Michael Mansour

Hello all,

I have an S5 turbo 2 motor that's Bridgeport with a Holset hx40 @~20psi. I'm running stock FC ignition components and BUR9EQ plugs. I have an adaptronic, and run about 11 degrees of timing @20 psi. Let me run you through a senario, I can hold it in 3rd @3500 and mat it and it'll build to it's 20 psi around 4700 and it will pull clean to 7k only if I sit and hang in gear for about 5-6 seconds, but if I smash through 3rd and shift to 4th and go WOT I'll get this weird flutter noise like it's not combusing fully, and i will feel a loss of power, and my afrs will go rich ~10.3. Is this a weak ignition system, wrong plug choice, or combustion tems getting to high (i.e. need to get water/AI)? I appreciate any input.

Mods: 88 FC
S5 t2 block Bridgeport do

Slides

Sounds more like actual compressor surge. If it reads richer it is probably from manifold pressure oscillations, missfires will read leaner. If combustion is retarded you could drive it into surge if you are getting more turbine energy than usual wirh the higher loading in 4th.

I'd be putting fine wire plugs in it at the very least probably a step colder too.

most people would say you are pushing pretty hard on pump fuel but guys in Aus have run into the 20s boost on older to4 turbos with fat fueling on pump fuel.

Michael Mansour

I am running an antisurge compressor housing, Are you talking about the b10egv plugs/similar style that are gappable? I'm not understanding when you say the combustion retarding driving it into surge, could you elaborate?

Thanks

Slides

If your ignition timing is soft, which is has to be you could be putting a fair bit of additional energy into the exhaust manifold, in lower gears where just speeding the turbo up to keep up with the motor absorbs a decent amount of power, in the higher gear where engine speed increase is slower the turbo may be hitting it's surge line. You can get jerkiness from top end missfires though. The charge burning in the exhaust will put a lot of energy into the turbine too.

no egvs are for gokarts, you want 5501 (this is the new stock code) NGK 7420 in 10 heat range, at least for trailing 9 or 10 for leading. Or the equivalent denso plugs. These are a fine wire irridium electrode, they require less voltage to spark over and last longer, they are a rotary plug.

Michael Mansour

Interesting, you are suggesting that I advance the timing in the high rpm high boost, thats always scary! Ill be sure to get a set of those plugs, and see what happens

Slides

Definitely not suggesting that, in reality you are almost certainly knock limited, don't have the luxury of pushing that hard on a rotary. But it does mean there is a lot of exhaust energy compared to ideal (if you were on race gas etc). You might find it cleans up with decent plugs in it anyway.

j9fd3s

iTrader: (3)

+1 on the plugs.

you might also try lowering the boost, and see if it still does it. at lower boost, maybe you have more leeway to try a couple degrees more timing, maybe. plugs first though

Michael Mansour

I can hold boost back by partial throttling it, it pulls clean to 7k when partial throttling(12-16psi). Looks like I just need to spend 120$ on plugs rip.

Turblown

iTrader: (12)

Oem plugs do not work for higher power levels. Gap is too big.

Michael Mansour

Got these plugs but still getting the flutter...

Slides

What AR turbine housing?

you can gap the plugs a bit

what ignition dwell?

what is your intercooler setup? Definitely couldn't have got a bit of rag or plastic stuck in there? You are probably pushing the limits of that ignition system but the rich reading makes me think it is genuine compressor surge and some kind of flow restriction.

Michael Mansour

I have a 1ft (tall)x2feet (wide) front mount, big ***... For sure nothing is in the intake tract I've had it running for some time and that would have banged something in the engine. Turbine is a stock S5 which I believe is around a ~ .90 AR. Plugs gapped at .022. ignition dwell is 3ms across entire board (stock).

Slides

As in a mazda turbine housing openned up to accept the holset? That could be the problem, in high gear with the engine accelerating slower you will build more turbo speed and boost, al lower rpm. How long have you had the setup? Is this the first time the current arrangement has seen cooler weather? That will bring it on earlier which is why you might only be seeing it now if it is a new setup. If that is the case you might like to set up boost target vs rpm to run just under the surge line.

denser charge will put more load on the ignition system too but I would expect leaner not richer wideband readings if missfiring.

