Well I'm considering going with a rebuilt 350TBI engine to replace my current 305TBI setup. I have headers and full exhaust, along with the open element mod.

The main thing I'm wondering is what differences there would be between these engines besides C.I. Will I just be able to take the old one out, and put the new one in and reconnect everything or will there be problems with the computer?

The setup I'm looking at makes about 300HP/350TQ (I'll be getting a new tranny) and the company will make a custom PROM for me. Also, the new engine will have a better TB unit as well as better injectors. Will I run into any issues? New fuel pump?

 

I dont think you would have to replace the fuel pump unless you have experienced problems with it, i didnt replace mine and i put a 350 in to replace the 305 5 years ago. i had some slight problems with the computer but bought the stuff to program my own chips, but if the company that is doing your motor will program a chip for you than you shouldnt have to worry about it. Everything will bolt right up and connect the same. One thing with the chip, i would check and see if they are going to just pop in a 350 chip, or are they going to tune it for you, (datalogging, and burning a chip, datalogging, burning a chip) going over that process until the engine runs really well. Because if they just pop in a 350 chip, you engine still might not run right, it might need tuned, mine did a little, about $130 of equipment and a few evenings of driving and chip burning got me a good setup. Let us know what you come up with.

Moderators: While im on this subject i was thinking about disecting the "come in for a free tune" thread and making a step by step guide for the beginners on how to get started and burning chips, everything from what equipment and where to get it, to little tips and tricks that i learned but not neccessarily posted in that thread, let me know what you guys think, i think it could help out alot of these guys that need to get into tuning.

 

Okay then I guess as far as hardware is concerned I should be good to go. As far as the computer is concerned, it might just be a "pop in 350 chip." They make TBI engines for all of the vehicles that had them stock, so they might have a custom chip for each type (Fbody, Pickup, etc). Since it comes with it free I would probably just use it, but I'd like to know more about tuning myself like you did. What is needed and involved in that?

Also, did you do the 305-350 swap yourself? I've worked on my car and done basic things: oil change, replace fuel filter, put on headers, open element mod, swaped out rear end. Would this be something I could do in a few days, or are there a bunch of wires and hoses that take a long time to work. THe main thing I'd be worried about is the wiring and fabrication, since I dont really have a shop, just a nice tool set and a garage.

 

the main difference mechanically from the 305tbi and the 350tbi is the injector size(305=55lb/hr 350=61-68lb/hr, I believe) and the knock sensor, if I remember correctly.

you'll need the 350 chip or something tuned similarly to it for the engine to run properly BECUASE of these two things.

if you're getting a rebuilt 350tbi fully loaded, there's nothing to worry about(that I can think of) except getting the chip to work, but if you're transferring the fuel injection from your 305 to the 350, you could run into issues.

this is of course assuming that the 350 is a stock rebuild, and the difference in the 350's fuel injector sizes also has to do with which version of the stock 350 tbi you have.

 

Unless you're just set on fixing up the 305, I say go for the 350 hands down, if that is what you want and it's something you can afford. The swap is pretty straight forward as long as they give you everything and aren't trying to reuse things like the injectors, etc. as others have mentioned. Since you say the chip does come with the swap for free, just use it temporarily while you research burning your own chips. Just check out the PROM section here.

I would recommend changing the fuel pump while you're doing this also, that way you can do it properly the first time. They say the stock LO3 fuel pump can barely feed a modded 305. A nice choice is one you can order directly from the dealer, it is the stock fuel pump out of the Typhoon and Syclone (turbo'd Jimmy & Sonoma). Since it is a high flowing pump you can audibly hear it whining while the car is on, especially around 1/4 tank & lower. Don't be freaked out, most high flowing fuel pumps are known to make noise.

 

the stock tbi fuel pump goes up to i believe 18psi, the stock setting being between 9-13 on both 305's and 350's(as i said, the difference was in the injectors), the stock pump will get you somewhere in the 300-340 range(depending on what injectors you have) and run out of juice.

but, it also happens to be 15+ years old, so ya, you're probably gonna wanna change the pump, but only if you modify the engine past that point.

if you're simply replacing the motor, then there's no reason at all to do so.

 

Well the engine I'm looking at is a complete, rebuilt 350. It has everything from the oil pan to a new bored out TBI unit. I don't believe it comes with new injectors so I would get a new set of those (are they adjustable, or is that done with a fuel pressure regulator?). I would also replace the fuel pump just to have that done anyway. Would a Walbro 255 work? Those are all over ebay and online for about $99...

