Is a turbo bypass wishful thinking?

[foxdie]

I might be a little insane in thinking this, but I'm putting this idea out there to see how feasible it is.

My idea is thus..

1. A series of products similar to this to effectively isolate turbo(s), it would allow selection between a true N/A intake + free flow exhaust and forced induction + slightly restricted exhaust because of turbo
2. A selectable fuel map to suit each application (via a ViPEC or something else)
3. All controlled via a single dash switch / key switch that will select the correct fuelling map and bypass valve positions at the same time
4. Fuel economy and performance on par or better than a V6-24 when in bypass mode (for city driving as an example)
5. Turbo powah for when you want to play (do I need to give an example of this? )

It'll require a fair amount of pipework and space might be a restricting factor, but doe it sound too far fetched?

turbo-bypass.png

[miller]

engine compression differences says no

[Mark 4]

Just fit a big single turbo that will not spool up when driving at low revs around town.

[foxdie]

My line of thinking is that the turbo being in the way of exhaust gasses in itself causes a small loss of performance, I was hoping to be able to completely remove it from the equation to get as much economy out of it as possible, lean it out as much as it'll safely go after doing so, maybe get 30+ MPG

*dreams*

[Davezj]

i was told engine would not like it due to the compression ratio as well when i asked this question a few years ago. i will see if i can find the thread.

[Davezj]

Found it
http://www.clubvr4.com/forum/showthr...e-to-stay-open

[foxdie]

Hmm, good read that.

Anyone know if there another way to achieve what I'm trying to do? It's almost like a "Valet Mode", lock away the horses and get better fuel economy during the weekdays or if the car is lent to a friend, and then unlock the beast for playtime.

Would replacing the wastegate for one set to 0.1 or 0.2 Bar (and then naturally use an actuator to hold it closed for high boost) be a more valid option?

Edit: That or maybe start investigating throttle-by-wire? (That'd definitely need an aftermarket ECU / control system, but could smooth out acceleration changes for economy and sharpen it up for sport).

[miller]

Jase,

Just drive sensibly. I would imagine it would take longer to recoup the costs of this exercise (if it would work which i dont think it would) than the costs of LPG installation. LPG at best is a two year recoup on installation costs versus fuel saved.

In the meantime, drive it for fun. If its not fun filling up then maybe its time to change overall to an mpg muncher.

[foxdie]

Drive sensibly???

As Dave said in that thread linked above, when you know the powers under your foot you're gonna use it

In all seriousness though, this threads idea probably isn't feasible like you all said; Compression ratio.

[lancerevo3]

just buy yourself a n/a v6 or a micra

[Turbo_Steve]

Learn to drive the VR4 economically.

Fit an aftermarket ECU (Motec, Vipec) and map for lean cruise and allow it to control boost - allow it to control boost and have switchable low/hi boost targets

Fit bigger turbos to stay out of the "boost region".

Combine the above with LPG.

Get some better cams ground.

Get the head skimmed something silly / different rod/piston/crank combo to reduce CR and increase torque.

Stop wasting time trying to turn an inherently thirsty car into an efficient one, and buy a 300+bhp diesel, enjoying 50+mpg cruise and plenty of go.
By the time you've spent out on most of the above, you may as well have done the last. There are some margins in the mapping, but I think it would take a long time to pay for itself.
Learning to drive it more economically makes a huge difference, but I have to confess I haven't manage to do it consistently on anything other than a long run - the VR4 just eggs you on

[Wodjno]

I think it's feasable It's something that has crossed my thought process in the past..
Regarding compession ratio? VR4 compression ratio is low, even for a Turbo charged car! Up the compression ratio. This isn't going to hurt VR4 power to a point that will be that noticeable.. Change the Cam duration. Scavenging is a biggest issue here. So i reckon it's feasable But then i could be wrong

[bradc]

V6 pistons will fit straight into a VR-4 to help off boost driveability, but obviously comes at quite a big cost.

lpg makes more sense than any of the other stuff talked about in this thread so far

[Louis]

Jase,

Just drive sensibly. I would imagine it would take longer to recoup the costs of this exercise (if it would work which i dont think it would) than the costs of LPG installation. LPG at best is a two year recoup on installation costs versus fuel saved.

In the meantime, drive it for fun. If its not fun filling up then maybe its time to change overall to an mpg muncher.

