18:1 Compression Ratio

[More Power]

Yes, a typo. It should read 21.3:1 CR....

I should add that our 18:1 6.5 was first run during the winter of 1998/99, and that I scrambled to increase the first glow cycle duration in an effort to improve cold starts. With an unmodified glow controller, the first glow cycle at a cool 25 degrees F was approximately 8 seconds in duration. The 18:1 6.5 produced way too much white smoke with that combination of temperature and glow time. Increasing that first glow cycle time to 12 seconds produced typical 6.5 cold starts at that temperature. In later years, we increased glow time to about 15 seconds (w/AC-60G glow plugs). This is easy to do with the 1985-93 glow controller, and there are a couple of articles currently available in the subscriber areas that show how to increase glow cycle times for the 1994 or newer electronic trucks.

There are at least two ways to reduce compression. 1- Use pistons that were manufactured with relocated piston pin bores, which is what Peninsular does. 2- Machine the piston crown.



The above Ron Schoolcraft image shows how KennedyDiesel.com does it. Ron sectioned a stock 6.5 piston (not shown) to show how thinning the crown doesn't appear to materially affect the strength or durability enough to matter. The factory 6.5 piston crowns are anodized, so machining the tops removes the factory coating. I'd recommend either ceramic coating or anodizing the tops to return the piston's heat tolerance, which I think KD does.

Which method of reducing CR is better? Good question. One could make a good argument for either method, as each has been proven during real-world durability tests.

I've heard mention of raising 6.5 compression ratio above stock. Other than being a really bad idea, I'd like to know how someone would raise CR? The head deck is already flat, and stock 6.5 pistons can already protrude a few thousandths above the block deck at TDC. This is why thicker head gaskets are available (are required) for those engines that have had their blocks decked during a rebuild.

Jim

[a5150nut]

Low compression and lots of boost is how the older Cat equipment motors were built. They also had a glow cycle. The in line 6 cylinders produced more usable torque than the newer V-8's. The 633 C model scrapers had an in-line 6. When they came out with the 633 D's the old 6's would out work them in the hills. You could pull them down in the RPM range and build power back up. The V-8's you had to run more like the old 2 stroke Detroit's. Keep them near max RPM or the bottom would fall out of the power range.

Then there was the duel overhead cam V-12's in the 660's and triple 6's!

[Robyn]

The later Cat truck engines (3406E model) have been a real treat.
For an inline 6 these little monsters will flat turn out some power.

I was yacking at a fellow from up Noth of the border that routinely pulls some very serious weigh on a Super "B" train and has had his 3406 spooled up to produce close to 1000 HP.
I have no way to verify this particular case but I know from chatting with the Cat boys that the outlaw shops can and will do it for a price.

The 3406E 600 HP engine can easily get there. It produces a whopping 2000 Ft lbs torque at 1200 RPM in stock trim so I can only imagine what it will do when the computer gets mauled by the outlaw programers.

My Western Star was purchased a little too early in production to be able to get the 600.
I even had to wait to get the 500, which is a real monster when it comes to hauling heavy loads.
^^
I can have it tweeked to 575 at the local Cat > . < Shop.
--
The 600 has a different bore and stroke I believe.

The 500 I have is rated at 1800 ftlbs torque at 1200RPM and its stock.

The boys over at the tranny companies were literally crappin in their shorts when the Cats, Cummins and Detroits showed up with all that power.
The only tranny I had as an option was the 18718B fuller 18 speed.
The clutches were another bone of contention too.
Full ceramic was the order of the day but now the new Kevlar is the hot ticket. I bought one 2 years ago and its is a super clutch. This thing does not eat the flywheel and the pressure plates and will hold the power well.

The boost on the kitty is right at 30 PSI.
The new low emission cats are running 50 PSI with twin turbos.

Back to the 6.5
I personally think that if you are going to build a custom 6.5 that the 18:1 pistons and some serious boost are the way to go.

Myself I am very happy with the stock compression along with the power chip and the turbo master.
The DaHooooley is very responsive and also very civilized. I personally have dusted off some late 90's 7.3 strokes and there was no doubt that the little 6.5 was in command of the situation.

