When it comes to automobile enthusiasts, very few will tell you that their engine makes too much power. In fact, producing more horsepower has become an endless quest that owners embark upon after an infectious encounter with the power bug.
Fifty-four-year-old Steve Coombes of Liberty, Texas saw the birth of musclecars and their subsequent demise. And in between, he enjoyed the power that could only come from large V8 engines. By 1988, Coombes had raised a family and made a stake in two very large Texas flea markets. The bug began to nibble and Coombes thought it was time to sample some Americana in the form of a tried and true musclecar. While he was originally looking for a 1969 Camaro Z28, he found that the collector car market prices had skyrocketed, dashing his hopes of purchasing the Chevy road racer. However, all was not lost, as an all-original Pontiac Trans Am would rescue him from the throes of mediocre classics.
This 1970 1/2 Lucerne Blue Trans Am was purchased from a collector in Tennessee. Coombes was rather interested in having a restored classic, so the low-mileage Bird was a perfect choice. It didn't need much to make it perfect. The options list was rather short and included a console and floor mats, but the factory go-fast goodies were what Coombes was after.
A 3.73-geared, Safe-T-Track rear received the grunt from the numbers-matching Ram Air III 400 mated to a Turbo-400 transmission. Breathing through a shaker hood scoop, the Ram Air Pontiac engine did a good job of moving the F-body's 3500+ pounds, but the power bug bit a little harder this time and Coombes found himself calling on long-time friend John Dinkel at Punisher Automotive in Austin, Tex., for a little tuning. While Dinkel's forte is dealing with small-block Fords, he took to the Trans Am like it was one of the blue oval's finest.
Minor tinkering with the T/A began with a change to roller rocker arms, a little bit of port work on the heads and exhaust work. This was about all Coombes was allowed to do for the NMCA class he wanted to run. With times in the high 13s, Steve was beginning to like the feeling of speed. Dinkel kept toying with the Pontiac by adding a 280* cam, an 11-inch TCI converter and 1.75-inch diameter headers, and the ET plummeted to 12.85. At this point, the year was 1992 and the Trans Am was campaigned in the NMCA E/Top Stock class. It briefly held the record for both ET and mph in its class and this was when the power bug really began to sink its teeth in. Out came the 280 cam and in went a solid roller. A Victor intake manifold and Holley carb topped the engine and in this 0.060-over, 412-cubic-inch configuration, the motor made 560 horsepower on the dynamometer. As you may expect, elapsed times also dropped--to the 11.40 range.
Coombes now had a blistering fast Trans Am, but occasionally it was driven on the street, which was one of the reasons why the Firebird kept a stock appearance. "I refuse to put big hood scoops on it and have retained a somewhat original look with the Fiberglass Trends bolt-on hood, and the American Racing Torq Thrust wheels look period correct," said Coombes. Although the F-body looked fairly innocent (at least as much as a Trans Am can), it packed a powerful Pontiac punch under the fiberglass shaker hood, a punch that would get stronger yet.
While 11-second ETs are good, 10s must be better, right? As mentioned earlier, you'd be hard-pressed to find someone who will tell you his or her engine makes too much power. Of course 560 horsepower was enough for a while, but it was also about all that the factory motor was going to withstand in Steve's eyes. He didn't want to chance throwing a rod out the side of his numbers-matching block so he called his friend Skip Fix for another block. You may remember Skip's name from our December 2000 issue. He and his 11-second '78 TA competed in our Pontiac Pavement Pounders Shootout. Coombes procured a 1970 YS-code 400 block from Mr. Fix and when asked why he didn't opt for the 455, his answer was "I wanted an engine that was oversquare (bore is larger than the stroke). The 455 is undersquare (bore is smaller than the stroke) from the factory, so we went with a 400 with a 4.165 bore) (400 bored .045 over) and a Crower billet crank that has a stroke of 4.125 (stock 400 crank stroke is 3.75). I also wanted the 400 because of its 3-inch main bearings (less friction than the 455's 3.25-inch mains) and thicker cylinder walls."
