Low compression pistons

[Snowbound98]

Hi all. Just wanted to share something with everyone about lowering compression on a 6.5. I'm in the process of rebuilding my engine that spun the balancer and sheared the keyway off the crank and took a chunk out of it. I looked at buying a reman engine with the updated block but after researching the parts and checking my block I determined I could get more out of my engine by rebuilding it than I can buying a reman. I purchased a scat crank, main and head studs (ARP), and had machine shop go thru my engine. Cam bearings, freeze plugs, line honed, centerline checked, decks cleaned up, and painted. I have the infamous cracks between the valves on my heads but were never a problem. I was having a local head shop install coolant passage upgrade kit, do a 3 angle valve job and set all spring pressures and of coarse pressure test them. I was porting heads, and gasket matching myself. Anyway, make a long story short, I wanted to drop my compression ratio down to somewhere in the low 19:1 range. I didn't want to go to the 18:1 because I've heard they do get a little harder to start in the cold weather. I just wanted to add a little more boost but still have reliability and easier start up. So before I could have my rotating assembly balanced I needed pistons or mine dished out to lower compression. I emailed Kennedy diesel because I saw on their web site :

"Custom CNC machined dish design allows the compression ratio to be dropped to most any desired number. The dish design allows the piston to be installed with the factory spec protrusion. The dish shape along with 0 to +.oo7" protrusion along with a perimiter "squish" band, concentrates the fuel/air charge in the middle of the chamber, promoting more efficient combustion, and reduced stress on the head gasket. The domes are then ceramic coated for durability and heat rejection while the skirts get a moly dry film coating applied to reduce friction."

I asked John there if he had a set in my desired ratio in a standard bore? This is the email I received back from John Kennedy:

"An 18:1 engine will start fine in most any climate with proper glow support and tuning. I haven't done any of these pistons in quite some time. Too many requests for std bore tells me that there is too much desire to cut corners where they should not be cut. This also tells me that there are not many that would spend $995 on a set of properly built and coated pistons.
ANY quality engine build starts with a freshly bored and honed cylinder preferably with a TQ plate"

Isn't that nice? Cut corners? Can't afford? I was shocked when I opened this email. I don't know about any of you guys but if it were my business I would sell a customer anything they wanted. Especially in this economy. If I had a guy wanting to buy a set of pistons for $1000 I would jump all over it. If they are custom made there is no refund. If the customer puts them in and he has piston skirt slap because he didn't check his block then he bores it and I sell him a new set of pistons. I gotta say I saw red when I read that email! I was pissed. Like I'm a complete idiot. And a broke idiot at that. His words. This is what I responded to him:
John,
Thanks for getting back to me so soon. I understand that this engine can start in cold temps with a lower compression ratio. But on your website you say "Custom CNC machined dish design allows the compression ratio to be dropped to most any desired number. The dish design allows the piston to be installed with the factory spec protrusion. The dish shape along with 0 to +.oo7" protrusion along with a perimiter "squish" band, concentrates the fuel/air charge in the middle of the chamber, promoting more efficient combustion, and reduced stress on the head gasket. The domes are then ceramic coated for durability and heat rejection while the skirts get a moly dry film coating applied to reduce friction."
So I was asking for a reduced compression ratio piston in a standard bore. I just want to add more boost and do it safely. As for boring the engine, why do you assume that I'm not using a 6.2 bored to 4.057"? Why do you assume that I'm not using a new 6.5 block? Why do you assume that I'm a complete idiot and would pay $1000 for pistons, have the rods, bearings, cam, rockers shafts, rockers, intake runners, and combustion area on heads all coated, run ARP main and head studs, a stud girdle, scat crank, and fluid damper but not check cylinder bore taper and run out or have the block magna-fluxed and hot tanked and line honed and crank centerline checked? Every site I went to could not resource rod bolts for me or said reuse the old ones but I stayed persistent and found a set in Utah. Is this what you do to all your potentially new customers? Talk then out of buying your product? Should I have lead with I'm an ASE certified diesel technician and I have a 6.5 diesel with 20k on it and the only reason it's apart is because it sheared the keyway off the front of the crank and I have measured my bore and it has a taper of .0004" and a out of round of .0003" averaged? And $1000 is a drop in the bucket for what I have spent on this engine. Maybe you should ask someone what it means to ASSUME. Thanks for your time. I'll try to help ya out and I'll let as many people know as I can that they are too stupid, cut too many corners, and are too broke for Kennedy diesel parts.

