| Author |
Message |
truthhunter@shaw.ca
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 12, 2005 - 10:28 pm: | |
Just can not forget those old Ram Air kits on the engine air intake that I saw many times back in the late 70's. Has any one ever played with them on a 8V71.
I am considering fabricating one on the MC-8 seeing how it tends to burn rich anywhere near full pedal(I do not know what size injectors ). Besides the "quick to get dirty filter" problem are their other concerns about causing engine damage if I try this.I was thinking of puting a large scope just above the roofline on the drivers side. Will it add any hp increase at higher speeds and reduce the rich burning? Will I acomplish anything besides keeping myself occupied for a few days. Who thinks that scoops should only be used to clean up after the dogs and not for N/A diesel engines? |
Craig (Ceieio)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 1:20 am: | |
The biggest benefit to ram air is cooler air temp on the intake that leads to a higher charge density (cooler air holds more atomized fuel). There really is no "supercharge" effect of higher (highway) speeds on a "ram air" system (also known as a NACA Duct). |
Marc Bourget
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 1:31 am: | |
A scoop might look pretty but a waste of effort until, or regardless if other "unanswered" questions are resolved.
You said rich at near full pedal, what RPM? Have you a "tattle-tale" on the intake system downstream of the filter?
Though not as significant at Bus speeds (drag goes up the square of the speed increase) unless you carefully designed the scoop and followed Reynolds effect in tapering your intake "plumbing" as you observed, you'd probably introduce more drag or restriction into the intake system than you already suffer (or enjoy depending on your point of view) Either way, the drag penalty is greater than HP gain. One of those "laws of physics" things.
I'd consider whether your interests and pocket book could tolerate a 6V92TA since you're comfortable enough with the bus and unsatisfied with the power sufficient to notice that you're occasionally "asking" too much (the black exhaust) of this powerplant.
Mind you, I'm not faulting your driving technique. I've got a fresh o'hauled 475 HP 8V92 for my MCI-9 and I'll be going to a 4 stroke instead.
Onward and Upward |
TWODOGS (Twodogs)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 5:12 am: | |
air scoops always 'looked' cool...never improved performance |
Ed (Ednj)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 11:03 am: | |
Heres a good artical--http://users.cwnet.com/~thall/fredhobe3.htm |
Johnny
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 2:44 pm: | |
2D: Flat-out wrong. I've seen proof that they do work. |
truthhunter@shaw.ca
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 3:00 pm: | |
Johnny please do share what you can remember or know!
Two dogs I am not sure I can agree about those scopeslooking cool, but then estetics are similar to belier. |
Marc Bourget
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 3:17 pm: | |
Johnny,
I note that we're now speaking to cooling systems, not the intake scoop issue that started this thread.
I think, before you state such an emphatic conclusion, you should be careful to set out just what facts and conditions are predicate to your "proof" that they "work".
On a properly constructed and maintained system, (OEM - no scoops) cooling system scoops should not be necessary. I agree that they will "show" some benefit to a poorly maintained and/or poorly driven bus. I also note that women's corsets were, at one time, banned for much the same concern.
On a intellectual, scientific and efficiency basis, they don't really "work", they're a band-aid with a higher energy cost.
Having said that, I recognize that practicality may justify band-aid fixes. It's expensive to "properly" go through a cooling system, or the engine as a further matter. Depending on the usage, current budget, interest, future plans, I might fit scoops to my own bus as a stop-gap measure.
It bears repeating for the newby or those who haven't considered this point in previous posts.
In any case, it's more conducive to good practice to back off the throttle than add scoops and punish the cooling system and engine.
The old saw still reigns supreme! Ya makes your choice and pays your price and hope the alligators don't get you in the meantime.
Onward and Upward. |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 4:14 pm: | |
Marc: "On a properly constructed ...."
Designing a simple thing like a cooling system needs the knowledge of a variety of engineering specialties so that very few end up perfect.
If I remeber correctly, back in the days of the MC-8 or MC-9, MCI supplied air scoops as an aftermarket item for their busses that ran in hot climates. Maybe just a bandaid for a poor design but you are probably the only one on the board with the ability to redesign and reconstruct it.
As to the matter of increasing power with an air scoop I had good results on a bus with a DD 4-71 with a five speed stick. By providing some ram air to the filter with a scoop I gained one gear on grades without any other change. |
gusc
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 5:51 pm: | |
I have to go along with Marc on this one. I think that if a scoop is added and improves cooling or engine air intake it is pure luck. If it works, great, but your chances are slight.
