High Compression Pistons

[fox]

I can't answer the original question.

I can add that the gas counterparts were run as high as 12 to 1 until they wanted a broader power range. Then they went to roots type blowers and 8 to 1 compression.

Even the top fuel cars, who run a huge boost number run 7:1 Or 8:1 compression.

Raising the compression on a Cummins ( or any diesel) from stock will require boost to be limited below stock capable numbers.

 

[Forrest Nearing]

you're going in the wrong direction... if you want power, lower compression reduces stress on components!



lower compression in a forced induction application makes the engine effectively "larger" at a given static cylinder pressure as you increase boost to level out the dynamic compression ratio.

 

[Bugracing]

There are several custom piston manufactures out there: Arias, CP, JE, Ross, Wiesco... . Most os them can build a piston to your specs, but I have only seen Ross and Arias mention diesel applications.

Moonranch: thank you for your input. I have not yet contacted these companies yet as they do not have diesel / Cummins applications listed.

Many thanks also for staying on topic.





As for the higher EGT, there is a higher EGT at the tailpipe because of the DPF. that is why "cooling" slits have been cut into the exhaust pipes right before the tailpipe tip.



Again, everyone's feedback on compression ratio changes is much appreciated and it is always nice to see everyone's philosophy on this topic.

 

[AH64ID]

As for the higher EGT, there is a higher EGT at the tailpipe because of the DPF. that is why "cooling" slits have been cut into the exhaust pipes right before the tailpipe tip.

I am not refering to the 6. 7, which is the only cummins with a DPF, but to the 5. 9, specifically the 04. 5-07 5. 9. . where they OEM EGT's get way above 1400* due to retarded timing...

 

[KLockliear]

If one takes a look at younger (current) diesel engines it is very obvious that compression ratios have been dropping.

Actually, compression ratios have been INCREASING. Current model trucks are 17:1, where a 2000 24v was 16. 3:1.

I have not yet contacted these companies yet as they do not have diesel / Cummins applications listed.

Most companies can't/won't build a Cummins piston due to the fact that the aluminum casting/forging has to go around a steel insert.

As for the higher EGT, there is a higher EGT at the tailpipe because of the DPF. that is why "cooling" slits have been cut into the exhaust pipes right before the tailpipe tip.

Actually, the max accepted TIT (turbine inlet temp) or "pre-turbo" EGT as spec'd by Cummins increased with the CR motor in 2003 to 1450*F from the previous 1250*F. In 2004. 5, with the 325/600 motor, it went up again to 1550*F. DPF didn't come into play until 06.

 

[AH64ID]

Actually, the max accepted TIT (turbine inlet temp) or "pre-turbo" EGT as spec'd by Cummins increased with the CR motor in 2003 to 1450*F from the previous 1250*F. In 2004. 5, with the 325/600 motor, it went up again to 1550*F. DPF didn't come into play until 06.

Where did you get this info? I can't find anything on it, and cummins told me the max TOT was 1050*, and that the incylinder temp was approx 1350*.

 

[KLockliear]

From some people at Cummins. TOT is not something we want to use in the performance aftermarket. In cylinder temps are way higher than 1350*F as well.

 

[KHaines]

Im not sure why everyone thinks a Cummins can't hold together with a higher compression ratio unless the studs are added & bottom end built. I had a 6. 2 with 19:1 pistons that would peg my boost gauge(15 psi). The turbo that was on it probable put out about 20 psi. Stock headgaskets & only a girdle added to the bottom end. Why can a Cummins last with 19:1? If my 6. 2 could than my Cummins should. If it can than maybe I should just go back to a V8. My personal opinion is that 21:1 may be a bit much. But I like the idea. How much will it affect MPG? Would it be 10% or more? If so that would be a great option for someone who is rebuilding a engine for max efficency rather than power.

 

[Forrest Nearing]

a Cummins can hold more compression ratio, and if you're wanting more off-boost torque, and/or want some help at higher altitude? go for it.



but if the ultimate goal is POWER, there's simply no need, and going in the opposite direction will allow more power per a given peak cylinder pressure

 

[AH64ID]

From some people at Cummins. TOT is not something we want to use in the performance aftermarket. In cylinder temps are way higher than 1350*F as well.

