Wild one
Senior Member
- Joined
- Jan 17, 2016
- Posts
- 13,718
- Reaction score
- 23,372
- Ram Year
- 14 Sport
- Engine
- 5.7
The 6.4 truck has a lower compression ratio,then the 5.7's do. 6.4's are 10:1 , 5.7's are 10.5:1. The 6.4 in the HD trucks is designed to run wide open for 12 minutes at full load on 87. Not saying your post is wrong or anything,just pointing out one of the reasons why you don't notice any differance between 87 and 89 in your 6.4 HD truckI'll go ahead and throw in my $0.005 worth on the topic.
The first thing I will say is that I worked for 12 years as an automotive test engineer specializing in fuel economy testing. Manufacturers of complete vehicles down to some crazy "as seen on TV" aerodynamic bolt on or snake oil would hire our company to perform industry certified fuel economy testing. There are several industry standards from enclosed dyno cell cycles to over the road testing based on the SAE recommended practices. I am in no way trying to say I'm the foremost expert in fuel economy testing, nor trying to say anybody else posting about this is wrong. However I will say that nobody I have ever seen on one of these posts is even close to performing what would be considered a certified or industry recognized fuel economy test. Again, not saying anybody is wrong and they can draw their own conclusions on what they have done and make decisions based on what they have done but no manufacturer, big investor, etc... who use that data to make a business decision.
I have a '16 Power Wagon with the 6.4 and have done a couple of "studies" between 87 and 89 octane. Always ran at least 3-4 tanks of either octane in a row. Have never noticed any "seat of the pants" power or performance difference, and there was no obvious fuel economy difference that I could tell....at least not obvious enough to justify spending the extra money for 89 octane. Yes, I agree with previous posts saying that the ECM may be pulling timing out of the engine with the lower octane which would lead to reduced power....you don't know unless you are monitoring the data. But keep in mind you are rarely ever using the full power of the engine. The horsepower rating of the engine is the maximum power it can achieve, and not what you are using the vast majority of the time. It doesn't matter that the engine is rated at 410 HP because it doesn't take anywhere close to the much power to cruise down the freeway at 70 mph.
But hey, if people want to spend their money on 89 octane I don't have any problem with it.
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