454 Efficiency - Compression vs port velocity

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Re: 454 Efficiency - Compression vs port velocity

Post by burbfixer » Sat Oct 21, 2017 12:36 pm

Thanks again for the input everyone, it's interesting to hear your viewpoints. I wondered about whether a "low rpm, part throttle, efficiency" question would get any hits at all on this forum, or just make everyone doze off. There will end up being compromises - for sure - but this input will help me make smarter compromises. So far, most seem to feel that for my purposes, highest compression is more important than highest port velocity. It's been interesting to hear the thoughts on piston domes. In terms of combustion efficiency, compression is clearly one of the highest priorities. Also in terms of combustion efficiency, if a dome is required to achieve the compression, at some point it must start to become a liability instead of an asset?

Zmechanic,
I see your point. So given the 119ish cc open chambers I have now in my small port heads, how much of a dome would you think is "small mostly unobtrusive"? In your opinion is it worth sacrificing a bit of the compression to keep the dome smaller?
pdq67,
The best running engine I ever owned was a 402 with those heads on it. I knew very little about engine building or theory at the time, and probably had too small a cam in it, but I really liked the way it ran. I had alot more disposable income then too. If I only knew then... I've thought about doing what you suggest with a set of 290 heads I can get (I know about the potential gasket sealing issue). That's one of the things that led to my initial question about low rpm, part throttle efficiency. Design wise, a flat top or dished piston is supposed to be best (+1 for the closed chamber option) Theoretically at least, the small peanut port with higher port velocity should be most efficient for my purposes (-1 for the closed chamber heads). It's still an option I might consider though.

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Re: 454 Efficiency - Compression vs port velocity

Post by gottago » Sat Oct 21, 2017 10:39 pm

A little late commenting but also on side with the importance of compression #1 port velocity a close second for a configuration as this. I've experimented a bit with larger sbc and bbf and did find some interesting effects. The dome issue isn't a real issue at low rpm with a decent ignition system, propane, and with everything else working together.

There are ways to raise or lower compression via cam duration and lsa. You could tighten the spread up a bit to raise your compression ratio or start with a higher static compression ( more dome) and then lower compression a touch with more duration and or lsa. You get quite a different driving feel from each. Cam choice should be made at the same time along with piston/ head choice. They all need to work together. Maintain as high a compression as possible using a cam piston head combo that places peak torque a bit past cruise rpm imo. Intake manifold to match. Its quite easy to get a super torquer out of a high compression big block if that's the intent but it might not be the nicest daily driver. I'd go for a little longer broader pull. The intake close point needs to be looked at even for low midrange power applications, it makes a considerable difference.
any cam suggestions for this?

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Re: 454 Efficiency - Compression vs port velocity

Post by pdq67 » Sat Oct 21, 2017 11:33 pm

I want to throw this out here just for.......

Dave F. made a 400+hp/305 once that had worked over -041 heads on it that were planed something like .100" or so!

Why I bring this up is that you can gain CR by planning your heads and using shim head gaskets! But you also have to make sure that both your intake and exhaust manifolds fit properly.

Only problem here is that once the parts are cut, they are dedicated parts for your combination.

Oh, and btw, ol' Dave beat on that little engine until he blew it up just for..... if I have my story right!

pdq67

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Re: 454 Efficiency - Compression vs port velocity

Post by burbfixer » Sun Oct 22, 2017 1:13 am

gottago,
I was hoping the thread would run long enough to add cam choice to the discussion! I understand any engine is a package and the cam choice can make or break it. For discussion purposes I wanted to focus on compression and port velocity first. I believe that because I use propane, I could really maximize both and - with attention to air and coolant temps and tuning - not worry too much about detonation, even with the stock cam in place. Even at 10.5 I should have some safety margin with cylinder pressures.
The engine will get a cam, but this is where I lack experience. Back in the day a Crane HMV 260 was my answer to everything, and everyone I knew that used one thought it was great. That's the cam that was in my 402. Later I had a stock low compression 77 454 pickup with headers and exhaust that I tried a Comp 212/212 cam in, and was never too impressed with how it pulled - now I know that cam needed more compression to work well with propane.
I do know a couple of things - the one I choose for this engine will be a flat hydraulic, and likely single pattern. The part I'm most uncertain about is the lsa. After reading his books, I'm super curious about how using the 'David Vizard method' for choosing a cam would work out in my combo. Going that route would mean a much tighter lsa than usual. There's strong opinions about using wider lsa's too. I could just go 'safe' with a common 110 or 112 lsa cam, but if I could make a better choice for my combo I'd like to. I welcome any input on this!

