[V8] gearbox swap questions

[Scott Justusson]

 There are those that have been there done that on a dyno, and those that believe the theory that a dyno will not vary it's calculated 'hp' number based on 'other than engine' variables..  I too have seen significant (20-30hp) differences between 5 and 6 speed transmissions, because driveline "dynos" are inertia calculators.  Which means any changes that affect inertia calculations is a VARIABLE to the calculated result.

That would include gear change, final drive change, rotational mass, tire slip, gear mesh and even stabilizing the torsen torque split.  Been there seen that.

Anyone that wants to claim that is not the case, doesn't understand what Scott (now x 2) is saying.  Never did he claim, nor do I, that the *engine* is in fact gaining or losing HP/Torque.  What goes to the ground changes, and significantly, which is exactly what the inertia dyno will indicate as a true statement.  How much change?  Depends on the dyno software, and the black box software correction factors within the calculator.  Even how well the tech put the tires on the rollers....

I've seen it, with no other changes than transmission.  You can tell me it's something else, I call that the difference between understanding a dyno as a tool, and it's theoretical ideal.

My .02

Scott J
92 v8 ABT Chipped
91 v8
91 200tq 20vt


 

 

-----Original Message-----
From: Scott DeWitt <scotty at advancedautomotion.com>
To: john <john at bysinger.net>
Cc: V8 at audifans.com <v8 at audifans.com>
Sent: Mon, May 27, 2013 4:55 pm
Subject: Re: [V8] gearbox swap questions


Professor GT is correct a transmission will not make an engine produce
more power, however that is not what I said. I've been part of dozens of
C5 5hp24 to 01E 6speed swaps and can tell you an engine will register more
wheel hp with a 6 speed than with the 5HP24. Ive seen before and after
dyno charts which show this. No where did not say the engine would make
more power due to the lack of a manual. Mr. GT took it to mean something
else.

Fuel economy is also improved considerably.

Automatics are also not more efficient than manual transmissions (I don't
care what automatic we are discussing), an Automatic trans has a torque
converter which can have double digit inefficiencies depending upon what
torque converter we are discussing, and an automatic has a fluid pump
which unless the laws of Physics have changed consumes engine power to
run. This is power that does not reach the wheels.

Also VW/Audi have seven speed DSG transmissions which are essentially a
computer controlled manual trans which have remarkable better efficiencies
that a traditional automatic trans. Porsche has it's 7 PDK based off a
similar design. Although the DSG transmission do have a fluid pump to
power the hydraulic actuators and clutch packs, they do not have a torque
converter hence one reason why DSG's are more efficient.

But I digress the point of this thread was swapping a 5hp24 into place of
a 4hp24, not the newest ZF transmissions.



Scott









On Mon, May 27, 2013 3:50 pm, John Bysinger wrote:
> Scott, he's right.  Though the only real correction has to do with the
> power conversion of a torque converter, there are torque gains at a cost
> of
> hp losses during launch/acceleration.  (Though I'm pretty sure he's aware
> of that, just simplified it for arguments sake.)  But for the purposes of
> accelerating that's exactly what you want, and it doesn't negate his
> argument.  There is _nothing_ a transmission can do to increase hp.  Ever.
>  With regards to his discussion of gearing, and why the industry is moving
> to automatics he's spot on.
>
> I think the reason why automatics have a bad rap from the
> aftermarket/tuner
> crowd is there is an illusion of more power with a manual.  You can hold
> out on shifting past the ideal point and hear the beautiful sound of the
> engine screaming towards the redline, a very addictive feeling, but not
> the
> most efficient method for extracting the most power you can get from the
> machine.  Unless you're driving a Nissan GT-R with the gizmo-dash that
> shows you live power output readings, and have skill like the Stig, odds
> are your shifts suck compared to a modern automatic's computer.  Combine
> that with the slushbox reputation that older (sloppier) automatics had in
> the 70's and 80's and you have a perfect storm of misinformation.  It's
> easy to lump our older V8's into the slushbox category because of it's
> age,
> but you're talking about a transmission in what was Audi's flagship that
> was years ahead of mass production cars at the time.  Combine that with a
> trans computer that pretty much lets you do what you please in manual mode
> (without all the modern nanny-safeties like forcing shift before redline),
> you have something as close to the best of both worlds as you can get.
>  Really the only thing missing is that your left foot is bored.  This is
> why you'll find most people on this list giggling at stories of 'power
> gains', your argument might be valid for an early 90's Honda Accord, but
> not for the car/trans we're discussing here.
>
> That said, I'm a sucker for a manual, they're fun.  Lots and lots of fun.
>  And I too like to use my left foot while driving.  Plus you CAN do things
> with them that an auto won't let you, but those things aren't going to
> magically add power or get you there faster, mostly because they're the
> opposite of what you should be doing.
>
>
> If he's wrong, maybe I should ignore my BSME since it obviously taught me
> incorrectly. :)
>
> -John
> '91 V8
>
>
> On Mon, May 27, 2013 at 11:04 AM, Scott DeWitt <
> scotty at advancedautomotion.com> wrote:
>
>> It's apparent you know very little about the subject so I'll end the
>> conversation with a Happy memorial day!
>>
>> Scott
>>
>>
>>