Vette’s driv­ing force an up­dated old friend

Winnipeg Free Press - Section F - - AUTOS - By Graeme Fletcher

THE his­tory of Chevro­let’s Small Block V-8 en­gine is mind-bog­gling. In­tro­duced in 1955, it has been the an­chor of GM’s en­gine lineup and the Chevro­let Corvette’s driv­ing force. When it went into pro­duc­tion, it dis­placed 265 cu­bic inches (4.3 litres), rel­a­tively small for a V-8. Re­mark­ably, when the Turbo-Fire V-8 ar­rived, it was 19 kilo­grams lighter than the Blue Flame in-line six it re­placed!

You name it and a Small Block has likely been that size — the list of dis­place­ments is be­wil­der­ing in its mag­ni­tude. It has been ev­ery size, from the afore­men­tioned 265-cu.-in. mo­tor right through to 400 cu. in. (6.6L) and it has touched just about ev­ery dis­place­ment in be­tween.

The sec­ond-gen­er­a­tion Small Block de­buted in 1992, mean­ing the first gen­er­a­tion had a stag­ger­ing 37-year run, and dis­place­ment aside, it had re­mained ba­si­cally un­changed. The sec­ond it­er­a­tion’s de­but co­in­cided with the pro­duc­tion of the one-mil­lionth Corvette, a white con­vert­ible.

Since then, there have been a num­ber of gen­er­a­tions. The fifth-gen­er­a­tion Small Block will de­but in the 2013 sev­enth-gen­er­a­tion C7 Corvette when it hits the road next year. It’s an im­por­tant con­sid­er­a­tion, given that the Small Block has been a key com­po­nent of the Corvette makeup for the past 57 years.

The lat­est Small Block is a V-8 that still uses good old pushrods to open its valves and not the twin-over­head cams and tur­bocharg­ers many had pre­dicted. The new 6.2L, which is named LT1 yet again, is com­pletely new. The only car­ry­over parts are the starter-mo­tor bolts and valve keep­ers. That’s it.

It took more than six mil­lion hours of com­puter time to de­velop the com­bus­tion cham­ber, the shape of the pis­ton crown and the place­ment of the fuel in­jec­tors rel­a­tive to the spark plugs within the cylin­der.

This was done to en­sure the very best fuel econ­omy with­out giv­ing up on the quest for power. The new LT1 pro­duces 50 pound-feet more torque than the out­go­ing en­gine, and it de­vel­ops the same amount of torque be­tween 2,000 and 4,000 r.p.m. as the mighty 7.0L V-8 that pow­ers the Corvette ZO6.

Now for the all-im­por­tant num­bers, al­beit the pre­lim­i­nary fig­ures: The lat­est Small Block pro­duces 450 horse­power at 6,000 r.p.m. and 450 lb.-ft. of torque at 4,000 r.p.m., which will give the C7 Corvette a claimed run from rest to 96 kilo­me­tres an hour of less than four sec­onds, which is pretty darned quick.

The high out­put and fuel ef­fi­ciency (GM claims an av­er­age fuel con­sump­tion rate of 9.0 litres per 100 km) is due to a num­ber of im­por­tant fac­tors. This en­gine em­ploys di­rect in­jec­tion, a first for an over­head-valve en­gine, con­tin­u­ously vari­able valve tim­ing and a high 11.5:1 com­pres­sion ra­tio. The lat­ter is al­lowed be­cause di­rect in­jec­tion cools the cylin­der, which pre­vents det­o­na­tion and the need to re­tard the tim­ing to pre­vent it. Though it does mean the en­gine prefers pre­mium fuel, it will live on a reg­u­lar diet.

The cam phas­ing al­ters the in­take and ex­haust open­ing and clos­ing points in uni­son over a 62-de­gree an­gle. Some will ar­gue this is not as ef­fec­tive as al­ter­ing the in­take and ex­haust camshafts sep­a­rately, as is the prac­tice in mod­ern over­head-cam en­gines. GM coun­ters that the LT1’s sys­tem de­liv­ers 80 per cent of the ad­van­tage as­so­ci­ated with cam phas­ing with­out the cost and com­plex­ity.

It weighs just 211 kilo­grams. By way of com­par­i­son, BMW’s 4.4L twin-turbo V-8, which de­liv­ers 400 hp and 450 lb.ft., tips the scales at 228 kg. The dif­fer­ence is the mass the en­gine places over the front wheels and the ef­fect it has on han­dling. GM says the C7 Corvette will have less un­der­steer be­cause of the light­weight all-alu­minum con­struc­tion of the en­gine. Like­wise, the com­pact height al­lowed the C7’s de­sign­ers to in­cor­po­rate a lower hood line with­out im­ping­ing on pedes­trian-im­pact reg­u­la­tions.

As for ef­fi­ciency, the key in a largedis­place­ment en­gine is cylin­der de­ac­ti­va­tion — it’s the most im­por­tant fu­el­sav­ing de­vice. The new en­gine will spend a lot of its run­ning life in its four­cylin­der mode. GM says this is why it picked the larger 6.2L dis­place­ment. When op­er­at­ing in four-cylin­der mode, the op­er­a­tional cylin­ders still dis­place 3.1 litres.

A smaller-dis­place­ment en­gine may have been more fuel-ef­fi­cient when all cylin­ders are fir­ing, but it could not spend as much of the time re­ly­ing on four cylin­ders. As it stands, GM claims a 20 per cent re­duc­tion in fuel con­sump­tion when the en­gine stops fir­ing cylin­ders one, four, six and seven. At the heart of the hor­ri­bly named Ac­tive Fuel Man­age­ment is an elec­tro-me­chan­i­cal sys­tem that bleeds off the oil pres­sure in the lifters, which then de­ac­ti­vates the cylin­der.

As for some of the stuff in­cluded, the new en­gine has oil-cooled pis­tons, a forged crank and con­nect­ing rods and there is an avail­able dry-sump de­riv­a­tive that is bet­ter able to with­stand the lat­eral g-forces the en­gine is sub­jected to in a track en­vi­ron­ment.

Fi­nally, the fear a Corvette op­er­at­ing on just four of its eight cylin­ders would sound more than a lit­tle wimpy is a non­is­sue — as throt­tle in­put is small and the en­gine loads are low, the ex­haust note would be muted any­way.

The new 6.2L, which is named LT1 yet again, is com­pletely new.

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