Inliners International Forums General Discussion Blown and Injected tbi take boost?

Hello party people!

I'm curious... will a gm tbi take boost? Like 15-20 psi of boost.

I'd like to go efi but cannot afford it at this point. A tbi is much more cost effective and will be an improvement over my ill tuned carb.

Thoughts?

Nobody wants to chime in?
I figured someone would have tried this before.

I think overall that TBI is the better route for injection on the siamese port head compared to EFI, but it still doesn't outshine a good carb setup. So most guys just don't spend time and money doing it. That's probably why there is little or no feedback available.

I started a turbo/TBI project several years ago but have not completed it. The plan was to use an early '80s Firebird draw through turbo set up with a TBI from a '89 GMC 305 on a 292. I got the mechanical part to a mock up stage and built a Megasquirt but got bogged down in the computer side and pretty much lost interest for now. I was going to use big block injectors to supply the extra fuel. I think it would work fine.
292

With the turbo I just bought today, I am going g to start with a draw through setup. Perhaps once money allows I will switch to blow through with intercooler.
I like the reliability of the tbi which is why I was looking to blow through one.
I would use a stock computer and tbi from a 350.
The O2 should richen the mixture fast enough to not lean out during boost. There would be a Meth kit anyway.

I don't think the stock 350 injectors will supply enough fuel under boost that is why I was told to use the BB injectors. The computer from a 90 degree V6 would be a better choice and could run ignition as well as fuel. I think there is a thread here somewhere about using a V6 computer to run injection on an inline.

The 02 sensor would not compensate for boost nearly fast enough, you would want your computer reprogrammed with "boosted" fuel tables that go above atmospheric pressure.

I wonder if Mega Squirt would be a good alternative to the factory style computer.

I plan on using MegaSquirt on mine. It'll be a steep learning curve, but for the cost and the features it really can't be beat. Plus, I like buying things that need to be assembled vs spending extra money I don't have! IIRC, Megasquirt has an onboard 1.5 BAR map sensor for up to 7 lbs of boost. If you need more, put an external 2 or 3 bar and use the onboard for atmospheric pressure measurements. Remember, the higher BAR sensor the more concentrated (less accurate) the signal. You go from reading 20 psi in 0-5 volts to 40 or 60 in 0-5 volts. One of the reasons a MAF is still desired, more accurate air measurements.

A 2-bbl TBI will not supply enough fuel for 15psi of boost. The biggest injectors you can get are 95lb/hr and they will not get you much past 350 HP naturally aspirated, and even less boosted.

Expecting the O2 sensor to automatically correct for boost is no way to tune, but a quick way to melt pistons. There is ZERO chance a stock computer will compensate for the boost and fuel mixture change.

There are on board MAP sensors available for Megasquirt that are 4 bar. All my megasquirts are upgraded to it.

I don't know a single person that did better with a MAF than standard speed density. Usually a MAF is a bottle neck for airflow unless you spend high dollars on one, then it's just a bigger bottle neck. Though I suppose a V8 MAF on a six probably is bigger than it'll ever need...

The last big question is actually one I don't have an answer to and have asked before, how do TBI's internal fuel pressure regulators reference themselves? They operate between 12psi and 20psi depending on the unit you get, and without fuel pressure increasing as boost rises the fuel flow will drop off. I don't know the answer to this one, but on the same token you need a fuel pump that can flow enough under boost and make good pressure from possibly as low as 12psi to as high as 35psi depending on the TBI you have. I've never put a high pressure pump on a TBI, but I "hear" they don't do well with high pressure MPI pumps. Never tried it though.

Fair enough.
I guess it is safe to say scrap that idea.
I would love to do efi, it is just the cost that I cannot afford at this time.

I am going to start with a draw through until I can afford to upgrade. At least that will get me boosted!

You can buy the newer cartridge style of MAF and put it in whatever size tube you'd like. I have this done on my 3.5 inline 5 cylinder. Factory was, IIRC, 2.5" tube and new is 3". When I sent the computer to have the theft removed I had him remap(term?) the MAF for the larger tube.

There is no reason why you cannot bypass the internal TBI FP reg and run an external FP reg that is boost reference - just make sure the pump/lines are rated for 100 psi in case the reg ever sticks closed - fires are not a good thing.