Location: Little Rock, AR, USA
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Poor man's LS1 ITB

April 7, 2010

I want to share a project in which I've fabricated a fairly economic alternative to the hugely expensive aftermarket ITB hardware for the LS series motors.

Economic aftermarket ITB options for this motor will run about $3600 and up for hardware alone (does not include electronic controls) and is usually designed for under-hood clearances (short, or laid on their sides). So I looked for a cheap alternative that would provide the traditional upright-runner appearance (for my specific application).

The parts I started with are:

Intake Manifold - Edelbrock Pro-Flow XT intake manifold. This is an 8-runner common plenum intake that is very tall and resembles an EFI version of a tunnel ram. Below is a couple of photos of the intake on the motor. The lower photo is a concept drawing of what I envision when this project is finished.




ITBs - Chrysler LHS throttle bodies. The 3.5L motor has two 48mm throttle bodies manufactured by Holley that are fairly straight-forward in that they lack most of the "garbage" that a typical manufacturer's throttle body contains. The box of throttle bodies bellow cost about $200 at the local pick-n-pull.



Materials to Put it All Together - various aluminum plates, screws, bolts, shaft couplers, etc.

Cost Comparison - With ITBs mounted, connected, and on the motor (no linkage thus far, total cost is less that $800 as compared to $2600 for comparable aftermarket set-up.


Let's get started!

First thing that had to be done was to modify the cheaper $400 Edelbrock intake (brand new, so this took some courage to put it on the table saw and start cutting it into pieces) to accept ITBs. This was done by cutting the intake in half through the center of the plenum. This way, all the runners were still rigidly held in place both at the base and at the top of the runners: 


Then I cut a wedge out of each runner near the base so as to make the runners more vertical and simultaniously separate the left and right banks from each other:


Once the banks were straightened out, they were welded up and the top was then cut off the runners exposing each individual runner:


Next a top mounting plate was welded over each runner. The plate then allows an adapter plate (for any variety of Weber based, or ITB hardware to be mounted) to be bolted onto the left/right banks of runners:


The Adapter plate had to be machined (drill press and some careful measurements) to transition the round ITB ports to the semi-rectangular LS1 intake ports. This was 3/4" aluminum plate that had the OEM Chrysler throttle body studs screwed into the plate to help index/align each ITB to their respective holes:



The ITB adapter plate is then bolted onto the runner banks:



Shaft couplers are used to connect the individual ITBs. These came from McMaster-Carr. The linkage to active the shafts was fabricated for a previous Weber 48 IDA set-up, but never used:


Tuning stacks are then fabricated to provide performance as well as aesthetic improvements in order for this induction system resemble what was used in the original M8B McLaren CanAm car:









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