[SenderPiggins]

Apologies to @axelr for helping hijack his DIY Engine Build thread. Much better to have throttle body banter in a separate thread.

@nicklulu measured errrrrthang in post #183 (go there for photos)

OE	Diameter (mm)
Entrance	59.80
Middle (Butterfly Area)	56.95
Exit	60.56

FP Billet	Diameter (mm)
Entrance	70.00
Middle (Butterfly Area)	67.00
Exit	65.00

Mustang TB (Maxbore)	Pre (mm)	Post (mm)
entrance	65.90	66.84
middle (butterfly area)	59.95	62.11
exit	61.95	64.77

RS tb options

OEM Mustang 2.3 - 60 mm
BBK Mustang 2.3 - 65 mm
Ford Performance Mustang 2.3 - 70 mm

Boring Options

maxbore.com

Parts Needed

Harness extension, longer bolts, new gasket

 

[Skidro87]

So in all honesty though, is having the bigger throttle body actually worth it on a stock turbo? Is there any dyno graphs that show the gains up top?
First of all it seems you need to upgrade your intercooler pipes to get rid of the choke point in front of the TB, and then it looks like the aftermarket hardpipes don't line up properly!

 

[BigFatFlip]

In for more education.

I've followed @axelr engine build thread, but I'm curious what others think. I've always been of the school of thought that on a turbo (or really, any FI) application, a larger throttle body won't really be worth it since everything from the turbo, to intercooler, pipes, etc. will all be seeing the same boost. The only benefit really is in instances where a high CFM is needed (ie up high in the rev range) where the throttle body may then act more as a restriction. That said, if any part of the air path way is more of a restriction (charge pipes, exhaust, etc.), a larger throttle body won't still buy you anything.

 

[Si2RS]

So in all honesty though, is having the bigger throttle body actually worth it on a stock turbo? Is there any dyno graphs that show the gains up top?
First of all it seems you need to upgrade your intercooler pipes to get rid of the choke point in front of the TB, and then it looks like the aftermarket hardpipes don't line up properly!

This discussion has been going on for a little while over in @axelr 's thread (sorry for thread jacking, axel!). You can check out the last few pages for some pretty in depth discussion about it. I'm more interested in the improved throttle response aspect rather than the minor bump in power, which may or may not occur. If you had all stock piping, I don't think upgrading the TB alone would be worth it. Only reason I am doing it is because I just bought the Mountune charge pipe kit, so figured why not swap that out while I'm in there. However, none of the "off the shelf" options listed in the OP would work with my set up, because those all require a 3" inner ID coupler on the TB side. Since the Mountune cold side hose is silicone, you can see why this wouldn't work. Those would only work with a hard cold side pipe, and the coupler that comes with the kit listed in "parts needed" section in the OP, which also comes with a harness extension because the TPS sensor plug is in a different location than stock, and longer bolts because "thicc."

All that being said, I am going with the maxbore option using a stock RS throttle body. Figured why not since I am planning on getting another tune (for E30) after I get everything installed. Looking forward to it.

 

[nicklulu]

The funnel on the cold side OE charge pipe restricts a lot.

The viable option to the soft charge pipe is to bore an OE TB.

the Mustang, BBK would need a hard pipe swap to benefit to a 2.5" the FP one is 2.75" and only CP-e makes that big of a cold pipe

 

[big jim]

maybe our guy Shimmer could help us out with this predicament?
he might also be interested if there is a performance benefit? which i think there would be.

 

[Randy]

To anyone who says they want to change the TB for improved throttle response... that can be done in the software.

 

[nicklulu]

To anyone who says they want to change the TB for improved throttle response... that can be done in the software.

A bigger TB diameter does help on the car to breath better and getting it tune with the hardware change is beneficial, correct?

 

[BigFatFlip]

To anyone who says they want to change the TB for improved throttle response... that can be done in the software.

Would that be just tuning of the throttle body control? Ie more opening for less throttle input?

