This page contains some of the common questions I have been asked about converting a side draft Zenith Stromberg carbed engine to Throttle Body Fuel Injection.

What about performance?

The TBI conversion has been done to a stock 1971 Triumph TR6. Driving impressions are excellent with much improved driveability and a noticable performance gain. Actual horsepower gain is not really known at this time although testing with a G-Tech accelerometer showed delivered (rear wheel) horsepower of ninety seven. There have only been a handful of G-Tech runs made and this is the best of the bunch so these figures may not be accurate. Considering drivetrain inefficiencies of 20% a reasonable flywheel figure is 121BHP. Originally the carbureted car was rated at 106BHP.

Fuel economy?

So far fuel economy has been great! On a 200 mile trip with a combination of mostly rural and about 15 miles of highway driving Aaron got 29.8 miles per gallon. I’m sure city figures will be lower. Update November 2004: Mileage figures around town are in the 27.1mpg area! Up from 18!

Can I use my Pertronix or Crane ignition system?

Not really as the computer (ECM) is looking for timing pulses from the original distributor that has been converted to electronic ignition. The GM ignition module works beautifully, is inexpensive, and will work with the ECM to control spark advance. This module also has a built in “limp home mode”.

Can I reprogram it myself?

Yes CustomEFIS offers a Flash programmer for an additional $100. Both fuel and ignition are fully programable

What if I have a modified engine?

The present system is designed for a stock engine. CustomEFIS can tailor the software for most any modified engine or you can purchase equipment from them to create your own profiles.

Can a triple ZS carb setup be converted to TBI?

Not with the system at present however CustomEFIS belives it may be possible.

What about datalogging?

Yes this system has the ability to datalog. A laptop can be used to record all the engine sensor readings as well as fuel and ignition timing while driving down the road. While tuning Aaron’s car we would take 15 to 20 minute trips with a variety of conditions and driving styles, the resulting datalog was then emailed to CustomEFIS and an updated profile promptly returned that could be reprogrammed in with the Flash programmer. It only took four datalogs for CustomEFIS to perfect the profile.

Are parts available?

Yes. Parts are mostly common GM items that your local parts store will carry. Because the parts are used in so many cars, the price is correspondingly low.

I am not a mechanic, can I do it myself?

Yes. There will be a very good set of instructions with many photos. If you are somewhat mechanically inclined or have a buddy willing to lend a hand it goes quickly and easily.

What type of injector is used?

The adapters are designed to use standard GM throttle body injectors from 80’s cars and trucks. A good choice for the TR6 is injectors from a 2.8 or 3.1 V6 engine, GM 5235130.

What is BLM?

BLM stands for Block Learning Mode. This GM ECM has the ability to learn about how you drive and adjust accordingly.

Special Tools?

Not really but a bung needs to be welded to the exhaust header for the O2 sensor. If you can’t do this any muffler shop or neighborhood garage can do it very reasonably. Beyond that a few common hand tools, a hole saw, a 3/8″ pipe tap, and a voltmeter are all that’s needed.

What is the cost of the kit?

February 2005. Coordination of efforts between CustomEFIS and myself has been worked out. A complete bolt on kit would be about $1300. The optional Flash programmer will add another $100.

What is in the kit?

The “Kit” actually comes from two sources. My portion is the actual hardware unique to convert the ZS carbs and the TR6 to fuel injection. It consists of two TBI adapters, a throttle position sensor bracket, lever, throttle position sensor, a mounting plate for the GM ignition module, and bypass block off plates. This portion is $500. The CustomEFIS kit contains a “plug and play” wiring harness, ECM modified for Flash programming, fuel punp, regulator, sensors, and incredibly important- programming support. The profile currently running Aaron’s car is just about as good as it gets. At this time, the CustomEFIS kit is $800. Additionally they offer a Flash programmer for $100.

Can the process be reversed?

Sure. Converting the carbs back to carbureted use takes only about fifteen minutes if you leave your old fuel pump and lines in place. Just remove the TBI adapters from the carbs, drop in the pistons, and put the domes back on. Switch the fuel source back to the mechanical pump and you are right back to a carbed engine. The only caveat is that if you wanted to mask the TBI installation, modification to the original carb dome is required and that precludes it’s return to carb use. A spare set of domes is readily available if needed. Of course I can’t imagine you ever converting back anyway.

Supercharger? Turbo?

No. This TBI setup is not presently compatible with a supercharger or a turbo.

How long does it take to install?

Installation can easily be done in a weekend. Half that once you have experience.


Now. I can’t speak for CustomEFIS but expect the electronics, harness, etc are available right now.

Can I buy components to build my own system?

TBI conversion adapters will be available separately for use with your own engine management system.

More questions?

I’d be happy to answer your questions. Just contact me on the Contact Us page.


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Rick Patton
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