Michael Mansour

Yes a Mazda turbine opend for the Holset. The setup ive had for about 4 to 5 months, but ran wastegate open at beginning making low boost(12psi) but with even an 8 psi wastegate it over boost to 20psi quite easily. Also first time setup has been in cold weather. I'll see about lowering the boost but it's hard on stock opened up wastegates

Slides

If the thing overboosts/surges badly in the cooler weather and you want to keep the stock exhaust manifold you could just run the wastegate on the can and run a solenoid on a BOV on the intake to bleed off a bit of charge, should be able to use the standard boost control output with the correct porting of a solenoid. I can draw something up if you can't work it out. Would be separate to a conventional bov if you choose to run one, but i'm not a fan unless you are running methanol drag car boost or a pre-turbo MAF.

Michael Mansour

I have no blow off valve, but I will try to run with the wastegate arm disconnected entirely to see what the minimum amount of boost it makes in all gears

Slides

keep us updated. I think to get the best compromise of response without surge and to maintain boost in the top end you will be best serve with a bit of intake wastegating in the transition to full boost and then just relying on the exhaust gate in the top end.

Michael Mansour

An intake wastegate is interesting, wondering about the downsides of bleeding off some of th charge...I've never seen it before either is it a common thing?

Slides

There are a few people doing it, it isn't as efficient in terms of delivered crank power for engine air/fuel flow and will result in higher exhaust manifold pressures than control with exhaust gate, but in your situation where your conventional wastegate arrangement isn't enough, that is a mute point as you can't run at lower boost/out of surge otherwise and you just want to augment control a bit not control the thing entirely from the intake side, as such and given that it is really only in transition to boost that you want to bleed off a bit (which electronic boost control will allow) on transition to full boost I don't think there are any downsides. I will try to draw a plumbing diagram for how I would set one up, if you could find a BOV with swapable springs or a threaded adjuster you could set it to just run a lower boost target in wet weather etc then wind up for regular use without solenoid control, but with a decent ecu there is no reason not to use solenoid control and means there is no risk of it bleeding unintentionally in the top end. I think a simple boost target vs rpm table using the conventional wastegate control functions in the ecu would be fine. Are you using a solenoid in the line to the factory wastegate now or straight into the diaphragm from the pressure source?

Michael Mansour

I was thinking about this all day, it makes sense it would just lower the efficiency of the turbo and put a higher heat load on the components for no reason. But, I was thinking, do they not make large pressure relief valves that I could put in my intercooler piping, it would be as simple as a spring and a diaphram, requireing no solenoids and no ecu control. A pressure relief valve would stay closed only until it saw 18+ psi from the intake charge, which would push the diaphram/spring up and bleed pressure... What are your thoughts. I do not get this surge mid throttle it's only in high rpm, this I tried looking for a supercharger bypass valve but I don't know the right key words.

Slides

You could use a conventional waste gate with a moderate spring in the intake (I have seen one set up as a supercharger bypass, with diaphragm referenced across the throttle), generally most of the external types will maintain about 2.5 times the rated spring pressure for conventional exhaust operation with no differential across the diaphragm so you would probably find using a spring rated about half the boost pressure you want to run would be a good starting point and just leave both sides of the diaphragm open if you don't want electronic control. If you can find an adjustable BOV or one you can replace the spring in it is effectively the same as a gate for this arrangement, the only difference is generally the underside of the diaphragm in a BOV is the piston area itself whereas with a gate it can be referenced to something else and has a larger area than the sealing piston/valve.

In saying all of that if you are having that much trouble with the internal gate I'd be temped to have a bit more of a go at it with die grinder and radius flow paths from the turbine housing and open right out under the flappers. Divorcing the gate into a separate tube could help too if not done already.

Michael Mansour

I can always give it a try, just not keen on pulling it apart when its decently reliable and I'm at school. I get that the bov has less flow compared to an actual gate, but it may work for my purposes and I can start there

Michael Mansour

Could I simply buy one of the fleabay universal wastegates, mount it to the intake piping and adjust the spring accordingly to relieve at the desired PSI? If I have an 18 psi spring adjustment In it, I would imagine it would stay closed until the 18 psi resulting in no spool loss..? Let me know your thoughts.

Slides

Yes if you want to plumb the diaphragm that should work.

Michael Mansour

Whats interesting though is I've gotten this flutter at high rpm in lower boost senarios, would it possibly have to do with injector dead times? I'm using an interpolated 1050x table because it has many more data points than are provided by injector dynamics. I'm just trying to assume it's not high rpm surging to theorise other avenues the problem may originate from.