Look what I found -- a technote on how to do your own 52mm TB upgrade plus some interesting flow numbers on air foils:

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Converting your 48MM Stock throttle body into a 50-54MM tire burner!

CFM charts on a flow bench:

48MM Throttle body w/o airfoil: 783 CFM
48MM Throttle body w/a airfoil: 821 CFM

52MM Throttle Body w/o airfoil: 848 CFM
52MM Throttle body w/a airfoil: 898 CFM

Roughly we figure about 8.15 CFM per MM (understanding a TPI/LTI throttle
body consists of TWO holes, not one, so a 48MM throttle body is REALLY
96MM).

Airfoils appear to provide different increase results based on different
size throtle bodies. On a 48MM throttle body, it increases by about .40
CFM per MM. On 52MM throttle bodies, the increase is roughly .50 CFM.

So, assuming this math, a 50MM throttle body (100MM total) should flow:

Without airfoil: 815 CFM (roughly)
With an airfoil: 860 CFM (roughly)

Now keep in mind, that it really doesn't matter what your throttle body will
flow unless the rest of your system can keep up with it. For example,
a stock Bosch MAF sensor with screens flows only about 520 CFM, and with
the screens taken out, its barely 660 CFM.

If you have an 85-87 TPI car, your induction can only flow about 500 CFM.

Suposedly 1988-1992 induction assemblies flow a bit more. In fact, SLP uses
the rubber plumbing and only provides a different airbox for their "1,000
CFM cold air assembly".

On a side note, SLP also up until recently manufactured 52MM throttle bodies
by using new plates, and boring 48MM units. SLP sold these units for
$399.00. The people who made their plates went out of business, so SLP had to
discontinue selling this item.

So taking your motor and breathing requirements into consideration, here
is my warning.


Warning!!!

52MM Throttle bodies can flow over 800 CFM, and up to 900 CFM
with an airfoil.

54MM throttle bodies can flow over 900 CFM, and up to 950 or more
with an airfoil.

Unless your motor is heavily modified with a combination of the bellow
recommended items, you probably should not consider going to more than
a 50MM or 52MM bore.

A) Have bigger heads
B) Have a big cam
C) Been bored over
D) Have a high Flowing intake
E) Produce at least 315HP w/out nitrous or a blower

Obviously what we're trying to say is, flowing this freely will cause
air speed to slow down, thus low end torque will suffer, and your car might
not even make it to the RPM range required for power. However, on a built
up motor with breathing problems this may be the ONLY solution.


So with that said, on with the requirements!!


Part requirements:

- 52MM

Two single 52MM throttle bodies from 2.8 MPFI or 3.1 MPFI GM cars
(camaro/firebird, some buicks and olds, etc)

Holley also sells 52MM throttle plates.

- 54MM

54MM plates can be machined, or you can use two plates from newer
5.9 liter EFI Ford crown victorias. These plates are 65MM, and MUST be
machined down to 54MM, or whatever size you choose your bore to be.

You can also bore the holes to 68MM and sleeve them if you wish.


Labor requirements:

About 2 hours, perhaps more if bolts snap and need to be
re-tapped. My throttle body dissasembly was 30
minutes. (This does not include machine shop time requirements)


Machine shop requirements:

Match boring of the dual 48MM throttle body, to match the plates. It is
HIGHLY recommended that you make your plates, or find plates FIRST - then
have a machinest match your bore. This will keep consistancy, and also will
allow the bore to be of the same "clearance" as factory.



Theory and practice: (52MM method)

What your doing essentially, is utilizing a 52MM throttle plate (two in fact)
from a 2.8 or 3.1 MPFI GM car. These cars use a 52MM size plate, to compensate
for the lack of a duel air inlet. TPI V8 cars use dual 48MM inlets.



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P H A S E O N E

Throttle body dissasebmly:

1>

Its best if the throttle body is completly dissasembled. The machinest will
appreciate it, plus it will give you an opportunity to clean the entire unit.

2>

Using a T10 torx bit, remove the screws holding the bottom peice (where the
IAC and colant lines come in), as well remove the top "Tunes Port Injection"
plate.

3>

Using a T8 torx bit, remove the screws holding the throttle plates on the
aculator rod.

4>

Remove the throttle position sensor.

5>

Using a die grinder, grind down the bevels on the opposite side of the screw
holes - this will allow the acuator to slide out after the next step.

6>

A rectangular area is beveled where the TPS connects to the actuator rod.
This needs to be ground down so that the TPS lever can be pried off (carefully).

Grind this area down, and evenly pry off the TPS lever.

7>

Remove both washers under the TPS lever, and using a small punch tool and
a hammer punch the acuator rod out of the throttle body assembly.

Remove the plastic spring retainer from the throttle body assembly.

