Throttle response improvement : Steeda throttle body spacer or BBK Throttle body ?

[BmacIL]

I'm actually a fan of that mod myself. Looks stock, and will flow more. Any time you smooth a bore, and open it up a bit, you gain some CFMs. Whether or not they are needed, and how much they can hog them out both affect power levels. But, should the engine need (Or can take advantage of) the added airflow, then you will actually get more power.

If the butterfly is stock sized, then it shouldn't have much of an effect, with a possible exception if there is a lip on the back of the stock butterfly (There for the butterfly to "sit" on). Otherwise, and it my impression, that these bored out TB's have bigger throttle blades. Ford seemed to think the GT350 needed more air, so they made it bigger. One could presumably argue the coyote could benefit from it, again, Ford seemed to think so by including it in their stage 2/3 performance pack kits. Nevertheless, and to oversimplify things, suppose the ECU says at 10% foot throttle, it says to open the throttle blade 10 degrees. If you compare the CFM at 10 degrees of the stock vs hogged out TB, you will see a dramatic increase of CFM just because of the geometry.

For the heck of it, I did the following. I don't feel like doing calculus on a Saturday, and covering ever nuance such as PT tables, BMEP and blah blah blah...so I'm once again doing some horrid back-of-the-napkin math here. Suppose your butterfly valve is a 80mm x 80mm square. And the hogged out one is 87mm x 87mm. I picked those numbers because of the GT350 TB. Assuming the same 10 degree butterfly valve, and a linear airflow velocity right at the speed of sound 343mps (So as to be just at the cusp of a whistle) your 80mm TB flows 70.93 CFM while your 87mm TB flows 83.46 CFM. While it doesn't sound like much, that's ~17% more CFMs. And that's with a square blade...If I did this properly using proper math to calculate the elliptic area of a tilted circle in a cylinder, the CFM increase would be higher than that.

^ All this mumbo jumbo means that yes, holding every other variable constant, going with a larger throttle body will effectively translate to more throttle, faster (Or at less pedal travel...however you want to look at it). This is also why people either:

• Love the bigger throttle bodies because the pedal is "so much more responsive" or "Feels faster"; or
• Hate the bigger throttle because of "drivability". I seem to remember the conversion of twin bore throttle bodies to monoblades were particularly nasty, but that is based on my fading memory and second-hand observations.

The fact remains to be seen if the ECU can figure this out using it's suite of sensors (read: learn you changed something), and then rescale the tables (read: booo, it figured it out), and if so, then the TB size increase won't do anything until you would have been starved for air and the new increase can actually fulfill the needed air. Or, you end up with a situation that was extremely common with the SRT4's where you would literally reboot the engine computer (e.g. put a switch on your dash to power off/on the ECU) because it would pull boost/timing once it learned you tweaked something beyond what it liked. (And yes, these things could be tuned out by someone who knows what they are doing)

To each his own here, but if I was going to drop $150 (or more) to get the sooner-onset torque, I'd do it as you did it, and actually increase the CFMs/Pumping ability of the engine. While it may sound like it, I absolutely mean no disrespect to bjstang (or others) at all. I'm just saying if it were my money, that's what I'd do.

The GT350 throttle body is an interesting piece. I did give it a go when I did the initial installation of my 2018 GT manifold. Because of the orientation of the blade at "closed", it makes for a VERY non-linear pedal feel. The blade sits at something around 30 degrees from the plane of the flow direction, and thus even the smallest opening change results in large increases in flow. The GT throttle body is much closer to vertical orientation, so it has much higher resolution at low throttle inputs. I did not like the idle quality nor normal speed drivability of the GT350 TB, despite the fact that it probably made a few more hp (from Shaun @ AED). Upon switching to the stock one, all my drivability concerns vanished. There is some trickery going on with the pedal map or low speed demand tables to mitigate this on the GT350 itself, as I've logged over 1000 miles driving one and it did not exhibit this behavior, despite the physics of it. A ported GT throttle body would be interesting to test.

Food for thought!

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[GregO]

Any time you smooth a bore, and open it up a bit, you gain some CFMs.

So everyone understands, Brett neither opens the aperture or smooths the I.D. bore walls.
No magic here, just the application of surface tension and boundary layer reductions to increase CFM’s
Kinda like in the old days when NASCAR learned to go fast again with restrictor plates.

 

[CrashOverride]

So everyone understands, Brett neither opens the aperture or smooths the I.D. bore walls.
No magic here, just the application of surface tension and boundary layer reductions to increase CFM’s
Kinda like in the old days when NASCAR learned to go fast again with restrictor plates.

Thank you, there isn't a lot of information I could find on his services (The facebook page is pretty sparse if you ask me). These throttle blade openings are a real problem even for cable throttle bodies. Check out the little spoiler (I'm calling it that because I think it is literally designed to spoil the airflow) that is tacked onto only the bottom of the SRT4 throttle body (Left picture). I had another throttle body that was bored out, and it removed the spoiler, and the throttle was extremely jerky - way too much throttle to modulate the clutch when in traffic.

Regarding the other comment: I'm in the west coast (PST) so it was 0100 my local time. And there was no calculus there, at most some very basic trigonometry. Nevertheless my "dedication" is nothing other than passing time because I have insomnia. I think you're right, if I had $150 and wanted more low end torque the F150 intake is a better use of money.

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