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Discussion Starter · #1 · (Edited)
5.0 TB for a 94-98 V6, 1/2 shafting How-To and TB sizing guide >

Here is the whole 5.0 TB how-to text...

If anyone has pix I will be happy to add them!


1. Re-drill bolt pattern for V6 TB pattern (a gasket helps alot)
2. hack off MOST of the throttle arm, leaving the return spring portion,
the shape will resemble a diamond.
3. grind the remaining surface FLAT.
4. weld on MOST of the 3.8 throttle arm, less the return spring portion, just reuse the part the throttle cable hooks to.
5. making the crossover tube larger is a MUST and a big job! 54-55mm at least... that matches the flow rating of the 60mm TB (remember, no shaft to block airflow)
6. Re-use your 3.8 IAC (idle bypass motor)
7. SPLICE in the 5.0 TPS to your 3.8 wiring harness. The 3.8 TPS is "clocked" 90* off from the 5.0 TPS... and does not bolt on to the
5.0 TB. Use the wiring chart below.

Other than that, it is a "simple bolt-on!" (haha)

60mm is also the practical limit for the 3.8 Upper, the "choke point" can only flow about 550 CFM and the 5.0 TB is rated by FORD to flow 535-540 CFM. However you can weld the exterior of a crossover tube and port it
even more, figure about 2 to 4mm smaller being the minimum size for a
given TB. (65mm would need 61 to 63mm, etc.)

5.0 TPS to 3.8 wiring harness wiring schematic:
(for use without the Ford adapter, apparently it does not work for the V6)

5.0 TPS colors.................goes to..................3.8 harness


base color/tracer (stripe) color
**** Note! Not all 5.0 TPS's have the tracer color, but it is listed
for those that do.****

When cutting the 3.8 harness wires, leave enough wire on the plug to reinstall it in the future
if the car is ever returned to stock condition. Use butt splices and shrink wrap to connect wires.

1,001 Posts
Discussion Starter · #2 · (Edited)
Another Sticky: (after we get it trimmed down)

IM convo about TB half-shafting mods!

(I popularized this for the V6 TB's, it goes back to 1998
and I figured it out because the 5.0 TB's are 1/2 shaft
from the factory. It gives at least 15% more flow according
to the cross sectional area calculations. More with porting.)

Better how-to's exist, with pix, I will see what I can find.

White95v6: now how do you get 15% more flow out of the tb?
rtgreene1: Remove the front 1/2 of the shaft
White95v6: i will be up all night writing this down.
rtgreene1: old Carb porting trick :) (and 5.0 TB, see above)
White95v6: explain the shaft
White95v6: i haven't been into a tb yet
White95v6: i know you have a plate in there
rtgreene1: it is round, and a slot is in the middle for the butterfly
White95v6: just like a carb
rtgreene1: U remove the butterfly, (2 screws) and then the TPS
rtgreene1: yup, like carb
White95v6: what part do i take out
rtgreene1: basically all of it
White95v6: ok then what
rtgreene1: (it is off the car already)
rtgreene1: OK?
White95v6: lol
rtgreene1: it is round, and a slot is in the middle for the butterfly
White95v6: just like a carb
rtgreene1: you remove the butterfly, (2 screws) and then the TPS
rtgreene1: yup, like carb
rtgreene1: then you pull the shaft out
rtgreene1: once it is out
rtgreene1: You can hacksaw the FRONT half of the shaft off
White95v6: ok pull shaft out
rtgreene1: gotta keep the back, it has the threaded holes
rtgreene1: cut off the FRONT
rtgreene1: got it?
rtgreene1: FRONT (I emphasized this 3 times because it is CRUCIAL!!!)
White95v6: the part the faces the intake tube
White95v6: right?
rtgreene1: Correct. Now then you have to file the cuts smooth
White95v6: ok
rtgreene1: You can re-use the same screws, but I like flat heads, they would need to have the plate countersunk to work properly.

rtgreene1: A CAI will help also.
rtgreene1: but this is better
rtgreene1: both will rule!
rtgreene1: OK, back to the TB

rtgreene1: I also loc-tite the screws when I put them back in
White95v6: good idea
rtgreene1: Or use a centerpunch and peen the back of the screw (both is best)
rtgreene1: Do not centerpunch the head of the screw, hit the part in the shaft.
White95v6: yea I know what you mean
rtgreene1: that and loctite should hold thru anything
rtgreene1: also grind off ALL extra screw length
rtgreene1: before peening/punching
rtgreene1: and also polish and smooth the inside of the TB itself (while it is apart)
White95v6: ok
rtgreene1: but do not remove any appreciable amount of material where the butterfly is when it is closed, or U will have a high idle.
rtgreene1: just lightly polish in front of the plate (butterfly) and behind it
rtgreene1: and knock down that "step" in front of the plate too
rtgreene1: back up to speed?
White95v6: yep
rtgreene1: OK, just polish it out and re-assemble it all
White95v6: that should put the tb cfm to over 400 right
rtgreene1: no, but up to ~370CFM (by calculations)
rtgreene1: it has to be bored to 52mm to go over 400 cfm (he proved me wrong! It was more!)

