flat top you can run a cam alot bigger in lift then what he was asking about.

so with a Dish and a nice valve relief aslong as its placed right you should be able to get away with alittle more. :)

Stupid Canuck
09-21-2007, 11:15 PM
Are you also aware that the stock SC's valve springs bind somewhere between .480 and .510, depending on who you listen to, and they're mush at high rpm?

Comp 942's are a little better. Beyond .520 would involve machining or different valves.

white95v6
09-22-2007, 11:48 AM
Are you also aware that the stock SC's valve springs bind somewhere between .480 and .510, depending on who you listen to, and they're mush at high rpm?

Comp 942's are a little better. Beyond .520 would involve machining or different valves.


yea but he asked about Piston to Valve clearance. lol

springs are a Whole different subject. ;)

Flex
09-22-2007, 06:18 PM
While the stock springs may bind at .520 lift, custom machining is not the only answer to solve that problem. A cheaper and more effective solution is to use a beehive spring such as Comp's 26918 effective to .600 lift. It is the spring set Comp suggests for our application.

Flex
09-22-2007, 06:19 PM
heretic,

Dave Dalke (XR7 Dave) has used a .491 lift cam to make 400 hp in a unmodified short block app.

I just bought one from him for my brother's buildup.

heretic
09-22-2007, 10:59 PM
I checked my clearance today via stuffing some of my nieces old plado in the piston dish to see where the valves would hit and they seem to clear fine:D....

However I was comparing a set of scorpion roller rockers to the stock stamped unit and come to find out the push rod is not long enough to fit the scorpion rockers......:mad:

So I have decided that I want to run a new cam with either .480 or .500" lift.....

Ira R.
09-22-2007, 11:03 PM
I checked my clearance today via stuffing some of my nieces old plado in the piston dish to see where the valves would hit and they seem to clear fine:D....

However I was comparing a set of scorpion roller rockers to the stock stamped unit and come to find out the push rod is not long enough to fit the scorpion rockers......:mad:

So I have decided that I want to run a new cam with either .480 or .500" lift.....

Well, if you are interested I have one with .491 lift - 210/220 duration I am letting go of. PM me if you want.

Ira

heretic
09-22-2007, 11:09 PM
I have some serious questions to ask about this situation and I need to think them over but will get back to this thread tommorow

Flex
09-23-2007, 12:01 AM
Heretic,

Are the Scorpions 1.73 pedastal mounts? You can't just use any rocker.

heretic
09-23-2007, 01:37 PM
Yes the scorpions are pedestal mounts and they come straight from supercoupe performance... so I expected them to be the right part!!!

I also expected them to fit with stock pushrods but I was wrong.... they are off by as much as .120" on the tappet side...

There is some error in this because the lifters were collapsing slightly during test and I should have measured from the other side... However they still don't fit.

anyone else have this problem?

Flex
09-23-2007, 01:58 PM
Dude,

If your engine is stock, you should have no problems. Are you saying they are .120 too long? You must ensure that the cam is at the base circle on the lobe you are working on in order to install the rocker and verify pushrod length.

heretic
09-23-2007, 02:06 PM
No the pushrod is too short and the motor is completely stock as far as cam and the valvetrain goes....

And with the rocker fully mounted the pushrod just wobbles around without touching the seat of the rocker.....

the rods are 7.136" inches long

Flex
09-23-2007, 03:28 PM
Those are not factory SC pushrods. Factory pushrods are 7.3 inches long. There's your problem.

XR7 Dave
09-23-2007, 11:01 PM
No, the Scorpion rockers do require longer pushrods. Stock is 7.136". I do not normally install roller rockers on stock motors but with a reground cam most often you'll want to run either a 7.266" pushrod or a 7.300 depending on various factors.

Harland Sharp is the only company that offers an actual 3.8L V6 rocker arm. All others are 351C or 460BBF rocker arms and there are some variations out there in terms of reach and installed height. These are simply things that an engine builder deals with on a daily basis. Roller rockers are not really a 100% do-it-yourself bolt-on mod. Selecting the right pushrod and maintaining good valvetrain geometry is always the responsibility of the installer. You really can't blame the part manufacturer.

People often make the mistake of worrying only about lifter preload when installing rocker arms but the truth is that the process starts with valve tip alignment and pushrod length is a secondary consideration. Just because a rocker arm bolts on and you achieve proper preload doesn't mean you have a working combination.

Flex
09-23-2007, 11:11 PM
You are correct Dave. I forgot to write down the one when I checked length and ended up with 7.3