pdq67,
Yes, heavy milling is an option. I think at best milling and a shim gasket will only get me to high 8's or 9 to 1, considerably less than I'd like for propane. If anyone knows what the safe maximum would be for milling 236 heads, I could do the math on that option. I like the thin gasket idea for quench improvements too. I have just recently pulled the motor from the donor vehicle, but haven't pulled the heads yet to measure the deck height or cc anything. Once I do that, I'll be able to crunch the actual numbers.

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Re: 454 Efficiency - Compression vs port velocity

Post by MadBill » Sun Oct 22, 2017 8:59 am

Maybe David will step in with some guidance, but I believe his LSA selection program is aimed at well-equipped race and strong street/strip engines and is intended to maximize the scavenging effect of a good set of headers. I suspect it's not the best path for your app, but I'm sure research has been done on optimizing specs for a propane RV-like vehicle. :-k
Felix, qui potuit rerum cognscere causas.

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Re: 454 Efficiency - Compression vs port velocity

Post by burbfixer » Sun Oct 22, 2017 12:00 pm

MadBill,
You could be right...
This combo will definitely have long tube headers and good exhaust.
Mr Vizard, doesn't mention part throttle or fuel efficiency very often - it's not the purpose of his books - but what makes me curious is that his former bbc book had pages of actual cam spec suggestions. The lowest end of the chart is a 262 (219) cam. A notation is also made that refers to the lowest 3 cams on the chart being good fuel mileage cams.
By the way, I'm purposely referring to fuel use as efficiency, not economy. Big engines in big vehicles will never be 'economical' to drive, I know that - especially when I can get in my wife's civic and easily get 50mpg - but I think they can be made to use fuel efficiently.
It's interesting to me, but admittedly a bit challenging, to try to find things in tech information that I think might still apply when I filter it thru the realities of my combo - higher than normal compression, dry vapor fuel, and a useful rpm range that extends well below where many dyno charts begin. Then I try to factor in the constantly varying part throttle so I can answer the question I'm usually wondering about : In my vehicle, how would this actually feel to drive??
If a tight lsa were the way to go, I've wondered if it might be best with a bit shorter cam than his smallest suggestion. If I recall correctly, when I tried to use his formula the spec I come up with was way down in the 250's somewhere.
Input is welcomed!

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Re: 454 Efficiency - Compression vs port velocity

Post by gottago » Sun Oct 22, 2017 2:27 pm

In my vehicle, how would this actually feel to drive??
What do you want it to feel like? DV cam equation may be helpful even just to know where peak torque is but won't tell you what it "feels" to drive. Most 454 propane powered vehicles I've been around were work or tow vehicles. Some worked very well for what they were intended. Not sure that's what you want. Compression changes the feel quite a bit more than you may be expecting. A tight lsa and shorter duration will gain a ton of low end. Can even get brutal. You could gear it up for a very low rpm cruiser and that may suit you but it is a truck/tractor like power and won't run up in the rpm nicely and car like. Go too far that way and the power will be quite intense but short lived. By the way, a 454 1 ton at an auto wrecker near me got best fuel mileage and power with a midrange cam on 110 lsa and dual mixers on a tunnel ram. Go figure..

Have access to a dyno sim program?

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Re: 454 Efficiency - Compression vs port velocity

