Bill Guzman demonstrates the vacuum gauge engine tuning technique to Paul Schils
Bill Guzman demonstrates his vacuum-gauge engine-tuning techniques to Paul Schils

British V8 2006 Tech Session:   MGB V6 Engine Conversions

as published in British V8 Newsletter, Volume XIV Issue 2, August 2006

presented by: Bill Guzman of Classic Conversions Engineering
coverage by: Curtis Jacobson

The theme of Bill Guzman's tech session at British V8 2006 was: "Keep it simple!" All too many people who start engine conversion projects never complete them. If one allows their project to grow complex, it will also grow in time and monetary investment required. I think he really struck a chord by essentially stating that none of us likes to see an abandoned project car or a hack-job. If there's one piece of advice we should share with newbies it's "Keep it simple." Bill's company, Classic Conversions Engineering, provides kit parts that simplify performance modification of MGB sports cars. Bill's products span the functional areas of the car: engine conversions, brakes, traction/suspension, even aerodynamics. So despite its title, Bill's tech session covered a lot of ground and offered new wisdom even to though of us who've completed and are driving project cars.

Although it took awhile for Bill to get to the core subject, I'm going to start there.

Bill strongly recommends the GM sixty-degree V6 engines for MGB sports cars. This family of engines, he explained, has appeared in many different cars including both front wheel and rear wheel drive models. They were used in 1985 to 1995 Camaros and Firebirds, the Chevy Celebrity and Citation (including the X11 variant that produced 155hp), and some S10 pickup trucks (although 90 degree V6s were also used in that model.) The sixty-degree V6 is available in different displacements and states of tune. (The '93 to '95 Camaro had the L32 3.4L with sequential port fuel injection and distributorless ignition in a RWD configuration, but) Bill's all-round favorite is the crate-motor 3.4L V6 which can be purchased new with a factory warranty starting at about $1800.

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Classic Conversions offers various engine installation kits. The most basic contain motor and tranny mounts, plus headers. They also offer different pulley systems, intake manifolds, etc. Bill likes carburetors, but can also help his customers set up fuel injection systems.

Speaking of carburetors, Bill branched off to talk about engine tuning. When people have problems cooling their newly engine-converted MGB's, the first thing they should check is the engine tuning. From Bill's experience, it's most likely that the engine in question is running lean. "Nothing cools like fuel." Rough or large scale adjustment is done by changing jets... and the classic tried-and-true approach is to shut down the engine fast, pull a plug, and check the color of combustion deposits. This will at least get you within a jet size or two, after which performance testing will get you narrowed down to the correct jet. Once the jets are right, the next step is to adjust the idle air mixture.

Bill then reviewed the classical technique for dialing in ignition advance and idle air mixture, as follows: Connect a vacuum gauge to the "direct vacuum" port on your intake manifold, disconnect your vacuum advance and plug the carburetor's vacuum-advance orifice, start the engine, let it get to running temperature, loosen the distributor clamp, rotate the distributor to advance the ignition timing until you get the highest vacuum reading you can at IDLE, then retard the timing until it reads 1" (of mercury, which is the normal unit of measurement shown on the face of an automotive vacuum gauge) less vacuum to avoid pre-ignition (aka "pinging"), then tighten the distributor clamp and re-connect the vacuum advance. Proceed to adjusting the carburetor.

Use the same vacuum gauge to adjust the carb, simply turning the idle air mixture screws until you get the highest vacuum reading you can. Drive the car. After a few miles, recheck as follows: bring the engine up to 2000 rpm and while at this rpm (with vacuum advance connected), loosen the distributor and rotate to advance the ignition timing a little bit further until you get the highest vacuum and the engine revs itself up a couple hundred RPM. (Maybe it will settle in the original speed, or maybe you will pick up a couple of hundred RPM...)

Another topic Bill discussed was dyno testing. Bill gave us a word of caution: it's hard to compare dyno results that come from two different dyno operators. Dyno operators like to have happy customers, so they very often allow test parameters to be a little "optimistic". Bill has particularly noted that where and how the operator places their temperature sensor on the top of the intake manifold can skew results. Some dyno operators will fudge numbers by entering the wrong bore and/or stroke parameters into the computer program that generates the results report. Seemingly small changes in these areas can significantly change calculated performance curves.

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On the topic of getting power to the pavement, Bill provided a hand-out for a great afternoon project: making simple traction bars from old, discarded leaf springs. Bill's concern is that solid traction bars that are used to control leaf spring wind-up (and thereby reduce tramp) produce unintended and undesirable consequences on street driven cars, including especially roll oversteer. Bill's testing reveals that solid traction bars aren't always as helpful on the dragstrip as people assume either. Bill feels that spring energy can actually help launch a car from the line, and that solid traction bars weaken the launch on cars with less than, say, 400lbs of torque.

Click here for Bill's "Easy Traction" instructions.

Disclaimer: This page was researched and written by Curtis Jacobson. Views expressed are those of the author, and are provided without warrantee or guarantee. Apply at your own risk.

Photos by Curtis Jacobson. All rights reserved.

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