Join Date: Jan 2008
Location: Seattle, WA area
Re: Turbo coupe performance
OK, you have a number or changes you can make to improve response or max HP of a stock TC. However, you cannot randomly mix 'n match the changes. So, some changes are to increase low-end power (off-boost), such as bumping the base timing 2 or 3 degrees. This is nice for daily driving. On the other hand, you can install a manual boost control valve (MBC) to increase boost, improve onset of full boost (wider power band), and raise max power - but not likely with added timing for low-end power. Bad combination with pump gas. There are limitations based on the programming of the stock EEC.
One problem is the knock sensor in them. While it works for what it's supposed to do (detect detonation and retard timing) the response is a little too sensitive, and it also retards for an extended period. This means it may give retard when there is no detonation (greatly reducing power), and hold the retard for what seems like an eternity before restoring full timing. It is the safe way to go though, and the only thing to save some un-knowing folks if they accidentally put Regular grade gas in.
In-fact, the faster stock TCs generally disconnect the knock sensor and tune for det like any other turbo engine - by ear (or ear amplifiers) and reading spark plugs repeatedly. With small changes and testing, you should be able to give it 15 to 17 psig with the boost controller, while adjusting base timing (if necessary with your available fuel) to ensure no det. You can then try reconnecting the knock sensor to see if it throws false signals and retard. No? Then drive happy. Yes? Then drive happy but always be vigilant for any signs of det, especially after every fill-up.
There are a gazillion mods you can do to these things for performance, and although much of the info is quite old (20-25+ years by now) it all applies with consideration of newer versions of parts and techniques. Take your time while you 'learn' your engine and you can re-tune your ride to give an impressive amount of power with very high reliability.
BTW - be sure to check you fuel pressure and flow to ensure you can get enough fuel at higher HP, or just plan to upgrade to a 160 or 190 LPH single in-tank pump. Some of them have two puny EFI pumps in the tank. Some have two pumps - one low-pressure in-tank and one high-pressure external. If you're lucky, you have the 2-pump system with the external factory second pump mounted on the frame rail. That one will push enough fuel for 400+ hp, but only if it's tested or fresh.
-=≡ If it was easy everyone would do it ≡=-
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