nah, i'd bugger off that TPS switch for sure. you definately want an on/off somewhere handy, mine is on the centre console. the car is tuned to idle with the blower on (slight intake positive pressure) and doesn't like to idle with it off. with a good bypass setup, you won't notice any difference to every day drivability and will still get good economy. mine has not changed noticeably since the blower conversion, and still gets 400-450 km to a tank.
Quote:
Originally Posted by StockyMcStock
mine has not changed noticeably since the blower conversion, and still gets 400-450 km to a tank.
it does better skids too which u still need to let me have a go
Some original photos have not been recovered yet.
Stocky is spot on. Trying to describe how the supercharger bypass works to someone, and put it into words is pretty difficult. If you could see it working on the car, you would quickly realise what a simple idea it really is.
Toyota use an identical system on all their factory supercharged engines, but the whole thing is built into the inlet manifold casting. There is no way you can just grab a Toyota supercharger bypass valve and adapt it to another engine.
I have experimented with this for years, and the best system by far, is to adapt a turbo external wastegate. The only thing you need to do to it is fit a suitable spring, and it will make a perfect very smooth operating proportional bypass valve.
As Stocky says, you can set it up so the engine runs without the blower working, up to some suitable throttle opening. Boost then comes in smoothly above that up to full throttle. You can set it up any way you want by changing the spring force in the wastegate. It will feel and drive like a factory setup. You can drive it around all day in traffic and never see boost. Ease down on the pedal a bit more, and away you go under boost........
here's a problem i was thinking about a while back. not sure if it's an issue though....
consider that your turbo's wastegate gets its reading from the plenum. if you have a bypass system and are running say half throttle just cruising up a hill for instance, the plenum is reading (say) atmospheric pressure.
if the engine is under load though, it's still going to spin that turbine up pretty hard. this will mean that boost might actually continue to increase up to (say) 5psi with the same throttle opening, no adjustments from the driver, as the turbo feeds more air into the blower, which then feeds it to the engine.
because the bypass can only flow so much at a certain pressure, increase the pressure in the piping behind it and more will make its way into the plenum. does it cause a positive feedback loop or am i missing something? ever experienced it tony? a LARGE poppet valve would virtually eliminate the problem but it would still occur if the valve was JUST open a bit.
No nothing like that ever seems to happen. I have never experienced any form of instability either from the turbo or blower. The turbo works exactly as it would without the supercharger. With a supercharger fitted, the turbo "thinks" it is fitted to a much larger displacement engine. That is why you can run a much larger turbo.
The bypass around the blower is actually a very strong negative feedback device, which is why it is so smooth and drivable. If the airflow through the part open throttle increases, the pressure drop across the throttle also increases, opening the bypass further. No doubt you have tried disconnecting the hose to the wastegate and tried to drive it with the bypass permanently shut. You know how jumpy and harsh it feels to drive. But the bypass system smooths all that right out.
Fitting a turbo to it just makes it a lot more powerful without any loss of the great drivability and throttle control you already have. I think you are in for quite a surprise when you get the twincharge system going eventually. It is vastly better in every respect than either just a supercharger, or just a turbo. It is pretty difficult to describe really.
hehe yeah i did try that once, bloody thing was nuts off the line, you'd open the throttle 1/2 way and break traction. the gearbox didn't like it and you couldn't cruise effectively, i very quickly put it back on!
at the moment tony i'm trying to decide whether or not to go twin cam head, i think it may end up being cheaper in the long run because i won't need forged pistons. but changing the head means new blower mounts, so yeah i'm still deciding. turbo will probably be a T-66 or T-70, or if i can't afford those then a T04E with 1.22 exhaust housing. still a long way off though, need to get my fuel delivery sorted out and get the management in (have it, but haven't installed it yet) with a front mount.
anyone want to donate 10 grand to the fund?
That is a tough decision, I suppose it depends on your final power goal.
A twin-charge setup will make more power and have less detonation at any given boost level than a straight turbo setup, because boost can always be kept higher than total exhaust back pressure.
So the ET head is still going to be capable of some very serious power. If I had to choose between a DOHC head and an RB25DET manual gearbox, I would fit the gearbox.
i have basically two options:
1. rebuild an n/a bottom end to standard specs with new rings, bearings seals etc and put a twin cam head on it. the head i could get for 600-800 and the rebuild would be about the same price. this will lower compression to 8.3:1 or so and would support the 250rwkw which is my aim.
2. rebuild an n/a bottom end with forged pistons (+$1000 or so) and leave the SOHC head on. this would also be fine, and i could specify my compression ratio.
so in actuality it looks like it could be cheaper to put the twin cam head on, which is an interesting situation. i would have to change my top blower mount but there's a way around that, i'm sure.
as for gearboxes, i'm hoping a KEAS jatco will be put behind it, but otherwise it's a 25DET 5 speed i think. all comes down to money!
If you can get the head fitted for that, it would be a good investment. I was thinking more around $1,000 to $1,200 total for a DOHC conversion with all the extra small parts required. If a complete rebuild is planned at the same time, so much the better. The top blower mount is nothing. It's the blower location, drive system, and lower mount that is the real pain in the bum to get right. The top mount is just really a simple compression strut, not really under any sort of severe load. Fabricating a new one is going to be about a two hour job.
I worry about an auto behind an engine like that. Full throttle up changes put a pretty big strain on an auto where there is a lot of torque. Boost tends to spike a bit as well as engine Rpm is suddenly pulled down, placing even more strain on the clutches/bands in the auto. Still I think traction is going to end up as being the limiting factor to on road performance.
At some point in the future I am definitely going to build another twin charged car. The biggest limitation with the Laser 4WD is gearbox strength, which is why I never went any further with it. My next attempt will be with a 4WD Skyline. These have an extremely strong driveline. Driveline strength and traction is what finally limits you.
