Hello. I want to spend some effort towards a custom EFI for my TBI 1984 vette. I know, that the main limitation is ECM, and even with performant heads/cams it won't give any benefits. I plan to try to run rusEFI on it. There is still big potential in TBI hardware.

I'm gathering information, about potential compatibility and upgrades from another model. Custom new parts are insanely expensive, the budget is limited but junk yards are our everything.
For the custom EFI we need to have TPI with injectors, and throttle body. And it's all available in the latter models.

Are the 1984 TBI and 1985 TPI heads the same? Can TPI 1985 manifold instead of TBI? How hard would it be to backport TPI air filter box under the TBI hood (near the radiator)? I understand, that hoods are different (air intakes)

I couldn't find any mods for vanilla TBI ECM. Is there any experience with tuning/flashing/upgrading ECM?

Sorry, I might be lame in the industry, so please forgive my naiveness =)

 

https://www.xfireperformance.com/
For the ECM you're wanting^^^^^^^.
The heads on an '84 and '85 are the same. To make the TPI air cleaner assembly fit, you would need to change the upper radiator shroud baffle (the part with the jack handle would need to go)👍

 

You can gain a lot of performance just by opening up the intake ports and upping the fuel pressure. Guys used to claim better than tpi performance.

 

Years ago when I built my Crossfire I used a 7747 ECU pulled from a TBI 350 truck. It was easy to program and to burn chips for. I used a zif socket in the ECU so I didn't bend pins. I just used a wire pin out to wire the newer ECU right into the factory harness. It even ran the dash.

But I wouldn't do that swap now. Modern aftermarket ecu's can do anything you want and give way more flexibility. A Mega Squirt would be a budget option. a Holley would cost more but be easier to learn how to program. The nice thing about the aftermarket options is if down the road you decide to swap out to TPI then you already have an ECU that can do it. Whereas the factory stuff would need swapped out.

 

Hood is diffrent on 84 so you wont be able to run a TPI setup with out cutting the hood. for the air cleaner.

I'd suggest a Performer RPM intake and a BBC TBI throttle body setup from a 90's truck with out the water heater base plate.. The 90's truck ECM and aftermarket harness are the go to solution for many EFI upgrades. There are carb manifold to BBC TBI adapter plates. If you go this route you wll need to take a SBC adapter plate and enlarge the holes to the BBC size. This would be a good in-period upgrade for a C4 and you'd have a bit less work on the fuel system since TBI pressures are retained. I recently did one of these setups on an Oldsmobile 403 and with heavly reworked Performer intake (hood clearance) and Mondelo heads and roller cam. Wow, it runs great,

 

I TPI swapped my 84 before I LS swapped it. The TPI fits fine under the 84 hood. I just put a filter right on the throttle body. I used a speed density ECU so I didn't need a MAF. But you are correct if you want a factory TPI airbox then the hood ductwork would need cut.

 

Wow, thanks for the answers and suggestions.

It sounds promising, but I didn't fully get it. Is it a carb intake? Do you add custom TPI injectors then? If we keep TBI injectors, what's the point then? Is it just for performance, while the architecture remains the same? Am I wrong to believe that EFI implies TPI? Anyway, knowing that possibility is great, just want to make sure I understand it correctly.

Are there any other replacements for TBI -> TPI conversion other than ECU, harness, intake, fuel pump, and air filter box.

Thanks a lot

 

Okay I'll try and break this down.

Is it a carb intake?

You could call it that. So a lot of people will use a square or spread bore "carb style" intake manifold for EFI. The Holley Sniper is a great example of this. It uses a large throttle body that bolts to these kind of manifolds. They have two large high pressure injectors inside to allow a performance bolt on EFI option. There are people pushing over 1000 hp on the larger versions of this kind of setup,. On the smaller end this option can be more expensive. But offer a lot of good reliability and convenience. These bolt on and when used with an aftermarket ECU tune easily.

Do you add custom TPI injectors then?

You need to choose injectors based on A LOT of factors. First would be how many you need. A Tuned Port Injection (TPI) would need 8. A throttle body system like the Crossfire injection (CFI) only needs two. The Holley Sniper also only needs two. So you need to choose what style of fuel injection you plan on using first before thinking about injectors. Other factors like performance level, naturally aspirated vs boosted, altitude and fuel type also come into play. There are some very good fuel injector size calculators that will help you here.

