My MCI 5A has had serious heat issues since I bought it. 6V92, (350HP) auto. 12" X 12" blowers, small pulley,new radiators made w/ dimple tubes, and serpentine fins, original tanks were used. I need more rads I know but this issue is worse than it should be. Also just had both heads replaced due to small cracks in both due to Po's inability to keep the heat in check. Also new turbo.
My question is: The muffler on my bus is 5" inlet and 4 1/2" outlet. It is not straight thru, and the size leads me to believe it might be just a resonator. Regardless on whether it's a muffler or resonator would the smaller size outlet contribute to heating of the motor? I drive it by the boost gauge. The engine heating is directly related to the amount of boost I'm running NOT the amount of pedal I'm using. For instance: I'm in the top of third approx. 50 mph @ 2100 rpm and I'm using enough pedal to have 10 LBS boost, then I shift up to 4th and the boost drops with the same pedal pressure. I can give it more pedal pressure to achieve the 10 LB boost mark. This leads me to believe that it's not as much fuel related as it is an air flow problem. The air in is fine so that leaves the exhaust. Also I can't seem to get the boost past 15 LBS.
Can anyone provide me with a definitive answer on how much this exhaust
(5" inlet 4 1/2" outlet could be affecting my engine??
Don & Sheila
Highly recommend you change to a 5" inlet and outlet-that's what the trucks have on them. I installed an 10" x 15" oval muffler that is 26" long with the inlet and outlet on the same end. When I bought it, all that was inside was the pipe perforated with holes. Otherwise was just straight through. Granted it is a bit noisier than stock, but then again, I like the tone. It made a big difference getting rid of the giant muffler that was stuffed up to the point that it didn't make any exhaust noise. Mine is made for turbo's and is just one of many sizes and styles that Donaldson has available. Mufflers are around $250-350. Good Luck, TomC
I have a 36"x10" 5 in 5 out muffler on my 350 HP 6V-92. I have tried using a 4" tail pipe and it has no effect on engine temp or power compared to the straight 5". Mine makes 20+ lbs of boost and always runs 180-185. You can't just add big injectors to a 6V-92 to get 350HP. There are a lot of bits and pieces to go with them or you won't get the airflow through the engine. It will just produce a lot of heat. Donn
My 1991 Eagle DDEC2 6v92TA gets about 23lbs of boost. I removed the clogged muffler and am straight piping. I gained about 3-4 lbs of boos by doing this and throttle response greatly improved. The sound is louder but not too bad for me. My muffler had about 500K on it and looked pretty bad inside.
On my Lexus SC400 I wanted to evaluate the exhaust system. I mounted an 18mm nut on the side of the pipe immediately after the cat. I registered 1.5 pounds of back pressure at WOT at redline. Not bad I guess but I am not positively sure of the relative merit of that backpressure figuire. I then cut out the center resonator and replaced it with a piece of 2.5 inch pipe. My back pressure went to zero...or at least I could get no reading on my gauge. The system still had two resonators and two mufflers and was reasonably quiet. I stopped moding anything on that system as zero was as far as I could conceive going. My question is: what is a tolerable back pressure at the inlet of the muffler on a 6V92 Detroit? If that was measured and found acceptable you could start looking for a heat problem or more power somewhere where you might be able to realize some gain and some bang for the buck. NOTE: I noted that trying to use the O2 sensor port gave ten pound reading, by comparison. I attribute this to the port being canted slightly twoards the gas flow and I think it acted like a scoop. What shape port would minimize that action and accurize the reading.....engineer???
I really liked that straight pipe idea even though I had one lit off at 6am right next to me and I thought Judgement Day was upon us. I think it actually vibrated me around in the bed....Sweet Lord! Still, I like the idea of cheap zero back pressure.
John
With a turbo engine as close to zero as you can get it. Good Luck, TomC
Tom,
Thank you. I want to know how much backpressure I would have to have for that to be a problem that I would want to address. How much is simply cheating me of a little power? How much is causing excess heating of the engine? Maybe this is a 4 cycle or 2 cycle pecular data and I would be happy to know anything about either. I cringe at the thought of changing any part of my exhaust as a "trouble-shooting" exercise. Yee gads, Kids! We are mose talented and resourseful than that. "Hope your new muffler helps with your on-going overheating problem of 3 years". The HOPE and HELPS part scare me. 3 years is no confidence builder either. I say this admitting that I am and have been in the same boat many times and some sage advice would have done wonders for my success stats.
