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HP rating

4vette

Member
Joined
Apr 27, 2005
Messages
5
Location
los angeles ca.
Corvette
67 droptop,91 coupe ,02 coupe
hi does anybody know where hp ratings are taken rear wheels,flywheel,???.the 2008 vette is said to have 430 hp thats 8% more than a 2007 , a big increase or a change in the way hp is measured?i know that hp measurments have changed before ,has this happened again? in the 60's hp was on a engine dyno at the back of the crank if i remember correctly,then i recall something called brake horsepower,and of course rear wheel horsepower measured on a chasie dyno anyone know what is the standard now and do all factorys use the same rating system[i see tv ads for 250 hp 4 cyl toyotas ]
 

Victory Red C6

Well-known member
Joined
May 10, 2007
Messages
205
Location
Gibbon, MN
Corvette
2007 Victory Red Coupe
I don't know about any change to the method of measuring the horse power.

There are a number of changes/improvement to the 2008 models Vs. prior C6 Vettes (2005 -2008 models). The changes include a larger displacement engine up from 6.0 L to 6.2 L. Other improvments include the following:

The pistons for the larger 6.2L engine also are new and are designed for its high-rpm performance capability.

Breathing for the new 6.2L engine is accomplished via new, high-flow cylinder heads. They're based on the large port/large valve design found on the LS7 engine and other GM L92 engines, with larger-capacity, straighter intake ports. The design optimizes intake flow to the combustion chamber and the exhaust ports are also designed for better flow.

Complementing the larger-port design of the heads are commensurately sized valves. The intake valve size alone increases from 2.00 inches (50.8 mm) to 2.16 inches (55 mm) – an increase of nearly 9 percent. The intake valves feature lightweight hollow stems, which enable the engine's 6,600-rpm capability. The exhaust valves also are large, measuring 1.60 inches (40.4 mm) in diameter.

To accommodate the engine's large valves and enable more direct intake port flow, the intake-side rocker arms are offset 6 mm between the valve tip and the push rod. Actuating the valves is a new camshaft, with intake-side lobes providing more than a 5-percent percent in increase in lift, from 0.521-inch to 0.551-inch (13.25 mm to 14 mm). Exhaust-valve lift remains unchanged from the LS2. The camshaft timing was revised to optimize performance with the higher-lift intake cam profile.

Ensuring the cylinder heads receive all the air they can handles falls to a new, acoustically tuned intake manifold. The composite design is manufactured with a “lost core” process that improves runner to runner variation and reduces airflow losses. An acoustic foam material is used to reduce radiated engine noise; it is sandwiched between the outer top of the manifold and an additional “skull cap” acoustic shell. Also new beauty covers atop the engine shield the rocker covers and also feature a noise-reducing, acoustically tuned insert to provide a more refined engine sound.

Exhaust system – Optional on '08 Coupe and Convertible models is a new, two-mode performance exhaust system. Similar in design and function to the system used on the Z06, the dual-mode exhaust uses vacuum-actuated outlet valves, which control engine noise during low-load operation, but open for maximum performance during high-load operation. It is not identical to the Z06 system; the Coupe/Convertible uses a 2.5-inch-diameter exhaust, while the Z06 uses a three-inch system.

With the new, dual-mode performance exhaust, power output for Coupe/Convertible rises from 430 horsepower (321 kW) and 424 lb.-ft. of torque (575 Nm) to 436 horses (325 kW) and 428 lb.-ft. (580 Nm). This system gives the Corvette a more aggressive exhaust sound character that will appeal to performance enthusiasts.
 
Joined
May 10, 2002
Messages
2,254
Location
Boise, Idaho
Corvette
2002 electron blue Z06
I believe the HP rating is at the flywheel with all accessories attached. This is the "net" HP rating in use since 1972 or so. The old "gross" HP was also at the flywheel, but without the accessories attached. Gross numbers are about 20% higher than net. Rear wheel horsepower is 15-20% lower than at the flywheel.
 

Gersh

Well-known member
Joined
Apr 1, 2005
Messages
218
Location
Kentucky
Corvette
"06 Z06, Kawasaki ZZR, "66 supercharged Chev 489
I believe DRTH is right about the ratings. The net ratings are pretty accurate these days, as they are checked by an independent enginneering association. The difference (from one type of car to another) between gross, net, and rear-wheel HP will vary quite a bit, especially going from auto to manual tranny (some auto transmissions lose a bunch of power.)
Gersh
 
S

starvin4speed

Guest
60's muscle HP underated by factory

I saw a program on tv the other day. They tested the old muscle car engines from the late 60's to see if the mfr rated hp was accurate. They put vintage engines on a dyno and tested at the flywheel. I don't remember all the engines, but the one that had the most underated power was the 426 hemi.

This engine was advertised as 500 hp, the dyno showed 820 hp!!!!! I think the pontiac engine came in second, then the ford.
 

Gersh

Well-known member
Joined
Apr 1, 2005
Messages
218
Location
Kentucky
Corvette
"06 Z06, Kawasaki ZZR, "66 supercharged Chev 489
I saw a program on tv the other day. They tested the old muscle car engines from the late 60's to see if the mfr rated hp was accurate. They put vintage engines on a dyno and tested at the flywheel. I don't remember all the engines, but the one that had the most underated power was the 426 hemi.

This engine was advertised as 500 hp, the dyno showed 820 hp!!!!! I think the pontiac engine came in second, then the ford.

I have a '68 Charger with a 440, rated at 375HP. In the Charger at least, the 426 Hemi was rated 425HP.

I have heard it was under-rated, but there is NO WAY I'd ever believe a stock hemi made 800 HP. No way. Didn't happen. Somebody's dreamin' or entered a ringer.

Gersh
 

NORTY

Well-known member
Joined
Sep 7, 2006
Messages
851
Location
Carlsbad,Ca.
Corvette
2006 C6Z DSOM
I have a '68 Charger with a 440, rated at 375HP. In the Charger at least, the 426 Hemi was rated 425HP.
True the 426 was rated @425hp. (It was severly down~rated, however.)
I have heard it was under-rated, but there is NO WAY I'd ever believe a stock hemi made 800 HP. No way. Didn't happen. Somebody's dreamin' or entered a ringer.

Gersh
Actually, they did everything possible to not have a "ringer." I about fell off my chair when they showed the pull. Torque was huge also. (700+)
Remember, it had dual quads that were 715CFM each.
That's over 1400CFM!

No wonder Keith Black, the NHRA, the IHRA, the ISBA use the Hemi design...


I would like to know who's fuel they used for the dyno tests.
 

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