crrllmich

Recently I found an auction for a TBI that flows 750 CFM... I do not want to give a exact link because I do not want to advertise but here are some of the stats:

Ultimate TBI modifications + bore yield

"Up for bid is our 50mm bored SBC GM TBI throttle body for your 87-95 GM TBI motor – Chevy, GMC Trucks, Cars, Buick , Pontiac and Cadillac (exchange) - more torque, more horsepower, more air. We take the stock 1-11/16 inch (42mm) small block throttle bodies and bore them to 50mm, cut down the throttle linkage, smooth the throttle bores, which equals up to 750CFM with the injector spacer available separately and is good for motors up to 450HP."

I would also purchase the spacer...

Does this sound realistic? If it is I am sure it would flow enough for a 350 running fastburn heads rated to 430HP correct?

BMmonteSS

Some guys have had luck with those TB's. Keep in mind they are bascially the same thing as a big block TB only you don't get injectors with the converted TB's. Air is only half the story on big HP TBI's, fuel is going to be your problem. Your going to need 90 lbers and the fuel pressure is going to have to be in the mid to high 20's to get enough.

Do a search for "how much HP can TBI make" and start reading this has been discussed ALOT.

crrllmich

Well if I upgrade the fuel lines to steel... get a fuel pump that can push that much...and change the Fuel Pressure Regulator... I can push as much as 40 PSI so I do not feel that would be an issue...

Am I missing something? I did your search but get a lot of people trying to push power out of a 305 while I need a little bit more

BMmonteSS

Keep looking there have been at least a couple dozen post about how much HP TBI will support. But in a nut shell, getting the fuel pressure is not a problem a 255 walbro will handle that. Being able to tune your ecm to have a nice clean idle while also feeding your WOT needs is the real hurdle.

Some people just can't get the hang of DIY prom tuning. Some people pick it up right off the bat. As of right now Ben is the only documented guy in the 12's, and there are several others dabbling in the 13's. All of these guys have lots of time invested in tuning. Notice I said time, not money. You won't make any kind of reliable HP and have decent street maners with a mail order tune. So start looking there and post up any questions.

Edit:
A quick search turned up these links

https://www.thirdgen.org/techbb2/sho...HP+TBI+support

https://www.thirdgen.org/techbb2/sho...HP+TBI+support

https://www.thirdgen.org/techbb2/sho...HP+TBI+support

Go here to start learning about DIY tuning:

https://www.thirdgen.org/techbb2/sho...hreadid=305250

crrllmich

I am computer engineer I should figure it out ;-) lol

crrllmich

Basicaly I just want to make sure this wasn't a dead end road. Maybe I can break the barrier and put her in 11's with a little boost of a bottle.

BMmonteSS

ohh crap....didn't realize you were a computer engineer. Yeah you should figure it out. Start reading and it'll all start falling into place. Being what your interest are your gonna love being able to tune your car with a laptop.

Ohh and putting the bottle to it would be cheatin.....right Dewey?

Seriously though I think you can feed your motor, but it's going to take some serious tuning. You'll see that the base 746/747 ecm's probably aren't going to cut it and that a newer TBI ecm is the way to go...at least till the Speedreader and Rbob's ultimate TBI code come out.

Fast355

iTrader: (2)

There is nothing wrong with the 746, 747s tunability. Yes it datalogs a little slow, but drive enough and there won't be a problem. You are working off of long-term averages for the most part anyway.

crrllmich

See I do not get why people down the TBI.... if it can push as much as a 750CFM carb.... whos complaining?

Fast355

iTrader: (2)

The people that down TBI are the ones that don't do chip work. They slap togather a mis-matched combo, use a cam that is too big for a carbed car (messes with the O2 and MAP), etc. Then they turn around and blame the TBI for their troubles. Fact is the TBI is speed density and it can only guess at airflow through the engine from its calibrated tables. Modifications change the VE tables and spark requirements. Its like taking a carbed engine, never playing with the jets and leaving a mid-70s like advance curve. Build a computer compatible engine, do the datalogging, tune to your datalogging and TBI will suprise you.

I've added as much as 40 RWHP to a stock L03 305 with a low restriction exhaust, headers, and chip tuning.

dimented24x7

iTrader: (2)

Might want to look into using a 7749, or a later PCM. The stock ecm isnt set up for a high revving motor.

BMmonteSS

There are limitations in the stock code. One being the resolution at higher RPM. The ecm will work fine up there, but you start getting limited on how you change things past 3600. It's nothing ground shattering, and completely tunable above that, just slightly limited compared to other ecm's. You also have to keep in mind that we are a wet flow system, and that takes some finagling compared to a multi port setup.

You also have to deal with the crappy AE (pump shot) routines in these ecm's. You don't realy notice the problems till you really get in there and start fine tuning stuff. It's a trick in any ecm, but you have to have your game face on to get it right with our crappy AE vs. TPS tables we have.

Don't even get me started on the ASYNC routines. Thats another mess in itself. I've disabled it for everything except AE, which is hardcoded in.

Rbob's ultimate TBI code addresses all these issues and more. Ahem, WE WANT THE SPEED READER!

Keep in mind that you would be hardpressed to ever be able to tune a carb anywhere near the precision we can with these ecm's. So consider me spoiled on what "can" be done with computers.

dimented24x7

iTrader: (2)

With code other then what came with the ecm the stock peice isnt half bad. The code on here though is a bit primitive and limited. Newer stuff has alot more to offer, like multiple VE/spark tables, higher ALDL speed, improved idle control, etc...