Decades old question that has been long since answered. A tailgate down
or removed will actually increase the trucks drag rather than the
expected decrease. In tests I have seen the resulting mpg change is
negligible. If your intent is to increase mpg then you'd be wasting your
money with a vented tailgate. If anything it would go down but more
likely no measurable difference.
Thanks to everyone who responded it really helps with a new baby. I
don't want to be spending any extra money if it's not going to help me
save any money in the long run. What is everyones thoughts on a K&N
(http://www.knfilters.com /) products would anything like that help me
get more MPG or would that be just a waste of money too? I really
don't care too much about the MPG if if it's a drastic increase I
wouldn't mind adding it to the truck. I used to have a diesel and I
was putting $90+/- a week into it now I'm only putting $60+/- a week
and that has been saving me a lot of money already.
Where is this cold air coming from? Usually from the engine compartment.
Anyway no matter where it get's the air it travels through a tube that is
hot as hell, so any cool air is now heated. The getting isn't worth the
going on a stock engine imo
Yes but depending on the material used any transfer of heat in the split
second the air travels through the tube is negligible. Some of the all
metal single layer tubes I suppose could conduct too much heat.
Roy, what is your point? Are you saying that the old fashioned air
cleaners that sat above the engine and drew hot air from INSIDE the
engine compartment is just as good as a ducted system that pulls in air
Cold air from outside the engine compartment can give gains on many
vehicles which when stock pull hot air from inside the engine compartment.
If you are talking about a cowl induction from days gone by I'd venture that
the cowl induction is better. Direct shot of coldd air into a carb.
If you are talking about today, by the time the "cold" air travels through
the filter and through the hot tube to the tb it is no longer "cold" and not
of much if any benifit to a truck running along at 2500-3000 rpm that is
having it's air fuel mix controlled by a 'putor.
Here's the thing Miles, the air is not pulled in it is forced into the
filter by the speed of the truck. If the speed of the truck isn't in excess
of 80+mph there isn't a whole heck of a lot happening.
That simply isn't true at all. For that to happen heat would have to
conduct rapidly through whatever material was used for the duct. You
would be correct for some of the cheaper thin walled plastic that could
conduct heat. However, the better styles are double walled or made of
thicker materials that don't conduct heat all that well. The air is
traveling through the duct much too fast to heat up appreciably.
What type of truck are you talking about here? Very few trucks have
forced air intakes. We are talking about stock trucks. They are not
forced. Cold air drawn in is preferable to hot air from inside the
engine compartment. A proper duct will not conduct significant heat to
the air being drawn in.
Let me try again. The material that the tube is made from is going to aquire
the same temp. that the rest of the engine does, or darn close to it. That
heat will transfer through the walls of the tube so that the inner wall that
the air is passing through is also the same temp. Now you introduce air that
has already been slowed by the hot filter and then has to proceed through
the tube to the tb. Seeing as it isn't a forced air induction there isn't a
heck of a lot of velocity moving it. What makes you believe that this air is
moving so fast that it won't pick up heat from whatever it travels through?
The air will pick up a bunch of heat as it passes through the filter and
tube. Thus the gain in performance or mpg compared to factory is going to be
Sure it is. But you aren't going to get there by changing the tube and that
is pretty much what you have done. Heat is heat whether or not it is the
factory tube of aftermarket
You are saying that a tube heated for a hour or so in a stock truck in
normal driving won't transfer the heat to the air that passes through it
with zilch for velocity?
Miles, I played with forced air on drag car's years ago. True it is now old
tech, but pretty much the same deal.With a hood scoop and a velocity stack
sealed to the scoop, good for maybe 1/2 second in the 1/4. That is on a
modified engine at wot. That is with cold air being stuffed dirctly into the
carb through a cold 6" tall velocity stack with no filter at at all.
You won't see that on a stock truck under normal use with a your tube and
filter. You won't notice a mpg change that will offset money spent on the
tube and filter imo.
No Roy. The engine metal temp is much hotter than the compartments air
temp but I assume you meant air temp.
With that logic your homes A/C would not work. It travels through duct
work often through attics that can get quite hot. Here in Phoenix my
attic can get well over 120 degrees yet I have nice cold A/C coming out
of the ducts which travel through that temperature.
It takes time for the air to heat up. How long does air take to travel
through the duct in your view? Again, with your logic your homes A/C
would not work very well. The velocity produced by the A/C's fan on say
low isn't very much. The engine does draw in air more than fast enough.
Tell me Roy. Why do so many auto manufactures install ducts to the
outside of the engines compartment when doing so costs extra money if
according to you there is nothing to gain?
I change the duct from one that draws air inside the engine compartment
to one that draws it from outside.
We aren't talking about a/c. We are talking about the benifit of this setup
on a stock daily driver truck.
For the same reason they put big assed decals on them and tell people they
Some do, some don't.. DC didn't with the Charger SRT8, and the SRT boys were
after all the go that they could get.
But this is a stock truck, remember.
Hmmm. Answer the question. No heat transfer after the truck has been
operated for a hour or so.? Where are you getting all this velocity after
The length of time is irrelevant. Heat is heat and the ability of that
heat to transfer through the plastic enough to heat the air running
through the tube is negligible especially if per you it would take an hour.
Your splitting hairs miles I said the drive the truck for a hour. Drive it
longer. The continueing heat transfer is still there. No where is the
velocity comeing from.
It still won't help a stock truck.
The heat would have to transfer through the tube wall fast enough to be
able to heat the air passing through it in the time that air spends in
the tube. It makes no difference if you drove an hour or 5 hours.
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