Hi,
I have a kit car with an rx7 turbo II engine installed in it. It has an external wastegate and a boost controller installed.
I\'m struggling to understand the relationship between how the spring combined with the boost controller controls the minimum/maximum boost.
I\'ve recently had all of the exhaust/turbo dismantled to replace a gasket between the manifold and the turbo. I\'ve reassembled all of this and there are now no leaks. As part of this I also replaced all of the hoses from the turbo to the boost controller and from the boost controller to the wastegate. I did this because on inspection the hoses were in a bad way. Also, before I bought the car, the previous owner put a new wastegate on the car.
After I put it all back together the car is making more boost than it previously was. With the boost controller turned off the car was making about 0.7 bar boost. This doesn\'t sound like a lot but this engine makes about 400bhp with 0.8 bar boost which is what the car is mapped for. Previously the 4 settings on the boost gauge gave varying maximum boost levels which were 0.2, 0.4, 0.65 and 0.8 bar boost and this is the state I\'m trying to get back to.
I can program the level of boost with the controller by adjusting a level on the controller. This is a value between 1 (lowest) and 100 (highest). With the system rebuilt with no leaks and the controller set to level 1 I get 0.7 bar boost. With the controller set to level 2 I get 0.85 bar boost. This clearly doesn\'t give me much control over the boost levels, certainly not the level of control I\'m after.
I read that a boost controller helps control boost but the minimum level of boost is controlled by the spring. Therefore I swapped the spring out for a weaker one. Now, with the boost controller in the off position I\'m getting 0.5 bar boost which is more like it. Then I programmed the boost controller to level 2 (out of 100) and this gives me 0.6 bar boost. Encouraged I then start to increase the boost controller level but I can\'t now increase the boost level past 0.6 bar even by going up to level 40 on the controller.
At that point rain stopped play as I was getting wheel spin in 2nd under boost and the tests started to get a little dangerous.
Is my understanding of how these components work together correct? If it isn\'t can someone let me know where I\'m wrong. If it is correct can someone give me an idea what might be happening based on the testing detailed above?
I understand that a conclusion may be that I\'ve plumbed the new hoses in incorrectly and while I agree that there is a chance it should be unlikely as I took off one hose, cut a new one to size and replaced that hose. That is I didn\'t take them all off but did them one at a time.
The other potential issue is that I definitely have an earthing issue somewhere which I need to resolve and this could, I guess, be affecting the way the boost controller is working. This manifests itself as the engine speed dropping when extra electrical load is placed on the engine such as the lights, the radiator fans and so on. I believe this to be an earthing fault which results in the alternator being loaded up causing the engine to run slow.
Anyway, enough of the ramble... any comments or pointers regarding controlling the boost with the system I have would be most welcome.
Thanks,
Mark
PS. Another quick question... would the system I have benefit from a dump valve of some kind? When I change up gear I can hear the turbo making that fluttering noise that I understand implies that the turbo is stalling as I lift off. To be honest there\'s absolutely no lag whatsoever on gear changes and it behaved itself impeccably on the last track day but would a dump valve be beneficial for turbo longevity?
the with/ without dumpvalve debate is likely to open a can of worms again :evillaugh
It sounds like the spring in the wastegate is too weak and the exhaust gasses are simply pushing the wastegate open meaning you can\'t build boost.
What turbo do you have and what boost controller? Might be an idea to post up specs on your car :)
Quote from: m1tch;828625It sounds like the spring in the wastegate is too weak and the exhaust gasses are simply pushing the wastegate open meaning you can\'t build boost.
What turbo do you have and what boost controller? Might be an idea to post up specs on your car :)
Of course, sorry. The boost controller is an older style blitz SBC controller, the turbo is a garret T04E with a 1.0 turbine housing, the wastegate is a 60mm wastegate.
Regards,
Mark
Wow a 60mm on a T04E lol slight overkill, might be why you aren\'t getting any more boost, the wastegate opens and lets so much exhaust out lol
Ok. I\'m afraid I don\'t know enough about how these things work to justify the sizing of the wastegate.
If it helps explain why this system is the way that it is this car was built by Tony/antnicuk and with his level of experience I\'d be surprised if it was the wrong choice. I haven\'t asked Tony for his advice on this by the way as I\'ve asked him a fair number of questions already and don\'t want to take him for granted.
Going back to basics though... without a boost controller I understand that the spring dictates the level of boost but shouldn\'t the boost controller regulate when the wastegate opens by providing positive pressure which will work against the spring?
Also, with the original spring that was in the wastegate when I bought the car it does make 0.7 bar on level 1 and 0.85 on level 2 on the boost controller. Therefore the system can easily make the boost level I require (0.8 bar) as it stands. The question I have is how I combine springs and boost controller settings so that I can vary the required maximum boost levels from something like 0.2-0.4 bar up to a maximum of 0.8 bar?
Many thanks,
Mark
Ah you have the white track car?
The boost controller regulates the amount of boost/vacuum the wastegate gets
Here is a short video on wastegate springs etc:
http://www.youtube.com/watch?v=LStlqe64m4M
Quote from: m1tch;828636Ah you have the white track car?
The boost controller regulates the amount of boost/vacuum the wastegate gets
Here is a short video on wastegate springs etc:
http://www.youtube.com/watch?v=LStlqe64m4M
Thanks very much.
Yes, it\'s his old white track car.
Regards,
Mark
Its impossible to have your boost lower than the spring pressure. The pressure hose from the turbo goes into the bottom chamber in the wastegate and pushes a piston/diaphram which is connected to the valve against the spring, this is base pressure.
Without that hose fitted it will over boost to turbos maximum.
The boost controller dictates how much pressure from the turbo pressure hose gets put into the top section of the wastegate ("T"d from top hose) which pushes against the piston/diaphram, canceling out the bottom hose.
Pressure in the top, boost rises. Vented top, base pressure, the controller does this on/off very quickly constantly keeping the pressue stable.
As a rule big wastegates are better at controlling low boosts and small wastegates are better at controlling high boosts.
Hope this helps.
Figured it out... the diaphragm in the wastegate had deteriorated and was not air tight. Replaced it with a new one and all is working as normal again.
Thanks for the info and help.
Regards,
Mark