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Author Topic: How much to increase HP on 8V71  (Read 5367 times)
Stolaas
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« on: September 23, 2010, 12:11:22 AM »

So I got everything ready to and head out, just to find that I could hardly make it up the hill near my home.  I've seen some places (here included) about new injectors increasing HP just havn't seen a price tag attached. What kind of injectors would you go for and what would be the cost for them plus installation?

Without a stronger engine we just cant keep it.
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HighTechRedneck
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« Reply #1 on: September 23, 2010, 04:45:56 AM »

Seems like an 8V71 should have more power than that.  Might benefit from getting the rack run by a good 2-stroke mechanic.  Huntsville isn't far from Chattanooga.  Bring it up here to the Choo Choo Express garage.  Joel is very talented with 2-stroke Detroits and at $55/hour, the hourly shop rate is half that of the big DD shops.  While tuning it up they could also make other recommendations for increased performance.
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luvrbus
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« Reply #2 on: September 23, 2010, 05:07:02 AM »

When a 8v71 acts that way first thing to check is the engine shut down they have a habit of sticking and don't have power but it will start and run fine

good luck
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« Reply #3 on: September 23, 2010, 07:03:11 AM »

Check the fuel filters also. Crapp blocks fuel!! Don't ask me how I know that !! LOL
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Stolaas
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« Reply #4 on: September 23, 2010, 07:18:44 AM »

Well the rest of the story is I was pulling a Dodge 2500 diesel which weighs in around 6500lbs. I was barely crawling (20-25 mph) in sencond gear and didnt think i was going to make it to the top, so once we did, we unhooked and drove the two vehilces back home  Huh

When I climb the hill without a tow vehicle it is slow but average 30-35mph On flat its fine with easy 60-65 mph.

Has anyone put new injectors in theirs?

I was hoping I wouldn't have to buy a different tow vehicle and it would still have to weigh about 4500lbs because I have a family of five  Grin
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RickB
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« Reply #5 on: September 23, 2010, 07:27:19 AM »

20-25 is realistic with a good running NA 8V71. That's just they way the cookie crumbles at altitude with a non-turbo motor.

Sorry to be the bearer of bad news. I am planning on turboing my 8V71 over the winter and that will make the mountains more beareable but I'll still be doing 30-35 up those hills. If you want to run up the hills you're gonna need a series 60 or a Cummins ISM or a big Cat to accomplish that. if I lived in the mountains i would not own a bus without a 4 stroke turbocharged motor.

A non turbo motor loses 4% of it's power every 1000 ft above sea level you climb.

That means at Eisenhower pass 11,100 ft you or I are at around 130-150 hp. Kinda tough moving 32k lbs up a hill in a hurry.

Bigger injectors, having the rack run, installing a turbo and checking the earlier post's for HP robbing issues will help but 20-25 is the norm for our buses. My motor runs great and I was in 1rst gear at 19 mph up a pass in Montana this summer.

I feel your pain.

Rick
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Dreamscape
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« Reply #6 on: September 23, 2010, 07:33:23 AM »

When we have to climb long grades, I just punch 'er down to a lower gear, throttle to the floor at the governor and get to the top and enjoy the ride. With the 8v71 it's not the quickest, but it will get you there.

The speeds you mentioned sound about right, you just have to adjust your thinking. You are not driving a sports car, it's a heavy pile of metal and fabric. Grin Of course pulling an additional 6500 lbs add to the mix.

We don't climb that many hills so it's of no concern to me. It's not how fast you get to the top, it's that you do.

If you want more power you can spend the bucks and also add a bunch of heat.

If your shutdown is sticking, you will be blowing lots of black smoke. I do know how that works, it has happened to us. Only in our case the flapper was completely closed. If you listen to Clifford's adivce, you will learn from the best!

Like Mike suggested, have a good two stroke guy run the rack then see how she runs. Doing that first may be the ticket. Then determine from there what to do.

Paul
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kyle4501
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« Reply #7 on: September 23, 2010, 07:37:44 AM »

You might need a different mindset.
Your total rig is probably in excess of 40,000 pounds. It ain't gonna move like a car or your truck.

If you want it to move like a car or your truck, you're gonna have to get the HP to weight ratio the same - which ain't gonna happen with an 8V71 (well not for very long anyways.  Wink )

Tuning your engine is a good idea, but it isn't likely to increase your power enough to take hills at the posted speed limit.

Having the power to flatten hills is usually very expensive & requires a re power -The cost is very subjective & depends on everything.
I got a quote for having my transmission changed to an automatic - over $10,000 in parts alone.
I've seen here where someone spent over $30,000 to add a turbo to his 8V71 in a GM transit bus. & he still doesn't have the power to do a speed limit ride up all hills.

My suggestion:
Have the engine looked over by a good 2-stroke mechanic & follow his recommendations.
Get a comfortable driver's seat & good mirrors.
Now, you can sit back & really enjoy the ride while watching the scenery.
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RJ
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« Reply #8 on: September 23, 2010, 08:46:16 AM »

Stolaas -

"Without a stronger engine we just cant keep it."

That's not true.  What you're describing is perfectly normal for a stock, non-turbo, 8V71 in an MC-9.

Have you weighed your rig, completely ready to roll with the toad attached?  Until you know what weight you're dealing with, all else is pure speculation.

