Benefits of Cam Swap

[SDunkle600]

I am looking for the pros and cons of doing a cam swap. I found a few posts on this in the third gen forum and several in the second gen forum. I know that with the 04. 5s-up the timing is greatly retarded (no pun intended) and a cam PDR or Helix H2, could advance the valve timing much closer to ideal for efficiency. I want to try to understand the good and bad to doing this though. I understand Cummins has a complicated combustion process and I am hoping some of you guys can shed some light on this.



Thanks



-Shannon

 

[RobertP]

well some postives on this subject are that a cam will lower your EGT's and improve spool up.

 

[SDunkle600]

Thanks Robert. I was also wondering if there are any pros or cons with the reliability of the engine. If dwell time is increased via the cam, wouldn't that build greater cylinder pressure by holding valves closed longer? I am still pretty new to diesels.

 

[PRattenbury]

Then you have the question of all questions. Do you buy a reground stock cam or one cut from a new blank? And who sells which?

 

[WUnderwood]

the only one that I know that uses a new blank is Formula 1 Diesel

 

[JHardwick]

The only way to get a radical grind is to start from a fresh blank.



Or, go to a smaller circle with longer pushrods on an existing cam.

 

[Morse]

I have had distributers tell me different stories. . Some say it makes a very noticeable difference, some say they see very little if any difference at all. . I guess if I end up with EGT problems or spooling issues with the new combo I'll find out. .

 

[Matt400]

the only one that I know that uses a new blank is Formula 1 Diesel

PDR's cam for 3rd gens is new. They couldn't get the grind they wanted from a re-grind.

 

[OT-OF-HERE!!]

Sorry, but not so,.....

The only way to get a radical grind is to start from a fresh blank.



Or, go to a smaller circle with longer pushrods on an existing cam.

Your statement about the radical grind is only possible from the fresh blank is incorrect according to both Don M and Greg Hogue. There is a whole evenings reading over on Competition Diesel under the Dodge segment about this where they compare the Helix and Maxspool and there is a wealth of info on every aspect of cams. Now be ready for some jabbing at one another but you filter all that out and there is a lot of info and both obviously have outstanding products with very few failures. It depends on what your specific needs are as to which will serve you better.

 

[JHardwick]

Your statement about the radical grind is only possible from the fresh blank is incorrect according to both Don M and Greg Hogue.

I haven't read it, but after years of reading on the subject you have to grind to a smaller base circle and lengthen pushrods ... ... ... ... . or add material by spray welding or some other sort of overlay.



No way around it, you only have so much material to work with.

 

[Matt400]

I would think it has allot to due with what cam you start with.

The oem cam I pulled out of my 05 has a much larger diameter than the PDR I installed.

The PDR cam is actually a Cummins blank to begin with, just not a late model blank so its much skinnier. PDR gets them with the journals finished but not the lobs, and grinds from there. It even has a Cummins part number stamped on it.



I can't envision a way to regrind the 05's cam for the same lift, its just too fat. I didn't need longer push rods but the adjusters had to move a long ways to make up for the skinny shaft.

 

[WUnderwood]

PDR's cam for 3rd gens is new. They couldn't get the grind they wanted from a re-grind.

yeah, sorry, I forgot about them

 

[OT-OF-HERE!!]

This isn't a quote, but an interpretation....

Of the Comp Diesel Forum thread. The larger the lobe size then the LESS agressive the grind. I'm no subject matter expert but that's the jist of it. The quicker the ramp design then the more agressive the grind as the valve is opening and shutting quicker. From what I gathered then we should be especially interested in how quick the exh valve closes as that will increase spool. So the advantages of the diesel cam is not necessarily hp increase, as I've read several times per Don M that the hp increase is in the 20hp range. What I noticed with mine is better spooling (exh valve closing quicker), a much smoother idle, generally an engine that sounds more in sync, and reduced EGTs. I no doubt missed something that someone more expert than myself will tell us for sure.



Also the comments about rocker ratios,. . extended push rods and such are gasser mods and certainly work well but not on a diesel with the tolerances sooooo darn close. Another key issue that both Don and Greg made crystal clear was that we all need heavier springs. Fact. The number one weakest link in the Cummins, per Don is the valve seat issue and that is primarily caused by toooo weak of springs. A number of guys Don spoke of that did no more than change their springs had very positive results in performance and egt control. It would appear that it is a simple fix as you can easily do it with little labor as from what I understand the piston can be brought up to TDC and you can depress the stocker and replace it with the hp spring. The tolerances are soooo close you don't need air pumped into the cylinder to hold the valve up as in a gasser. The valve will rest against the piston at TDC. This is all my take on what I've read but I did change mine, fyi. Hope some of this helps others with their decisions.

 

[SDunkle600]

Thanks all for your responses. I had read issues with springs and cam swaps. I didn't realize that just swapping out springs would make much of a difference with still using the stock cam.

 

[MrBee]

A valve only works if it is seated and with the currnet boost pressures and moving mass, valves with low seat pressure will float and that may actually cause the seat to burn. Once that happens tough to get a good seal afterward.

I read that the cam change can net up to 2 mpg, increase torque and generally make it run smoother. The factory valve timing is what it is not because it is the best performing grind, but the best that EPA will allow. They have many masters to answer to so compromises should not surprise anyone.

 

[Matt400]

Of the Comp Diesel Forum thread. Another key issue that both Don and Greg made crystal clear was that we all need heavier springs. Fact. The number one weakest link in the Cummins, per Don is the valve seat issue and that is primarily caused by toooo weak of springs. A number of guys Don spoke of that did no more than change their springs had very positive results in performance and egt control.

What is happening with the valve seats?

It would appear that it is a simple fix as you can easily do it with little labor as from what I understand the piston can be brought up to TDC and you can depress the stocker and replace it with the hp spring. The tolerances are soooo close you don't need air pumped into the cylinder to hold the valve up as in a gasser. The valve will rest against the piston at TDC.

Hrmm... didn't know that, seems the valve would need to be closed up all the way to get that done and if the clearance was that close any valve float from weak springs would result in bent valves. Thanks for sharing what you have checked out.

 

[SDunkle600]

I was also wondering how valve timing related to injection timing? Meaning that if you advance injection timing via hacked CPS, tone ring mod or even bigger injectors then put a performance cam in, how do they work together?

Sorry for all the quetions, just trying to understand how a diesel engine works a little more.

 

[DerekW]

well some postives on this subject are that a cam will lower your EGT's and improve spool up.

now for the biggest CON: your pocket book immediately after. i hope you dont have a wife that does all your accounting!!! she may not allow unless you pull the ole truck broke down had to get it towed to the shop game.



wade dont say a word!!!!

 

[Tinman]

Yes it is expensive, but the improved mileage should pay for it. There was an article on this in a recent TDR mag about the PDR cam. It gave a solid 2 MPG increase. This would pay for itself is 40-60K miles depending on how you calculate it. This, plus the inhanced drivability and quicker turbo spooling, has me thinking hard about this mod. The valve springs do increase the cost but might as well do it right.



I am also interested in the above stated question about valve train timing and injection timing.



Speaking of mileage, does a good honed or edm injector tip give a significant mileage improvement? If your gonna tear into the engine, might as well do it all at once.

 

[wcjp]

I was seriously considering a cam swap. Smarty was cheaper and also resulted in lower EGT towing and improved mileage.