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Author Topic: 8v71 adding a turbo  (Read 2515 times)
Purplewillie
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« on: January 12, 2013, 04:20:49 PM »

I am really enjoying all the info that everyone has posted on 8v71 and turbos. I have a 4905 gm with a 730 allison. I am curious as to how much power the 730 will take? 
Thanks Mark
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Mark & Char
1976 P8M4905a 8v71 v730
British Columbia Canada
bevans6
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« Reply #1 on: January 12, 2013, 04:33:05 PM »

Hey, Mark - welcome from the other coast of Canada, Nova Scotia.  Ask your questions and you will get answers from someone who knows!

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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1978 Lola T440 Formula Ford
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Purplewillie
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« Reply #2 on: January 12, 2013, 04:42:23 PM »

Hi Brian, Thanks for the welcome. I enjoyed reading about your turbo adventure!
Mark



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Mark & Char
1976 P8M4905a 8v71 v730
British Columbia Canada
Geoff
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« Reply #3 on: January 12, 2013, 04:46:57 PM »

According to the V730 manual, it will take 840 ft lbs of imput torque.

According to actual testing, it will take 1050 ft lbs of torque with a 350HP 6V92TA.  It will even take more from a 370HP 8V71TA.
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Geoff
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Purplewillie
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« Reply #4 on: January 12, 2013, 05:37:16 PM »

According to the V730 manual, it will take 840 ft lbs of imput torque.

According to actual testing, it will take 1050 ft lbs of torque with a 350HP 6V92TA.  It will even take more from a 370HP 8V71TA.
Thanks Geoff, that exactly the info I was looking for!
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Mark & Char
1976 P8M4905a 8v71 v730
British Columbia Canada
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« Reply #5 on: January 12, 2013, 10:49:48 PM »

Seems there also may be a practical useful idea of using a smart right foot.  If you use the extra power carefully, (pretend there is an egg between the sole of your foot and the gas pedal) you might be able to occasionally use MUCH MORE TORQUE.

If the convertor is locked up, then your major concern is the physical torque strain against the gears, clutches and tranny case.  Once in 2nd and 3rd gear, such physical strain is reduced.  Practically speaking, once up to about 45 miles per hour...

...maybe you can occasionally employ FULL POWER.  They also make gadgets that fit on your fuel rack that prohibit full fuel while in the first gear.  This also limits the torque the tranny must deal with.  Finally, the physical structure of the coach...

...must be able to absorb the added stress.  Might pay attention to the structure and mounts the engine hangs in.  In cruise mode going down the highway, the added torque can then just be used to keep the coach up to speed.  HB of CJ (old coot)
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TomC
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« Reply #6 on: January 12, 2013, 11:08:41 PM »

When I had my 8V-71 turbo'd and air to air intercooled, I had Don Fairchild install 7G75 injectors that put out 375hp and 1125lb/ft torque (on engine dyno). Also had the V730 rebuilt and the rebuilder beefed up the shifting modulator to give a stronger shift under full power. I typically don't floor it while accelerating-only use full power once in gear. I also have an auxiliary trans cooler with thermostatically controlled 12v fan on the inlet side to the normal shell trans cooler. This takes alot of initial heat out of the trans fluid before reaching the shell cooler also keeping the radiator from overheating. The V730 has worked flawlessly the whole time with no complaints from me.
I seem to remember one guy that was running 90 injectors in his 8V-71 that would give him 450hp and 1350lb/ft torque-but at 30,000mi, he was already seeing signs of his engine getting worn out-higher oil consumption, and smoking. But-his V730 still took it. Keep in mind that the V730 is a HT740 without 1st gear. The weak spot is the quill shaft between the torque converter and the bevel gears-that could snap. But, again with turbo engines, the power turns on relatively slowly compared to say a 12V-71 non turbo. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #7 on: January 13, 2013, 04:46:33 PM »

Excellent answers and thank you.  Could specifically the quill shaft be beefed up?  This would be after the heat problems are addressed.  Curious, how much $money$ would be involved having a custom quill shaft fabricated that is much stronger than the OEM part due to materials, heat treat, inspection; etc..?  How much strength could be gained?  Reasons are that the 730 works sooss well and might be able to work even better against more power.  HB of CJ (power crazy old coot) Smiley
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Purplewillie
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« Reply #8 on: January 13, 2013, 05:26:49 PM »

