In­ter­cool­ing with nitrous

Chevy High Performance - - Wrench - ✜ TEXT & PHO­TOS: Richard Hold­ener

There is a war out there in LS land, and it’s be­ing waged be­tween the nitrous and turbo camps. If you fol­low the usual build pat­tern of most LS own­ers, the first mod­i­fi­ca­tion is a camshaft and valvesprings. The right cam can add 50, 60, 70 horse­power or more to a typ­i­cal LS com­bi­na­tion. Even more im­por­tantly, the cam sets the stage for fu­ture mod­i­fi­ca­tions, in­clud­ing nitrous or boost. Add ei­ther one to a stock LS en­gine and it will per­form well. Add ei­ther to a cammed LS and even bet­ter things hap­pen. While nitrous ox­ide might take top honors in the bang-for-the-buck cat­e­gory, tur­bos are the more pop­u­lar go-to power-adder for higher horse­power lev­els. Add the right turbo to a cammed LS and you can top out the flow limit of the turbo, mean­ing 800, 900, even 1,000 horse­power or more with one of them se­ri­ous whizzy wheels. As good as nitrous and tur­bos work sep­a­rately, we de­cided to see how well they per­form to­gether by us­ing nitrous as the in­ter­cooler on a turbo LS.

Why on earth would we com­bine two power-adders with the po­ten­tial en­ergy of a turbo and nitrous? The an­swer is, as al­ways, be­cause we are look­ing for more power, but there is ac­tu­ally an even bet­ter rea­son: cool­ing. You see, while nitrous ox­ide is fa­mous for im­prov­ing the power out­put of any en­gine, it also pro­vides sig­nif­i­cant charge cool­ing, just like your av­er­age air-to-air or air-to-wa­ter in­ter­cooler. The rea­son for this is that the boil­ing point (where the liq­uid nitrous turns to a gas) is a chilly -129 de­grees. While we can’t hope to get the air in­take tem­per­a­ture of our turbo en­gine down that low (un­less we run straight nitrous), the in­tro­duc­tion of even a small sam­ple of nitrous at

-129 de­grees has a pos­i­tive ef­fect on charge cool­ing. How much, you ask? That’s what we’re here to find out.

To un­lock the hid­den cool­ing mys­ter­ies of nitrous ox­ide, we took Nitrous Ex­press up on their of­fer to sup­ply a wet fog­ger noz­zle for test­ing. Us­ing the nitrous kit, we were able to pro­vide nitrous to a non­in­ter­cooled turbo LS en­gine. Along the way, we mon­i­tored the power out­put, the boost and back­pres­sure, and the all-im­por­tant change in in­let air tem­per­a­ture.

The turbo test en­gine was a fa­mous one, hav­ing pro­duced 1,543 hp at

29.2 psi for an episode of En­gine Mas­ters TV. Mak­ing this all the more im­pres­sive was the fact that the high­mileage Gen IV LY6 short-block was

stone stock. The only ex­cep­tions be­ing a re­gap­ping of the fac­tory rings and adding ARP head studs. The stock bot­tom-end 6.0L was aug­mented with CNC-ported Trick Flow Spe­cial­ties

225 heads, a stage 3 turbo cam from Brian Too­ley Rac­ing, and (for this test) a Dor­man LS6 in­take. Also present were 120-pound Hol­ley in­jec­tors, an Ac­cu­fab throt­tle body, and a sin­gle Lil John’s Mo­tor­sport So­lu­tions (LJMS) BorgWarner S475 turbo. The turbo was fed by (of all things) a set of stock, cast-iron truck man­i­folds and cus­tom Y-pipe. The 2.5-inch Y-pipe from JFAB was de­signed to ac­cept an adapter to al­low the in­stal­la­tion of a va­ri­ety of dif­fer­ent turbo sizes. The T4 S475 from LJMS was ca­pa­ble of sup­port­ing some­where near 1,000 hp, but for our non-in­ter­cooled turbo test, we ran it at a safely re­duced boost level. Con­trol­ling the boost was a pair of Tur­bosmart Hyper-Gate45 waste­gates. To en­sure safety and al­low us to run suf­fi­cient tim­ing, we ran all of the test­ing on 118-oc­tane Rockett Brand race fuel, though the 7.5-psi boost lev­els were cer­tainly pump gas friendly.

The first or­der of busi­ness was to run the 6.0L turbo en­gine on the dyno with­out the nitrous in non­in­ter­cooled form. Di­al­ing in the A/F ra­tio and tim­ing curves was easy on the Hol­ley HP man­age­ment sys­tem, and in no time we had the turbo en­gine pump­ing out 723 hp at 6,800 rpm and 641 lb-ft of torque at 5,100 rpm. The boost curve pro­duced by the S475 turbo hov­ered over 7.0 psi for most of the run, with a peak of 7.5 psi. We took the lib­erty of mon­i­tor­ing back­pres­sure as well, and the peak back­pres­sure read­ing checked in

at 14.4 psi at a boost level of 7.4 psi (a ra­tio of 1.95:1). Dur­ing the runs, the in­let air temps at 7.4 psi reached a peak of 176 de­grees, with an am­bi­ent air temp of 78 de­grees. After in­stal­la­tion of the NX wet fog­ger noz­zle in the dis­charge tube, we sup­plied jet­ting that should pro­vide an ex­tra 100 hp. Upon ac­ti­va­tion of the NX nitrous kit, the air temps dropped by over 50 de­grees and power out­put jumped to 907 hp at 6,800 rpm and 882 lb-ft of torque at 5,500 rpm. The nitrous dropped the air temps, but in­creased the boost pres­sure, to a peak of 10.6 psi near the ac­ti­va­tion point, though this dropped to 9.4 psi near the power peak. The NX kit upped the power ante by 184 hp and dropped IATs by over 50 de­grees. I guess chilling out this turbo stuff re­ally works. CHP

Boost is per­haps the best thing that ever hap­pened to the LS, but it gets even bet­ter when you add nitrous!

01 | Our test en­gine was a stock, high-mileage LY6 short-block with in­creased ring gap. It was aug­mented with a set of Trick Flow Spe­cial­ties 225 heads and BTRStage 3 turbo cam. Run in nat­u­rally as­pi­rated trim, the 6.0L pro­duced 514 hp.

02 | For this test, we in­stalled a Dor­man LS6 in­take and Hol­ley 120-pound in­jec­tors.

03 | Feed­ing the Dor­man in­take was a 78mm Ac­cu­fab throt­tle body.

04 | For this turbo ad­ven­ture, we re­lied on a set of 6.0L truck man­i­folds to feed our sin­gle turbo. The fac­tory man­i­folds were re­versed, but still of­fered per­fect plug ac­cess and elim­i­nated any con­cern for burn­ing plug wires.

05 | The truck man­i­folds fed a cus­tom 2.5-inch Y-pipe built by JFAB. Note the dual waste­gate pro­vi­sions.

06 | The Y-pipe joined to­gether to a com­mon 3-inch V-band de­signed to ac­cept adapters for T4 and T6 tur­bos. Note the ex­haust back­pres­sure probe in the Y-pipe.

07 | To prop­erly con­trol the boost, we re­lied on a pair of Tur­bosmart Gen-V Hyper-Gate45 waste­gates. The open port next to the vac­uum/boost ref­er­ence line was for wa­ter cool­ing.

08 | Tur­bosmart also pro­vided one of theirRace Port blow-off valves (BOV), though this one was the old de­sign, and de­spite hav­ing seen plenty of years and runs, it still worked per­fectly.

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