Sequential or normal dump valve for 200SX?

[Twakkie]

which would work better on a stock 200SX?

Soes a sequential BOV only work with high boost setups? i heard that sequential is better for cars with air flow meters as it wont open under idling or something?

[Enzio]

The S13 did not come with a dumpvalve stock, because it doesn't need one.

So the best one would be none.

[NIZAN-R]

dito

[Twakkie]

Okay, doesn't really answers the question but not the less. why is it then that they don't need one? isn't it bad for the turbo? where does the excess boost go when you shift?

[Daniel]

The best bov would be the recirculating type.

Failing that I personally prefer running without a bov for low boost applications.

[phoenix s14]

Boost under 0.5bar - No dumpvalve possible.
Over 0.5bar - Dumpvalve required.

However even at low boost levels compressor surge WILL break your turbo. Thus a BOV needs to be fitted. Piston type BOV is great for higher boost levels and with a stiffer spring work well. Tial recommends that idle vacuum be checked and your BOV spring be selected that way as to ensure that the valve remains shut during idle and low rpm when surge is non existant. Problem often with BOV is that they are sometimes either to stiff (causing surge) or too weak causing unwanted opening under vacuum which really messes with your fueling due to air that has not gone through the airfilter and MAF/AFM entering the engine which the ECU has not calculated for. Problem also is that this air is also "Dirty" unfiltered air entering the Engine.

Recirculated BOV is thus much better as ALL air passing through the BOV has been calculated for even air sucked through an open BOV under vac. So no matter what BOV you fit - RECIRCULATE IT if you run a AFM/MAF with stock ECU. Also when not recirulated the rush of air passing through the MAF when the BOV opens caused the ECU to adjust for the more air and you get a over rich mixture.

Sequential BOV or pull type valves are only different in the way they operate. The valve pulls open into the boost chamber and the boost pressure actually help the valve seal and not leak boost. Piston type valves are dependant on the spring and the small amount of boost behind the diaphram to keep the valve sealed thus the valve is very dependant on the spring to ensure the valve does not leak. They are however better at staying closed under vacuum since the vac in the boost pipe also help keep it closed.

Both thus have advantages and disadvantages and it does not matter what you choose. The perfect setup to me would be a dual BOV. One sequential one recirculated to ensure better fuelling etc and a piston BOV with a stiff spring for when there is lots of boost to get rid of. In this schenario the recirc valve will handle all the small duties and the piston bov will get rid of big boost. thus you will get the best of both worlds. Typically a recirculated HKS SQV and TIAL Q BOV. The HKS fitted to the hotpipe and the Tial to the cold pipe.

Hope that helps.

[Twakkie]

Shot Phoenix!!!

[Enzio]

Finally got the answer you wanted to hear, good

[Christiaan]

Finally got the answer you wanted to hear, good

I liked your earlier advice. So, what will one gain by fitting a BOV to a stock standard CA? Sometimes it is better not to hear what you want to hear and stick to a well engineered recipe. Or will this BOV be fitted for sound effects only?

[phoenix s14]

Fit a BOV to recirculate after the afm/maf but before the turbo... Nissan realised their mistakes later and fitted one to the other turbo cars. Will have less lag due to turbo not surging and turbo will last longer.

[troopiec]

Dont worry with those expensive sequential dump valves, just get a simple piston one with a single outlet that you can put nice pipe onto to recirculate it behind the maf, i installed my BOV before i knew about reciruclating it, and to dump to the atmosphere does actualy effect your feuling a lil, ive noticed if i drive my car hard and let off the throttle it will dump and a sometimes puff of black smoke will shoot out the exhaust from the excess feul because the afm has told the management that you have so much air being delivered and it feuls enough petrol to mix but then the dump valve just releases that accounted air and thus richens the mixture for that small time, i have not noticed any effect in performance but its not ideal. But dumpvalve is defenitately a healthy addition to save your turbo and will get you better response.

And speaking of OEM dump valves i can tell you of 2 examples, i started working at bmw recently and ive seen on the new COOPER S there is an electronic dump valve fitted onto the turbo itself, and when it dumps it releases the unused boost from the compressor outlet directly infront of the intake turbine, even on the 335i it has 2 dump valves recirculated one for each turbo on the boost pipes.

[troopiec]

heres a quick picture for interest sake of how the new spec cooper S turbo looks with its built on dump valve, its quite clever, im sure theres other manufacturers that are using a similar set up, the dump is actually very loud with the air inlet pipes off, but you dont hear it with everything closed up:

[phoenix s14]

Ag shame that is so cute! And I thought an OEM S14 bov was tiny! lol! nice pic though. Makes you wonder how bloody expensive those hairdryers will be...

[troopiec]

lol it is cute hey, but dont let its size fool you, i dont know how they do it but that small turbo, on a 1600 with dual vanos and they push out 155kw and 260nm (john cooper works), the normal cooper S is 135kw and 240nm, only difference between the normal S and the JCW is the JCW has a airflow meter and different software, i must ask howmuch the little turbos boost though, it must be high, but i was surprised the first time i drove one, they pull hard, havent taken one on with my sx yet but im sure itl beat my stock sx easily, oh and that little hairdryer costs +/-R18 000

[Twakkie]

That's very interesting!! i've been in one of those 155kw coopers that's been chiped, they pull hard!! no way my SX will run with it. i must confess the hole recirculate business is still a bit confusing to me. MAF is mass air flow meter right? but that is that metal section with the black box mounting directly into the air box is it not? i don't understand what it would help recirculating it between the air box and the turbo? wouldn't the excess boost blow through the air filter anyway?