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TPI 355ci Small-Block - Something Old, Something New Part IV - Tech

Part IV: 416HP, 486 TQ Our TPI is greater than the sum of its parts

Ray T.Bahacz Nov 1, 2006

Often, what makes something a success can not be identified as a single element. It is usually a combination of events or circumstances that produce either failure or success. The same holds true when building engines. Two engines can look almost identical on paper but produce a huge variation in specific output. Under examination, there may not be any striking difference that would have you proclaim, "That is where the horsepower is." Yet there is no denying that a huge deficit exists in the lesser power plant.

Turning the clock back a little more than one year now, GMHTP, RaceKrafters Automotive Machine, and the author embarked on a journey that would apply the latest in technology to what would now be considered by many an antiquated engine, a TPI 355ci small-block. The impetus for this exercise was the affordability and history the TPI 350 brought to the table. The cars are attractive, and don't look dated (Third Generation F-Body and C4), the parts are relatively inexpensive, and the technology is simple by today's standards. In addition, the GM performance limelight was stolen by first the LT1 and then the stunning LS1 and later series of engines. No one can deny that a 400 hp, 400 ft-lbs of torque LS2 is a sweet piece, especially when it is produced by a displacement only a touch larger than the TPI's 350 cubic inches. The question posed and the basis of the exercise was, can an old dog run with the new kid on the block?

As explored in Part I of this series, the TPI 350 had a lot going against it when compared to the newer generation small-blocks' airflow capacity. Being a torque-biased design, horsepower was never a TPI forte. Large amounts of torque were its hallmark. Could RaceKrafters produce results with a 355 TPI engine that would gain the respect and attention of GMHTP's audience? That question was answered on Saturday, July 8, 2006, at 4:03 PM.

On the pumpNever in the author's career has the combination of high-quality machine work and assembly procedures along with the proper mix of parts ended up disappointing. The only question was how happy you would be at the end of a dyno session. Though there are computer simulation software programs to predict power produced by an engine, and even a rudimentary equation (airflow @ 28 in. H2O X 0.257 X # cylinders = power), you never really know what you have until the water brake loads it. A good, educated guess comes close to the power produced, but the real deal is what spits out of the dyno printer.

As the author, I never publicly stated a goal for this engine. But in my mind, I set a minimum that I would feel qualified as a success. Given the fact that in production form a TPI 350 was rated around 245 hp and 345 ft-lbs of torque, I felt if our engine produced about 100 more than those figures, idled at 750 rpm, and ran on pump gas, no one could consider it anything but a success.

Three hundred and forty-five hp would have beaten a stock LT1 and placed it right at the level of a production LS1. Since the GMHTP/RaceKrafters engine employed production GM Vortec cylinder heads and factory-style induction system, results in that range would be very pleasing. Our engine would allow an old F-body or C4 to run right with a new version at the drag strip, for substantially less money.

With the little 355 sealed up, the oil changed and the DFI system dialed-in by Bob Wise, the final numbers were in. How does just shy of 420 hp and 490 ft-lbs strike you? That is correct, Something Old, Something New (SOSN), blew us away by producing almost 175 hp and 145 ft-lbs of torque more than a production version. In addition, the 355 made 15 more ponies and nearly 90 more ft-lbs of torque than the much-lauded C5 Z06's LS6 engine! I do not care what camp your loyalty lies in, you just have to love this little 355. To boot, it only wanted 26 degrees of ignition timing (This will promote good octane tolerance), idled like a stocker at 700 rpm, and at peak torque was so fuel efficient it had a BSFC Of 0.40.

What was especially interesting about this engine was that from 2,343 rpm to 5,970 rpm, the AVERAGE torque was 454 ft-lbs! At 2,400 rpm this thing had 424 ft-lbs! What this means is the engine would be happy in variety of contrasting environments. Need to pull your race car to the track? SOSN would be happy doing that all day long in a pickup truck or Suburban. Want to run in the 11s with an older TPI car and still get 30 mpg or better on the highway? No problem for SOSN! Do you want to go to the track and play with C5 Vettes with an engine equipped with cast-iron cylinder heads and a stock-looking injection system? This engine is ready, willing and able to do all of this and more.

Being true hot rodders, stunning results are never enough. The next and final step for our project is to pull the 355 back apart and send the internal parts to Swain Tech Coatings, to once and for all prove what this technology is worth. It should be interesting.

Customer: Gmhtp
* Engine: 355 Vortec Tpi
* Ign Timing: 6
* Comments: 210/220-.500/.510-114-110 Vortec Heads/Sd Vortec Base/Accel Large Runners/Accel 58mm Tb/ 24# Inj./ 43# Fuel Psi/ 93 Pump Gas/ Complete Msd Ignition Controlled By Accel Gen7/1-3/4 Headers W/2.5 Flowmaster Dual Ex./


RaceKrafters Automotive Machine, Inc.
Lancaster, PA 17601



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