The Fifth Di­men­sion, Part IV

Dyno test­ing the Gen V LT1 to the tune of 518 hp out of the crate!

Street Rodder - - Contents - By Jeff Smith Pho­tog­ra­phy by the Au­thor

If you’ve been fol­low­ing our se­ries on the LT1 then you’re up to speed on our look at Chevy’s lat­est-gen­er­a­tion small-block. We fi­nally aligned all our ducks beak to tail and mounted the LT1 up on Westech’s engine dyno; the pur­veyor of truth, jus­tice, and the cool power num­bers. So let’s get right to it be­cause there is some ex­cel­lent power and in­for­ma­tion to be squeezed out of this Gen V engine.

GM rates the nor­mally as­pi­rated LT1 at a rather cau­tious 460 hp. There are rea­sons for that con­ser­va­tive num­ber that we’ll get into but with a lit­tle bit of tim­ing and fuel ad­just­ment we were able to crank a much more im­pres­sive 518 hp and 520 lb-ft of torque out of this di­rect-in­jected engine. But peak num­bers only tell part of the story. There’s much more data hid­ing in be­tween the lines on the dyno curves.

There are sev­eral rea­sons why there is a big dis­par­ity be­tween the num­bers we gen­er­ated on Westech’s Su­perFlow dyno and the fac­tory num­bers and it’s worth dis­cussing why the num­bers are dif­fer­ent. Yes, our num­bers en­joyed the ad­van­tage of a set of head­ers but that might only be worth 10-15 hp. So how do we ac­count for the other 40-odd horse­power? Some naysay­ers will im­me­di­ately claim that Westech has a “happy” dyno. Westech’s test­ing pro­ce­dure is very dif­fer­ent from the OE ver­sion and that’s where the num­bers be­gin to di­verge. Let’s get into why both the GM and af­ter­mar­ket dyno num­bers are ac­cu­rate yet dif­fer­ent.

Be­fore the early ’70s, there re­ally were no spe­cific rules on ad­ver­tised horse­power so the fac­to­ries used the more op­ti­mistic gross horse­power num­bers and used the then-stan­dard cor­rec­tion fac­tor of sea level pres­sure (29.92 Hg), zero hu­mid­ity, and an in­let air tem­per­a­ture of 60 de­grees F. This would be a re­ally cool day at ocean side with no hu­mid­ity. As you can imag­ine, this isn’t a con­di­tion that oc­curs very of­ten, ex­cept at the beach.

By 1972, the fac­to­ries be­gan us­ing the new J1349 stan­dard that changed the cor­rec­tion fac­tor to a much warmer 77 de­grees F and low­ered the air pres­sure to 29.23 Hg while re­tain­ing the zero hu­mid­ity point. This

re­duced the crank­shaft power from the pre­vi­ous cor­rec­tion fac­tor by roughly 5 per­cent. An engine mak­ing 400 hp on the new stan­dard would make 420 hp us­ing the old cor­rec­tion fac­tor.

Later, other changes were in­au­gu­rated, in­clud­ing re­quire­ments that en­gines run at nor­mal­ized op­er­at­ing tem­per­a­ture and that the full ac­ces­sory drive and ex­haust also be in­cluded. All of these re­quire­ments re­duced the power out­put com­pared to the older “hot rod” ver­sion cor­rec­tion fac­tor that is used in all mag­a­zine sto­ries.

Now let’s look at how the mag­a­zines test en­gines at Westech. They use the old stan­dard hot rod cor­rec­tion fac­tor but also test en­gines with hot oil and a start­ing wa­ter tem­per­a­ture of around 140 de­grees F. On a 400hp engine, this change in wa­ter tem­per­a­ture alone is worth 10 hp com­pared to test­ing at 180 de­grees F. Plus, Westech prefers to elim­i­nate the en­tire ac­ces­sory drive from the front of the engine and use an elec­tric wa­ter pump. This makes cam swaps eas­ier, al­lows cool­ing the engine in be­tween runs, and frees up some power. A re­cent LS ac­ces­sory drive test we per­formed re­vealed be­tween 8 and 11 hp im­prove­ment when we re­moved the LS ac­ces­sory drive.

