Chevrolet Corvette Stingray C7 Forum - View Single Post

snizzle · 11-09-2011, 12:27 PM

Found this snippet at LS1tech:

http://ls1tech.com/forums/texas-memb...rformance.html

"OHV configuration is almost the best bet. There are talks of a "revised" camshaft location for better valvetrain geometry."

Same thread, a good comparision between the two major options:

(1) Pushrod OHV = More Power + Less Weight + Smaller Engine Compartments. An OHV engine is smaller and lighter because its heads are so much smaller than the wide and fat DOHC heads. Eg. A GM LS3 6.2 liter V8 -- despite its larger displacement -- is more powerful, more compact and lighter than a BMW S65 4.0 liter V8. How much more powerful? 430 hp / 424 lb-ft for the LS3 vs 414 hp / 295 lb-ft for the S65. How much lighter? 183 kg for the LS3 vs 202 kg for the S65. Hence, if you want the most power in the smallest, lightest package, the Pushrod OHV design is superior. And, had the M3 gotten Smallblock Pushrod power it'll be a faster car.

(2) Pushrod OHV = Better Fuel Economy. A Pushrod V8, 1/4 has many camshafts, 1/4 as many cam sprockets and bearings and 1/2 as many valves. Hence, a Pushrod engine tends to have lower frictional loses. Aspiration losses is about the same at cruise simply because no matter how well an engine breathes (and DOHC motors do breathe better), at cruise the engine is being choked by the throttle body. This restricts airflow to the minimum amount needed to burn a given amount of fuel to produce just enough power to maintain speed. All of this is compounded by the fact that lower torque DOHC motors of smaller displacements tend to need to operate at higher rpms at cruise -- which further increases frictional losses. Eg. Despite a nearly 4,000 lbs weight and blocky areodyamics, a Camaro SS gets an EPA rating of 16 mpg (city) / 25 mpg (hwy) with a 6.2 liter 400 hp motor, whereas a BMW M3 gets 14 mpg (city) / 20 mpg (hwy) from its 4.0 liter 414 hp engine and a C63 AMG gets 12 mpg (city) / 19 mpg (hwy) with its 451 hp 6.3 liter M156 DOHC V8. This is despite both Germans having 7-speed transmissions to the Camaro's ubiquitous 6-speed 6L80.

(3) Pushrods can incorporate VVT or even Independent VVT. You can put a cam phaser on the in-block cam just as easily as you can on a SOHC motor. You are looking for independent Intake and Exhaust phasing, you can still do it on an in block cam pushrod engine -- you'll simply use a concentric cam-in-cam setup. In fact, this has already been used in the Dodge Viper 8.4 liter V10.

(4) Pushrod OHV = Lower Cost. Less parts, less complications, lower costs. Not much to explain here.

11-09-2011, 12:27 PM	#28
snizzle Recalled user Drives: '12 Camaro SS, '18 Colorado Z71 Join Date: Mar 2009 Location: Richmond, VA Posts: 3,527	Found this snippet at LS1tech: http://ls1tech.com/forums/texas-memb...rformance.html "OHV configuration is almost the best bet. There are talks of a "revised" camshaft location for better valvetrain geometry." Same thread, a good comparision between the two major options: (1) Pushrod OHV = More Power + Less Weight + Smaller Engine Compartments. An OHV engine is smaller and lighter because its heads are so much smaller than the wide and fat DOHC heads. Eg. A GM LS3 6.2 liter V8 -- despite its larger displacement -- is more powerful, more compact and lighter than a BMW S65 4.0 liter V8. How much more powerful? 430 hp / 424 lb-ft for the LS3 vs 414 hp / 295 lb-ft for the S65. How much lighter? 183 kg for the LS3 vs 202 kg for the S65. Hence, if you want the most power in the smallest, lightest package, the Pushrod OHV design is superior. And, had the M3 gotten Smallblock Pushrod power it'll be a faster car. (2) Pushrod OHV = Better Fuel Economy. A Pushrod V8, 1/4 has many camshafts, 1/4 as many cam sprockets and bearings and 1/2 as many valves. Hence, a Pushrod engine tends to have lower frictional loses. Aspiration losses is about the same at cruise simply because no matter how well an engine breathes (and DOHC motors do breathe better), at cruise the engine is being choked by the throttle body. This restricts airflow to the minimum amount needed to burn a given amount of fuel to produce just enough power to maintain speed. All of this is compounded by the fact that lower torque DOHC motors of smaller displacements tend to need to operate at higher rpms at cruise -- which further increases frictional losses. Eg. Despite a nearly 4,000 lbs weight and blocky areodyamics, a Camaro SS gets an EPA rating of 16 mpg (city) / 25 mpg (hwy) with a 6.2 liter 400 hp motor, whereas a BMW M3 gets 14 mpg (city) / 20 mpg (hwy) from its 4.0 liter 414 hp engine and a C63 AMG gets 12 mpg (city) / 19 mpg (hwy) with its 451 hp 6.3 liter M156 DOHC V8. This is despite both Germans having 7-speed transmissions to the Camaro's ubiquitous 6-speed 6L80. (3) Pushrods can incorporate VVT or even Independent VVT. You can put a cam phaser on the in-block cam just as easily as you can on a SOHC motor. You are looking for independent Intake and Exhaust phasing, you can still do it on an in block cam pushrod engine -- you'll simply use a concentric cam-in-cam setup. In fact, this has already been used in the Dodge Viper 8.4 liter V10. (4) Pushrod OHV = Lower Cost. Less parts, less complications, lower costs. Not much to explain here.