8V71 turbo specs

[windtrader]

A bus I am considering is a 4107 with a 8V71T motor. I need to get more details about this specific motor and the history of how it came to be in this coach. Research indicates there are various configurations that affect the power rating. See below

Common sense tells me if the turbo came with the coach from the factory than the supporting systems are engineered to meet the output of the motor. If it is a repower it might have cooling problems if the radiator was not upgraded. The TA indicates the block may be slightly tougher to handle the extra power. If the motor was a standard 8v71N with the turbo added later than it may not be durable as it should be. What do I need to ask to extract the specifics of this motor/coach combo? thanks

8v71T   308hp with n65  injectors   865 lbs torque 
            335hp   "    n70     "           920      "           
            350hp   "    n75     "           965      "         

8v71TA 370hp with 7c75 injectors 1064 lbs torque 
8v71TT 305hp   "     n75     "         1038      " 

8V71TA 400hp with 7G80 injectors 1200lb/ft torque
8V71T? 375hp with 9G75 injectors  1125lb/ft torque

[chessie4905]

If you read the serial number off the engine, it will indicate it's original configuration. Unless you were interested in having the after cooler  in the cylinder block, I wouldn't worry about block strength. Anything over 65 injectors is going to make overheating a issue you'll have to be careful of on long hills and really hot weather, unless the radiator has been upgraded/ mister system added. Pull the rear valve cover to red the injector tag number. Easy to remove; two knobs or bolts. If I was considering this coach, I'd pull an oil sample on it and have it checked, unless someone just changed it. I'd be interested in pictures of the engine layout with respect to turbo mounting and associated exhaust/intake plumbing, as I have been considering turboing mine.

[bevans6]

You can tell if it is aftercooled (TA spec) by looking to see if there is a coolant hose coming out of the middle of the valley between the cylinder heads (just behind the fuel pump) to the right hand (facing out on a transverse engine) thermostat housing.  The TA cooler is on the floor of the blower valley, roof of the airbox, the blower forces the air through cooler.  As far as I know the 4107 was over in 1969, and wouldn't have had a turbo engine stock (8V-71T came out in the 1970's, I seem to recall), so what you have is almost certainly a re-fit.  If it's a refit then someone could have turbo'd the stock engine, or fitted a turbo engine.  The main difference is the compression ratio, the turbo engine has a 17:1 compression ratio while the N engine is 18.7:1.  Someone could have turbo'd an Natural engine and left the compression at 18.7, turbo'd an N engine core block and changed the pistons, etc.  It being a left hand rotation, I don't know if any factory turbo automotive engines were ever produced, but there are lots of RHR turbo engines around.  a 4107 with a 350 HP turbo engine would be a real sports-car!

Just below the serial number of the engine (back of the block, towards the rear, below the exhaust manifold, so you can't see it easily on a transverse engine) is an engine type code.  Yours will be a 708X-4YZZ.  The 7 means V71 series, the 08 means 8 cylinders, the X is a vehicle type designation, the 4 means left hand rotation, the Y is a design variation.  In this position, 0 means Natural, 1 means 2 valves, 2 means 4 valves, 3 means turbo, 4 means turbo aftercooled, 5 means custom spec., 6,7 and 9 mean California or constant HP spec.  ZZ is a specific model number that might mean something or not.  There are some detail differences between the N block and a TA block (mostly the hole for the coolant hose to come out of the block to the thermostat housing) but I'm not aware of any strength differences.  Lots of non-TA engines were built with TA blocks and the hole for the hose just blocked off.  Mine is like that (I have a factory turbo 8V71 NATO engine)

Brian

[windtrader]

Thanks busnut as always. I'll report back what's up.

Sent from my SM-N910V using Tapatalk

[chessie4905]

If it is a ta
block without intercooler installed, it will have a 2 inch (approx) hole plug in the valley between the heads. Personally, I wouldn't want the intercooler in the block...expensive, another place for potential coolant leaks, and that heat from compressor air from turbo just adds more heat to cooling system. Add engine oil cooler and, if equipped, auto trans oil cooler, you re asking a lot for the radiator that is in that coach.
If you purchase this coach, definitely add a good mister system if it doesn't already have one. They are relatively inexpensive to make.

[eagle19952]

or it could be a low boost turbo contraption with the NA pistons still there...some awful abortions have been accomplished...
the serial# config might reveal the truth...
and it might not...

