Are Carbs Still King?

Part 2: LS3 In­take In­san­ity

Hot Rod - - Contents - Richard Hold­ener

In the July 2018 is­sue of HOT ROD, we hatched a plan to test ev­ery in­take man­i­fold for the LS3 en­gine that we could get our hands on. Given the pop­u­lar­ity of the rec­tan­gu­lar-port LS3 con­fig­u­ra­tion, it was only nat­u­ral that the af­ter­mar­ket em­braced it with open arms and of­fers all man­ner of in­take man­i­folds, both car­bu­reted and fuel in­jected. In fact, there were so many in­takes avail­able for the LS3, we had to break our test into two parts. Part 1 cov­ered the EFI in­takes; in this in­stall­ment, part 2, we tested a va­ri­ety of dif­fer­ent car­bu­reted in­takes. Af­ter all, man does not live by EFI alone, and carbs are plenty pop­u­lar for many per­for­mance ap­pli­ca­tions. Thanks to per­for­mance prod­ucts like the MSD ig­ni­tion con­troller, adding a car­bu­reted in­take to your LS3 has never been eas­ier. But which one do you choose?

Much like our test on the EFI in­take shootout, we need to point out a few facts be­fore we get to the re­sults. For this test, we com­pared all of the in­takes to the fac­tory LS3 EFI in­take. The com­bi­na­tion of av­er­age and peak power makes the stock man­i­fold dif­fi­cult to beat. If you don’t be­lieve us, just check out the re­sults of part 1. Know­ing that an in­take should be cho­sen for the in­tended com­bi­na­tion, and no test en­gine will of­fer the right com­bi­na­tion for all in­takes, we de­cided to throw in a twist for part 2. Rather than use the cammed LS3 crate en­gine in part 1, we stepped up and built a 415 stro­ker us­ing com­po­nents from Wiseco, K1, and AFR. Us­ing an LS3 block from Gan­drud Chevro­let, we as­sem­bled a pow­er­ful com­bi­na­tion that we hoped would bet­ter fa­vor the power po­ten­tial of some of the sin­gle-plane in­takes from Edel­brock, Mast, and TFS. Of course, this wilder com­bi­na­tion was less well suited to the dual-plane in­takes, but such was the trade-off in­her­ent in test­ing them all on one en­gine.

The var­i­ous LS groups might grav­i­tate to­ward the big peak num­bers, but as al­ways, there is much more to any given com­bi­na­tion than sim­ple peak power and torque. A com­par­i­son be­tween the least pow­er­ful dual plane and the most pow­er­ful sin­gle plane re­vealed a dif­fer­ence of 54 hp, but that hardly tells the whole story of the com­par­i­son be­tween these two ex­tremes. Though the sin­gle plane of­fered as much as 63 hp at 7,000 rpm over the dual plane, the dual plane of­fered an ad­di­tional 62 lb-ft of torque at 3,500 rpm. For any kind of ac­cel­er­a­tion con­test, the sin­gle plane would be the clear win­ner, but not ev­ery LS3 owner is look­ing for low elapsed times and high trap speeds. The dual plane even of­fered more low-speed torque than the fac­tory (long-run­ner) LS3 in­take, which is no easy feat!

Know­ing there are end­less rea­sons be­hind choos­ing an in­take, we in­cluded not only peak power num­bers but also things like av­er­age power pro­duc­tion from 3,500 rpm to 7,000 rpm, as well as torque pro­duc­tion at 4,000 rpm. As in­di­cated in part 1, if you are look­ing for the most pow­er­ful man­i­fold ever made, you are look­ing in the wrong place. It sim­ply doesn’t ex­ist. How­ever, the in­for­ma­tion pro­vided here should help you choose one to suit your car­bu­reted ap­pli­ca­tion. Be sure to check out our video to hear them run!

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