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Thread: 6.5 Precups - Power -OR- Economy?

  1. #21
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    One benefit to having a fan clutch that does not disengage completely is that it provides airflow for the intercooler and AC condenser even when the engine temperature is under control...
    The Constitution needs to be re-read, not re-written!

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  2. #22
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    Shouldn't the exposed frontal area of our trucks handle that heat load at speed?? The only time that would not be so would be at low speed manuverings?
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  3. #23
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    Quote Originally Posted by JohnC
    One benefit to having a fan clutch that does not disengage completely is that it provides airflow for the intercooler and AC condenser even when the engine temperature is under control...
    That's probably a good point. With the A/C on it would probably have to lock up the fan or command it to be on very frequently to generate airflow in around town driving. With the A/C off the clutch might do great for mileage but might deliver poorer mileage with the AC on. Maybe if you wired the fan to the compressor or something so that when the compressor turned on, so would the fan. I don't think you would want the fan locked up the whole time the A/C is blowing.

    Art.
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  4. #24
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    Electrics you see used in production all come on with A/C. Some have two fans. One of the two fans may be dedicated to the A/C and the other fan could still be off.

    By the way almost all electric fans I have seen were on vehicles that did not have an option. Either due to motor alignment or positioning in the vehicle, or lack of room.

    Also I pretty much run my A/C all the time if needed. If it's hot, or if the windows are fogging up. In humid areas it's needed a lot.
    Last edited by 65TD; 02-08-2007 at 18:20.
    95 C1500, IC, 3" to 4" Exhaust, Turbo Master, Max E Torx.

  5. #25
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    Default Pre-cup results

    I am curious to know if anyone has some solid data on MPG numbers when running the 6.2 pre-cups in the 6.5TD. I too have spoken with several people saying that I should avoid using those pre-cups in a 6.5 due to power lost. However, most of these people are power junkies and think I should be shooting for 500+ hp. I would like when I rebuild the motor in my '94 suburban down the road... to install the earlier pre-cups and get that increase in mpg. the burb is used as a commuter, and for long trips to various whitewater rivers around the northwest and I have no need for tons of hp.
    Thanks in advance.
    '94 2500 suburban (first diesel), '97 cooling mods, new heads, 4" SS exhaust, towing chip, guages, new IP, LP, OPS, wastegate solenoid

  6. #26
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    Most 6.5 owners would not likely experience a difference in power, but they would see a difference in fuel economy. On the other hand if "Power" is the mission, the turbo cups would be the obvious choice.

    In 1991, Motor Trend magazine compared a brand new 6.5TD powered truck to a prior year 6.2L equipped with a Banks turbocharger. The Banks 6.2 outperformed the new 6.5 by a slight margin.

    Jim

  7. #27
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    Any idea what kind of MPG we are talking about here? Is it .5 MPG or 2MPG? Just curious.

    Art.
    Art Paltz
    1999 Suburban K2500 6.5TD (stock)
    2000 Undercover Dragster, 468 BBC, 7.74@173MPH, waiting on new 622 aluminum BBC to be finished.
    1992 Tube Chassis Camaro, 468 BBC, 8.54@157MPH (SOLD)
    1987 Buick Grand National, 11.8@114, pump gas (for sale)
    1969 Camaro SS/RS 396-350HP, stock restoration, it never leaves the garage...

  8. #28
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    Quote Originally Posted by TurboDiverArt View Post
    Any idea what kind of MPG we are talking about here? Is it .5 MPG or 2MPG? Just curious.

    Art.
    I too would like to know how much the precups will improve it. And a set of theromastiacally controlled daul electric fans should pick up what 3mpg over the stock fly swatter?
    Shane

  9. #29
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    The 6.2L and the 6.5TD longblocks are basically the same, with the exception of bore diameter and precups.