How do I measure the back pressure?????? ??? ??? ??? :-* ;D
Luv ya'll..really.
John
How's the intake? Filter clean and unobstructed?
You maybe want to know for sure that the parts in the engine (injectors/turbo) are the right spec, before considering the extremities.
Oh, the fan door is properly sealing, isn't it? No air through the rads if the fans are pulling air around or through gaps.
good luck! And keep us informed!
happy coaching!
buswarrior
Whether it be a too small air cleaner or a stuffed up muffler, usually black smoke will be your guide. If you think it is the air cleaner, simply disconnect the air cleaner and take it for a short, relatively dust free drive to see if there is a difference (a short drive with minimal dust won't do anything to the engine). If you think it is the muffler, do the same thing-although it will be a bit on the loud side. Good Luck, TomC
Well we're back from the Black Hills. I put a Donaldson muffler ( 5" IN X 5" OUT 9" X 27"
body), on before we left. Turn out it was 5" in AND out. I was reading in a flat area of the tail piece. Anyway I pulled it off and there is a perforated pipe the length and there is a disc blocking the pipe in the middle. The exhaust has to go around thru the perf holes then back out the perf holes on the other side of the disc. I figured that has to have alot of back pressure. I bought a new one along with elbows etc... and rebuilt it all. I punched out the disc in the middle and had all of the elbows and pieces welded. DAMN IT'S LOUD NOW. My initial/gut feeling is the 6V92 mechanical wants some back pressure. I think it lacked power, just a little, from before I punched out the disc. and I think the heating may have been just a little worse. It DID NOT help at all. I may be wrong on this but it's just so little change, except for the sound, it's hard to say if it hurt at all. VERY minor IF AT ALL. I'm going to try the Areo muffler next as this thing isn't much more that a straight pipe, and the Jakes OMG.
Anyway I've done EVERYTHING except more Rads SO... that's this winter's project. Two more rads to bring my BTU capability to 20% more than the motor can produce. Then I can use all 350 HP.
Thanks for all of your input guys.
Don & Sheila
Don, I've kind of figured that the back pressure caused by the exhaust passing through the muffler and pipes was taken into consideration by DD and GM when they engineered these busses.
They seem to work all right as long as they are operated as designed, more or less. Forty years ago, people didn't object to smoky exhausts like they do now.
If a person increases the amount of air pumped into the engine by using a blower, does that raise the amount of fresh air that gets compressed? I think that with the ports and exhaust valves open at the same time, the increase is much smaller in a two stroke than a four stroke.
For what it's worth.
Tom Caffrey
Ski,
If you have back pressure you will generate a little more heat in the engine. Way back in the day all cars had what was called a heat riser valve in the end of the exhaust manifold. You can't make this up....honest. The job of the heat riser was to PLUG up the exhaust and expedite the engine coming up to operating temp. At temp a bi-metalic spring would position the buterfly to "open". They also had thermostats in those days. So plugging the ex will increase temp....ok. The rub is "HOW MUCH BACK-PRESSURE" and "HOW MUCH HEAT"? I know what the principle is and the results.....HOW MUCH? I admitt my ignorance and even to the point that I don't know where to go to get the info except here.
For your situation: You relieved the back pressure and that must have reduced the temp by some amt. Again HOW MUCH? Less back pressure will allow you to get more fresh air into the cylinder on each charge cycle and that will result in more power and MORE HEAT from that sourse. Did you generate more heat than you lost? Don't know.
I completely disagree with the statement that DD designed the engine to operate with some normal amt of back pressure. Every tech article I have ever read said "OPEN THE INTAKE" and "OPEN THE EXHAUST". If this were a tuned ex system there would be some merit to the back pressure theory but that back pressure would be in waves of reflected energy that stuffs the charge back into the cylinder...deep stuff.
What concerned me with your post was that you seemed to be poised to plug up your ex to get power back. If I am wrong on any of this I sure hope you guys don't let me stay stupid.