Post by burbfixer » Sun Oct 22, 2017 8:10 pm

gottago,
No, I don't have access to a dyno sym program, but your comments are exactly the kind of input I can use. It sounds like you and others here have played with enough engines to have experience in what certain types of combos act like in a vehicle.
You raise a good point, about taking things to an extreme and focusing too much on 'tractor torque' in a very narrow rpm band, but killing rpm potential.
In my first couple of posts on this thread, I tried to give some indicators of what I want the engine to feel like, but maybe I can expand on it a bit. It's not that I hate rpm and horsepower, it's just that I rarely go to wot and rarely go to redline. When I do though, it would be nice if the engine was pulling hard to 4500ish. If it pulled to 5000 I'd be beyond pleased. I'm not sure if that's enough to fit the 'longer broader pull' you referred to earlier.
I'd like for my engine to have enough low end torque to 'play with' at part throttle - say no more than 1/2 to 2/3 throttle - and really feel it in the seat of your pants. Not necessarily 'brutal', but enough that it gives you the feeling the engine is effortlessly accelerating the weight of the vehicle without much 'commotion'. My cruise rpm now is 1300 - 1600 depending on speed, so the engine needs to have good torque from as low as maybe 1000 rpm.
All of this would, of course, be much easier if I had lots of money to spend. I could just build an engine with way more power than I need, and be done. If I can get the engine I have to run the way I want, and do it inexpensively though, that would be great.
I'm fairly certain I will meet my goals with this engine, I'm not worried about that. But I thought it would be cool to bounce some of my questions and thoughts off the people on this forum first, and the input from you and the others has been great.
Given this info, what type of cam specs would you choose? Even 'ball park' figures would be of interest to me.

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Re: 454 Efficiency - Compression vs port velocity

Post by gottago » Mon Oct 23, 2017 3:47 pm

I don't have much real life experience with bbc on propane, the bbf we did were roller cam. The sbc were in a much lighter vehicle with way different gears. The bbcs I have been around were work vehicles but one was high geared with similar high compression as yours. Was extremely reliable 200,000 + trouble free miles on it now. Was mainly a highway hauler in mountainous country. Difference being that had a 5 speed transmission but in high gear it was at 1600 rpm and it easily and smoothly pulled any hill with any load with minimal down shifting . It too was a 110 lsa cam of medium low duration. Around 224 ? and .510 lift. Been too long for the owner to recall accurate numbers. Not sure what head is on it either but has a good low rpm torquer intake. It wouldn't call it real responsive but its a big 4x4 dually. Owner says its the best of the 5 engines he has had in that truck.

One other that I was a bit more impressed with power wise had a similar cam but on a 108 lsa. Idle was more noticeable and it had lower gears. Not sure what heads either. Pulled really well and was more responsive but fuel mileage apparently suffered. Both of these were work trucks and 4500 rpm was likely tops. I'm not a bbc guy so hopefully someone else can give you some better pointers. None of the simulation programs are much help for such low rpm. If you look around for a cam card that shows an rpm range starting around 1000 or 1200 rpm and wanting around 9.5 -10:1 compression max on gas your 11:1 on propane should be fine. Do the calculations though for the actual dcr. I'd keep a fairly tight quench even for propane. You don't want to have to compromise ignition timing on this to keep it as responsive as possible. Years ago I used a cam I believe was called the crower beast in a heavy 4x4 ford. It did reasonably well and the mileage was decent.

Hope some of this helps, I too know how hard it is to find info on combinations that produce power and mileage. Seems its one or the other for most folks. Good luck..

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Re: 454 Efficiency - Compression vs port velocity

Post by pdq67 » Sun Oct 29, 2017 7:34 am

Back again, if you need a crank, then make a 496!!

The late JL did a couple of mag. articles with both, the 496 and 502 and he made a, "tow-truck", engine using something like a CC 252 HE cam.

Might look them up and study both articles.

pdq67

PS., one of the mag's had the teal painted '57 Chevy, "Chezoom", on it's cover, don't remember what was on the cover of the other mag, sorry.

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Re: 454 Efficiency - Compression vs port velocity

