muffler size/engine heat issues

[Stan]

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.

[skihor]

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

[JohnEd]

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

[DrivingMissLazy]

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

[RJ]

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. . .

[JackConrad]

    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

[Stan]

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.

[skihor]

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

[Stan]

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.

[RJ]

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. . .