Thanks
John
I'll be eagerly awaiting results.
Tom Caffrey
John,
I think I'm creating just a little more heat than I eliminated by your reasoning of more air to compress. I'm not going back to the Donaldson muffler because I think the (plug/disc) in the tube is a little too much back pressure. The Aero muffler is quite unique in it's construction and claims increased MPG, free flowing, (BLAH, BLAH, BLAH) rhetoric most likely. But it will provide just a little back pressure, which I think my 6V92 wants. Not much, just a little. Plus I can't live with what is basically a 40" straight pipe. LOUD doesn't begin to describe it.
May be a wrong comparison but my 1972 Shovelhead (Harley) has a 12%+ increase in horsepower with a 2 into 1 exhaust with a muffler, over straight, dual drag pipes.
Don & Sheila
p. s. I remember the spring butterfly in the exhaust manifolds. always rusty always stuck to some degree. We just took the butterfly part out and left the pivot shaft in.
According to an old copy of the DD Field Service Data Manual:
Series 92 (non turbo):
Exhaust back Pressure--Inches of Mercury - Full Load: 1200rpm = 1.5 1800rpm = 3.3 2100rpm = 4.0
Series 92T 8V and 16V
Exhaust back Pressure--Inches of Mercury - Full Load: 1800rpm = 1.8 2000rpm = 2.2 2100rpm = 2.5
The MC-5A originally came with a 6V71 or 8V71 so if the engine and HP are raised with a 6V92 then you have to have the cooling system for a 6V92. Obviously you have to have the correct rads and blowers but you also have to have the correct airflow. As buswarrior pointed out, you have to be sure that the blowers can only suck air through the rads. The increased air flow from the bigger blowers has to have some place to go. Have you increased the size of the openings in the floor of the blower compartment, increased the size of the openings in the side doors and have free flow under the rear bumper.
There have been hundreds of threads on cooling MCIs with all kinds of exotic ideas, but almost always it goes back to the radiators and air flow. MCI buses with the two top rads were borderline on heating when new, so boosting HP will always create more heating problems.
Stan, Dallas gave you the correct max reading for the 92 they require some back pressure but not much if you do not have a mercury gauge check it with a low pressure air gauge by using the formula psi x 2.07 = mercury
Quote from: JohnEd on September 03, 2007, 08:46:32 PM
Ski,
If you have back pressure you will generate a little more heat in the engine. Way back in the day all cars had what was called a heat riser valve in the end of the exhaust manifold. You can't make this up....honest. The job of the heat riser was to PLUG up the exhaust and expedite the engine coming up to operating temp. At temp a bi-metalic spring would position the buterfly to "open". They also had thermostats in those days. So plugging the ex will increase temp....ok. The rub is "HOW MUCH BACK-PRESSURE" and "HOW MUCH HEAT"? I know what the principle is and the results.....HOW MUCH? I admitt my ignorance and even to the point that I don't know where to go to get the info except here.
For your situation: You relieved the back pressure and that must have reduced the temp by some amt. Again HOW MUCH? Less back pressure will allow you to get more fresh air into the cylinder on each charge cycle and that will result in more power and MORE HEAT from that sourse. Did you generate more heat than you lost? Don't know.
I completely disagree with the statement that DD designed the engine to operate with some normal amt of back pressure. Every tech article I have ever read said "OPEN THE INTAKE" and "OPEN THE EXHAUST". If this were a tuned ex system there would be some merit to the back pressure theory but that back pressure would be in waves of reflected energy that stuffs the charge back into the cylinder...deep stuff.
What concerned me with your post was that you seemed to be poised to plug up your ex to get power back. If I am wrong on any of this I sure hope you guys don't let me stay stupid.
Thanks
John
Yes carburetored engines used to have heat riser valves but their purpose was to restrict the exhaust flow enough to force them through a passage under the carburetor. This warmed the carb and intake to give better vaporization and prevent icing. Some cars used an auto choke system with a bi-metal spring in a well in the manifold this was also heated by the exhaust gases flowing through the exhaust passage. In use these systems had many problems; the passage became blocked and no heat was supplied, the riser froze open and no heat was supplied, the riser froze closed and too much heat was supplied and often cracking the intake manifold. Some car makers went to hot water systems and electric choke heaters but finally fuel injection solved all these problems.
