Gear GrindQ I've got a 355 with a steel crank, Scat rods, and D-dished forged pistons for use with a blower. That's where I'm heading with this combo. I have the Comp Cams Nitrous or blower cam, 292 duration and 0.501 inch max lift. I just put the heads on the engine yesterday, but I'm getting conflicting arguments about my Pete Jackson geardrive and its harmonic something-or-other. I figure it's going to about 500-550 horses. Is there anything to worry about? Should I sell my geardrive and get a chain? Money is a factor here. Any input would be greatly appreciated...I mean, I saved up for the geardrive, thinking it was stronger. Thanks for your time.Michael Campagnoni
A Geardrives are the most durable camshaft-drive system available. Do they transmit crankshaft harmonics from the firing pulses of each cylinder back into the valvetrain? Yes. Is it a big deal? In your application, no. Where the geardrives get into trouble is when you're pushing the valvetrain dynamic to the max. The firing harmonics will aggravate the valvetrain stability. The firing harmonics will also affect the spark timing at the end of the camshaft where it drives the distributor. The best drive system for isolating the valvetrain from crankshaft harmonics is a beltdrive. Jesel released the first Gilmore belt drives for Chevys over 30 years ago. The rubber belt dampens the firing pulses.
Again, for your application, enjoy the whine of your Pete Jackson geardrive. Good luck with your blower adventure.
Impersonator Lite!Q This question concerns the article on the Impersonator buildup. Would you get similar results with 350 cid? I understand it would be considerably less on torque and horsepower, because it is less cubic inches. Or is this one of those combos that is optimal with the bore and stroke of the 406? The reason I ask is I already have a 350 with flat-top pistons, Vortec heads, an Edelbrock Performer RPM intake, and either a 650 Edelbrock or a 700-cfm Holley carb. I have not made a decision on a cam, but had considered a Comp Cams XE274. This engine is going in a '64 Chevelle with 3.73:1 gears, a four-speed manual trans, and about 27-inch-tall tires. I figured that you have seen and built lots of combinations that work well, and have some very good ideas and info. Thanks!Mark Richards
A The Impersonator was really a cool buildup. Sometimes you will fall into a killer package for the money, and that engine is one of them. Will those same pieces make a good-running 350? Absolutely! Now, your statement that we have some very good ideas is a real stretch...let's see if we can help.If you look at the power that the 406 made, it comes in at 428 hp and 525 lb-ft of torque. If you do a little math, that equates to 1.05 hp per cube and 1.29 lb-ft per cubic inch! Now, that last number is a biggie. One benefit of using the smaller-displacement 350 is that the small Vortec cylinder heads won't run out of air as early in the rpm curve as they did on the 406. The 406 had a horsepower peak of 5,000 rpm. With the correct camshaft, your 350 will peak around 6,000 rpm. This will carry the torque much higher in the rpm band, producing almost the same horsepower as the 406. The engine will lose some of the torque benefits of the large-displacement engine. Then it's time to look at camshafts.
You mentioned that you have an interest in using the Comp Cams XE274. That is a great camshaft, but for your buildup it's a little on the big side. You will give up too much torque with that camshaft, and only gain a few horsepower over the XE268. The 268 specs out at 224/230 degrees duration at 0.050 inch tappet lift, 0.477/0.480 inch max lift, and is ground on 110 centers. Yes, the 274 only has around 6 more degrees duration, but again, your Vortec cylinder heads run out of air by the time the engine can take advantage of the extra duration.