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Author Topic: Engine set-up advise  (Read 9190 times)
VanTare
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« Reply #15 on: February 08, 2009, 07:54:05 AM »

good for you JC I have a 1940 Ford coupe with the origanal 60 hp v8 and people are always telling me to install a small block Chevy and do away the 60 hp that is not going to happen with me , keep your history not enough left nowdays   

David
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Ed Hackenbruch
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« Reply #16 on: February 08, 2009, 06:11:26 PM »

Kinda ruins a Ford for me when they stick a chevy engine in it.....makes me want to buy a 57 Corvette and put a 351 Windsor in it and see what kind of reaction i get. Grin
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1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA
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« Reply #17 on: February 10, 2009, 02:28:37 PM »

Right on ED!
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #18 on: February 10, 2009, 02:31:38 PM »

As to horsepower difference between natural and turbocharged, take an 8V-71N with N65 injectors, and you'll have 304hp with 800lb/ft torque (net not sae horsepower).  Exchange that for a 8V-71TA with the same 65 injectors and you'll have 325hp and 975lb/ft torque.  Always more fuel efficient with turbocharging and intercooling.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #19 on: February 10, 2009, 02:53:15 PM »

Tom,

Not fair!  The HP is a function of the rate at which duel is consumed and by keeping the injectors in your example at N65 the HP remains sorta constant.....304 to 325.  That wouldn't inspire many to make the investment in a turbo.  Doesn't that 8V71 march right up to 400HP with the proper injectors...or was it more?   Or are you talking about the "smoke" turbo alone?

John
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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
“We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”
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lostagain
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« Reply #20 on: February 10, 2009, 05:28:55 PM »

I don't know about the numbers, but the difference in power after I installed the turbo 2 years ago is VERY noticeable. I gained 1 gear going uphill (5 speed manual). I also feel a definite increase in torque lower down into mid  rpm range. And no more smoke, except at start up, untill the turbo spools up. I am now looking forward to the results of my overhaul: x head pistons, rebuilt head with N 75 injectors, new radiator with dimpled tubes and serpentine fins, new rod and crank bearings, standard timing. Oh boy! I might have to paint it before I slide it back in! I am still looking at putting in an intercooler. It will be a chalenge finding a spot for it and plumbing it... I just have to do some more head scratching. I was thinking an intercooler is also good protection for the engine in case of the turbo disintegrating: the debris would be caught in the intercooler before it enters the blower and engine.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
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« Reply #21 on: February 10, 2009, 06:30:11 PM »

JC,

Part of the significant gain in HP from a turbo with the same cubic inches came from the reduced compression ratio.  You have a limit on the compression you can handle and the turbo increase the "effective" compression ratio.  The result is that with a simple turbo inst you can't use much boost and with boost comes power.  I think if you build a "turbo" motor correctly, you use pistons that yield lower static CR.  I think turboed diesels are harder to start for that reason but the CR is still so high it gets them lit without problem until they get worn out.

You mentioned the "X" pistons.  Are those 71 turbo items?  I envy you the adventure.  Have fun.

John
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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
“We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”
—Pla
lostagain
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« Reply #22 on: February 11, 2009, 07:28:04 AM »

I don't really understand why lower compression is better for a turbo. Can somebody explain.

My engine, like most older 2 stroke DD, have the one piece "trunk" pistons. I am installing the 2 piece "cross-head" , lower compression pistons. The crown is more resilient to heat, and the skirt is seperate and cools better. "The piston skirt, being seperate, is free from vertical load distortions; thermal distortion is also reduced as the piston crown expands." (From Da Book). Xhead pistons are the standard now for turgo charged engines.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
TomC
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« Reply #23 on: February 11, 2009, 07:49:52 AM »

I have the two piece higher compression non turbo pistons (18.7:1).  This is why we decided to keep the boost to only 15psi and use 9G75 injectors for 375hp & 1125lb/ft torque.  To slam more air into the combustion chamber, the compression ratio is lowered on a turbo engine to 17:1.  Still high enough for starting in cold, but enough to allow over 20psi of boost.  On some military engines, Detroit lowered it to 15:1, which Don Fairchild had an engine like that.  It smoked starting on a 70 degree day for quite awhile.
To get 400hp and 1200lb/ft torque, 80 injectors are needed (this is the highest stock power output that Detroit had for the on highway 8V-71TA).  90's can be used to boost up to 450hp and 1350lb/ft torque, but then you have an engine that will probably only last about 200,000 miles.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
lostagain
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« Reply #24 on: February 11, 2009, 08:46:02 AM »

I haven't got the new parts yet, so I'm still open to suggestions. The most I have seen from my turbo is 12 psi of boost. Should I get 18.7 to 1, or the 17 to 1 cross-heads? The head is being rebuilt and it will have N75 injectors.

You guys have to realize that this is my first time rebuilding any engine. I have been a shade tree half mechanic all my life, but I am really stretching my abilities this time... Although I like to learn and I'm loving every minute of this. I am going by the DD service manual, which is very good. So the wrenching is not really difficult. It takes some care and patience to do it right. It is taking more time than I thought, and I only average 2 or 3 hours a day, but I am aiming to be back together and running by spring. (April, early May). I am getting advise from my supplier Alberta Engine in Calgary. And I need to pick your brains here on the board, to figure out what is best as far as what parts would be the right parts. I really appreciate any and all sugestions.

