Yeah with all your mods that doesn't surprise me
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| Turbo Boost http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=37524 |
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| Author: | mackruss [ Thu Nov 20, 2008 6:39 am ] |
| Post subject: | Turbo Boost |
At what RPM should i expect the turbo to kick in at. I know the turbo is driven from the exhaust gasses but is there a specific RPM. The reason i'm asking is an older 2.5 currently undergoing a service seems to be kicking in at over 2000 RPM which seems to be a bit high . Any help on this will be appreciated thanks. |
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| Author: | warp2diesel [ Thu Nov 20, 2008 7:41 am ] |
| Post subject: | Depends upon load |
RPM is not always the best determination as to when the turbo starts to provide boost. If you are going up a hill or towing a load, the turbo will boost at a lower RPM due to the higher load. Going down a hill, don't be surprised if the turbo is sitting at zero boost even at 3,000 RPM. I can get my turbo to boost below 1,000 RPM if I am holding the brake at a stop light and touching the accelerator. Then I blow away the Tahoe big block next to me at the light. |
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| Author: | mackruss [ Thu Nov 20, 2008 7:53 am ] |
| Post subject: | |
Yeah with all your mods that doesn't surprise me
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| Author: | gmctd [ Thu Nov 20, 2008 10:57 am ] |
| Post subject: | |
Correction: turbos function on the energy in exhaust gas: volume, rate and btu - low energy = low output - you EXPO guys have the manual trans version so you won't see turbo action as readily as the auto trans versions - reason? The hydraulic coupling (torque convertor) keeps constant loading on the engine, even at idle, where the m.t. version is unloaded until clutched-in - when we rev up to 2krpm at a lite, the engine is under load and exhaust volume\btu energy is high - when you m.t. guys do it, you're just idling a little faster, still not loaded, and exhaust has more volume\rate but not much more btu, which is the real energy - makes it difficult to compare Boost levels, even when loaded, because each time you de-clutch to shift gears, engine immediately goes unloaded, rpm drops, EGT energy drops, turbo de-spools, Boost drops off quickly, then you have to start over again in each range - the hydraulically-coupled a.t. never loses loading, thus EGT energy remains high - additionally, the 2.5 is prolly configured completely different that the US 2.8 versions, incl our VGT turbo, which is a small turbo at low EGT energy levels for quick spool-up, ECM-reconfigurable to large turbo when EGT levels are high |
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| Author: | warp2diesel [ Thu Nov 20, 2008 1:29 pm ] |
| Post subject: | No load, no exhaust volume no..... |
....energy to turbo, no boost. Stomp the accelerator in neutral, you are loading the engine with the inertia of the flywheel, inertial damper, crank, and cam, engine needs more BTU of energy tlo generate moire power, more exhaust to drive turbo. Old Chicken or Egg debate. Some feel the turbo is the main item and the engine is just a parasitic device to create flow to drive the turbo. Since the exhaust does not create enough thrust like a jet engine, this argument of the turbo being the center of the power plant holds no water. Both chicken and eggs taste good if they are fixed right. BTW: I have not hopped up my ECM or hung on an power module yet. |
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| Author: | mackruss [ Thu Nov 20, 2008 1:40 pm ] |
| Post subject: | Boost |
The owner of the 2.5 said that his turbo was only kicking in at about 2200 RPM, i'll get two drive it tomorrow and see what it feels like. Will cleaning the MAP sensor help him and i think that these models have a vacuum actuator for the turbo ( please correct me ). |
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| Author: | retmil46 [ Thu Nov 20, 2008 2:27 pm ] |
| Post subject: | |
If that's a fixed vane turbo on the 2.5, you'd be comparing apples to oranges trying to go by what the variable vane turbo on the 2.8 does. On my old '87 MB, 3.0 L I6, redline of 5 grand and max torque at 2400 rpm, that old fixed vane Garrett T3 turbo doesn't even put out enough boost to register on the gauge until you hit 50 to 55 mph - around 2200 rpm. |
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| Author: | mackruss [ Thu Nov 20, 2008 2:32 pm ] |
| Post subject: | |
retmil46 wrote: If that's a fixed vane turbo on the 2.5, you'd be comparing apples to oranges trying to go by what the variable vane turbo on the 2.8 does.
On my old '87 MB, 3.0 L I6, redline of 5 grand and max torque at 2400 rpm, that old fixed vane Garrett T3 turbo doesn't even put out enough boost to register on the gauge until you hit 50 to 55 mph - around 2200 rpm. Bingo , that i think explains the difference in the 2.5 and 2.8 models. Perhaps UFFE can plug in here. |
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