18:1 Compression Ratio

[More Power]

Yes, quite a few 6.5 pistons have received the ceramic crown treatment.

Jim

[jggiedeman]

Baqk to the 18:1 CR ratio. When I decided to lower my CR I bought some Zollner pistons off of E-Bay. Excellent pistons and they would have dropped my CR to around 20:1. Too bad the machine shop decided to ignore my written instructions and force me to move to a larger set of pistons. I went back to Peter Bierman's article of how he measured his final CR. The heads I bought from CCH had a larger precup area so I decided to CC the heads and Ricardo cup area. Wound up with 29 cc's for the head, 4 for the piston ricardo area and area from piston ring up, .010 gasket and piston depth(machined .020 off and ceramic coated) at -.018 gave me another 15 cc's. 820 + 48 / 48 gave me around 18.1:1. I also reduced my height of the pistons by relocating the pin bushings .010.

I'm glad that I had to do some measuring after the machine shop so efficiently hosed me over because my CR might have been much lower had I gone with true 18:1 pistons. Lots of ways to get down there and my method is far from the ideal setup but was born out of necessity.

[Robyn]

Sounds like you have it handled.
Should work sweet.

I have seen this trick done in several ways and as long as the results are the same it works.

???? did you ballance the rotating assembly after all the mixing matching and machining.

Having a good ballance on the engine is a must.

Be sure to ballance using the Damper, pulley and flex plate you will use.
Witness mark the pulley assembly to the ballancer in case its off a little.
Make good and sure that your ballancer rubber is in good shape as well as the dampened pulley assembly.

Good luck

Robyn

[6.5 Detroit Diesel]

I am looking at a few kits off E-bay right now. The one has an option to upgrade to Mahle 18:1 pistons for $300 more. How much boost can you run with the stock compression. If I could run between 12-15 psi with an intercooler I would be happy to stick with the stock pistons. Do you need to go with 18:1 to run that much boost?

[Kenneth]

With the stock CR you can run the boost up to 15 psi efficiently with a chip and intercooler. Over 15 psi and you need to lower the CR to 18:1 to handle the higher boost.

[Robyn]

Im running a performance chip in my DaHooooley and it has stock ratio.
Turbo master and 3-1/2 exhaust without CAT.
10-12 PSI max without charge cooler.
Truck runs great and plenty of power.

I personally would keep the boost with stock comp at no more than 12 PSI

With 18:1 and a charge cooler the addition of a better turbo can allow 15 plus.
The issue is the IP supplying the fuel. I DB2 pump can be turned up quite a bit.
The DS4 will only allow what the performance chip will give it.
I believe 91mm is the limit on these pumps.

I would recommend a max of 12 PSI even with a cooler and enjoy a long engine life.
Keep the EGT in line and do the cooling system mods as well and your little creature will buzzz along as happy as can be all day long.

Looking for the last ounce of horse pressure from a 6.5 can be like searching for Eldorado, "Not a fruitful endeavor"
The engine reliability can and will go south when you take it out on the edge of the envelope.

Even with reasonable mods and 12-14 PSI absolute max boost, you will need to drive this thing on the gauges. The truck will not be a get in and plant your boot on it and go thing. You will be fine cruising light but once the load goes on it you will have to pay attention to the gauges like a hawk.

There are many good people here myself included that will help anyway we can with advice.

My most important piece of advice in powering up a 6.5 is DONT GET GREEDY

The edge of the envelope can be flirted with but there is a bridge too far and its hard to tell exactly when your there until something melts.

Have fun and enjoy

Robyn

[6.5 Detroit Diesel]

Ya, it is the DB2 pump so I don't have a chip and can tune the pump myself. Or at least try to.... From what I have been reading unless big bucks are spent it is dangerous to cut corners and try to make power while keeping reliability. I want the truck to last and so I want to get the most power possible without driving down the reliability level. I figure while doing a rebuild on it I might as well go all the way and build it for what I want. I think an intercooler is a good idea especially if I am going to keep the stock CR.