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18:1 Compression Pistons

C

Chevy Diesel

TinkereR
Messages
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0
Location
Indiana
All,

I was wondering if anyone knows of a good outlet for 18:1 compression pistons 0.030" over? I had ordered a set through Peninsular but the factory that was supplying them has decided to stop making the 0.030" over. This throws a big monkey wrench in my rebuild, so if anyone has any information to help me out it would be much appreciated!

If noone has an outlet for 0.030" over 18:1, has anyone sleeved their block and had good luck with it? I couldn't find the discussion, but I thought I remembered someone saying NAY to sleeving.

Thoughts?

Thanks,
KV
 
18:1 can also be harder to start when its real cold.

Played with that idea and decided to go with stock compression when rebuilding mine.

If you need 30 over you might be stuck. I saw some 18:1 20 over's might be available.


Good luck
 
Yea, I am going w/ Peninsular's 70g glows and a longer glow cycle, and their intake heater, shouldn't have any un-surpassable problems. We have the technology :thumbsup:

Where did you see the .020" over John? I could probably get away with 0.020" over on 7 and have to sleeve 1 of 'em. I only had one that was pretty sloppy.

Thanks
-KV
 
thanks for the assist racer but:

"Name: Mahle pistons for 6.5 18:1 compression ratio
Category: 6.2/6.5 GM
Sub-Category: Engines - 6.2/6.5
Price: $500.00
Reduced compression height piston for 18:1 CR by sinking piston into the bore. Set of 8 with rings. Typically stocked in .020" oversize with larger sizes available. Std bore is no longer available.
These pistons have been discontinued by the mfr due to lack of demand. I would suggest the Kennedy reduced compression pistons as they are a superior design."
 
Can that be done, or should i say, should that be done? I will do the math to see how much needs to be removed to lower the CR from 21.3:1 to 18:1. It Seems like most of the pistons I see advertised on ebay are 20.2:1, is there a reason for this? I was only aware of the 21.3:1 CR. What years ran the 20.2:1?
 
I haven't heard of anyone doing that on these engines, probably because most, if not all, were able to get the 18:1s they needed. I haven't read anything bad about these connecting rods, and have not had a negative experience with them, admittedly this is my first engine rebuild ever. I will look when i get home if shortening them will weaken their structural integrity.

Thanks for the suggestion AKDD!

Everyone else, shortening the rods, in my opinion, will be my last ditch effort, so I would still like to try and get the 18:1 comp pistons rather than modifying rods that much if possible. So please let me know if you know of a place I could try other than Peninsular and Kennedy (I have an email out to Kennedy waiting on reply in morning).

Thanks
KV
 
Shorter rods is not the answer.

I'd try and schmooze a CNC mill operator into cutting a little off commonly available .030 slugs.

Here's interference with just a rod bearing missing. See where the crank throw was smacking the pin boss? Highlighted in red.

Pic:

DSC01601.jpg
 
I might be able to hook you up with a good machinist, or you could go plus ten gaskets to go down one point without any problem. Sleeving all eight wouldn't be a problem either ran a few motors sleeved for a reason. i like sleeves myself.
 
Why not run shorter pistons that are made for a decked block? Not sure how much shorter you would need but I would rather do that than shave the pistons and they probably come in .030 over.
 
guess I never checked to see how much room was under these pistons. I know that to shorten rods they bore the rod end slightly oversize and then machine the bushing with an offset to it
 
thicker head gasket,lowering piston,shortening rod... all will reduce compression ratio, but it will also remove quench area, resulting in a lower power producing engine. better to mill the valve seats to get a wider throat around the valves, and improve airflow while reducing the CR...
 
I have experienced more power with quench area increased,and it also helps eliminate carbon build up.
 
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