Our LT1 test­ing started with a set of head­ers. We orig­i­nally wanted to base­line our LT1 with the truck-style man­i­folds be­cause we didn’t have a set of adapters to con­nect the stock Corvette ex­haust man­i­folds with 3-inch ex­haust pipe. We thought the truck man­i­folds used the same three-bolt ex­haust flanges but only the pas­sen­ger side was the same as our flanges so that didn’t work ei­ther. So we be­gan our test­ing with the JBA head­ers that were in­tended for a '16 Ca­maro. These are long-tube head­ers with a short 3-inch col­lec­tor that we fed into a length of 3-inch tub­ing from Sum­mit Rac­ing and at­ten­u­ated with a pair of Flow­mas­ter muf­flers.

So if we start with GM’s 460hp rat­ing and add 20 hp for the dif­fer­ence in cor­rec­tion fac­tors, 10 for the wa­ter tem­per­a­ture change, an­other 8 for the ac­ces­sory drive, and 10 more for the head­ers, we’re al­most ex­actly at our 507 hp ini­tial power num­ber. These num­bers are ap­prox­i­ma­tions and it’s likely the head­ers and ex­haust are

worth even more.

But thus far, we’ve looked at just the peak num­bers and they don’t tell the whole story. If you study the torque this engine makes at the be­gin­ning of the test, you should be im­pressed with the 480 lb-ft of torque fig­ure at 3,000 rpm. This is not a misprint. While the long-tube head­ers cer­tainly help at this rpm, this is a big bump over a “nor­mal” 6.2L torque of an LS3 of around 380 to maybe 400 lb-ft. Much of this torque pro­duc­tion can be at­trib­uted to a com­bi­na­tion of this di­rect-in­jected engine’s in­creased com­pres­sion ra­tio, its di­rect in­jec­tion, and the magic of vari­able valve tim­ing (VVT). Here’s where VVT is your friend. Too many peo­ple want to im­me­di­ately dis­able this func­tion, but it’s ob­vi­ous from our test­ing that VVT is a good thing.

Ac­cord­ing to Ja­son Haines who owns Prod­uct & Ser­vice So­lu­tions, an en­gi­neer­ing and prod­uct de­vel­op­ment com­pany, the VVT sys­tem has the

ca­pac­ity to move the cam through­out a tremen­dous 62 crank­shaft de­grees of move­ment (31 camshaft de­grees). The ECU man­ages oil pres­sure to move the cam and for the LT1 swings the cam over 20-plus crank­shaft de­grees of move­ment. At low rpm it ad­vances the cam and then slowly re­tards it from full ad­vance as engine speed in­creases to­ward peak horse­power. The con­trol is ac­tu­ally far more so­phis­ti­cated than that de­scrip­tion, but for the sake of this story that will suf­fice.

We ex­per­i­mented with mov­ing the cam in the VVT seg­ment us­ing HP Tuner’s soft­ware and quickly dis­cov­ered, not sur­pris­ingly, that the GM en­gi­neers have this area cov­ered and with the stock camshaft con­fig­u­ra­tion, there might be 1-2 hp to be gained by mov­ing the cam around slightly. Real­is­ti­cally, they’ve maxed out the VVT im­prove­ments for the stock engine and camshaft.

To put this into per­spec­tive, we have a light­weight, all-alu­minum, 376ci engine that makes 480 lb-ft of torque at 3,000 rpm and over 500 hp at its peak. Those are mild big-block Chevy num­bers. As a point of com­par­i­son, the Chevro­let Per­for­mance 454 HO makes roughly the same torque at 3,000 rpm, peak­ing at 500 lb-ft at 3,500 and only 438 peak horse­power at 5,300 rpm. So our header-equipped LT1 is roughly 150 pounds lighter while twist­ing more torque and more horse­power than a 454 HO. So there’s

some­thing to all this tech­nol­ogy.

Next, we plugged the LT1’s power curve into the Quar­ter Pro dragstrip sim­u­la­tion pro­gram. We plugged in a 3,400-pound car with a driver, an au­to­matic trans, 3.50:1 rear gear, and 26-inch-tall rear tires. The sim­u­la­tion says the car would run 11.50s at 118 mph all day long. That’s out­stand­ing per­for­mance for a stock engine. If you plugged this engine into a lighter 3,200pound car, the num­bers fall to 11.20s at 121 mph! That’s knock­ing on the door of the 10s with a near-stock mo­tor.

