Checking for a friend of mine that has an 86 T/A 305TPI that he's getting a new cam for.
What is the max lift that the stock valvesprings will handle??

Thanks,


Ken

 

Check the cam in my sig. That's with stock springs, but some say it might be pushing the envelope a little.

 

Generally, the max recommended is in the .450 range, give or take a few thousandths.

 

it wouldn't matter to me when i change cams i change springs and trash the stock rotator set up. i'd think .450 would be the top limit for stock springs.

 

O.K. - I'll jump on the wagon, too.

0.450" is safe with stock springs, but not much more. And that isn't only because of coil bind and interference, but the seat pressure of stock springs is generally inadequate to control the valve train when a cam with .450 lifts or greater also has a ramp profile that creates a lot more linear accelleration of the valve (because of the greater travel distance over the cycle time). Valve float and seat bounce can start to be a problem at higher RPM ranges, and the extra heat generated by the longer motion is tough on stock springs. Couple that with the extra mass of the stock exhaust valve rotators and spring shields, and the stock setup gets very marginal above .450" lifts.

.450" is not just some arbitrary number thrown out as a reference - there are some reasons for it and it's been a while since anyone has posted those. It's generally better to not only understand the "what", but also the "why".

 

Any reasonably streetable hydraulic cam for a 305, will
have a valve lift under .500". As far as coil bind interference
is concerned, your stock springs will handle this to about 5500rpm. But for maximum rpm potential you might want to replace the stock springs with a stock diameter (1.26") replacement high perf spring. You can buy them from various manufactures.
Crane, Comp cams, GM, Isky, K-Motion. Look for something with
about 100/120 lbs seat pressure and 290 to 340lbs open pressure.