I want to compare two TB's, an 87mm and a 100mm TB. Knowing the weight of a CF of air, and assume I use similar air temps/baro readings, can't I measure HP and also compare airflow through each TB? I am at 645 RWHP with 100mm TB. I am just wondering if 87mm GM TB can match flow of 100mm TB at max RPM..
87mm will not flow what a 100mm will flow. MAF, BARO, air temp, RPM, and engine displacement will get you VE and theoretical load. Not a good way to calculate HP unless you have a comparison dyno load. Even then dyno's can lie with mistaken or purposeful number changes.
I understand about additional flow from 100 vs 87. Just trying to determine if a stock 87mm will support 645 rwhp (dynojet) rwhp. Originally, I was lead to beleive that a stock 87mm tb was close to max'd at at 650 flywheel HP. I am seeing results indicating the 87mm tb is capable of supporting 650 rwhp..
I am just looking for a way to compare airflow b4 and after swapping TB's. MAF seemed like a reasonable tool to measure airflow..
MAP will be a more direct measurement, anything from the MAF's output will depend on the calibration. MAP is just MAP - closer it is to atmo, the less restricted the intake path is, and if the only part you change is the TB then it's apples-to-apples.
As long as the constants do not change, meaning leave the MAF values and timing values alone in the ECU, then yes you could use the MAF's reading of air volume to see if there is a difference in airflow. An increase in airflow would directly relate to an increase in Horsepower. Also, calculating HP from airflow has been around forever and is viable. However, the initial airflow values have to be correct to have accurate numbers. But even if the airflow values are not correct, as long as they remain constant between the two throttle bodies, you can use the delta in reported airflow to see if there is a positive gain in HP.
The MAP is another way to see if there is more airflow. An increase in MAP value would indicate more airflow, however the MAF would be a far more granular measurement. Just don't change the MAF values in the tune when you compare the TB's.
I use it all the time to get a rough idea of what the car is making. BUT there is no way its going to be consistent enough to see gains from a throttle body. Its good for guessing say within 20 rwhp what a car will make.
I hate to break peoples hearts but it is really hard to have even a 3 RWHP gain from a throttle body on most applications. The ones that pick up BIG are the positive displacement type builds.. magnacharger LSA whipple etc.
I think people feel the midrange difference and assume they are good bang for buck mods. I've swapped enough on the dyno to know they don't pick up much at all.
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I don't disagree with gains. Not even sure anything larger than 87/95mm is essential. What peaked my interest was the impact of reducing restriction posed by 103mm TB and 87mm snout. I just recently changed snout to NW 103mm and 103 snout Richard Holdener of TV/YT fame. Chatting with him about pd motors and subject came up about PD blower and impact of opening up snout/TB. He was emphatic about benefits of opening up flow with 103 snout/TB. especially with pd blower.
Truth is I probably would have done 103 snout and TB anyway..
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