Chevy Performance Tech Q&A - August 2014

Kevin McClelland Jun 26, 2014 0 Comment(s)
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Big Al

Last month I left you guys with a teaser that we would be building a couple of engines with our good friend Greg Ventura. I believe I wrote a couple of years ago that we lost Greg’s dad, Big Al Ventura, to cancer. I met Al Ventura back in the early ’80s, racing at Orange County Raceway in my Project Pro-Gas ’57 Chevy that I built. Al had a show-car-quality ’55 Chevy with a nasty big-block running in Super Gas. I was the punk kid rolling into OCIR, and Al was the cagey veteran holding down his turf. Greg was in his early years, riding around on his BMX bicycle and causing trouble for his dad. Al and I hit it off, since we were into Shoeboxes and mine was blue, as was his.

Al retired as a mechanic, taking care of heavy equipment. On the side for many years he had Ventura Racing Engines building any type of engine from street performance variants to Pro Mod nitrous-fed big-block Chevys. Over the years, Al passed the driving duties to Greg and we faced off many times. Al and I always respected each other’s talents and I looked up to him, as—I’d learn later—he did I.

In the last year we had Al around, he was collecting parts to build a really nasty big-block for their ’66 Nova to run Top Sportsman. He had acquired a tall-deck aluminum Brodix block with a raised camshaft tunnel. This block and rotating assembly came from a Top Dragster racer who decided to get out of the expensive game—he’d had very limited runs on the block and rotating assembly. As Al was collecting parts for his dream engine, we learned of the Big C, and we lost him within eight months. Awhile after Al’s passing, Greg came to me as he wanted to build this engine in his dad’s honor. We’ve lovingly named the engine Big Al, and we will try to do the name justice.

Greg’s plan was to complete the engine with a set of Big Duke cylinder heads that they’d run on various combinations over the years. These heads are related to a Pro Stock design from about 10-15 years ago. They used shaft rockers with large exhaust rockers and large offsets to get around the intake ports. Well, cylinder head technology has moved miles in the past several years and the latest conventional-style big-block cylinder heads flow serious air, and use conventional valvetrain components common to big-blocks for the past 50 years. We landed on a set of the new Brodix SR-20s and the matching single-plane racing manifold. The “20” in the name refers to the intake valve being rolled to a 20-degree angle. The intake sports a 2.400-inch valve with a 440cc inlet runner. This CNC port, out of the box, flow’s an outstanding 507 cfm. The exhaust port squeezes in a 1.800-inch valve and flows 335 cfm! Now, they consider this configuration a conventional head, but it requires a specific dome to mate to the 95cc, specific shaft rockers for this valve angle, and valve covers. Brodix did stick with the GM design on the valvetrain and made subtle changes for the valve angles.

In the coming months I’ll report in on various other trick components on this 601ci behemoth that I’m having a ton of fun building. Our main goal is to make Al proud. We want to get their ’66 Nova into the 7s without any power-adders, and enter one Top Sportsman race and have Al ride along while Greg turns on win lights. Stay tuned.

Edelbrock Pro-Flo XT

Q I have a ’69 Chevelle SS with a ZZ502 crate engine from Chevrolet Performance. It used to have a carb, but I’ve installed an Edelbrock Pro-Flo XT EFI.

The car has 17-inch wheels, a Hotchkis suspension, Wilwood 13-inch front discs, and Stainless Steel Brake Corp 11-inch rear discs. Power runs through a five-speed Tremec and a 3.73 12-bolt GM rear.

I’m in the process of installing an EFI gas tank from Tanks. I’m hoping this will solve my fuel starvation problem when I hit the gas. The new tank will have a reservoir for the fuel pump. Right now my fuel pump is on the framerail. I’m hoping putting it in the tank will take care of my bog.

Is there anything I’m missing? Thanks!

Nick Moscato
Rockville Centre, NY

A Sounds like you’ve got a really nice build on your hands. We’ve always had a very soft spot for ’69 Chevelles. Big-block Chevelles are hard to beat on the smiles per mile!

The way you have described your problem, it sounds like the engine bogs or starves for fuel when you hit the throttle. We assume you’ve checked the fuel pressure with a gauge to verify that you are truly losing pressure at the hit of the throttle. With a full tank of fuel, there should be no way the pickup in the tank could be uncovered and suck air. After reviewing the Pro-Flo XT system, we believe the big-block, PN 3567, comes with a baseline calibration for a 502-cid big-block with a 236-degree duration at 0.050 inch tappet lift camshaft grind. The separation angle falls right in Edelbrock’s recommendation of 112. What they are trying to say in a nice way is that you need to limit the overlap of the cam to make the EFI happy. Your ZZ502 camshaft is a mild street grind, coming in at 224/234 degrees of duration at 0.050 inch tappet lift, but is ground on 110 centers. This camshaft profile gives you a nice chop at idle, but really has less overlap than the camshaft Edelbrock did its calibration on. The ZZ502 camshaft should have no problem interfacing with the Edelbrock system. Also, the coolant temperature is very critical so you pull from the proper fuel tables in the EFI calibration. Edelbrock clearly states that you must have an engine coolant temp of at least 175 degrees F or the engine controller will constantly run in an enriched warm-up mode. If you’ve been trying to adjust the fuel tables for your possible lean bog, you could be chasing your tail unless the engine is up to operating temp.

We gave Clayton a call on the EFI Tech line at Edelbrock, and he recommended you start by downloading the Quick Start Guide for the Pro-Flo EFI systems. This explains the basic calibration methodology you should use. After discussing your issue, we came to the same conclusion: You may need to add what is referred to as “transient fuel.” Adding fuel to this table is just like adding a larger accelerator pump shot nozzle on a Holley carburetor. Larger-duration camshafts, and large plenum inlet manifolds, require adding transient fuel to prevent bogs. The Pro-Flo XT inlet manifold is as close as you will come to a tunnel-ram design in an EFI format. We believe this is where you are going to find your sag or bog on transition. If you have any other issues Clayton recommended that you call in directly at 800.416.8628.

Adding your Tanks fuel system is nothing but a good thing, as you will have a production-like fuel tank with a controlled reservoir around the pump and pickup. Also, upgrading your system with a wideband O2 sensor will give you much better information for your air/fuel tuning decisions. The production narrow-band O2 gives you little information as it only lets you know when you switch from rich/lean at 14.7:1 AFR. The wideband O2 system is sold under PN 3532.





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