what would happen if you forced the wastgate to stay open?

[Davezj]

as the title says

what would happen?

would the turbos make any boost at all.

would the turbos make boost but it would build up very slowly.

what would happen to the fuel going in to the engine?

if no boost was made, eg much less air pass the MAF (maximum of 1 atmosphere pressure, 0psi) would a wide open throttle still dump the normal quantity of fuel into the engine or would the ECU back it off to match the air flow.

just thinking of fuel economy.

and before anyone say why did you buy a VR4 if you are worried about fuel economy (i know i have in the past) i am just interested and there are sometimes when even i think of economy.

i am going to be playing with a manual boost controller with a max boost, standard boost, and eco boost settings.

[Nutter_John]

the air going past the MAF is always at or around 1 bar so changing the wastegates will not alter this

if you leave the wast gate open you will get a small amount of boost but very little , and the ECU will still fuel for the given amount of air as it does not see the MAP

[Nick Mann]

John, whilst what you have said is right, you have missed that with low or no boost, there will be much less air than normal in the cylinder for the same tps/rev combo, so therefore less fuel.

IMO this would make the car slower than a non-turbo, due to lower compression ratios etc. Just drive the car keeping the revs under 2000, or get a boost guage and keep the needle in the vacuum area..

[Davezj]

i can do the "keep the needle in the Vac area" but it is soooo hard to do knowing there is all that ooomph under you right foot.

Nick, point taken about the lower compression, hadn't thought about that. but yes it would make sense that it would be slower than a N/A car,

i am not that reserved when it comes tto the right foot.

i was after a ECO mode that i could flick it into so i couldn't do the no fuel, no fuel, no fuel being used, bucket loads, bucket loads, watch that fuel gauge drop.

Kieran came up with a good point about the fuel maps not coping with much less air senareio, as it does with the too much air senario not coping above a certaing amout. maybe it would cope 80% low but then it would run out of mapped point in the table and just revert to a fixed quantiy of fuel per degree of throttle position. which would end up massively over fuel with no boost.
If that makes sense.

i might try it to see what happens.

as a temperary measure i could just open the wastgaes manually and put a clamp on the bar to stop it goig back in to the actuator to see what happens.

it shoud start all right but after that i am not quite sure what to expect.

[Turbo_Steve]

Airflow will be measured by MAF and ECU should calculate load correctly and will fuel appropriately. It may over or underfuel a touch (Map is unlikely to be very accurate at 5500rpms with no boost) but it should be very safe...though it's going to drive like an absoloute dog due to the compression ratio, as mentioned.

If you want an "ECO" mode, replace or piggyback the ECU. Have it set a boost target that is equal or approximate to actuator pressure. Make the boost curve as gentle as possible, to prevent early spool.
Then ajust partial throttle tables to minimize "spot" fuelling, and make sure it's running as much timing as possible throughout the map, whilst keeping things as lean as possible below 50% load (but obviously watching det and egts). Water Injection will help here.
Why will this work? Delivering as much power as possible without using a significant amount of boost will mean you actually use less throttle, and tend to vary it less (responsive throttle results in less anticipatory acceleration, ergo less partial throttle, ergo less spool, ergo less fuel usage).

These cars seem to fuel viciously on spool.....I've followed ours, and it's rich as an oil baron. Partial throttle seems almost paranoid on the std ECU maps.
Turbo'd cars also tend to run extremely rich on boost to attempt to keep cylinder temperatures down. There are better ways.

[Kenneth]

I have to disagree with anyone who says the mapping won't be accurate.

It might not be ideal, but it'll be just as accurate as on boost.

Don't forget the mapping is LOAD vs RPM = Target AFR. Once the target AFR is known then the MAF sensor can be used to calculate exactly how much fuel is required to attain that AFR.

Sure, you may have a pod filter which screws the MAF reading, but then if you still have a pod filter you deserve bad fuel economy.

In saying that, I suspect that having no boost won't alter fuel economy much anyway. The reason being that the fuel enrichment on throttle change seems to be quite high. This is almost certain to be where the VR-4 uses most of its fuel, having no boost isn't going to re-map the ECU to dump less fuel when you hit the gas.

The only way to conserve fuel is to be gentle with the throttle.

[Turbo_Steve]

Not sure about the VR-4's Ken, but older Evos and Scoobs have odd maps in the more extreme areas. Innaccurate was probably a poor choice of words, but (for example) high revs, low load on an MY95 UK Impreza will result in AFRs of 11 or 12! Likewise, high load / low revs seems to be absurdly rich: 2800rpms with high load can see 10:1!
My Evo seems to have some frighteningly lean areas: at 4800rpms, but load less than 10% seems to have 44degrees of advance but a target AFR of 16:1...it even shows some light Detonation on UK fuel at this point.
It's weird. I don't doubt manufacturers have some reason for this (anti-stall? Something to do with GrpN? No idea) but when you deviate from normal operation I've seen some odd stuff.


The 300 had a huge fuelly lump (12.8:1) between 2600 and 3300 at loads less than 50%. I can only think that they were worried about Det if the throttle was snapped open, so over compensated: this was missing on later spec ECUs as well as aftermarket items. So, yes, Innacurate was a misleading choice of words, but I always have a vague distrust of factory maps in unusual zones.

[Kenneth]

Sorry Steve, I am a bit anal sometimes about terminology.
I guess what you would mean then is that it may not have been mapped to suit running without boost.

I would agree with that, as you can almost guarantee the TPS load modifier would be inconsistent with the actual MAF load calculation. Not sure if it would be off enough to change load points, but it very well could.


In saying that, I did dive my old car a very short way with the MAF attached directly to the throttle body, and that behaved perfectly

Was part way through intercooler mods and had to shift the car... I was rather gentle with the throttle, but it all worked!

[Turbo_Steve]

Ken, that's fair enough: things need to be right, and I can be a bit vague (especially on forums where you try and keep things "punchy"..usually cos you're supposed to be working )

I'm amazed the MAF was that reliable in those circumstances! I'd normally associate the Manifold inlet with a fair amount of turbulence. Guess you never know until you try

I've run a MAF with a 6 inch pipe to the turbo inlet on a big-turbo conversion. That proved to be a mistake!!! The vortex generated by the turbo inlet was sufficient to cause a poor enough reading to stall the car as it started to spool!

[Davezj]

Wow this is great info and i like to see 2 people have a reasoned and well put together discussion keep it guys, i am finding this very helps.

the more info i can get the better.

It is sounding that the car should run ok with the wastegates open but not sure if it will actually help with the fuel economy.

and we all know there is only one way to find out and that is to try it.

i will post up what happens when i try it!

[Turbo_Steve]

I like that attitude! If you DO intend to stick with any "wastegate staying open" shenannigans, though, I'd definitely consider borrowing an AFR off someone for a few days.

[Davezj]

Haven't done it yet as was surprised to see the front actuator rod is burried under the exhaust manifold andi think it is going to be a right pain to get to, unlike the rear one which is right o top.

i won't be only opening one up as that would just be all wrong.

will have to think again about how to do this, i might have to make something to pressurise the actuator line with a gas bottle and regulator connected at the T point of the actuator pressure line.
i will be able to set the pressure to 7psi which will ensure the actuators are open fully.

what is the fully open pressure for the actuators. any ideas?