So to sum this up, the LT1 is a win­ner. Right out of the box it makes se­ri­ous 500hp power with no mods and big-block torque right off idle with the help of fac­tory VVT. Plus, with the LT1’s di­rect in­jec­tion and fac­tory tun­ing, cruis­ing with the help of an over­drive trans you could ex­pect 20-plus miles per gal­lon with the same engine that will run mid-11s! Some rod­ders may have is­sues with late-model per­for­mance, but it’s hard to ar­gue with these num­bers. The fu­ture of per­for­mance has ar­rived

With all of the pre­lim­i­nary con­ver­sion work out of the way, it didn’t take too long to mount the engine on the dyno. We did dis­cover that the top two bolts for the rear cover hit the bell­hous­ing and needed but­ton head bolts to clear. Westech’s Troy Goldie also had to ma­chine a lit­tle hair­cut off the top of the scat­ter­shield to clear a hub on the back of the pas­sen­ger side cylin­der head. Westech used spe­cial met­ric ARP 12-point bolts for the fly­wheel. Note that all Gen V en­gines use an eight-bolt fly­wheel that is the same as the pre­vi­ous LSA en­gines and oth­ers.

While Chevro­let rates this nor­mally as­pi­rated LT1 at 460 hp, we made sig­nif­i­cantly more with fi­nal tun­ing de­liv­er­ing 518 hp and 520 lb-ft of torque with head­ers. But there’s much more to this story than just the peak power num­bers.

The Gen Vs all use a unique ex­haust flange com­pared to Gen III/IV en­gines. It only uses five ex­haust flange bolts and the gas­ket will only fit one way as the bolt flange is not sym­met­ri­cal.

We used a set of Pa­triot/JBA 1-7/8-inch head­ers orig­i­nally in­tended for a late-model Ca­maro for the dyno test. The pri­mary tubes clear the spark plug boots if you re­move the metal covers and slightly bend the con­nec­tors.

The JBA head­ers came with oxy­gen sen­sor bungs al­ready in the col­lec­tors and sealed with a slick V-band flange, so we or­dered a cou­ple of sim­ple Sum­mit Rac­ing V-band flange clamps and our buddy Scott Gill­man from Galpin Auto Sport (GAS) welded the flange to the Sum­mit 3-inch tub­ing.

The LT1 uses a dif­fer­ent spark plug con­fig­u­ra­tion than the older Gen III/IV en­gines with a longer thread length called the reach. This is the stock fac­tory A/C plug.

These late-model en­gines are very sen­si­tive to place­ment of the mass air­flow (MAF).This sen­sor is both di­rec­tional and should be placed within a straight length of 4-inch­di­am­e­ter in­let tub­ing in or­der to func­tion prop­erly. This length of straight Spec­tre tub­ing has the proper MAF fit­ting welded in, which saved us some fab­ri­ca­tion work.

Chevro­let Per­for­mance’s in­struc­tions sug­gest run­ning with a pulse-width-mod­u­lated (PWM) fuel pump, but a tra­di­tional pump and reg­u­la­tor will work fine as long as it’s ca­pa­ble of 45 gpm at 72 psi. The Aero­mo­tive A1000 is ca­pa­ble of roughly 120 lb/hr of fuel at 70 psi so fuel feed was not an is­sue.

Be­cause the stock MAF re­quires a sig­nif­i­cant length of straight tub­ing on ei­ther side of the sen­sor, we placed the MAF roughly in the mid­dle of this 30-inch over­all length of straight Spec­tre tub­ing.

Westech’s Eric Rhee per­formed the tun­ing on our LT1 with help from HP Tuners soft­ware. De­tails on the screen are too small to read in the photo, but the soft­ware dis­plays air/fuel ra­tio as equiv­a­lence ra­tio. At 3,933 rpm, the equiv­a­lence ra­tio was 0.837 that equates to 12.3:1 air/fuel ra­tio (14.7 x 0.837 = 12.3).

We also had to in­te­grate the fac­tory fuel pres­sure sen­sor into the fuel de­liv­ery sys­tem so that the fac­tory ECU knew fuel pres­sure was con­stant at 68-72 psi.

That’s dyno guru Richard Hold­ener fac­ing the cam­era who has all but taken up res­i­dence at Westech do­ing dyno test­ing for the mag­a­zines.

In­stalling the ECU and har­ness isn’t dif­fi­cult, but it may look in­tim­i­dat­ing. Here, Steve Brulé is do­ing his best Sgt. Rock im­i­ta­tion with an LT1 har­ness in­stead of crossed ammo belts.

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