I agree, but thats what Cummins puts out, the also specifically state they do not want customers having a TIT gauge.

 

[Forrest Nearing]

I agree, but thats what Cummins puts out, the also specifically state they do not want customers having a TIT gauge.

where is that stated? our industrial engines have pre-turbo specs, and the manfolds come pre-tapped for a pyro

 

[AH64ID]

where is that stated? our industrial engines have pre-turbo specs, and the manfolds come pre-tapped for a pyro

I have been told by several Cummins techs that they do not recommend pyros in the manifold due to pyro failures. Maybe thats just ISB, but its what I have been told... . but these are also the same folks that say the 325/600 won't go above 1350* cylinder temps.

 

[Forrest Nearing]

cummins techs are the lowest level... all they do is turn wrenches... There are some very smart ones, but there are plenty of idiots.



if the FAA approves pre-turbo thermocouples in airplanes, they're fine in your truck. You will have molten pistons, trashed turbine wheel, etc. before you'll hurt the thermocouple

 

[KLockliear]

To expound on what Forrest said, a Type K thermocouple is designed to accurately READ to 2502*F, so it will certainly live above that temperature.



Has anyone actually seen a thermocouple failure not caused by engine failure (parts coming out and hitting it)? I have not.

 

[ENafziger]

Has anyone actually seen a thermocouple failure not caused by engine failure (parts coming out and hitting it)?

I've seen two on engines we run at work. In both situations, the TC was instered about 4", and apparently after very high temps, heat cycles, and vibration, they snapped off. Both of these were pre-turbo, and fortunately, neither one got "eaten" by the turbine wheel before the engine was shut down.

I believe one was an Omega, the other Watlow, type k, 1/8", grounded tip.

However, we have thousands that have been used with no problem.

--Eric

 

[AH64ID]

cummins techs are the lowest level... all they do is turn wrenches... There are some very smart ones, but there are plenty of idiots.



if the FAA approves pre-turbo thermocouples in airplanes, they're fine in your truck. You will have molten pistons, trashed turbine wheel, etc. before you'll hurt the thermocouple

I guess tech might not be the correct term, its whoever you talk to when you call 1800CUMMINS, or whatever it is... you know where they read from a script...



And I agree completely, I have mine pre-turbo.

 

[Vaughn MacKenzie]

a Cummins can hold more compression ratio, and if you're wanting more off-boost torque, and/or want some help at higher altitude? go for it.

but if the ultimate goal is POWER, there's simply no need, and going in the opposite direction will allow more power per a given peak cylinder pressure

The discussion is about more efficiency and response out of the good ol' B series, not more power. I know it's hard to imagine modding a Cummins without any of the objectives being more power

 

[Forrest Nearing]

The discussion is about more efficiency and response out of the good ol' B series, not more power. I know it's hard to imagine modding a Cummins without any of the objectives being more power

man... I swear I really did read the entire thread... it just didn't compute!



in that case... yes, jacking the compression ratio a couple/few points will help a lot with off idle/off boost throttle response, and will make the truck feel "closer to the sea" when at altitude. make sure you've got head studs in it, and enjoy!

 

[Bugracing]

Forrest and Vaughn;



You have guessed right – my goal is to improve the pre-turbo/off-turbo efficiency of the 5. 9 liter common rail. This mean less reliance on turbo boost at low RPM and burning off more of the fuel already entering the engine.

This will be accomplished with higher compression ratio.

Yes – this modification will require other changes such as stronger head studs to hold the head on under stock level turbo boost.

The end result of this modification will more overall horsepower and torque, but more importantly, the engine will have improved responsiveness and will make more power pre-turbo boost.



Again, I appreciate everyone’s opinions on this topic, but the initial question was not about opinions but about locating suppliers of high compression pistons.

 

[KLockliear]

Again, I appreciate everyone’s opinions on this topic, but the initial question was not about opinions but about locating suppliers of high compression pistons.

I think I gave you this answer on post #25.