January 2011 Chevy High Performance Q&A - Performance Q&A

Tom Truty Dec 9, 2010 0 Comment(s)
View Full Gallery

Holley carburetors have a very convenient hole at the bottom of the throttle bracket that looks like it would work perfectly; however, it's around 1.375 inches from the centerline and is too far forward as compared to a mid-'80s Q-jet. The best template to use would be an old Q-jet and duplicate this cable mounting point on your Holley throttle arm bracket. We usually make a very short tab that will bolt into that hole on the throttle arm; it will allow you to move the cable pickup toward the centerline of the throttle shaft and move the cable mount slightly rearward. Between these two adjustments, you will have a pickup point very close to the original Q-jet design.

As for full throttle, there are several throttle cable mounting holes in the throttle arm. The top hole usually won't give you enough travel to achieve full throttle. Unless you have a good deal of pedal travel in the car, you won't see full throttle. Move the throttle cable mount to a lower pickup point in relation to the throttle shaft centerline. This will give you full throttle, but the throttle will be more sensitive.

After checking and adjusting your TV cable ratio and cable mounting, we hope your transmission shifts. It doesn't take much driving with low line pressure to hurt the gearbox. Good luck with your project.

Beyond Old School
Q: I have a '56 Chevy Bel Air with a '59 283 bored 0.060-inch over and completely blueprinted. It is the engine from Jon Calendar's old '59 Chevy that he won Jr. Stock with at Indy in 1965. It still has the original heads and all the old-technology parts in it. I was considering upgrading the top end to a set of aluminum heads and a better cam, probably around 0.500-inch max lift. It now has an aluminum intake and a Holley on it that was from an early '70s Z28. When I was racing it, if you missed a shift, it was very easy to bend a valve. With more cam, I would think the valves would be nearly hitting the pistons. Are the newer heads of a different angle so the valves won't hit the pistons? If you have any recommendations on a cam I would appreciate it. I always look forward to reading your column and I am amazed on your wealth of knowledge on the Chevy engines. Thanks in advance.
Jerry Marteney
Louisville, OH

A: You actually drove the car back in the valve-bending days? Look how far we've come ... we're still bending valves in Stockers in the water box if you rev the engine too quickly during a burnout! At least there are rev limiters to help with the missed-shift overrevs.

With any engine, you can run out of piston-to-valve clearance based on the duration and lift curve. The original heads on your '60's race engine have 23-degree valve angles. This is the same angle on 95 percent of the small-block cylinder heads on the market, until you get into the very specialized racing heads. With these heads, they have flattened out the valve angle (18 degrees or 15 degrees) to reduce chamber size and burn efficiency of the combustion space-nothing you're going to want to do with your little 283.

As for a camshaft for your little Mouse, you've given us very little info on what you intend to do with the engine. Is it going to be used to pull your '56 around on the street? We'd assume this with the max lift in the 0.500-inch range. We're sure the major issue with the valves hitting the pistons back in the '60s was the lack of valvespring pressure. As soon as you missed a shift, the revs went north of 8,000 rpm. When this happened, the lifter had no chance of staying in contact with the lobe and lofted right off the nose of the camshaft. When the piston came up the bore it was introduced to the intake valve! Now we have plenty of spring pressure and camshaft lift profiles that will keep everything under control. You'll want to install an ignition system that will allow you to control the max rpm if things get out of hand.


Connect With Us

Get Latest News and Articles. Newsletter Sign Up

subscribe to the magazine

get digital get print