OHC vs. Pushrods: The Domestic V8 Myth Exposed
The popular automotive press has long had a bias toward overhead-cam powerplants. Much like the effect of the liberal media on mainstream America, the “informed” auto-buying public has generally accepted the supposed supremacy of OHC engines over their pushrod contemporaries.
This perception has transcended the old “import vs. domestic” quandary and morphed into a GM Gen III vs. Ford Mod motor argument. The battles are fought on message boards like this one and others, where members make compelling arguments for both sides. The basics of these debates are pretty simple:
Post #: The motor in the Mustang GT sucks because it doesn’t make as much power as an LS1-equipped f-body.
Reply: Well, your LS1 has over 60 cubic inches on it. It ought to make more power! We make more HP/liter!
Reply to reply: That may be true, but you have more cams and valves and need to put a blower on your valver to almost make the power of an LS6…
And the battle goes on.
After seeing this play out over and over in different places, I wanted to get beyond the rhetoric and into some hard facts. What I found was somewhat surprising, given this seemingly apples-to-oranges comparison.
Ford’s ubiquitous truck and pony car engine is the 2-valve 4.6 liter engine. In current tune, this motor makes a rated 260 HP @ 5250 RPM and 302 lb-ft @ 4000 RPM. This engine gives up approximately 65 cubic inches to an LS1, and anywhere from 45 to 90 HP, depending on the vehicle in which it’s installed. Doesn’t seem like a real fair comparison, does it? Well, the closest thing to a 4.6 LS1 would be a Gen III Vortec 4800 truck motor...4.8 liters, or roughly 292 cubic inches. Here's how it compares to the Ford Mod OHC offerings (Cobra not included for obvious reasons!):
GM Vortec 4800 (4.8L): 285 HP @ 5600 RPM 295 lb-ft @ 4000 RPM
Ford SOHC 4.6 (GT): 260 HP @ 5250 RPM 302 lb-ft @ 4000 RPM
Ford DOHC 4.6 (MACH 1) 305 HP @ 5800 RPM 320 lb-ft @ 4200 RPM
So, from a strictly power standpoint, the Gen III motor is every bit the equal, and in fact surpasses the 2V 4.6. Obviously, the extra 11 cubic inches the Gen III has can’t possibly account for the 25 HP advantage it maintains over the OHC Ford. As basis for further comparison, I included the DOHC 4V MACH 1 motor. The pushrod 4.8 engine is actually closer in HP to the 4V Ford MACH, than it is the 2V version.
Take a step up in displacement, and you get an even more interesting comparison:
Ford 5.4 liter 3V: 300 HP @ 5000 RPM 365 lb-ft @ 3750 RPM
GM Vortec 5300 (5.3L): 300 HP @ 5300 RPM 330 lb-ft @ 4000 RPM
The displacement and horsepower figures are nearly identical. What makes this so intriguing is the fact that the Ford has one extra intake valve per cylinder. The 9.5% torque advantage was most likely a tradeoff the Ford engineers made, since this is (until 2005) primarily a truck engine. Still, it’s quite interesting that an “old-tech” pushrod motor can match the HP output of a multi-valve OHC motor of the same displacement.
Instead of discussing all the remaining variations of these engines, lets go straight to the top:
2003-04 Cobra 4V 4.6, Supercharged: 390 HP @ 6,000 RPM and 390 lb.-ft. @ 3,500 RPM
2002-04 LS6 5.7 L: 405 HP @ 6000 RPM and 400 lb-ft. @ 4,800 RPM
At a glance, we’re back to that 65 cubic inch advantage discussed above. What throws a wrench (no pun intended) into this equation is the positive displacement supercharger sitting atop the Ford engine. Despite that distinct advantage AND 4 valve, DOHC cylinder heads, the Ford engine doesn’t quite make up the difference in HP or torque of the top-of-the line, normally aspirated Gen III GM offering.
Through this exercise, we’ve proven two points: First, at any given displacement, the GM Gen III V8s are the equal and, in some cases, superior to a 2V Ford V8. Second, adding valves and cams doesn’t always equate to distinct power advantage. While some of the mod motors offer a higher specific output than a similar Gen III motor, they don’t enjoy overwhelming superiority.
Of course, these facts apply to engines in stock trim. Anyone can argue that, by adding modifications, one engine will make more power than another, which is obvious. Ultimate power output of a given design is a debate for another time.
Of course, as technology moves on, and the figures above may be obsolete in small number of months, as both sides upgrade their arsenals. What I am attempting to demonstrate here, is the fact that the pushrod engine is and will be a viable configuration in both the performance and truck arenas. Their relative simplicity and low cost, when compared to OHC designs, will allow GM to compete, possibly at an advantage, in segments (Vette, GTO, trucks, etc) where performance per dollar is the key to market share.
No one will question the value and common sense of the small-displacement multi-cam, multi-valve 4 or 6 cylinder engine. In terms of power, economy and smoothness, the OHC configuration is superior. But when it comes to making gobs of cheap V8 power, the “old skool” pushrod V8 will always reign.