That's it Boys and Girls! It is exactly the same for ANY TB with a full shaft! (5.0 60mm TB and most aftermarket TB's
are already half-shafted)

Matt Neuharth (White95v6) then flowed his TB on a flow bench and got
~455 CFM @ 28" H2O!!! He did basically everything above. I think the
'bench was a bit optimistic, but most are usually within 10% of reality.

Just over 400 CFM is not bad when you started with ~300 CFM!

1/2 shaft is worth ~45 CFM on the stock 94-98 TB's. (15%)

1,001 Posts
Discussion Starter · #3 · (Edited)
...and more...


"Can I use a 65mm TB on a 94-98 Mustang 3.8 V6?"
> OK, in short, the answer is NO. The 65 is too big for a fully modded
> crossover tube, (unless you weld) and it is WAY big for
> the airflow needs of the engine!
> consider this: a fully P&P'ed engine (heads, Intakes, etc.), heck, lets
> it a 4.2 just so U guys can see that even with a stroker a big TB can be
> more than enough. 4.2, fully P&P. Cam, good exhaust, everything.
> A wild street 4.2 only needs ~440 CFM TB to rev to 6000 RPM at 100%
> Volumetric Efficiency. According to theory ;)
> I simulated a VERY well built v6 this morning and it only reached 87% VE,
> making 260 BHP. It only used 400 CFM flow @ the TB.
> Apparently the sim uses the same theories :D
Note: due to the length of EFI induction systems, bigger TB's do help
even though the engine is using less CFM than the TB flows. The higher
RPM flow is enhanced while the low RPM torque is still excellent, you cannot
"over carb" in the traditional sense, as the TB does not meter fuel at all.

> A Fully modded stock TB (bored to 52mm and given the full TLC) flows
> 450 CFM+ and is just right for a hardcore 3.8, and a 60mm (fully modded) TB
> flows well over 540 CFM! I do not push this except to the blower guys.
(60mm Works great for NA I have found, on single port... SPI can go bigger)
> so to answer your original Q, a 65mm TB will not be needed (nor an adapter
> plate, a 60 does not use one, and I suspect you mean an EGR spacer,
> but the 3.8 has an EGR on the crossover tube) and the stock upper needs Major Mondo
> welding to get the crossover tube big enough to accept the necessary boring.
> BTW, a 65mm TB flows about 650 CFM which will allow a 3.8 to rev to
> over 9,500 RPM! Another thing, a 65mm TB flows OVER 100 CFM more than a
> unwelded ported crossover tube can handle...
> Bigger is not always better in engine component selection.
But!!! We have since found that the TB size is not really hurting the
low end at all, and helps the top end alot. Good running 94-98 V6's
can use a 60mm TB for NA use, and up to a hot street 4.2 SPI needs
a 70mm TB to get the flow needed to feed that beast. I believe it has
to do with plenum fill rates, whcih is much different that carb sizing
and also the TB does not have to meter fuel, so low end is unaffected.

So in short, size the TB for at least what the CFM calculations call for,
using 85-90% VE for a ported & cammed street engine. Use this as a
minimum starting point, and get at least the next biggest TB that fits.

Here is a TB size/flow rating chart, listing popular TB sizes, bored and
1/2 shafted sizes are included as well.

All figures are calculated using 146CFM/sq. inch flow rating @ 28" water depression.
Note loss of ultimate flow capability with the ACCUFAB 90mm TB. Possibly due
to the airhorn not having a proper radius, so as to fit into the stock-type 5.0 inlet tubing.
Calculated by RGR...

Stock 50mm TB: ~329.3 CFM (calculated, but it was just under 300 CFM on my 'bench)
1.969" opening, with a .400" full shaft.
3.043 sq" less .788 sq" shaft area,
2.255 sq" WOT.

Half-shaft 50mm TB: ~372.4 CFM (43.1CFM over stock)
Ported & 1/2 shafted 50mm TB's flow substantially more on the 'bench!
1.969" opening, with ~.250" half shaft
3.043 sq" less .492 sq" shaft area,
2.551 sq" WOT.

