they are.Quote:
Originally Posted by slug_burner
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they are.Quote:
Originally Posted by slug_burner
Dont believe the torque figures at all I am afraid.Quote:
Originally Posted by Bearman
Purely my opinion, but I have found that when you have lots of touque available, and it comes one nice and smooth (like a 4BD1-T) you are less likely to brake things than when you have to ring the neck of an engine to get it.
When I'm out with other people, I can usually pick the people who are going to bust their drive train because they are revving and jumping around all over the place. The td5 is a really nice engine but you have to rev it to get any touque out of it.. and IMO this rough application of power is what brakes things 'in real life'.
Were as with an 4BD1(-T) you can just idle up (or give it a small amount of accelerator) to get up the same things that other engines would have to rev and burst.
This isn't really on topic.. but I do think that 'in real life' it makes a huge difference.
They aren't scaled to engine rpm so no they aren't correct. If you can work back through the gearing to convert the road speed to rpm then you can scale the torque to where it should be.Quote:
Originally Posted by Psimpson7
But honestly it doesn't matter much. My stock 4BD1T was around 330Nm and running lean at 13psi boost.
15psi boost and more fuel. 380Nm.
24psi boost and more fuel. 580Nm roughly and still burning clean.
20psi intercooled, 650Nm roughly. Haven't intercooled yet.
These are just rough figures, +/-10% if you like. They are well past the TD5 figures posted earlier.
I don't have a dyno, but I did have a man made viaduct of known slope. With 20psi boost I was putting 76kw to the ground at 2000rpm. If you allow 35% drivetrain loss, that was 535Nm. At 1000m altitude.
But the main problem with the 4BD1T's screwing gearboxes is torque pulses. My 2.2 diesel work car has a heavier flywheel than my 4BD1T. Cummins 4BT engines flywheels are roughly twice the weight and comparable diameter.
why is drivetrain loss a % and not a fixed amount?
2WD vs 4WD, auto vs manual, front wheel drive vs rear etc.
So the solution to the gearbox issue is a heavier flywheel? On paper would work since lightening the same gets better power delivery from engines. Hmmm, machined steel flywheel with cast iron friction insert.
Hi Dougal,Quote:
Originally Posted by Dougal
I guess, I am not arguing that the 4bd1t has a higher percentage of its torque avaialble at lower revs than some other engines, I am however still not convinced that the figures of most of them are anywhere near as high as some people are suggesting.
Also the td5 chart above is all at std boost I believe or certainly close to it, so they I think would be around 15psi or so, and in that scenario the td5 was 420ish as opposed to your calculated 380. (The stage 2 puma produces 450Nm!) IMO widing the boost up and the corresponding fueling upgrade (or with a VNT) would generate similar gains, albeit, probably reducing life of all drivetrain components to an unworkable level!
I would still like to see some actual charts as a comparison.
Justin, the Disco you refered to, was that MG's? If so that had a weird remap issue that on some days seemed to have less power than standard, and on some days flew... It was a soldered in chip.
Cheers
Pete
A heavier flywheel on a manual gearbox only reduces power during rapid acceleration (mostly in first gear), at a steady speed there would be no difference. In an auto during gear changes it would be a possible liability as the clutches try to match speeds.
clubagreenie, was the first part of your post a response to mine?
Because it's easier that way. To measure the losses accurately is really hard, to throw a percent out is really easy.Quote:
Originally Posted by uninformed
Hi PeteQuote:
Originally Posted by Psimpson7
To increase the power of a diesel you are increasing the fuel. But to increase the fuel more than a few percent your A/F ratios get too low, resulting in smoke and dangerous EGT's. To fix this you need more boost.
It's not possible to get 420Nm from a TD5 with stock boost without risking meltdown and blowing huge amounts of smoke. My calcs put 25psi as a safe figure for 420Nm from a TD5.
Diesel performance is simple.
Your max A/F ratio is limited by thermal limits of the engine (EGT) and smoke avoidance.
The power you get from the fuel is set by your engines efficiency.
The airflow you get is the displacement, boost and intercooling.
Now the TD5 and 4BD1T are both direct injection diesels with comparable efficiency.
The A/F ratios you can run on each are the same.
Hence the power and torque you will get is dictated by the displacement, boost and intercooling.
The result of this is pretty simple. With the same boost and intercooling a 4BD1T will beat the TD5 by the ratio of displacement. 3.9/2.5 is 1.56 times.
The 420Nm from the TD5 becomes 655Nm from the 4BD1T. There is no contest here. If the numbers sound a bit strange, ask for a drive of one that has been a bit tweaked. Because these engines have a quite short rpm range, a VNT turbo isn't necessary to get good low down torque and good power. But the lacking rpm does restrict power compared to the likes of the TD5 which spins higher. It's easy to increase the rpm limit of the Isuzus, but big engines don't feel good spinnng fast.
The 380Nm I mentioned earlier from a 4BD1T, that is 15psi, no smoke, clean/safe EGT's and no intercooling.
The same A/F ratio on a TD5 with no intercooler would give well under 300Nm.