The popular automotive press has long had a bias toward overhead-cam powerplants. Much like the effect of the liberal media on mainstream America, the “informed” auto-buying public has generally accepted the supposed supremacy of OHC engines over their pushrod contemporaries.
This perception has transcended the old “import vs. domestic” quandary and morphed into a GM Gen III vs. Ford Mod motor argument. The battles are fought on message boards like this one and others, where members make compelling arguments for both sides. The basics of these debates are pretty simple:
Post #: The motor in the Mustang GT sucks because it doesn’t make as much power as an LS1-equipped f-body.
Reply: Well, your LS1 has over 60 cubic inches on it. It ought to make more power! We make more HP/liter!
Reply to reply: That may be true, but you have more cams and valves and need to put a blower on your valver to almost make the power of an LS6…
And the battle goes on.
After seeing this play out over and over in different places, I wanted to get beyond the rhetoric and into some hard facts. What I found was somewhat surprising, given this seemingly apples-to-oranges comparison.
Ford’s ubiquitous truck and pony car engine is the 2-valve 4.6 liter engine. In current tune, this motor makes a rated 260 HP @ 5250 RPM and 302 lb-ft @ 4000 RPM. This engine gives up approximately 65 cubic inches to an LS1, and anywhere from 45 to 90 HP, depending on the vehicle in which it’s installed. Doesn’t seem like a real fair comparison, does it? Well, the closest thing to a 4.6 LS1 would be a Gen III Vortec 4800 truck motor...4.8 liters, or roughly 292 cubic inches. Here's how it compares to the Ford Mod OHC offerings (Cobra not included for obvious reasons!):
GM Vortec 4800 (4.8L): 285 HP @ 5600 RPM 295 lb-ft @ 4000 RPM
Ford SOHC 4.6 (GT): 260 HP @ 5250 RPM 302 lb-ft @ 4000 RPM
Ford DOHC 4.6 (MACH 1) 305 HP @ 5800 RPM 320 lb-ft @ 4200 RPM
So, from a strictly power standpoint, the Gen III motor is every bit the equal, and in fact surpasses the 2V 4.6. Obviously, the extra 11 cubic inches the Gen III has can’t possibly account for the 25 HP advantage it maintains over the OHC Ford. As basis for further comparison, I included the DOHC 4V MACH 1 motor. The pushrod 4.8 engine is actually closer in HP to the 4V Ford MACH, than it is the 2V version.
Take a step up in displacement, and you get an even more interesting comparison:
Ford 5.4 liter 3V: 300 HP @ 5000 RPM 365 lb-ft @ 3750 RPM
GM Vortec 5300 (5.3L): 300 HP @ 5300 RPM 330 lb-ft @ 4000 RPM
The displacement and horsepower figures are nearly identical. What makes this so intriguing is the fact that the Ford has one extra intake valve per cylinder. The 9.5% torque advantage was most likely a tradeoff the Ford engineers made, since this is (until 2005) primarily a truck engine. Still, it’s quite interesting that an “old-tech” pushrod motor can match the HP output of a multi-valve OHC motor of the same displacement.
Instead of discussing all the remaining variations of these engines, lets go straight to the top:
2003-04 Cobra 4V 4.6, Supercharged: 390 HP @ 6,000 RPM and 390 lb.-ft. @ 3,500 RPM
2002-04 LS6 5.7 L: 405 HP @ 6000 RPM and 400 lb-ft. @ 4,800 RPM
At a glance, we’re back to that 65 cubic inch advantage discussed above. What throws a wrench (no pun intended) into this equation is the positive displacement supercharger sitting atop the Ford engine. Despite that distinct advantage AND 4 valve, DOHC cylinder heads, the Ford engine doesn’t quite make up the difference in HP or torque of the top-of-the line, normally aspirated Gen III GM offering.
Through this exercise, we’ve proven two points: First, at any given displacement, the GM Gen III V8s are the equal and, in some cases, superior to a 2V Ford V8. Second, adding valves and cams doesn’t always equate to distinct power advantage. While some of the mod motors offer a higher specific output than a similar Gen III motor, they don’t enjoy overwhelming superiority.
Of course, these facts apply to engines in stock trim. Anyone can argue that, by adding modifications, one engine will make more power than another, which is obvious. Ultimate power output of a given design is a debate for another time.
Of course, as technology moves on, and the figures above may be obsolete in small number of months, as both sides upgrade their arsenals. What I am attempting to demonstrate here, is the fact that the pushrod engine is and will be a viable configuration in both the performance and truck arenas. Their relative simplicity and low cost, when compared to OHC designs, will allow GM to compete, possibly at an advantage, in segments (Vette, GTO, trucks, etc) where performance per dollar is the key to market share.
No one will question the value and common sense of the small-displacement multi-cam, multi-valve 4 or 6 cylinder engine. In terms of power, economy and smoothness, the OHC configuration is superior. But when it comes to making gobs of cheap V8 power, the “old skool” pushrod V8 will always reign.
