What now?

Sorry my bad I wired the VDO egt guage up and at first thought there may be something wrong but I tested the circuit and everything was fine the problem not enough fuel turned the screw out to allow the cam to roll back to give more fuel but there was no increase in smoke or temps that's with the screw all the way out:( so then took a 17mm cap covering a screw on the drive end of the pump screwed it in then played with the cam and it now has more fuel but it is not enough only getting to 300c after turbo on a big hill but even with this terribly small figure the low down seems awesome (yes am getting converted) but problem now is going up a hill pull 4th gear and slips the cluth :( feels like engine does not care about the hill but the clutch does! (time for new clutch).
Hop out feel the inlet to the intercooler it is hot and feel the outlet of intercooler and it has no heat what so ever :) new clutch then 600c temps and i will retract all statements most likely

Post turbo EGT were common back in the day, but this was usually as a driver aide and many were just marked with a green and red face, hit the red change down a gear ( on hills) another comment I was told is that again back in the day, the EGT could come off and pass though the turbo etc.
but that’s a driver aid, you need your egt for tuneing

Manifold and back pressure. obviously you need pressure to spool up your turbo but you want that pressure at the turbo and not at some point before the turbo.

Think of it this way, the combustion chamber has the same pressure in it as the manifold when the valve is open. so if your boost is 14psi then your manifold pressure will be 24psi ( for arguments sake) and with a good manifold lets say it would be 20psi. that’s an extra 4 psi. you may be reading 14 psi boost but in reality you only have effective 10psi boost.

similar to fitting a 200 tdi manifold to a 300 tdi, there are gains to be made.

Now the math’s isn’t quite correct but it is there to give you an idea. No doubt some one will chip in to say in wrong

No problem with spooling it up it is way more responsive than a 200tdi (hav to get them reving before the turbo even thinks about kicking in) where as just driving steady there is about 5psi and with the slightest tap of the right foot boost guage leaps (in proportion obviously) as for manifold restrictions I get the jist but when people said at the start abbot a bodged manifold I can understand were they are coming from but I would like to point out 2 things that make it less of a worry 1: there has been talk about a turbo being on intake side of engine and still running perfect 2: some race engines I hav seen hav turbos that are not bolted directly to the manifold they hav about 1m of exhaust pipe then turbo bolted on the end (one that comes to mind is a 4cyl ofenhauser)
What sort of engine is in your county?

I have no idea what you've done with those screws. Can you take a photo and show us.

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Originally Posted by c.h.i.e.f

No problem with spooling it up it is way more responsive than a 200tdi (hav to get them reving before the turbo even thinks about kicking in) where as just driving steady there is about 5psi and with the slightest tap of the right foot boost guage leaps (in proportion obviously) as for manifold restrictions I get the jist but when people said at the start abbot a bodged manifold I can understand were they are coming from but I would like to point out 2 things that make it less of a worry 1: there has been talk about a turbo being on intake side of engine and still running perfect 2: some race engines I hav seen hav turbos that are not bolted directly to the manifold they hav about 1m of exhaust pipe then turbo bolted on the end (one that comes to mind is a 4cyl ofenhauser)
What sort of engine is in your county?

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What you have said is true about remote mounted turbo. BUT. and this is a BIG but. You may fined that the manifold although longer is probably tuned. Timed gas pulses as well as overlapping sonic pulses can enhance well actually do enhance over all performance.

one of mine a 908 Cummings with twin tubos toped 1400hp at 2750 rpm but when we tried to up it from there we hit a wall, just couldn’t evacuate thus we couldn’t push any more in. after a re think we settled at 1600hp at 2550 rpm and smaller quad turbos. cosworth had the same problems in the late 80s

I have the same manifold as dougal, but my math’s sagest that the turbo should be 1.560" further away. or I make up my own, but then there’s no point in doing that if i don’t at least look at the head. and there’s no point in any of that until gearbox, clutch etc etc so im playing with a V8 disco at the moment

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Originally Posted by Dougal

I have no idea what you've done with those screws. Can you take a photo and show us.

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x2


On the manifold, it is best to place the turbo as close to the exhaust ports as possible. The OEM turbo manifold does that quite nicely, and is also well designed internally.

People with remote mounted turbos have stated they are happy and the turbo spools up fine. However the ISUZU has bags of torque from idle - so it is not like an 80's 2L petrol turbo. I would place money that the difference between a remote mount and oem manifold would be noticeable in straight line acceleration (all else being equal - turbo, fuelling, tyres, vehicle etc...).

Your setup will probably be fine, but that depends on how you have grafted the turbo on.

