Precup's

[LUCKY_LARUE60]

I was wondering what would happen if you remove the plate that covers the precup chambers and installed the heads how that would effect the motor. I know it would lower the compression but how much, I am sure it would be hard starting? Just thinking, what is the purposes of precups any way?

Jim

 

[typ4]

The headgaskets wouldnt seal for one.
They are to create a high temp ,high swirl area for the fuel to ignite in. Read that in an old Buda engine manual.

 

[Diezel_Cowboy]

But first a story:

..................... The atf pours out directly into the vessel which is gravitationally aligned with the port in the trans, which happens to be my left eye. My exaggerated motion for head removal then removes my eye from strategic bombing and replaces it with my left nostril followed by my front teeth which I found out were exposed because of this annoying habit of mine of having my mouth open while under duress.

Then app. 2 qts of atf spilled on the driveway.

So my left eye now matches the stain on my sweatshirt.

Good start, eh?

Very nicely said.........enough so to make me laugh!

 

[tractorman86]

it's christene reincarnated!

 

[Agnem]

I was wondering what would happen if you remove the plate that covers the precup chambers and installed the heads how that would effect the motor. I know it would lower the compression but how much, I am sure it would be hard starting? Just thinking, what is the purposes of precups any way?

Jim

Perhaps a baby step would be to open up the hole in the precups and see what happens then. That would solve the sealing issue. I think it would decompress a good bit since you would be making a good bit of room for more air to compress into.

 

[92F350CC]

Reckon that if this works out, it'll be the key to 350-400 hp IDIs?

 

[Ironman03R]

If you look at the big picture, that hole in the precup is the restriction in these engines, ALL air has to pass through it! I think opening the size of it would allow the engine to breath better.

 

[Optikalillushun]

Hrm...perhaps u are on to something here?

 

[tractorman86]

i always wondered about that but didnt want to front the bill to find out!!

 

[tractorman86]

hey looking at a set of reman heads at our shop , the precups look to be pressed in, if so i'd like to get ahold of a set of two and modify accordingly if they are not too spendy

 

[sootman73]

im havin a hard time picturing the precups. does any one have a picture and an explanation as to what they are?

 

[tractorman86]

ill try to put up a pic today

 

[sootman73]

thanks

 

[icanfixall]

Don't mess with the precups. All the air does not flow thru them at all. The air into the cylinders flows in thru the the intake port. Then the piston comes up pushing just some of that air into the precups. Then the injection pump while being timed properly forces a measured amount of diesel into about 950 degree heated "air" where it ignites. Thus causing a burn that rushes out that small opening. The precup has some design built into it to create a swirl patter so we get a better burn. Now it you try to open up this tiny port in the cup you will need a compatator tool so you know each port is exactly the same. Otherwise the power made by differant port openings will cause a power balance problem. Kinda like one cylinder wasn't getting the same amount of diesel or air. I tried this on my firts heads. I didn't like the "feeling" it made and I did have the comparator machine so things were as close as possible and equal in all respects....

 

[Ironman03R]

Icanfixall, I remember reading that you did this on the first heads, do you know how much you enlarged the hole? Also, did you change the shape of it any? I understand what your saying about not all the air flows through it, but I'd say about 80-90% of it since there is no combustion chaimber in the head and the pistons do stick up out of the block some. I guess what I was getting at is when the piston comes up, where does all the air go?
Through that hole into the precup.
From my research I found that the turbo 6.5 GM's have a larger and different shape hole into the precup. Since the 7.3 was never really designed for a turbo, all the cups were the same, so my thought is, why did GM change the design with the addition of a turbo?