A The L98 tuned port- injected engines were great mileage engines. With an overdrive transmission they will knock down 24-25 mpg! You're right on target to get very close to your 300hp bogie. The engine from the factory was rated at 240 SAE corrected horsepower. The performance aftermarket speaks in "standard corrected horsepower." This means the engine is rated at a more favorable barometric pressure reading and lower inlet temperature. With these better atmospheric conditions the engine makes about 5 percent more power than the factory rates the engine. This brings your 240 SAE power up to around 252 hp.
First, the Vortec head swap, the Scoggin-Dicky TPI base, and a set of tuned-port runners will give your engine a breath of fresh air. This swap alone will extend the L98's rather short rpm range. Stock L98s run out of air around 4,000 rpm. Yes, they will wind up to 5,500 rpm, but they stop making power around 4,200 rpm. Well, you must make torque higher in the rpm range to increase the horsepower. This combination should give you a horsepower peak around 4,800 rpm and extend the usable power to around 5,200 rpm. You should realize a 30hp gain with these parts on the stock engine. With the headers and exhaust system, another 20. The 1.6-ratio rocker swap is an easy 10hp gain on this combo of parts. Without changing the camshaft we've talked ourselves over the 300-plus power range, and you've extended the engine's powerband without losing slow-speed torque. Would we change the camshaft? Well, I'm on the conservative side; the stock camshaft will give you an excellent balance of power and fuel economy.
As for the throttle body, we have made well over 400 hp with a stock throttle body. At the power level you're asking for, stick with the stocker. Good luck, and have fun driving past those pesky gas stations.
More Than Just AluminumQOther than the aluminum block, were there any differences between the '69 Chevrolet ZL1 and L88 engines? What is the duration and lift of both cams?Doug JesserVia e-mail
A OK, for this info I dug back into my original Hot to Hot Rod Big-Block Chevrolets. This book was first published back in 1971, with revised reprints in 1972 and 1977. I've had it since 1977 and have worn out every tattered page. Back in the day, GM rated its camshafts not at 0.050 inch of tappet lift, which is an SAE standard, but at 0.008 inch for hydraulic lifters and 0.015 inch for mechanicals. This is the lift off the base circle, which GM believed represented taking up the lash in the valvetrain. The L88 camshaft was sold under PN 3925535 for chain-driven camshafts and PN 3925533 for the gear-driven models. These camshafts won't have the part number stamped into them; you will most likely find ID number 8911. The very long duration numbers come in at 326 on the inlet and 334 degrees on the exhaust, with a max lift of 0.540/0.560, and 133 degrees of overlap, respectively. As for the ZL1 cam, it was sold under PN 3959180. The ID number of this shaft is 9181. This camshaft came in with numbers of 347/359 duration at lash point, 0.560/0.600 inch of max lift, and 135 degre of overlap. One last cam that was available was the fuel-injection cam for the ZL1 Can Am engines, sold under PN 3994094. Its numbers are a wild 360/366 degrees of duration, 0.600 inch of max lift on both the intake and exhaust, and a whopping 148 degrees overlap. Even though Chevy offered geardrive camshafts, all the L88s and ZL1s were chaindriven from the factory. As I made my way through the years of GM Power Books and GM Performance Parts catalogs, I found where they actually spec'd the cams out in '97. Now, these numbers differ slightly from the early '70s numbers. I'd suspect these numbers were generated by a Cam Doctor, which allows you to digitize the profile into a computer to analyze the camshaft's profile. The L88 cam, PN 3925535, has 264/270 degrees duration at 0.050 inch tappet lift, 0.536/ 0.554 inch max lift, and is ground on a 112 separation angle. The ZL1 shaft, PN 3959180, spec'd out at 262/273 at 0.050 inch tappet lift, 0.556/0.594 inch max lift, and a 110 separation angle.