Today, I am hoping to have the clutch and flywheel housing off, to get at the timing gears to move to standard timing, and to replace the crank shaft oil seal. I will take a picture or two then,  because that is as far as I will go dismantling. It will be a big moment, because I will start the rebuilding process after that.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
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« Reply #25 on: February 11, 2009, 09:58:50 AM »

JC,

I admire your enthusiasm.  I think you need more help and hand holding than you "seem" to be getting.  Go with the "turbo" piston which has the lower compression ratio.  It will give you much more HP even if you don't install the correct turbo.  You should have more than 25 pounds of pressure out of the turbo....don't quote me....verify.  The 15 psi turbo you have is a smoke turbo or might have the waste gate set for 15 psi and be the right item after all....verify.

S. Oregon diesel, Dave, showed me a 8V71 that had lost the cam timing gear.  Was overhauled a few months prior by another shop in another state.  As Dave told me "it has a few bent valves.  Shouldn't be too hard to FIX, right?"  and we laughed.  The owner was not present.  So many things to verify.  Got mics?  Dial indicators?  And I wish not to discourage you.

About that compression ratio:  If you have two engines and one has more displacement than the other, the bigger wins...right?  The reason is because you can get more fuel and air into the larger.  Now, if you psi in the intake is 25 and the displacement is 100 ci the volume of gas inhaled will be some quantity over 100 ci due to pressure.  Now, if you reduce the CR you are effectively increasing the volume of the cylinder at Bottom Dead Center , BDC, cause to reduce the CR you had to move the crown down so when it went to TDC there was a larger volume and less compression...right?  That larger volume associated with lower CR is filled up with more air than the higher CR.  In short, it acts like a larger CI engine.  5 psi is better than N and 20 is better than 5 and 25 is better than 20.  You are stuffing more air.....you can also stuff more air into a bigger hole.

From what Tom says he seems to have normal compression 2 piece pistons and 15 psi boost.  Lower compression pistons with that same 15 psi would seem to be able to get him more power and certainly lower CR with 25 psi would be bigger still.  Now the question is "why did so savvy a guy opt for this lower power configuration....especially when he sunk $10+ into the overhaul".  Enquiring minds and all that....I pondered this long ago when I first heard the story. 

Don't think I have the official answers on this....I don't.  My only objective is to inspire you to asking the board all the right questions as far as I can.  I think I will get something out of this as well so it ain't charity.  Risky behavior, though, on my part.

John
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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
“We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”
—Pla
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« Reply #26 on: February 11, 2009, 11:55:13 AM »

John- I overhauled my engine in the first year after the conversion was done-in 2001.  Basically at that time the block was bored .010 over so that I had to replace the liners to fit the .010 block overbore (to correct a shabby liner fitting by the PO).  The pistons were retained and the engine was built to what it was before- a brown tag N65 non turbo engine.
Fast forward now to 2006 when I had Don Fairchild turbo charge and air to air intercool the engine.  Since it was still fresh, I didn't want to spend the extra money on a new set of pistons, and was more interested in high altitude power without the smoke.  The turbo was added, along with air to air intercooler, bypass blower valve, fuel modulator, bigger injectors (9G75), along with bigger radiator, air cleaner, muffler, and auxiliary transmission cooler.
As to turbocharging an engine without injector increase, remember that turbocharging will keep the power the same on an engine up to 10,000ft elevation, whereas a non turbocharged engine will loose about 5% power per 1,000ft of elevation.  So at sea level, both a turbocharged and non turbocharged engine with the same injectors will have about the same power.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #27 on: February 11, 2009, 01:27:28 PM »

John, do I understand that a low comp. piston is shorter from wrist pin to top of crown? So there is more volume of air both at BDC and TDC. I didn't know that. This is great, thank you. Maybe I missed it in Da Book. I'll have to look again.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
VanTare
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« Reply #28 on: February 11, 2009, 01:51:15 PM »

Lostagain diesel engine compression come from the depth of the bowl on a piston unless the 2 strokes are totally different the deeper the bowl the higher the compression works this way on Cat,Cummins and the 60 series.They make gauges to check for the depth   


David
« Last Edit: February 11, 2009, 02:09:59 PM by VanTare » Logged
pvcces
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« Reply #29 on: February 11, 2009, 08:44:24 PM »

Lostagain, I don't think you can get your top fuel economy with the lower compression ratio. And there are plenty of people around who do not like taking an ether can to their recent rebuild where they have lowered the compression ratio.

I know of cases that the owners said that they couldn't start their turboed two strokes below 40 degrees without ether. And the higher the elevation, the sooner you have to use ether.

For me, I would want the economy and easy starting as much as the additional horsepower. So, I would look for the best solution that I could get with the higher compression ratio.

Good luck with your rebuild.

Tom Caffrey
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Tom Caffrey PD4106-2576
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