outdrifting wrote:
ok quick update this turbo is on my car now, its running stock boost since it hasnt got a computer yet. It is laggier than a stock t25 but when comes on it comes harder.
I should have a computer, cams and injectors done in the same hit in 2 weeks so ill post up a dyno sheet from when it gets tuned.
Intersting that you found it laggier I found after I got the tune right that it crapped all over the T25.
DumHed wrote:
The difference is pretty simple.
When calculating the Air / Fuel ratios, the mass of the air is the important part (because the volume and density change with temperature, altitude, etc).
A hotwire MAF (Mass Air Flow) sensor directly measures the air mass entering the engine, so the ECU can calculate the fuelling easily from that.
A MAP (Manifold Absolute Pressure) sensed setup guesses the air mass based on the pressure in the manifold, and a separate air temperature sensor. Non linear relationships between pressure, temperature, and flow - as well as a sensitivity to any modifications the engine's flow or efficiency mean that the MAP sensed system can never be as accurate or repeatable as MAF.
On serious race cars it's less of a problem, to the point that most race engines only use the MAP sensor to work out the atmospheric pressure on the day, and all airflow calculations are based purely on throttle position.
Turbo engines need the pressure sensing obviously, but due to the inaccuracies present a larger error margin needs to be included in the tune.
It's very easy to pick a car running an aftermarket MAP sensed ECU compared to a MAF setup. There's always some areas of slight hesitation and roughness in the tune.
Factory MAP sensed cars do a bit better, but only while all parts are factory. Change the exhaust and you'll need to re tune. Change something like cams and the car won't even start...
Spot on about the cams
I poured black smoke out the back when I changed the cams but I did change from 370cc injectors to 650cc injectors so we have to cut it some slack.
badhairdave wrote:
There's definately a restriction somewhere based on your boost level and your injector duty.
Stock intercooler is probably the prime candidate causing a restriction in the inlet that limits the flow to the turbine blah blah repeating cycle bullshit. It's easy enough to check boost before and after the stock cooler to find out if it's a restriction.
I doubt the inlet manifold is causing a restriction, and i don't think the exhaust will be hurting it that much either
Turned out to be the cams that were holding it back. After I changed the cams it made 20psi on the same combo.