142 Blower Opportunity
Q My 1985 Monte Carlo SS has a 358 small-block covered by ported and polished S/R Torquers 67cc chambers. I have a Holley 750 3310 on top a Weiand dual-plenum tall-platform intake. Valves are opened via a Comp Cams 12-243-3 dual-pattern. The exhaust exits via Flowtech Afterburner headers and old-school, three-chamber 50-series Flowmasters. Finally, the power is transfered through an Art Carr 700r4 rated at 800 hp and 3.73s to both wheels, thanks to Auburn Gear.
I purchased a rebuilt B&M 142 supercharger kit that I'd really like to bolt on my powerplant. I have planned on installing thicker head gaskets to reduce my compression a bit. I am concerned about my ring gap. I read an article in which a 142 Weiand blower was bolted to a 383: "1972 Chevy Nova Weiand 142 Blower Upgrade - Boost Machine, January 2009." The engine was built for an alternate purpose. The engine was reused for new article. The article did not say anything about ring gap. I want to know if piston ring gap was opened up for the additional blower pressure or not. My top compression rings come in at 0.018 inch gap. Can I run my 142 blower with my engine as is? I have planned on installing thicker head gaskets to reduce my compression a bit. How would my Torquers react to the blower addition? What would be a good cam and head setup? This is a street-driven car that I take the kids to baseball in. It also gets me to work when the weather is good. Thanks, and keep up the good work!
St. Joseph, MI.
A Great job keeping us honest. On that specific 383 engine with the Weiand blower install, the ring end gap was not increased for the blower installation. We're glad to see you have your thinking cap on when considering the blower install on your small-block. Let's talk through a few things—we think you're going to like the answers.
First, we're going to assume you have either forged or standard cast pistons in your 358 if you built your engine with a 0.018-inch ring end gap. If you were running hypereutectic pistons, your engine would have already butted the rings with the above spec. As for your build you've used the standard street performance spec of 0.0045 inch gap per inch of bore. This is a relatively safe spec for most performance applications. When you start throwing large doses of nitrous or boost at the engine, you need to open the top ring gap up into the 0.006 inch per inch of bore. Again, that's large doses of nitrous or boost.
Your 142-cid B&M blower will probably give you 6 to 8 psi of boost at full song. The larger the displacement of the engine, the lower the boost will be. At these boost levels it's completely safe to leave your ring end gap where they're at. All the aftermarket blower companies sell blowers to the masses and they pop them on top of stock short-blocks with these types of boost levels. Again, we believe you're good to go with your short-block.
As for your camshaft and cylinder heads, the COMP Cams' 12-243-3 is the Xtreme 4X4 X4270H, which specs out at 226/234 degrees duration at 0.050 inch of tappet lift, 0.480/0.498 inch max lift, and is ground on 111 centers. This is pretty aggressive for stable idle with the 226 degrees intake duration, and the relatively tight separation angle for a supercharger application. Obviously, you've been happy with this engine combination with the rest of your drivetrain. The converter in your TH700R-4 must be enough to handle the duration and overlap that this cam has. Swap the blower straight onto your current long-block and see how you like it. The Torquers will work just fine as you will be pushing the air into the cylinders.
If the cam gives you fits trying to control the idle once the blower is installed, swap it out for the COMP Cams' Nitrous HP cam, NX262H. This shaft specs out a 218/230 at 0.50, 0.462/0.480 inch max lift, and is ground on a wider separation angle of 113 degrees. We really like the 12-degree spread on the dual-pattern, which favors the exhaust side. When you boost the power by either nitrous or aupercharging, you need more exhaust event. This camshaft would really make a snappy throttle response, and make good power to 6,000 rpm.
Your kids are going to like their ride to the baseball games—that ride's about to get faster! Good luck with your swap and enjoy the power.