Thread: 4BD1T Turbo Sizing and Performance Prediction.

Originally Posted by Ancient Mariner

With a bit of wet weather got back on the Isuzu I asked the consultants the question but I think they had other things on there mind. Best place for EGT probe? I would rather put in the bend after the turbo instead of pre I would imagine there would be a certain amount of heat loss you would have to allow anybody with experience of either?

Thanks AM

Why would you build a manifold like that. It might be ok on a rice racer, on a diesel it will be terrible. There is a reason that just about every manifold on diesel and petrol turbo vehicles are cast iron log style. Keep the gas hot and keep the runners as short as possible to keep the gas moving through the exhaust turbine as quick as possible.

Originally Posted by Bush65

Had I known you were going to fabricate a manifold like that I would have given you the details for a pulse converter.

As Ben said, pre-turbo is where you need to know the EGT. If measured post turbo, then it is a guessing game, unless you have previously measured both pre and post and can be reasonably sure of the difference for your particular application.

Or you stay conservative just to be sure.

The expansion ratio and hence the temperature difference across the turbine depends on too many variables to be comparable from one system to another.

It will be a guessing game anyway, the amount heat loss will be immeasurable.

Originally Posted by two up

It will be a guessing game anyway, the amount heat loss will be immeasurable.

Tho the loss of heat will improve efficiency due to cooler running the gas speed will be improved by the equal length runners performance wise it will out do any of the log style manifolds .
Tho a log manifold is all that is needed to get good results the extractor style wins hands down why do you think all the high end jap turbo stuff is made this way from stainless its not for looks that is for sure
My hat is off to the AM this is just another of his master pieces but hay every body has their own opinion

Whhhhaaaaatttttt. If you are talking turbo petrol, you are right, tuned length split pulse manifolds work much better, because heat loss is not a factor, hence all the YouTube videos of red to white hot manifolds. Diesel completely different story, hence people getting manifolds and turbine housings ceramic coated to keep the heat in and keeping it compact to keep gas speeds up. Think of it as losing drive energy to the exhaust turbine. Turbos for diesel engines are smaller than a comparatively size petrol engine due to the low revs, that's why its important to keep the gas temp as high as possible once its left the cylinder.

This is a picture of a ford typhoon exhaust manifold that makes 440kw at the rear wheels. No offence but that tuned length manifold will make less power than a standard log type manifold.

Why because 1 . I am different 2 . because I can 3. I like to stuff around .Turbo manifold designe is a pretty controversal subject with the general consensus being a heavy wall equal length runner the best compromise With each engine - turbo- gearing- driving style and application different to make a statement that a tuned length manifold will be uesless is stupid IMO But been wrong before will be again

Thanks AM

Originally Posted by two up

Originally Posted by Bush65

Had I known you were going to fabricate a manifold like that I would have given you the details for a pulse converter.

As Ben said, pre-turbo is where you need to know the EGT. If measured post turbo, then it is a guessing game, unless you have previously measured both pre and post and can be reasonably sure of the difference for your particular application.

Or you stay conservative just to be sure.

The expansion ratio and hence the temperature difference across the turbine depends on too many variables to be comparable from one system to another.

It will be a guessing game anyway, the amount heat loss will be immeasurable.

The turbine converts heat energy to mechanical power to drive the compressor. To say the heat loss is immeasurable is absurd, it can be of the order of tens of kilowatts.

Originally Posted by Bush65

The turbine converts heat energy to mechanical power to drive the compressor. To say the heat loss is immeasurable is absurd, it can be of the order of tens of kilowatts.

That's right, with that manifold unless you measure just after where the runner exits the head, pre turbo will mean nothing. There will be so much heat loss along those pipes that measuring will be meaningless.