The rear of a bus is subjected to tremendous air turbulence simply because of its shape; ie, a streamlined brick. Air turbulence and the usual resultant low pressure are not conducive to efficient air intake.
A properly designed air intake system would almost surely require wind tunnel experimentation, not something the average bus owner has available.
High bus scoops merely take slightly cooler air a few feet higher above the pavement which in hot climates is very hot. |
Johnny
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 7:02 pm: | |
I mean an air intake scoop, as originally mentioned. I've seen them worth noticeable power. |
TWODOGS (Twodogs)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 7:05 pm: | |
anybody that thinks a scoop ads more air....still believes in santa claus |
Johnny
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 7:14 pm: | |
No, but it's pretty obvious that there's more power when a car traps at 99MPH without the scoop & 102 with it. This was a shaker-type setup on a 1974 Firebird (which now traps a good deal faster). The difference would probably be larger in a car lighter than this seriously-porky 'Bird. |
Marc Bourget
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 8:15 pm: | |
In the interest of prompting further information gathering on the “Yeah-sayer's” part . .
Thank you Stan for your comment on cooling systems, but I don't profess to have an expertise in cooling system design. I do have the advantage of numerous episodes with one of the legendary aerodynamicists, John Thorp. We had numerous discussions of air and liquid cooled aircraft installations and, with regard to ground vehicle liquid cooling systems, more exposure to someone at an expert level than most anyone. Bob Sheaves did a bunch of original cooling system design work while at GM Military Vehicle Operations, including mods to the RTS. I believe the early MCI scoops were a stop gap until the larger radiators/fans, etc. came out. If they were a boon rather than a band-aid, they’d be on the busses today.
With regard to your experience with the 4-71, Your observations are undoubtedly correct. I don't question what you observed. I believe it’s possible that the conclusions and basis for those conclusions is poorly understood and for all intents and purposes, probably worthless. The setup must have been really ugly to get the benefit observed. The airflow demands are so modest and achieved as such low (relative) vehicle speeds that you could probably get more benefit paying attention to the ducting alone and leaving the scoop off.
For example, the scoop alone is almost insignificant at road speeds because you can make or break the benefit it obtains very quickly within a few feet of ducting from the roof by failing to pay attention to such factors as the duct cross section in relation to the Reynold’s Number.
Johnny, I’ve met Grumpy Jenkins at a friend’s house. Frank won the Winternational’s at Pomona one year. Other than driving technique, the discussion was all about airflow. Frank owned a header company. A rather brilliant technician here in Stockton that does my engines does Head Work for GM’s racing division. The engineering effort that goes into the correct pressure recovery for those “shaker hoods” is phenomenal. But the goals achieved are so different from a bus application that they’re of little value to us.
Incidentally, the Israeli Army has the highest cooling system standards in the world. During Bob's visit to Bussin 2000 we did a walkabout discussing cooling systems. I’ve got all the formulas written down somewhere but failed to go back and consolidate my notes so I doubt I would be able to recreate his load calcs at this time. But, we still talk so I don’t really have to.
Bob won’t speak to me about a radiator installation for my repower until I build a model and run it in the University’s wind tunnel. Stan, there are variables, but the criteria exists to cover the range of uncertainty.
I want to close by commenting again that what you guys observed is correct, none of you are lying or mistaken. What I’m speaking to is the reasoning behind your choice of words and opinions expressed. I wouldn’t want to leave these things alone and see one of you make an assumption on faulty information that appeared reasonable and have it melt down your engine, and things of similar misfortune. |
truthhunter@shaw.ca
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 9:45 pm: | |
Marc have you ever heard of an addiction or overdependency on academia. I hope all that access to "luxury labs" has not impeded your basic concept designing "undersite"? (I am only tryng to offer you some constructive critism here not belittle you) I do value all imput of relavence. One needs to keep the fear of failed design in prespective to the entire investments value that may be jeprodized. The major impedment to many a "professinal's" progress is the huge (almost bueracratic like) infastructure that they are a part of. Not that I am invocing the Keep IT stupid SIMPLE philosiphy, as the manditory details of machines are often complex. There is often a time when a deducated guess is a good place to put down the pen and pick up the hamer & vice grips.
I am making my "scoop design poential" assumptions that any extra power that a intake air scoop might contribute to a overfueled 8v71 would come from more complete combustion durng the rich burn times. This would come from a cooler(denser)air charge and mild increase in boost pressure to what the supercharger is allready pushing into the cylinders. Is there any reason to worry that the slightly leaned combustion would burn a piston. Well at the intake end of the scoop, design turbulence would effect the flow dynamics at the scoop and in the delivery tubes, I can not imagine any effect down wind of the supercharger other than a somewhat cooler and slightly higher pressure avaiable to fill the cylinder. The cooler charge should offset the added heat of a slightly leaner burn. Have I miss something critical in this simple laymens interpretation of a fake turbo -like the fuel timing?
