Replacing engine

[Pitbull_James]

I'm currently using a Terrano with a Z24 engine. I plan to replace it with a TD27 turbo diesel engine. Will there be any conflict with the gear ratio?

[88pathoffroad]

I doubt it. Whatever gears are in it can stay put unless you really want to re-gear both diffs or replace them.

[Diesel Boy]

Make sure its a TD27(t)!!!!!!!!

With out the turbo you will be bitterly dissapointed!!!!!!!!!!!!!!!

You realise fuel lines, and tacho, intake, fuel pump among others will have to be changed to become compatible with a diesel??

[Guest Leprecaun]

Make sure its a TD27(t)!!!!!!!!

With out the turbo you will be bitterly dissapointed!!!!!!!!!!!!!!!

You realise fuel lines, and tacho, intake, fuel pump among others will have to be changed to become compatible with a diesel??

Hell yeah. I have a td27t and as a test while working on it disabled the turbo, ohhh man as soon as it cooled down it went back on. I installed a boost controller to help the turbo from low to midrange and with reduction gearing, its has that much power in lowrange I can walk up rocks, without the turbo, i'd have to be running.

[Diesel Boy]

You sound like a Knowledgable guy with Turbos, so what is the theory behind the boost controller.

I realise it is used to controll the pressure generated in the intake manifold, but how do you use this to your advantage to gain performance at low RPM???

i.e, do you turn the boost pressure up at the lower RPM or what???

Very interested in this!!

Ever considered a BOV??

I was tossing that idea round, as i can hear the pressure being released quite clearly through the snorkel every time i take the power off, especially in low range if you are giving her heaps trying to get unstuck of attack a bank of somthing.

Pete.

[88pathoffroad]

Diesels don't have BOV's. The noise you're hearing is the wastegate shutting. BOV's are used on gasoline engines because when the throttle closes after running the engine at high RPM's, an excess amount of air is still being compressed by the turbine, which would create a terribly lean condition inside the combustion chambers, plus it will backpressurize the turbine, possibly causing damage to that. Running a turbocharged gasoline engine too lean is a recipe for disaster. Dumping the excess pressurized intake air via the BOV when the throttle plate shuts prevents this. On a diesel it doesn't matter if it runs lean, because it's built to detonate on purpose. The internals will take it. Adding forced induction is simply an easy way to pack more fuel and air into the combustion chamber and produce more power.

 

Manual boost controller theory:

With no or low boost, the wastegate is "closed" and all the exhaust from the exhaust manifold is routed through the turbo's turbine to spin it up. Under stock conditions, as the turbo produces boost pressure, it is transmitted to the wastegate via a small hose--a positive-feedback loop. When the pressure rises to a point which is set inherent to the manufacturing of the wastegate, the wategate "opens." This allows exhaust gases to bypass the turbo and therefore keeps the turbo from spinning even faster and creating more boost. Without a wastegate, the turbo would keep spinning faster and faster as the exhaust gases increase, until the turbo bearing gave out and the turbine self destructed--this would hopefully be before the pressure ruined your engine!!

 

The wastegate on a Lotus Elan, for example, is set to 0.40 Bar--this setting is inherent to it and NOT changeable. Thus at this pressure the wastegate opens and no more boost will be created. The purpose of the manual boost controller is to create a "controlled leak" in the feedback line to the wastegate. This effectively "tricks" the wastegate actuator into sensing a lower pressure than actually exists.

 

The MBC is a valve that bleeds off some of the pressure out to the atmosphere away from the wastegate actuator. The size of the leak is controlled by your adjustment of the manual boost controller. With the MBC in place and active, as the boost rises, the wastegate actuator is sensing less pressure than than it should since some pressure is escaping from the feedback line before reaching the wastegate actuator. The boost will therefore rise higher as some pressure is vented and a new equilibrium will be created at a higher boost level--this will be sensed as (whatever pressure is created by your particular vehicle's turbocharger) by the wastegate, and it will open. This is how your "free, increased boost" is created!

 

That's for a manual boost controller. A computer-controlled one is lots more expensive, but almost infinitely adjustable and tuneable.

[Diesel Boy]

Right.

Soooo, a MBC will have very little bearing on throttle response and engine out put at low RPM as the waste gate is closed and there is no controlled leak to reduce the speed the turbine is spinning etc.

Right, waste of space.

 

Next, the BOV.

Thats my understanding to a certain extent.

Except:

Anti lag. The purpose of which is to keep the turbo spinning in the right direction and at a high speed in order to reduce the lag/time it takes to build up pressure in the intake manifold once the throttle is applied.

 

So to date my understanding of a BOV has been to release the pressure in the intake manifold, for perhaps the reason you mentioned, but also as a way of reducing the lag.

Its all about pressure equilibriums. when the turbo reaches max pressure, and then you release the throttle, the pressure in the intake manifold exceeds the presure in the exhaust manifold.

Naturally the pressurised intake air wants to reach equilibrium with the atmostpheric pressure.

It does so by escaping back the way it came, out the turbo.

In doing so it spins the turbo in reverse, and the next time you go to put your foot on the throttle it has to correct the direction the turbo is spinning in and also rebuild the pressure in the intake manifold.

Thus, it creates our fravourite friend TURBO LAG>

A large number of cars come out standard with a turbo and no BOV. The throttle body controls air flow. The computer reads whats going on in the combustion chambers and adjusts the mixture accordingly. Leaning is predominantly a carby and turbo prob.

 

Cheers for the info,

Pete.

[Guest Leprecaun]

With a Nissan Terrano, I noticed I can adjust this manual waste gate, which is controlled by a screw just behind the main turbo, a small bell like thing. Does this have any effect of the turbo as I really don't want to blow thr turbo up. I will be putting a boost controller on it though. I go offroad every couple of days and would like the turbo to be more available in the mid range area. What recommendations do you guys have for low range work and touring driving about 80kph for extended driving so that its a bit more diesel efficient?

 

Thanks guys!