The DS4 pump is the limiting factor IMHO and with the chip its giving the engine all that it can deliver. 91mm

If I were serious about a build I would think about a DB4 pump that can really stuff the fuel at the little diesel Rat.

I am running 12 PSI max on DaHooooley and with this the EGT is about 800 (POST TURBO) on a hard pull with a 6K trailer behind.

Anything more than this needs a cooler on the inlet air to help out.

I am also a fan of the coated pistons that use a relocated wrist pin to do the honors of dropping the compression.

Good luck with any projects

Robyn

[arveetek]

I had the Diesel Depot make me some custom .040" over bored low-comp pistons. They machined the surface down and then ceramic-coated the tops. After decking the block and using standard 6.2L gaskets and topped pistons, I ended up with a CR of around 19.75:1.

I'm running a 6.5L pump, 6.5L injectors, DSG gear drive, Garrett turbo, 3" downpipe to 4" exhaust, and with these components I see a peak boost of 18 psi at 1050 degrees. I have very responsive boost as well. Just touch the throttle and she jumps to life. I can build around 12 psi when doing a powered launch.

The 19:1 pistons were cheaper than the 18:1 Peninsular pistons, and I believe is a good compromise for anyone building a 6.2L on a budget that will be seeing any kind of towing use. In reality, any CR drop is good!

Casey

[rustyk]

Back to the 6.5
I personally think that if you are going to build a custom 6.5 that the 18:1 pistons and some serious boost are the way to go.

I'd have to agree. The AMG/Peninsular Engines 6.5L TD I had installed was significantly better than the stock 6.5L TD (Early '92 manufacture). At first, I was a bit disappointed in the ability to use all the power in the replacement engine (230HP vs. 190HP stock), but the issue was a defective turbo, which failed eventually; the replacement has given me the engine I expected. With the original turbo, I would hit the EGT wall fairly frequently, even on moderate grades. With the new turbo, I've yet to be able to hit redline. I attribute the performance to the lower CR pistons.

The 18.1:1 pistons give up nothing in performance over the stock CR, and economy is up 15%. Now, I don't engage my 17K lb. motorhome in drag racing, but it'll suck the doors off of gaso-powered RVs in the same size range.

[More Power]

No...

If you do a lot of heavy towing, or are building a more performance oriented 6.5 and plan to run up to 20 psi boost pressure, then yes 18:1 CR would be a good choice. The 18:1 pistons are no more expensive than factory CR pistons (Peninsular type pistons).

If you use your 6.5 as a people mover, commuter car, soccer mom rig, or grocery getter, then you could be better served with the factory 20.2:1 CR.

Jim

[78Chev]

No...

If you do a lot of heavy towing, or are building a more performance oriented 6.5 and plan to run up to 20 psi boost pressure, then yes 18:1 CR would be a good choice. The 18:1 pistons are no more expensive than factory CR pistons (Peninsular type pistons).

If you use your 6.5 as a people mover, commuter car, soccer mom rig, or grocery getter, then you could be better served with the factory 20.2:1 CR.

Jim

I understand from this discussion what the benefits of 18.1 are but what are the advantages of staying stock 20.2 as you suggest for people moving, commuting, etc.? Is the only downside of 18.1 the potentially harder cold starts? I will be in a 6.5 rebuild project soon. I plan to tow a horse trailer a few times a year over the mountains to Montana so I am still trying to make up my mind. Thanks.
Randy

[CareyWeber]

The factory 6.5 piston crowns are anodized, so machining the tops removes the factory coating. I'd recommend either ceramic coating or anodizing the tops to return the piston's heat tolerance, which I think KD does.

Which method of reducing CR is better? Good question. One could make a good argument for either method, as each has been proven during real-world durability tests.

I've heard mention of raising 6.5 compression ratio above stock. Other than being a really bad idea, I'd like to know how someone would raise CR? The head deck is already flat, and stock 6.5 pistons can already protrude a few thousandths above the block deck at TDC. This is why thicker head gaskets are available (are required) for those engines that have had their blocks decked during a rebuild.

Jim

Jim,

Do you know where to get pistons anodized?

Carey

[More Power]

Jim,

Do you know where to get pistons anodized?

Carey

Shouldn't be too hard to find a source. Googling produced this list.

Jim