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Cost to power gain ratio.... 6.5L vs 4BT vs 6BT

Discussion in 'The Garage' started by PhoenixZorn, Oct 11, 2006.

  1. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Very simply, which engine do you guys think is the most cost effective to build to "max" power and torque? Now that I own a 6.5L, I have my own opinion on the matter, that for less actual money, you can have the same power in a 6.5L that you can get out of an absolutely blown 4BT...

    Max power numbers in trucks are close to 300hp and 500ft-lbs for both the 6.5L and 4BT engines, possibly a tad more if you figured out a new mod for the 6.5L, but that seems to be the "safe" max...


    Max power numbers for the 6BT is obviously higher, but in my opinion should cost more in the long run, especially if everything you do to it is mechanical in nature... My former boss is currently running around 340hp and 700ft-lbs in his 97 Dodge Dually... and I met a Diesel Tuner Dyno guy last year at TDI Fest who's 02 Dodge Dually was puting down a tremendous 1200ft-lbs of torque (sorry, don't remember his hp.) The 97 was all mechanical mods, and the 02 is mechanical mods plus computer mods.

    The things I know...
    • a 300hp 6.5L custom built engine costs about $10,000 from Peninsular Diesel, and that to build the same motor in your truck it would cost about $4000-6000. A new "Stock" 6.5L engine runs about $5000 in case you needed to start from scratch, and comes with 195hp/???ft-lbs of torque for the 97+ model. That's a good start.
    • a new 4BT costs somewhere in the neighborhood of $4000... it starts out with 125hp/250ft-lbs of torque... enough to move our trucks, but it NEEDS mods to be effective. Incidentals include tranny adaptors, fabrication mods, fitment... Add in all the mechanical mods my ex-boss has on his truck, about $3000, and you are already at $7000 for just the motor and mods, not including the actual cost of installation.
    • a new 6BT is just well... unreasonably priced... around $10,000 if memory serves, and it puts out something like 230bhp/330ft-lbs stock... in the 12v version... add in the same $3000 for mods, and more for fabrication and fitment...
    So, being that you can get a reliable 300hp/500ft-lbs out of a 6.5L TD, why would you go to a 4BT or 6BT? The ony reason I can see switching to a 4BT is the improved mileage... promises of 30+MPG in a K5 almost made me put one in my own truck... The only reason I can see switching to a 6BT is the possibility of more power later down the line... and I know the used ones don't cost that much, but can you really keep your total cost under $4000-6000 and get 500ft-lbs of torque in a 5.9L? Likey, yes... and the promise of being able to go even further would tempt me, but do I really need 1000ft-lbs of rear wheel torque in a blazer? I think not.
     
    Last edited: Oct 12, 2006
  2. k204dr

    k204dr 1/2 ton status

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    how are you getting 300 reliable horsepower from a 6.5?
    I like the 4bt myself, and will be putting one in my scout soon.
     
  3. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Without getting into too much technical detail, here is a list of mods to reliably break the 300hp mark with a 6.5.

    • Peninsular Diesel marine DB2 fuel injection pump
    • Peninsular Diesel hi-flow Bosh marine injectors
    • Peninsular Diesel 18:1 pistons
    • GM piston ring set
    • BD 4" exhaust system
    • Turbo Technology intercooler
    • EGT, Boost, Tachometer, and Trans Temp gauges
    • DSG Dual-Idler gear drive
    • 130gpm GM cooling system
    • Engine related machining costs
      • Engine machining
      • new cam, rod & main bearings
      • Balancing and port matching
      • Assembly of shortblock
      • Head rebuilding and decking
    Total cost should be somewhere near $5000 with all of that... starting from scratch with a rebuildable block. Without the internal engine modifications (pistons and machining) you can pull 250hp out of these engines with the rest of the listed upgrades. With the lower compression pistons, you can up the boost level to about 15PSI, which is just about in line with stock Cummins and Powerstroke boost pressure.
     
  4. mikey_d05

    mikey_d05 1 ton status GMOTM Winner

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    I can peg the 35 psi guage I put on our p-stroke....
     
  5. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Pardon me, I missed some information there... The 15PSI boost along with those other upgrades puts the power of the 6.5 in the same performance range as stock Cummins and Powerstrokes....

