C5 Modifications To Avoid

By Al Engel

Corvette owners seem to be tinkerers. On the older Vettes we could play with timing advance, timing curves, carburetor jetting, etc. without dissembling the engine and getting into the engine internals. The computer controls of the C5’s LS1 engine remove any ability to adjust timing or fuel mixture...unless you "trick" the computer. Now I know some of you are saying "Just a minute Al, you can reprogram the PCM to yield different timing advance schedules, mixture ratios, RPM limits, etc." This is true, BUT any such software modification requires a high level of understanding and experience to improve on Mr. Goodwrench’s factory calibration and any such tinkering will void your factory drive train warrantee.

For the above reasons, "Go Fast" after-market suppliers of horsepower enhancing parts are focusing on the pieces that trick the PCM into applying the old fashioned and proven HP enhancing ingredients…timing adjustments and fuel ratio modification. Some of these do provide meaningful "seat of the pants" (SOP) horse power gains, some only provide marginal improvements that do not translate into measurable performance improvements, others either don’t work…or produce negative gains...and some are dangerous. (See me and I’ll share my two favorite, backyard mechanic HP enhancements that provide real SOP improvement, and do not void your Goodwrench warrantee).

What I want to talk about today, however, are two popular "snake oil" remedies being pushed by the after-market boys that promise gains in horsepower, but in my opinion, provide no SOP improvement, are harmful to your engine (and its performance), and are potentially dangerous. The two products we will look at in this article focus on temperature tricks that attempt to cause the PCM (Power Control Module, a.k.a. the computer) to lengthen the injector pulse width (make the mixture richer).

Snake Oil Elixir # 1: The "Throttle Body Coolant Bypass Tube", $19.95: The claim is, "cooler air through your throttle body = more HP". My Opinion: Under "ideal conditions", the TBCBT might reduce the intake air temp by less then 1/10 of a degree. Not enough to provide even 1 HP of improvement. Think about it…. Where do you produce peak HP? At the high end of the RPM scale, say 5,500 RPM. How much air is that LS1 gulping at 5,500 RPM at Wide Open Throttle (WOT)? About 650 Cubic Feet of air per Minute (CFM). 650 CFM moving through a hole less the 75 cm in diameter is moving at a speed well in excess of 250MPH. The Snake Oil salesmen are trying to convince you that the small area of the throttle body affected by the presence of warm engine coolant will pick up a meaningful amount of power robbing heat. The area of the throttle body heated by the engine coolant is a tunnel less then 2 inches long. At 250 MPH in air velocity the air molecules do not hang around in the heated throttle body long enough to pick up any heat. There is no meaningful heat pick up to the passing air through a "stock" throttle body assembly. A waste of $19.95, and the chance of a serious problem being created.

The throttle body, as described above, moves a lot of air, at very high velocities, in conditions of vacuum. The laws of physics state such a condition will rob heat from the surfaces in contact with this flow. In conditions of humidity, ice may form at the critical location of the throttle butterfly, freezing its ability to move (translate this ice induced paralysis into an inability to close the throttle). Throttle stuck open, car and engine accelerating, sharp curve ahead, and you want to decelerate…do you see a potential problem here? The purpose of that coolant tube is to prevent "icing" of the throttle body. "But Al, I only use my C5 in the warm weather." Great, I like it warm too. So does your throttle body. Icing can occur at temperatures well in excess of "freezing" ambient temperatures. Two NASCAR accidents (one resulting in a driver fatality) in Brookline Mass this summer were attributed to "stuck throttles", most likely ice induced. This is a modification, that in my opinion, provides no benefit, and a very real possibility of a serious derivability control issue. Don’t do it!

Snake Oil Elixir # 2: The 170 Degree Thermostat. $69.95: Claim, "lower engine temperature = more HP and greater engine life". My Opinion: "BS." Anyone need a translation of that one? Fact: the LS1 engine develops its best, dyno proven HP and Torque at 195 – 210 degree operating temperatures. Fact: water vapor (condensation) in your oil is an enemy to the durability of your engine… and condensation is inevitable in any situation where metal goes from hot to cold (whenever you turn the key to the "Off" position). There are two ways to remove condensation from you oil: 1. Change it; 2. Get the oil temperature to a level where any water in the oil will boil off as steam, be drawn into the combustion process through your LS1’s PCV system, and exit the engine as water vapor out the exhaust pipe. To do this "boil off", the oil temperature needs to get to 230 degrees. 212 degrees is not high enough as the crankcase operates under pressure. So, to encourage getting the oil up to a "boil off temperature" to provoke this important oil decontamination process let’s remove the factory 190 degree thermostat, and replace it with a 170…smart! OK, check the scorecard… no dyno proven HP gain at lower coolant temperatures, and adverse affects on the oil quality by allowing condensation to build up in the oil circulating through your engine.

To those of you who may have spent your hard earned money on these snake oil elixirs, and swear you have increased your RWHP (Rear Wheel Horse Power) by 20+ over stock, my congratulations to you. Besides, nobody really believes engine performance is based on physics and the chemical transfer of fuel to mechanical power through combustion… we all know its really pure freakin’ magic… and magic potions... and snake oil elixirs.

Psssst, wanna buy some snake oil?????

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