M35 Boost Spike/creep

[bigkevracer]

are you sure you have the solenoid plumbed in correctly?

ive seen similar problems where people install it the same as factory, when the aftermarket ones generally aren't designed to work that way.

I think so Iain, and it was working correctly. But I'll look into that next.

If you are still having issues you may have to look at the split dump unfortunately. Quite often the wastegate pipe flows poorly causing boost to skyrocket once power goes up.

Did a proper check on mine & just on the wastegate spring it hits 24psi at the top of the rev range (holds 15-16psi till then). I'm running your dump pipe Scotty, so in my case I think it's the wastegate itself that is too small.

I think when I had your spring on the factory turbo I had no problem holding 16psi, so you may be onto something re the different dump pipe.

I'm pretty sure it isn't the dump pipe. The problem only manifested itself when the car was tuned (or being tuned), and there's no problem with the flow of Andrew's dump pipe design.

I've fixed a couple of hose issues I've seen and now it's not so bad. Still spikes to 19PSI with or without the EVC on, however behaviour seems similar to Leon's: EVC off, it holds 15PSI until it hits about 5,500 rpm, then it'll go up to about 19PSI.

With the EVC on, it'll hit 19PSI too. So I'll adjust the offset on the EVC and see if that makes any difference, and just replace the rest of the vac lines when they turn up. Rocker cover breather is getting replaced tonight.

[scotty nm35]

With more power comes more exhaust flow, and more wastegate flow. If some part of the wastegate system can't bypass enough the gasses will flow through the turbo instead, causing spiking. How you can rule out the dump even though it's untested is a little concerning. Changing to a bellmouth design is the usual fix for poor wastegate flow, do some searches in the forced induction section if you don't want to believe me.

If you can fix the spiking issue you will unlock more power as you will have gained exhaust flow.

[bigkevracer]

I'm not completely ruling it out, however there are other far more likely suspects that are also easier to change that I'll be looking at first, like dodgy original vacuum hoses that aren't as sealed as I first thought.

What PSI do you think this new wastegate spring should be at?

[scotty nm35]

Get it on the dyno and get a printout of the boost ramp, it will show you where it's spiking and also what the wastegate is holding. It should be around 15-16psi if you run the actuator directly off the boost source.

[bigkevracer]

Ok. We have progress.

Had a bag full of ebay goodies turn up today, some more vac hose, some t-pieces, cable ties and hose clamps.

Replaced the 3mm hose from the end of the plenum to the stock boost sensor. Made no difference, but I'm glad the piece of crap that was on there is gone. Brittle thing was dying a slow, painful death.

Then it occured to me randomly, while I waited to catch up with the SAUSA member that I bought a cheap boost gauge off of, maybe the boost controller is hooked up right, but the hose for the boost sensor part isn't? I'd connected the hose to what I thought was the factory boost sensor originally, in the pipe the BOV is connected to before the throttle body.

Swapped this hose with the hose I'd set up for the currently unused MAP sensor, which was tapped into the line running from the plenum to the top of the BOV.

Drove off. Pressures looked a lot better. Suddenly I have a feeling it wasn't reading vacuum in the original location, which it is now. I'll swap back over tomorrow or Saturday to double check this.

Driving it, boost seemed to be well in check, about 15.3PSI (set to 15PSI low boost), hitting about 16.5PSI higher in the rev range.

Pulled over, turned the boost control part of the EVC off, reset the peak boost, and drove off. So the actuator was the only thing controlling boost. Started by topping out at 15.5PSI, spiking to 17.9PSI higher in the rev range, before reaching 18.9PSI at one point.

So two steps forward, one step back. I'll redo some of the vac line plumbing over the weekend, and replace the last remaining standard vac lines, then repeat the experiment.

So far I feel like an epic dunce, but this is outweighed by the fact that this issue seems to be almost resolved, which is a lot better!

[bigkevracer]

Ran new vac hoses this morning for the MAP sensor, EVC, factory boost sensor and the hose to the power steering.

Also trimmed a couple of hoses, replaced the hose to the BOV (which had a splice into it for the MAP sensor) and replaced a couple of hose clamps that looked like they'd lost their tension. Every hose is now cable tied or hose clamped.

Will go for a drive soon - hopefully it's helped. There's only one more hose to replace, the one that goes really low down the drivers side. CBF in this heat, I'll deal with it later. Hopefully it's not the cause of the trouble.

[Jetwreck]

with all this hose replacement you have kept in the little restrictor haven't you?

[bigkevracer]

The plastic thing hose clamped in the middle of one of those short central hoses? Yes, kept that.

When I was starting out I would actually cut the old hoses down the middle looking for other restrictors and found none.

[bigkevracer]

Was still getting spiking, just not as bad.

Did a full reset of the EVC, and redid the setup. Now seems to hold 17.5psi fine.

Now to see if I can lower the boost and keep it working. Might need a different spring.

[Tommy Kaira RL]

I would of thought that you wouldn't need the restrictor. I was looking at another HKS boost controller and the diagram doesn't show it. Usually the nipples on the solenoid have there own restriction or they air in the air filter that goes to the manifold or return pipe.

If you haven't got it sorted I would go back and read the install manual again.

I think from memory you put the solenoid near your brake booster. Which going by the manual its to far from the actuator. The hoses should be as short as possible without going over 100cm.

I could be wong on the above I was just going from what an earlier model says.

[bigkevracer]

Not sure which HKS boost controller you were working with Brad, but it doesn't specify 100cm as an ideal length, just says as short as possible. I remember when it was plumbed in I wasn't sure if the hoses would be too long. Not too had to run it on the other side of the engine bay for now, worth a shot, thanks!

[guestauto180]

He said they shouldn't be over 100cm. You are correct I that they should be as short as possible and preferably sourced from the hot pipe. You also don't keep the factory restrictors in the hoses when running a/market controllers, I think you left hem out anyway?

The only others causes to over boosting will be restriction on the exhaust side of the turbo, be it from the exhaust, wastegate or exhaust housing itself. I would look at wastegate or dump pipe. I'm not sure how well the factory turbo holds boost up top but if its anything like the s13 t25g it can only hold 10-11 psi up top but to do this it will spike up to 16-18 psi and the small wheels just aren't efficient enough. I would suspect the small wheels in your factory turbo could be much the same cenario. Don't forget different intake temps from ambient air temp can and does effect boost pressures, ie: cooleder air usually causes slight boost spiking, especially during cold winter nights. Probably not so much of an issue for you this time of year.

Cheers.

[Tommy Kaira RL]

I was reading the evc 4 manual. Also you should enter your car into AJD at glenelg this year. It's a good day out.

[bigkevracer]

Looks like you were on the ball Brad. Moved the EVC and it seems to be holding boost almost perfectly. Minor adjustment of the boost controller, adjust offset slightly, and it should be right.