    The 1999 6.5 Turbo Diesels are puting out 215HP and 430 lb-ft of torque, with about 7PSI of boost MAX and no intercooler. Both the 1999 Powerstroke and Cummins motors put out 15-20PSI of boost and came from the factory with intercoolers.

    In TheDieselPage.com's "Pull Off", the 1989 6.5L powered GMC K2500 finished second in a 6% grade hill climb with the 1999 Ford and Dodge, and beat both trucks in straight line acceleration from 0-60. The project truck had all the upgrades and mods I listed above, as well as a GM-8 upgraded turbo... (the stock turbo is a GM-4 I think.)

    I'm not arguing your ability to peg your boost at 35PSI... my friend is driving a 1996 Cummins and says the same thing... 30-35PSI in heavy acceleration. I'm just saying that the 6.5L when properly equipped, is more cost effective than shoe-horning a 6BT under your hood... unless you are building a competition truck that needs 1100+ lb-ft of torque...
     
  6. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Moving reply here...

     
  7. mikey_d05

    mikey_d05 1 ton status GMOTM Winner

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    Wasn't trying to be a dick, just saying that 15 psi is low for the other two motors.
     
  8. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Again, not disagreeing, just adding information I think to be accurate... not necessarily my own opinion...

    My understanding of gasoline engines, is when you add more horsepower through engine modifications or what-have-you, most of the time, the engine will get less miles per gallon than a lower powered, similarly sized engine. For instance, a SBC 350 in stock form and a carburator might produce 12-14MPG if driven conservatively. The same engine with fuel injection might produce 16-18MPG if driven the same way because of better fuel delivery control. If however, you were to add performance parts, such as internal upgrades, turbo charger, etc, you would get less MPG if driven exactly the same as the lower power engine because at the same RPMs it would use more fuel.

    In a Diesel, with performance modifications, you get the higher power and torque, but if driven the same as you did before the modifications, your MPG will remain the same or improve because the engine becomes more efficient at burning the fuel and producing power. Bigger exhaust, less back pressure, better turbo action, more air entering chamber, more efficient fuel burn, more power per stroke, better mileage. Intercooler, 100+ degree intake temperature reduction, more - denser - air entering chamber, etc, leads to better mileage. Better flowing air filter or bigger turbo, same results as above. In any case, at the same RPMs, a stock motor will produce less MPG than a modified motor because it is more efficient, and diesel is all about efficiency.

    Gas engines become less efficient as you increase displacement and horsepower, evidenced by the fact that you can get 300+hp out of a new GM 3.8L V6 engine, but adding 2 more cylinders and 1.9L of displacement (5.7L - 350), only adds ~50hp. When was the last time you saw a stock GM 350 puting down 400hp from the factory? Physics would dictate that if you have a 3.0L V6 producing 300hp, a 4.0L V8 should produce 400hp if all conditions are equal. Simply, a theoretical 50hp per cylinder whether there are 2 cylinders or 20. However, gas engines are not operating in ideal conditions, and get progressively less efficient the larger and more powerful they become.
     
  9. bear76

    bear76 1/2 ton status

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    There is power in all stock engines that can be found by letting air in and out more effectivly, but only to a limit. At some piont you have to add more fuel to the fire, gas or diesel. Then your MPG's start dropping.
    You have to find that medium of max power per 'x' units of fuel/air to be efficiant.
     
  10. Hossbaby50

    Hossbaby50 3/4 ton status

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    Do keep in mind though that with the Cummins motors you are getting a medium duty motor that has been de-tuned to for light duty use. The motors LD stock numbers are about 195-235HP & 390-440TQ. Tune them back up (which doesn't take much money) and you are looking at a truck with a the same 300HP & 500tq numbers that the worked over 6.5L has. To get back to the 300HP make with a 94-02 Cummins takes about $200-600.

    The 300 HP 6.5L is built but the 300HP Cummins has barely hit its stride. Cummins motors routinely go 300K+ were I doubt a worked over 6.5L is going to do that with as much frequency.

    Also remember that if a Cummins is making 300HP then its TQ number should be in the 600-700 range instead of the 500 range like the 6.5L. The inline 6 is a better design for more torque.

