Compression
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Mountain Pass
Joined: Apr 2004
Posts: 132
Likes: 1
From: Montana
Compression
Can someone please explain to me why a "lower" compression ratio is marketed to be better for pulling than a high compression ratio? I have been told many times that the older trucks for pulling/hauling had lower compression ratios. Thanks
Laughing Gas
Joined: Dec 2020
Posts: 869
Likes: 186
From: Near my truck
Totally agree with 440's first sentence.
Didn't know about the second sentence reasoning. I thought the lower compression was for BS emission purposes.
My engine's increase from 8.5 to 10.2 resulted in more torque and hp across the entire rpm range, and used 10% less gas whilst driving to do it !
Something tells me that more torque is more useful for pulling/hauling.
Super Moderator
Joined: Apr 2004
Posts: 34,466
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Lower compression was used to improve survivablity under extended loading long before it was used to reduce oxides of nitrogen.
Prior to '72 and a little later, it was not unusual to have a valve job at under 100,000 miles, sometimes earlier. (41,000 on our '66 wagon 390 2V 9.5 compression, and that was mostly before I got my license and started beating it like a rented mule)
Ahh, the good old days, with wheezer motors running low compression, single exhaust, rich carbs, and a 3 speed transmission.
Prior to '72 and a little later, it was not unusual to have a valve job at under 100,000 miles, sometimes earlier. (41,000 on our '66 wagon 390 2V 9.5 compression, and that was mostly before I got my license and started beating it like a rented mule)
Ahh, the good old days, with wheezer motors running low compression, single exhaust, rich carbs, and a 3 speed transmission.
Lead Driver
Joined: Jul 2017
Posts: 9,545
Likes: 1,156
From: San Jose, CA
And it wasn’t that long ago that cylinder heads and piston tops (i.e. combustion chambers) were not that effective at reducing detonation or emissions.
So lower compressions were put in engines that weren’t meant for high performance, but more for towing and hauling and driving the kids around town.
Back then mostly only high-performance engines had compression ratios over nine something. While now it’s not even uncommon to see compression ratios of 9 and 10+ range on turbocharged engines!
So, along with better engine control systems, they can get away with a lot more nowadays.
As was often the case, they were just doing what they could, with what they knew, and with what they had.
So lower compressions were put in engines that weren’t meant for high performance, but more for towing and hauling and driving the kids around town.
Back then mostly only high-performance engines had compression ratios over nine something. While now it’s not even uncommon to see compression ratios of 9 and 10+ range on turbocharged engines!
So, along with better engine control systems, they can get away with a lot more nowadays.
As was often the case, they were just doing what they could, with what they knew, and with what they had.
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erikl85
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