What's involved with the knock sensor? WOuld I just be able to get a new one at Autozone/Napa? Would it work with my 305 wiring?

 

who's boring out the tbi unit? the fuel pressure is controlled by a regulator stock, but if someone is boring out the tbi, you could have them set it up to be adjustable.

as for the knock sensor, if it's a full engine the one you need will be in the block already, so no need to worry about that.

a walbro 255 would be overkill, actually. you'd never use it to it's full potential, even with a 350. but that doesn't mean you shouldn't get it. the regulator will keep you from feeding too much fuel to the engine, so you could either get the 255, 190, or your average tpi fuel pump, they would all work.

 

what company online sells 350 tbi's for this setup?

 

Read again

 

I guess I should clarify.

with a 68lb/hr set of injectors at say, 11psi, you're at a stock ~230 range(61 @ 210) I believe(they only used 68's on cop cars), with the same stock tbi pump as the 305's(which use 55lb/hr injectors at say...11 psi), you could push the psi another 5-7 psi and pull around 300hp out of the 350, wheras you would only be able to make 225-250 in the 305, due to it's smaller injectors.

that is, assuming, that the stock pump is still in good shape.

I refuse to say that it's inadequate from the factory, though. while it would've made far more sense to throw the tpi pumps in the tbi setups and save us all some time, they didn't, and what they left us with was STILL plenty for our stock motors, even left us a little space for some modification. certainly not inadiquate from the factory.

 

If you search on eBay you can find a some rebuilt TBI engines and other parts. Just put in "TBI" or "TBI engine" in the search field. There are some shops selling 350's that make 300HP/370TQ. As far as if they really do make those numbers, I'm not sure.


Back on topic though, a Walbro 190lph would be sufficient then? And if the knock sensor is already there, is there anything else I need to prepare for or worry about?

I might just have a shop rip out my 305 and put in the 350, even if it costs $500-$1000. It'd be a stretch to do it all myself since I just have a garage and not a shop. Still I'd like to know if there is anything else I need to take into consideration as far as neccessary parts go. I wouldn't want a shop charging me $299 for OEM 350injectors when I can get some for about $99......

 

buy anything that the engine doesn't come with...if you're getting the tbi seperate from the engine, make sure that it comes with 350 injectors, if not, buy some.

does the 350 come with the accessory setup? is it serpentine? is it a roller block(honestly I don't know that that makes a difference, but the serpentine setup was started in the same year as they switched to roller blocks, so it could be an issue if you're switching out your 305's accessory setup)? most of the parts you'd need from your car are interchangable, but find out what it doesn't come with so that you know what you may or may not need to buy.

yes, the 190 is good to go with.

as far as I can tell, from what you've said, all you need to worry about are the injectors and the chip, although you may want to get a stock chip from gm if it's cheaper.

 

T/A

 

They used 68# injectors on 3/4 and 1 ton trucks with roller cams as well.

The 30 PSI GM fuel pressure regulator is a good investment, if you put a TPI pump in the tank. That will make standard 61 lbs/hr fuel injectors flow 96 lbs/hr or standard 55 lbs/hr injectors flow 87 lbs/hr.

I put the Walbro 255 to good use on my TBI builds, although a Walbro 190 would probably borderline suffice. The thing is, I have made 326 RWHP out of a mild 355 TBI, Dart Iron Eagle 180s, and a Production LT4 cam. I am planning to add another 100 HP by spraying it, I think the ARP studed 4 bolt main block, PM rods, Forged ZZ4 crank, and LT1 style Hypereutetic pistons will handle everything just fine.

 

following your storey on 305 to 350 swap thiis is my first car im pouring my heart and $ into since my gto 10 years ago At 36 now T/As are in my history and U guys are making me look at the walls with the pictures 78; 80 another80 84 190hp 85 TBI 5sp AT20yrs old an88 an88GTA ,an89IROC 350 and 91 rs conv camaro .I never paid more then 5,000for any of them though they all lookeed exellent when I sold them never made a profit but felt Im keeping these great cars going . Anyway now I have a 92 conv firebird with the 305 TBI So slow!!! anyway spent the 1st yr makeing it looker freindly with ram air hood new paint and 78 old engliish T/Adecals. This year it got new suspension/e biach springs adj. shocks and struts swaybars panhard bar lower control ams BILLET as well as polligraphitebushings and BILLLET driveshaft shift kit and aWillwood brake kit Also got from the junk yard a set of GTA rims but then spent $500 to have them pollished and painted Now just finnished redewing the GTA seatsIpaid 2 much 4 all ripped up but now look great with covers from classic ind. 4 $400 pluss $200 4an embroideryshop 2 make some custome 79stylebirds in them covered them myself just to tell anyone else Ucan 2 Im not real computer litterateso Icant give a picture yet BUT this is my dailly driver and Im torn what 2do motor wise. WHAT is a real HPyou can still get out of TBI350. What aftermarket TBI is there carb wise Summitt sayes they dont have one. can u get more HP with TPI in aftermarket form Main point if I buy a345HP TBI motor that supposedlyhooks up 2 a TBI . should the same set up give u more HP intpi or is 345HPjust riddiculious from a TBI manifold anyway