I don't know, maybe he wanted to push the parts he already has on the shelf. Maybe he just didn't want me to buy his product. Am I over reacting? Just burned me up. So now I'm gonna have to call a different vendor and ask them if they want my hard earned money cuz he sure didn't.
Thanks for reading my rant. Maybe I should just throw my block and parts in the scrap yard and add to the dying breed of 6.5 owners out there. :(

[Kennedy]

The truth blunt and to the point is what you get from me and I make no apologies for that. There just is not the demand nor the budget in most 6.5 builds these days. Most every option for production based low compression pistons is gone and there's far less demand for standard bore plain and simple.

Where's the rest of my email text?

[Snowbound98]

Blunt and to the point? Or rude and unprofessional? I was asking for some help in getting lower compression pistons so obviously there is a market for this and you do claim to sell these. But since its in your opinion, not budget friendly or a heavy market, it can't or shouldn't be done? Thanks but I'll get there without you.

[Kennedy]

There is no tone to an email unless read into it by the recipeint. The statements that I made are factual based.

Additionally, every email that I send has a copyright notice on the bottom asking that it not be disclosed. There is a reason for that. I could clam up and not offer opinions of one product over another or I can speak my mind knowing that it will not get plastered all ovet the internet.

If I wanted to call you names I'd have done it plain and simple.

"An 18:1 engine will start fine in most any climate with proper glow support and tuning. Fact

I haven't done any of these pistons in quite some time. Fact

Too many requests for std bore tells me that there is too much desire to cut corners where they should not be cut. Reasonable opinion based on fact

This also tells me that there are not many that would spend $995 on a set of properly built and coated pistons. Reasonable opinion based on fact

ANY quality engine build starts with a freshly bored and honed cylinder preferably with a TQ plate" Fact

Where did I call you an idiot in there? Grow up already.

[john8662]

Gentlemen,

I think what's been said, has been said in the context of getting something off chests. But, this isn't the place for it.

Private conversations held between adults via email shouldn't be posted in quotes. Its just unsightly aired underwear.

Questions regarding build preferences and techniques are welcome here, but slamming of one mans opinions over anothers isn't.

Please don't continue to banter here on the forums.

[john8662]

With what was said above, a few things come to mind from the conversation based on build preferences.

First, 19:1 vs. 18:1.

One of those, tried it and can't tell any difference between the two startability wise. I've had 2 18:1 spot on engines, and one 19.5:1 engine and a 17:1 engine. All 6.5's with 6.5 cylinder heads. Three of them used "topped pistons" one had the KD custom pistons @18:1.

The 19.5:1 engine started the same as the 18:1 engine I had in the same vehicle did with the same ECM/Programming. Poorly with stock timing. The engines would both start up but then start missing and smoking due to the need for sufficient after glow and a longer glow time. Exactly the same. I had the same logic of trying the slightly higher CR to help in starting. It didn't help.

Now with that said. 18:1 is the standard because it's really about as low as you want to go and keep something that resembles startability with proper glow time etc. A 17:1 engine (actually mine is 17.1:1) is miserable to start and requires very long glow times (~20 seconds with quick heats) to start evenly and w/o the smoke.

Kennedy is right in that lower CR startability can be solved with proper glow timing. His ECM/chip programming completely solves the startability issues, it's actually humbling to see the change because the way one starts before the proper glow timing makes you worried that somethings actually wrong with the engine/components. So 18:1 is no worry at all.

Changing subjects.

Bore size.

If you've got a bore that's standard and meets the specifications you're looking for clearance wise and cylinder taper wise even after a proper hone, sure, use it.

It's going to be difficult to find a block that meets these requirements though.

I'd like to see .004" on Cylinder 1-5 and .0045" on 6-8 for piston to bore clearance.

I saw the mention of a Torque Plate above. The factory blocks are not machined with a Torque Plate. If you want a really nice bore for final assembly, the TP is the way to go. These blocks REALLY do distort when the heads are torqued on. I think this is what leads to the blow-by when hot situation these engines have stock (pull CDR valve with engine running and see the blow-by on a good engine, they make a bunch of blow-by stock).

So, I see it's recommended to bore the block so that you can get a perfect cylinder size, better than originally. Since you have the chance.

Just an FYI on the torque plate, My machinist here locally uses the plate for boring and for honing. He did one engine for me just using the torque plate on the hone portion and said it was almost too close that it didn't work after being bored.

They're a little flimsy up top.

You also can't use a TP on a finished machined/honed block to "touch up" the hone job.

I think that's what Kennedy is trying to get at with recommending at least a .020" size piston if you're doing it and want it the best it can be.