 

[big jim]

To anyone who says they want to change the TB for improved throttle response... that can be done in the software.

we know that Sir...lol. but can high rpm hp be gained by opening the intake pipe / TB?
i would think hp would be lost if installing smaller diameter pipes and TB.
just my feeble-minded thinking 🤪

 

[floridars]

I went kinda deep at the enthusiast level on this this am, but not so deep as to bust out the calculator. 😂

I went and found some TB sizers, the Focus seems marginal. When you compare to equivalent NA HP ratings the TB is tiny, however I expect the decision is in part to help off boost throttle response and drivability. The 60mm seems to make more sense though.

This lead me to conclude Ford chose the ST parts to save money as the RS has more swept volume and a higher specific output, and surely drivability would’ve passed even OEM tests at 60mm.

So how big? If you have 2.5” piping, and our stock intercoolers are 2.5”, a 63.5mm (2.5”) TB makes sense.
The CPE intercooler can be changed to a 2.75” output which is 70mm, or a nice match for the FP TB, however it looks like hot side piping is still 2.5”.

If you use turbine energy to pressurize higher for a given mass flow, you pay the price, so you shouldn’t assume boosted apps don’t matter. My plan is 2.5” piping and a bored TB for now. 2.75” and 70mm if I finally get around to the build I want to do.

 

[Si2RS]

If you use turbine energy to pressurize higher for a given mass flow, you pay the price, so you shouldn’t assume boosted apps don’t matter. My plan is 2.5” piping and a bored TB for now.

This was my thought as well. Technically, the turbo would be able to hit the same manifold pressure target on both sizes of TBs. But I would think it would be less stress on the turbo with a larger opening. Obviously, there is a point of diminishing returns if you start going too big. But I would think at least matching the bore to the piping diameter would be ideal. My plan is the same as your plan.

 

[big jim]

max bore is the plan?

 

[Si2RS]

max bore is the plan?

Yup!

 

[big jim]

Yup!

 

[nicklulu]

Mine is a bit different.

Waiting for the measurements for the Mountune manifold.

The OE plastic mani is 64.5 (IIRC) so the BBK would be the closest fit. For $24 more for the FP TB I gladly pay for the difference and get the CP-e cold side pipe.

I already have the boost hose kit from Mountune...... so if the Mountune mani is the same as the OE and I cant bore it out, I'll go with the maxbore route.

No sense I think to go with the Mustang TB if its 60mm if you can bore the OE one to little bigger.

Getting the Mustang TB and getting it bore like the BBK might be a little cheaper than getting the BBK one, but not that much and all the time getting it and shipping it out, might as well get the BBK one!

 

[nicklulu]

The reply I got from Mountune UK:

Thank you for getting in touch and apologies for the delay in our response,

Unfortunately we cannot disclose any of the information regarding measurements etc in regards to this part but we can say that this is a direct fit item. Which means that if the item will fit on the standard inlet then it will fit on ours in theory.

But our Development team have informed us that they do not believe the Ford Performance throttle body will be compatible as it is not similar to the standard OE throttle body.

We hope this helps

---------------------------------------------------------

I am still waiting from someone in the UK to reply since they bought the mani two weeks ago. He'll measure it for me.

I got a notification it was available this morning, then when I was checking out... sold out!

if the FP TB bolts on the Mustang and the Mustang TB bolts on our RS, logic dictates the FP will bolt on RS. It would need a different cold side pipe, silicone coupler, and wire extender but it should work.

Waiting for that damn mani to be available again.

 

[gbassrace]

floridars - One thing left out of your calculation is the TB plate and bar. That all takes up a lot of space so something larger ie 70mm would match 2.5" piping. Yes, and the manifold inlet should be bored at that point. Fairly easy to do. I would love to see dyno results of all of this but it seems like a no brainer. Also, a meth plate would be considered too. Larger.....

 

[SenderPiggins]

Found this thread on LX forums, might be worth a read. Not sure if 100% applicable. A real engineer should try doing the maths.

Throttle Body Selection with a Pocket Calculator


@nicklulu If I was a betting man I'd say it's the same 64.5, since most of these AF parts are made to fit stock parts.

 

[gbassrace]

Wow - cool, and he accounts for the internal bar area. Written for both N/A and supercharged apps, how does that work out for an RS ultimately?