Thread: Another turbo question-- or 2

I dropped my phone today and broke it, so pics are a challenge I'll see if I can get the photos off it..

The manifold has the turbo mount at the same level as the bottom of where the top studs go into the head. (I hope that makes sense). The far edge of the turbo mount is 190mm from where it mounts to the head. This is against the A/C fan motor if you have that.

The turbo mount is about 450mm from the firewall, and 350mm from the edge of the bonnet - which puts the turbo under a bonnet reinforcement in the depression in the lower part. My unscientific measurements give you around 140mm of vertical clearance between the manifold and the bonnet at this point. I measured this against things in the engine bay that touch the under bonnet sound mat.

My turbo is 176mm high, so no chance of fitting. I'm not sure the clearance measurements of the Puma bonnet as its at my office (and amusingly I can't get it home without the County.. hehe yeah.) That said, the turbo should be in the bulge..


BUT:

With this manifold, and a puma bonnet it /may/ be possible to mount a turbo and keep the county A/C. The BW turbo mount positions it so that most of the turbo is over the top of that manifold. I'm not certain as I might have to move the bypass actuator... but it will be close.

The older Isuzu IHI manifold is a split pulse design, pulses from 1-2 and 3-4 are kept seperate right up to the turbo flange. The T25 version of the same manifold doesn't have the divider plate at the turbo flange. If you map out these pulses you'll see it's not spreading them separately, it's combining them, giving two strong pulses instead of 4 evenly spaced ones.

It's worth noting that all modern diesels are using log manifolds. We're talking engines that are beating all previous entries for both fuel economy and power. The reason they do that is simple, minimal volume for fastest spoolup and best drivability. The 1988 onwards manifolds are of this design for the Isuzu too.

If you don't care about transients so much, then an equal length runner manifold could give some gains, but make sure you wrap them to keep the heat in. Turbos feed off heat, the hotter the gas the less drive pressure they need.

Four cylinders are also in a bit of no-mans-land for exhaust pulses. 6 cylinders are perfect with running each group of 3 together. The best theoretical arrangement for a 4 cylinder is to pair 1-4 and 2-3 together at the halfway points. But this is very messy to actually build, I've only seen photos of one home build manifold where this was acheived.

Pulse tuning at a specific rpm doesn't really work on turbo vehicles. The pressure and temperature in the manifold vary too much and too often. The speed of sound through gas is highly dependent on temperature, the constant temperature changes result in your tuned runner lengths effectively changing continually.