"TB SIZING and FLOW RATINGS CHART"
"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
make
> 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
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.
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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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