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Ask Anything - July 2014

Standing Tall

Michael Zehl; via I recently read the EFI test article in the Mar. '14 issue of Car Craft. I found the article incredibly informative. I am planning an EFI swap on my '78 Trans Am barn find. I had been struggling with which one to choose. I am left with one question your article did not cover: How well does each of these units fit underneath a stock air cleaner? My TA with a shaker scoop leaves no room for any spacers of any kind. It is currently running a Pontiac 400 with a mild cam, Edelbrock Performer manifold, and a Q-jet carb. It fits the height of my hood perfectly. I think your article covered the systems very well, except on this part, and I was very happy to read it. If you have any information that may guide me in my selection process, it would be greatly appreciated.

Jeff Smith: Great question, Michael—had we thought of it, we would have given you the specs. We still have all these systems, so we measured each throttle body from the base where it bolts to the intake manifold to the ring that mounts the air cleaner. First, we started with a standard square-flange Holley carburetor, a Rochester Q-jet, and then all of the EFI throttle bodies, including the Professional Products unit. As you can see, nearly all the throttle bodies will probably work, with the possible exception of the FAST EZ-EFI 2.0, although 0.060 inch is probably not going to cause a major problem. We used a drop-style, air-cleaner base on our big-block test Nova to help clear the stock hood, and none of the throttle bodies caused any fitment problems, although the EZ-EFI 2.0 was a little tight to the air-cleaner base in one spot. In the past, we have had fitment issues with a short throttle body where the throttle linkage hit the base of the air cleaner at roughly three-quarter throttle, but we minimized this problem with an extra gasket between the throttle body and the air-cleaner base.

More Info

Holley Performance Products; 270/781-9741;

Carburetor/TBI Height (inches)
Holley square-flange carburetor 3.25
Rochester Q-jet 3.25
MSD Atomic 3.125
Edelbrock E-Street 3.25
FAST EZ-EFI 2.0 3.3125
Holley Terminator 3.00
Professional Products Powerjection III 3.187

High School Stroker

Brody Malsom; via Hey guys, great mag. I've been reading and learning so much from your articles in the past five years I've been subscribing. I'm 18 and in my senior year in high school, and my buddy and I bought a '66 GMC pickup together. We are going to ditch the tired V6 for a 383 stroker. As of now, the block has been bored 0.030 inch, and we have a Scat series 9000 stroker kit on the way for it. My question is what cylinder heads would be the best for us since we're not trying to make a butt ton of power and not spend an arm and a leg on this build. I have experience with rebuilding engines, but as for this stroker combo, I have no idea where to start when it comes to looking for heads that will make decent power. Also, I was wondering about the cam—again, I have no idea where to even begin. I appreciate your time and look forward to your advice. Thanks for all the great info and knowledge.

Jeff Smith: We always try to help out the younger readers, since they are going to be the ones to continue our hobby/sport, so let's take a shot at your question, Brody. Assuming that you purchased the entire Scat 9000 rotating assembly, you didn't mention what piston came with the system. We looked at prices at, and we'll also guess that since you are a high school student that you went with the least-expensive kit that features a hypereutectic flat-top piston with 5cc piston valve reliefs. While the longer 3.75-inch stroke creates additional displacement, it also has a direct effect on increasing compression ratio, assuming all other components remain the same. As an example, with a 355ci engine with a 3.48-inch stroke, a flat-top piston with 5cc valve reliefs, a 64cc combustion chamber, 0.041-inch-thick head gasket, and a 0.015-inch piston-to-deck height will deliver a 10.0:1 compression ratio. But change the stroke to 3.75 inches (all other specs remaining the same) and compression jumps to 10.7:1. So the piston style has a significant effect on what we can now suggest for a cylinder head.

Let's assume that you went with the less-expensive flat-top piston kit. This means we need to look for a cylinder head with a minimum 70cc chamber to keep the compression pump-gas friendly. Because this will be a street truck, we should also keep the cam timing conservative. This will work better with a budget cylinder head, but short intake duration numbers also affect the compression. As you can see, all these factors are interrelated. We really need to keep the compression around 9.5:1 so the motor is still snappy and responsive, yet doesn't build excessive cylinder pressure so that it detonates. Let's first take a look at the cylinder heads because once we select a head, this will help determine the cam timing.

Cylinder heads are the big determiner of power. A stock replacement iron head will be the cheapest, but frankly this will limit both torque and horsepower. I found an interesting 72cc combustion chamber iron head from Summit Racing. This is more of a stock replacement head with a 165cc intake port, 2.02-/1.60-inch valves and screw-in, 3⁄8-inch studs with stock 1.25-inch-diameter single valvesprings. I don't know much about these heads, except that they are certainly priced attractively at $635 for the pair. You really can't properly rebuild a set of used stock iron castings for much less than that. With a 72cc chamber and a flat-top 5cc piston, this would place static compression at 9.84:1, which is a bit high but still workable. This assumes the piston is 0.015 inch below the deck surface.

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