Valve spring shims what's the thickest I can use

[Guest]

My cam regrind is supposed to be good to at least 6500 rpm, since I already have shims from iron heads that I can use, what's the thickest I can use on the aluminum heads without coil bind bearing in mind I have a max cam lift of .468.

Shneider also stated that since they only removed .040 from the base circle of the cam I could still use my original pushrods without a power loss.

I'm still curious about whether or not the reduced preload will some how predispose the lifters to float.

This is on a 3500

[RacerX11]

stock 3500 springs?

[Joseph Upson]

Yes, stock everything except the cam

[geoffinbc]

Install LS6 Springs. Shit stock springs float on a stock cam

[Joseph Upson]

Install LS6 Springs. Shit stock springs float on a stock cam

I don't have LS6 springs I have shims that I would prefer to use if they will be helpful, otherwise I would invest in the Comp Cam springs which fit without any modifications. They just aren't high on the priority list right now.

[Joseph Upson]

One more reason I don't want to change out the OE springs is I don't know for sure they are not better than the springs used on the 3400 since GM shows a different listing for the springs used on the 3500 and 3900 compared to the 3400. The heads are different so it's a possibility the springs are also.

[SappySE107]

Well, I need a 2nd test somewhere else but the 3500 springs are weaker on the tester at the shop I use. Its not accurate though but it should still read closer to the 3400 than it did. I don't remember the numbers now. I only needed to know they sucked worse than the 3400 springs.

[Joseph Upson]

Well, I need a 2nd test somewhere else but the 3500 springs are weaker on the tester at the shop I use. Its not accurate though but it should still read closer to the 3400 than it did. I don't remember the numbers now. I only needed to know they sucked worse than the 3400 springs.

That would explain why they're cheaper than the 3400 springs then, so it's not a more efficient manufacturing process. Now how beneficial are .050 shims to crappy springs which are already good to at least 5500 rpm or more if the VVT engines dyno sheets are any indication, and 6000 rpm if the same spring is used currently on the 07 3900 which may or may not have a repositioned spring seat for higher opening pressure since it has a different head design than the 3500. I can't reasonably assume the springs are inefficient from the factory at some point earlier than its SAE rated max power output rpm.

[SappySE107]

The 3900 springs are in some sheilds and we never took one off. I can't tell you what the new pressure would be with a .050 shim (where are you getting a .050 shim?). I would need the pressures again. Ill take a 3500 spring to the shop with me and verify they are weaker but the numbers are worthless from their tester.

[Joseph Upson]

The 3900 springs are in some sheilds and we never took one off. I can't tell you what the new pressure would be with a .050 shim (where are you getting a .050 shim?). I would need the pressures again. Ill take a 3500 spring to the shop with me and verify they are weaker but the numbers are worthless from their tester.

The shims were removed from a set of cast iron heads from a Fiero 2.8L I acquired some time ago, I thought I might be over on the thickness but I just measured them and checked my caliper against a feeler gauge and they are .050 shims. When I checked GM parts they list the 3500 and 3900 for the same spring however they could be different for 07. I just don't care to remove good OE equipment that can be given an edge with a little help. I don't intend to run above 6500 rpm and will probably program the ecm to limit the engine to 6600.

[geoffinbc]

[SappySE107]

Go table man (brad). Well it looks like the 3500 springs are the same as the 3400 for specs and the 3900 got some weaker springs. Kinda odd since the 3900 has bigger valves, which are normally heavier.

[Joseph Upson]

Go table man (brad). Well it looks like the 3500 springs are the same as the 3400 for specs and the 3900 got some weaker springs. Kinda odd since the 3900 has bigger valves, which are normally heavier.

The reduced number of coils on the 3900 spring suggests that the valve stem might be shorter possibly compensating for the increase in valve size and don't forget the valve on the 3900 has a hollowed center with a gas charge to help lighten it. It's apparent that GM feels very comfortable with these springs all the way up to 6000 rpm at least so the .050 shims should work fine for a little added pressure insurance.

[geoffinbc]

Thats on a stock cam with a different ramp. So dont just asume it is good on any cam up to 6000. A more agressive cam may cause the the lifter to bounce if there is not enough spring pressure. Find a cam online with similar specs and see what crane and comp would recommend for spring pressure.

[Joseph Upson]

Thats on a stock cam with a different ramp. So dont just asume it is good on any cam up to 6000. A more agressive cam may cause the the lifter to bounce if there is not enough spring pressure. Find a cam online with similar specs and see what crane and comp would recommend for spring pressure.

It's a reground stock cam so there is little room for an agressive ramp, just a little more lift and duration