Valve spring shims what's the thickest I can use

The closest comparison I could find was a 4.3L cam with about .040 more lobe lift than my cam, the 3.8L and LSx series cam specs were not listed I guess for competitive reasons they want you to call about those. The spring listed for all the 4.3L cams you could veiw the specs for were double non behive with a max open pressure of 310 at 1.2 open.

A general comparison of the beehive springs showed about a 14lb pressure increase per .050 increase in lift so maybe I'll gain about 12lbs by adding the .050 shim. I calculated about 1.272 open height with my cam so by the 4.3L spring recommendation that would be about 284lbs however the 4.3L has a heavier valve train than the 60 degree V6. I believe the valves and lifters are heavier at least I recall the roller lifters for the 60 degree engine being smaller when I compared them years ago.

Not sure how much spring load savings that would translate into. The valves being splayed also help in reducing the amount of spring tension needed by the amount of sine(angle) times the weight of the valve since it's not being lifted at a 90 degree angle.

Dur. 212 208
Valve lift: .468 .454
Lobe sep 114
Roller cam int -6 BTDC 38 ABDC
Exh 40 BBDC -12 ATDC

I'll look into the cam spec comparison for spring tension, since I'm using twin turbos with a cam that was cut for turbocharging and higher rpm it's likely my redline will be above the 6500 rpm rating. According to Desktop Dyno it's right about 6500 as indicated but the high flow of two turbos might take it higher.

That high volume oil pump nearly sprained my wrist when I primed it with a drill, that's a lot of horsepower being lost over the rpm range.

[geoffinbc]

Yea I am not a fan of HV pumps either. Even stock pumps provide way more volume than needed and will also feed mild race motors. I have 30 PSI of pressure at idle on SAE 30 in the middle of summer. Really you only need 10PSI. So that there tells you how much the pump is working.

But like I said earlier see what Crane and Comp specs for springs on a cam of similar specs. They both sell 60* camshafts so take a look.

What are your specs anyway?

Well suit yourself. I know people have had valve float issues with stock cams and stock springs. So be warned. Just because GM uses it to 6000 RPM doesn't mean it is the best way to get there. Springs go along way in valvetrain stability and lifespan. Especially if you like to go wide open often.

It sounds like your are trying to justify not spending a little extra cash. But it will go along way in terms of performance and reliability. You've gone this far, another hundred into the project for new stronger springs sounds like a good investment to me.

Actually justifying spending more cash under the circumstances where I have parts that may be appropriate for use. It is apparent from my observation that everyone believes the right way to do something is to spend money on assurance without the burden of proof under the assumption you can't go wrong that way. Having done that in the past and realizing thousands of dollars later that spending without planning or justification can be just as bad, I make it a point to evaluate first.

Higher performing springs would be my preference, but having had at least one high performance spring break under average use and no original equipment spring failures, well hopefully you get my point. As mentioned before they are low on the priority list, I have the shims and if they will prove to be beneficial at the moment that would be the best approach.

I'm not aiming for the moon just spring pressure a little above stock which I should get without a problem.

I've also had a high volume oil pump ruin an engine.

One important thing I can say about original GM parts is this, dependability has been much greater for the original parts than for the aftermarket parts that I have purchased over the past 20 yrs.

I do appreciate your input, and although I'm on a budget even If I were rich we might still be having this conversation because of priorities, if I don't need it for my purposes I don't want to buy it. That's how garages are filled because it's just hard to throw away good parts.

[geoffinbc]

Well suit yourself. I know people have had valve float issues with stock cams and stock springs. So be warned. Just because GM uses it to 6000 RPM doesn't mean it is the best way to get there. Springs go along way in valvetrain stability and lifespan. Especially if you like to go wide open often.

It sounds like your are trying to justify not spending a little extra cash. But it will go along way in terms of performance and reliability. You've gone this far, another hundred into the project for new stronger springs sounds like a good investment to me.

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

[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.

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.

[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.

[geoffinbc]

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.

[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.

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]

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.

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.