Just wondering here. I was told my car is a 305 TBI (Throttle Body Injected). I was curious to see how it works so I went to www.howstuffworks.com and typed in Throttle Body Injected and the page that came up was talking about carberators. Is TBI the same thing as a carberator?

 

carb uses a bowl and float to distrubute a corret amount of gas. TBI is like a fuel injected carb. instead of a bowl with a float the lowers to allow mor gas in. TBI has a computer tell it when to injct the gas diretly into you your intake manifold. So a carb is more of a manual type.

 

Computer eh!...now your talkin my language. We recently burnt a mod chip for my Tempo that fixed the car from running rich "due to intake and exhaust mods" which caused the car to run more efficiently as well as more power. Is this option also avail for the computer on my Trans Am?

 

Yes it is. You can really improve by changing from the stock prom. I would learn up a bit more on what makes a TBI run before you go off and start to tune. But on the good side, it is never to early to learn how to burn chips for these cars.

 

go to the DIY PROM boards, there is SO MUCH information and it is amazing how much people have done for thirdgen F-body computer tuning.

 

One thing I really enjoy about TBI (minus obvious inferiorities to TPI) is most Carb parts work with them! I have an Open Element air cleaner (see webiste) originally designed for a carb and it gave me a good boost in throttle response and increased top-end acceleration. Only cost me $30 and was a PIECE OF CAKE to install...

Bruce (90RS305)

 

I loved the instant power I had with my open element install. I still say that gave me the biggest SOTP feeling over any of my other mods. Well since I am putting in a new cam that may all change

 

By open air element you mean by removing that black saucer thing and the snorkel attached and having the filter exposed? I wonder if I can get that at Canadian Tire.

 

Actually, you showed up at just the right time. I recently released a complete .ECU as well as a massivly expanded tunercats definition file based off of the ECU file for the '88 8063 tbi ecm so theres no need to use tuner cats and their somewhat aneamic definition file. Although id still recommend checking them out. Their software package is very nicely done. Definatly worth the money with a good tdf available. Have a look .

 

btw, i love that license plate!

 

Thanks...those are the plates that are going on my t/a

 

I'd like to quote a source of info I got while researching the install of TBI and/or MPI onto my Jeep engine...from the guy that runs CustomEFIs.com....(sung to the tune of "Here Come The Clowns")
"TBI is in no way inferior to MPI or TPI." This is a DIRECT quote.
No $hit. He actually told me that. If I still had my Texas-state e-mail address, I'd send you a copy of the e-mail he sent to me. Do I believe it? Hell no I don't. The differences are immediately obvious to anyone.
Anyway...cool plates. Mine say TIPOVR (on a 1980 Jeep CJ7).
BTW...the GM TBI install on the Jeep engine is going pretty much as planned. Just a few more little parts and it'll all be done. I knew this would take a while...can't wait to drive the results!
Merry Christmas and Happy New Year to all on the TGO board!!

 

I was actually reffering to TPI vs TBI on ThirdGens. A stock TPI 305 will blow the doors off a stock TBI 305. Heck, that was for the most part the only diff. between the first IROC's and RS's. I know there is no inferiority factor in most cases though. As far as TBI is concerned on a whole it's more upgradeable than a TPI, and for a lot cheaper too. So yeah, shoulda probly elaborated a lil' more on the first post!

Bruce (90RS305)

 

Here's a list of sites that will tell you (and anyone else who wants to know) anything and EVERYTHING you'd ever want/need to know about TBI, L03's, and the 3rd gens they came in!

What Is TBI??
TBI Diagram. The Real Story of The L03!
How to get the most out of your 5.0 liter L03 TBI fed V8!
Modifying Your ThirdGen F-body! (the basics)

 

Are you saying that the only difference between these engines is the TPI and TBI? If so, that's way off. The reason the TPI 305's were faster than the TBI 305's is because the TPI cars had better heads, better cam, more free flowing exhaust, and I believe the Prom's in the TPI cars had a bit more aggressive timing tables and a more performance oriented tune. That is why the TPI cars were faster.

 

I wasn't trying to flame anyone here on TGO...I WAS flaming CustomEFIs.com, however.
I could tell you the whole story, but the long and short of it was that I was looking into a custom built MPI system for my Jeep based on the Edelbrock Torker manifold. He helped out some, but he was fairly vague in what he would and wouldn't say...unless I sent him $25 for a subscription to his website and archives. I will admit that he stopped me from putting together a bunch of mismatched parts that would have been a large waste of time and money. Armed with what I know now from this board and past experiences, I could probably build the system the right way now and I may in the near future once I get the thing (Jeep) up and running with the TBI system.
It seemes like he was REALLY trying to sell me a TBI system back then...he hawks TBI for Jeeps at $895 and up...MPI for an AMC V8 will run you $1600 or more depending on what you want.
I firmly believe that TPI has a more efficient fuel delivery manner than does TBI. The "wet manifold" concept leaves too much chance for fuel puddling in the runners. TPI effectively eliminates that problem.

 

your absolutly right about that. Thats one of the only real advantages to a stock tpi over a tbi. Its a dryflow system. Fuel puddling has always been a problem for me.

