• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Looks like i have a problem

Ya shop wasn't really sure what would cause it. I also found 3 new main web cracks in the old 599, thinking its headed for scrap pile. I did find a sweet deal on a amg optimizer block with a casting of 02 but that will be in a different thread

Sent from my SM-G930V using Tapatalk
 
chevyCowboy said:
Ya shop wasn't really sure what would cause it. I also found 3 new main web cracks in the old 599, thinking its headed for scrap pile. I did find a sweet deal on a amg optimizer block with a casting of 02 but that will be in a different thread

Sent from my SM-G930V using Tapatalk
Click to expand...
Yeah, sounds like it's trying to implode itself. That block's gone through a lot in its life.
 
Im dropping the new block off at machine shop tonight so im sure i will pick up the junk heads and post some pics. The heads i got with navistar block have a date stamp of 99 so i would guess they are just gm heads

Sent from my SM-G930V using Tapatalk
 
I have seen all the different heads out there, the best are the p400 heads, I have cut them apart and shown the differences, yea they are more money but ya get what ya pay for... If rebuilding these motors and going with a better turbo, more fuel etc, you should lower the compression, a 21:1 motor builds so much cylinder pressure that it kills the parts in short time.. in stock form they break under normal driving, add more air, fuel,boost and the like and breakage will ALWAYS follow...
 
The Kennedy pistons are a very good design and he now offers them again, the same shop that is machining them will be machining mine for the p motor, there is a some what long lead time as they are machined when ordered.. and I will be doing the coating for them also...
 
sctrailrider said:
I have seen all the different heads out there, the best are the p400 heads, I have cut them apart and shown the differences, yea they are more money but ya get what ya pay for... If rebuilding these motors and going with a better turbo, more fuel etc, you should lower the compression, a 21:1 motor builds so much cylinder pressure that it kills the parts in short time.. in stock form they break under normal driving, add more air, fuel,boost and the like and breakage will ALWAYS follow...
Click to expand...

Does the lower compression cost MPG or power? Sure the turbo makes up for it. Just that power is from compression to a point: where that point is diminishing returns and need for cold weather starting requires high compression regardless? Asking for your thoughts/take on the question esp. since the high compression 6.2 started as a NA design.
 
No, the lower comp doesn't hurt anything, it helps everything, what does it take to make power... air & fuel.. the more you have of each the more power you have ... fact... less stress on the entire system, including back pressure, the added volume needs a p;ace to do it's work...

Ever wonder why the big 3 diesel makers dropped their ratio's ?? You can only force so much air & fuel into a given space, give a little more space and ya gain more...

I couldn't see any difference starting in cold temps, I think most have the impression dropping the compression causes lots of trouble when it just isn't true, all hear say....

I can say this as a fact, with the stock compression if ya add a bigger turbo, add more fuel, sooner or later things will break, this isn't a motor that can take that in stock form, and don't think head studs is the cure either, it's just a band aid, the stress will find a way out...
 
sctrailrider said:
If rebuilding these motors and going with a better turbo, more fuel etc, you should lower the compression, a 21:1 motor builds so much cylinder pressure that it kills the parts in short time.. in stock form they break under normal driving, add more air, fuel,boost and the like and breakage will ALWAYS follow...
Click to expand...

What is the best method of lowering the compression?
 
1994ch said:
What is the best method of lowering the compression?
Click to expand...

The pistons will need to be machined..... the thicker gasket will only get around 1/2 a point, the gaskets are designed for use when a head or block has been lightly cut, the .010 is nothing when attempting to drop 3 points compression...
 
For those interested here is a flow chart that shows cylinder pressure, the inputs can be changed so you can see different numbers, and see the effect boost and compression has vs cylinder pressure.
 

Attachments

  • Engine Pressure & Flow Calculators-Ver1.2(1).xls
    73 KB · Views: 10
You can also use marine pistons. Half a point is still half a point with the thicker gaskets. Many on here have used them in their builds to drop compression with no ill effects.
 
Husker6.5 said:
You can also use marine pistons. Half a point is still half a point with the thicker gaskets. Many on here have used them in their builds to drop compression with no ill effects.
Click to expand...

I didn't say they weren't ok to use, just isn't going to achieve much...

And there is the old way of cutting the tops off, I don't have any reason to care how someone decides to do it or if they decide to at all.. I do think that keeping a squish band on the tops provides a better flame path, and the cut that kennedy uses is the best I have seen so far, but that's just my opinion...

And ya know what they say about opinion's right :brb:
 
Stock marine pistons are like hen's teeth to find anymore. I just don't sit well with the idea of taking more material off the face of these stock comp pistons. Wish there was enough of a demand to get Mahle to design a new lower comp piston casting for the 6.5 in stock, .010, .020, and .040 over.
 
I never did long term runs on low compression 6.5. We dropped the 1/2 by oversized gaskets, maybe. Really we were over tightening the studs so that why we ran them. Later the fat, comies but those are not good for more than 100 miles anyways.

I always like the higher compression and less leaning on the turbo, but if I understood turbos better it might change my mind.

I never did see engine comparisons of only compression drops. It would be interesting to see before and after numbers with no other changes.
 
Just a little more info for this thread...

ALL boat 6.x motors have dropped compression, 18:1.... and they use 160* t-stats...

The dropped compression has been shown to build more power & have less stress when the motor is under WOT for extended times, like a boat is....
 
Yesterday I was at a store and saw a guy fighting with a liftgate on his truck. I walk up and asked if I could show him an easier trick I learned. He said a line we've all heard before "I've been doing this 20 years." To which my favorite response is usually "You've been doing it WRONG for 20 years mother f****r !!!" To him, since he was polite, I skipped the last 2 "non church words". Then I said let me show you- now his job will be easier time he uses it.

I have always held to the thought of keep the pressure high, and need less turbo. As I read your last point and think to myself, yes that works, but if you just kept the pressure up like I have for the last 20 years...Then I hear my son in the other room laughing as he repeats the words I said to his friend telling the story.

It takes hearing my own words at the right time sometimes to consider. Have I been doing it wrong for the last 20 years?:nailbiting:

I am very reluctant to give up the power in compression. I know I don't want to for the hummer until I can fit a real turbo and compensate. Are there builds done still running a gm6 with higher boost numbers and maybe a wicked wheel that can compensate the loss?

I am going to print out the charts you posted and study them till more clicks in my head. I have great concearns about worn rings dropping compression on already lowered compression and hard starting. I get when everything is new it will fire easy. But once there is 150,000 milesor more on it...??

My mercedes diesel is the great 6 cylinder that has 22:1, the only one touted as a better long life is the 5 cylinder om617 which has 21.1:1. I know different designs on many things, but the same idi, piton top, injector style, precup style, crank to rod/piston weight ratio,bore to stroke ratio,... basically Detroit/GM copied all the key factors from the 1970's Mercedes Benz design table and made it a v8 for GM to work off of. Then GM made multiple key changes, all of which are the problems we all know of today. Idk, have the MB guys learned to drop there compression also? Some reading in my future.

I am trying to accept what you are saying, but hard to swallow this pill. A more open mind is going to read on and try to find old 6.5 info... please continue to share:wideyed:
 
You must log in or register to reply here.
Back
Top