Diamond Pre cup questions

[83Blzr62]

I bought 6.5 head for my 6.2. They were rebuilt by a good shop in town but the original purchaser backed out so they sold them to me for 400, with the valve liners in the cooling passages and everything new. They have the 2 dot precups. They were resurfaced so if I wanted to put diamond pre cups in them they would need more machine work to fit. What kind of gains could I expect when using diamond pre cups over the others? Would it be worth the extra work?

[More Power]

Smaller port pre-cups deliver better fuel economy - larger ports enable more boost & fuel (power)... How much of a power difference? When an engine is built to deliver up to 200-hp, probably not very much. If your goal is above 200, then it might be worth using larger pre-cups - at the expense of fuel economy.... I don't know of any data that compares the two extremes - except for personal experience with two engines built to opposite ends of the spectrum.

Jim

[Bnave95]

Smaller port pre-cups deliver better fuel economy - larger ports enable more boost & fuel (power)... How much of a power difference? When an engine is built to deliver up to 200-hp, probably not very much. If your goal is above 200, then it might be worth using larger pre-cups - at the expense of fuel economy.... I don't know of any data that compares the two extremes - except for personal experience with two engines built to opposite ends of the spectrum.

Jim
What pre-cup came with the f eng?

[Robyn]

Just my observation
My 94 had single dot precups when I overhauled it recently. The heads were junk so I used a set from Clearwater. The ones I got had the single Diamond on them. The truck runs sweet and so far I cant tell the milage but the power is good.
The 6.2 is not going to benefit much from the large cups.
Turn or have turned up your pump to J specs if its not already and do an exhaust system that flows good and thats about all you can do for the little diesel rat.

[83Blzr62]

I am doing an entire overhaul for power. It is an 82 red block with 19.5:1 compression ceramic coated pistons, gm - 4 turbo, with 3-4 inch exhaust, 4911 injection pump, turbo inejectors, stud girdle kit, timging gears,serpentine system, high flow water pump, and duramax fan, so i guess I will go with the diamond turbo pre cups. My original plan a year ago was just do a rebuild for relaibility with no turbo, then I found a rebuilt turbo for cheap and one thing led to another. I was hoping to have it done by august but now I have to wait until Christmas break because of parts issues. I guess that is the nature of the beast.
Thanks for the advice,
Kyle

[More Power]

Turbocharged engines came with cups designed for use with a turbo. The "F" cyl heads I've seen had the "T" pre-cups (shown on the right side of the photo in the recent 6.5 cyl head article).

Jim

[john8662]

A '96 Vin F engine that I recently disassembled had small cups in the heads. But... I can't swear the heads were original, as the gaskets were not.

The exhaust valves were stamped "T", so I assume that these were the appropriate turbo heads, but then again Vin S engines are turbo and have the smaller cups.

[Bnave95]

Just my observation
My 94 had single dot precups when I overhauled it recently. The heads were junk so I used a set from Clearwater. The ones I got had the single Diamond on them. The truck runs sweet and so far I cant tell the milage but the power is good.
The 6.2 is not going to benefit much from the large cups.
Turn or have turned up your pump to J specs if its not already and do an exhaust system that flows good and thats about all you can do for the little diesel rat.
Have'nt done a milage check yet? Your Eng. is probley still in the brake in mood.

[arveetek]

Kyle,

I just used the stock precups in the '86 C code heads I ended up using. I'm really happy with the power output of my engine now...don't really need any more power. I just need a better way to transfer the power to the ground, such as through an NV4500 or Allison. Looks like your engine is pretty much going to end up like mine.

Casey

[john8662]

Use caution with heads that have been surfaced, especially if they surfaced the head with the cups installed. You won't have the ability to swap out new cups into those heads if the existing cups were shaved in the head.