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Originally Posted by 85 county

What you have said is true about remote mounted turbo. BUT. and this is a BIG but. You may fined that the manifold although longer is probably tuned. Timed gas pulses as well as overlapping sonic pulses can enhance well actually do enhance over all performance.

one of mine a 908 Cummings with twin tubos toped 1400hp at 2750 rpm but when we tried to up it from there we hit a wall, just couldn’t evacuate thus we couldn’t push any more in. after a re think we settled at 1600hp at 2550 rpm and smaller quad turbos. cosworth had the same problems in the late 80s

I have the same manifold as dougal, but my math’s sagest that the turbo should be 1.560" further away. or I make up my own, but then there’s no point in doing that if i don’t at least look at the head. and there’s no point in any of that until gearbox, clutch etc etc so im playing with a V8 disco at the moment

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So you have the top mount IHI manifold? Mine has been butchered, the neck is chopped and flipped with the internal pulse divider not lining up afterwards. I milled, broke and ground out the remains of it to smooth things as much as possible.

I have a later style manifold as well to try, but it bolts up to completely different turbos so any comparison will be rather stretched. It's a compromise between the flow that I think works best and a manifold that is compact enough to let me use the turbos I want.
All modern turbo diesel manufacturers seem to have abandoned any form of pulse tuning in favour of minimal volume. BMW, Honda etc are using simple log manifolds on their diesels.

How did your boost/backpressure measurements work out? I was finding crossover at 600C with my little T25. At cruising temps backpressure was higher at about 1.5 times boost. Cold acceleration gave backpressure as double boost. There was a sweet spot of low rpm, high EGT (above 600) and on boost that would give boost higher than backpressure, but not by much.

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Originally Posted by Dougal

So you have the top mount IHI manifold? Mine has been butchered, the neck is chopped and flipped with the internal pulse divider not lining up afterwards. I milled, broke and ground out the remains of it to smooth things as much as possible.

I have a later style manifold as well to try, but it bolts up to completely different turbos so any comparison will be rather stretched. It's a compromise between the flow that I think works best and a manifold that is compact enough to let me use the turbos I want.
All modern turbo diesel manufacturers seem to have abandoned any form of pulse tuning in favour of minimal volume. BMW, Honda etc are using simple log manifolds on their diesels.

How did your boost/backpressure measurements work out? I was finding crossover at 600C with my little T25. At cruising temps backpressure was higher at about 1.5 times boost. Cold acceleration gave backpressure as double boost. There was a sweet spot of low rpm, high EGT (above 600) and on boost that would give boost higher than backpressure, but not by much.

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Well actually i haven’t quite got that far yet.
your IHI manifold i suspect may actually be better than the turbo manifold in the 2500 rpm - 2800rpm range.

As for manufacturers we do see a glimmer of tuning every now and again. TD5 as an example. But like the TD5 it introduces manufacturing problems. TD5 and the old 245 & 265 manifolds leap to mind.

Way back in the day when we were bolting blowers to boxes with carbs inside, an older engineer said to me. That tuboing is a good way for a manufacture to mask a poorly designed motor. And there were some glaring examples of that no so long ago even some today IE the rotary’s

electronic management and good turbo design can and is used to mask other design shortfalls. As always the best way to start and to get a great turbo motor is to start with a great motor

The Isuzu has 3 inherent problems, that aren’t really problems but they do exist. Oil relief, balance, or overall weight of reciprocating parts. and outlet porting. None are an issue for any user on this forum. but they exist none the less, this is no worse or better than just about any other motor available today, (Want to talk about the puma?)

anyway, before you dump your manifold, make up a spacer, match it and drop the turbo by about 1.5 inches, i recon there’s about 10% there at lower rpm. There was a reason there was a web in the manifold, not a good one and it was to mask another problem.

cruseing temps and pressures you use for economy tuning, high load is for power tuning. BUT as you said your cold BP was 25% more than your hot BP ( i assume at the same boost). This reinforces my previous post of Mass + velocity are the terms you must think in when working out turbo placement.

Your sweet spot. this would be worth investigating. and i would suspect that if you double the reve's that there may be another sweet spot again, but this may be masked by the isuzu having fallen off the torque curve.

if its at about 1250 rpm i think i could guess why

Oh simple log manifolds, not so bad as you would think, but a very narrow power application. bottom end sort of thing where there is a lot of suck push going on in there

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Originally Posted by Dougal

BMW, Honda etc are using simple log manifolds on their diesels.

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Car/engine manufacturers use CFD for designing just about everything these days. I am sure the manifolds are quite well optimised.

As well as flow though, heat is an important consideration - i.e. making sure things are hot enough downstream of the turbo to regenerate the DPF.

Some friends who work for DPF manufacturers are given specs of up to 1300oC :eek: by the engine manufacturers.

Ill try and get some pics up soon of things I hav done. Supposedly the screw I wound in at the front of the pump allows the rack to slide forward more allowing more fuel delivery.i was told this is done so that there is only a little bit of fuel adjustment via the external screw to stop people being able to over fuel but hard to explain without pics:( I can undetstand the exhaust impulses but at the moment the manifold that I hav modified for the turbo I hav is working because as we know the td5 turbo has a triangular flange which means no matter what manifold I get it will hav to be modified in some way. Maybe some photos of there manifolds and what turbo they hav might be handy?