Stock+ 52mm TB: ~361.1 CFM (31.8 CFM over stock)(11.3 CFM less than Stock + half-shaft)
2.047" opening, with .400" full shaft
3.292 sq" less .819 sq" shaft area,
2.473 sq" WOT.

52mm w/half-shaft: ~405.7 CFM (76.4 CFM over stock)
2.047" opening, with .250" half shaft
3.291 sq" less .512sq" half shaft area
2.779 sq" WOT.

54.5mm (maxed out stocker?): ~402.7 CFM (73.4 CFM over stock)(3 CFM less than 1/2 shaft 52mm)
2.146" opening, with .400" full shaft
3.616 sq" less .858 sq" shaft area
2.758 sq" WOT.

54.5mm w/ half shaft: ~449.5 CFM (120.2 CFM over stock)
2.146" opening, with .250" half shaft
3.616 sq" less .537 sq" shaft area
3.079 sq" WOT.

56mm (BBK, thin shaft, 2 sided): ~482.2 CFM (152.9 CFM over stock)
BBK appears to be able to be bored out well past 60mm, up to 64mm
by my measurements. More than nearly any singleport V6 could use with
the fully-modified stock upper anyway. If you need more get a custom upper.

2.205" opening, with .250" thin shaft
3.818 sq" less .551 sq" shaft area
3.303 sq" WOT.

60mm 99^ 3.8 TB stock: ~501.8 CFM (see 5.0 TB for half shaft flow rating)
2.362" opening, with .400" full shaft (standard)
4.382 sq" less .945 sq" shaft area
3.437 sq" WOT.

60mm 5.0 TB stock: ~540 CFM (210.7 CFM over stock) (553.5 CFM calc., 540 CFM, as published)
2.362" opening, with .250" half shaft (standard)
4.382 sq" less .591 sq" shaft area
3.791 sq" WOT.

63mm (max bored 99^, w/full shaft): ~560.5 CFM (see max bored 5.0 for 1/2 shaft flow rating)
2.480" opening, with .400" full shaft (standard)
4.831 sq" less .992 sq" shaft area
3.839 sq" WOT.

63mm (max bored 5.0): ~614.7 CFM (285.4 CFM over stock)
2.480" opening, with .250" 1/2 shaft
4.831 sq" less .620 sq" shaft area
4.211 sq" WOT.

65mm 4.6 TB stock:~601.4 CFM
2.559" opening, with .400" full shaft
5.143 sq" less 1.024 sq" shaft area
4.119 sq" WOT.

65mm FMS TB: ~657.4 CFM (328.1 CFM over stock)(650 CFM advertised)
2.559" opening, with .250" 1/2 shaft
5.143 sq" less .640 sq" shaft area
4.503 sq" WOT.

Anything over a 65mm TB would require excessive welding and modifications
to the stock upper intake of the 94-98 Mustangs. A custom Upper is desirable
after this point. But the 65mm TB has been proven to support 400+ HP on
highly modified 5.0 engines, naturally aspirated.
A 99^ 3.8 should be able to fit up to a 70mm TB (possibly a 75!) on the TB
flange the engine is equipped with...

70mm FMS TB: ~770.3 CFM (750CFM advertised)
2.756" opening, with .250" 1/2 shaft
5.965 sq" less .689 sq" shaft area
5.276 sq" WOT.

75mm FMS TB: ~892.1 CFM (850 CFM advertised)
2.953" opening, with .250" 1/2 shaft
6.848 sq" less .738 sq" shaft area
6.110 sq" WOT.

80mm (not produced*): ~1022.4 CFM
3.150" opening, with .250" 1/2 shaft
7.791 sq" less .788 sq" shaft area
7.003 sq" WOT.

85mm (not produced*): ~1161.9 CFM
3.346" opening, with .250" 1/2 shaft
8.795 sq" less .837 sq" shaft area
7.958 sq" WOT.

90mm Accufab TB: ~1310.4 CFM (1096 CFM advertised)
3.543" opening, with .250" 1/2 shaft
9.861 sq" less .886 sq" shaft area
8.975 sq" WOT.

105mm TB (not produced*): ~1808.6 CFM
4.134" opening, with .250" 1/2 shaft
13.421 sq" less 1.033 sq" shaft area
12.388 sq" WOT.

* Not produced by any major manufacturer known to me, but I have seen an
80 and an 83 in print, (for SuperCoupe) but no listed manufacturer...
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