Hard Parts For Your Fuelie Part II

throttle body

In the last segment of Hard Parts For Your Fuelie, we took a detailed look at Holley’s modular Hi-Ram intake.  If you recall, the Hi-Ram is essentially a modern high tech tunnel ram arrangement that can accept carburetors or throttle bottle injectors.  There’s a special top available that allows you to use a lower profile air intake with a front mount throttle body.  Holley offers several different throttle bodies for this application – 90-mm, 35-mm, or 105-mm models.  In this article, we will take a look at each of these. The 105-mm job is available with either a straight bore or a  tapered bore (we’ll get to the differences down the page).  FYI, the various throttle body mandate a specific manifold top.

For our purposes, we’ll zoom into the 105-mm jobs (with photos), but the 90-mm and 95-mm models are much the same.  The smaller billet Holly throttle bodies are all built with what Holley calls a “Low RPM Taper”.  That means that there is a tapered transition machined into the body that eliminates low speed (low RPM) drivability issues.  Essentially, tapered models offer more pedal to throttle travel at low engine speeds to improve drivability on street and similar applications.  As pointed out above, the 105-mm throttle bodies are available with a taper or with a straight bore.  Throttle bodies without tapers are maximized for “RACE ONLY” applications.  The actual throttle bores in all of Holley’s throttle bodies are larger compared to those found on competitor’s throttle bodies, too.

Holley uses a unique TPS “clocker” that allows the TPS to be rotated back into the ECU’s required idle voltage range.  As a result, modified engines no longer suffer from problems related to TPS voltage.  A PCV passage valve is included in the throttle body.  This means that in forced induction applications, there’s no need to physically block the PCV port.  Additionally, the PCV port can be rotated if there is a need for a different (than stock) orientation.

Holley also fits the throttle body with a bleed screw.  Now, assuming that an engine has a very long duration, high overlap camshaft (with low manifold vacuum), a situation may exist where it is difficult to tune a poor idle by way of the ECU.  With Holley’s throttle bodies, the included idle bleed is an adjustable passage around the throttle blade to increase idle performance, if needed.  The bleed screw allows idle adjustment without affecting blade position and TPS output voltages at idle.

The actual body is machined from billet aluminum.  You’ll note that the throttle plate is “slabbed” (heavily profiled) to improve airflow.  The body is black anodized too.  This means that it is resistant to corrosion.

All of Holley’s premium throttle bodies are engineered to work with cable drives.  All have a cruise control provision as well.  In terms of applications, Holley points out that the throttle bodies fit the following intake manifolds: Stock LS2, Stock LS3, Stock LS7, Holley LS Mid-Rise, Holley Hi-Ram (85 and 105-mm tops), Fast™ LSX, Edelbrock Pro-Flo XT using 4 bolt TBs as well as most other 90 through 95-mm LS intakes using 4 bolt throttle bodies.

Finally, Holley offers a throttle cable bracket for the big 95-mm and 105-mm throttle bodies used on Hi-Ram and Mid-Rise intake manifolds.  This bracket has an allowance for throttle pedal adjustment or the addition of a nitrous plate.  It works with throttle cables from 1998-02 5.7L Camaro and Firebird (GM Part Number 12563339) or aftermarket versions patterned after the GM component.  You can also fit a cruise control cable from the same applications (various GM part numbers).

For a closer look at the billet throttle body, check out the following photos:

throttle body
Holley manufactures several different billet aluminum throttle bodies. This is their large 105-mm job with a special low RPM taper. This means it is very streetable. The text offers more information.
throttle body
Looking at the throttle body head-on, you can see the large slapped throttle plate. It’s carefully contoured to ensure maximum flow.
throttle body
Here’s a look at the backside of the throttle body. The basic configuration fits a wide range of intake systems, although in this particular case (105-mm), you’ll need a dedicated intake (top) to accept the large bore.
throttle body
It might not look like much, but this bracket is important. It allows you to hook up the throttle body to a conventional production line GM cable. It also allows the installation of cruise control (cable) using factory parts.

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