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Reducing the boost on a stock KO4 from a Mazda 2.3l

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Reducing the boost on a stock KO4 from a Mazda 2.3l

Old 03-18-2012, 05:53 PM
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Default Reducing the boost on a stock KO4 from a Mazda 2.3l

I have two Ko4'sd they are the OEM turbos used on Mazda 3's and the CX7. They are the perfect sized unit for my 924s turbo project. They have an internal wastegate that is set to 15lbs (I will test this to make sure). I want to reduce that down to around 8-9 lbs or so. My first thought was to just weld the internal WG shut and use a remote mount but the engineer in me kept saying that there has to be another way and I think I have come up with it.

What I am proposing is to install a spring over the WG rod. The spring would be a 7 lb linear one with a travel of about 1.2 inches. The back of the spring would be compressed against the bracket that holds the WG and I would put a clamp on to the rod so the spring would push on the clamp and effectively the rod. When the WG is closed the spring would be at 90% compression and at full open the spring would be at about 90 percent full extension. The springs I am looking at maintain even pressure over there entire compression/extension. My theory is that by adding a spring that is pushing in the opposite direction from the one that is in the stock WG it will reduce the effective rate of the WG by the amount of the spring pressure I am adding. So if I am starting with WG that has a 15 lbs spring and I add a spring that has 7lbs of force pushing the opposite direction in theory it should only take another 8 LBS of boost to open the wastegate. What do you all think? I am going to order the spring or two from McMaster Carr (it is stainless steel) and the clamps that hold it to the rod are available at the local HW store. I am going to test it using compressed air and the WG so see if my theory works. This will allow me to use the KO4 with the stock WG just modified to reduce the pressure to where I want it for now. Later on I can either play with different springs (of lesser lbs) to increase the boost.

The good site is if it does not work I am out less than $5.00 if it does work I have saved the cost of an external WG.
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Old 03-19-2012, 01:31 PM
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make the wastegate rod adjustable. its a simple conversion and all you need is simple parts from the hardware store and a tap/die. if you shorten the wastegate rod boost pressure goes up. if you lengthen the wastegate rod then boost pressure will go down.

cut the wastegate rod in the middle. thread both ends. purchase two nuts with the same thread and a thumb type screw with the same thread.

heres an example:

Attached Thumbnails Reducing the boost on a stock KO4 from a Mazda 2.3l-28541d1192148286-wastegate-adjustment-vac-lines-adj_wastegate.jpg  
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Old 03-19-2012, 02:54 PM
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Doesn't that in effect just cause the WG to bleed exhaust gasses all the time?

Also how consistent is that "fix" across the RPM range? By extending the rod it will cause it to bleed exhaust gasses all the time to prevent it form spinning the turbo I could see boost creep as RPMs increase as the amount the WG is open will not change until the WG actuator moves however the volume of gases will be increasing as rpms increase thus I suspect that the boost will increase with the RPMs.

Or you would have to tune it for the max boost you want at max RPM. I am still going to try my idea and see how it works. This way it will spool up to the boost pressure I want and then open the WG and in theory then hold the boost constant through the RPM range.

Or am I completely out to lunch on this one? I have two of these units so I could try it both ways.
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Old 03-28-2012, 09:30 AM
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to a point it loosens the wastegate flapper. when you lengthen the rod your just removing some of the tension on the wastegate actuator spring inside the canister. you only need to lengthen the rod enough to put less tension on the actuator spring. the flapper will still be closed under spring tension just a little less.
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Old 03-28-2012, 06:05 PM
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I actually set up a rig to see when and how much the WG opened using compressed air and a regulator I cobbled it together from a new regulator for my spray gun some quick conects and some vaccume line.

It was interesting to note that it starts to open at about 8.5 PSI and opens very linearly from there as PSI increased. This has me wondering if the WG on this thing is actually set a lot lower and the electronic boost controller (that is still attached to one of the turbos I have) is actually keeping things at the max boost of 15 psi. I am betting that if you run this turbo with the WG only controlling the boost I bet it will be lower than how mazda runs it. I am betting that 12 PSI will be the max that this thing would be able to get to as the WG valve is about 1/3 open by then.
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