Chevy Small Block Testing - Legendary Small-Block Shootout

We Pit The DZ302 Vs L76 327 Vs LT-1 350 In A No-Holds-Barred, Dyno Dogfight.

Richard Holdener Sep 1, 2009 0 Comment(s)
Sucp_0909_23_z Chevy_small_block_testing Valves_springs 1/26

The heads all received new 2.02/1.60 stainless steel valves, valve springs (with 125-130 pounds of seat pressure) and factory retainers. Each head was given a factory-style valve job but no porting of any kind was employed to the otherwise stock castings.

As indicated previously, our original intention was to top each of these legendary short blocks with the same set of 64cc chamber iron heads. As luck would have it, we found period-correct head castings for all three of our test motors. The 492 castings would be run on the LT-1, while the 327 received a set of big-valve, 461 heads and the DZ 302 was toped off with a set of 186 castings. Our pair of 492 heads actually came from two sources, one from Westech Performance and the other from L&R Machine. Both 492 heads were in excellent condition (the one from Westech was untouched) and prior to assembly on the awaiting LT-1 short block was treated to a fresh valve job using new stainless steel 2.02/1.60 valves from Pro Comp, a set of Comp Cams valve springs that offered 130 pounds of seat pressure at 1.825 installed height and a light surface to ensure straightness.

We measured the chamber volume of each head and they checked in at 62cc in both cases. The 461 heads for the 327 and the 186 heads for the 302 were given the same treatment, basically bringing them up to factory fresh condition (but no porting of any kind or any special valve job).

Given the wild cam timing and more-than-adequate static compression ratio of each of our small blocks, it was actually the cylinder heads and intake manifold that held back each of these factory motors from offering even more power. It might be interesting to see what one of these short blocks motor might do with a set of AFR heads and a single-plane intake.

Sucp_0909_17_z Chevy_small_block_testing Flow_rate 2/26

The flow rates for all of the heads are listed in the head flow data chart, but know that most big-valve performance (production) heads offer very similar flow numbers. There seems to be as much difference between two sets of heads of the same casting number as two set of different casting numbers.

Speaking of intakes, our mills all received period-correct intake manifolds. The early 327 featured an original L76 dual-plane high rise (461 casting) courtesy of a seller on Ebay, while the same source was used for the LT-1 intake. Since the intakes used on the 1969 DZ 302 (610 casting) and 1970 LT-1 (110 casting) were nearly identical in terms of design and performance, we elected to run both of these with our over-the-counter factory replacement (024 casting).

All three were originally equipped with Holley 780 (3310) 4-barrel carbs, but since that carb was no longer offered by Holley and a restored unit was well out of our price range, we decided to top all three with a modern Holley 750 Street HP. Pony Carbs offered up an original 780 Holley for testing but we just couldn't bring ourselves to dismantle the carb for jetting and secondary spring changes necessary to work with each configuration.

In terms of the ignition system, these engines were originally equipped with points distributors, but we elected to run an electronic ignition on the dyno. We wanted to ensure adequate spark energy to maximize the power potential of each legendary combination. We also ran the engines with optimal timing rather than factory-spec.

It should also be mentioned that the Elgin reproduction flat-tappet cams were combined with the factory long-slot, stamped-steel rockers (from Comp Cams) and a set of hardened pushrods. If not factory equipped, the heads received an upgrade in the form of screw-in rocker studs (from Comp Cams), but the factory valvetrain components were run to ensure accurate dyno data.

Basically, we were running optimized combinations of each of these motors in the same way enthusiasts might have tuned their motors back in the day. Rather than choke each combination with the restrictive factory exhaust manifolds, we opted to run the same 1.75-inch dyno headers on all three combinations.

No question, the Street HP carburetor added some extra horsepower, too. A Meziere electric water pump replaced all of the factory accessories.

MORE PHOTOS

VIEW FULL GALLERY

COMMENTS

subscribe to the magazine

get digital get print
TO TOP