Un-throttling a V8 TTurbo with AFM

[pir4teParticipant Mallala640 HP hyper-cruising SS-V Flagonwagon View build HERE Member since: March 2, 2015 Posts: 154]

christov wrote:

I’m having real trouble finding the right spec’d camshaft that can retain AFM and Street-ability for my FI application…. It’s looking like it will be a shit load easier and cheaper to just have the AFM/DOD removed and a very mild cam, or retain stock cam and have some internals tweaked. I’m starting to think my ‘goal’ of having 450+RWKW and sub 9L/100km fuel economy (highway only) is a tad far fetched considering Mercedes new 4.0L V8 TT hardly gets there.

What’s the problem with using the existing cam with a twin turbo?

Naturally as-pirated, all-motor.

[pir4teParticipant Mallala640 HP hyper-cruising SS-V Flagonwagon View build HERE Member since: March 2, 2015 Posts: 154]

Stock L77 cam is actually really good, the key is using valve events as per Miller Cycle.

To achieve this you require more scope / flexibility in your valve timing using a cam phaser, like I have.

450rwkw out of a twin turbo 6.0 V8 is a known thing, scaling back your effective volume to a highly efficient 3.0 on AFM and from around 4.0 on highway cruise is also known.

The naturally aspirated version of scaling down effective displacement is called Atkinson Cycle, and is what I’ve done recently with mine using VVT.

With VVT the ECU continuously controls the valve timing, so when appropriate it leaves intake valve closing very late such that it eats into the compression stroke. This creates short compression but normal expansion, huge thermal and energy efficiency per charge.

Obviously when power is required it utilises all eight cylinders, max volume, and uses valve events to spool faster and build boost.

Means you also don’t need two of the biggest turbos, or change cam, pistons, lifters, just add VVT.

Naturally as-pirated, all-motor.

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