    I will not tell you that a Cummins is the right application for everyone but if you are looking for longevity, power availability, MPG, & towing the Cummins will beat the 6.5L hands down. If you are looking only on budget factor & ease of install then no a Cummins might not be the most economical choice.

    Harley
     
  11. muddybuddy

    muddybuddy 3/4 ton status

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    i wonder how a fully built 6.2 would compare as well.

    i read a dyno sheet from banks, at the wheels - 249hp and 445tq...that would be close to 300hp/500tq at the crank wouldnt it?

    i cant afford to do the cummins swap, and 6.2 is more redily available right now.
     
  12. 6.2Blazer

    6.2Blazer 1/2 ton status

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    I think it would be hard to beat a built 6.5 in a K5. Sure, the 6BTs are great engines...for what they are designed to do, and that's haul heavy trucks or trailers around and up hills. Just empty driving even a mild built Cummins isn't that fun in my opinion as it still seems slow and not nearly as "quick" as a built small block or big block (though towing a trailer is quite different).

    The other issues is simply fitting a 6BT in a Blazer, dealing with the weight, making the motormounts, and getting a trans to work.
     
  13. MTMike

    MTMike 1/2 ton status

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    From what I understand, the 6.5 has a 21.3:1 compression, and the max boost it can handle is about 15psi before head gaskets start to die horrible deaths.

    6BT/Pstroke/Dmax run lower compression ratios (somewhere in the neighborhood of 16:1) and thus can handle higher boost, in the 30+psi range

    I'm no expert but that's what I've been hearing & reading

    My vote is for 6BT - a little more spendy but you'll never be wishing for more power. I'm a firm believer (after plenty of experience otherwise) of doing it right the first time.
     
  14. Robert79K5

    Robert79K5 1/2 ton status

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    I have been mulling this same question over myself actually. My thing is I don't care for my Blazer to be a hotrod, so Im confortable with a lower powered engine that will still lug around and have ample torque for crawling.

    That being said I still would like to squeeze the maximum amount of streetability out of an engine that I can. Things I like about the 6.2/6.5 is that it is a bit lighter than the 4bt which I believe weighs around 700lbs. Also from what I have seen the 4bt maxes out at around 2200 RPM where the 6.2/6.5 can spin up to what like 3200 RPM? I like having that extra RPM range available to me. I have a 79 Blazer that I put a bone stock naturally aspirated 6.2 in and with the SM465 it had plenty of power for wheeling and once up to speed had no problems hauling the Blazer around. The only thing that was bad about it was the way it would fall flat on its face in between gear shifts. I think a lot of that could be remedied with a rebuild and a new injection pump.

    The more I think about it the more I am leaning towards rebuilding that 6.2 to put into my 90 Blazer as opposed to going the 4bt route. So what I will have a diesel that will only go a couple hundred thousand miles. At the rate I put miles on my Blazer that will probably last the rest of my life. Even if it would cost the same to go either route I think I personally like the idea of the wider power band and lighter weight of the 6.2 for my purposes.
     
  15. bowtiepower00

    bowtiepower00 1/2 ton status

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    Dollar for dollar, there is no cheaper Diesel to mod than a 12V 6BT with a P-pump. It is also the strongest of the bunch. The biggest hurdle to making power with the 4BT is the injection pump and lack of intercooler (in most apps.) If you can find a P-pump equipped 4BT, then it would be just as easy to mod as the 6. As far as doing a cheap swap, if you can find a SM465 equipped bread van then you may be able to do the swap relatively cheaply, too many variables to sort out. Same with a 6BT swap. Used, I've seen both motors go for as little as a grand to well over $5000 for a lightly used 6BT. If you already have a turbo 6.5, then it would probably be cheaper to build one of those. Again, lots of variables. I think that the 6.2 and 6.5 are great motors with a few problematic years, but you will never get one to put down the power that a cummins does with as much reliability. That being said, for the majority of towing and hauling needs, especially in a 4L80e equipped rig, do you need more than 600lb of torque? Not really. Any more than that is overkill in a light duty application, though it is nice to drive a bombed truck.
     