Dallas,
At last, at last! Real numbers and a way to go. Those people that thought they had a plugged up muffler can now be certain of the internal condition and servicability of their equipment. As is the case in autos, new replacement items are sometimes such very poor performers that they worsen the condition. Glass pack straight thrus comes to mind.
These bus mufflers are anything but cheap and the labor is serious. Having it done at a shop is @ $100/hr. You have taken the guess work out of this heating/power/smoke thing once and for all. At 1,800 rpm you should have 1.8 inches of mercury, or less, with a 8V92 Turbo. I suspect the turbo and NA are using different mufflers but 1.8 is all that matters. Get that or less and exhaust back pressure is NOT YOUR PROBLEM AND TAKE THAT TO THE BANK! So says DD. Money and attention elsewhere for the fix. Thank you, thank you.
Now these guys that get 2 MPG less than a similarly weighted and powered coach have something to look at for an answer. And something to verify to be working properly.
I know that I should measure this at the outlet of the ex manifold to be sure to get the piping into the measuerment. I used a turbo boost gauge that only went to 25 pounds to do my car work. I measure the pressure that presented itself at a 1/4 inch hole I drilled in the ex pipe. I tried other ports and got "crazy" readings caus the holes there were angled into the ex flow. Any engineers care to speculate? My readings were valid cause I only wanted to see a delta and the absolute was not as important.
Sincere appreciation,
John
just my 2 cents but the statement that less backpressure is good and more air flow is better is a little misleading. if you run a carburated or mechanical injected motor and remove the back pressure yes you will flow more air but with no other changes you will run a leaner burn. more air, same fuel = lean burn, less power, more heat. with some electronic motors you can also create a problem if it a system that doesnt monitor certain things or is capable of only adjusting a given amout. changes to exhaust to reduce back pressure can help assuming you make changes to the whole system to work with the changes. if not you can hurt more than just the power it makes.
steve
Dallas, that is just the info that I was looking for.
Steve that was my gut feeling on the change I made to the backpressure. It was not a major difference but one I thought I could feel. It seemed to have a litt less power and seemed to get hot faster. I had to run 1 LB of boost less than before to maintain the temp at approx. 185*.
By the way I talked to a tech at AERO Mufflers today and he stated the 5" IN X 5" out muffler for diesel's has a back pressure of .4 @ 2500 RPM.
Not enough according to Dallas and DD.
THANKS Dallas for that info. It saved me from another $275 experiment.
Don & Sheila
Ski,
Talk to your Aero rep again and ask if you NEED some back pressure in a diesel. I think the ans is the less back pressure the better. The figure qouted by DD is the expected MAX. If you have more than that you have a plugged or too small a muffler. The stock muf was designed for space and noise and weight considerations and it was old technology. Aero is better these days. As I recall, back in the day,now, FIRETRUCKS ran without mufflers. They WANTED to make noise and they got more power from the practice. My uncle was a fireman in Pa. and I got to ring the bell when I was still in short pants.
Please confirm: My engineer neighbor says that you DIVIDE the psi number by TWO(2) to get inches of mercury. I looked at his formula process and it looked solid. Anybody?
Thanks,
John
In the DD manual its says
inches of water = psi x 27.7
inches of mercury = psi x 2.04
thats their formula in the manual
John: To convert PSI to Inches of Mercury Multiply PSI by 2.036.
Don -
A few random thoughts on this topic:
Remember the Corvair turbocharged Spyders and Corsas from the '60's? Chevy designed the muffler on those engines to produce sufficient back pressure at 5500 rpm to cause the turbo to cavitate (or stall, not sure of the correct term), thereby reducing boost and increasing the longevity of the motor. Granted, the little air-cooled flat six leaked oil and had a tendency to flip off the cooling fan belt, but it was awfully hard to break one. Point is that the factory sometimes does things to protect us from ourselves. . . LOL!! But Dallas came up with DDA's specs, so now you've got something to work with.
