Piston Bowls

[Stingpuller]

Motors

Simon i agree it can be tuned out to not smoke. I never had any trouble with the low comp tuning wise I just noticed it didn't have the snap it had. My motor as it was run last year was 16.5 to 1 and I run 70 to 75 lbs of boost with no intercooler. That is with a single 80mm cast wheel turbo. I just don't see the reason to lower the comp and give up power. Now maybe if I was having problems with the bottom end then I guess I would have to drop it some. I think if you have unlimited air then lowering the comp and adding air will make more power.

 

[duratothemax]

http://www.youtube.com/watch?v=p2oy3pS59CA&feature=youtu.be

Watch and tell me if you still think low compression is laggy for driving. Ben, yours was laggy because of your twins, I had the same issue when I install MPI base kit on my truck and it took me a year to get them figured out and get rid of that lag your referring to. With a lower compression motor(if you have the parts combination set up right) you will get more work out of the fuel charge and that is a fact. That is where you power comes from.

I never had a year to figure the issue out, the motor blew up before I made it that far.

 

[duratothemax]

Jeff , I know your not into the tuning game. but changes can be made ( Ben as a tuner, beta tester ) should know this that adjustments to tliq, base tq will help spool timing adds or subratcts heat and then there is fuel press to stop hazing..... it can all be done!

simon you're putting words in my mouth.

im not saying its totally detestable or unlivable. Most people might not even notice it, but im picky....and I noticed it. Now that I live at 6,500', I would probably notice it more.

For a race truck going for ultimate performance/HP I would definitely run a lower static CR. But for a truck that I literally drive/use every day and maybe only really crank up/race every other weekend, id rather keep the snappiness of stock CR.

You can compensate a lot of it out with tuning, but that last little bit is just a trait of running low static CR on a turbocharged diesel.......

 

[ecc_33]

Eric, the haze at idle is easily compensated with fuel pressure, inturn the milage is done with fuel Vs boost

Its not a constant haze at idle. I already tuned that out. Lowered pw and raised rail pressure. Its when its cold. My truck hasn't been started in 10 weeks. I started it up last saturday. It was around 35* outside. It bellowed white smoke like a prostock pulling tractor for like 10 minutes. The warmer the engine got it finally went away. If I would have drove it down the road it would have been gone within 2 miles. Once the engine is up to operating temps ALL smoke is gone.

 

[bigmackmiller]

Good stuff in here :thumb:

 

[MarkBroviak]

I never had a year to figure the issue out, the motor blew up before I made it that far.

Yeah, that was a bad deal all the way around! As soon as I put the twins on my stock motor I wasn't happy with them at all becuase I was used to driving my truck with my 2.6 VGT Stg2 and it was very fast responding. Found that I was creating engine vacuum at throttle tip in and I fixed most of it by making a custom mouthpiece to flow more air to the small charger and upgrading the atmosphere charger to an 80mm. The exducer tip height on the 80 combined with its size increase allowed more cfm flow through the cover at very low shaft speeds and that got rid of 90% of the lag I was experiencing. Still was not as responsive as a high output single vgt but was way better than when I started with it.
If I do build another one I will be going down into the 14.5:1 range with it. If I was building one to run at stock or below power levels(Like Adam's over the road hauler) then I would leave the compression at stock LBZ levels. As soon as you want to really increase the hp and rpm then it is time to start dropping the compression. When the compression ratio is lowered, compression temperature and pressure at TDC decrease allowing you to inject more fuel and air for more hp. Consequently, ignition takes longer even when fuel is injected nearor slightly before TDC, enabling better mixture of air and fuel. This alleviates the formation of NOx and soot because the combustion becomes more uniform without localized high-temperature areas and oxygen insufficiencies. Furthermore, injection and combustion close to TDC result in a highly-efficient diesel engine, in which a larger amount of actual work (or, a higher expansion ratio) is obtained than in a high-compression-ratio diesel engine. Due to the fact that diesel engines generally have a high compression ratio, the compression temperature and pressure at piston top dead center (TDC) are extremely high. If fuel is injected under these conditions, ignition will take place before an adequate air-fuel mixture is formed, causing heterogeneous combustion to occur locally. As a result, the formation of NOx and, due to combustion with insufficient oxygen, the formation of soot are brought about. Hope this makes some sense to ya.

 

[ikeG]

I wish you would chime in on more topics, Mark!

Thanks.

 

[Vsouth]

I put some in mine.....

