Re: 454 efficiency - Maximum CR
Posted: Thu Dec 07, 2017 12:56 pm
Burb that was funny.. I went with the 377 combo partly due to what you describe with your 396.. Huge torque will break things. I also wanted to experiment with the upper rpm capabilities of propane power. I've been around a lot of work vehicles and some big torquers but I haven't had one that could be classified as a screamer. I got into watching the mileage /power tradeoffs some time back and always thought there was more potential than what I ended up with. A long rod 377 was a good starting point.. yes, 400 block, 30 over.. scat crank, 3.5 stroke, Its in a fairly lightweight 89 reg cab chevy shortbox.
The tunnel ram was a big contributor to the increased fuel mileage and the midrange torque. Strange as it may sound.. Highway I'm at about 2200 rpm. Fuel mileage is just average at that, 18 if you drive nice, 16 if a bit on the aggressive side up to 2800 rpm. 700r4 trans.. Where the mileage is exceptional is the lower speed around town sort of thing.. Stop and go and running around like a normal driver I can get up to 25mpg. $50.00 is pretty well 12 hours driving time. That's if you can keep your foot out of it, but I don't mean babying it either. I have a fairly aggressive tune and I'm using vacuum advance. Retarding the cam did something that I can't quite fathom or explain. It seemed that propane liked something about that. It lost some of the low end intensity but broadened it out so nicely it was well worth the tradeoff. In effect the intake / ex close points moved out further but the openings were delayed a bit. That little draw on the intake that overlap provides and when may be why it does what it does. I have a set of 12.5:1 kb domed pistons in it so the dcr stays up with the bigger cam. That was the theory anyway.. It was supposed to take as much advantage of the propane octane as possible. A ft cam is cheaper to experiment with than a roller but a smallish roller may be the way to go.
The afr numbers I get are quite normal. Two mixers did not throw it off at all. I can set them easily for cruise anywhere from 15 - 19 on the gauge. They are responsive and I dip to about 12:5 on the afr at wot. That low end driving around spot where the big mileage numbers show up is at 17 plus on the afr gauge. The power does not lack even this lean, just roll on the throttle and not even all the way and you go up in smoke. Starting did not take much effort at all but I did change technique and added a primer button. Warm starts are immediate on first revolution.
I'm running a set of aftermarket rhs vortec heads. The ones Vizard and Joe Sherman used for their quite impressive cheap sbc builds you find written about in some older magazines. They aren't real big valve or big port heads. They have been smoothed over a bit and run better springs etc.. Size wise, are really small for what they do. I don't know if these results can be replicated in other engines or what parts of this are applicable to any others but I suspect there are some pretty basic underlying fundamentals that could be extrapolated. I know and I should remind people that this combo isn't exactly the traditional way to build a propane engine but its interesting information..
I am going to make one more change on this combo mainly just to see the end results. If you gain more power pretty well all the way through the power band when you heavily retard a cam past its recommended icl that is supposed to tell you something. Like you need a different cam. But by doing so, is that where fuel mileage goes south? I got to where I am by experimenting and I guess I'm obligated to finish the experiment. Might have some more updates for next year.. Meanwhile, some of this sort of thing might make a very nice broad powered fuel efficient big block without having to run out to the extremes on compression etc.. or maybe it won't?
The tunnel ram was a big contributor to the increased fuel mileage and the midrange torque. Strange as it may sound.. Highway I'm at about 2200 rpm. Fuel mileage is just average at that, 18 if you drive nice, 16 if a bit on the aggressive side up to 2800 rpm. 700r4 trans.. Where the mileage is exceptional is the lower speed around town sort of thing.. Stop and go and running around like a normal driver I can get up to 25mpg. $50.00 is pretty well 12 hours driving time. That's if you can keep your foot out of it, but I don't mean babying it either. I have a fairly aggressive tune and I'm using vacuum advance. Retarding the cam did something that I can't quite fathom or explain. It seemed that propane liked something about that. It lost some of the low end intensity but broadened it out so nicely it was well worth the tradeoff. In effect the intake / ex close points moved out further but the openings were delayed a bit. That little draw on the intake that overlap provides and when may be why it does what it does. I have a set of 12.5:1 kb domed pistons in it so the dcr stays up with the bigger cam. That was the theory anyway.. It was supposed to take as much advantage of the propane octane as possible. A ft cam is cheaper to experiment with than a roller but a smallish roller may be the way to go.
The afr numbers I get are quite normal. Two mixers did not throw it off at all. I can set them easily for cruise anywhere from 15 - 19 on the gauge. They are responsive and I dip to about 12:5 on the afr at wot. That low end driving around spot where the big mileage numbers show up is at 17 plus on the afr gauge. The power does not lack even this lean, just roll on the throttle and not even all the way and you go up in smoke. Starting did not take much effort at all but I did change technique and added a primer button. Warm starts are immediate on first revolution.
I'm running a set of aftermarket rhs vortec heads. The ones Vizard and Joe Sherman used for their quite impressive cheap sbc builds you find written about in some older magazines. They aren't real big valve or big port heads. They have been smoothed over a bit and run better springs etc.. Size wise, are really small for what they do. I don't know if these results can be replicated in other engines or what parts of this are applicable to any others but I suspect there are some pretty basic underlying fundamentals that could be extrapolated. I know and I should remind people that this combo isn't exactly the traditional way to build a propane engine but its interesting information..
I am going to make one more change on this combo mainly just to see the end results. If you gain more power pretty well all the way through the power band when you heavily retard a cam past its recommended icl that is supposed to tell you something. Like you need a different cam. But by doing so, is that where fuel mileage goes south? I got to where I am by experimenting and I guess I'm obligated to finish the experiment. Might have some more updates for next year.. Meanwhile, some of this sort of thing might make a very nice broad powered fuel efficient big block without having to run out to the extremes on compression etc.. or maybe it won't?