[Jarhead0514]

I dont have the compression ratios on hand nor am I familiar with compression ratios of the 4.0 V6 however, can anyone confirm that our engines are classified in the high compression class? Thank you for any input?

 

[whistler]

I would not put it in a high compression class
Does not require high octane gas.
If it needs to use race fuel, than I would.

 

[Skinny06]

@whistler pretty much nailed it.

No need for higher than standard 87 octane in the 4.0 trucks means lower compression ratio.

 

[Iffin'itaintbroke]

I believe it's 9.7:1 or something close to that. I know it's not an even number like 10:1. It's higher than others but no, it's not "high compression." I had done a lot of internal work on an old honda v twin years ago, had 11.5:1 compression, broke alot of starters...

 

[Jarhead0514]

Awesome thanks for your guys response. Just interesting to read and know.

 

[The other Sean]

Another thing to consider is "high compression" isn't an actual number. An old 350 Chevy with a carburetor and cast iron heads and a newer fuel injected engine with aluminum heads are going to have the ability to run certain octane differently.

 

[bajasam]

Lol..compared to a 78 chevy 350, yes its a high compression race engine. I think an 1980 corvette topped out at 180hp.

 

[RamTest]

Lol..compared to a 78 chevy 350, yes its a high compression race engine. I think an 1980 corvette topped out at 180hp.

A lot of those HP ratings back then were "net hp", that is, measured at the rear wheels, installed in the vehicle with accessories on. Since that didn't help sales numbers, they reverted back to traditional methods of measuring, with the engine on a stand bolted directly to a dyno, or an engineer's calculation.

 

[RyanD1966]

A lot of those HP ratings back then were "net hp", that is, measured at the rear wheels, installed in the vehicle with accessories on. Since that didn't help sales numbers, they reverted back to traditional methods of measuring, with the engine on a stand bolted directly to a dyno, or an engineer's calculation.

Net was not measured at the wheels, that's WHP. Gross horsepower was on an engine dyno with no power-robbing accessories installed ( IE no generator / alternator, and no water pump, cooling was by external pump loop, ignition electrical power supplied by an external DC power supply ). Net HP was with all accessories ( including A/C compressor if A/C was available ) installed and operating, and through an exhaust system similar to the vehicle installation including catalytic converter(s) when applicable. The Net numbers were far worse and made the anemic engines of the 1970s look even more downright pathetic.

 

[phatB]

New (or reman) chevy 350s that you can get from places like napa still only put out like 190hp rated, so maybe 250 at the flywheel... super cheap though!

 

[whistler]

The manufacturers listing of hp is still at the crank.
That way, they don’t need to list hp with different models and equipment.
My Dodge is rated 325hp , 600 ft lbs.
Bully Dog added 90hp at the REAR wheel!
Got to be pushing close to 450 at the crank.

 

[RyanD1966]

The manufacturers listing of hp is still at the crank.
That way, they don’t need to list hp with different models and equipment.
My Dodge is rated 325hp , 600 ft lbs.
Bully Dog added 90hp at the REAR wheel!
Got to be pushing close to 450 at the crank.

Whistler's correct, it is still crank HP. Different implementations of the same engine often have different ratings per platform, whether by intake and / or exhaust design, or internal corp politics ( The Camaro back in the day always was rated lower than the Corvette with the same engine, and the all aluminium twin-turbo V6 that the Fiero was supposed to get was cancelled because it would have been much faster than that model year's fastest Corvette. ) The Grand National and GNX are a whole nother story.