Am I wrong to believe that EFI implies TPI?

Yes you are. Electronic fuel injection (EFI) implies just that. Electronically controlled fuel delivery. And the CFI system is in fact EFI.

 

ok. thanks a lot for the clarification, makes much more sense. So, formally it remains TBI, not TPI. but it's still EFI and custom ECUs support the setup. great input!

what are the main theoretical disadvantages of TBI vs TPI other than poor implementation/management? I mean, of course, 8 separate injectors give better precision, but in terms of power (amount of burnt air-fuel mixture per time), there shouldn't be limiting factors.
Is that intake shape? What does "tuned" in TPI exactly mean? Longer path? better mixing?

I appreciate your responses so much!

 

I still research the question of TBIs vs TPIs, manifolds etc. I'm leaning to the TBI setup, and my goal is having about 300-400hp ideally.

Do I understand correctly that if I take intake manifold with BBC TBI, the height will be bigger, so I need to do something with the hood?
I see that BBC TBIs (2bbl, 4bbl) just pour in the center of the intake. But on the 1984 corvette, there is CrossFire (diagonal setup). Is there any point of it? Is there big difference vs a common intake for both banks, or two separate chambers for each bank separately?
Are there big difference between 2bbl and 4bbl?
Are there compatible heads with bigger CFM I can find on junk yards?

Do I understand that the main limitation of TBI is lack of aftermarket options for manifolds, heads, ECUs etc. TPI setup has 10x more options to buy.

Thank you

 

I'd get a vortec 350 long block. Find a vortec tbi intake (they pop up on marketplace once in a while) and a holley tbi unit for an 87-89 truck (marketplace too). Wiring will hook right up. Hood clearance won't be much of an issue with that set up. A few more details to use the vortec engine like oil pan and water pump, but not impossible. Vortec engines have roller cams and great flowing heads.

 

yes, carb intake. Performer RPM is known to fit on a C4 and is well documentated to be a great intake for a great price on a SBC. Proven tech, no guess work, useable power band at a reasonable price. Known good performance + low price = good value.

Simply replace the carb with a BBC throttle body and adapter plate. BBC TBI is the Same height as a SBC throttle body but with a larger bore. I forgot to mention there is a 20$ injector spacer that moves the injectors pod up and out of the way so the TBI's throttle bore and will flow 50 CFM more. Then the adapter plate gives you some flexablity. They come in a few configurations so you can mount the TBI further back if needed. You can also make your own plate out of 1/4 flat alu if needed to get the TBI exactly where you want it.

I also think is would be possible to get the 84 ECM to run the two injectors in the BBC TBI. Not sure about IAC and TPS but I'd give it a try because they look the same. Retainging the 84 ECM would cut the cost in half and could simplify the project and offer similiar performance to the later TBI truck ECM which does have far greater support for tuning though. You 'could' do this wth 'no tuning' initaially, just reuse your 2 Crossfire injectors in the BBC pod and bump the fuel pressure wth a shim in the pressure regulator from 12 to 15 PSI and see if that covers the extra RPM.

Nothng "wrong" with TPI, just in your case TBI is easier becasue less fuel system work. Might get more performance from a hot rod TBI and it might be far easier and lower cost. We all know TPI is all done by 5200 RPM. Performer RPM is good to at least 5500 and with a small performance cam they will make power to 6000.

I never enjoy workign wth after market fuel management. Too many options sometimes one size fits all is one size fits none with a high price. I do enjoy working within the confines of period correct hardware. More options, processing power isn't always the best answer. NASA managed to put a man on the moon with 64k of memory and a 40mips proccesor. A task we have not repeated despite exponetally more compututing power in our pockets. It's about will and focus.

