The old saying has been repeated so many times that it goes beyond the realm of the mere cliche, "Horsepower costs money--how fast do you want to go?" To a large extent, it is completely true, especially in the upper echelons of sanctioned racing, where teams will spend tens of thousands of dollars to pick up single-digit horsepower improvements over their competition. It is also the case in the "trick of the week" realm, where the "next big thing" comes with a price tag that will discourage all but the most hardcore enthusiasts. To those who simply must be the first on their block, it's a necessary evil. The horsepower return on the dollar is rarely very good, though.
Then there's the other 95 percent of the automotive hobby, those who want to go fast, but have to deal with the financial realities of their personal situations. Families, mortgages, and other grown-up responsibilities usually take precedence over shiny new parts and with them goes the majority of the monthly income. In place of stacks of cash, many hobbyists have taken some unconventional and more economical paths to big horsepower gains and have been rewarded with large amounts of affordable power.
The Junkyard Turbo Movement
The Internet has been responsible for a quiet revolution in the past few years, one that has seen thousands of bucks-down performance fans scouring the local wrecking yards for high-performance componentry. That of course, is nothing new, it's the essence of hot rodding. Instead of looking for a long-gone 455 H.O. Pontiac or hi-po big-block Chevy, they are now searching for rebuildable turbochargers off of '80s-era 4-cylinder Thunderbirds or even 2.2 Mopars. They know that a pair of these little hairdryers will be sized just about right for a pushrod 5L V-8 and when mated to a properly prepared short-block, will supply enough air to support 550-600 hp, more than enough to make for a devastatingly fast street machine.
Obviously, that is a bit of an oversimplification, but a quick scan of the message boards devoted to this practice, such as Yahoo's JY Turbo or Blow-Thru Turbo, will open up a world of possibilities. Many of those who post on these message boards have quite a lot of experience making horsepower on the cheap with used turbos.
There are options for owners of larger engines as well, using turbos off of diesel trucks. Though one's initial reaction might be "If I can get that much power out a 5L engine, just think what I could get out a really big engine!" durability becomes a factor with larger production-based engines. Cast-iron, long-stroke bottom-ends are simply not as durable as their shorter-stroke brethren.
Secondly, larger displacements usually come at the expense of cylinder wall thickness and head-sealing capability. In the case of a Pontiac V-8, the same basic block architecture that started out as a thick-walled 287 grew to a relatively thin-walled 455. Not only that, but the larger bore compromised head gasket sealing areas. Though not insurmountable, these problems have to be addressed when building a large-displacement, forced-induction engine.
Nevertheless, it is indeed possible to build truly brutal big-inch Pontiac V-8 in this manner. One must make the distinction between max-effort; all out turbo race engines such as the 2,200-plus horse Indian Adventures-based 440 Pontiac in Rodney Butler's tube-framed '65 GTO racecar (HPP, May 2002) and a production-based street performance engine. Just because Rodney can stuff air in his engine at over 25 psi doesn't mean you're going to be able to with your cast crank, stock block 400 or 455. By setting realistic goals, one can achieve a very high horsepower to dollar ratio and do it with a good margin of durability. The secret is to keep boost and rpm levels relatively low, as well as keeping timing and detonation under close control.
Brad Bunger, of Topeka, Kansas, has worked out a very nice combination of power, reliability and affordability with the turbocharged 455 Pontiac in his '79 Trans Am. Using good old Yankee ingenuity in place of cubic dollars, he carefully crafted a turbocharger installation that is simple and very effective. Oh yeah, it makes gobs of power, too.
With cost being a primary concern, Brad decided to forego the usual items that are associated with a contemporary turbo installation, such as electronic fuel injection and boost control, intercooling systems and other "exotica." He even passed on custom headers, preferring to use cast-iron exhaust manifolds, which might have cost some power but are very durable.
The Hard Parts
The system is centered on a used Schwitzer 3LM turbocharger, a fairly large unit, which reportedly came off of big-displacement Cummins diesel engine. It is similar in size to an AiResearch/Garrett TO4B. After analyzing the factory-supplied turbo map, Brad determined that the turbo would flow enough air to support about 575 hp. Figuring that a 575-horse 455 would be making well over 600 ft-lbs of torque, he decided that it would be a great choice for a street machine, though it is probably a bit too small for all-out race use.
A well-seasoned 455 that Brad built back in 1991 before he became interested in turbocharging, became the basis of the buildup. It is a very typical street performance setup, using .030-over TRW forged pistons on stock cast rods, a set of gasket-matched 6X-8 heads, with stock 2.11-inch intake valves and 1.77 exhaust valves replacing the factory-issue 1.66s. Stock-style head gaskets have held up so far with the boost levels he is working with.
