Rocker Or Cam Swap?
I have a '78 T/A with the stock 180-horse engine. The car is in good shape, and the engine was rebuilt to stock specs many years ago. It has low mileage and runs great.
I dumped the 2.41 rear gears and installed 3.23s. The transmission is a Turbo 350; the carburetor has been rejetted and the distributor recurved (36 degrees total at 2,400 rpm). I also added a true dual exhaust with twin cats and mufflers. Currently, it runs 14.50 at 95 mph.
My friend tells me the stock cam (I don't know the specs; can you tell me?) is hold-ing me back, and at the very least, I should change the rocker ratio to 1.65:1 to make more power with that cam-or I should spend the money and swap the cam. What do you think? Will the 1.65-ratio rockers get the job done or do I need a new cam? If so, which one? I don't want to rebuild the engine if I don't have to-it runs great and has passed a compression test.
Frank Odom
Via Internet
Paul Spotts Responds:
Your 180hp 400 should be a code YA or YU with 6X heads and 7.6:1 compression. Your stock cam is No. 471. I was surprised to see it's a straight-pattern cam with an advertised duration of 274/274 degrees and only 0.374 lift. This same cam was also used in the 301 engine.
Was the exact same cam reinstalled during your rebuild? If a new stock cam replaced the original, I very well doubt a 471 cam (only available through Pontiac, as far as I know) was installed.
Most aftermarket stock-replacement cams purchased through a parts house or machine shop usually have 270-280s advertised duration and lift of 0.406. I seriously doubt you have a 471 cam with 14.50 timeslips, but I could be wrong.
Although you don't know what cam you have, you can measure the lobe lift with a dial indicator. Most/many hobbyists don't do this and blindly install higher rocker ratios. You should never-this is important-never install 1.65:1 rockers (or 1.6:1, 1.7:1, and so on) without knowing your cam lift and valvespring and retainer clearances. If the resulting lift is more than the valvesprings and retainer clearances allow, you'll bend pushrods, break rocker studs, wipe out a cam, and so on.
It's safe to install 1.65:1s with stock cams in most applications, especially with a 471 cam. The lift with a factory 471 cam and 1.65:1s is only 0.411. The 0.406-lift cam with 1.65:1s installed is increased to 0.447-still safe in most applications.
I would say your friends are partially correct that your cam is holding you back, but you didn't supply enough information. Is the intake a stock '78? Do you have manifolds or headers? An intake swap to a '71-'72 or aftermarket unit would help, as would headers over manifolds.
With that said, I would replace your cam with a Comp Cam 51-222-4. This is the max effort cam with 7.6:1 compression. The specs are 262/270-degrees advertised (218/224 at 0.050) duration and 0.462/0.470 lift with 1.50:1 rockers. This Extreme Energy cam makes good power with low compression because of its modern ramp design and tighter lobe separation.