Do you have a gravel shield/mudflap hanging directly below the back bumper to keep stuff off your toad? If you do, chances are it's trapping hot air under the engine compartment. GMC put a full-width mudflap across the rear of the coach directly behind the drive axle. This created a low pressure area under the engine, thereby helping to draw the hot air out. Hanging one off the back bumper defeats what the factory was trying to accomplish.
Will have to agree with Buswarrior and others regarding the sealing of both the radiator compartments and the blower compartments. Bad seals = overheating.
Do you still have operating air-powered dampers for the blowers? If so, might want to check their operation, to make sure they're opening fully.
IIRC, MC-5As have slotted openings in the side engine compartment doors, both street and curb sides. Might consider installing an electric fan off a front-wheel drive GM or similar on the inside of these doors to boost the air flow thru the engine compartment, especially when climbing grades.
Speaking of climbing grades, Detroits do best between 1700 - 1900 on a partial throttle when pulling a hill. You should still be able to accelerate from this rpm, but for controlling cooling, it's best to keep the engine in this operating rpm range on a partial throttle. If you cannot hold this rpm, it's time to downshift to a lower gear. (Trivia note: On a 200-mile run from Fresno to Los Angeles, the time difference between climbing the Grapevine on I-5 at 45 mph in 3rd vs 35 mph in 2nd is a grand total of less than FIVE minutes. Something else to consider.)
FWIW & HTH. . .
;)
Once again- with any turbo engine, the closer to zero back pressure the better. Any back pressure will keep the turbo from fully spooling up possibly causing black smoke or slower spool up response time. On trucks, 5" exhaust in and out of the muffler is always used. Good Luck, TomC
TomC,
I talked with the DD 2 cycle rep here in Eugene. He said that the DD 6V92 TA needed "a little bit" of back pressure to function properly. I did not think to question whether he was talking about an electronic engine or mechanical. AND THEREBY HANGS THE TAIL. I talked to a local builder with a good rep and he said that as a general rule the lower the back pressure the better the potential engine performce in all regards....period. Real wishey-washey like. He added an interesting exception, however. He said the newer engines sampled the exhaust back pressure as a computer input and if you changed that it confused the computer...and we all know what that means. He said he was sure that "some" of the systems COULD NOT be reprogramed and that those would be considered to NEED back pressure. I think this must be a DDEC III but I don't know.
There is a "lab for diesels" in town and they do rebuilds and consulting. I spoke to the rebuilder and he confessed to not being steeped in the theoretical or abstact specs. He did say that "all the engines I see from quarries and the such that are used for scrapers and movers have a pipe right out the bottom and they were 6 and 8V92's and 71's. I mentioned the firetrucks running straight pipes and he said "yeah, and they ran the 2 cycles". He must be old!
So less is MORE unless you are running an electronic engine that samples the ex back pressure and even then you can probably have the computer reprogramed if you go to a high flow muffler. Considering a stock muf might cost $1K and after market hi-flow is $250....maybe??? Find out for sure first.
I love it when we all are right, sorta.
Thanks TomC. I would have dropped this if it weren't for your last. This was fun!
John
Back pressure is not an issue until just recently. It would be for Caterpillar since 2002 since their engines have catalytic converters in them. And now for the 2007 engines with particulate traps, it is also important for back pressure. But for any of the two stokes, if you have a turbo, whether it be mechanical or electronic, if you have a pre catalytic converter and pre particulate trap 4 stroke turbo, the lower the back pressure the better. Good Luck, TomC
I have NOT read the other posts, sosss if I am repeating stuff, sorry. Sounds kinda like you may have some incompatablilty inside the engine, like pistons, timing, blower bypass, turbo type, injectors, rack settings, etc.. Don't want to sound too negative here, but your boost gage should not be responding in the matter you report. It should be more throttle related than rpm related within the normal operating rpm range---say from 1500 to the governed rpm of around 2150 or soosss.
Do you also have a pyrometer and air restriction gages? Sometimes a marginal air intake filture/intake system can cause other problems difficult to determine like overheating. Would seem to me the less exhaust resistance the better with a turboed Detroit. Not necessarily soosss with no turbo. If you keep your foot out of it, (and it seems you know how) then your Detroit should NOT be overheating at partial throttle--but only when your stand on it. Don't know what else. Good luck.
