How much lift will the stock 1988 LO3 TBI valvesprings handle?

 

When they were new, they would barely handle the .400" or so that it has. Now.... somewhat less than .400".

Yes, if you're replacing your cam, you need to replace the springs. Don't even think about re-using your stock ones, they will end up costing you far more than you will save.

 

No offense, but I'm running 0.411 lift on 14 year old springs.

Peanut cam + 1.6 rockers.

The 187 casting heads, found on TPI and TBI have springs good to about 0.480 lift. Age and wear though may beat that limit lower. The key note is that you should ensure that the springs aren't experiencing coil bind. You should be able to fit a 0.015 inch feeler guage between the spring even at full lift.

It's always a good habit to change springs with a cam change.

 

So 0.435" isn't out of the question? Is there any way to check coil bind without taking the old cam out and putting the new one in? I'm planning on changing cams from the stocker to one with around 0.435" lift and I'd like to make sure I can use the bigger cam without taking the old one out.

 

Comp cams says you should have .060 between the coils at max lift. I don't see why stock would not go by that rule.



Brian

 

.060" between the springs.

It's not just coil bind. When going to a higher lift either with a cam swap or 1.6 rockers, you need to make sure the bottom of the spring retainer doesn't hit the top of the valve guide. This can cause more problems than just having coil bind.

 

That is so true I destroyed a set of guides on a set of vortec heads because I didn't go back and check the machine shop's work. I do believe stock 305 guides are good over .480 though where vortec are only good to .460


Brian

 

On top of all that measurement stuff, you need to make sure that the springs can actually return the valve to the seat in real-world operation, and hold them there. That's where a bunch of worn-out stock springs can really fall down with a real cam.

 

In other words, the spring RATE is as important a figure as the coil bind height, installed height, and intitial pressure. Stock springs tend to have a much lower spring rate, and while they might not heat as much as higher rate springs, can't effectively control the valve on a high ramp cam lobe at higher RPMs, like 4,500 or so.

 

while you're putting the new springs on since you'd rather spend 50 dollars that risk breaking something in the valve train spend another 40 or so on aftermarket retainers and trash the factory rotator set up.

 

So true. Had I known that I would have put in new springs when the heads were sitting on the bench. Now it floats them at 4000. The right springs are just as important as the cam that you choose.