hi guys, this is our first thread started on here, we are not international IDI owners, but when it comes to upgrades, all the IDI platforms benefit in a similar manner... with that being said, i am interested in what kind of thought and research has gone into precups, both stock and modded.....

in the detroit diesels, there have been many different sizes and cups used, the first ones being the small c-code(emissions), great for economy, buts lacking in the performance departement, next being the standard j-code 6.2l ones, good all around N/A cups, although prone to cracking past the fire ring when stressed for a turbo app.( we have changed out these ones twice on one of our motors due to compression starting to leak into the coolant) next we have 6.5l N/A, these are slightly larger than the j style, used in vans, and the N/A version motor for the military, next we have the first version of turbo cups, t-cups, these are good cups for power, although they can be stressed past the limits in high boost app, then we have the current diamonds( called this for the diamond stamped in the faces), these are also machined more inside for dropping the compression down a point on the newer (96 up) engines, and make decent power, and are the chosen by those who are doing rebuilds......

currently we are running a set of modded diamonds, which have had the "mouths" machined back .010" on each side and blended back inside to increase flow, low smoke and a definite improvement in low to mid range power....

so, who has experimented with precups, what differences have you noticed? also on a side note, would be interested to know the actual physical dimensions between the navi ones and the detroit ones, later here i will do some measuring and post up our detroit dimensions.... thanks....J&J....

EDIT: tried starting this topic on the OBN about 2 years ago, and there was minimal interest in it, but from seeing what goes on here i think it will be an interesting discussion...

 

I briefly came across some information a while back on pre-cups and performance and I am not familiar with performance directly related to pre-cup selection/mod- I am interested in the topic. I'll do some research on the matter. Good luck.

 

I read some where that one guy homed them out to and had very bad results.
Then a friend told me to put a groove in them, now the doesn't remember where it was so I can't fallow up.

 

we have a set here that are un tested up til now, bored them straight on the sides, started at zero up top, and milled them almost .040" at the bottom, plus took .010" off the "floor" of the cup, we spec'd them at giving 1 point of compression drop, also opened the "mouth" up almost .015" each side.... when we assemble the motor and run it, we will come in here and post pics and a vid of how it runs... we are not shy to post up results whether good or bad, this is how things can be changed and modified for the better, when everyone shares results, whether good or bad... looking forward to what you find out....

 

For ~our particular engines it seems that the pre-cup design is pretty good, and most who are seeking performance are working on other things... But there was a pretty thorough thread on our pre-cups on PSN a couple years back. Check it out...

Pre-cup size fuel charge ratio request for review and ideas [Archive] - PowerStrokeNation : Ford Powerstroke Diesel Forum

 

The Pre-cups are a touchy issue, and I know you GM guys are more **** than we are.

I was going to try the 7.3 cups in the 6.9 heads on my new engine, but couldn't find my 8th 7.3 cup, and the heads had to go to the shop. That being said, I think there is more to be gained with having a large throat with a small chamber volume, and a high pop pressure. The 7.3 cups only differ in the sense that they have a broader throat, the volume is the same. The volume difference is in the head casting.

My opinion is this....

The Displacement is a constant.... The prechamber volume is a constant... The throat orifice is a constant.... Our variables are fuel, air, RPM, and injection duration. I think that the constants can be "pushed" against by manipulating the pop pressures and timing advance to fit the other variables in the mix, resulting in a more tuned setup. It is much easier to change the injection duration through pop pressure, than tune the combustion event through a different size precup.

 

So where are you Racin, you should be in Arizona by now. Hows the truck doin?

 

Ill update my thread here in a bit.....

 

these are the 3 dif pre cups for are motor, 7.3 6.9 an 83 6.9. the 83 seems to have the biggest throat an lowest compression

left is the 7.3 - 21.5:1CR , middle is the 84+ 6.9 22.5:1CR , right is the early 83 6.9 20.7:1CR

the 7.3 cup is 20.42cc's, the middle 6.9 cup is 18.34cc', an I am not finding any info on the 83