With this plan set, Coombes sent the block to CHS Racing Engines in Austin. There the raw hunk of metal was turned into a machined piece of high performance iron. Dave at CHS assembled the now 450 cubic-inch engine using the aforementioned Crower billet crank, Crower billet 6.8-inch long (stock Pontiac rod length is 6.625 inches) big-block Chevy connecting rods and custom JE forged flat-top pistons. Back at Punisher Automotive, Dinkel took the short-block and added a Melling MS54-F oil pump, a Canton 6-qt. road race pan with built in baffles and windage tray, a crank scraper and, of course, a Fram HP-2 oil filter. Once the engine was flipped over, Dinkel installed the custom UltraDyne solid roller camshaft. Sporting a split duration of 279*/287* at .050, the bumpstick was ground with a lobe separation of 110* and it provides a mammoth .704/.680 lift when combined with the 1.65 intake and 1.60 exhaust roller rocker arms. Said rocker arms ride on T & D shaft systems, which are mounted on a pair of custom Edelbrock 6050 aluminum head castings. The Isky solid roller lifters are actually Chevy spec. Coombes and Dinkel used these in combination with a set of CV Products chrome-moly pushrods, which have a wall thickness of 0.0080-inch and are 8.05 inches in length. These pieces utilize a 0.150 pushrod offset to make the pushrod angle nearly vertical.
The cylinder heads were heavily modified to make sure that the potent 11.2:1 engine would not be held back. Jack Gonzalez in Orlando, Fla. received the virgin heads and began by drilling the 0.170 offset for the 2.150 intake valves. A set of 1.765 exhaust valves were added and all are held in place using Isky 9365 springs and titanium retainers. The Edelbrock pieces also got a full race porting and the runners were modified. When all of the work was complete, the heads produced flow figures of 329 cfm for the intake and 248 cfm for the exhaust at .700 valve lift at 28 inches of water on a Superflow bench.
Now that the mighty Pontiac motor had a healthy set of lungs, it was time to make sure that it would get fed properly. Dinkel port-matched an Edelbrock Victor intake manifold and topped it off with a DaVinci 750 Holley that has been modified and utilizes an 850 base plate and no power valves. Supplying the cavernous carburetor is a pair of Holley Blue fuel pumps, which pull the Howell 105-octane race gas from a 12-gallon Jaz fuel cell and send it up to a Mallory 5-port regulator. "I've always felt that running a good fuel system is not overkill," said Coombes. "We were running a single pump at a race and it went out on us so we weren't going to let it happen again." High compression and high octane fuel need a good spark to get the fire going so an MSD billet distributor and 7AL-2 work with an HVC coil and crank trigger to send spark through a set of Taylor Pro Race 50 ohm plug wires.
The previous set of 1.75-inch headers made way for a set of Hedman Huslers with 2-inch tubes that dump into 3.5-inch collectors. A Dr. Gas X pipe of the same dimension crosses beneath the T/A and sends the exhaust gases to a pair of Walker Race Magnum mufflers. Torque Tech 3-inch tailpipes exit under the rear bumper, like the stockers would.
While a Hughes Performance 5200-stall converter and a manual valve body contribute to the Turbo-400 transmission's performance beneath the floorboards, shifting duties were left to a B&M Quicksilver shifter, which was installed for both its precision and custom application for the factory GM console. With the kind of times that the T/A was expected to produce, there was no way of getting around a roll bar. Yes, it screams race car but that is about all you will find on this Pontiac that does so. The racing bucket seats were treated to matching upholstery from SMS Fabrics of Portland, Oregon, stitched by a local guy, and it perfectly disguises the racy nature of the seats. The only other race car concession to the restored factory interior is the addition of AutoMeter gauges, which have been carefully and tastefully placed in the factory gauge panel. We haven't mentioned much of the suspension up to this point and one would expect that this monster of a Pontiac would need some elaborate underpinnings. However, this is quite the opposite of the truth.
