454 efficiency - Maximum CR

Propane, Butane, LPG, GPL, C3H8, C4H10
Posts: 177
Joined: Thu May 24, 2012 7:39 pm
Location: British Columbia Canada

Re: 454 efficiency - Maximum CR

Post by gottago » 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?

Posts: 7
Joined: Mon Nov 06, 2017 10:07 am

Re: 454 efficiency - Maximum CR

Post by burbfixer » Tue Dec 12, 2017 2:15 am

The experimenting you and your friends have done has confirmed some of what I've learned from 30+ years of propane experience. AND completely blown some of it out of the water! Good for you! I don't think I've ever heard of that combination of economy/performance in a V8 propane street vehicle, so your efforts are certainly beyond successful already. With few exceptions, the high performance propane engines I've been around have all been in big heavy trucks. When I was ripping around BC & Alberta having a blast with my heavy 396 4x4, I was always just a bit curious how it would have felt if it were lugging around 2000 lbs less truck! If you can pull 25mpg out of a high winding 377, maybe for me 18 or 20 out of a carefully built, fun to drive 454 isn't out of reach!

And I agree, just because a combo is unique, doesn't mean some of the lessons can't be applied to any V8 2valve engine using the same fuel. I personally don't believe engines are fundamentally that different. When you push the limits and think outside the box as you and your friends have done, that is where you really learn some things. As you've expressed several times now, answering one question sucessfully often just raises 2 or 3 more, but It's still good progress. I do have a concern about your statement that you should 'finish your experiment'. After chatting for a while now, I'm doubting someone like yourself will really ever 'finish' :) But at least it's a hobby with a tangible benefit - lower operating costs! As long as parts aren't putting you in hopeless debt, or the time isn't costing you something more important like your family/marriage, carry on & have fun! It does sound to me like you might be flirting with the outer limits of cam optimization with your combo. Actually, is there such a thing as a truly 'optimized' camshaft, especially in a street driven vehicle? It's precision metal stick that has to open and close valves in a complex machine operating in an insanely varying set of circumstances. You've already tweaked and tuned yours to the point that it's doing pretty much everything way, way better than average! I'm not saying stop what your doing, just take a moment now & then to look back at what you've accomplished there!

Everyone, let's re-cap. gottago has just told us that he gets up to 25 mpg in what's likely a 4000 lb pickup truck that smokes the tires at will and revs to 7000 on a fuel that typically costs about 30% less than regular gas where we live. I'm listening, and I hope anyone else interested in affordable propane performance is too!

It also sounds like you're doing all this without the use of feedback control. In the past I worked on the vapor feedback systems every day for years, and briefly even used one myself. They were fine, and seem to do what they were supposed to in a stock application, but in my experience, careful open loop tuning gave better power and mileage results. I also respect the current injection technology, but it seems these systems have also made conversions cost prohibitive for the average user, including me. That's why I stick with the older vehicles and vapor equipment - I can slap on an open loop dry gas system, tune and tweak it as I have time, and the rest of the time it still runs and drives great day to day. Plus I can afford to drive my vehicle.

Any idea what your horsepower is? Since you've been around both the big heavy torquers and the lighter screamer now, how do you think your 377 would be (as is) in a larger, taller geared 4x4? Your trans may not be set up in such a way that you'd know for sure, but do you get the impression the engine would dislike a lower cruise rpm, say 1500 -1700?

Posts: 177
Joined: Thu May 24, 2012 7:39 pm
Location: British Columbia Canada

Re: 454 efficiency - Maximum CR

Post by gottago » Wed Dec 13, 2017 12:56 pm

Thanks for taking note of all that burb.. To answer your question how this would feel in a heavier vehicle and at lower rpm..; I do have to say that the 377 combo is around the weight and rpm range where it works best now. The 377 is known to lighten torque and only make power with rpm. Weight and gearing would lessen the benefits so I would want to go to a big block or at least a longer stroke combo.

I have a half dozen or so other engines and numerous parts still kicking around so you are correct, I will be experimenting with propane power for some time yet. But the 377 is nearing the end for what can be done to improve it. The engine dyno simulation programs are likely biased too high number wise but I use them to see where changes might help. The estimated max hp on this comes in around 427 at 6500 and 437 torque at 4500. Torq stays above 400 right from 2500 rpm to 5500 rpm. That's where it pulls really nice and its not screaming. Above that rpm I suspect some sort of ramming going on but its really a bit much for most usual applications. Was just nice to hear a sbc sound like they used to and to be doing it on propane. .. I've mentioned most of the factors that contributed to the outcome but there are a few points I probably skipped. One being an onboard electronic timing control that hooks up to an msd box. You lock the distributer and then adjust with three tuning dials. I just lengthened the cables to be able to do so while driving. That helped big time to get the amount and rate of curve right. There really was one spot that you had to find that would have taken a lot of time or a dyno to discover. High compression is finicky that way. Theres a narrower band to work with but the benefits are higher too.

Someday I too am likely to go the bbc route. My younger brother is trying to talk me into building one. It has potential to amplify that sweet midrange pull that I favour, (2000- 5000 rpm)
For you..
maybe for me 18 or 20 out of a carefully built, fun to drive 454 isn't out of reach!
exactly... I believe it is possible, just how to get there? What worked for a long rod short stroke motor isn't totally apples to apples here. Some of the theory behind what it did and why may be able to be bent a little though.. One point you made about how propane mixers work and how two may not be detrimental to mileage is a good point to keep in mind and maybe incorporate even for a low rpm application. I used the 377 / cam combo to lighten the pull, drop vacuum etc at low rpm to see how mileage responded. Two mixers were better than one. There are a couple of schools of thought on that alone.. In effect I worsened performance from where it could be at low rpm in a way that decreasedflow and thus decreased cylinder filling. Less fuel going in. Compression becomes vital, you have to maximise every bit of what you have left. I don't have many supporters on this point but I don't have a lot of other explanations for the good low speed mileage either. My gearing worked with that too, yours won't.. Where do the extra cubes come into play to compensate for dropping some early max torque in exchange for mileage and a broader power band ? ? Somewhere in here the extra power of a big block will compensate for what has to be done to raise fuel mileage as long as compression stays in the right range. Will even allow for the higher gearing and increase mileage even further if you get it right.. I have mentioned about how just adding cam lift dropped fuel mileage for me and I have avoided the all out rv grinds since. Duration isn't supposed to help mileage much either but within reason it is the lesser of the fuel killing evils imo.. There is a balancing act to it.. Flow through head matching duration and lift resultant compression, vacuum draw etc.. .. Have fun!

User avatar
Posts: 512
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: 454 efficiency - Maximum CR

Post by storm » Wed Dec 13, 2017 2:30 pm

gottago wrote:
Wed Dec 13, 2017 12:56 pm
There is a balancing act to it.. Flow through head matching duration and lift resultant compression, vacuum draw etc.. .. Have fun!
This is what its all about.
Fuel flow requirements calculations viewtopic.php?f=5&t=1638

Post Reply