DodgeRam24V

i am replacing my 99's 53 block, what is the difference in HO pistons and 235 HP pistons?
the compression ratio is slightly higher in the HO, is it worth the change?

money is no object

edmeyers

Put RV 275 pistons they r partially coated

DodgeRam24V

would you happen to have a piston or part number?

edmeyers

I'll check

edmeyers

Here is an old email
From when I bought mine


No the grade A,B,C has to do with piston protrusion. You would either need to get the part numbers off your pistons and cross reference them over or measure your protrusion.




Doug Smith
----- Original Message -----
From: Ed Meyers
To: Doug Smith
Sent: Saturday, January 12, 2008 10:14 PM
Subject: Re: pistons

is the grade a the same as standard bore and b 0.010 and c 0.020 over or is that a quality of piston if so which ones do i use

On Jan 11, 2008 8:09 PM, Doug Smith < dfsjetpilot@isp.com> wrote:
· grade A = 3802927
· grade B = 3800333
· grade C = 3802929




Doug Smith



--
Ed Meyers
XtremeShowHorses.com
emeyers@xtremeshowhorses.com

Paoli, OK
405.620.6733

DodgeRam24V

is it worth the the added compression? not much of a change.
memory says: 16.8 to 17.2?? or something like that.

HOHN

HO is 17:1 on the button for a VP44 truck.

If you have any high performance inclination or are running more power than stock, use the lower compression pistons.

JH

Tate

SO CR is 16.3:1. HO has a 2mm narrower bowl. Takes less timing to spray outside of the bowl. The higher compression should help with bottom end and mileage. Zach Hamilton is testing out higher compression pistons in his 12v, coupled with a new, taller 5th gear for the NV4500.

HOHN

Higher CR can help a little with bottom end and MPG-- but the higher you go, the less benefit if offered by the next step up.

Peak cylinder pressure is also a huge concern with CR. That's why it's better to drop CR if you are going up in power at all.

No, it's not just headgaskets that are affected by PCP. At high PCP, the combustion face of the head flexes a lot more. This exponentially accelerates fatigue.

If you run really high cylinder pressures (lots of fuel, bumped up timing) at high loads (heavy towing), then you are begging to crack the head. Cast iron isn't a very ductile material, so it's not amenable to high cycle fatigue.

If you have a newer head with valve inserts, it doesn't take that much to drop a seat. We all know what happens then!

JMO

totalloser

Higher compression also affects cylinder temps. Pressure/heat failures become more of a risk.

Short answer IMO is that if you are going for a mild build centering around fuel efficiency, the higher compression will be superior. Not only torque and efficiency, but also LONGEVITY. A "tired" diesel engine usually is a low compression diesel engine. Valve seat/face wear drops compression making a high miler more difficult to start. Higher compression makes for easier starting.

High horsepower build with lots of boost and timing, I'd think you'd want lower compression.

As to grades, I could be wrong in this particular case, but generally "grades" of pistons refer to the diameter and are matched to bores accordingly. Machinework precision can only get so close, so pistons and bores are assigned grades to match them more closely.

Piston protrusion is usually accounted for by different thicknesses of head gaskets, and not always on direct injected engines since they are lower compression. IDI engines often have different thickness gaskets to accomodate dialing in the compression ratio after piston protrusion and valve depth is all set up since VERY small changes are drastic due to the higher compression ratio.

If I were to approach it myself with no budget considerations, I would consider NEITHER PISTON. I would get all steel pistons and fire ring/stud the head. Personally efficiency is more important to me so I'd go higher compression but if going twins or something obviously that wouldn't be the route to go.

The weak links generally are the head gasket and piston when you reach high cylinder pressure, so this would address these issues and allow a significant bump in egt survival. In short more cushion before a eroded/melted/cracked piston or a spit/melted head gasket.

Tate

Cummins uses 3 grades of pistons for accounting for piston protrusion. All available in STD, 0.5 and 1.0mm overbore. You can get thicker gaskets, but those are in .010" increments. The grades of pistons are of a smaller variance.

DodgeRam24V

Thanks guys.

i think i will just stay with my old compression ratio. the truck pulls a 44 foot goose-neck trailer to and from race tracks, no racing or pulling with it, i am very happy with the power it has now.

i may sell my 01 that also has a 53 block then put the Quadzilla in the 99 some day?

last question, do you use the stock thread head studs? and is the genuine Cummins head gasket the best to use?

Mike Holmen

Are you planning on decking the block? Usually cummins 5.9L need 1-3thou cut on the deck, to get them true again. Like Tate said the HO has a narrower piston bowl than the SO. Also have the cylinder bored to mid grade specs. To tight of piston to cylinder clearance, you'll get piston skirt damage. Carefull on what cam bearing you buy, typically the machine shop puts in the wrong bearing, either you have to much bearing clearance or its really tight. I've must have built a half dozen 53 block engines now, no issues. Have the machine shop do a manuflux checks and pressure test the block. New frost plugs should be staked in, new ones have issues with them popping out.

Any QSB marine pistons that I've bought never came with ceramic coating, they typically have more heat treatment cycles for less expansion. I would run the SO pistons and measure your piston protrusion. There are better ways to get fuel mileage improvements.

Remember valve seat placement effects the valve spring seat pressure. If the valve sits to high on the seat, chances are you'll have valve spring binding issues. If the valve is sunk, you'll issues with not having enough seat pressure on the valves.

edmeyers

If I remember right spec on protrusion is 22 to 24 thou

You need to check both front and back of the pistons

I run a 20 thou over head gasket