Modifying And Testing A Dodge 360-Cube LA Small-Block On The Dyno

There’s no denying that when it comes to the battle of the small-blocks, the two major players have a bowtie and an oval associated with their names. Generally, when you think Mopar, it’s usually the big-block engines that get the lion’s share of the attention. However, the LA-series, and less-common A-series, small-block Mopars are no slouches.

Even though they are often overshadowed by the other two-thirds of the “Big Three,” the small-block Mopar engines have just as much potential as the small-block engines of other makes. Luckily, Richard Holdener is about as anti-brand-fanboy as they come. As such, he has this LA-series 360 engine out of his 1975 Dodge Tradesman van with which to conduct his usual dyno experiments on.

Starting with a bone-stock 360, Holdener got a baseline before throwing the kitchen sink at the engine, in terms of bolt-on modifications. With a two-barrel carb, factory air cleaner assembly, alternator factory cast iron exhaust manifolds, and the two-inch-diameter exhaust as it came out of the van, the engine produced 225 horsepower at 4,500 rpm and 338 lb-ft of torque at 2,900 rpm. A high-revving beast, this ain’t.

Gee... Who'da thunk these OEM parts might not be good for power? While it's no surprise that these OEM pieces were restrictive, even on the factory 2-barrel setup, just HOW restrictive they were is a little surprising.

Making Mo-Power!

The first thing Holdener tested was pulling the air cleaner assembly. While that might not seem like much on an engine making mediocre power, it did pick up 6 horsepower and 5 lb-ft of torque at the peak, with the gains seen under the curve, across the board. Swapping to a factory four-barrel intake manifold and an Edelbrock quadrajet carburetor saw significant gains above 2,800 rpm, both in peak numbers and under the curve. A new best of 264 horsepower and 359 lb-ft was established slightly higher RPM with the four-barrel induction.

The next step was to swap to 1-5/8-inch long-tube headers. As expected, peak gains were had, with another 13 horsepower and 14 lb-ft for peak numbers of 277 and 373, again, a little higher in the RPM range. However, Holdener points out the biggest gains are in the midrange, where the headers added up to 30 lb-ft of torque at some points. “The extra scavenging of the long tubes will build up power down low, which is what we like,” Holdener says.

The LA-series 360 went through several rounds of modifications in the name of science. Once Holdener finished his mad scientist routine on the engine, he actually reinstalled some of the milder parts for use in his van.

Stepping Up The Game

The next round of modifications was serious, with Holdener swapping both the camshaft and cylinder heads. The cylinder heads were a set of factory 360 heads with mild porting, new 2.02-inch intake and 1.60-inch exhaust valves (which is only a mild increase in size over the factory intake valve and the same size exhaust as stock). “All we did was go in and clean up the bowls a little bit. A little fluffing on the entry, but mostly bowl-work,” Holdener explains.

For the camshaft, Holdener went to COMP Cams for one of their Xtreme Energy street cams. Grind number XE250H is designed to make power between 800 and 4,800 rpm and has .432-inch of intake lift, .444-inch exhaust valve lift, only 206-degrees/212-degrees of duration at .050-inch, and a 110-degree LSA. While conservative, the cam was designed to make a lot of torque, get solid mileage, and idle nicely. Since this engine would be going back into Holdener’s van, those were all desirable qualities for him.

The heads and camshaft were worth another 60-plus horsepower and 40-plus lb-ft of torque, for new peak numbers of 339 horsepower and 414 lb-ft. If you look back at the baseline pull, Holdener has picked up well over 110 horsepower and almost 80 lb-ft at this point. Of course, he wasn’t done there.

Both intake upgrades — the factory four-barrel intake on the left and an Edelbrock RPM Air-Gap on the right — were a worthwhile upgrade over the factory two-barrel intake manifold.

Feeling there was some additional power to be had in the induction tract, Holdener swapped on an Edelbrock RPM Air-Gap dual-plane intake and a 650 cfm Demon carburetor. While the peak gains were relatively minor, showing only three horsepower and 14 lb-ft, the area under the curve from 3,100 to 5,100 says otherwise, with significant gains seen.

Getting into “kitchen sink” territory, Holdener then replaced the factory shaft rockers with a set of COMP Cams roller rockers. That brought peak power to 354 horsepower and 428 lb-ft of torque with additional gains seen under the top-end of the curve.

Finally, Holdener had one last trick up his sleeve, and that was another camshaft. Also from COMP Cams, this one was the XE268H grind, with an advertised powerband of 1,600 to 5,800 rpm. With .477-inch of lift on the intake and .480 on the exhaust, 224-degrees intake and 230-degrees exhaust duration at .050-inch, and the same lobe separation angle as the previous cam, this cam is definitely more performance-oriented.

Peak power jumped up another 33 horsepower, peak torque was up a scant 6 lb-ft, but made a significant increase in power and torque from 3,100 to 5,600 rpm. Final numbers on the 360 cubic-inch LA engine were 387 horsepower and 434 lb-ft of torque. That means a net increase of 162 horsepower and 96 lb-ft of torque over the OEM engine configuration.

While this isn’t a monster-power build by any means, it also doesn’t have any extreme parts on it, either. Sure, you could get crazy and get the engine to make whatever power numbers you want, because after all, an engine us just an air pump. What this does prove, is that the Mopar faithful aren’t crazy for liking something other than a Hemi, and really aren’t at any inherent disadvantage, save for parts cost (based solely on the economy of scale).

More Sources

About the author

Greg Acosta

Greg has spent fifteen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
Read My Articles

Hot Rods and Muscle Cars in your inbox.

Build your own custom newsletter with the content you love from Street Muscle, directly to your inbox, absolutely FREE!

Free WordPress Themes
Street Muscle NEWSLETTER - SIGN UP FREE!

We will safeguard your e-mail and only send content you request.

Street Muscle - The Ultimate Muscle Car Magazine

We'll send you the most interesting Street Muscle articles, news, car features, and videos every week.

Street Muscle - The Ultimate Muscle Car Magazine

Street Muscle NEWSLETTER - SIGN UP FREE!

We will safeguard your e-mail and only send content you request.

Street Muscle - The Ultimate Muscle Car Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...



Classic Ford Performance

Street Rods

Classic Chevy Magazine

Street Muscle - The Ultimate Muscle Car Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

  • Classic Ford Performance
  • Street Rods
  • Classic Chevy Magazine

Street Muscle - The Ultimate Muscle Car Magazine

Thank you for your subscription.

Thank you for your subscription.

Street Muscle - The Ultimate Muscle Car Magazine

Thank you for your subscription.

Thank you for your subscription.

Loading