 

I havent quite got my car fully up and running yet, but I did a FiTech TBI on my '84, I can say this, it's a different animal so far! I'm using an Edelbrock Torker II intake with the Go-Street EFI 400HP model. I have a K&N Flat base with a 14x2" filter and it clears the hood. I replaced the fuel pump with one that can handle 340L/h and replaced the rubber lines, clamps, and filter to high pressure. It was a fun project and the car feels really good so far, I managed to keep the ignition timing controlled with the factory ECM. I even have all factory gauges working with the most likely exception of fuel mileage (it's still putting out numbers, I don't think I can really trust them), even the check engine light goes off with ignition. You can check it out HERE

 

would vortec 350 heads fit to the stock vette block? I suspect they might have different timing housing or so. I know, that vortec has different bolt pattern for intakes, but I'm asking about heads to blocks. also, I guess I need to adapt headers too, since they are incompatible.

wow, that's cool. thanks for sharing

 

I really inspired by Ravendagrey's report about 1984 TBI. Especially I loved how stock air filter and cover remains. so, after plenty time spent on my options, I stopped with Performer Intake 2101 for my heads + adapter BBC TBI. The intake works from idle to 5500, that's range of my engine. I'd prefer low rpm torque rather high RPM. Plus my internals are total stock, so I guess 5k is the redline.
No need to change to Vortec since it's another level of upgrade. Next step would be manual porting my stock heads to gain another 30% CFM.

The rest I hope I could tune by custom ECU. rusEFI is an open source solution, and I already flashed a board to play around, and it looks promising.

Found the intake, still need to find BBC TBI for that.

Do you think that stock hood and cover could remain? At least stock hood, but I prefer the cover because it has matching air inlets


Are there specific models to lookup? Are those C/K 1500 trucks or you mean big industrial trucks? How do I know that there is no water heater base plate? Am I looking for 350 block or something bigger (considering custom EFI and that I can control the fuel delivery)?

Thank you

EDITED: Ok, I got it. TBI for 454 7.4L truck is 52mm bore. Found on eBay for $50 + delivery in unknown state. I'm excited!

 

I'm a little confused on what exactly you are trying to do? Are you keeping the CFI OR moving on to a single TBI system with the rusEFI? If you are keeping the CFI system, the EBL is hands down the best way to go and is much more user friendly IMO when used in conjunction with TunerPro RT as the editor which is free. The EBL is 100% laptop tunable and comes with a good stock tune to mod if you are going to be modding the motor with other things like heads, cam, exhaust etc... GL whichever way you go. .

 

So I'm switching to a single TBI system with two injectors because it gives freedom of custom manifolds. The stock CFI manifold is pretty inefficient. and throttle body bores are smaller. I ended up with 52mm TBI from 454 engine (7.4L).

rusEFI is generally the same role as EBL but gives freedom of hardware customization. I could backport newer WB O2 sensor, knock sensors, install CKP sensor, etc. In the worst case, I can modify the software to support my custom setup
Id say that my goal is more having fun process rather focusing on the specific results.

 

Interesting. I followed the link you posted to Ravendagrey
That was a nice job he did there with the FITech.

I'll be following your adventure.

 

Just to keep the thread updated. I'm slowly preparing for the custom ECU and high HP out of stock TBI with minimal efforts ($, not time).

I've bought 2" TBI from 454 engine for $70, rebuild kit for $50, TPS and IAC for about $70 and OG board with card edge for about $30 to build my custom ECU setup.



The bores are actually huge


It has the card edge that must fit the stock ECU harness connectors (just need to cut the gaps)

The TBI injectors are low Z. If you connect them directly, they consume too much power. I connected my PSU 12V 5A, and they consumed 40W at 7V (PSU can't give more). They definitely need to have some driver. I ordered LM1949 and necessary aux elements from Aliexpress, going to build a pick&hold drivers for those.

I have rusEFI installed on the STM32F407 discovery board. Going to go that way, using the given breadboard, and pre-built PCBs (like 3.3v to 5v adjusters). Will test everything before I'll build own PCB.

I bought Performer dual plane Intake 2101. I didn't take RPM because I don't expect higher RPM (need to change springs, internals etc), so I target torque on lows.
I see that people sell 3D printed adapters on ebay, so I'm going to 3D print my custom adapter using composite material ($45 per kg). One of the requirements is to keep the stock air filter, CFI cover and stock hood. I don't know how height gap I'll have, but with 3D printer I can make the correspondent spacer. Once I took off the stock CFI and manifold, I'll know the height difference

P.S. Also, I finished my front suspension (new bushings and new brake pads), report is here: https://www.corvetteforum.com/forums...ed-photos.html

Total spent so far: ~$400

 

You probably going to need one of these throttle arms to hook up a tv cable and cruise control. Easily enough to grind down the welds, I found my stock cables were long enough.