Another turbo question-- or 2

I dropped my phone today and broke it, so pics are a challenge :mad: 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.

Thanks Flagg, I have already cleaned and painted the bonnett, so wont replace with a puma at this time.
I dont have a county a/c - I have windscreen flaps :p so just the normal heater box. I plan to fit the Defender a/c later.
My issues are what turbo will fit and bonnet clearance. Approx 140 is not much room.....
I will wait till the new year and start looking at this again.

Looking forward to seeing how your setup works out.
Cheers,
David

Quote:

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Originally Posted by dobbo

Perhaps I am missing something obvious, why would it make that much of a difference which way an exhaust manifold effects the exhaust gasses when the next place the gasses pass through is the turbine where it is all compressed? The factory setup is far from free flowing? Should I look at getting some custom headers built up (anyone done this?)

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Short answer is yes, but since sonic pulse from a diesel is a lot less but then the exorst gas,s are a bit more dense than a petrol. non-the less the combined effect is less than a petrol if you are going to manage them in a traditional scavenger fashion ether 2 stroke or petrol 4 stroke, the main reason is that there is no valve overlap or less than in traditional petrol motors.

but to answer your question, is it beneficial for a turbo to have a tuned manifold-- Hell yes, but you must be careful.
if you doint get it right and have say 2 converging pulses hitting the turbine at the same time, or you have ill-regular pulses hitting the turbine, you ended up with a similar effect as a 4bd idling and chewing out the input bearing on its gearbox.

if you look under the bonnet of a lot of modern jap diesels they get away with this by using what looks like poorly designed manifolds or even a log manifold. rather than try to manage the pulses they scramble them until they have no effect. the 4bd manifold fires pulses into each other rather and sliding them along with each other. how ever there is still a sweet spot at i think about 1800 rpm where the pulses collide bag center of the manifold

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.