Printable View
They have a pretty titanium MSM up at the Mazda dealer in Irving, so the ::Curls:: and I stopped to take it for a test drive. I really liked the way the car looked and it was fast if you kept the revs up, but boy, the lag was really bad. I know the turbo lag is not news to most and I was already aware of it, but it was more than I expected. I now know why it did not do all that well in AX, but it would still be a hoot on the street.
You need to go for a ride in Magma's car to experience how the mazdaspeed miata should have came from the factory.
On the couple of MSMs I have driven I was always disappointed in the 3,500 RPM fuel cutoff it seemed like the Turbo just figured out what it was doing... bap... bap... bap...
Maybe they will do better with the NC Mazdaspeed. ;)
Quote:
Originally Posted by POS Racing
??? I have not experienced a cut off, the stock car has issues when transitioning from open loop to closed loop, but I have fixed that
I think he's saying from 3500 to redline is so sudden it feels like a 3500 cut off.
its not lag, its boost threshold that takes 4000rpm to spin the turbo because the ugly ass manifold is so choked off. If that turbo were mounted to a real manifold, it would probably make 10psi or so at 2800rpm, maybe lower considering people are making that much boost at that rpm in larger turbos. The tiny exhaust doesn't help either.
lag = the time it takes to hit target boost within rpm threshold
So lag isnt the time it takes from hitting the throttle to having boost? It seems that no matter the cause whether it is a small manifold or a big turbo you have turbo lag.
say your turbo makes target boost at 4000rpm (which is a big turbo, like a gt30r)Quote:
Originally Posted by Majik
below 4000 rpm, you're out of boost threshold. If you step on the gas pedal, it won't make target boost until the motor pumps enough air to spin the turbo. The problem is that your turbo is too big to to spin fast enough to make positive the target manifold pressure.
Above 4000rpm, enough air is flowing through the motor to make the target boost. This is where lag comes in. Its the time it takes for the turbine to spin up to the target rpm (of the turbo) to make pressure. This measurement is pretty much instantaneous on a turbo made in the last 20-years. Lag was a big issue in the 70's with the 911 turbo (the real 911 generation). You had to anticipate the time it took the dinosaur turbo to spin up to target rpm, and the power came on thick, causing glorious oversteer in the rear engined horror.
In the 21st century we have things like ball bearing turbos, electronic boost control, appropriately adjusted timing, insanely efficient turbos with all kinds of awesome technology. Turbo "lag" is a dead concept.
Sean, correct me if I'm wrong:
The problem with the msm is pretty much an engineering disaster. The engine management side has a pig rich fuel map in general with excessive fueling at open loop below 4k rpm, timing is too conservative, and the manifold is a choker.
The turbo on the MSM is tiny, smaller than a gt2554 and hits 10psi at roughly 4000rpm (butt dyno in my sister's car).
The gt2860rs moves roughly 3x the air on the compressor map, and the turbine housing is 20% larger at .84ar, with a much less restrictive turbine wheel (spins slower for less restriction), and judging from others running this turbo, they're hitting 9psi (with 3x the volume) at 3500rpm, making 250whp+ on 2.5" exhaust with proper tuning and exhaust parts. Keep in mind that they're also making boost from roughly 2000rpm up.
/diatribe
essentially you could do rpm based boost control to smooth out the torque hump and people wouldn't cry about how the power comes on.
More faqs on turbos from garrett.
http://www.turbobygarrett.com/turbob...r/faqs.html#t3
how is my apartment?Quote:
Originally Posted by johnwag
The Corky Bell book "Maximum Boost" is a pretty good overview of turboing. Bit dated, but most is still valid.
Corky has been working on a revised version for a while now, should be available pretty soon if he doesn't get too distracted with other projects...
While it doesn't explain the physics, this is the best demonstration of turbo lag I've ever seen:
http://www.youtube.com/watch?v=RM1sGPwVSrU
The last 2 pulls show it nicely.
no, its not. This vid demonstrates boost-threshold. You need to read the garrett link. Did you even read this thread?Quote:
Originally Posted by mk2tmr2
As for the vid, I'm not surprised than an idiot in a lime green supra can't figure out that he needs to drop it down a gear.
At this point, I am frightened to ever say the T---o L-g word on this board ever again.
lag...........the amount of time it takes for your vehicle to start accelerating after planting your foot in it..........& turbo cars have a lot more of it.....unless the revs are up that is;)
turbo cars have none of it if you have a turbo made in the last 15 years. I don't care if you have a blower or a turbo, if you're stomping on the loud pedal at 2000rpm, you're not in target boost.Quote:
Originally Posted by VFR750
don't be. Everyone on here thinks their blowers make 250lb/ft off idle. Besides everyone knows that "turbochargers are laggy and unreliable!!!!!!!oneone1111"Quote:
Originally Posted by jrj512
Lag is the delay between a change in throttle and the production of noticeable boost when engine rpm is in a range in which boost can be achieved.
Boost threshold is the lowest engine rpm at which boost from the turbocharger will increase power over the engine's atmospheric equivalent. More simply, the lowest rpm at which noticeable boost (usually 1-2 psi) can be achieved.
Learn your ::Censor:: terms.
this video, of my car, demonstrates lag: http://www.youtube.com/watch?v=ub5VwlHRa8E
turbo lag =! vtec lag