A single-pattern Comp Cams hydraulic stick with 230 degrees of duration at .050 and .480-inch lift with a 110-degree centerline was chosen back then. And though Brad admits that this isn't really an optimal grind for this combination, it's what was in the engine already and he didn't want to change it. Also in a way, it's in keeping with his philosophy of this project.
"Jim Hand lives near me and I admire this guy like you wouldn't believe. He has spent an immense amount of time researching and sciencing out his wagon and it is an amazing machine," Brad explained. "The thing is, I didn't have the resources or time to research my particular combination out like that. What I set out to do is to take this turbo that I bought on eBay and see how much power I could get out my 455 with a simple installation and have it live. I wasn't concerned about wringing out the last ounce of power because I knew it would cost a lot more money and get much more complicated."
Mating the Schwitzer turbo to the 455 took a great deal of planning and preparation. Here's how Brad did it. After doing a lot of measuring to determine the best location for the Schwitzer turbocharger, he settled on the passenger side, near the rear corner of the engine. It appeared to have the most available room to accept all of the exhaust tubing that would run to and from the unit.
He bought some PVC pipe and mocked up the system running from both manifolds to the turbo and then from the turbine outlet to the existing exhaust system. Next, he went to a local muffler shop and had them exactly replicate shape of the PVC pipes in steel exhaust tubing. All he had to do then was take the new pipes home and install them.
After the turbo connected to the engine, Brad turned his attention to lubricating it. He tapped into the oil filter housing to get a supply of pressurized oil and ran a 5/16-inch line to the turbo. Then he pulled the oil pan and welded in a 3/4-inch heater hose nipple on its side, above the oil level. From there, he ran a 3/4-inch return line from the turbo to the pan.
With the turbo oiling system completed, the focus then turned to the fuel system. When blowing through a carburetor, a few things need to be addressed. First, the floats have to be resistant to boost pressure or they will collapse. Brad installed solid floats in the 750 Holley Double-Pumper to prevent this problem. Most new Holley carbs now have them factory installed. He then richened up the primaries one size to #74s and the secondaries two sizes to #84s.
Secondly, the fuel pump must be boost referenced in order to compensate for the boost pressure or else the fuel will be pushed back into the gas tank. Brad installed a 140 gph Summit electric fuel pump with a boost-referenced Mallory 4309 fuel pressure regulator. The setup provides six pounds of fuel pressure above boost pressure to the carb, allowing it operate normally. This necessitated the addition of a 5/8-inch return line to the fuel tank.
Originally, Brad had fabricated a carburetor bonnet out of 3-inch steel tubing. The ducting from the compressor to the bonnet had a radiator cap added to act as a boost controller and pop-off valve. He has since replaced that setup with a modified carb hat from West Coast Fabrication.
Bunger has done some experimentation with various components to arrive at the present combination and he'll no doubt be doing more research as time goes on. Additionally, Brad experimented with an intercooler from a Volvo diesel but found that while it did cool the charge, it proved to be a major restriction in the intake tract, costing a full 2 pounds of boost. He removed it and in his typical low-buck fashion, Brad designed and built a water/methanol injection system that lowers intake charge temperatures over 100 degrees F and does an excellent job of warding off detonation.
The system consists of a heavy-duty Shurflo pump, which injects a mix of water and methanol into the turbo outlet duct, just ahead of the carb hat. A McMaster mist head provides proper atomization of the anti-detonant. When the boost reaches 5 pounds, a Hobbs switch, which senses pressure, triggers the system into operation. According to Brad, the turbo can make more than 5 pounds of boost instantaneously, even off idle, so this system is necessary for engine longevity.
Does it Work?
So what about performance? There is certainly a large improvement, to the tune of 1 full second and 9 mph in the eighth-mile, going from a best of 8.61 at 82, which translates to an approximate 13.34 at 101.62 in the quarter. With just 7 pounds of boost, 110-octane race fuel and 30 degrees total advance by 2,500 rpm, the Trans Am responded with a 7.62 at 91, which roughly translates to a quarter-mile pass of 11.81 at 112.84. This by launching at idle and shifting at 5,200 rpm.
On the street, Brad runs 91-octane fuel and reduces the timing to 25 degrees total at 2,500 rpm. In this state of tune, it has run a best of 7.79 at 87 mph, converting to a 12.07 at 107.88 in the quarter. Not bad for a total investment of just $813.26!
So what are Brad's future plans? It looks like a rebuild will soon be necessary, as piston ring blowby is preventing the engine from making more than 5 pounds of boost. It still runs very well, but a lot of power is going to waste past the rings. Though one might blame the turbo for the current state of affairs, the truth is, the engine had 12 full seasons of bracket racing under its belt before the turbo conversion. With a freshening up, the 455 will be able to make the most of the boost available. It's probably within the realm of possibility to make 10 pounds of boost reliably, which will put the two-ton Trans Am deep in the 11s at 118-plus mph.
