C-2 Valve Train/ Performance Upgrade

[Doug #42330]

I was wondering what the conventional wisdom is in regards to upgrading the unseen valve train. (Or anything else inside the engine) I'm tempted to go with all of this performance stuff and keep the exterior of the engine stock looking for obvious reasons.

Do restores generally go with valve train kits such as roller tappets, rockers and or high performance cams, rods, pistons, etc. etc. or just leave well enough alone with more or less what the engine came with? The reason I ask is that I know I will lose HP when I make it a "pump-gas" motor so would like to compensate in other areas such as a "cam-up"

doug

[Chris D.]

Re: C-2 Valve Train/ Performance Upgrade

Doug,

Restore vs. improve will take you in different directions in the Corvette hobby. While this site leans heavily to the former, there are some old racers among the many experts on these pages so I would tell you to check the archives for more informed and detailed opinions.

General answer, stick with stock for the most part. If you are looking for a little more oomph, pocket port the heads. Sticking with solid lifters? Upgrade to better con rods as the stock rods of the era were not that reliable at extended RPM.

Making a "pump gas" motor should not involve major changes. Perhaps someone told you to drop the compression ratio? Don't do that. Lowering compression and then grabbing a hotter cam is going to guarantee disappointment. Many folks on this site have made high horse engines run well on pump gas. It only takes some closer attention to dialing in timing and fuel curves.

It depends really on what you ultimatly want to do with the car, what you have that still works, and what you want to spend. Your profile hints that you're after a sharp driver that looks bone stock. How much of the '63 340hp motor do you have? That was the last year for what is called the Duntov cam. You might upgrade to the '65 cam or the later LT-1. You'll definatly need to update the distributor. The '63 timing curve was not ideal for the hotter cams.

Othewise, I would stick with most of what you already have, perhaps switch to the period correct Holley carb, intake and air cleaner to make it appear closer to a '65.

Parting thought, if you are bent on adding aftermarket AC (profile) it won't look stock anyway. Crossing that bridge then suggests maybe one of the available modern crate motors would give you a stronger, cheaper option.

Parting thought on Hot rod parts. With darned few exceptions, I have found that most "trick" parts are designed to trick money from my wallet. For the street, the stock combinations usually worked better and lasted longer.

[Duke W.]

Re: C-2 Valve Train/ Performance Upgrade

Valvetrain upgrade? The LT-1 cam with massaged heads will make peak power at about 6500 and rev reliably to 7000, while making 80 percent of peak torque at less than 2000. It doesn't get any better that that unless an engine has variable cam indexing, valve timing, and/or inlet tract length, which are modern engine features.

The OE SB valvetrain has been proven over 50 years and millions of engines. The soft action of the OE SHP cams and standard production valvetrain parts are as good as it gets for a high performance street engine.

Other than some early problems with valvespring failures, the BB valvetrain is almost equally reliable when used with the OE cams.

The only upgrade I recommend for SBs is using the "late" 3911068 vavlesprings (which went into production circa '66) on earlier engines, and upgrade SB connecting rods, especially on mechanical lifter engines. The early rods up through '65 are WEAK! The last design is okay for L-79 and medium performance engines if properly qualified during rebuild including Magnaflux inspection. Press in studs are usually okay with OE springs and cams, but it's fairly easy to convert to screw in, and this should be done if the heads have a history of pulling studs.

With the exception of the rods use all OE or OE equivalent parts and you will end up with a very sweet engine that wants to pull past the redline and is more reliable than OE.

You select the cam to achieve reasonable low end torque, and work the heads to maximize top end power.

Don't get sucked into the hot rod parts route. It's all marketing hype, myths, and misinformation!

A lot of guys lower compression excessively, which is a big mistake. The OE replacement forged, domed pistons, typical machined deck height and a composition gasket will yield a true CR in the range of 10.2-10.5:1, which is okay for a SHP cam and pump premium. If you put a set of "9:1" pistons it will probably be closer to 8.5 and this combined with a high-overlap SHP cam is a recipe for a dog. You can't compensate for lowered compression with a "cam". If fact, most aftermarket cams have more overlap than OE cams of similar duration and adding more overlap to a lowered compression is like mixing ammonia and bleach!

Target 9-9.5 for 300 HP engines, which is about what you'll get as above with the OE flat crown pistons and a composition gasket.

Don't believe any specified "compression ratio" numbers. TAKE ALL THE MEASUREMENTS so you can COMPUTE THE ACTUAL CR on your engine, and any adjustement to lower it to acceptable levels can usually be made with head gasket selection and chamber grinding. CR is EXTRMEMLY sensitive to critical dimensions such as deck clearance and gasket thichness. All other things being the same, the difference between a typical compositon gasket and the OE steel shim gaskets is about half a point.

Duke