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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old February 8th, 2013, 03:08 AM
Mike Caldwell Mike Caldwell is offline
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Default comparing torque numbers

How do modern dyno numbers compare with the specs listed on the GMC V-6 page?

I was looking at the results from some modern engines and was wondering if anyone had good numbers.

I'm confident my 401 will perform quite nicely in my Willys (when it gets there) but meanwhile I'm curious about the numbers game
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Old February 9th, 2013, 02:58 AM
raycow raycow is offline
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Default Re: comparing torque numbers

Unfortunately, today's dyno numbers can't be directly compared with the advertised specs for these engines when they were new. The reason is that the procedure for measuring hp and torque was changed in the early 1970s so that identical engines would produce lower figures under the new system. I believe the specific differences involved the accessory loads and possibly also the exhaust system.

The net result is that an engine rated say, 300 lb ft today will pull harder than a 300 lb ft engine from the 1960s. To get an accurate comparison you would have to re-test a vintage engine using today's methods rather than relying on advertised specs from when the engine was new.

Ray
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Old February 10th, 2013, 05:53 PM
turbobill turbobill is offline
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Default Re: comparing torque numbers

Actually the rating system has changed twice over the years (for the cars anyway). Once in 1971 and again in 2005. The SAE net figures used on cars starting in '72 was as "as installed" figure. The figures from otherwise identical '71 engines was down 30 to 35 percent. The 2005 change to "Certified Horsepower" was far less dramatic and resulted in little change.

Many of the old sources that quote our truck engine figures are give them both in SAE gross and SAE net, which is representative of the engine with all accesories installed and the exhaust system.

The V6's forte is torque at low RPM's. The restricted breathing and higher internal friction will restrict horsepower to relatively low levels, compared with anything modern.
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Old February 10th, 2013, 08:32 PM
Mike Caldwell Mike Caldwell is offline
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Default Re: comparing torque numbers

Here's the data from the engine page

Engine Model Gross Horsepower Net Horsepower Gross Torque lbs. ft. Net Torque lbs. ft.
401 V6 205 @ 3200 rpm 178 @ 3200 rpm 377 @ 1400 rpm 351 @ 1400 rpm

So the "Net" numbers are more comparable to current type of results we could expect from a dyno run now?
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Old February 10th, 2013, 08:57 PM
turbobill turbobill is offline
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Default Re: comparing torque numbers

Quote:
Originally Posted by Mike Caldwell View Post
So the "Net" numbers are more comparable to current type of results we could expect from a dyno run now?
No. The readings from a dyno shop would more resemble the old "gross" ratings. The gross ratings are an unencumbered engine free of all accesories (except the waterpump and unloaded alternator), no air cleaner and free flowing exhaust.

The "net" ratings are more typical of the torque/HP delivered at the crankshaft in an "as installed" condition. ie: all accesories installed and operating, air cleaner and any silencers, and full factory exhaust with muffler(s). This is basically what the car manufacturers have used since the '72 model year.
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