Since most of you don't own MC5A's...might I step in here and add some thoughts based on the fact that I too own an MC5A, albeit with an 8V71 engine.
In this model bus the exhaust feeds off the left side manifold (there's a crossover pipe from the other manifold like most MCI's...but the exhaust feeds into the 5" inlet...goes forward...makes a 180 degree turn and exits the muffler (yes, it's a muffler) through the 4 1/2" outlet to a 'fishtail" to dump it outboard of the body of the bus. I have no idea how the rest of the MCI's route their exhaust. ;)
The 1/2" reduction in the size of the inlet and outlet would make sense...for inherant back pressure which Detroits need to keep from 'wet stacking' at low idle speeds.
Here we have a completely different situation. a 6V92 in a bus designed for an 8V71. I take no issue with the repower (wouldn't do it myself because of all the horror stories I've read about cooling those monster 92's)....in addition this one has a turbo.
First, Don, since you can't enlarge the fans (no room) I'd contact Fred Hobe for one of his larger pulleys to drive the fans faster. You're limited as to the size of the radiators...except thicker. If the Shutterstats are gone...good riddance. You need to contact a cooling specialist about more core area.
Another thing. I've found, contrary to what the GM boys say, that a full mud flap across the back AIDS in cooling. It forces the waste hot air out through the side louvered doors (if you still have them) that's the way the cooling system was designed.
If you could somehow use a (for the life of me I can't recall the brand name...but they're at all the big bus shows) Turbo-flow, straight through muffler and find a way to get it outboard of the body without scalding the rears...you might have the answer. The 180 turn has stymied me since I've owned my bus!
It might be that all this is for naught...but then if it opens doors for thought or ideas...that is my intent.
I sure would like to be around for the archiving of this thread and wish all who offered opinions, well.
NCbob
What is most confusing on this thread is that people have introduced evidence from gasoline engines (both air and water cooled) in cars and from four stroke diesels of various brands mounted in trucks and most of the data is not transferable to a DD two stroke diesel engines mounted in a MCI MC-5 bus.
I think the bottom line here is DD's (two strokes), need just a little back pressure. My 6V92 turbo didn't like having an open pipe. Kind of like glass packs for a car, just a perforated pipe straight thru.
Don & Sheila
TomC,
I am with you on this. The rebuilder that I spoke with that mentioned the need for back pressure for the sake of the computer was not specific as to which engines those were and i don't think he sounded like he had facts in that detail at hand. He did say "modern" though. I was guessing that "maybe" the DDEC III might have been one of them and you have cleared that up as far as I am concerned. I read the bottom line as what you posted succintly in your first post "the less back pressure...the better". Thank you for hanging in there and being patient with me.
Sincerely and with appreciation,
John
When I first purchased DML with 8V92, she had a straight pipe out. The people I talked to about it indicated that the turbo was supposed to act as a muffler of sorts.
One of the most beautiful sounds I ever heard was driving down some of the LA freeways which have 15-20 foot walls on each side of the highway (for example I-210 in the Pasadena/Arcadia area) and turning on the Jakes at about 1800 rpm. WOW. Music to the ears. Another good example is coming down the Grapevine. I did eventually install a muffler as I was concerned about getting a ticket.
Richard
Quote from: NCbob on September 07, 2007, 02:43:47 PM
First, Don, since you can't enlarge the fans (no room) I'd contact Fred Hobe for one of his larger pulleys to drive the fans faster.
Another thing. I've found, contrary to what the GM boys say, that a full mud flap across the back AIDS in cooling. It forces the waste hot air out through the side louvered doors (if you still have them) that's the way the cooling system was designed.
Bob -I'm a little confused by your suggesting a larger pulley to drive the fans faster. Are you talking about a larger diameter crankshaft pulley, or a larger diameter squirrel cage pulley? Can you clarify your thinking on this?
Your comment about the bumper mud flap is intriguing, since you suggest that it tends to force air out the side louvered engine access doors. I don't recall ever seeing an MC-5A series with an OEM mudflap hanging off the rear bumper. All I can recall is just small mudflaps equal to the width of the duals directly behind the rear axle, and pics in Larry Plachno's book show the same.