 

Are you going from LO3 to LO5 mainly because of cost? At this point I would consider an L98, LT1, or LS1 depending on my budget and luck at finding a good motor for sale somewhere.

In any case, if my LO3 didn't run so fricken good, I would replace it in a heartbeat (of America).

 

First I cleaned up your post to make it easier, for me to read.

Second 345 HP is VERY achievable with the right parts selection.

A stock TPI setup is lucky to make 320 FWHP in most cases. The runners are just too restrictive for it to do any heavy breathing at high RPMs. A full aftermarket TPI setup can support very high HP numbers with the right tuning.

Here is a Mustang Dyno, dyno sheet from my 10:1 355, Dart Iron Eagle 180s, and a Production LT4 cam. I am running an Edelbrock Performer TBI intake, 3704 bored to 2" with a 2" bore 454 TBI unit and a 14x3 open element air cleaner. The headers are 1 3/4" x 3.5" with dual 2 1/2" exhaust through the cats. The first lower dyno is through the full exhaust system. The higher numbers are achieved through open exhaust right after the header collectors.



https://www.thirdgen.org/forums/tbi/...tbi-power.html

 

Clint--Holley makes a 670 TBI unit. You can upgrade and put in 80lb injectors later on. Look at the holley total systems as some make up to 400 hp.

 

thanks guys Just read your engine build recomendation,Fast355 followed along untill you talk about ECM options fuel ratio formulas. I can take anything on my car apart and put it back(though I choose my battels) but I cant find the K on the keyboard no less program a computer.Anyway your help and others is appriciated. So here is what Ihave. 92 firebird conv. 305 Tbi 700r4 273 rear . Upgrades Ram air hood K&N OPen air cleaner Trans Dapt swirl carb spacer,160 therm,March polished underdrive kit,splitfire plugs ,Taylor wires,all sensers ,vacume & radiator hoses new,Edelbrock ceramic headers, single 3inch Flowmaster AmericanThunder Duel exit no cat straight pipe(Florida no inspection)Trans go shift kit, crome finned pan /Inland Empire aluminum driveshaft with forged yoke & Ujoints.Ialso have in the box aPowertrax Lock rite, Richmond 373 gears & install kit to go in by December All parts are new and I only bought what I thought wood work with any small bock so the computer doesnt even have an upgradedchip to help the other mods incase Ibought a non computer motor.This is my daily driver and Ineed it Monday-Friday,just no ware to park another car at this time. wanted to just get the most HP for around $5000 I could & bolt it in in a weakend to weak tops 400-500 FWHP sounds possibble for carb to pan without a roller, or computer motor however,times change and legislation could anytime ware Iwould need to go through inspection. SO what CAN A GUY LIKE ME get out there that could be made smoge legel if nessesary installed in week with say an aftermarket computer or custume made chip to plug and go in the 350 to 400HP range at about 5grand$ THANK U all replies welcome PS sory cant type or spell

 

one more thing .the car has 147,000 miles and the only day in two & a half years it didnt start, it was the fuel pump. Monday morning ,turn key ,crank &crank no fuel pump noise .I told my mechanic to upgrade it for a350 as he had done other upgrades I wasnt willing to do at home .IE Headers and polligraphite front end kit shift kit and soon to be 373 posi rear. Iwill double check with him as I remember him saying it was the same. doesnt sound like it could he have ment305tbi to 350tbi the same as Uhave already answered the dif from 305tpi to 350 tpi thanks again

 

There is just no way around not learning to tune your car yourself. The only other option is to find a shop that can burn one for you with the car in hand. The mail order chip companies won't be able to do anything worthwhile for you. Expect to pay 400-500$ for a custom chip plus any dyno time if they have one. You can get all the chip burning equipment for 125-200$ Seriously, if you don't think there is any way you can learn to DIY then just swap to carb and try not to hack up the stock wiring harness so you can swap back to a stock motor if smog laws ever get enforced in your area.