RB20DETT TwinTurbo2Litre

[Ronin 09]

don't map sensors have trouble with idle and part throttle settings? something to do with not as fine resolution? and not that it would be an issue here, but MAP sensors are less fuel efficient (for the same reason)?

[Cubes]

Map sensors are also ever so slightly heavier on fuel. Hence they are not as accurate.

[MetBlue_GTST]

I run a MAP sensor and i have no problems with idle or part throttle (besides the rotational idle i run)... My fuel economy is about the same before i changed over to MAP and i'm making more power and using bigger injectors....

[rbs13]

if map sensors were so bad then all aftermarket ecu's wouldnt come with map sensors in the first place.. you only UPGRADE to aftermarket ecu's not down grade.. at a given power stage a afm will become a restriction weather it be 600rwkw or not, at some point it will end up restricting power or the abilitly to tune.

[shay]

have you considered 2 ca18 turbos? they flow enough for 130rwkw X 2 = 260rwkw. probably make it a bit more drivable too.

[Sydneykid]

Ho rbs13, you posted "if map sensors were so bad then all aftermarket ecu's wouldnt come with map sensors in the first place"

Nobody said MAPs are bad, just that AFM's are more accurate. The reason why some (not all) aftermarket ECU's use map sensors is because they are cheaper and can be integrated into the ECU itself (ie; small in size). Plus setting up an AFM on a car that does not have one can be tricky, no such trouble with Skylines that already have AFM's.

"you only UPGRADE to aftermarket ecu's not down grade"

The are plenty of OE ECU's that prove that wrong. They are way smarter and faster than most aftermarket ECU's. I would argue that the standard R32 GTST ECU (and it's 15 years old remember) is "smarter" than a lot of current aftermarket ECU's.

"at a given power stage a afm will become a restriction weather it be 600rwkw or not, at some point it will end up restricting power or the abilitly to tune"

True, but if that level is higher than your target power, why worry about it? Enjoy the smoother running and better fuel economy of an AFM equiped car. Two Q45 AFM's will handle 850 bhp, so there is plenty of room to move up.

There is a place for both MAP's and AFM's, but on road only and road/track Skylines, the AFM sensored ECU is still very hard to beat.

Hope that clarifies

[Cubes]

Originally posted by rbs13

if map sensors were so bad then all aftermarket ecu's wouldnt come with map sensors in the first place.. you only UPGRADE to aftermarket ecu's not down grade.. at a given power stage a afm will become a restriction weather it be 600rwkw or not, at some point it will end up restricting power or the abilitly to tune.

hrmmm .....

Who said map sensors where that bad?

Generally the main reason why people lean away from AFM's is because the power level they are after.

If they were building the car to be better on petrol (not likely) they would not ditch the AFM for the Map sensor.

600rwkw you wouldn't bother with AFM's unless you were going to run 2 Nissan Q45 AFM's.

[Warpspeed]

What I like about AFMs is that they are far more tolerant to slight changes in engine tune. They actually measure airflow directly, and that is a very important advantage in my opinion.

A MAP sensor cannot do this. A map sensor assumes that at a certain given manifold pressure, flow through the engine will be xxx CFM of air. But what if you move the valve timing slightly, or fit a different exhaust turbine housing ? You get to completely remap the engine because the breathing characteristics have now significantly changed.

This is fine for a competition car that spends more time on the dyno than on the track. But what if you are just an average joe with a car port at home, and you want to try a different exhaust muffler ? The change in exhaust back pressure might really screw up your mixtures, probably not by much but it will have some effect.

With an AFM, your new beaut muffler might change airflow, and the AFM just alters the fuel to suit the measured increase or decrease.

So, apart from all the theory, there are also practical considerations as well.

As far as restricting power, well, atmospheric pressure is around 410 inches of water, so if your airflow meter has a four inch water pressure drop, you are still getting 99% of atmospheric pressure and density. Not enough to really worry about I think.

The induction temperature at your cold air pickup point might be 300 degrees Kelvin (at 27C ambient), if you can lower this by 3C you will pick up 1% in air density which will easily compensate for the drop across your AFM.

So some guy fit two huge Q45 AFMs to reduce the imaginary horrible power loss, and then fits a couple of crappy pod filters right behind the radiator. I cannot understand the logic behind any of that.

[Cubes]

Hrmmm Interesting.. Thanx Warpspeed..

[slip]

Originally posted by R32 GTSTT

Very interesting, Do you think that i will need a bigger afm to support the larger airflow meter

Dude, do you know what an AFM is?

You've just asked if youll need a bigger AFM to support the larger AFM.

[R32 GTSTT]

the reason im putting RB20 turbos on is that i already had one, and they are cheap, when it is all up and running and if its really laggy, ill might have to consider a RB30 bottom end. But anit these alot weaker than my bottom end. What type of internals would i have to put in, like pistons? chankshaft? gearbox??

[Gradenko]

R32 GTSTT, please do a search to answer the rest of your questions. Pistons, crankshaft and gearbox for a RB30 have been discussed a million times already.

You still haven't told us how much power you're looking for. Do you expect to drive this car on the street?

[Cubes]

They arn't weaker.. They are the same.

The max you will need to rev it is 6500-7000rpm.

Read my pdf guide.

[R32 GTSTT]

im only puting rb20 turbos on cause i already had one.

[R32 GTSTT]

i haven't, just chose the rb20 ones cause i already had one. Does anyone know what a good set of upgraded injectors are for my rb20det, for 270rwkw

[R32 GTSTT]

i put r32 turbos on coz i already had one. Does anyone know what type of injectors to get to support 280rwkw?

[Cubes]

It won't make 280rwkw. Well maybe with a 1000rpm powerband..

[R32 GTSTT]

well i wasn't to concerned about the power it wil make. I have a open mind about it, i just want to make the most power out of these 2 turbos at the moment. I do plan to drive it on the street, and drags aswell. If it is extremely laggy then i will consider smaller turbos, or doing a RB30 conversion. The main concerns i have at the moment are if my fuel pump, injectors, and afm, and ecu. Just wondering if u guys think if any of these things will be holding back my power?? Cheers

[Cubes]

Its not that they will be holding back your power but it may cause you to blow a motor if it leans out.

So.. Get it on a dyno AS SOON AS the turbo's are fitted.

Drive it off boost until you get it to the dyno.

[R32 GTSTT]

yer cheers, i think i will, just have to find the right place to go in perth. Say the stock turbos come on boost at 2800, ppl r saying two wont spool up until twice that say 5500rpm. But doesn;t the car produce more exhaust gas between 2800-5500 than it does from 0-2800. So wouldn't it take much less than twice the rpm??