It would be interesting to see what the slipstream airflow is doing when it reaches those side access doors, both with and without a flap. Perhaps one of you who own a 5A would be willing to experiment with some yarn tufts and a video camera in a chase car??
Stan -The point I was making (using the Turbo Corvair muffler as an example), is that sometimes powertrain engineers at the factory do things for reasons we, as the motoring public, are not aware of. The comment was not intended to confuse the issue. I'll agree that it wasn't focused directly on the repowered MCI MC-5A bus, but conceptually, the point is accurate.
Don -Another random thought just rattled around in my muddled mind: Possibly changing the water/coolant ratio. Depending on where you live, you may not need the freeze protection of a straight 50/50 mix. Perhaps a 60/40 water/coolant ratio might be better, since water conducts heat better than coolant, keeping in mind the correct SCAs(?) Detroit recommends.
All -I think that each and every one of us is aware that cooling a rear-engined vehicle is a unique challenge - from the factory engineers to the shade tree converters. Compounding the issue in a vehicle which has the aerodynamics of a brick that's got a souped-up repowered drivetrain, and the head scratching really begins!!
This has been an informative, interesting thread, and I think this is a good example of how so many things on our engines are inter-related - how changing one thing can end up with a large "ripple effect".
Eventually, Don will get his problem solved, we'll all learn something, and be entertained in the process!!
FWIW & HTH. . .
;)
I think FRed Hobe puts a smaller fan on the squirrel cage. There is a specific diameter he uses because the belts in the big sizes have more difference between belts (differences are in inches instead of fractions of an inch). Jack
A quick note on the fan pulley. The MC-5 came with the option of a 3.36 or 4.10 rear axle and the fan pulley was smaller (with a shorter belt) for the high speed rear end. The object was to increase fan speed when running at lower engine RPM.
Hi all,
Thank you all for all of the suggestions. My main problem is I don't have enough radiator capacity. I've just been trying to fix all of the perifials that could contribute to the heat issues. I had new ones built with as much as could fit in the original dimentions. Dimpled tubes, serpintine fins. I was told that I should have increased the cooling by 20%. I saw no noticable improvement. The PO had put the larger blowers in 12" X 12" and increased the opening into the engine compartment. He also put a solid pulley on the blowers. It's 7 3/8" I think. I was told anything smaller and you risk cavitation of the air thus making it worse. I have 170* t-stats. I have scoops on the body for the main rads, and no shutterstats. PO put expanded metal in their place.The trans has it's own cooler. I'm not willing to risk re-enginering the rear bulk head and the blower "tray" so I could fit larger rads in the original placement. I intend to have two more rads custom made to fit behind the lower doors. I will also put scoops on the doors with electric fans drawing inward into the engine compartment. Draw backs are: No access to the motor from the side any more, Affects changing the fuel filters, and the coolant filter on the right side, and affects the access to the air filter on the left. Not to mention anything you might have to do on the motor. When I put a mudflap across the rear under the bumper it destroyed the negative air pressure in the engine compartment and made things worse. Kept the oil on the toad to a minimum tho.
The lesson I've learned here is: Be happy with what you got. If you want to have a hot rod either buy a coach with the motor you want or be prepared to do a lot of enginering to accomadate the cooling needs and all of the problems that come with it.
Thanks again for all of the info you all have given,
Don & Sheila
Don: If you still have the original coach heat system, there was a post on the board from someone who made a duct to exhaust the hot air to the outside and used the central heat coil as an extra engine radiator.
Don -
If you add the additional radiators/electric fans to the side access doors, I'd like to suggest you mount them directly on the doors with sufficient hose to allow the doors to be opened, thereby maintaining engine compartment access.
How would you plumb these extras? Directly from engine and then to the OEM radiators, or from the OEM rads down thru these? With sufficient hose, it might be easy to try both ways, to see which is most effective. My initial thought would be from the engine to the extras first, then up to the OEMs. Sort of a "pre-cooler".
Gotta use BIG electric fan/shroud on these. Possibly off a V-8 powered front wheel drive GM or similar.
Might also try the GMC trick of the full width mudflap across the coach directly behind the rear axle, to increase that low pressure area. You've already found that the bumper-mounted one didn't work.
FWIW & HTH. . .
;)