I am looking to, in the near future, swap my 305 TBI to a 350 TBI Vortec with the ultimate goal of getting around 350-380HP. I am wanting to make sure all the gauges, lockup for the transmission, and AC work once the swap is complete. I am unsure what to do about the ECU, though. I have been told that the current stock 305 ECU would work fine because I am swapping to another TBI. I am also being told by a few others that the stock 305 ECU would not work and that I would need to switch it out, but they never told me to what.

I'm also curious if an early 90's P4 ECU would work if a swap is required.

If anyone could help that would be greatly appreciated.

 

It's REAL EEEEZY.

Get yourself a 4-bbl intake manifold for Vortec heads. Edelbrock Performer RPM is probably the best choice. Get a 4-bbl/TBI adapter, make sure it's NOT the one that moves the TBI to some other non-stock location. Get the TB, or at least the injectors, off of a 350 TBI (L05 from a 87-95 truck or Caprice); also the knock sensor, ESC module, and PROM. The 305 stuff will "work", in the sense that it will run and drive; but will cripple the project, and render the 305 -> 350 swap mostly void.

You can keep the 305 ECM or use the 350 TBI one your PROM comes from, I doubt it would make any difference.

None of this affects AC, lockup, or gauges in any manner way shape form or fashion.

Long-term, I'd HIGHLY recommend some tuning. Probably the easiest way to accomplish that in a TBI setup is the EBL.

This all is assuming of course that the L31 you use remains completely stock. You're not gonna make 350 HP with that, let alone 380. 275 might be a reasonable goal, if everything is set up and tuned well, and also of course, if you get rid of THE ENTIRE 305 TBI exhaust, from the heads to the street, and replace it with something that's bigger than a coffee stirrer. I'd suggest the best quality headers you can find that are SPECIFICALLY FOR 82-92 Camaro/Firebird, that is to say, NOT "universal", "block huggers", or ANY of that; preferably stainless, preferably coated; and the cat & cat-back of your choice. I think Dyno Don is still making headers, in which case that's probably about the best choice going.

Once you get to that point, and you get your honest 275ish HP, maybe it'll be time to come back and consider what to do to get to 350 or beyond. It's by no means impossible, in fact over 400 is regularly obtained with those heads; but that will require an appropriate cam and all the supporting hardware PARTICULARLY valve springs, and probably some other induction system besides a stock TBI, like maybe a Holley Terminator or similar. Having a 4-bbl manifold with the 4150 flange will make that easy.

 

I plan on doing headers and a different cam when doing the swap, along with a few other minor changes, to get the 350-380HP. I'm more worried about the ecu with all of these changes than anything. I read another post in here last night that said you need a chip or to swap to a specific 350 ecu, but then I see it's not required even when swapping the engine, cam, etc.

What would be the reason to change the ecu and is it necessary for it to properly run?

 

No need to change the ECU itself, as far as "need". I told you what you need. No need to argue about it.

Now, 350 HP, ... ,,, ... ,, that's a WHOLE OTHER MATTER entirely.

Get your car to run. Learn how it works. Worry about 350 HP LATER. No point in creating a 2575.8 HP lawn ornament and driveway leaf weight, all at once.

 

The 4-BBL to TBI adapter causes flow issues and would raise the TB higher, which means I will have clearance issues and would also need to either alter or replace my current hood.

I'm not arguing either. Not really sure why you think I am, lol. I am already set on the engine swap. I have done research on it and know the main things I need to do to get what I am looking for. I am more concerned about what to do with the ECU in the route I am going. Being I am swapping the cam that comes with the Vortec I assumed the ECU should be swapped, but I don't know much about ECU's to be certain. I am also getting mixed replies on if I do or not the other places I have asked/researched. That is why I came here as I have had good luck in these forums in regards to being pointed in the right direction. What I have been told is that if I do not swap the ECU than I will have injector problems, but I don't know how true that is.

 

An adapter is about ½ - ¾" thick.

Plenty of people have used one without clearance issues.

No flow issues I've ever heard of either. Sounds like Friday night McDonalds parking lot monkey-spank. Seems like you've "been told" alot of crap that's not backed up by reality. Happens alot. Learn to ignore it.

Now of course if you want to go out and buy a TBI Vortec intake that'll outflow the combo I gave you, be my guest.

Not sure about "injector problems". Sounds like that tidbit of fantasy came from the same place that the "flow problem" make-believe did. That's why I told you to get the TB, or at least the injectors, off of a 350, along with the ESC module, a new 350 knock sensor, and the 350 PROM (aka "chip"). Now if you really went wild somehow, not sure how wild you'd have to go to get to this point, you could use injectors off of a 454. I'm not thinking you'll have to, but that option is certainly out there.

Or of course, use something like the Holley Terminator or the FI Tech, on that same intake manifold, without the adapter.

Degree of tuning difficulty, ECM suitability, etc. will depend on cam selection more than anything else. Just sticking a stock 350 truck tune on a motor with anything very much beyond a stock cam isn't going to be very satisfactory. Which is also why I mentioned EBL. Likewise, the cost of running Vortec heads goes up REAL QUICK when certain limits on the cam selection are exceeded. Best way to avoid that is to use LS6 valve springs (or equivalent such as PAC 1218), and the Comp "adapter" retainers for them; and set them up at 1.800" installed height. (stock, for them) That combo will support around .550" of lift in those heads, which will support plenty of cam choices in the range appropriate to a 1st-timer project. Keeping the cam within reasonable limits avoids many problems. Don't get too greedy.

 

Get the Vortec specific TBI intake. Have it bored to accept a bored 46 or 50 mm TBI. Bigger injectors. More spring. Tuning.

 

Yeah, I agree. That is the one I had plans on getting. It isn't much more expensive and it's the correct one for the setup I am going for.

 

I bought a nice bored TBI unit from SPR Performance. You can get them in 46 0r 50mm with adjustable FPR also. I had my stock intake bored to match and ive been pretty impressed with mine.

 

Edlebrock air cleaners, which is what I have and plan on still using, are taller than stock which that in addition to an adapter to make a carb intake work on a TBI means there would be clearance issues. Not to mention the intake you suggest is also taller than stock. It would make more sense to me to pay an extra $150, give or take, to use a proper intake rather than getting one meant for a carb and then adding an adapter.

When it comes to flow issues, I was looking at photos of the intake and adapter and it appears the adapter makes it slightly offset which would disrupt the flow to the runners. I am curious if this is just an issue with certain adapter brands rather than an overall characteristic of all adapters, though.