[luvrbus]

Your torque and hp numbers mean very little if you don't know how the engine is configured injectors alone are just another piece in the puzzle 

[TomC]

I converted my 8V-71N to a turbo. Don Fairchild first looked at the piston rings and determined they were the tight fit rings-as compared to the looser rings that truck engines run. We kept the 18.7 to 1 pistons that were two piece (only difference between turbo and NA two piece pistons is the deck height). I added an air to air intercooler in front of the radiator (luckily had the room). But also had to increase radiator and also add misters. Increased air cleaner from 6" to 7" hose, added auxiliary transmission cooler with thermostatically controlled 12v fan, changed stuffed up muffler to turbo muffler, added by pass valve to blower, added fuel modulator. Was extensive, not cheap, but the performance is truly different. My fuel mileage is the same-mainly because we didn't change the cylinder liners or cam timing. But comparing the N65 injectors at 300hp @ 800lb/ft torque to the now 7G75 injectors at 375hp @ 1125lb/ft torque, you can see the difference in hill climbing with the torque increase. Good Luck, TomC

[windtrader]

Thanks Tom, I knew you'd comment. Don F and you reviewed made the modifications to do this upgrade properly, ensuring long term reliability. It seems unlikely the same care was done with the upgrade on one bus under review.

Update: After speaking to the previous owner who knew more about this specific coach, it seems there is no verifiable documentation on the motor, period. It is a turbo but it is a repower, so the related systems are not engineered and designed for the higher power motor except a larger radiator. He stated the bus does well going up hill and you really need to watch the temps.

The pro on this one is it can trade hands at a price on the low end of the market value. But the discount is reflected in the risks on this one. Before I nix it for good, I'll touch base with Fairchild to see if there are other checks to assess the motor condition, other than it don't smoke and it don't clink or clank.

[windtrader]

New twist to thread. Variations on the 8v71N using different injectors.

Injector size is directly proportional to the horsepower and torque the engine produces.

Researching how much one can improve performance from natural 8v71 using different injectors.
What does the busnuts say?

N55- 260hp and 680lb/ft
N60- 280hp and 740lb/ft
N65- 304hp and 800lb/ft
N70- 320hp (or 318hp if you prefer) and 860lb/ft

7G65 - Uses a different metering system, more accurate delivery, atomizes the fuel better,has better spray pattern,more adjustable ability and a higher pop pressure makes for cleaner burning  better injector than the N series

A timing
N65 - Involves pulling the rear cover off (removing the trans from the engine).  
N70 - Increase to 318hp and 860lb/ft torque.

[luvrbus]

You can use 7E65 injectors without A timing a 8v71N/A, 304hp with 818 ft lbs of torque @2100 rpm.A timing a bus engine is a waste of both time and money unless you have a 10 speed Roadranger transmission IMO

[Utahclaimjumper]

 The 4107 was still produced in 1975.>>>Dan

[wildbob24]

The 4107 was still produced in 1975.>>>Dan

Dan,

According to the GM production lists, the last 4107 was delivered in June, 1969. The 4108 was introduced in 1970 and produced until 1978.

Bob

[luvrbus]

What is the difference between the PD-4108 and the P8M-4108A I have a buddy that owns a P8M-4108 A

[Geoff]

New twist to thread. Variations on the 8v71N using different injectors.

Injector size is directly proportional to the horsepower and torque the engine produces.

Researching how much one can improve performance from natural 8v71 using different injectors.
What does the busnuts say?

N55- 260hp and 680lb/ft
N60- 280hp and 740lb/ft
N65- 304hp and 800lb/ft
N70- 320hp (or 318hp if you prefer) and 860lb/ft

7G65 - Uses a different metering system, more accurate delivery, atomizes the fuel better,has better spray pattern,more adjustable ability and a higher pop pressure makes for cleaner burning  better injector than the N series

A timing
N65 - Involves pulling the rear cover off (removing the trans from the engine).  
N70 - Increase to 318hp and 860lb/ft torque.

Once you get higher than an N60 injectors in an original 8V71NA with standard timing, you have to change the timing to A (advanced) timing to run N65 injectors with the 304 HP.  Not a good idea in the older engines with large oval air box covers that didn't cool the lower part of clyinders which resulted in cracked bores. (dry blocks vs. wet blocks in Detroit terminology).  

Without changing the timing, the engines​ would smoke under load and acceleration. The E injectors were used with the 92 Series and as far as I know were used in CARB (CA EPA) 92 engines (the G injectors we're Federal).  I know Don Fairchild did a lot of experiments with Detroit engines and has formulas with mixing this and that for increased horsepower, but I haven't heard of improved fuel mileage with his expensive changes and additions.

--Geoff