TB Bypass? - Chevy Impala SS Forum
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post #1 of 8 (permalink) Old 09-10-2001, 08:09 AM
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Can someone please tell me what this does & how to do it? Thanks in advance!
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post #2 of 8 (permalink) Old 09-10-2001, 10:06 AM
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The ThrottleBody Coolant Bypass (aka TB[Coolant]Bypass) defeats a factory designed safety feature which was only needed in cold, humid climates by engines which mixed fuel into the air before the intake manifold.
Very hot - steamed? - coolant is routed right from the heads directly to the throttlebody, and then on to the coolant reservoir. This keeps the throttleplates from freezing stuck in an open position, and condenses any steam in the coolant by adding heat to the air ingested by the engine.
Hotter intake air robs horsepower, and increases the chances for ping and knock.
The TB Coolant Bypass prevents coolant from heating the throttlebody by sending it directly to the coolant reservoir.
I suspect that it's worth one tenth the ambient heat index in terms of horsepower. In other words, if you live in a climate where no one ever wears bathing suits, you may not want to do this mod.

0) Incidental advice mostly amounts to temporarily setting aside the intake, the hose from the valve cover that leads to the TB, and the Throttle Position Sensor connector. AND DON'T GET ANY COOLANT ON THE OPTISPARK DISTRIBUTOR (that thing behind the waterpump)! I CAN'T STRESS THIS ENOUGH!
1) Pinch off, then disconnect the coolant line connecting the throttlebody (driver's side, by the throttle cable) to the coolant reservoir, at the reservoir. Allow it to drain. When drainage is complete, reconnect the line to the reservoir.
2) Disconnect the same coolant line, this time at the throttlebody. Put a rubber cap on the opening you just made[on the throttlebody]. Set the hose aside so it doesn't drip, or drain it just in case.
3) Locate the throttlebody coolant feedline (between the passengerside valve cover and the intake manifold), and its connection to the under-and-passenger-side of the throttlebody. This connection is probably a small piece of rubber hose bent 90 degrees held by two [email protected]$$ squeezeclamps. If you are indoors, turn the AC on (not the car's), and prepare to swear.
4) Do whatever it [email protected]#ing takes to remove[and dispose of]that connection and those damn clamps. In the absence of 4 agile hands and/or the proper tools, this will be VERY trying, so feel free to take breaks.
5) Once you finally sever[and dispose of]the connection between the coolant feedline and the throttlebody, take the line hanging off of the coolant reservoir and connect it to the coolant feedline.
6) Either blow out or suck the remaining coolant from the throttlebody. Close off the throttlebody's coolant passages with some rubber caps, or whatever.
post #3 of 8 (permalink) Old 09-10-2001, 10:47 AM
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Some others maintain the whole reason for its existance is to condense the steam before going to the resivoir. Either way, I did it to one of my bbodys with no ill effects.

post #4 of 8 (permalink) Old 09-10-2001, 12:22 PM
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Thanks Cheavy for the details! I appreciate it very much and will give it a shot when I get some free time.
post #5 of 8 (permalink) Old 09-10-2001, 02:19 PM
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A word to the wise. in an effort to get the damn hose of the passenger side of the TB, DO NOT PUT ANY LEVERAGE ON THE TPS (Throttle Position Switch) - it Snaps real easy !

post #6 of 8 (permalink) Old 09-10-2001, 03:02 PM
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Been there, done that. Actually, mine was an edge of the clamp underneath the TPS was caught on the TPS and cracked it coming out.
post #7 of 8 (permalink) Old 09-14-2001, 02:05 PM
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I just happened to do this mod today, and the procedure above is pretty good...I found that the little elbow on the passenger side, with those DAMNN clamps, was easier to just cut..i cut at the bend, then just grabbed the damn hose with some pliers, and slightly twisted as i pulled the hose of...mine was melted onto the throttle body or something, cause i could not get it off till i cut it..there just isn't enough space..good luck!!
post #8 of 8 (permalink) Old 09-14-2001, 07:39 PM
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I did this before last winter(it was a bad one here), and had no problems. So the Denver weather did not hurt, but if I lived in Alaska though I would think twice.

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