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overboost problem


L33

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Cheers for the help guys

 

it would be nice to see the light at the end of the tunnel

 

I will try and see what happens tomo

 

I don't really understand the WG stuff tho? Why is there different spring sizes? What's the benefits of different sizes? And not quite got my head around if the manifold is causin a restriction why it would over boost? In my head I'm thinking restriction/blockage would cause under boost as can't release? I no this is wrong but don't understand why

 

I have been patient that's why I've had so many problems/been ripped off and walked all over but hey I have my car back :)

 

Wastegate is for getting rid of unwanted boost pressure.

 

If the WG pipe hole is to small it cant get rid of the unwanted boost, that unwated boost then causes the turbo to "overboost"

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The WG spring rate detemines the minimum boost the engine will produce. This is the base level boost, an EBC is then required if the boost level needs to be raised (same as a UK car going BPU).

 

The manifold issue mentioned can be caused by the route to the wastegate being too small. The wastegate bleeds off exhuast gas away from the turbo to regulate boost pressure the turbo produces. If the feed to the wastegate is too small, under very high load, the exhaust gases get pushed up through the turbo instead of out the wastegate. This means the turbo produces more boost and effectively renders your boost controller useless.

 

Think of it like this, if the wastegate hole is blocked off completely (i.e. no wastegate) - what happens? The turbo will massively overboost (talking way over 2 bar here!). If the hole from the manifold to the wastegate is too small to bleed off the gasses these are forced up through the turbo increasing boost regardless of BC settings

 

Edit - or as Jamie said, but much quicker :D

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That's made sense now thank you! I'm a bit of a simpleton when it comes to engines :(

 

With regards to all my problems, its made me more willing to give my time helping others to avoid this and have been talking to jamesy recently as he is about to take the single route! Just means he can avoid all this but I'm sure he wil be fine, he is using a different garage which is a win straight away

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Just a thought, my wastegate must be working ok as when I'm on boost even if I gradually come on boost the screamer pipe kicks in?!

 

So what is the spring sizes available? You say the spring determines minimum boost....so correct me if I'm wrong but if I get for argument sake a 1.5 bar spring I won't need a boost controller or does it not work like that?

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Just a thought, my wastegate must be working ok as when I'm on boost even if I gradually come on boost the screamer pipe kicks in?!

 

No mate, all that means is that the wastegate is opening, it doesn't mean the wastegate is opening correctly or that the wastegate feed pipe on the manifold is large enough.

 

Back to basics first - turn off the BC, take it for a few hard runs in 3rd gear and see if the boost is at a constant and stable pressure after the turbo is spooled.

 

BTW, in case you're not already aware, if you see pressures higher than it's mapped for, give up testing and take a steady drive home :)

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So what is the spring sizes available? You say the spring determines minimum boost....so correct me if I'm wrong but if I get for argument sake a 1.5 bar spring I won't need a boost controller or does it not work like that?

 

Essentially that's correct, however you cannot reduce pressure below the level of the WG spring. In an ideal world the WG spring rate should be the minimum boost you want to see (normally 0.8 bar), the EBC is then used to raise it to your desired level at that time - i.e. your settings could be 1 bar, 1.2 bar, 1.4 bar and 1.6 bar.

 

It's good for use during poor weather conditions when you don't want 500+ib/ft at 4k rpm!

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Well I'm on the motor way tomo so I will do some tests, glad I got the defi stuff now so I can do my peaks :) I'm not fully boosting much any more any way for a few reasons....no matter what speed when I put my foot flat to the floor the back of my car thinks its the front, the sudden kick of power is light going into lightspeed and the screamer pipe is beginning to irritate lol

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Great :( I do go very steady scared not to! If I'm doin about 40 and plant it it does step out a bit! Standing starts are impossible as it really stepps out, I have to go steady when pulling away from people my ass don't hit them! I'm looking into better tyres was quoted 200 each for the r888 from camskill

 

Since I pulled the trac fuse out I can now spin the wheels as I had to see what diff it was, I have a torsen as there is 2marks and not a lsd as I tested when on a ramp off ground as I was able to stop a wheel with my hand

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Great :( I do go very steady scared not to! If I'm doin about 40 and plant it it does step out a bit! Standing starts are impossible as it really stepps out, I have to go steady when pulling away from people my ass don't hit them! I'm looking into better tyres was quoted 200 each for the r888 from camskill

 

Since I pulled the trac fuse out I can now spin the wheels as I had to see what diff it was, I have a torsen as there is 2marks and not a lsd as I tested when on a ramp off ground as I was able to stop a wheel with my hand

 

It will want to step out in low gears when the turbo spools, that's normal, but it should be easy to control. If it's throwing the car sideways there's an issue (tyre's/drivetrain?)

 

Torsen is LSD.

You cannot check for a torsen diff by jacking and spinning the wheels. Torsen mean "Torque sensing". I.e. if you jack the back up, there's no torque on the other wheel so it will act like an open (non-LSD) diff.

 

The only real way to make sure is to take the back plate off the diff and see whats there, or do the burnout test. I prefer the latter :D

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Great :( I do go very steady scared not to! If I'm doin about 40 and plant it it does step out a bit! Standing starts are impossible as it really stepps out, I have to go steady when pulling away from people my ass don't hit them! I'm looking into better tyres was quoted 200 each for the r888 from camskill

 

Since I pulled the trac fuse out I can now spin the wheels as I had to see what diff it was, I have a torsen as there is 2marks and not a lsd as I tested when on a ramp off ground as I was able to stop a wheel with my hand

 

 

Hi mate. So if u havent got an LSD fitted surely that will help you not to slide the back around too much compared to if u did have one.

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A torsen is not a lsd! A true lsd u would never be able to stop a wheel if up on a jack apparently, and was mentioned before think by jamie p a torsen is not lsd

 

I thought both wheels spinning would stop the car stepping out as its equal power through the wheels

 

I don't think its a problem just a power thing, mainly when going slow and the tyres causing that problem

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A torsen is not a lsd!

 

A Torsen diff IS an LSD mate. When torque is lost on one axle it applies power to both axles, therefore limited slip.

 

There are many different types of LSD, torsen being only one of them.

 

For the record, the supra only ever came with two diff types from the factory, open and torsen.

 

Anyway, we digress from the original topic :D

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