Inches and Pounds - L98 turbo article

Guys, this was an extremely interesting article and proves that there's life in the L98 yet...

...but... (there's always a but!)

I'm struggling to understand how a BONE STOCK L98 with nothing more than a cam, long tube headers, electric water pump and FAST XFI can put out 331hp - that's almost 50% more than the stock output!

Also, getting 481hp at only 7psi doesn't seem to add up - getting that kind of figure out of a stock LSX engine would be pretty good!

Help!  If this can be done, then I'm sold!

For info, I have an '88 GTA with an '86 Corvette L98 (aluminum heads), adjustable FPR (running at around 50psi), uprated ignition system (wires and coil), throttle body flow straightener and a set of ceramic coated Heddman shorty headers - soon to have an aftermarket chip fitted too...

Chris St Clair  

The first thing I notice in trying to determine where the big difference between the factory rating of 245 and the dyno results in the article of 331 is that the test motor is run with no accessories or emissions equipment.  This is much the same as the cars before 1972 (I believe) were given gross horsepower ratings.  I don't know exactly how much this dropped the power, but I've seen numbers between 10% and 35%.  Call it 15% and the net rating of 245 hp rating becomes 290 hp gross.

Now take into account that they had a FAST XFI engine management system, which I would think was tuned for optimal performance, unlike the factory computer from which they got the factory 245 hp numbers.

Add to this the cam (if I remember correctly, the factory TPI cams were tiny) and you can see why they were able to get 331 hp out of the engine with the setup they had.

As for the comparison between this motor with the 7psi turbo setup vs an LS1 with a similar setup, the LS1's would probably make somewhere in the 450 to 480 horsepower range at the rear wheels with all the accessories needed to run it in the car.  If you took the TPI engine off then dyno stand and installed it into a a driveable car and then threw it on a chassis dyno then you would see that 481 horsepower number drop way down (probably to well under 400 horsepower).  

I'm definitely no expert (just an enthusiast like yourself) so take everything I say with a grain of salt, but I believe that these observations will get you on the right track to figuring out the horsepower descrepancies.

GM High Tech staff, great article!  Mr. Holdener, all of your writings are always very interesting with real world results.