Post by burbfixer » Fri Nov 03, 2017 2:38 pm

pdq67,
Thanks for the tip, I'll check it out.
496's are good.... wish I could. My brother & I did a propane 496 for a friend who used it in a 1ton 4x4 to haul a large horse trailer in & out of the mountains. I didn't live nearby, so never actually got to ride in or drive that truck, but reports were that the available torque was beyond impressive, and with the loaded trailer behind, it would gain speed on steep grades in high gear.
I've been doing a bit more research on the cam question on this and other sites, and it seems those who've played with propane performance engines in truck applications favor the wider lsa's. Not surprising, that's definitely the safer, 'tried & tested' way to go, and fits with what I've already experienced in the past with my 396.
That propane engine had 10.25 to 1, the stock closed chamber heads (pocket ported), and the stock 68 cast iron high rise manifold with headers and 2.5 " exhaust. It was used in a 4x4 with 44"tires, 4.56 gears and a truck 4 speed. It was my daily driver in that configuration for several years, and was definitely fun to drive. I never felt like it lacked power, even spinning all 4 tires in deep mud. Because of the tall overall gearing, I used a Crane 'low torque' cam with 204/216@.050. 484/515 lift, and 112 lsa. It was capable of 14 mpg (imperial) on a highway trip, which I always felt was not bad, all things considered. If I let it lug down to under 1000 rpm it would pull from there no problem. Only 1 minor 'complaint' I had with the engine : at 4000rpm it was over with. The engine would rev higher than that if I needed it to in mud, but out on the highway, pulling the weight of the truck up through the gears, there was no point at all in taking it higher than 4000. The engine ran so well otherwise, the low shift point was hardly a 'problem' though. After driving it a few years like that I added a Paxton blower and at 6 ish pounds of boost it dyno'd (with the 44's) at 330 rwhp. It ran good... Timing was much more critical though. It ran great in the cooler north, but then we took it on a trip to where the weather was warmer. I rattled the engine so hard we actually got out and looked because we thought the fan was hitting something! The engine survived (thank-you forged pistons), I reduced the timing a bit, detonation stopped, and ran it several more years with the blower in place.
I will likely use something similar to that 396 cam in this engine, but I'm considering splitting the difference in those cam specs and using a single pattern cam with something like 208-210 or so and a 'normal' 110 or 112 lsa.
But... Dang it, I'm still curious about what Vizard teaches about narrower lsa's. I've seen a few comments now that say some have experienced lower fuel efficiency going that route. I believe what they report, but there's reasons I wonder if that would necessarily be true in every case. Might try to start a new thread.

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Re: 454 Efficiency - Compression vs port velocity

Post by Newold1 » Fri Nov 03, 2017 2:53 pm

Not that knowledgable on propane compression factors and limits but I would say that compression and as much as you can everyday, every drive use without reliability or damage issues is what I would recommend. I know that usually most propane vehicles need special attention to valves, valve lubrication, seats, head preparation issues and this should be addressed no matter what head and compression. In my opinion the port velocity will be more affected by the camshaft and its design in that using a big cc intake port head for this engine is uncalled for and counterproductive. Use any good 205 to 260cc head and your going to be just fine. Pay more attention to determining the ideal compression ratio for your propane build and put your efforts into cylinder head preparation and camshaft selection.

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Re: 454 Efficiency - Compression vs port velocity

Post by burbfixer » Wed Nov 08, 2017 10:58 am

Newold1,
Thanks you for the thoughts!
It adds weight to what several others have expressed also. This thread has helped a great deal with my initial question about compression vs port velocity.
"Camshaft selection"... it's so easy to say, but..... This is where I wonder if I can improve on my past selections. I have a few questions, that if I find answers to, would help me home in on the specs I want. Will start a new thread.

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Re: 454 Efficiency - Compression vs port velocity

Post by gottago » Wed Nov 08, 2017 6:32 pm

In regard your comparison engine...
That propane engine had 10.25 to 1
I've run propane big blocks with that compression ratio before and can tell you there is a substantial difference stepping up to 11.5 or higher. Increased burn rate and all that which also allows for a longer duration cam to maintain same dcr as shorter duration lower compression combinations, resulting in the ability to rev higher..

In regard Vizards cam speccing process, just a side note, I'd once run a smallish 104 lsa cam in a sbc at 12.5:1 compression for a year or so on the street. Interesting, fun, and pretty good fuel mileage.. Rattled the hell out of myself and that truck though, idle sound was what lots of people were impressed with but it got real tiring.. The 108 lsa bbf was a performance orientated unit and it would rev out, cruise nicely, and smoke the tires at will, down side fuel mileage. So yes, I think it can be done where the lsa can get tightened and the mileage won't suffer too badly but its a pretty finicky cam and gearing pick in combination with everything else that gets you there.

Also, a single mixer won't cut it.. That'll shut you down at 4,000 rpm highway even with a more appropriate cam. imo

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Re: 454 Efficiency - Compression vs port velocity

Post by gnicholson » Thu Nov 09, 2017 9:10 am

you need a pair of 96 and later l29 100cc heads

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