Stovebolt.com Forums The Shop Area The HiPo Shop Back to the Future - GM TBI

Yes. But you must wrap them in Dynamat to help with the sound.

Dynamat or Dianabol? Some guys I knew in college used to take that to bulk up. Wait...never mind. You said bulkheads. Not bulk up. We'll go with the Dynamat.

The TBI units have the same problems as carb when it comes to fuel distribution between the cylinders. Multi-port injection addresses that issue by having an injector for each cylinder.

The big advantages to TBI systems are (in nor particular order):
-You don't have to change the tuning for environmental effects such as temperature, altitude, etc because the computer manages all of that for you.
-You don't have to worry about floats, needles, etc. Fuel pressure has a much lower effect on a fuel injection system.
-The fuel system is sealed, so you can leave it sitting for months and it will still start right back up without cranking and pumping and fighting with it.
-Closed loop tuning is possible using an O2 sensor.


The GM tbi units are pretty robust. There are a decent number of free tuning tools available for them, but a prom writer is required. There is also a company (I can't think of the name at the moment, will add if I come up with it) that sells tuned chips for different engines. Parts are easy to come up and fairly cheap.

The FiTech units (in my experience, Coilover seems to like them better) tend to have a much larger issue with inconsistent fueling per cylinder. They claim that their annular ring injector head design helps with it, but their design is kind of censored poor. The pressure differential around the ring results in more fuel spraying in from the injector sides. With it coming in sideways, it does not distribute well. If you look at the promo pictures they publish, you can see the uneven fuel distribution. If your intake works with the fuel distribution of the injectors, the autotuning works quite well.

The Holley system has a much more traditional design based on the GM sysem. You can actually use the GM TBI unit with the Holley controls if you are willing to get creative with sensor installation. The tuning has more options than the FiTech units.

Both the FiTech and Holley units can both control your timing, which is a nice bonus. I know the later (late 90s) GM systems had a smart distributor that was controlled by the ECU, but last time I tinkered with on you could only use that feature with a lot of extra hassle.

I have not personally used a megasquirt, but I have looked at them several times and been unimpressed. You have to be careful to get one assembled by someone competent. There are a lot of sketchy sellers that don't use quality parts or assembly practices. They have a limited codespace and tuning options (number/size throttle tables and such). If someone is considering one, I strongly recommend doing some in depth research.

Going with an aftermarket ECU like a Haltech is not cheap, but you can use it with a great many hardware options and the tuning is extremely flexible. It has a lot of options for boost, nitrous, transmission control, etc. I am toying with getting one for my daughter's j**p project.

Might be more info than you really wanted...

Not too much at all, Fibonachu. I was hoping for someone to reply who had fiddled with both the GM and the aftermarket types.

I’ll ask a question out of ignorance. I know just enough about LS swaps to be dangerous. Those who run them with the factory ECU have to have the VATS removed. But that’s more or less all it takes to get one to run. I don’t ~think~ the VATS step would be part of the TBI system.

Let’s pretend someone went and got a GM TBI, harness, and ECU from an early 90s 4.3 V6. Mounted it on a Stovebolt with all the sensors located, wired in, and such. Perhaps with an HEI distributor to supply that input. Would it run at all? Even poorly without a tune? Would the different firing order from the V6 computer totally hose things up?

I have not tried converting a V6 to an I6, so this is speculation:

A 4.3L is ~262CI, so the overall displacement is similar. If I had to make a guess, I think it would run but pretty badly.

The injectors are batch fired, so the cylinder firing order would not matter for them. You could deal with the timing differences/firing order in the distributor (just use a traditional distributor with vacuum advance instead of the computer controlled one).

I expect the fuelling would be an issue with the lower compression and different cam profile. Given the torque/hp curve differences between a V6 and an I6, I also expect there to be enough differences in the details of how they need to he fueled to cause issues. I strongly suspect tuning would be necessary to make it run acceptably, let alone well.

Additionally, by the time you do the machine work etc to install the GM TBI on that engine you would likely have spent more money than a Sniper (Holley) unit costs and be running 30+ year older technology.

If your goal was to keep it all GM and be able to scrounge junkyard spares, that might be worth it to you. If your goal was an economy fuel injection build, that is probably not the best approach.

Howell is the place that sells the conversion kits and they have 261 kit. Reading the description, I am not sure how much customization they are actually doing.

https://howellefi.com/product/hc261-chevrolet-261-cid-tbi-conversion-kit/

I have a friend who put one of the Howell kits on his Jeep Gladiator with the 360. It worked reasonably well. That kit was based on the Chevy 350 TBI system so the original displacement was similar and they were both V8s.

I had seen the Howell stuff in my poking around. They actually sell the complete set for several inline 6’s, including the 261. Like you, I have my doubts in how much custom tuning is done on each. And it’s far from a budget approach.

Wonder if you could buy just the “custom” chip or ECU and source the rest yourself?

If you could, I suspect that it would not be much of a savings. That is the only part unique to them and the kits are a lot more expensive than the sum of the parts.

Couldn't hurt to ask though.

A very lengthy thread from several years back. It appears this bolter got his 235 running with TBI. Trail goes cold before we hear any final tuning results.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/813034/1.html

There's another thread that I started on the subject using the Holley Sniper designed for the Ford 170/200/250.

A member (D B Cooper) responded that he successfully installed it on a 235. It wasn't done for performance enhancement. It was done to end the carburetor/fuel pump problems.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1482871/1.html