Is 18:1 CR right for me

[Rob4]

My trusty 6.5 bit the dust with a cracked piston, cracked block and cracked heads. It had about 225,000 miles on it and had never been abused. It ran fine until the cracked piston caused blow-by into the crankcase. The two cracks in the block and the small cracks between the valves never caused any problems. My question is should I now consider a lower compression ratio for my next engine? Will a lower compression ratio give the engine a greater chance for long term survival? I intend to keep it forever. It's my understanding that I will lose some power as the standard turbo can't produce the boost needed for the lower CR but the up side is that the engine will run cooler. Is this correct? What other things would be different? I use the truck mainly for local driving but a few times a year I head out a few states away and haul back a truck or tractor or such. I just want to make sure that I can have the most reliable engine as possible. I know there are no guarantees but you know what I mean. Thanks for any help.

[More Power]

You can read more about 18:1 CR at the following link:
http://www.thedieselpageforums.com/tdpforum/showthread.php?t=29913

There's also an expanded version online in the Member's Area (http://www.thedieselpage.com/password.htm).

You said:
It's my understanding that I will lose some power as the standard turbo can't produce the boost needed for the lower CR but the up side is that the engine will run cooler.

We built a performance 18:1 6.5 that ran the factory GM-8 turbocharger. I've yet to ride in another 6.5 that could accelerate in 3rd gear with a 10K trailer on a 6% grade (albeit slowly). That 6.5 could when tested in October of 1999. Schoolcraft's 6.5 produced the best top speed in the measured mile on a 6% grade and with a 10K trailer during an instrumented test in the summer of 2006, but he ran in 2nd gear. His Suburban lost speed in direct. Our Project 6.5 didn't have the turbo it needed to run at high rpm. So no, it's not a rule that you lose power when running 18:1s and the factory turbo. I don't know of any 6.5 owner who has performed a documented before/after performance test, which is what would be required to lend credibility to a statement that you lose power when running 18:1s and the factory turbo. :)

Jim

[Robyn]

My answer to your question will cover a couple areas.

(One)
If you want to build an engine that you are going to set on Kill with all the mods you can bolt onto it to build as much power as a 6.5 can muster then I would definately go the 18;1 route along with a charge cooler and all the other goodies.

(Two)
Now if you want a good realiable little creature that will serve you well for another 200K+ then I would consider scrounging up a good block and salvaging your rods and as much of the original engine as you can to build the new one.
Some mods you should consider would be the HO water pump and dual stat water outlet.
Certainly some fuel management upgrades as well as exhaust upgrades if you dont already have them.

A good ballance job on any 6.5 is a real good thing to do.
A fresh harmonic balancer is a must do.

The bottom line is how much do you want to spend. :eek:

With 200+K I would be very nervous about reusing the heads. The rockers may well be fine, just look the mating surface over where they contact the valves. if they are not worn then reuse them. Replace the guide buttons.
The cam can be reused if the lobes are good, just replace the lifters.

You can buy GM/AMG heads or you can use a set of aftermarket heads from a couple different sellers.

DSG ( A TDP supporter) offers aftermarket heads as does Clearwater in Florida.
The later company does not support the page but to date there does not seem to be any issues to speak of with the product.

The crank in your engine may be fine. Have it magged and check the journals for size and wear.
I have reused cranks in these engines with 250K on them with no issue.
The thing with the cast iron 6.5 crank is that there is no way to tell if the particular unit has used up all its duty cycle and is ready to snap.

You can get cast steel cranks from Scat to replace these.

Now depending on your $$$$$ you may be better off getting a crate engine built by AMG/GEP

Personally I am a scrounge and would, if it were my rig, scrape together a good used block thats crack free and get a fresh set of pistons and a set of aftermarket heads and then replace bearings, timing chain, lifters, injectors and such along with the incidental gaskets head bolts and such.

A fairly nice job can be done for around $1500 if you shop at places like ebay and pick up name brand stuff at right prices.

These are suggestions and options and there are certainly other choices that one can make.
The bottom line is how much can you or are you willing to spend to build the engine and what do you want it to do.
If this is basic transportation, grocery getter and so on with some pulling or hauling spending the big $$$ may not be the best choice. The final choice will be yours.

Building a performance 6.5 with all the goodies is not a cheap undertaking. However a very good and serviceable unit can be done on a budgit.

I have done that part recently and it came in around $1800.
The rig runs sweet and serve me well.

Just a side note. A 6.5 block that is well seasoned 100K or more and not cracked probably is not going to.

Once a casting has been stress relieved it generally is done moving and after a buttload of miles they dont seem to break after that. Not that it could not happen but as a general rule they live.

Just some thoughts, hope this helps

Robyn