2.5NA to 200tdi conversion questions

[tombardier]

Greetings,

Bought myself a lovely looking discovery 200tdi engine last weekend. It started easily and sounded great when we fired it up in my garage! Just a couple of problems though.

One is that it looks like the turbo impeller has chewed on something in the past, and although it sounds alright, and there is no significant play in it, I'm a bit worried about whether it's still balanced because the fins are a little bit mangled So I'm on the hunt for a cheap turbocharger, which I can't afford until the end of the month having laid out for the engine anyway.

The main question I'm seeking the answer for though regards the exhaust. I'm wondering whether I need a new one to guarantee back-pressure for running the turbo. I have a 2.5NA, and the exhaust was replaced with a bearmach one by a garage a year ago or so. My friend did the 2.5TD to discovery 200TDI conversion a while ago, and we seem to have the same diameter of exhaust piping coming from the downpipe, so we're not really sure whether I'm going to need to change my exhaust or not, as his seems to be fine. I'm wondering whether my replacement exhaust may have been made for a TD anyway, in which case, I don't need to worry so much!

Any ideas would be welcome!

 

[jamesmartin]

check for shiney edges where contact with housing may have been occuring ,but they often look like that

 

[jamesmartin]

exhaust as big and smooth flowing as possible

 

[tombardier]

There really isn't enough play in the impeller to have caused that. I don't pretend to know all that much about them, but my friend, who's a mechanic, and frequents these forums too, he explained about how there was very little play, and there was no wear markings indicating that the fins had been touching the sides, but the fins were mangled, and he thought that maybe something had gone through at some point and been chewed up a bit. There is a kind of S shape in the fins when they should be straight. I'm led to believe that the engine had done 90K, and looking at how nice and tidy the rockers are, and how nice the engine sounded, and how easily it fired up after having been stood, and also how nice the engine oil looked, I believe it

 

[tombardier]

exhaust as big and smooth flowing as possible

ah, you see, I thought it might have to be tighter, to get more back pressure! I honestly don't pretend to know though

 

[jamesmartin]

if your worried run it with air intake pipe off and observe it ,i think it would have been touching casing by now if was damaged

 

[jamesmartin]

ah, you see, I thought it might have to be tighter, to get more back pressure! I honestly don't pretend to know though

the power off exhaust turns turbo so you dont want anything downstream to impede exhaust up stream

 

[tombardier]

Thanks for the replies James.

I'll take a photo of my impeller later, and perhaps people will have a better idea of whether it looks serviceable or not!

I'd rather not shell out on a new turbo if I don't need to!

Now, if only I could get the bolt holding the timing case in at the top right out!! grrrr

 

[munroe.frost]

ah, you see, I thought it might have to be tighter, to get more back pressure! I honestly don't pretend to know though

Big diameter exhausts aren't as great as people make out. For a Land rover where you don't rev it to bits you want to get the exhaust gas out quick and hot. A big pipe diameter means these gases cool down so you are pushing out cooler denser gas, restricting flow.

Second is that the diesels rely on exhaust pulses to line up. Every pulse leaves a vacuum behind it and pulls the next pulse along making the flow easier. The OEM parts would have considered this.

Just a few bits of knowledge I've picked up on the way.

Dave

 

[jamesmartin]

one its a turbo the other i dont think he was going to try and tune exhaust ,but he will want some thing bigger than 2.5 na

 

[munroe.frost]

Yea a exhaust for a 19J would be the best and cheapest exhaust.

Just clearing up a myth that big diameter exhaust is best.


Dave

 

[jamesmartin]

im not sure youve done that but opinions are good

 

[munroe.frost]

Forgot to mention that big diameter pipes muck up the pulses. Its really very hard to get it right. But thats why I'm doing it for my dissertation.

 

[jamesmartin]

we are talking turbo not n/a

 

[munroe.frost]

You are right that a big pipe is beneficial for a turbo on high performance engines. Where the pipe diameter diverges towards the exit. But a 200tdi is hardly that. Where at low speeds the mass of gas in the exhaust and turbulence make a difference. You want to remove as much back pressure as possible. A big diameter exhaust in this situation wont do that unless it is shortened.

For the purpose of this I found when i did my engine conversion a 19J exhaust was easy and cheap to fit.

 

[200tdi ayre]

When I did my conversion I used pipes from a 200tdi discovery, and made the exhaust up myself, thought it would be the best diameter as if it was used for the same engine on a discovery it should be right for a defender.

 

[tombardier]

If I wanted to keep costs down initially when I did the conversion, and stuck with my 2.5na exhaust, I could cope with only having an extra 45 bhp instead of 50, but would I risk damaging the engine in any way?

Also, out of interest, does anyone know what bhp and torque a 200di puts out (200tdi w/ turbo absent)

 

[tombardier]

thought it'd be better to pose the question regarding my mangle turbo to a new thread

http://www.landyzone.co.uk/lz/f7/photo-my-turbo-impeller-knackered-153302.html#post1499968