Valvespring question
 

Before searching, I bought a set of LT4 Valvesprings. Will these fit? If not, I have a LT4 Standard cam and I would like to get some budget springs. Suggestions? I run the car hard and go up to 5500 on almost a regular basis.

Should be ideal for this. From Chevy High Performance:

http://chevyhiperformance.com/techar...mage_small.jpg

The stock valvesprings (left) will handle the additional lift of the 1.6 roller rockers, but the best move is to install a set of GM Performance Parts LT4 valvesprings (right). These stiffer springs will bolt in place of the stockers with no machining required and can handle the lift of the GM Performance Parts Hot hydraulic roller cam that we’ll install next month.

Well. I'll measure them to make 100% sure.

LT4 valve springs have a 1.32" OD. The factory spring pocket is 1.26". Unless you have machined the valve spring pocket for a wider spring, then no, they will not fit.

If you want to retain the factory spring pocket size, the Comp 981's can do that. Of course, valve spring selection truly depends on which cam you have.

would a lt4, or lt4 hotcam work ok with stock 305 heads, or would I have some valve float problems without replacing the valve springs?

Valve springs (too little seat pressure) are what create valve float. Factory valve springs are probably too weak to handle an LT4 cam. I would upgrade. Usually 986 springs are good springs to run, however, they are a 1.43" OD, meaning the spring pocket would need enlarging. I have a box of Isky 235-D valve springs with very similar specs to the 986's and they have a 1.26" OD and can fit in the factory spring pocket. These springs are far better suited to handle a hydraulic roller to 6000 rpm or more, at least, better than any factory spring would. The other thing is the factory pull out studs. You would want a set of screw in studs. As you increase the spring pressures and rates and valve lift, you increase the likelyhood of pulling a stud. From the factory all you have is measily press in studs. You wouldn't be the first if one of yours came out. Mr. Gasket makes a set that doesn't require machining and all you have to do is tap them. I believe this can be done (carefully) with the heads on the car still.

The biggest issue you will encounter is the clearance between the top of the guide boss and the bottom of the retainer. On the factory setup, you have roughly .480" before they slam into eachother, physically halting any further opening of the valve. And at that, .480" is a general number. The actual distance may be less. The heads can be taken in to the machine shop to have the guide bosses milled down to increase the clearance.

If this is for the 305 in your info, look into an LT1 cam. With minor modification to the dowel pin it will bolt right in.