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

Tom Truty Dec 9, 2010 0 Comment(s)
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Ram Jet Injection
Q: Let me first say I subscribe to automotive magazines based on their technical Q&A. Therefore, I just get one magazine, CHP. Enough flattery. I have a complete Ram Jet 502 injection system, less fuel pump. Is this unit capable of supporting a much more aggressive engine? I currently run a 462 with 10.2:1compression, Brodix Racerite heads, and a hydraulic roller with 236 degrees of duration at 0.050-inch tappet lift. This is a street/strip car that weighs in at 4,300 pounds ('68 Impala), 4,000 stall, and 4.11:1 gears. The car runs 7.26 eighths at 90 mph. Is this injection system going to hurt my performance, or should I stick to my Holley 950? Also, who could help me on injector size and programming the ECM? Thank you for your advice.
Tyler Murdock
Cordova, AL

A: Ram Jet 502 intake manifolds are great for making torque. It just might be the ticket getting your 4,300-pound land yacht moving. However, you gave us just enough information to make us dangerous. What intake manifold are you currently running under the 950 Holley? Is that Holley a 950 4150 square flange carburetor or a Commander 950 TBI? The Commander 950 has a 700-cfm four-barrel throttle body. You can see where we're going with this; please send us as much info on your questions. We can always edit them down. Thanks.

Back to your question. The Ram Jet injection system was originally designed and sold by Arizona Speed and Marine. This EFI injection system has been around for many years. It's offered in both oval- and rectangular-port configurations. The manifold you have is the oval-port design that is installed on the GMPP Ram Jet 502. Those systems come equipped with 38-lb/hr injectors, which support around 520-540 hp. From your eighth-mile e.t., we'd guess that you would run somewhere near 11.30 quarter-mile at around 115-116 mph. To get your 4,300 pounds running this quick, you're currently pushing out around 600 hp out of your 462. To support that kind of horsepower with a little headroom we'd recommend going with 45-lb/hr injectors. That's an impressive number out of a mild 462. The Ram Jet may give you a little more torque than your current system, but we doubt you'll see that type of horsepower for various reasons. First, the runner length, and second the size of the 48mm two-barrel air valve. You could install a larger throttle body to get more air through the system, but the lengths of the runners are going to set the tuning of the intake.

Finally, OBD Diagnostics Inc. has very nice tuning software for all families of the Delco MEFI controllers. OBD offers tuning services and sells both standard- and professional-level software. The standard software gives you the ability to change fuel and spark calibrations, injector sizing, rev limits, and engine displacement.

You have a very nice package right now. The EFI would be trick, and may help in consistency with weather changes. We'd think long and hard before jumping in with both feet. Give OBD a call and get a feel for the calibration challenges. Sources: azspeed-marine.com, mefiburn.com

Missed it!
Q: I was reading your latest tech questions and saw a gentleman asked about some performance issues on his newly rebuilt TPI for his '92 Z28. Your mention of the wrong gaskets on the wrong sides of the TPI could certainly cause a vacuum leak, but he also mentions using a geardrive, which of course is a big no-no on TPIs and other EFI engines. Just thought I'd see if you can get that information to the reader.
Chris Maucere
Jamestown, NC

A: Sometimes we don't see the forest for the trees! You're referring to the noise and harmonics that come from a geardrive system will wreak havoc with the knock sensors and really screw up the spark timing. This could happen anywhere in the rpm band from idle, or throughout the powerband-or everywhere.


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