 

TBI is like a 2 barrel carb, nothing to brag about. If you want a fast TBI car get a 4barrel holley setup.

 

Guess I didn't elaborate enough in my second post as well. I was just trying to say it is a lot easier to work with a TBI as far as playing with it is concerned, but with a stock TPI your starting out with a more efficient setup. Trust me, I can make my way around a TBI no problem, but when you get into cfms and ratios and the like I'll just nod my head politley. I should be the mod on this board as well soon but that just to keep you jokers in like (j/k )

I know, and I agree with you too...

Bruce (90RS305)

 

dennis6, no flame intended here, just my opinion...
I'll politely disagree here. The 4V Holley set-up is cool, but you may as well bolt a POS 4V Holley 4160 carb in place of the 2V TBI unit. If you look at the flow of a set of 305 or 350 heads, you will see that they can't flow that much air and fuel. The 4V can actually provide too much flow for the engine IMO. I can't remember the website, but there is a site that compares flow data from various sets of heads and the OEM GM V8 heads are pretty much at the bottom of the pile IIRC. I am not flaming here, just speaking an opinion...I have a set of OEM heads on a 1979-model AMC 360 that (right out of the box) can outflow a set of OEM GM V8 heads. Now that they are ported and polished on top of a bored-out 360, I still can't justify that much flow from a TBI. Do the math and you just may find that about 580cfm is just right...give or take a few for differences in flow characteristics.
As for the 2V carb, I had a Motorcraft 2150 on this engine before I went to a 4V carb and eventually the 2V TBI. That "little" carb fed my engine with PLENTY of fuel and it would do it at some really weird off-camber angles. It was rated at about 550cfm. Why did I go TBI on my Jeep engine? In a nutshell...just to see if I could do it. Now that I have it, there is no way in hell that I would go back to a carb'd engine. That 360 got a whole new outlook on life with the Holley ProJection, even though I hated it 'cause it wouldn't stay tuned right. Now that I have the GM TBI system all but running, I am more than eagerly awaiting the results of my project.
Use the 4V TBI on a BBC and THEN you have done something worthwhile IMO...
Again, no flames meant and I hope I didn't insult anyone.

 

On a 305, you are probably right. A 2 barrel TBI could feed the engine. A 2 barrel carb probably could also.

On a serious 350 or larger engine, I tend to think the 2 barrel TBI unit would choke the engine. Holley makes different sizes of the 4 barrel unit to accomadate smaller engines.

 

Well, it IMO depends on your definition of "serious". Like I said before, I am running an AMC 360 +0.030" bore (works out to almost 370cid) with a set of gasket-matched/ported/polished heads and an Edelbrock Performer AMC intake (dual-plane for low-end grunt). My cam specs are something like 272/288 adv. dur., .472/.496 lift @ valve, 114 deg lobe CL. My ignition is a digital racing ignition. I run 2V TBI and it works REALLY well. I haven't seen any choking of that beast yet and it dynos @ almost 390hp and 410 lb-ft. In fact, it runs MUCH better than it did with the 4V Holley 4160 carb...I can't wait to test out the GM TBI. It seemed like the carb was dumping raw gas down the manifold. It smoked like crazy with a BRAND F'N NEW block and heads even after the break-in period. I rebuilt the carb twice to no avail. The Holley 2V ProJection cleaned it up and really helped, but it wouldn't stay tuned. That's why I hated it...that and the fact that it smoked TWO ECM's for no apparent reason. If I had so much as a wind direction shift, I had to re-tune the MAIN and ACCEL maps. Season changes took a while to tune for...worse than a carb IMO.
I'll agree with you on the fact that if you are trying to run 500hp from a SBC engine at 6800rpm, you probably do need a 4V TBI. A 383 stroker motor could probably use a 4V set-up. A BBC could definitely benefit from a 4V TBI. I may be reaching here, but IMO this is where the VE tables start to come into play. If the engine can move more air more efficiently, it needs more flow from any kind of aspiration...carb, TBI, MPI, TPI, etc, etc...If you sincerely think you need a 4V, look at your log results...or just put a 4V carb on it for a test run to see how it runs. With a 305, you may find it bogging out at low end rpms and your high end performance will probably degrade likewise. Too much gas can be just as bad as not enough. Get a copy of Desktop Dyno 2000 and see where your peak VE is with your engine config. If you don't want to spend the $45, email your engine specs to me and I'll run 'em for you...I might even be able to post a screen shot of the resulting tables and graphs.

 

Check out 5-7kids expierence with carbs. I think you just had a bad carb. Also check out holleys site for recommendations on carb size. Alot of people have went from 750 CFM VS on 305s to mechanical secondary carbs and found no bogs and a increase in track times. Vacuum secondary carbs are for towing, not for performance.

A good holley double pumper or Speed demon would probably change your mind on the 2 barrel vs 4 barrel thing.

The only real way to settle this would be to properly tune a mechanical 4 barrel carb and dyno it on your engine, and compare it to your 2 barrel TBI. A better comparison would be to use a commander 950 ECM with a 2 barrel unit and a 4 barrel TBI unit.

 

Thanks for the info man. Greatly apreciated. I need to get all the knowledge I can before the summer when the mods start comin in.