So let's speculate!

As an example, we'll use my 2007 Toyota Tacoma Double Cab Long Bed pick-up.  It has the 4.0L V6, which puts out 236 hp.  My truck weighs 5644 with a full tank of fuel and me in it.  That works out to 23.91 lbs per hp.   I'm not sure what a revenue-service (seated) MC-9 with a full tank of fuel and driver weighs, but IIRC, the GVW of the coach is 36,600, so I'll use that.  Based on the stock 275 hp 8V71, that works out to 133.09 lbs/hp.

Using the above guesstimates, you'd need a 1,500 hp engine in the back of your bus to equal the performance of my "non-hot-rod" Tacoma.

I can also tell you, from experience, that on the 250 mile run from Fresno to Disneyland, over the 6% Grapevine on I-5, the difference in travel time between a stock 275 hp 8V71-powered MC-9 and a stock, 400 hp 8V92TA-powered MCI 102A3 is all of five minutes.  That's right, only five minutes.  Oh, and for the round trip of 500 miles, the faster bus burned an additional 25 gallons of fuel.  That's $75 to save 10 minutes.

Crawl in the engine compartment and take off a valve cover.  On the side of the injectors, you'll see a round medallion that will have a letter-number combination on it.  My guess is N-60, which is stock.   For best results, when you go to larger injectors, you need to advance the timing.  To do so requires pulling the engine to get to the camshaft gears on the transmission end.  Do you want to go to all the time and expense involved so you can go up the hill at 30 mph rather than 25?

I've said it before:  These buses, which give us so much enjoyment in RV configuration, are, and will continue to be, the Tortoise of Aesop's Fable fame. 

Understanding that will give you years of enjoyment.  Thinking it's the Hare will bring you nothing but frustration.

FWIW & HTH. . .

 Wink
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RJ Long
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« Reply #9 on: September 23, 2010, 08:50:16 AM »

  An MC9 conversion pulling a 6500 pound truck? Even doubling the power to 600 HP your still going to go slow up a hill. Unless you have more gears. Guess it depends how fat your wallet is,and how fast you want to go up a hill. More power, more heat, more loading on critical driveline components. From reading it appears the 9's are about borderline for cooling in a stock configuration to begin with. More power exceeds the design of all the systems. More power can exceed the design of the transmission, driveshaft, ring and pinion, and the axle shafts. Its a vicous circle.  But at least you made it up the hill. I have a hill I dont know I can climb with the Bus I want to buy.

  Now insert scene of people throwing luggage and gear out the door of an airplane that just lost an engine and is losing altitude, while the pilot is dumping fuel.... There is no free lunch. You either have to lose weight, increase power, or a little of both.
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Sam 4106
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« Reply #10 on: September 23, 2010, 08:56:43 AM »

I agree with getting a tune up before going to the expense of different injectors. After the tune up on the 8V71NA engine in the GM4106 we had you wouldn't have thought it was the same engine. A tune up will be a small investment compared to different injectors. I also agree that you may have to change your expectations. If you have never driven a bus, or other large vehicle before, you probably did not know how your bus would perform. Try to look at the situation from the perspective of how few minutes you would save going up that hill compared to the cost of changing injectors or getting a lighter tow vehicle, if cost is a consideration.
Good luck, Sam MC8
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robertglines1
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« Reply #11 on: September 23, 2010, 10:08:33 AM »

I run or ran I 65 Thur your area several times a year..with the MCI 8 /8v71  pulling a jeep lots of the hills pulled me down to 50 to 55  didn't know Alabama was so hilly..I found out I ran the hills about as fast as a loaded semi in the truck lane..Mount Eagle was a 35mph climb..Now with the 8v92 in the 89 prevost it drops about 5 to seven mph in the hills on 65  pulling a Chev hhr....fuel went from 6.8 mpg to 5mpg...now doing 60 series and Eaton 10Sp auto shift;hoping for lots of improvement...get it checked out.and maybe look at a mini van or hhr to pull.really don't think family will mind a little extra time on the trip.I kept rpm 1800 and above when climbing hills..torque curve peaks about there. Does it blow black smoke when climbing?
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« Reply #12 on: September 23, 2010, 02:43:42 PM »

If there is no black smoke at full load and near max rpm, change the fuel filters.

If you have black smoke make sure your intake is clear all the way to the engine.  Air filters clean, no bird nests, mouse nests, ect.

If the intake is clear and you are keeping the rpms up and blowing some black smoke, bigger injectors probably won't help but a tuneup might.

Good luck
Don 4107

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Don 4107 Eastern Washington
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Stolaas
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« Reply #13 on: September 23, 2010, 05:41:34 PM »

It was just very disappointing. I just finished the conversion and now this. I am going to change the fuel filter and hope that helps. The PO hadn't ran it for four years while he did some of the work but it is a new engine so it may be dirty fuel and has been stired up since me putting more in. The grade I was climbing was no 6%,  it was montesano mountain if any of you all have come through Huntsville.

I am used to pulling 5th wheels so at 20k lbs I'm at half but still at that weight I could pull pretty dang fast.

After I unhooked it it did seem to run the slower than the first time I drove it while coming home.

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kyle4501
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« Reply #14 on: September 23, 2010, 06:42:48 PM »

Yep,
A fresh fuel & a tune up will likely improve your performance noticeably.
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