Thanks Tom, excellent info! Now I'm wondering if my wallet will hold up! I'm interested in 8v71turbo mainly for the mountain roads around here, it would be nice but not required, as greyhound and charters travelled these roads for years with 8v71 and no turbo.
I see a 8v71T on the 'bay right now. 375 hp. Runs the wrong direction for me,but do I need a complete motor? Does it have the blower I need? Turbo I need? What parts are required to turbo mine?  Pistons maybe, rings, different blower,turbo,air to air, bigger injectors,exhaust manifolds?
I'm going to drive it as is for this summer and if we are in a rush I do own a 600 horse LS7 mid year vette that we could use!
Thanks again



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Mark & Char
1976 P8M4905a 8v71 v730
British Columbia Canada
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« Reply #9 on: January 13, 2013, 05:31:08 PM »

TomC,  I ran large injectors in a NA 8V-71,  A timed and 1.460 pin, melted the top pf piston, lost compression etc.  Not real bright but a good learning experience, knew it was way too advanced, but being akid, I just had to try it. The engine ran super clean, crisp and great power right up till the tops of the pistons melted, stuck comp rings.
Oh Joy, When eventualy moved to the 12V, ran more reasonable injectors and timing.
Then on the -92, ran different injectors playing, with the 120 injectors, and the 6V-92 turbo, blew off the alumium port covers, made them out of 3/8 steel plate. Last was the 9200 injectors, still very spunky 580-600 range
Dave M
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chessie4905
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« Reply #10 on: January 13, 2013, 05:34:21 PM »

  They used that v730 for years in city buses; 8-71, 6-v92 turbo. Constant full power starts and run all day long with max load, for thousands of miles summer and winter with few issues. Don't worry about it or the quill holding up.
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GMC h8h 649#028
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« Reply #11 on: January 13, 2013, 07:01:01 PM »



  Mark,

Like you I also climb the seven hills of hell [Hwy 3 ] going and returning to Alberta a few times each year. I tow a 4200# liberty.
I was concerned with the 28 mph hills and more power.
Under 70 kph ,my flashers work great.

Last year I installed jakes and N70 injectors[$2500] and I had most parts.
Love the jakes, use brakes for backup only.

As the shop was already working on the top of the heads, I inquired about putting a turbo on my 8V71.
I inquired... and still have a 8V71N/jakes.
Too,Too, many unknowns..pistons, big gear blower, cooling, etc, etc.
To find out if the block has proper holes for blower is about a $1000.
take down.  All toll, about another $3000. to put on a blower.

My motor runs like a singer sewing machine now and it shall continue to do so without a blower. Kind of like if it ain't broke don't "F" with it.

I am retired and fully expect to reach the top of every hill God puts in front of me and my "Bus".

I also had a Chev LS7 motor, but I had it in a 18 foot ski boat.
RCMP radared me at  152 MPH on a local lake, and suggested it was too fast for general public use. Bought fuel from Calgary airport to get the 150 octane needed. Got 24.5 hours out of motor before first rebuild.
Oh ,to have that power in a bus.
Regars  Bob










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84  mci 9   8v71n N70 Jakes 740 auto   Oliver, BC
Purplewillie
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« Reply #12 on: January 13, 2013, 08:00:10 PM »

Hi Bob, my 8v71 also runs awesomely .110,000 miles ,fresh top end, and jakes. No Klingons (toad) so I think I'm going be happy just the way it is.....for now!



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Mark & Char
1976 P8M4905a 8v71 v730
British Columbia Canada
TomC
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« Reply #13 on: January 13, 2013, 09:15:14 PM »

Since my bus was a transit, the 8V-71 had the tight fitting rings (best for turboing) and also had the two piece iron top pistons that won't melt like the aluminum pistons could. I also had a custom air to air intercooler made to keep the intake air cool and dense. Hence the only modification that was done to the engine to make it a turbo engine was the bigger injectors, adding the turbo, fuel modulator and bypass valve on the blower. Because I still have the 18.7 to one pistons, I am only running the 75 injectors and a Series 60 turbo keeping the boost down to around 15psi. Not much done to the engine, but all accessories had to be enlarged. Bigger radiator (with misters), bigger air cleaner, turbo muffler (same 5" system), auxiliary trans cooler, two rear vents in the engine door, extra vent on the intake stack. REALLY love the way it runs and flattens out the hills. My Grape Vine 6% grade climbing went from 28mph to an easy 45mph. BUT-since the engine still has the bigger liner ports, I'm not getting the best fuel mileage I could get. I get 5-6mpg with just the bus and can get into the 4's when pulling my car and running the generator for A/C. Since it performs well and doesn't smoke at altitude, I don't really care. Since turboing the engine there are a few hills I've come across (18% grades in the Sierra Nevadas) that I know the non turbo engine would have stalled out on-really messing things up. The short coming of the V730 is that it only has 3 spds-like a HT740 starting in second. And reverse is like second gear (I've gone 40mph in reverse!).  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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