GTO Dyno Shootout

It's not often that we can gather a group such as this in the same place at the same time for chassis dyno testing, in fact this is the first time. So knowing full well that this story could open a large can of worms, we still took advantage of the situation to create this dyno shootout. The plan was simple. We had a 2004 GTO to strip test in Southern California. Our parent company Primedia also has a tech center with a chassis dyno at its Placentia-based editorial offices. So after running the '04 at the track we wanted to get some chassis dyno numbers as well. We figured hey why not round up some classic GTOs to run on the dyno and see how they perform. Easy right? Well not really. Of course there was a time crunch so the word went out to every Southern California contact that I had and GTOAA member Mike Radke devoted considerable time to locating the Goats.

It soon became apparent that stock perfectly running models were few and far between in this day and age since so many people had rebuilt their engines and changed the compression ratio and/or mildly modified them, so the search opened to include very mild modifieds. No aftermarket intakes or headers were allowed. Persistence on the part of Radke and a few others provided the following 3 examples to run with the '04.

THE GOATS
Tom Burton's '71 455 H.O.-equipped GTO (it was originally a 400) was absolutely breathtaking in Starlight Black. This show winner features a .030-over block with an aftermarket cam, 1.65:1 rockers and a slight increase in compression. The fire is lit with an HEI, while the remainder of the combination is correct for the year down to the casting codes and carb jets. A 4-speed transmission backs the engine and 3.07 gears are found in the Safe-T-Track rear.

Gregg Miller's '70 Judge in Palisade Green is also an eye-popper with its seldom seen color. It features a Ram Air III engine bored .030-over and is fitted with a Ram Air IV cam. The rest of the combo is stock, including the compression ratio of 10.5:1. Greg's Judge is fitted with a 4-speed trans and 4.11:1 gears in a Safe-T-Track rear.

Norm Shaughnessy's '66 Tri-Power GTO was detailed to perfection and was the most stock of our competitors. Though bored .030 during a rebuild, the cam is a stock replacement and the factory block, heads, carbs, intake, exhaust manifolds and distributor remain, as do the factory jets and the 10.75:1 compression ratio and 4-speed and 3.55 rear.

AT THE DYNO
Since we usually test engines on engine dynos and cars at the track, a few words regarding chassis dynos are required for this story. Please bear in mind that with our Dynojet chassis dyno the mass of the drum (roller under the rear tires) is known and is a constant. The computer uses a mathematical equation based on how fast the drum is accelerated to measure horsepower and then mathematically calculates torque. Conversely, an engine dyno measures torque and mathematically calculates horsepower from that. So gear ratios in the trans and rear, the converter stall speed and tire height will affect the output on a chassis dyno. This means that it's possible that the same car with a 3.08 rear could make less power than said combo with 4.10s. How much of a difference is application specific. So there is really no way to directly compare our 4 GTO's engines unless the transmissions, rear gears and tire heights are identical. Also the power figures will be lower than you are used to seeing as compared to gross and net numbers at the flywheel.

All of the GTOs had manual transmissions and all were tested in 4th gear, which has a 1:1 ratio. This eliminates differences in torque converters and transmission gear ratios but rear gear ratios ranged from 3.07 to 3.46 to 3.55 to 4.11 so there is a variable and the tire heights were different for each model--another variable. Nevertheless, we still thought this shootout would be interesting reading so we forged ahead.

Early on Friday the 13 in February 2004, we arrived at the Primedia Tech Center to run the GTOs on the Dynojet chassis dynamometer. Jason Scudellari is the dyno operator and he was in charge of actually running each GTO and providing the charts that you see in this story.

This is a somewhat different situation than we have at the drag strip shootouts. First, the owners are not actually performing the runs, which requires a lot of trust on their part since they have no control over what happens to their GTO on the dyno. For that reason, each was asked to provide an rpm limit that they were comfortable with. The advantage of having Jason do the runs however, was his experience. He can tell by sound and feel what is going on with each engine and he knows when to back out of it in a hurry. He can also feel when the engine is nosing over after it reaches its power peak. Thankfully we had no detonation and no breakages for the duration of the test.

'04 GTO 5.7 LS1
Our '04 GTO test car would rev freely to its 6,000 rpm redline. As you'll see in the dyno chart, maximum horsepower was made at approximately 5,700 rpm and max torque checked in at 4,300 rpm. The best pull of 3 resulted in 297.38 hp with 314.58 ft-lb of torque. Other runs were close at 293.74 hp and 294.61 hp. If you use the rule of thumb that power to the rear wheels is 15 to 20 percent less than net hp at the flywheel, the reading would have been 280-297.5 hp based on the 350hp rating. So the GTO is right there.

'71 GTO 455 H.O.
Tom Burton's 455 H.O. engine sounded downright mean on the dyno and we were looking for some impressive numbers. Unfortunately, Tom, who drove in from Phoenix the day before, suffered a back injury that kept him away from the festivities. Since he was staying with friends Otto and Debbie Tharp, Debbie brought the GTO to the dyno for us to test.

Because Tom was not on hand to watch, we set a conservative rpm limit of 5,200. But as you'll see it didn't diminish the power numbers at all because this combo made peak horsepower at a low 4,700 rpm, posting a best reading of 283.38 hp. Is it lower than the 2004? Yes but it was available at lower rpm. The '04 was making about 270 at 4,700 rpm and we haven't discussed the torque yet. The mild mod 455 H.O. produced a peak torque figure of 356.63 ft-lb--42 ft-lb more than the '04 and it had a flatter curve from 2,800 rpm though the rev range. A set of 3.07s in the rear and tall 275/60-15 tires may have held the ultimate power numbers back a bit but we wouldn't know unless we did a gear swap and I doubt Tom would go for that. Regardless, this engine is a stump puller and very nicely matched to the heft of a '71 GTO for blistering street performance.