I totally agree with Mike. Do you have a boost gauge fitted?, I can drive "normally", a lot of the time, and the boost gauge hardly goes above the zero, even when accelerating. so the turbos are hardly working at all. the down side is as mentioned then they are possibly a block in the pipe!, but they are spinning all the time, just not boosting more than normal pressure.
You are only using stupid fuel when the boost is up, as the ecu dumps fuel in to COOL the engine, so it is wasted. So stay off boost!.
I have driven (in a controlled environment) at a steady 90mph on a flat road, with the vacum reading -0.4 (so the engine is sucking more than the turbos are boosting), and the A/F guage flashing red because the mix is lean, so, as economical as it gets. If I get to a hill and push the throttle then the vacume changes etc.
You can also stay off boost by changing gear manually, if you come off a round about and accellerate, the car will stay in 5th and the turbos will boost up while trying to move the car in 5th, (unless you kick down, and it goes on boost anyway). If you change down to 3rd manually (in trip mode) you can accellerate without goin up into boost.
But I totally take the point "if it's there you are going to use it".
But I reckon that whatever you do would cost so much that it would make it unfeasable, or uneconomical. You could move the tubs further back and put electric exhaust cut outs to a turbo bypass pipe, but the space and work to do that would be mental!.
I think your best bet is switchable LPG and a full tank of gas, (although you ecu will learn from knock and restrict power until it re learns, so not a quick switch over from gas to petrol), but a few folk are running LPG and say it is good!

(Turbo cars have lower compression ratios than N/A cars)

[The Vee]

V6 pistons will fit straight into a VR-4 to help off boost driveability, but obviously comes at quite a big cost.

Is that the only change that Mitsi did to alter the CR? Hmmmmm..............................

[fluffnik]

You can also stay off boost by changing gear manually, if you come off a round about and accellerate, the car will stay in 5th and the turbos will boost up while trying to move the car in 5th, (unless you kick down, and it goes on boost anyway). If you change down to 3rd manually (in trip mode) you can accellerate without goin up into boost.

Has anyone looked into reprogramming the gearbox ECU?

Suppressing light throttle downshifts would certainly help economy...

[Davezj]

i forgot to say i came up with a method of seeing what a VR4 would drive like with very minimal boost, well that is what i think will happen.


wastgate open fully at about 7-8psi.
get a some compressed gas at max 14psi as this is the wastegate max safe working pressure according to the manual (how you get it is your choice).
connect gas to wastegates.
apply gas to wastegates via some kind of valve.
they will open fully and you effectivly have the bypass of the turbos as the wastegates will be fully open allowing most of the exhaust gas to bypass the exhaust side of the turbo so it does not spin up.

let me elaberate,
compress gas could be got via the following metheds, some easier than others.
1. get welding small gas bottle with regilator set to 14 psi and pressurise the wastegate boost pipes while disconnecting the boost line from the manifold via a solenoid valve.

2. get a canister with 2 ports on it, one port is a one way vlave into the canister connected to the manifold. the other port is regulated to 14psi and is switched on and off with a solenoid valve. extra solenoid valve fitted in line with normal boost pipe from manifold and wastgates.
how it works:-
inline solenoid valve is open to allow normal boost pressure to wastegates.
canister starts empty.
go for a drive give it some right foot canister gets filled with 7-14psi boost gas via one way valve as pressure equalises acress all available volume which is open for it to expand in to.
when you lift off accelerator manifold pressure is vented via BOV, but canister remains full of 7-14psi air.
now you want to open the wastegates. so simaltainiously close the inline solenoide valve in the boost line and open the solenoid valve that releases presure from the canister to the wastegates. this wll presurise the wastegates to a presure slightly less then what is contained in the canister as pressure drop when gas expands into a larger volume (not quite sure by how much).
you are now running with the wastegates open and only minimal boost should be generated.

so method 1 is much simpler to use a test bench. but method 2 does away with having to replace the gas bottle every so often.

hope my explanation is understandable, if not just say and i will draw some pictures and upload them.

[bradc]

Andy, the shape of the heads could well impact the CR as well, but V6 pistons are different, so changing to them would bump up the compression. Random fact - a V6 and VR-4 share the crank and rods!

[The Vee]

Cheers Brad - Knew there was a reason for keeping my old V6 lump. Time to fiddle with it methinks

[Nick Mann]

A while back I destroyed a turbo enough so it occaisonally stalled. This lead to zero boost pressure and a strange whistling noise as the turbo that was still spinning drove the air the wrong way through the cold side of the stalled turbo. The car was painfully slow when it happened. MUCH slower than a V6. I'd compare it to my non-turbo diesel van, when it is fully loaded! I'm assuming the fuelling was still good as the maf would have been reading the flow right and there certainly wasn't any soot behind the car as you get with a boost leak. I realise that a stalled turbo is potentially a restriction on the system that a bypass would avoid, but even so, I think that the car would be massively gutless if they were bypassed.

If you really did want to peg the car back then surely there must be a way of fitting a dump valve that opens above a certain boost pressue? Maybe use an external wastegate on the inlet system? It would need to be plumbed back in to the inlet system before the turbos to avoid upsetting the MAF readings though. Maybe you could modify the dump valve so it has a mechanical switch to hold the diaphram open?