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Blanking off recirc valve?


dezmond_vr6
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Hi I'm just wondering how long the turbo will last of I blank off my recirc valve. As I fitted HKS ssqv and was losing boost preasure.

So I'm thinking of blanking it off for the flutter but would like to no how long turbo will last if I do this. I'm running 350bhp with a map exhaust and air filter if that is any help.

If possible is like replies off ppl that are or have run there own cars like this rather than just something ppl have read thanks. Mine is a 03 STI type uk I think they run a vf34 but couldn't be sure.

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I'm told the maf sensor on these can't tell the difference between air in or out so as the presure goes out after release of throttle it reads it as intake air therefor furling the car again to compensate thus overfueling the car and ultimately in the long run engine goes buy buy

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venting the pressurised air to atmosphere as you would have being doing using the HKS causes the mixture to run rich due to the loss of air hence the reason for a recirc valve maintaining a closed loop circuit for fuel and air.

 

removing the recirc valve and blanking it off means the circuit will stay intact but will suffer from pressure build ups - this shouldnt affect the fuelling as there is no loss of air or fuel, it will however impact the turbos ability to spool due to back pressure created

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I see well like I say the other read up I read described the maf as not knowing which is air passing in or out therefor trading no matter what passes even if it's air going out. Because even tho the preasure is going back through the turbo dies t it still pass out of the air filter to some degree? That then reading as air coming in and then feeding more fuel??

Some other ppl had a plate made to go behind the recirc with a 10mil hole thus relieving some of the strain on the turbo which then still gives the flutter just not to the full effect of a complete blank. ??

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The pressure does not flow backwards and forward across the maf as you describe - there is air flow in one direction just more or less dependant on your engine speed sucking air in as long as the engine is rotating at least one cylinder will have valves open and draw air in maintaining the suction, the rotation of the intake turbine is dependant on the exhaust gases rotating the other blades, these gases flow less as you dip the clutch to change gear and revs fall. This in turn slows the speed of the intake turbine, as the revs climb once the gear is engaged and the revs start to rise the turbine is fighting with the previous built up pressure remaining as it has not been expelled via dump valve, gone into a recirc system or gone into a cylinder via the valves. As the exhaust turbine has no pressure on the out let side this is where you get the mismatch in the forces which balance out as the turbo spools up again. The delay in spool up is what gives the lumpy changes

 

Many cars had turbos fitted without dump valves or recirc systems for years and did not eat engines through running rich

 

as an opinion and from an engineering perspective I dont see the point of drilling small holes in plates to fit behind a recirc valve unless they just want to generate the flutter in which case the wear would be to the turbo

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here is the Wiki info on the subject of flutter etc - it describes compressor stall where pressure escapes past the turbine and also the wear on the turbo itself - MAF (or equivalent) an a relation to over fueling is not mentioned - in my previous post I had omitted the bit about the throttle body and just mentioned revs dropping when clutch was dipped when changing gear )also assuming that a drive by wire throttle and flat foot shifting is not a consideration

 

There is confusion in the automotive world about so called "wastegate chatter" or "turbo flutter". A noise created on lifting off the throttle in a turbocharged car, commonly described as a chipmunk or a rattlesnake, is often stated incorrectly as being a result of the turbo's wastegate closing.


The noise is in fact the air compressed by the turbo passing back through the compressor wheel of the turbo after the airflow is abruptly
halted by the throttle plate closing, called compressor surge. However, in some cases, i.e. where the blowoff valve/recirculation valve does not open fast enough or is set up to only react to high boost, some chatter will remain. Surge can occur on diesels when the turbo is attempting to pressurize the air at a higher pressure ratio than the compressor wheel can flow at a given speed. Most Diesel engines have no use for a blowoff valve as they do not have a throttle plate. The chatter noise is very noticeable on World Rally Cars, where anti-lag is used.

 

A compressor stall like this can cause excess stress and wear on the turbo's shaft or bearings under higher load applications of the turbo
(around 15 pounds per square inch (1 bar) and greater depending on the trim and flow rate of the compressor side).


Actual wastegate flutter occurs instead under partial boost conditions such as partial throttle near the boost threshold. It sounds like FftFftFftFft not ShuShuShushu and is caused by the rapid opening and closing of the wastegate at boost levels near the spring pressure. It is commonly heard more clearly
and may be more prominent on cars with modified intake silencers, up-pipes, downpipes, or an oversized wastegate incorrectly matched to that specific engine. Also, vehicles using on/off solenoids to control boost can do this under certain conditions. It is not harmful to the engine. Some may claim that it can damage the wastegate, which may be possible under some circumstances, however some vehicles flutter regularly inherently from the factory without any consequence.

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Thanks for that jay [emoji106]

At least I now know why I get chatter even though I now have a dump valve fitted .

Because I only used 0.5 bar and then backed off the throttle (due to it needing a remap)

As far as I'm aware blanking off the dump valve causes strain on the turbo due to the abrupt stall caused by the drop in exhaust gasses when you let of the throttle .

most people say that the journal td series turbos handle it better than the roller bearing vf series turbo's. As td's rely on oil to reduce friction on a single shaft rather than roller bearings in a casing .

If my home made fmic pipework with a dump valve take off can't handle high boost on the dyno Wednesday[emoji120]

I'll be fitting a better shape blank piece of pipe (instead of the bit with the dump valve take off) and going valve less and I'll let you know the outcome Wednesday evening[emoji6]

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Thanks jay that's opened my eyes mate. To be honest I do want the sound but also dnt want to lose performance that's why I took the hks back off as it was losing boost for some reason but with recirc back on its fine again just quiet now which is a shame.

And yes like I say some described putting the plate with a smaller hole in to still give the flutter but also not have the full strain on the turbo as some will still pass through the recirc valve.

Well now it's just a choice of noise or not then and weather I want to repair my VF turbo in time by blanking?? What to do lol

Cheers guys.

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I would be interested to understand why you were loosing boost with the HKS as they are a quality piece of kit and shouldn't impact performance.

 

Fingers crossed for you Savage looking forward to the results though :)

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I honestly dnt no wat it was mate if I tried to pull from lower range revs it would go into full boost and then chatter at off top of boost gauge and u can Hear it aswell. But also feel the loss in power it had no pull. But now recirc Is back on u can still slightly hear it happen but u dnt feel the hesitation or loss of pull so I can only omagine it was that. But I also need to have a good investigation into a leak in pipelines.

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Apparently my mapper contacted ecutec today and ask about the air passing back through the air intake and they said that some does escape back through the filter there for will tell the car to put more fuel in.

They did say the best thing if I wanted to blank was to fit a plate in behind the recirc with a 10 mil hole to let some air still circulate in turn will help the turbo and should stop air passing the maf.

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I stand corrected, currently investigating directional airflow sensors to understand just how much of this leakage occurs...

 

There is always the option of mapping the car to run without a MAF but first before any more mods are completed I would be keen to understand and resolve the issue of the boost loss

 

Will you be changing your turbo to the journal type mentioned by Savage if you fit the blank?

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Yea is like more info on the air passing back through and just how much overfueling it does cause.

I will be looking thirteen into the leak or watever it may be as it's a lot better now it's git recirc back on but still flutters and makes a noise if it's on full chat from lover range revs in a higher gear if that makes sence?

But yes in time is like to maybe have new injectors FMIC and different turbo. And might have to get it mapped without the maf if I'm going to do the blanking plate.

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running rich isnt too bad - picture a bunsen burner with the valve closed, big yellow flame (and possibly some out of the exhaust) versus running lean which is your blue flame that melts pistons

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