custom throttle body

[peter.blais]

Ok... I'm going to pull some numbers out of my... hat... to illustrate what we are trying to tell you.

Say, for sake of conversation, that the OEM throttle body flows 500cfm @ 100% throttle position, and as the throttle blade opens flow increases linearly (not quite in real life but for our purposes that will due fine)

So that gives us approx:

250cfm @ 50%
125cfm @ 25%
just over 0 cfm @ 0% due to idle screw or bleed


For convienice, i'm going to say that this engine uses 250 CFM @ 50% load and ~500 cfm at full load...

Now here we come with our monster throttle: I'm going to continue to make up some numbers here... Say it flows 1000cfm for a nice round number.

that gives us:

500 CFM @ 50%
250 CFM @ 25%
125 CFM @ ~12%
~0CFM @ ~0% idle screw


Ok so say your pulling out of a bank, and you give it a stab of throttle... With the OEM throttle body, 50% throttle gives you ~50% load... exactly what you expect... Put the larger throttle on there, which flows twice as much air, and 50% throttle gives 100% load!

This is exaggerated at low throttle openings... Makes the car really ****ty to drive on the street.

You can engineer / design your way around this by machining an elliptical / progressive throttle wheel for the throttle body. Basically, you need the radius to change, so that the first oh say- 75% of foot pedal movement only opens the blade ohhh say 33%, the last 25% opens it the other 66%! Getting this to work 100% right is going to take some trial and error for it to feel right as well, which is why the majority of people end up just sticking a smaller throttle body on there because the gains from a massive tb are pretty minimal anyways.

[Runner4404spd]

the trick is to calculate the air flow based on cross sectional areas, without a flow bench all we are doing is guessing. a flow bench isn't that hard to build but you need to figure out what you want to achieve. yes you will need a progressive cam on the throttle shaft. at a minimum this should be tailored to give the same rate as your stock throttle body in terms of the progressive linkage. at this point you'd want to try and match the open cross sectional areas at various points in the throttle plate location and then interpolate a curve based on that.

[peter.blais]

Yea, I was just posting those numbers for comparison... I definantly could use to build a flow bench haha... Problem for me is I'm a bit tight on time for another project- Need to find a flowbench kit or just a used flowbench.

[FPV_GTp]

Originally Posted by NC Cams Two words that will make nearly any throttle body.................. .................in closing, just because something big 'fits', that doesn't mean that it will 'work'.

PMSFL ..... sory NC had to make omment , try and say that to a woman


cheers

[ZeroTolerance]

Originally Posted by krymis I have bobcad v21 for cad cam, mach 3 for interpretur, and a few machines i can use. I want to make an aluminum throttle body for a turbo project i am building. The setup is a 2.0L engine being stroked to a 2.3. I made a custom intake but wanted a custom 70-75mm throttle body to go with the intake. Can anybody help me get designing and machining a prototype. I will be machining it out of tooling board before using the aluminum. I want to make the butterfly and shafts and all. Where do i start. I want a 3-3.5 inch opening and the intercooler end caps and piping will be sized to what ever size the throttle body is. I have a prototype 3 inch maf made with my polymer setup.

I have a 70 mm throttle body, if you want to buy it. I actually build/machine/design throttle bodies for high end high boost engines, let me know whats going on with your project.
John

[FPV_GTp]

To build a one off throttle body is it worth all the effort one is going to be doing ?

Just obtain a throttle body of a V8 EFI engine Ford , GM , Chrysler and so on ..... which in general most are around 65mm to 75mm in inside diameter. There is also room to bore them out a further few mm's to increase their size .

Since this is boost application and depending on spool time's and pressures and inlet air temperatures will govern how well this will work amongst many other variables that need to be considered.

Good luck with the experimentation.

cheers

[Grp Racing]

Wouldnt it make life easier to modify a newer intake setup first which will get you to the single inlet stage instead of the dual butterfly first? Then you would have a more efficiant transition into the engine. From what I see you are wanting to take a 12mm oversized and round TB and have that force feed into a smaller and oval inlet. And you are not going to do this in a slight transition but all at once.

Remember that you are working on a turbo car, where flow is very important! I am running a 10 second talon right now with 2/3's the turbo your talking about and a stock 60mm tb. I daily drive it so there is no need for super large but the fact is that all you want is smooth in and smooth and quick out. In my opinion, you are not gonna gain if you funnel air thru that throttlebody in a few inches down to the stock size.

I am hopeful that you get to build it and try it out but your making a funnel and this is a turbo car not a N/A car dumping air and fuel.

Good luck with it. I will keep watching.

Gary