We seem to have some concern deteriming a good throttle body diameter
for a blown Ford Flathead that we are building. Here are the details:
271 C.I V8 Flathead
Front-draft (crank driven) Detroit 3-71
~8 of boost (max)
2 Throttle bodies
*Previous research we have found on similar Flatheads shows we need around 750CFM to flow through the throttle blades without causing resrictions*
I have found info on NA engines, but I realize that boost is a different situation. We also dont want to over do the size as to not cause the related probs.
If you have any info on the topic, or examples of throttle plates on
engines with boost let me know.
Thanks
Throttle Body Size, Blown Application
Moderators: jsmcortina, muythaibxr
as a general rule, you use the same throttle body size you would use for a non-blown engine of simular calibar.
For example, a "reasonable" turbo'd V8 (stock 350 SBC for example) engine will usually be happiest with a 600CFM carb. An extreme turbo'd V8, will be 800+ CFM.
I don't know what your HP goal is, but I would base it off what the engine is capable of NA. Its easy to get confused on the difference between CFM on a boosted engine, because CFM doesn't represent the pressure and velocity of the air charge.
For example, a "reasonable" turbo'd V8 (stock 350 SBC for example) engine will usually be happiest with a 600CFM carb. An extreme turbo'd V8, will be 800+ CFM.
I don't know what your HP goal is, but I would base it off what the engine is capable of NA. Its easy to get confused on the difference between CFM on a boosted engine, because CFM doesn't represent the pressure and velocity of the air charge.
It makes a fairly large difference whether the throttle bodies are before the blower, or after the blower.
If they are before it, treat them exactly the same as on a n/a engine making the same amount of power (BIG!), if they are after it, it isn't nearly as important, as you can push a lot more air through a given size TB then you can pull it.
If they are before it, treat them exactly the same as on a n/a engine making the same amount of power (BIG!), if they are after it, it isn't nearly as important, as you can push a lot more air through a given size TB then you can pull it.
'89 Honda Prelude 2.0SI 4ws
'76 Triumph TR7 fhc, soon to have ITB's and MSnS-e
'76 Triumph TR7 fhc, soon to have ITB's and MSnS-e