Which Intake

[Greg Hermann]

>Frederic Breitwieser wrote:
>>
>> > concern is where the throttle blades are located. The turbo will
>>quickly lose
>> > rpm with the blades after the turbo. To counter act that condition  a
>>relief
>>
>> But, if you place the throttle blades BEFORE the fresh air
>> side of the turbos, for a few seconds anyway, the turbo will
>> keep pressurizing the plenum while creating a vaccum on the
>> pre-turbo side... thus giving you less throttle reponse when
>> you let up on the gas pedal.
>
>
> Don't you want less throttle response when you let up? (sorry, Fred..
>couldn't help it on that one) Vacuum is good. <grin>
>
>>  Most OEMs, as far as I can
>> tell, place the throttle plates after the turbo, and I
>> copied this on my twin-turbo setup, with two throttle
>> assemblies.
>
> I can't vouch for what most OEM's did or didn't do, but I can tell ya
>what GM did on the Buicks. (I know the carbed cars had it before the
>turbo) The 84/5 non-intercooled turbo cars had the throttle body before
>the turbo. Maybe it's just me, but I feel that the vacuum caused when
>closing the throttle quickly, is actually is easier on the turbo than
>the "fart" caused when hammering the throttle shut, with the TB after
>the turbo . (such as my car does now) I do feel that the non-intercooled
>car's turbo's lasted longer, due to this design. No air (vacuum) =
>nothing to hammer the bearings.
> No matter what way it's done, they both have their advantages /
>disadvantages on different buildups.
> Either way works quite well. IMO :)

Hi Dan--

No question here that a draw through throttle set up will give you better
spool up from a turbo, shut-down lag is negligible, although a bit more
than with a blow through. You do need the premium compressor seal in a draw
through turbo.

I SUSPECT that the main reason why most mfgrs go with blow through set-ups
is because of the length of the emissons warranty they must meet--lose a
compressor seal, and the impact on emissions is VERY distinct and
immediate!

Also, with a properly sized compressor, their is NO WAY you ever put your
compressor into surge with a draw through set up. Nor, contrary to popular
old wive's tales, are you in any danger of overspeeding your turbo under
vacuum conditions. (To verify this statement, look at how turbos behave on
aero engines at higher altitudes.)

As far as I am concerned for a custom turbo set-up, draw through is the
superior way to go UNLESS you are using a VATN type turbo. If I ever get
around to figuring out a way to control the variable turbine vanes on a
VATN while running one of them in the draw through mode, I would be highly
inclined to use them that way too!

Regards, Greg
>
>
>***********************************************************************
>Dan Smith      84 Regal   12.13 at 112     GSCA# 1459
>St.Charles, Missouri
>mailto:dcsmith at bytes.net
>mailto:dcsmith at gnttype.org
>mailto:morepoweral at bytes.net
>mailto:morepoweral at gnttype.org
>mailto:morepoweral at tetranet.net
>mailto:smithd at fsi023.flightsafety.com
>http://www.tetranet.net/users/morepoweral
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