Piston Bowls

[MarkBroviak]

How much of a gain did you observe switching from the 8460 to the 9100? Did it make more hp or just move it up in the rpm range?

Depends on the charger/motor setup but technically the 9100cam in a 2.5 truck was all motor becuase the charger doesn't keep much pressure build up but it wanted to run more rpm but was able to lug it better. Throw a 3.0 turbo and it really picks up power and rpm range everything else being the same. But, with out being able it try every cam with every parts combination it is difficult to give a 100% clear answer. The cam that is in my motor(6480) we weren't as happy with it in some pulling applications but it is awesome in my motor combo so idk. When we did tony's motor on the engine dyno it was clear tha there wasn't huge gains from one cam to the next but it just moves the curves around so you have to find the one that fits your combo and desired power/rpm range that it will be operated at.

 

[CurtisEmery]

Thanks I was thinking the same thing. I'm going to run my 6460 for this year. I don't want to change my operating range a bunch and then have to regear. Thanks for the info and sorry for the derail.

 

[duramaximizer]

Sorry but I will have to politely dissagree with all of you on this subject. By your thinking my 15.25:1 comp motor should be a laggy, smoky, cold weather hating machine and that couldn't be farther from the truth. There is soooooo much more that goes into besides the compression ratio.

Prove to me! I don't know a lot, but gassers go up in compression to make more power. Reliability would be the only reason for me to go down in CR from what i've seen dyno and otherwise.

Both apples to apples which truck puts down more an LLY or and LBZ compression being the only major difference. You should have some pretty fair comparisons on the books.

 

[malibu795]

Remember, the ultimate efficiency of the diesel is based on the "Ideal" engine. Reality gets in the way.

There are many reasons besides blowby that reduce the efficiency as you increase CR.

High on the list is heat transfer. At higher CRs the chamber temps are significantly higher than lower CRs. Since the transfer of heat from the charge to the piston and block and head is driven by the temperature difference between the two, you lose more heat energy to the engine at higher CRs. A lot more. Heat energy is, after all, where all the power is.

while i havent disclosed this.. part of my engine build... its my fault for not asking fingers if the pistons i was buying off him at the time was stock CH or .010 shorter (thus needing the block to be decked to maintain .010 protrusion).. come assembly time, i check protursion to find that im -.001-0.0 with the deck.. with C grade gaskets this not only gives me .040-.043" qench but according to fingers calcualtion drops CR from 17:1 to 16.5:1 under stock 16.8.

i am currently running a slightly modified tune from when the engine crack the piston... the VVT adjustment the josh H did to fix my WOT surgeing and timing at low throttle % ie less then 25%

things that effect power and mpg..
tuneing
fuel (summer/winter)
engine effeciency..
with almost just over 28,000 mile to date... i submit this... last week of febuary i saw the BEST loaded avg mpg of 10.7mpg 2400 mile to 224gl used. did some running around that weekend got 12.1mpg with no trailer
this week im solidly in the 9s 8.5-9 have been what i am seeing..
i have hauled two loads both in the 9k range and ~23,000lb GCVW
first one was load of sheet mettel 3'x3'x10' from butler IN to chester/richmond VA i ran down to US 35 down to Charleston and across I64 into richmond.. there is at least two 5 mile 7% grades 3-4 3 mile 6% and probaly some dozen or more 5% or less grades
the second load was a (case 465 skid steer) was out of apex NC headed up to nepoleon OH ran I40 to I77 to I64 to US35 to US23 through columbus ohio.. this route has fancy gap grade which is a 7 mile 6% at the NC/VA state line. and plenty of 5-6% all the way through VA/WV/NC
if you want to humor me take a look at a topo map of each route, its propbaly the hilliest interstate route east of the mississippi

with that said, with stock engine i never had a problem staying above 60mph on any grade except the 7% grades on either route and still manage 10+mpg doing so. i avg 11mpg in the month of NOV the engine died thanksgiving eve.. i have never seen single digit mpg from the stock engine..
deadhead (truck and empty trailer avg 13.5-14mpg)
stock would run fancy gap grade at 65mph in OD at 25XXXlbs fan would jsut start to come on in the last mile or so of the grade....
with current engine i cannot maint 60+mph on hills
this time up fancy gap im out of OD, WOT to maintain 55mph fan cycling on/off and im ~2,000lbs lighter.
i find the tranny downshifting more for hills then before and having to mentally think about driving, as in slingshoting down one hill to shoot back up another much like a big truck...

