Have any of you guys ever attempted to blow boost though a throttle body based injection system, like a Holley sniper or somesuch? I'm concerned that the batch firing system will make it hard to tune and possibly lead to fuel pooling in the intake but it seems like few people have done this.
In reply to GIRTHQUAKE :
Fitech supports this. I believe that you would be looking at the "Power Adder" models. https://fitechefi.com/products/30004/
I have the Fitech and would not advocate for buying from them. Not that the product does not work ( eventually), just that, as a small company, the support infrastructure and QC from Fitech can not hope to match Holley.
Would I buy another TBI from either? Maybe, because I am invested in the learning curve at this point. Would I suggest that someone else buy either brand? Not really, because it is a huge learning curve and most people are not looking for an EFI education. The products are way oversold as an Easy Button.
Pete
I wonder if you'd have to get the shaft seals done like on a blow-thru carb setup?
Looks like the FAST setup did it years ago: https://www.youtube.com/watch?v=VI9RPnv71R4
We're running the Holley Sniper 4500 on the CAM-T Falcon Wagon. The build thread needs a little updating, so a lot of details aren't in it, like the new engine. Nonetheless, the system works great. It self-tuned very well and then we touched it up on the chassis dyno. We're using it to control both spark and fuel. I'll probably write a story or two about engine build and EFI tuning for GRM.
Depends on the TBI. Old oem tbis ran on such low fuel pressure that you would have to do a boost-referenced fuel pressure regulator, otherwise adding 7lbs of boost would cut your injector flow in half. Newer aftermarket systems that run on higher pressures may be able to tune around it without indexing fuel pressure to boost, like modern cars do. You'd have to find out for each system you were considering.
If at all possible, port injection.
We made a multi-tbi unit manifold for a 454 by using two stock ones. Ran out of fuel at a miserable 12psi.
Paul_VR6 said:If at all possible, port injection.
We made a multi-tbi unit manifold for a 454 by using two stock ones. Ran out of fuel at a miserable 12psi.
Lol, how much power does a 454 make at 12 psi with a decently sized turbo?
Anywhere from 500-1200 hp depending on how miserably stock it is. 
GM tbi injectors have a fairly low fuel pressure ceiling before they just lock shut and stop flowing anything, from what i remember reading. Considering that, way closer to 500 than 1200!
This is something that will "get 'er done" but fuel distribution is not as good as with port injection. And it's likely that just how bad the fuel distribution will be is going to depend on the mainfold and even the ducting arrangement above the TBI, so keep a close eye on your spark plugs (or better yet, run eight thermocouples... but that would kind of wipe out the savings of the TBI). There's a reason the Mitsubishi Starion was the only factory blow-through TBI car sold in the USA that I'm aware of.
MadScientistMatt said:This is something that will "get 'er done" but fuel distribution is not as good as with port injection. And it's likely that just how bad the fuel distribution will be is going to depend on the mainfold and even the ducting arrangement above the TBI, so keep a close eye on your spark plugs (or better yet, run eight thermocouples... but that would kind of wipe out the savings of the TBI). There's a reason the Mitsubishi Starion was the only factory blow-through TBI car sold in the USA that I'm aware of.
The G32B-T in the MIrage Turbo was also a blow-thru TBI setup. I had one, weird little car.
Vigo said:Anywhere from 500-1200 hp depending on how miserably stock it is.
Not enough, it was installed on a truck that needed to make WAY more power. We were better off turning down the base fuel pressure way far due to that exact issue.
slefain said:The G32B-T in the MIrage Turbo was also a blow-thru TBI setup. I had one, weird little car.
I should have known that if there were any other factory blow through TBI setups, they'd be lesser known Mitsubishi products. 
Tons of people have gone insanely fast on blow-through carb setups and on staged injector setups where you have multiple sets of injectors coming on at different points. That knowledge applies to Starions. The problem is that the people who worked on starions were not the same people capable of building those 1000hp 8 second cars that were blow through setups or had staged injection. I think the starion's issues surviving enthusiast ownership were more related to being able to diagnose a system you didn't understand than related to the limitations of its fuel distribution.
Even further down that rabbit hole are setups running 50+ psi of boost with no intercooler. They're dumping a huge percentage of their fuel in upstream of the turbocharger, but because they're running such high boost levels (charge temps might be close to 500f if there were no fuel) the fuel is totally vaporizing in the charge pipes and once it's fully vaporized the distribution issues are much less. If those setups injected all of their fuel at the throttle plate it may not have time to fully evaporate before leaving the plenum which would lead to greater distribution issues and higher charge temps entering the cylinder which, in spite of there being the exact same total heat energy in the cylinder, would be more likely to encounter detonation even if distribution was perfect!
So, i guess you could say a technology is only good if it matches up with your personal ability to understand, implement and diagnose it. By that standard a Starion TBI is not a good setup for a lot of people. It is simpler than port injection in parts count but how it works is less commonly understood so the likelihood of someone not being able to make it work properly and breaking their pistons is higher for that reason while somewhere else some other guy is using the same technology to trap 170mph in a 1/4 mile.
"The products are way oversold as an Easy Button." <<<< understatement of the year
There is a reason none of the OEMs offer a TBI any longer, TBI is only marginally better than a carb.
I will echo Matt's post about port injection being an order of magnitude better. I personally would not consider using TBI.
There is also another consideration that most TBI injectors will not be large enough for Boost. And also the capacity of an injector decreases as the pressure differential increases. In other words the injectors get smaller as boost increases. On a port injected setup this is balanced by applying boost to the fuel pressure regulator so fuel pressure rises with boost and maintains a uniform pressure differential.
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