 

[emiller3]

15:1 here and no problems ,drive it every day to and from work. Mileage isn't the best but still is a touch over 17 mpg.

 

[Hot COCOAL]

15:1 here and no problems ,drive it every day to and from work. Mileage isn't the best but still is a touch over 17 mpg.

What size tires are you running? Are you lowered at all? I dont really drive to achieve the best economy, but it would be nice to know if i could.attain better mpg if i didnt drive like a fleeing felon all the time, i run a 285/70/17 right now(33) and i am getting about 15mpg mixed city/hwy, but mostly city type.driving with 100mph spurts as much as possible

 

[emiller3]

265/75/16 stock height and baby it,sometimes

 

[paint94979]

So from everything I've gathered lower compression pistons hurt fuel economy. Besides higher(stock LLY/LB7) compression pistons being harder on hard parts what is the fear of running them?

 

[blackdirtymax]

So from everything I've gathered lower compression pistons hurt fuel economy. Besides higher(stock LLY/LB7) compression pistons being harder on hard parts what is the fear of running them?

I would have to agree with loosing fuel mileage

 

[paint94979]

I would have to agree with loosing fuel mileage

Thanks Trey.

So I understand Fingers Oval bowl piston design are still in the testing phase however they are obviously proving to be an equal if not stronger design. We would you sacrifice fuel economy in a DD application when you don't have to with these pistons?

 

[malibu795]

i know i have lost mpg in mine... im not sure how much is engine and how much is winter fuel... since the piston went in the last week of NOV..

as for power the stock 4l85 is the limit.. looking at getting the truck dyno'd to see what its atually doing power wise.. the truck is already "turned up" last i looks stock pulse width for a van is 700uS and truck is 1350uS im running 1000uS

on timeing i can give a practicle example the timing is power...
with stock tables i run a 5% grade at 30-35mph and hazzy exhaust at night
with the added timing same grade same load i run it 65-70 mph.. everything clears up..only thing that was messed where was the timing tables

to me i rather push the piston down as much as reasonably possible to get the most out of the injected fuel..

 

[Fingers]

The pistons are out of "Testing" IMO and just gaining some real world time. The design has changed very little in the last year. And then, only to accommodate customer requests.

As far as compression ratios go, I suggest 16.5:1 for the daily driver. Higher and they tend to rattle too much for my taste and any efficiency is getting offset by ring blowby anyway. Lower, and you need to adjust the tune a bit and have some cold weather haze.

I am running 17.5:1 now and have been thinking of bumping down. If only to quiet the rattle. I can't imagine the rattle of 18:1's I just shipped out.

15.5 is about as low as I feel comfortable going with Cast Pistons. The oil gallery gets in the way of going lower without taking more material from over the pins.

The lower limit for the forged is still up in the air. I am currently analyzing the 14:1 pistons here to see what the trade offs are. 15:1 is easy and 14.5:1 are doable as of now with valve reliefs.

Mark is by far my best customer so far for these pistons. If you haven't noticed, he loves them, and I am tickled that he, and his customers are happy. They have added a comfort margin to his builds that he was lacking before.

 

[Aaron@LDS]

I'm throughly impressed with this site! These are the kinds of threads I like to read, and learn about. Real R&D goes on here, and I really appreciate you all sharing it with us that cannot do it.

:thumb:

 

[nwpadmax]

When the compression ratio is lowered, compression temperature and pressure at TDC decrease allowing you to inject more fuel and air for more hp. Consequently, ignition takes longer even when fuel is injected nearor slightly before TDC, enabling better mixture of air and fuel. This alleviates the formation of NOx and soot because the combustion becomes more uniform without localized high-temperature areas and oxygen insufficiencies. Furthermore, injection and combustion close to TDC result in a highly-efficient diesel engine, in which a larger amount of actual work (or, a higher expansion ratio) is obtained than in a high-compression-ratio diesel engine. Due to the fact that diesel engines generally have a high compression ratio, the compression temperature and pressure at piston top dead center (TDC) are extremely high. If fuel is injected under these conditions, ignition will take place before an adequate air-fuel mixture is formed, causing heterogeneous combustion to occur locally. As a result, the formation of NOx and, due to combustion with insufficient oxygen, the formation of soot are brought about. Hope this makes some sense to ya.

:roflmao:

Nice cut and paste from a Mazda ad.

 

[duratothemax]

:roflmao:

Nice cut and paste from a Mazda ad.

holy stranger batman! How you been Mat???

 

[malibu795]

holy stranger batman! How you been Mat???

no shit!!

see him once in a while on compD