18:1 Compression Ratio

[More Power]

The statement about "running at rated power" came to me by one of the owners of Peninsular Diesel in 1997. By "rated power" I assumed that to be 190 FW. They developed the 18:1 pistons for the 6.5 at a time when the engines ran a DB2 (mechanical fuel injection) - likely an on-road factory calibrated DB2-4911. Last year, while visiting Peninsular in Michigan, they demonstrated dyno'ing an NA 6.5 for us on their in-house engine dyno. It ran with a large fan-cooled engine oil cooler and a huge fan-cooled radiator (looked like a big-rig radiator). It's amazing how much heat these engines generate when loaded hard.

I don't remember EGT's coming up in that conversation back in 1997, when discussing piston durability, but like John said, it was likely whatever was developed at WOT (or whatever), to get rated power.

Do you think cooler oil along with the oil sprayers would that have extended the run time with stock CR? Not indefinate but how about significantly????

I am just thinking about stuff can 2 different setup engines with the same EGT reading have significantly different thermal load on the piston and/or combustion chamber with the same load and fuel rate? I think so depending mostly on compression ratio.

Piston oil spray can help improve piston durability, that's why it's used in most diesel engines. Will that reduce or eliminate the need for lower compression? I don't have a firm answer, except that I know lowering compression ratio improves piston durability. Combustion temperatures are lower with a lower CR. I've seen the results of overheated 6.5 pistons... It's not a pretty sight...

EGT.... I heard from a non-turbo 6.2L owner a few years ago who ran his truck at 1000-1100 degrees for several hours. He was in a hurry, towing a trailer, and ran it to the ECT limit all during that time. He reported it still ran fine afterward. I'd have been sweating....

Jim

[Robyn]

Let me add this tid bit.

This is pretty much gospel as far as I am concerned.
"IF" you are going to runa 6.5 TD with some major power improvements you need a good set of gauges on the beast.

WATER TEMP, EGT, BOOST

you have got to drive these little monsters on the gauges and there is really no exception especially when your asking them to work hard.

The Coolant temp, EGT can all get hinky depending on the outside conditions (TEMP, Altitude and the load)

This is not a plant your boot and forget it engine, you have to be on top of things.

Just my opinion

Robyn

[arveetek]

EGT.... I heard from a non-turbo 6.2L owner a few years ago who ran his truck at 1000-1100 degrees for several hours. He was in a hurry, towing a trailer, and ran it to the ECT limit all during that time. He reported it still ran fine afterward. I'd have been sweating....

Jim

Jim,

When my '81 was naturally aspirated w/stock CR, I saw EGT's up near 1300 and spikes up to 1400. Towing my 5th wheel (like I did to Dayton in '01), I regularly saw 1100 to 1200 for hours on end. It never seemed to bother the engine.

Installing the turbo and 4" exhaust with no other mods reduced the EGT's to a max. of 1050 at 14 psi.

When I rebuilt the 6.2L a few years ago, there was really very little cylinder scoring, just some slight piston damage. It was running just fine at the time. I only pulled it to replace lifters and a few other things, and then those "might as wells" started kicking in...

I don't think high EGT's are nearly as critical on a n/a engine as they are on a turbo'ed.

Casey

[john8662]

The dangerious aspect of what Jim described above is that two conditions were at their maximum. The EGT's were at the engines designed red line and the ECT (Engine Coolant Temperature) was at it's near maximum. Those two conditions can get things too toasty.

Usually when under high EGT, the ECT will quickly follow, which seems to be a good way of judging the working ability of the 6.2 without a pyrometer installed.

I don't know how regularly the 6.2 will see high EGT's in stock and properly calibrated form (designed fuel rate, not turned up).

But, as guessed, n/a high EGT's are less detremental to the engine than Turbo high EGT's, for many reasons.

N/A engine has less backpressure (lack of turbo-backpressure generator), lets the engine more easily dissipate the EGT heat, rather than heat soaking the engine.

A Turbo engine, with it's added plumbing and added backpressure, less cylinder scavenging will retain more of the engines heat, by design. This can be a disadvantage when EGTs are at the limit.

Relating this to the compression ratio. A turbo is a device that supplies more oxygen to the engine, but because it's pressure also acts as a method to give the engine a varying compression ratio. With the turbo 6.5 and the non-turbo 6.2 having nearly the same compression ratio, the turbo 6.5 engine under full-boost will be running at a higher compression ratio. More compression, more heat due to compressing the air.

I don't think I'd want a n/a 18:1 6.5 tho!

J

[More Power]

Jim,

When my '81 was naturally aspirated w/stock CR, I saw EGT's up near 1300 and spikes up to 1400. Towing my 5th wheel (like I did to Dayton in '01), I regularly saw 1100 to 1200 for hours on end. It never seemed to bother the engine.

Installing the turbo and 4" exhaust with no other mods reduced the EGT's to a max. of 1050 at 14 psi.

When I rebuilt the 6.2L a few years ago, there was really very little cylinder scoring, just some slight piston damage. It was running just fine at the time. I only pulled it to replace lifters and a few other things, and then those "might as wells" started kicking in...

I don't think high EGT's are nearly as critical on a n/a engine as they are on a turbo'ed.

Casey

Casey,

Your experience does illustrate how a turbocharger reduces EGT under similar load conditions. EGT is a reflection of combustion temperatures (a ratio of), where combustion temps could be 3000+ at max load, but it cools to 1100-1200 when measured in the exhaust manifold (due to expansion and absorption). This also dispels the notion that the NA precups will suffer excessive damage when turbocharged. The EGT limit remains the same for either a turbo or NA 6.2/6.5 engine.

Back in the MFI days, diesel engine manfacturers rated their engines at a specific EGT (usually 1100 degrees F) and sometimes also exhaust opacity. This isn't true so much anymore with electronic fuel injection systems.

Jim

[Chevrolet4x4s]

Has anyone ever tried the piston heat barrier coating(cant think of the name of it) and would this increase the safe egt capacity?
Shane

[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