Mark Kuzia wrote:
> Actually if you do a little more research you will find that many TB's are
> flowed at 25" hg versus carbs are flowed typically at 28". This does make a
> huge difference, air at 25" is less dense, therefore you will get higher
> flow numbers. I believe that 1000 cfm TB is more like 700cfm of a carb.
This would be a "frozen apples vs burnt oranges" comparison to me as throttle
bodies and carburetors are not even close to the same thing.
> Not everyone cares about 3500rpms and below, some people have big enough
> balls use their engine for all its worth, and when shifting, the rpms rarely
> fall below 3500 anyway.
Uh.....in my opinion Mark, you and a few others are the exception rather than
the rule as the majority stay under 3500rpms. We are still talking about
"street" driven trucks huh?
> Your right, 1000cfm is too much for a stock engine if you are talking about
> carbs, but with a F/I system, fuel atomization and velocity do not play as
> much a role as a carburetor. A fuel injected engine is able to handle VERY
> large cfm ratings without problems. If you check with Holley, Edelbrock, and
> Accell, and look at their aftermarket port injection style F/I systems you
> will notice that they use 1000+ cfm t-bodies on engines starting at 350hp.
I agree with most of this. But - how many on this list are even close to
350hp? Exception again.
I think Bernd was trying to say that different engines (and different purposes)
will require different flowing "air doors". I say air doors because that is all
the TBs really are. They provide a way for the PCM to translate what the driver
wants to do (pressing the gas pedal) into a voltage and/or resistance that is
then processed as just another input in determining what fuel and spark delivery
to provide the motor at that instant in time.
Other than being an air metering device - they exhibit a few flow
characteristics mostly recognized by their WOT flow characteristics. At WOT -
this is simply an orifice. Some are bigger - some are smaller. Some have a
venturi shape, some have a straight bore. Some attempt to change the way the
air flows at high rpm, some affect the low rpm more. These are where the real
differences are - not in the friggen size of the hole.
For example, take a 4800lb truck and run it in the eighth mile. This is pretty
typical of whats going on w/most Daks in a street-light to street-light type
situation. Guess what? I'll bet on the one with the stock TB everytime given
everything else being equal. Why? Because the smaller bore stock TB has much
better flow characteristics at lower rpms. Think about air speed - not air
volume. The stock TBs have faster air speed than a larger bore TB. Imagine how
much slower the air flows in a 53mm TB vs a 48mm TB at say 1800rpms. That
smaller orifice and especially that venturi design will cause the speed of the
air to be faster than the air moving thru that 53mm TB. This works just like a
mini-supercharger - and results in more air in the cylinder at the same rpm.
Light that fire and the stock TB will kick the 53mm TBs butt everytime. This is
the whole premise behind the cross-ram small and big block manifold designs in
the 60s. And those wedge motors still rule at the dragstrip. It applies to not
only TBs but also intake manifolds. Remember the stock "barrel-type" or
"beer-keg" design? This is an attempt by the factory designers to duplicate
that same cross-ram intake that was so successful in the 60s. It will smoke an
MPI at lower rpms. I know this because I have 2 identical trucks one with the
stock design manifold/TB and one with an MPI/49mmTB. In a short race - all
other things being equal - the MPI loses EVERY time. On the big end of the
track its a much different story tho 8-). And I know that some of you are
launching at over 2500rpms and this really don't apply to them - remember tho -
this is the exception not the rule.
Testing TBs on a supercharged V6 (assumption) is almost completely useless to
this group as far as I am concerned because I can't think of but maybe one other
individual (ViperTruck or something like that?) that might could even use the
results. I would rather see a test of a bone stock (ok maybe a few typical
mods) trucks (Reg -vs- CC, 3.9/4.7/5.2/5.9L, auto/manual, 3.55/3.92/4.10, etc)
w/a stock TB, vs several other TB designs in a 1/4-mile, 1/8-mile, 1000-ft, and
60-ft type scenarios. These results might be more valuable to a larger crowd.
I think you might be surprised of the results.
Furthermore (oops another book - I can't help it 8) I do like the billet TBs.
Not only do they look cool as $hit - but the designer is in total control of the
end result. To really impress me tho - would be a billet design that had
variable WOT flow characteristics at each rpm step. For example - with the TB
blades fully verticle (WOT) - at less than 2000rpms it might have a 45mm opening
- between 2000-3500rpms it might have a 49mm opening - between 3500-4500 it
might have a 52mm opening - 4500 to 5500 a 53mm opening and for you yahoos (LOL)
even an adjustable 5500+ opening that ranges from say 53-60 or so?????? Kinda
like a VTEC situation where different profiles are selected based on rpm. Thats
actually what the manufacturers intake designers attempted in the beer-keg
design. An MPI intake w/a variable-flow billet TB would work better IMHO.
Whew - thats enough for now...
Latr,
Shane
-- '96 IndyRam-HisIndy-MPI/TB/Pulleys/AccelCoil/MPComp/HookerSuperComps/CompTAs '96 IndyRam-HerIndy-numbered(#142)"Track Truck" '74 Triple-Black Dodge Challenger Rallye 360 home-brew EFI R&D vehicle '68 Black Corvette Convertible 427 (For Sale)
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