TBI FAQ

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 first TBI conversion was 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. From what I've seen the average TR6 dynos with rear wheel horsepower of 60 to 75! 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.

UPDATE August 2006: Here we are two years later and 6,000 miles without a hitch!

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!

Dependabilty?

Absolutely! Tune ups are far and few between. Maintenance consists of changing filters, spark plugs, and a occasional gulp of fuel injection cleaner in the gas tank. Basic fuel injection components often go for 100K miles or more without adjustment or failure.

Can I use my Pertronix or Crane ignition system?

Yes

Can I reprogram it myself?

The short answer is yes, however AFI does not supply components or support for do-it-yourself tuning. If you wish to do your own programming there is a lot of support on the web from sites like tunercat.com. In fact, very very few people go this route as the professional tuning from AFI is so good.

Your system will arrive preprogrammed and the experts at Affordable Fuel Injection will help fine tune it to your car and your driving style. The kit price includes their support and up to three tuning chips. I would be surprised if it took more than one try to hit the mark for optimum performance. Should you at some point make significant changes to your car and have used up the three included chips, AFI will still work with you however there will be a charge for their efforts.

What if I have a modified engine?

The present system is running a stock or mildly modified engine. Affordable Fuel Injection can tailor the software at no extra charge up to four times for most any modified engine.

Where does the ECM computer mount?

Originally we mounted it on the right side withing the passenger footwell, and that's still my favorite location. The ECM has been mounted at the very far reaches of the passenger footwell under a panel, under a seat , or even in the trunk. The harness is long enough to mount the ECM nearly anywhere but the trunk will be a tight stretch.

Can I buy components to build my own system?

TBI conversion adapters and TPS kits are available separately for use with your own engine management system. Some folks are experimenting with low cost Megasquirt.

What type of hose is in the kit?

TBI systems such as this run relatively low pressures. The pump has the ability to put out a maximum of 30psi however the regulator bypasses all but 12psi, making the maximum pressure in the system 12psi so special purpose high pressure fuel line is not required. The fuel line in these kits, although marked "Not for fuel injection", is rated at 50psi, four times the operating pressure.

Can a triple ZS carb setup be converted to TBI?

Not with the system at present but we are working on it so "stay tuned" (Oct 07).

What about datalogging?

Yes this system has the ability to datalog. A laptop is used to record all the engine sensor readings as well as fuel and ignition timing while driving down the road. Tuning your system amounts to connecting a laptop using the ALDL cable and taking a fifteen to twenty minute drive in varied conditions. The resulting datalog file is emailed to AFI and a new profile is programmed into a chip sent to you for installation.

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 is 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.

Can I convert my TR4A or dual carbed MGB?

The parts will fit the carbs nicely however the rub is that the firing order and manifold layout would deliver an uneven fuel mix if trying to use the GM ECM. Sorry to say that at present the GM TBI computer is not compatible with most dual carbed British 4 cylinder engines. We are working on this issue and expect to resolve it soon. Presently it will work perfectly on the same engines when using a single carb. Stay tuned- this may soon change! (Oct 07)

Can it be installed in stages?

Yes you can still drive the car while much of the conversion work is done. Things that can be done ahead of time; coolant temp sensor, throttle position sensor, fuel lines, ECM mounting and harness, ignition conversion.

What type of injector is used?

The adapters are designed to use standard GM throttle body injectors from late 80's and 90's cars and trucks. We use the later style GM mini TBI injector because the smaller and fits better in some applications such as the SU HS6 carb.

What is BLM?

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

Elimination of IAC:

For those of you who have been following this project all along, the idle air control circuit has been eliminated. Fast idle is controlled by the original choke high idle cam. The short version is simply that at very low idle, the IAC was supplying intake air as it should but not picking up enough fuel at the throttle plates. By using the existing choke you can control high idle in order to warm up the engine. The car will start and idle just fine without the IAC, even if the engine is cold and the outside temperatures are very cold.

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 in the TR6 kit?

The Kit actually comes from two sources, sidedrafttbi.com and Affordable fuel injection.jpm. Included is the hardware unique to convert the ZS carbs or SU carbs to fuel injection. It consists of two TBI adapters, a throttle position sensor bracket, actuator, and bypass block off plates, a "plug and play" wiring harness, hose, filter, relays. ECM preprogrammed for your type of car, fuel pump, regulator, sensors, injectors, regulator, and incredibly important- programming and technical support. There may be a few minor hardware type items that will need to be sourced locally depening on how you layout your system.