    Assuming 3.73 gears, a 6.2 powered truck can deliver low 20's for fuel economy. With the same gearing, a 6.5 equipped truck can produce high teens. There could be 5-mpg difference. Some or most of which is, I believe, attributable to the precups.

    GM once sold a 6.5L diesel engine named the "Fuel Miser". The only difference between that engine and a typical 6.5 is that the Miser used smaller port precups and just the rear cylinders received oil spray.

    Jim

  10. #30
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    which pre cups would be good for a mild to medium twin turbo intercooled 6.5 built for economy? Also what years did the 6.5s get roller cams?
    Shane
    Last edited by Chevrolet4x4s; 12-13-2007 at 21:37.

  11. #31
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    I heard from a VERY reputable source that the problem with using small port precups on a turbo motor is that the cup will get excessively hot and you will get rapid erosion of the port. I wonder what material the precups are made of. They are simply called "stainless steel", but that covers a wide range of alloys, none of which are the best for a precup IMO. HD IDI's usually use a Nimonic alloy (similar to Inconel)... is that what the cups in the 6.x are that are reffered to "stainless steel", or is it some cheaper alloy...?

  12. #32
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    Arrow

    Quote Originally Posted by Chevrolet4x4s View Post
    which pre cups would be good for a mild to medium twin turbo intercooled 6.5 built for economy? Also what years did the 6.5s get roller cams?
    Shane
    I'd suggest using 6.5 TD cups. The gain/risk with N/A cups won't wash.

    6.2/6.5 engines have always had rollers.
    1985 Blazer 6.2
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    dmaxmaverick@thedieselpage.com

  13. #33
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    Quote Originally Posted by DmaxMaverick View Post
    I'd suggest using 6.5 TD cups. The gain/risk with N/A cups won't wash.

    6.2/6.5 engines have always had rollers.
    Well I shouldnt have to pull the heads then.Glad to hear that its a roller cam.

    Also which years of 6.5s had the 18 to 1 pistons and is there a casting number on the engine that will tell you if it is the 18 to one engine....Its a late 95 or a 96 engine
    Thanks
    Shane

  14. #34
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    No factory 6.5 ever had 18:1 compression. 6.2's and early 6.5's had 21.3:1 compression. Later they dropped the compression to 20.3:1. I don't remember when the change was made though...

  15. #35
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    Quote Originally Posted by MaxPF View Post
    I heard from a VERY reputable source that the problem with using small port precups on a turbo motor is that the cup will get excessively hot and you will get rapid erosion of the port. I wonder what material the precups are made of. They are simply called "stainless steel", but that covers a wide range of alloys, none of which are the best for a precup IMO. HD IDI's usually use a Nimonic alloy (similar to Inconel)... is that what the cups in the 6.x are that are reffered to "stainless steel", or is it some cheaper alloy...?
    The cups are, according to GM, stainless-steel.

    I have a disassembled 6.2L engine in the shop that ran for 200,000 miles with a Banks turbo. The cups are no more worse for wear... Peninsular produced turbocharged marine 6.2L diesels from 1984 till 1991. There is no more reputable source than Pen, for info concerning turbocharged 6.2 precup life.

    Jim

  16. #36
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    Quote Originally Posted by MaxPF View Post
    No factory 6.5 ever had 18:1 compression. 6.2's and early 6.5's had 21.3:1 compression. Later they dropped the compression to 20.3:1. I don't remember when the change was made though...
    Aaaw shucks further proof not to take everything in a wiki to the bank
    http://en.wikipedia.org/wiki/Detroit_Diesel_V8_engine on the 20.3 to 1 would 10-14 max psi intercooled with close watch on egts be ok?
    Shane

  17. #37
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    Actually....... AM General/GEP currently builds 18:1 6.5's on an infrequent basis. They all go to the marine vendors.... The 18:1 6.5's that Peninsular, Marine Diesel, and other marine vendors offer are all factory built as 18:1 engines. GM never offered them in their trucks/subs though.

    Jim

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