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Herd WebMaster
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Posted - 05/07/2007 :  11:12:33 AM  Show Profile  Visit Herd WebMaster's Homepage  Reply with Quote
1LE Throttle Body Inlet Duct:
By Scott Mueller.

I have some more information on the 1LE throttle body inlet duct that I installed on my Impala early in '94. For those of you who are new to this, this is a replacement for the stock rubber elbow duct that has the large triangular intake silencer (heimholtz resonator) attached to it. If you remove the silencer, then your stock duct has a big hole in it, which would need to be capped. I do not recommend capping this hole in the stock elbow since GM has available a replacement duct that will fit, does not have a hole, plus flows much more air!

The F-car (Camaro/Firebird) duct not only eliminates this hole, but has a much larger internal diameter especially around the bend. The B-car intake duct is by contrast much more restrictive. In my opinion, this would be a much better use of your money than these so called "airfoil" devices that go on the throttle body!

The standard F-car intake elbow does include a hole on the bottom for a tubular induction silencer (resonator) that serves the same function as the large triangular one on the B-cars. This tubular resonator connects to an oval shaped lip on the bottom of the intake elbow. On F-cars with the 1LE racing performance package option they use a version of the inlet duct that still has the oval shaped lip protruding from the bottom, but the inside hole is not cut through. In other words, they must use the same mold for both the 1LE and standard versions, but only cut the hole through for the baffle on the standard version.

If you want to look this part up in the F-car parts catalog, note that the book shows two different ducts for a given model year, one used WITH A/C (C60) and one WITHOUT A/C (C41, base heater only). Since the 1LE package cannot be ordered with A/C the ducts are listed according to whether the car has A/C or not, and the 1LE package is not actually mentioned. The way GM does it is that all A/C (C60) equipped F-cars get the elbow duct with the lower silencer hole cut through, while only non-A/C cars (C41) get the duct we want, which does not have the silencer hole cut through.

Note also that there are two versions of the elbow, which does not have the silencer hole. One was used in '93-'94 and does not have the little nipple on top for the distributor vent, which was absent on these cars. The '95 and up version has the little nipple, which is for the distributor vent tube that was added in '95. Here is a summary:
Description Part Number Price Comment
94 1LE F-car Duct 25147210 $70 w/o distributor vent nipple
'95 1LE F-car Duct 25147187 $84 with distributor vent nipple

These ducts include the MAT (Manifold Air Temperature) sensor, in fact you cannot order them without it. Also, the prices here are not the LIST price, but are what my dealer will sell them to me for. I would say that if you are paying much more than this, you might want to ask for trade pricing (or some other type of discount), or try another dealer.

The '94 and up B-car LT1 and '95 and up F-car and 'vette LT1 engines have a re-designed front distributor and distributor drive system. This newer system features an air vent tube that is installed into the stock throttle body inlet elbow. This was done to eliminate the problems they were experiencing with LT1 engines and moisture in the optical distributor system. Since it is mounted on the front of the engine down low, it was susceptible to water splash from wet roads, and also from coolant leaks in the thermostat and water pump area. This vent can be seen as the tube with the little blue elbow on it that sticks out of the top of the throttle body duct on your Impala. F-cars (and 'vettes) did not get this new setup until the '95 model year. BTW, the new distributor drive system also means slight changes to the end of the camshaft, the water pump, and of course the distributor itself.

When I ordered my 1LE F-car inlet duct in '94, F-cars still had the old non-vented distributor, which meant that the duct did not have the little nipple on it for the distributor vent tube. That was fine by me (actually preferred), since I just pierced the duct and installed the vent tube elbow in a hidden area on the inside of the elbow bend, where it cannot be seen from the front of the engine. The '95 and up F-car 1LE duct has the little nipple on it for this tube in the same place as the B-car duct. Again, I prefer the '94 version of the duct since it allows me to hide the distributor vent tube, plus it is a little bit cheaper.

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