The throttle body assembly should now be ready for machineing. Your machinest
should have:

1) The throttle body
2) The old plates for clearance matching
3) The new plates for bore matching


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P H A S E T W O

Throttle body re-assembly:


NOTE: It may be required to slightly machine the actuator rod, if the new
plates exceed the outer alignment. Use the die grinder to make this modification
if neccesary.


1>

Install plastic return spring retainer into throttle body, and push actuator
rod into throttle body assembly.

2>

Insert new throttle plates into assembly, and screw in. Tighten well, but do
not overtorque or the screws may snap.

3>

Install washers back into acuator, and install TPS lever. You will need to
tack or mig weld the TPS lever. If you cannot weld it, you may drill and tap
a small screw and washer into the actuator rod.

4>

Install TPS sensor, do not overtighten as adjustment will be neccesary.
Install "Tuned Port Injection" plate, using a new gasket or sealer. Install
bottom plate ensuring to use a new gasket or sealer around IAC
ports. (Or whole unit if re-connecting coolant lines)


Your throttle body is now ready for use. Ensure that you use a new throttle
body mounting gasket. It is highly recommended that the plenum be ported
to match the new throttle body bore size. Stock plenum holes are roughly
50MM.

If a small hole appeared in the top of one side of the throttle body, fill it
with JB-weld or similar epoxy, and smooth it out. Its not needed.


www.joesperformance.com
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That's interesting stuff.
Being as how a Busch MAF sensor can only flow about 660 cfm,
I've been checking into airfoils and what it is they actually do.
If I'm right (correct me if I'm wrong) they basically straighten or smooth the air stream to give a higher flow.

A question for the guys using them. Did you notice a difference at all?
They are suppose to be worth the money. Just like to know, cause it is an inexpensive mod.

 

i dont think that all your facts are right. 2x 48mm do not =96mm its a much smaller area. also TPIS rate a 48mm TB at only 668 cfm and 709 with their air foil. that a big difference forn the # you gave. where did you get your flow # from.

TPIS also only claims to get 40 cfm with their air foil in a stock TB. If thats the case i would bet that the real # would be even lower.

the 40cfm is also based on the fact that the hole induction systeme has been moded for better flow.
in a complete sys you can only expect to see cfm of 585 and thats with a high flow filter jutted MAF modded air box and a sir filter.

if your induction could flow 780cfm that would be enough air flow for a 400hp engine.

the # you gave seem to good to be ture.
also one last thing air pressure was use to get the flow rates. they will make a big difference like when some one talks about cams and are not useing @.50 lift they can cheat with numbers

 

next dyno day we can do some runs with mine out and in. i did a number of other things at one time so i can not say if it was a big difference.

TPIS claimed on a FULLY moded 350 they got 13 hp increase they dicribed a fully moded engines as siamesed runners,port and polished heads, max ported base, AFPR, roller rockers, cam and a fully moded induction(filter,MAF etc)

i think it will help more and more as your engine flows more.

 

It seems with these engines every little bit helps. Trying to squeeze as much air in and than get it out again.
Sure is easier on carbed cars.
Is it possible to ram air a MAF engine? I know it won't come up on a dyno, but for example, on 92zeddars (non MAF) car with the ram air, wouldn't that car have more hp on the road then the dyno shows?
Just food for thought.

 

Hi Scott,

They aren't my facts. I got them from www.joesperformance.com (I left the link in at the bottom of the technote). I wish they were MY facts cause then I would be alot less ignorant of what makes these things tick -- but I am not an engineer and couldn't say if the numbers are correct or not ?

The article's author seems to have an idea of what the issues are or atleast sounds like he's done homework so I put some stock in what he had to say. I found the airfoil points interesting and I think this is the first time I have read a non-TPIS source on airfoils. I don't put alot of merit in what TPIS says because I am never clear on their test methods plus I am always being 'sold something' when I call them to ask.

Basically it is a discussion on TPI cfm and how to improve the TB cfm performance level. I don't think he claims HP gains in the article.

RP.

 

I think the MAF system is at a disadvantage when it comes to air flow, compared to a speed density system. And I think this technote makes it clear -- with or without air foils. The MAF definitely has a choke point. Can you get larger diameter MAFs for 3rd gens ?

I have an SD so have nothing blocking my TB upstream like a MAF therefore the only restriction for say, a cold-air, is room to run the input tubing. In fact I had a 4 inch tube drawing air into my TB at one point but it got munched by the A/C compressor spinning -- too bad it worked really well until that point.

Now if I installed an airfoil and/or larger (50mm ? 52mm ?) TB I think I might see more cfm because I have no restrictions between my cold air and the TB. Not sure if my 305 heads/cam/exhaust could flow enough to take advantage of the increased cfm ?

I am going to try an air foil and will post the results.

RP.