How Much Power Is Lost Due to the Friction Of The Piston Rings?

GM doesn’t publish an exact LT4 ring-friction number, but we can estimate a realistic range from ring-friction percentages and the LT4’s 650 hp rating.

1. Baseline: how big is ring friction?

• EngineLabs reports ring packages can be about 37% of total engine friction, and that total internal friction can be up to ~40% of brake horsepower; they conclude ring friction alone can consume up to ~15% of BHP in some engines.

• JE Pistons notes that 50–60% of total engine friction is piston+rings, and about half of that is just the rings, implying ring friction of roughly 12–15% of total friction and several percent of total power.

• Total Seal cites studies showing up to 45% of engine friction can come from ring–liner contact.

Modern direct-injected LS/LT engines use very thin, relatively low-tension ring packs (e.g., 1.0/1.0/2.0–3.0 mm), explicitly to cut this loss versus older 1/16–1/16–3/16 sets.

2. Applying that to a 650 hp LT4

The LT4 is SAE-rated around 650 hp at the crank in Camaro/Corvette/Crate form.

Using a conservative, modern low-friction assumption:

• Suppose ring friction accounts for about 5–10% of brake horsepower in a late-model, thin-ring, low-tension, roller-cam, synthetic-oil engine like the LT4 (less than the “up to 15%” worst case older engines, but still a big piece of the friction pie).

Then:

• 5% of 650 hp ≈ 33 hp

• 10% of 650 hp ≈ 65 hp

So a realistic, order-of-magnitude answer is:

• An LT4 likely “loses” on the order of 30–60 hp at the crank to piston ring friction, with a reasonable central estimate around 40–50 hp under peak power conditions.