On a unrealated point, my MC 8 does have those aftermarket radiator cooling scoops but I have no comparison to make a guess on their added cooling or consumption of available power with the added drag. It would be better if these scoops were retractable/removable ,only deploying when the coolant tempature needed the exta cooling (to become more power consumtion neutral) or better still have a electric clutch or variable speed in the cooling blower system. I understand that later models do have such provision for a mutli speed radiator blower to reduce waisting energy on unneeded cooling. That dual shutter system to reglate cooling is really hooky (and half missing on my coach). This is a modification that could be worth the efficencency gain as repairs/replacement is required. There are times too re-invent the wheel, even if you have to resort to educated guessing, and adapting from other systems. Even Spock makes guesses. |
Marc Bourget
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 10:21 pm: | |
I understand the supercharger on a DD 2 stroke is for cylinder scavenging rather than super charging which acts by increasing the density of the air charge in the cylinder (in competition with compression heating which works against-making your point on charge cooling].
As to an addiction, I do not feel that I am compromised by my attention to detail or search for knowledge. I seek knowlege out of curiosity to augment my efforts, not to substitute them.
I certainly don't make knowledge an item of conceit (I'm better than you because I can add 2 plus 2, IYKWIM). The information is only for the curious. The others press on regardless to their own reward.
If I got pompous and started dictating, "You must do [this and that"], I hope someone would put me in my place or out of my misery. While I've been accused of such, re-reading the post fails to support the accusations.
I don't recognize the fear of failed design point you raise. I'm not spreading FUD Cooldfeet's "Fear, Uncertainty and Doubt")
I've seen several busses with roof top intakes the same size as the Air Filter-engine connection. These installations are the same diameter top to bottom, despite being several feet longer "in the tube". The problem is the longer the tube the more separation of airflow occurs and less total airflow results. What the Reynolds Number phenomena tells us is we need to taper the long intake tubes [a calculable amount] to prevent separation and flow robbing turbulence. If you do the calcs you can find out exactly what the taper should be. If you're intuitive enough to go BIG, (no real "academia" there - by increasing the pre-airfilter intake diameter, maybe 1-2") You'd probably be in the same general result, without the difficulty of manufacturing carefully tapered tubes and bends. Proof is simple, attach a Magnahelic Guage at various points in the tract and see if you get a pressure difference.
So, those that have the curiosity, intuition, interest and skill benefit by following up on those characteristics, the others pass me off as a pompous a**hole [their God given and Constitutional right] and suffer poorer performance. I only care about the former, the latter are left to their own devices. After all, this is a "discussion forum" not a "Bus Conversion Police" site.
I've always found that more knowledge promotes more intelligent choices. We're all entitled to take it or leave it. Ian hasn't put a word limit on posts.
In summary, don't do something because I say so, but because it sounds "right". I strive to sound "right" because my major definite purpose in spending the time I do on these posts is to help those interested be the best that they [and their conversion] can be.
Onward and Upward. |
truthhunter@shaw.ca
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 13, 2005 - 10:54 pm: | |
Naw Mark you do not come off as pompass, your "all right" in my opion. Just that some of the info you graciously share does seems to portray a bit of bias (to some of those that have not made your aquaintents), and any hint of bias does tend to raise the alarms of fact inquiring minds. Portraying beliefs is something I equate with salesmen and preachers. So stop implying you that any apology or other emotional responses is being demanded. It's everynoes right to express in thier own conotation of course and if someone doesn't like it, that shouldn't matter too you. It's everyones right & responsibility in a age of disclosure. We all must take these right for ourself (forgive my athiesitic views) as no one will give it us you (god is just dog in a mirror).
Back to bus business then.That was my thinkin too, the best solution between the Scoop and the Air cleaner should be a TAPERED DUCT with a water ejector and a diverter valve (to intake air from engine compartment) for real dirty conditions (heavy rain, snow, or dirt)that could be operated from the dirvers seat. |
Gary Carter
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 14, 2005 - 12:45 am: | |
Mooney (light airplane) used an air ram scoop to pick up a couple of inches of manifold pressure. Also had an air cleaner bypass, that you could use above the dirty air line. |
gusc
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 14, 2005 - 2:00 am: | |
Gary,
That Mooney airscoop manifold pressure boost was at appx 200 mph and was well engineered. You can be assured there was a bunch of wind tunnel time involved.