i think, the .043" quench(stock is between .015-.025" if i did my math right..) and .5:1 cr drop are both the main reason for power drop.. with winter fuel being right behind it for mpg/hp loss.. while 2mpg might not be alot(11 to 9mpg) for some.. i'll put it this way. @ $4.00 gallon avg 2mpg loss is a $0.05 per mile more in fuel cost.. at 30,000 mile thats an extra $1500.00 in fuel thus far and $5,000.00 per 100k miles.

im waiting to see what happens when summer fuel hits up here.. which will be about another 20k worth of miles on the engine.. and you get to see the burn pattern:thumb:

with that put out there.
i respectfully disagree with you and my real world expereince that less CR means better effcency.. isnt adding up... thus far... if you like i can dig up the mpg for ~45,000 mile the stock ran and the current one has ran

having ran gapless rings on gassers with pleasant results.. im very interested in running them on a diesel.. and IMO would be perfect time to swap the rings out..

by no means is this a stab at you, jon. you have reached your hand out farther then i have expected to help get me up and running and that i am deeply gratefull :beer:

 

[Fingers]

I don't know that these pistons are as efficient as stock. Probably not. Not enough miles to be sure. However, 30% drop in economy is not typical. Something is else is going on. IMO.

Since there are others out there banging around with these pistons. Anyone else want to chime in with their MPG?

I'm running around 17-18 MPG highway with the skinny tires 16-17 MPG with the fattys. Leaking intercooler and 100 over injectors. This is almost identical to the previous engine at 14.5:1 CR and all the same bolt ons.

Lets hear what others are getting MPG wise.

 

[Hot COCOAL]

Prove to me! I don't know a lot, but gassers go up in compression to make more power. Reliability would be the only reason for me to go down in CR from what i've seen dyno and otherwise.

Both apples to apples which truck puts down more an LLY or and LBZ compression being the only major difference. You should have some pretty fair comparisons on the books.

1) N/A engines go up in cr to gain power, typically boosted applications will have a lower cr to allow more boost and fuel into the cylinder, gas or diesel
2)as far as i know lly and lbz's use the same cr, just a different tune,that is how the power is different, not cr

I was moderarely suprised to read that the stock 6.7 cummins is turned up to like 19.7:1, which may be why dodges are so loud???

 

[malibu795]

I don't know that these pistons are as efficient as stock. Probably not. Not enough miles to be sure. However, 30% drop in economy is not typical. Something is else is going on. IMO.

Since there are others out there banging around with these pistons. Anyone else want to chime in with their MPG?

I'm running around 17-18 MPG highway with the skinny tires 16-17 MPG with the fattys. Leaking intercooler and 100 over injectors. This is almost identical to the previous engine at 14.5:1 CR and all the same bolt ons.

Lets hear what others are getting MPG wise.

at 300hp a ~10% hp drop is more vissible then at 700hp.. if the mpg doesnt come up with warmer weather and summer fuel.. im tightening the quench up. before next winter

 

[Fingers]

The limit on CR for gas engines is detonation. THAT is why they lower it in boosted applications.

Raising compression greatly improves the VE of the engine. Especially at higher RPMs. So going from say 8:1 to 10:1 would reduce the dead space in the chamber about 25%. This lets it breath better when spinning faster.

But the improvement is not so pronounced at our compression levels. Take the LLY at 17.5:1 for instance. Drop to 15.5:1 and the chamber has only changed about 15% for the same 2 point drop. The LBZ is only about a 5% increase from the LLY chamber size.

For all this talk about CR being great for economy, just look at the poor old 6.5s at 21:1 compression. Never saw anything close to my LLY's economy and they had iron heads.

 

[mtl_dmax]

For all this talk about CR being great for economy, just look at the poor old 6.5s at 21:1 compression. Never saw anything close to my LLY's economy and they had iron heads.

Correct me if I'm wrong but the reason for the old 6.5L getting worse fuel economy was the use of pre-chambers on the heads (less efficient design due to thermal losses). I think this is required for compression ratios above around 20:1 so it seems that the sweet spot for efficiency (CR vs thermal efficiency) would still be somewhere in the 17.5-18.5 range.

 

[Fingers]

Pre chamber was to keep the injector spray off the cylinder walls. Chamber in the head instead of the piston.