  16. 85-m1028

    85-m1028 1/2 ton status

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    I have to agree with the rpm factor making the 6.2/6.5 better for an off road application. The torque is there for crawling and technical stuff but when you need to generate some wheel speed the horses start coming in at 2500-3400 rpm for that slippery slope!!!
     
  17. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    MTMike, you are absolutely correct, a stock 6.2 or 6.5 has 21.3:1 compression ratio. That's why in the list of mods, you will find 18:1 compression pistons, and machining of the block, heads, and ports where necessary. You are also correct in saying that with a 6BT you'll never be wishing for more power.... IF you spend $10,000 building up the motor to 500hp and 1200+ lb-ft of torque. Plus the average cost of the motor itself, somewhere around $6-8k if you find a busted up truck. A brand new "crate" Cummins will run you somewhere in the neighborhood of $10-15k, depending on your included "accessories".

    On the whole idea of a Cummins being "underpowered" for Dodge applications, I beg to differ. One of our tow trucks has a 5.9L, and it is pushing around 250hp and 500lb-ft of torque. As far as I know it's completely stock, and really not that far off on the numbers of the stock Dodge application motor. My former boss's truck is running about 300+hp and 700+lb-ft of torque, and he's got about $2-3k into mechanical performance mods. If anything, the Dodge motor is the "stock" power specs for the Cummins, and they are modded for heavy truck use, rather than the other way around... It would cost Cummins more to de-power the engines than to just have upgrades available for tow trucks and OTR trucks.

    Also, I agree with the guys who said the wider RPM band of the GM motor will be of better use to 90% of those of us with Diesels. Most of us will never need to have any more than 500 or so lb-ft of torque unless we plan on puting 44s and Rockies under our trucks, in which case, you wouldn't be starting with a 6.5 in the first place. For those of us who are looking for more power, for the lowest possible cost (and a 6.5 is far cheaper dollar for dollar than a Cummins by the way - $12k total for 6.5 buildup with new block as compared to $18k+ for the 6BT with a new block) then the 6.5 becomes the way to go. If you want the ultimate, go with the 6BT... but if you just want Diesel Power, and you aren't planning on 2 1/2 ton running gear, then the extra ~400lbs and engine bay mods just aren't worth it, so go with the 6.5 or even the 4BT, a mighty engine in its own right.
     
  18. muddybuddy

    muddybuddy 3/4 ton status

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    i read a dyno sheet from banks, 6.2 with banks turbo and some other little things - at the wheels - 249hp and 445tq...that would be close to 300hp/500tq at the crank wouldnt it?

    how would that compare to moded 6.5 or other diesels?
     
  19. bowtiepower00

    bowtiepower00 1/2 ton status

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    If you're comparing engine buildup costs only- not the vehicles they came in or swap costs, then the Mechanical P-pump Cummins is king- period. 300/700 can be done with a fuel plate. A whole slew of TST stuff is still under a grand- closer to $500. The reason 6bt's are so much new is because nobody in their right mind would buy one new. Seeing crosshatch in the bores at 300K is not unheard of. The only people blowing them up are people getting just plain STUPID with the mods. Used 6BT's are relatively cheap, people find them for under two grand relatively often. You could find one for much less than that if you're talking about rebuildable cores from backhoes or other equipment. Plus, a 6bt is a 6bt, injection systems and accessories notwithstanding. If you are talking about the cheapest engine to make 500 lb of torque in a GM light duty truck, then the 6.2/ 6.5 would probably take the crown- depending on what you're starting with and how much work you're willing to do. However, you're going to spend a lot of time and money just getting the GM diesel to compare to a stock intercooled Cummins, and that's without touching the Cummins. Sure, the 6.5 can be built to make some power, but at those higher power levels you would probably be time and money ahead to do the Cummins swap and go from there, assuming you're able to do the work yourself.
     
  20. 85-m1028

    85-m1028 1/2 ton status

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    What kind of trans was the truck running? that sounds good!! the trick is in the little details, cylinder head precups, high flow injectors, four plunger injection pump "db-2831" not db2829, timing gears, free flowing exhaust, most importantly keeping the EGT down below 1150*, as long as these are similar the 6.2 /6.5 will produce similar results.
     

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