Marc,
Are you by any chance at COP or is it Stockton College now, I forget which way it went? I used to live in N Stockton years ago and learned to fly at Stockton airport. My oldest son was born at the Catholic Hosp there. |
Marc Bourget
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 14, 2005 - 2:16 am: | |
Yep, Gary, that's correct. But compare it to induction systems of other certificated aircraft. John Thorp, Lockheed Vega's liason with the piston engine manufacturers, one of the top aeronautical engineers of all time, related that studies and his own experience which showed the increase in HP from attempts to boost thru "ram air" always cost more in induced drag than was returned in thrust. I am the proud owner of John's personal T-18. He was very proud of the fact that he could "drive by the V-tails" with his little homebuilt. Think he would ignore a benefit that would witness him passing 310's and Barons? Hardly!
Additionally, the "HP increase" was reduced by propeller efficiency and other factors. It was a good source of marketing and advertising blurbs, but if it were true, all light aircraft would employ the technique. Dave Smead explains how marketers slip by the deficiencies of Ferro Resonant battery chargers, touting a weakness, diminishing charge rate as a "plus".
This drag increase is is more significant with aircraft as the drag increases exponentially with speed. Size of ducting and weight is not as critical with busses and the benefits are easier to ensure.
Truthhunter, IMHO, there's lots of dirt flying around in engine compartments, how boutjust below the top of the rear cap? |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 14, 2005 - 9:23 am: | |
Marc: As I mentioned previously a variety of engineering is required in all vehicle design.
All the wind tunnel tests you do will tell you nothing about the difference in reflected heat between asphalt and concrete, or weather conditions, or the difference in fuel from one fill-up to the next or a multitude of other things. However it wil tell you that a brick is not the ideal aerodynmic design. If that is what you want, you should not have started with a bus.
You were expounding on your theories on this board for a long time before you even had a bus. Why don't you complete your bus and then tell us all about the improvements you made? That way everyone can benefit from empirical knowledge instead of theory. Every year the aeronautical engineers come up with a new theory of why a bumblebee can fly. |
Vin (Billybonz)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 14, 2005 - 10:16 pm: | |
You guys are getting way to technical for me but all I can see is the blower spinning at a given speed. Will the ram effect really be able to stuff more air into the cylinder or is the benefit coming from the cooler intake air?
How bout spinning the blower faster? That would stuff in more air....or is that dumb?
Vin
73 GMC T6H4523A |
Marc Bourget
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 14, 2005 - 10:18 pm: | |
Sigh, I'm not giving directions here!
I began my interest in busses in 1978 and one was "in the family" since 1983 - guess who did the work? I got my first bus in about 1988. I was lucky enough to listen to those with experience and decided it wasn't a good conversion candidate.
Who knows more about converting busses a purchaser of a new Marathon or somebody like Gumpy who really had to work at it? My first bus was so bad it made Gumpy's 9 look good. But I learned lots about what you shouldn't do and that's what I try to share. I did pretty good with my current chassis.
One of the functions of a discussion board is to expose thoughts and theories to open evaluation. Rather than "dis" me for not having a bus, why don't you point out the errors and fallicies in my points!
The one inarguable point about conversions is that it requires the application of a broad spectrum of skills and knowledge. Except for high level electronics I've acquired skills in all facets of bus converting. I've even switched ring/pinion gears and rebuilt diesels. I believe I have plenty of empirical knowledge and enough understanding of theory to use that empirical knowledge to its best purpose.
Nobody has to do what I say because I'm the one that says it! They makes their own choice. I only seek to inform those with open minds. The rest will usually ignore me without an invitation to do so. Fine by me! |
gusc
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 14, 2005 - 11:21 pm: | |
Vin,
Oddly enough when a turbo/intercooler is added to a DD the blower ratio is decreased slowing it. When an aftercooler is added it is again slowed?? Probably has to do with cooler air being more dense. Also a slow turning compressor is usually more efficient than a faster one, just like an airplane prop..
The changes are something like from 2.6 to 2.05 to 1.95. Those are not exact because I'm too lazy to look them up but they are close. |
Vin (Billybonz)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 15, 2005 - 9:03 am: | |
See, shows how little I know....good to know since I was thinking about a turbo. I really need to get a manual on this engine. It's not covered in much detail in the coach maintenace manual.
I like to read all the different opinions here...this is hands down, the best bus board on the Net.
Vin |