Throughout the Trans Am's racing career, the factory suspension has done most of the work. Stock front disc brakes and rear drums remain, as does the rear leaf spring configuration. But who can blame Coombes for replacing the sagging rear arches with new 300 lb./in. Landrum pieces. The front springs have been changed as well to six-cylinder units and a set of Competition Engineering adjustable shocks aid in weight transfer. Steve used to run a pair of slapper bars but found that Calvert's Cal-Trac traction bars worked a little better. That's about it. No four link or coil-overs, just traditional replacements. The factory driveshaft was used for quite some time until it demolished the U-joints, but it has since been replaced by another steel unit and is surrounded by an approved loop. A set of 4.30 gears replaced the 3.73s in the rear and it was off to the track once again.
The Trans Am has been run in this configuration for about five years now. Its venture into the 10-second zone has come to a best ET of 10.602 at 127 mph. This happened at Norwalk, Ohio on a hot and humid summer day. Not bad for a 3,500 lb. car that has a race weight of 3,675 lb. While this is fast for some, the power bug isn't quite finished with Steve Coombes. He and John Dinkel have plans to change out the current 4.30 gear to a 3.73, add a shot of nitrous and shoot for 9-second territory. "I'm pretty much done with the racing thing, but I want to be able to say that I went in the 9s with it," said Coombes. It turns out that he feels the need to drive the F-body more often on the street than he has. So after they make some single-digit quarter-mile times, Dinkel and Coombes will be returning the numbers-matching block to the engine bay. The Ram Air III motor, though still a bit high for pump gas, has a little more street-friendly compression ratio and though the T/A is very capable of street operation as is, the milder engine will make cruising easier.
Has the power bug finally been defeated? It depends on how you look at it. Coombes will have gone into the 9s with a beautiful street car and will now be going backwards in performance. On the other hand, he will have the potential to be filling up at the local gas station and feeling the rush of acceleration on a daily basis. Either way, you won't hear him complain that the Trans Am makes too much power.
A Spartan engine compartment...
A Spartan engine compartment is home to a 680 horsepower 450 cubic-inch Pontiac engine. The stump-puller also makes 580 lb.-ft. of torque. Coombes has tried 950 and 1050 cfm carburetors as well as a Holley Street Dominator intake manifold, but the results were not exactly dramatic. The 950 improved the ET by .009 and the 1050 dropped the ET by .08, but added 1 mph at the top end. Dinkel has basically done an excellent job tuning the Bird, as they seem to have found the DaVinci 750 and Victor intake to be a good set-up.
John Dinkel doesn't hesitate...
John Dinkel doesn't hesitate to torture the Mickey Thompson 28 X 10.5-inch slicks mounted on American Racing Torq Thrust wheels. While Dinkel does most of the track driving, Coombes often drives the 11.2:1 compression, registered and inspected hot rod on the street. An identical set of the nostalgic Torq Thrusts wear a set of McCreary L60 street tires when the decision is made to go to the local cruise night or pick up groceries. There is nothing quite like a testimonial to support your claim and one that attests to the streetable nature of Coombes '70 T/A was made by Matt Dalton after he got the chance to drive it at Norwalk. "It was a fabulous weekend. I was extremely impressed with the complete and utter driveability of Steve Coombes '70 T/A. I have never seen a more manageable 680 hp. This thing idled like a baby, never got over 180*, and delivered 10.60 passes on demand. I was ready to drive it to the motel room."
Owner Steve Coombes (left)...
Owner Steve Coombes (left) and mechanic/ driver John Dinkel of Punisher Automotive. High Performance Pontiac was putting on its Pavement Pounder Shootout and asked Coombes and Dinkel if they wanted to come out and take advantage of the track. What ensued was a lot of 10-second track blistering and a feature photo shoot.