Can the process be reversed?

Sure. Converting the carbs back to carbureted use takes only about fifteen minutes especially 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 (it may be possible to use it with a "blow thru" type SU on a carb) but again stay tuned.

Can it be installed without altering the carb domes?

Sure, but the conversion will be obvious. Actually I think that it's cool to see something different under the hood. Optional cover plates.

Smog legal?

No. Although it is very likely that a converted car will easily meet your state's smog emission requirements there is no guaranty. In most cases it will run far more efficiently than as a carbed engine hence less emissions. But for legal reasons I must state "for off road and racing use only".

How long does it take to install?

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

Does the return line connect to the gas tank?

Yes, we have tried recirculating the fuel back to the pump but it heats up so it must be returned to the tank. The tank connection varies from car to car and year to year so you will need to look over your tank connections. Sometimes it can be connected to a vent line and at other times a fitting can be added to the sender for the return. Because of these variations you will need to determine how to connect to the tank. We can help with some applications and can modify or supply fittings for return via the sender at a small additional cost.

Availability?

Now.

Do I need a swirl pot?

In case this is a new term to you, a swirl pot is a small reserve tank that supplies fuel to the fuel pump during hard cornering. The stock TR6 fuel tank is not baffled so during a long hard left turn at low fuel levels the pump may starve for fuel. Not really necessary unless you are a very serious autocrosser or run on fumes all the time. A swirl pot can be be added just below the tank and a vent line run back up to the top of the fuel tank. Homemade pots are sometimes made from aluminum air conditioning filter/driers.

What size hose off the manifold is needed for the connection with the map sensor?

1/4" hose barb and keep it as short as possible. Under 10" of hose is best.

Will your TPS driver fit up ok with the round shaft end on the SU Carb?

Yes the SU driver is designed to fit the round shaft.

My carbs are old and in need of rebuilding. How sensitive is your TBI solution to minor leaks in the throttle shaft seals?

Minor leaks are no problem, they just supply a little extra idle air. Carbs work by air passing over a venturi to pick up fuel but in TBI applications fuel is squirted into the throat not caring much where the air comes from. Should be no problem unless the leak is quite severe making it idle fast.

I assume that the mount holes on your HS6 adaptor plate will matchup to the three bolt pattern on the HD6 carbs?

No problem. The HS6 adapter is round and held in place by three screws unless you modify the dome to hide / hold it down.

What purpose do the carbs have after this installation other then to house the injectors?

ANS: They are simply "Air doors" used to meter air into the engine and house the injectors.

Do the bowls still fill with fuel that's regulated by the floats shutting off the needle valve? Or is none of that necessary with TBI?

ANS: Nope- no fuel is in the carb float bowls. The troublesome floats and needle valves are not used.

What modifications are made to the SU carb dome? Is there a hole/slot needed to run the wires?

Ans: The domes are only ornamental with TBI. The system operates just fine without them however if you want to hide the conversion, modified domes can be refitted. To modify the dome, the guide tube for the piston is cut off even with the underside of the dome and in most cases the top post needs to shortened about 1/2". Once modified the domes can no longer be retuned to carb duty. The wires run out thru a slot milled into the adapters.

Besides the Oxygen sensor welding, what other modifications are needed e.g. you show the throttle position unit attached to the existing carb linkage. Is that just a snap on or bolt on using existing mounting points? I like to know all of the modifications up front as what's easy for you may be difficult for me.

ANS: The TPS just bolts onto the side of the carb using the carb mounting nuts. Other than replacing the throttle shaft nut with a special driver nothing is else modified. Just like unbolting the carbs, it is an easier job for folks with tiny little fingers. Installing the TPS can be done well ahead of the actual changeover as it does not affect the carb operation.

In the video, the return line looked like it connected to the fuel line between the filter and the pump. Is that correct or does it go directly back into the tank?

Ans: The video was made to show a vender around the prototype (Aaron's car) and really wasn't meant for public viewing but it does show the basic set up so we are still using it. We were trying a short cut with the return line and found that it needs to go back to the tank because of fuel heating. Recirculating that same pint of fuel over and over, heated it up so much you could hardly put your hand on the lines! Nope it has to go to the tank.

What wiring modifications are needed?

Ans: The harness is plug and play with teh exception of the battery connection The original TR6 harness is unchanged.

More questions?

I'd be happy to answer your questions. Just contact me at: rick@pattonmachine.com