ForumSage
I finally got around to finishing off my new turbo over the weekend. I've been running a T25 with a 0.49 A/R exhaust housing from a 1.8 litre petrol nissan for the last 3 years and for a short time before that too.
It pulled very well from 1000-2500rpm but has been losing boost lately and would struggle to hit 18 where it used to hit 20psi.
This turbo is a T28 core rebuilt with a T25 exhaust wheel, 0.64 A/R exhaust housing and a T25 compressor cover bored out to fit the 60mm T28 compressor wheel.
The reason for all these mods were to use the T28 compressor in a turbo that is externally identical to the T25, straight bolt in.
Last night it all went together and fired up without issues (big relief as all parts were well used before this started). The test drive gave me a whole lot more compressor whistle but only 12psi. So I still have to crank the wastegate adjustment up tighter.
Boost at 100km/h is down from 8-9 psi to 5-6psi and the low end kick has definitely been softened. I'll report back more when I've cranked the boost up.
The T25 has some debris erosion around the wheel tips. I need to check the intake pipes for rust.
ForumSage
Replaced the wastegate actuator with a threaded bar and went for another spin.
Hits 20psi now, it takes more rpm to build boost than the T25, but when it comes on it appears to climb quicker. It can also rev out to the limiter in 2nd and 3rd without problems.
Overall it's a more flexible engine than with the T25. The T25 however was fantastic for boost from idle offroad and for punch off the mark.
Next experiment will be variable vane, hoping to find the best of both worlds.
OldBushie
Hmmm, something wrong with your links to pictures, they don't seem to be working
ForumSage
Here ya go then.Originally Posted by rovercare
Hmmm, something wrong with your links to pictures, they don't seem to be working
Picture of the T28 compressor cover beside the smaller T25 compressor cover I bored out to replace it with.
Picture of both turbos side by side. New T28/T25 hybrid and old T25. Picture of new turbo installed and picture of the old T25 back in 2006 when it was all clean and shiney looking.
TopicToaster
SubscriberWhat is the exhaust manifold you have there Dougal?
It looks pretty much the same as the top mount T25 manifold that I've got on my bench, but upside down.
Steve
Master
You noticed it too, looks like an army manifold inverted, I saw it a thought bugger all that work I did to make up my exhaust manifold twisting it back around. I think Steve with the tubo under the manifold as in Dougals image then there maybe a few less issues to face than how I have done mine. Might even change mine like the idea of who he has done it. Dougal perhaps you could let us know what adaptions if any you did to mount it under .
Kindest regards
Was not laterally thinking
ForumSage
Unfortunately you can't just flip the manifolds, the bolt holes are offset and the ports won't line up.
This one has had the neck sawn off, flipped and rewelded. It is the IHI manifold used on the early 4BD1T's, there is a similar T25 version which has a slightly different bolt pattern and slightly different port shape.
I have slotted the bolt holes on my turbo so it fits the IHI pattern.
TopicToaster
SubscriberThanks - I didn't think it would be as easy as a simple flip or more people would have done it.
I've heard that welding cast iron is troublesome - did you do the welding yourself or take it to a specialist?
Steve
ForumSage
The welding was done with the engine conversion before I got the vehicle. I've never tried to weld cast but it's apparently quite nice with a TIG and cast iron filler. Letting it cool and destress slowly is quite important.
This manifold has done over 200,000km like that, so they obviously got it right. However this was a split pulse manifold and it didn't line up as it should. I've since cut/milled/broken out the offending web to smooth it out as much as possible.
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easy as
Gas = pre heat until your spit bounces ( when you spit on it) weld your Vee - ed join with cast filler ( not the best) or bronze rod. ( NB with Bronze tin both components before trying to weld them together), do the preheat thing again, wrap in a 12 pink bats and leave for a day.
Tig = same as Gas but slower
Mig = forget it. can be done either with cast wire or bonze wire. Both are good but not for this application.
Arc = Cast rod, in short a nickel rod. brilliant but you need the hands to be able to do it and not many have that, pre heating and post heating are a bit more critical. Its how I would do it but not the way if its not your thing.
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