Running on the street with the exhaust off isn't an option, but it did allow us to check how much power it was costing. With the exhaust off, WOT manifold vacuum went up to 1.5 inches Hg and power went up 15 hp. The manifold vacuum told us we were right on the edge with our carb size. Any more vacuum and a larger carb would be indicated.
Dyno Run 8:
With the fan unbolted, power swelled to 292.5 at 5,143 rpm. By now, a crowd had gathered and everybody thought this would be worth about 20 hp, but they were wrong. The stock non-clutch flex fan (which we recycled from our old 305) hogs only 10 hp. At this point we were looking for that 300hp number, so the next move was a COMP Cams 1-inch open carb spacer. This would give us more top-end power by allowing the cylinders to have access to all four barrels of the carb. The extra plenum volume would also have a positive effect on power, but how much?
Dyno Run 9:
The spacer adds a disappointing 5 hp, bumping the total pony count up to 297.8 hp at 5,019 rpm. Heads get together and calculate that the mixture is too lean, so fuel is added. The primary jets are bumped from 66 to 70, and the emulsion bleeds in the secondary metering plate (acting as jets) are bored out from .059-inch to .062-inch--the equivalent of going from 60 jets to 63 jets.
Dyno Run 10:
Wow! Power jumps to 311.4 hp at 5,168 rpm. That's a lift of over 13 hp. All agree it's the right time to reconnect the exhaust (and flex fan) to see where the air/fuel ratio is.
More top end was found by bolting on a COMP Cams VH311 polymer 1-inch open spacer, which costs $19.99 from Summit. The spacer took some tuning to maximize, but was ultimately worth 10 to 15 hp.
Dyno Run 11:
With the exhaust and fan hooked back up, peak power takes a nose dive to 279.0 hp at 5,134 rpm, a loss of 32 hp. That's a greater loss than the fan or exhaust added when taken off, so we're on to something. The air/fuel ratio is hooked up and measures 10.8:1, way too rich, so the primaries are leaned out to 66 jets (from 70s) and the secondary metering plate gets a new set of orifices drilled out to .059-inch (the same as in run number 9).
Dyno Run 12:
Power takes another dive to 269.7 hp at 5,137 rpm. Apparently, lean is not what our motor wants to see, so Habrzyk moves the other direction and fattens the secondaries up to .070-inch orifices (approximately 68 jets). The primary jets are left at 66.
At the track, we laid down a best ET of 13.35/105.85 with the new tune. That's a full half-second quicker and 4 mph faster through the traps. This matches our hp gain perfectly when compared to our previous best of 13.85/101.62. While we do think some seat-of-the-pants tuning would've helped, we doubt we would've been able to get this much power without the Westech chassis dyno and a wide-band O2 sensor. We've spent $19,879.50--that's close enough to $20,000 to satisfy us. What should we do with g/28 now? Let us know!
Dyno Run 13:
Bingo! The smog 383 responds with 292.1 hp at 5,155 rpm (up 22 hp)--and that's now happening with the exhaust hooked up and the mechanical fan running. Another heated discussion breaks out: Shouldn't we use a bigger carb than a 600 cfm? A bigger carb wouldn't be legal, but might be worth some information. We decide against it, as manifold vacuum at WOT was .8-inch Hg. More carb won't help with the exhaust hooked up and vacuum so low. Apparently, fat is where it's at, so instead, the secondaries are drilled out again, this time to .076-inch (approximately 72 jets).
Dyno Run 14:
Peak power drops a little to 290.1 hp at 5,072 rpm, but midrange power is up as much as 5 hp everywhere else. Habrzyk and Dulcich figure the fatter secondaries are probably covering a dead spot in the midrange. This will help us get down track quicker, so we decide to keep the 66 jets up front and the .076-inch orifices in the rear. All we need to do now is bolt on the K&N filter and drop base to see if it costs us any power.
Dyno Run 15:
With the filter on, power peaks at 290.0 hp at 5,212 rpm. We carefully close the hood to check clearance, and the carb spacer, carb, and air cleaner just barely rub the bottom of the hood. We decide it's no big deal since a short cowl hood is in our future. We're done, and now it's time for the track. We're up 39 hp, which should be good for four tenths, nominally. Will it work out that way? Check the photo!
The End Is Nigh
It's been a great ride with Project g/28, but it's time to bring the mods to a close with this installment. We set out to make our '76 Camaro an all-around performer, with the emphasis on handling, budget, and making it street-legal. We set four primary performance goals with a budget of $20,000: run the 420-foot slalom course at 46 mph or better, stop from 60 mph in less than 120 feet, circle the skidpad greater than .90g, and run the quarter-mile in less than 13 seconds. We accomplished the first three, and came darned close with the last, all while staying within our budget.
If you missed any of the nine installments prior to this one (we started back in the April 2005 issue), you can log on to www.popularhotrodding.com to read anything you missed. (catch up) Every test session, every bolt-on and every source can be found on our Web site, so if you're hazy about some of the details, don't be afraid to check it out.
So where are we going now? We have a few things we want to try on g/28 that aren't part of our original set of plans. Although the series is technically at an end, you can look for more stories down the line. Drop us a note if you have an idea!