A Session with David Vizard

by Charley Rockwell
Chapman Report - 1987

Somebody from Lotus West managed to get David Vizard, author of TUNING THE TWIN CAM FORD, to give a talk at the annual Lotus West inauguration banquet in Los Angeles. I have read all of David Vizard's books about modifying car engines so I flew to Los Angeles to hear him. David's work has always impressed me because he actually tests what he recommends. He knows if a certain modification will give you extra power and approximately how much you can expect to get. He does not represent any particular retail outlet or parts manufacturer, so he can be fairly candid about what works.

The following text deals with the main topics of David Vizard's talk with Lotus West.

Q: Are there any differences in brands of gasoline available today?
A: Lots of people are having detonation problems with today's gasoline. Twin Cam's had detonation problems even when 100 octane gas was freely available and things have only gotten worse wince them. I performed a series of tests with the name brand premium gasolines to determine which gasolines provided the best power. I used a 200 HP engine specially designed to maximize any differences in gasoline. I found that the difference between the best and worst premium gasoline was 65 horsepower! Here is how the different brands stacked up:

Best: Exxon, Chevron
Middle: 76, Shell, Mobil
Worst: Arco

Even with the best premium gasoline you may still have problems with detonation, so you will need an octane booster. I found that the ONLY octane boosters worth anything were 104 and Moroso. If you use either of these your engine will tend to build up carbon deposits. You can use a fuel additive called TK-7 that will clean out the carbon and it also makes a good lead substitute.

Q: What are the most cost effective modifications to make to a Lotus-Ford Twin Cam engine?
A: First, you should increase the air inlet area in the stock air cleaner housing. The standard air cleaner housing has two inlet horns and a small drain hole. You really need twice as much area for good breathing. You can expect a 4 hp increase with this simple modification and possibly even more if you substitute a K&N air filter element for the stock paper element.
Second, the Twin Cam likes a cold plug and a hot spark. You can realize a substantial increase in power by substituting a colder plug and installing an Allison electronic ignition to prevent the plug from fouling. I used to make all kinds of money by simply doing a first class ignition tune-up on cars. By the time I was done properly setting advance and dwell, and installing new plugs and points, the owner thought he had a new cam and stage one head!

Q: What can be done to reduce turbocharger lag on a street car?
A: Install a Nitrous oxide injection system. SERIOUSLY!! Besides the increase in horsepower, you get just from the Nitrous Oxide, you will also get an enormous increase in exhaust gasses. In a single Turbocharged Chevy V8, we installed 1lb HP Nitrous system. Formerly, the car took about 2.5 seconds to reach full boost. With the Nitrous, full boost was reached in only half a second. The Nitrous system would shut off as soon as full boost was obtained. A 15 Ib. bottle of Nitrous lasted a full three months with some VERY lead footed driving on my part. I plan to publish a book on Nitrous Oxide systems in the near future. Owners of turbocharged cars should give serious thought to installing a nitrous oxide system, the improvement in performance is rather spectacular compared to the money spent, even considering the cost of replenishing the nitrous bottle. Furthermore, it is fairly simple to get a nitrous system through the California SMOG inspection!

Q: Will water injection effectively prevent detonation with today's lousy gas?
A: Yes! I ran a Mini with 11.5 compression on regular gas with water injection. Spearco makes a unit that will work on Lotus Twin Cams with Stromberg or Weber carburetors.

Q: Will some of the new electronic ignitions retard the advance curve of my ignition system?
A: Yes. If you install an Allison or Pirhana electronic ignition system, then you will probably need to have your advance curve reset because most of these aftermarket systems alter the ignition timing.

Q: Will unleaded gas hurt the valves in my Lotus?
A: Most Lotus-Ford Twin Cams come with either hardened cast iron or hardened alloy steel valve seats. These seats can withstand unleaded gas, though they will last longer with lead. It is really not a problem. If you are going to replace your valve seats anyway, then you might want to install Nickel-Chrome or Stellite seats. Stellite seats could last 200,000 miles with negligible wear.