Our workhorse was the tried-and-true GM crate engine-the powerplant of a multitude of street rods on the road today and a perfect starting point for an affordable and powerful engine for any street rod.
In the last six months or so, we've been upgrading a pair of small-block V-8s-a Chevy and a Ford-by starting with stock crate engines, adding an assortment of aftermarket goodies, and then testing the engines on the dyno to eyeball all improvements. Hopefully, you've been following along; for those who missed the first few installments, we started out with a 290hp crate Chevy small-block that actually baselined at a more than respectable 309.5 hp-not too shabby for an extremely affordable crate engine.
This time, we went back to the small-block Chevy and our dyno experts at Westech to do a final bit of swapping and testing. The engine was initially equipped for these tests with a Weiand Air Strike intake manifold, a 650-cfm Holley carb, Hedman 1-3/4-inch primary tube headers, Magnum mufflers with 18-inch collector extensions, and an HEI distributor system. To this configuration, and for these new tests, we added a pair of RHS cylinder heads, a set of COMP Magnum roller rockers, and a trio (not at the same time, of course) of cool new flat-tappet Thumpr camshafts from COMP Cams.
This set of testing required us to reconfigure the small-block, yet again. The guys at Westech pulled the engine down to short-block form in preparation for a new series of baseline pulls.
In actuality, our focus was not only on achieving substantial gains in horsepower and torque but to also experience for ourselves the features of COMP's Thumpr camshafts, as we've been dyin' to hear its signature high-performance lump-not exactly a scientific endeavor, but a fun diversion for a hot rodder. For those who aren't familiar with the Thumpr, it's a COMP camshaft design that delivers true high-performance engine sound by "tightening" the lobe separation angle of the camshaft. This tightening creates more overlap between exhaust and intake events and the wild thump gearheads love. It's a pretty simple science, actually, and while logic would have you believe power is lost due to this overlap, results have shown the performance is actually up over similar camshafts due to COMP Cams' innovative lobe designs. Thumprs are available for small- and big-block Chevy, small-block Ford, and small-block Chrysler engines. They're available in three sizes for each application-the Thumpr, the Mutha' Thumpr, and the Big Mutha' Thumpr-and are simple drop-in units that don't require any other engine mods other than a check of valvespring condition, which would be the case with any cam swap.
The original intake and iron GM heads were removed first, and a set of studs were prepped to replace the OEM head bolts.
That said, we tested the trio of new flat-tappet Thumpr camshafts on the Westech dyno over the course of three days, and, as we said a bit earlier, we added a set of RHS as-cast, assembled aluminum cylinder heads (PN 12023-01: 180cc runner volume, 64cc chambers, angle plug design) to that starting mix. The dyno test was run through a range of 2,600 to 6,000 rpm, and several tuning tests were completed for each part's configuration, with the three best pulls averaged together to create a fair representation of the engine's power and torque.
Our first set of pulls got us a fresh high baseline of 318 hp and 355 lb-ft of torque. Over the course of these new pulls, we ended up with a best of 390 hp and 395 lb-ft of torque-a gain that definitely tattooed a smile on our faces.
Thumpr Cams Used and Subsequent Dyno Results 1. Baseline result before
Thumpr Flat-Tappet Camshafts Currently AvailableSmall-block Chevrolet'55-98 model years, 262-400 cid
Small-block Chevrolet'87-98 model years,OE hydraulic roller-equipped
Big-block Chevrolet'65-96 model years, 396-454 cid
Small-block Ford Windsor'69-95 model years, 221- 351W
Small-block Mopar'64-00 model years, 273-360 cid