'70 Judge 400 RAM AIR III
Gregg Miller's '70 Judge runs a Ram Air III engine. However, it was rebuilt like the others and now features a .030 overbore and the most popular Pontiac swap ever--a Ram Air IV cam (1.50:1 rockers were retained). Many builders will tell you not to make this swap into a 400 where the compression ratio was dropped to run on pump gas and they are probably correct. But Gregg did not drop the compression on his Ram Air III--it's still 10.5:1. He runs a mix of 92/112-octane gas to ward off detonation. How did the big cam 400 perform? Well Gregg's engine was a different animal from the H.O. as would be expected with less displacement a shorter stroke and more cam, and of benefit on the chassis dyno, short 225/70-14 tires and wild 4.11 gears. This powerplant screamed on the dyno so with Greg's approval, Jason winged the D-port Ram Air to nearly 5,600 rpm were he felt the engine to begin to nose over. The result was a best of 279.14 hp and 316.65 ft-lb of torque. Power dropped somewhat on subsequent runs so we stopped at 4 (actually the 4th was thrown away).

This number put the modified Ram Air III just 4.24 hp from the 455 H.O. but it made this power at approximately 5,500 rpm were the H.O. did it at 4,700. Peak torque is of course lower than the H.O.--39.98 ft-lb to be exact but its roughly 2 ft-lb better than the '04 GTO. In fact, the powerbands of the '04 and the Ram Air III with IV cam appear somewhat similar in this test.

On the street, the Judge offers a completely different driving experience than the 455 H.O. While the 455 is a cruiser with locomotive-type low-end torque to work well with a low numeric rear gear, the Ram Air III in Greg's Judge thanks in part to its Ram Air IV cam loves to rev and make full use of its 4.11:1 rear gears.

'66 Tri-Power GTO
Norm Shaughnessy definitely had the most stock combination of the group of vintage GTOs. His engine was rebuilt and bored .030 over but everything else is comprised of original or stock replacement parts. He even retained the 10.75:1 compression ratio and runs premium fuel with tetraethyl lead additive. Power is fed through a 4-speed trans to a 3.55 Safe-T-track rear.

Strapped down to the dyno, the 389 sounded very healthy and the result of 4 runs was a high of 200 hp at 4,900 rpm and 263 ft-lb of torque at 2,800 rpm. Norm warned that his GTO had a slow tach so the pulls were limited to 5,000 rpm, while Jason watched the tach on the computer screen. Jason noted that the power was beginning to flatten out over 4,900 rpm.

Yes, these numbers are less than the others but lets realize that this engine gives up displacement, head and exhaust manifold flow and mods to the other 2 traditional Pontiacs and it spots 39 years of engine development to the LS1. We reduced the timing from 36 to 32 degrees, but it didn't make a substantial difference. There was no detonation and no sign of an overly lean condition and the engine ran great.

Norm also reminded me that he had a copy of a car magazine from 1967 where the founding editor of HPP, Marty Schorr had gotten a Royal-tuned '67 400 H.O. GTO to race and that the initial runs on the Motion chassis dyno revealed about 180 hp to the wheels.

Also a friend of Norm's had already chassis dynoed his Tri-Power GTO with pump gas compression and saw 212 hp at the wheels. Given those instances it would seem that this '66 Tri-Power is right in the hunt.

Regardless, it's a gorgeous GTO that will snap your neck and toast the tires forever. And those are certainly attributes of which to be proud.

Jason Scudellari was our dyno... 

   

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Jason Scudellari was our dyno operator not only running the computer but also running the GTO's.

Conclusion
So what did we prove with this test? Well we really weren't trying to prove anything. As is true with all of our strip shootouts we aren't doing this to declare a winner. We simply want to offer for your consideration that these 4 GTOs with the modifications and tuning parameters discussed in this story performed in the aforementioned manner under controlled test conditions on the same day at the same location on the same equipment. Are there other GTOs that will perform better? Sure. Are there others that will perform worse? Of course. Regardless of those facts, each participant should be congratulated for not only having a great GTO but also for letting us flog them on the dyno while they were watching.

Special thanks to: Mike Radke, Debbie Tharp, and Jason Scudellari for their help with this article.

Norm Shaughnessy of Lake Forest, California, related that this '66 is a duplicate of one that he owned when he was 17. The 43 year old told us, "It's a very rare color combo [Martinique bronze with gold interior] I've only seen 2 and I've owned them both 25 years apart!" His goal is to keep this GTO as stock as possible. "Regardless of what others may think of me keeping my GTO stock, I have a blast driving it as is--it gives me a feeling of going back in time." One of his fondest memories behind the wheel came when he raced and beat a '63 R-code 427 Galaxie.

Owner Bio:
Tom Burton had this to say regarding his '71 455 H.O. GTO, "I really love the look of a black '71 with a wing and I wanted a 455 H.O. Locating the hard to find parts that came on a 455 H.O. with air makes this a very special Pontiac to me." The 62-year-old Phoenix, Arizona, resident shared that winning Best of Show at the 2033 GTOAA Western Regional in San Pedro ranks as one of his most memorable moment with his H.O.

Owner: Pontiac GMC

Owner Bio:
When asked why he first purchased this Judge, Gregg Miller replied, "It seemed like a good car to race (21 years ago). I did a lot of that back then." But as it turned out the Judge served well for other functions like giving his newborn daughter her first ride in it. Today 43-year-old Miller, a Corona, California, resident, is married with 2 children and while his trusty Judge ranks high on his priorities list, he says that family still comes first.