Sweet spot depends on the thermal losses to the engine. The more loss, the lower the sweet spot.

The lowest CR that a diesel is going to fire at is around 13:1. Starting a cold engine not withstanding.

 

[mtl_dmax]

Pre chamber was to keep the injector spray off the cylinder walls. Chamber in the head instead of the piston.

From what I understand putting the chamber deep in the head meant higher heat losses and as a result lower overall efficiency was it not? I thought this was also mainly because of the limitation of injection systems at the time (ie development of the high pressure CRD made now made this prechamber technology obsolete). Thus I thought going to direct injection CRD with chambers in the pistons then requires a drop in CR in order to have an acceptable balance of power, MPG, noise, emissions, etc.

 

[DMAXchris]

1) N/A engines go up in cr to gain power, typically boosted applications will have a lower cr to allow more boost and fuel into the cylinder, gas or diesel
2)as far as i know lly and lbz's use the same cr, just a different tune,that is how the power is different, not cr

I was moderarely suprised to read that the stock 6.7 cummins is turned up to like 19.7:1, which may be why dodges are so loud???

LLY has a higher CR than the LBZ.

 

[Bobo]

LLY has a higher CR than the LBZ.

There are two LLY versions offers in the pickup truck. There is the 04.5-05 LLY and a short run 06 LLY. The compression changed on the 06 version.

I'm not sure what version a 06 LLY van uses...or a 06 LLY Kodiak.....but I do know the pickup model was supposed to chang compression from 05 to 06.


Has anyone played with injector height to see how that changes mileage?

 

[Vsouth]

I have my truck back with fingers pistons in it. Only have 500 miles between half a tank and filling up. Will have preliminary mpg results is a week. This is a fresh motor though. Will need to be broken in good.

I am running twin's with 60% injectors and a cam. Looks like 15ish at the moment.

 

[juddski88]

There are two LLY versions offers in the pickup truck. There is the 04.5-05 LLY and a short run 06 LLY. The compression changed on the 06 version.

I'm not sure what version a 06 LLY van uses...or a 06 LLY Kodiak.....but I do know the pickup model was supposed to chang compression from 05 to 06.


Has anyone played with injector height to see how that changes mileage?

On a Cummins it has made huge differences, but they Dont have the tuning capabilities we do. I know different spray angles were tried, but who really knows anything these days...

 

[malibu795]

Correct me if I'm wrong but the reason for the old 6.5L getting worse fuel economy was the use of pre-chambers on the heads (less efficient design due to thermal losses). I think this is required for compression ratios above around 20:1 so it seems that the sweet spot for efficiency (CR vs thermal efficiency) would still be somewhere in the 17.5-18.5 range.

6.5 IDI in a DD application it wasnt uncommon to see high teens in a truck or 20 in a sub/blazer put any kinda of weight on it in towing your lucky to see double digits mpg you got BBC mpg without the BBC power..

IDI are generaly less effecient then DI engine prime example is the IDI 7.3 and the DI 7.3 powerstrokes

Bobo
one could legitemitly argue my injector tip is .020" or more out of the bowl then stock.. with the full width of a C grade gasket between piston and head.

hot cocoal...
the CTD are loud due to the weak/limited pilot timing setup and runing between 10-19* at idle.. mainly on the 12/24v setup the CR/CTD fixed alot of that noise

cut the pilot of a dmax and it will almost embaress a 24v at idle

 

[duramaximizer]

I was talking 05LLY to 06 LBZ . Not the tweener motors.

Stock pickup motors. Bolt up stage 2 danville chargers and big CP3's. where do they rate?

 

[whitelmmmax]

i have a good what if question. what if the injector nozzle was larger in diameter, with a more direct spray pattern downward into the bowl of the piston? Just something going through my head while im bored at work:roflmao:

 

[Fingers]

I have my truck back with fingers pistons in it. Only have 500 miles between half a tank and filling up. Will have preliminary mpg results is a week. This is a fresh motor though. Will need to be broken in good.

I am running twin's with 60% injectors and a cam. Looks like 15ish at the moment.

City? Hwy? Mixed?

What did you get before?

 

[bigmackmiller]

at 300hp a ~10% hp drop is more vissible then at 700hp.. if the mpg doesnt come up with warmer weather and summer fuel.. im tightening the quench up. before next winter

Why not up the power if your struggling to perform on the grades?