i waas searching the number on my BBk throttle body anf ran across someone saying its a 52mm number, but my car is a 96' and they posted a thread that has the BBK stamp numbers along w dates and stuff liek that. the stamp number mine has is matched for all cars 1985-1995 impala/camaro/corevette /firebird 5.0L or 5.7L. IF this is correct and this stamp number only ranges from years 85-95, then why is this on my 1996? the number is E.O. D-245-9. The stamp number for my year would be E.O. D-245-10 it says on the chart.. here is where the thread is at..i would like to know the correct size of my throttle body and why it is on my 96 car if its only for no later than 95. http://www.ls1tech.com/forums/lt1-lt4-modi...body-sizes.html

Difficult to say why it is on--could be that a new design was given a CARB EO number for exemption purposes and then a slightly newer design got a different exemption number, but that doesn't mean that one you have won't fit or work with your engine.

However, I would like to say that I'm really not in agreement with those that replace the throttlebody with something larger. A throttlebody is not a carburetor--it doesn't work the same way and air doesn't flow the same way. The standard 48 mm TB will flow enough air for a 500 hp 502 GM big block and the block comes equipped that way direct from GM. Another problem is that the PCM is mapped for the airflow thru a 48 mm and not for a 52 and a 58 is way out of whack. What the PCM tries to do is tune the differences out--usually, with a 52 it can compensate to a point, but the engine loses low end torque, and might actually gain some hp at the top end--but the PCM does try to tune it out which means no gain at all, but a loss of hp. With the 58, the PCM can't tune it at all and there is a loss of hp throughout the torque curve. Most owners deny that this happens, but it does happen. I guess if I had just spent about 400 bucks, I might be into denial as well. However, look at the air flow mapping within the PCM, it is calibrated to a certain blade angle as reported by the TPS for a 48mm TB and nothing else, and it must match. If it doesn't, the PCM tries to tune it out.

oh okayy..well idk what size mine is..supposebly the car has been tuned ona dyno but idk for sure. i know that when i let off the throttle it backfires alot..not like super loud but it pops here and there on slow down.

The engine PCM cannot be tuned by a dyno for the different throttlebody. That is an urban myth! This is air flow mapping done under precise conditions in a laboratory by GM. Read that as big bucks spent to make it right. That is the only way it can be done. In fact, if you were to pay to have it done for a 58 mm throttlebody (becuz it is bigger), it could cost you 10's of thousands of dollars and maybe much, much more and it still would not make any hp, none at all. It is the mechanical size of the engine (the displacement, cam, valve size, passage size, exhaust system, compression ratio, barometric pressure, rpm, temperature and per cent of water vapor) that determines how much air flow gets into the engine and not the size of the throttle body, but rate of flow is controlled by the angle of the throttle blades and that affects engine rpm. Air flow reported to the PCM is done by the TPS--a voltage (from 0.6 to 5.0) corresponds to a certain throttle blade angle and that voltage must corresond to the correct air flow mapping within the PCM, becuz that determines injector dwell modified by other inputs. If the TB is larger than stock for any given voltage coming from the TPS, the engine will run lean, becuz the TB is flowing more air than is being reported to the PCM by the TPS. Since that voltage corresponds to a certain injector dwell, the engine runs lean. The O2 sensors pick that up as too much oxygen (they report a larger voltage to the PCM) and the PCM tries to increase the injector dwell to make it run the recommended 14.6 ratio (it is not 14.7--that is a theoretical number). What generally happens is that the PCM tries to restore the proper ratio but can't do it--it can only work within a plus or minus 10% variation. If it can, then it simply tunes the new TB out of the equation and what the owner sees is no increase in HP, some dead throttle at the end of travel and usually a loss of low end torque.

Why a loss of low end torque? The engine is running lean and in order to correct it, not only is the injector dwell increased, but the ignition timing is retarded to protect against spark knock or ping and that is a loss of HP.

It is important to note that all the throttlebody needs to do is to not be a restriction to air flow at max engine rpm, and since the 48 mm TB can feed a 502 cubic inch engine to 500 HP, it can certainly feed a 350.

Looka here.... fuel injection TBs don't work like a carburetor. With an LT1, the intake manifold is designed large on purpose. The purpose was to get the air needed for each cylinder as close to the intake valve as possible. Each cylinder takes the air it needs as the intake valve opens up directly from the intake manifold. The necessary air to feed the intake manifold then comes in through the TB. In short, the throttle angle of the TB affects the rate of fill of the intake manifold and not the rate of fill of the cylinder. It is a whole new way or theory of operation and one that was abandonned by the LS series of engines. The purpose of filling from the intake is to get the air column as close as possible to the intake valve for a faster startup of the air column. This increases low end torque by a bunch and that is why the LT1/LT4 series has more low end torque than the LS series of engines. Since the intake manifold is what is filled, and only one cylinder is filled at a time (depends upon cam timing), then air goes thru the TB in gulps or bubbles if you want to think of like that. So, the TB only has to handle enough air at any one time to fill one cylinder--that is why a 48 mm TB can handle the output of a 502 cubic inch big block with room to spare for more improvements. And these bubbles start all the way north to the air filter and travel thru the entire air intake system.

The intake system of the LT1 is brilliantly designed and the only weak part is the crappy and too small air filter--I guess done for "packaging" reasons.