Brad Bunger has shown what can be done with a Pontiac V-8 by substituting creativity for unlimited dollars. By thinking outside of the box and spending less than $900, he put together one of the most cost-effective bolt-on performance upgrades ever devised. Best of all, this is a setup that could be as easily adapted to 350 or 400 smog motors as the 455, giving these rather anemic engines a serious shot in the arm. Brad is finishing up a manual to help hobbyists duplicate this conversion. Check out Brad's page on www.transamcountry.com which is run by Mike Barefoot.
Keep in mind that Brad Bunger did considerable research before he undertook this project and he invested many hours to see it through. If you have built your own engines before and have a firm foundation of mechanical knowledge, then have at it and save some cash. First check your local emissions laws if you plan to drive your turbo Pontiac on the street and check your local drag strip's safety regulations if you plan to race it. However, if you are not well versed in working on your own Pontiac and fabricating parts when needed, then this may not be the project for you.
Adding a Cummins diesel turbo to a 455 is a quick and inexpensive way to build usable stre
The turbocharger is a Schwitzer 3LM off of a large Cummins diesel. Pressurized oil flows f
This shot of the complete exhaust system off the Trans Am makes it easy to understand how
The front shot of exhaust system shows the neat packaging and effective layout. Stock log-
A two-into-one header-style collector connects the two banks of exhaust gases to the turbi
This shots shows the relative size of the turbocharger componentry. The turbine that drive
Brad's first carb hat was this unit he fabricated from 3-inch round tubing and flat steel
When first completed, the turbo system used an 850 Demon carb and the owner-fabricated car
The current configuration uses a 750 Double-Pumper Holley carb with #74 primaries and #84
The space where battery once resided is now taken up by the methanol/water injection syste
A close-up of water injection nozzle shows its hardware store lineage. The nozzle is a McM
Like most of the rest of the Pontiac, the T/A's interior is 100% factory-issue save a colu
|1979 TURBO TRANS AM SPECS|
|Engine:||Turbocharged 455 Pontiac|
|Year of Block:||1975|
|Displacement before/after overbore:||455 bored 0.030-inch 462 cid|
|Fuel:||93-octane pump gas for street, 110-octane race gas on boost|
|Carburetor:||Holley 750 Double-Pumper, modified for blow-through configuration. Original carb hat built by owner out of 3-inch tubing Current unit is a modified West Coast Fabrication design|
|Intake Manifold:||Edelbrock Performer|
|Fuel Pump & Flow Rate:||Summit 140 gph with Mallory 4309 boost-referenced fuel pressure regulator|
|Head Casting #:||6X-8, gasket-matched, large exhaust valves added|
|Valves:||2.11 intake and 1.77 exhaust|
|Piston Type:||Forged TRW|
|Rotating Assembly Balanced?:||No|
|Camshaft Brand:||Comp Cams hydraulic with 230/230 degrees duration at .050, .480/.480-inch lift with factory stamped 1.5:1 rockers|
|Camshaft Lobe Separation:||110 degrees|
|Camshaft Centerline:||110 degrees|
|Camshaft Installed Position:||Straight up|
|Distributor:||GM HEI, 25 degrees at 2,500 rpm|
|Headers or Manifolds:||'72 GTO with 2-inch outlets|
|Power Adder:||Schwitzer 3LM single turbocharger off of Cummins Diesel|
|Exhaust:||Custom exhaust system uses 2.25-inch crossover to connect both banks to turbo, 3-inch downpipe from turbo to 2.5-inch dual exhaust system using Walker Dynomax mufflers|
|Boost control:||No exhaust wastegate, radiator cap located before carb hat controls boost and acts as pop off valve|
|Transmission type:||Turbo 400 rebuilt by Kevin Hammond, no shift kit|
|Torque Converter/Clutch:||Fairbanks 10-inch converter with 3,500 rpm stall speed|
|Shifter:||Stock factory shifter|
|Rear Type/Ratio:||3.42:1 Safe-T-Track|
|Brakes Front:||Stock Trans Am 10.9-inch disc|
|Brakes Rear:||Stock 9.5-inch drum|
|Wheels & Tires, Front:||Weld 15x3.5 mounting Firestone 165/80-15 tires, 44 psi|
|Wheels & Tires, Rear:||Weld 15x7 mounting 28x10.5x15-inch Mickey Thompson slicks, 14 psi|
|Suspension Front:||Rebuilt factory stock suspension, including stock-rate springs, OE replacement shocks and 1.25-inch front stabilizer bar|
|Suspension Rear:||Rebuilt stock suspension, including stock-rate springs, OE replacement shocks and .875-inch rear stabilizer bar, no-name slapper-type traction bars (came with car)|
|Chassis Modifications:||None, factory stock|
|Interior Modifications:||Factory stock seats, dash and gauges, AutoMeter boost gauge mounted on steering column|