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dusky007

Install / Fit a BOV (blow off valve)

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The below is an article published in High Performance Imports Magazine (Issue #08) with story and photos by Martin Donnon.

Two things to note with this article. Firstly, it focuses on the installation of a aftermarket BOV on a CA18DET. Secondly, all SR20DET cars already have a factory BOV!

If you want to read more about BOV's in general, then there is a great tech article in issue no.26 of ZOOM magazine.

 

DIY blow-off valve fitting

 

Its really quite strange that Nissan never considered fitting a blow-off valve to the CA18 Turbo engine in the first place. There is no dispute that the Silvia and 180SX S13 platform cars were designed with sporting pretensions. Why Nissan never installed a cheap, relatively simple-to-manufacture part that would assist in the performance of the engine is beyond me. For those who aren't quite sure what I'm talking about, it may pay to cover a little theory first.

A blow-off valve (or, more correctly, compressor bypass valve) exists on turbocharged engines for more than just the pppshhhhh noise that it generates when the throttle is snapped shut (this may come as a shock to most readers!). The real purpose of the blow-off valve is to vent the pressure build-up that occurs when the throttle is suddenly closed under boosted conditions. This stops a massive air pressure wave bouncing straight back into the turbo compressor wheel and slowing it down. With a blow-off valve fitted, the theoretical advantage is, that after a full-boost gear shift, the turbo will be at a higher rpm, giving a greater amount of power/boost.

Fitting a blow-off valve to an engine like the CA can often be a drama, as a little fabrication will be needed to get a perfect result. Using an inexpensive off-the-shelf Turbosmart blow-off valve we'll show you exactly how it's done.

Selecting a blow-off valve for an airflow meter-equipped engine, such as the CA18DET can often be more difficult than first thought. If the blow-off valve is slightly open at idle, it can cause lean mixtures (and rich mixtures under decel) which will, more than likely, make the engine stall or at least run rough. One way around this is to get a blow-off valve with a 'hose fit' outlet, such as the factory-type Bosch units, and then recirculate the blown-off air back in front of the air flow meter.

We have never been great fans of this approach as the blown-off air is normally quite hot and, therefore, not something you want to feed back into the engine. The reason the manufacturers sometimes go this way is to control noise. Turbosmart get around this problem by giving adjustable internal spring tension, which allows the blow-off valve to be tuned (spring tensioned) until no escaping air can be felt around its bypass holes at idle.

The only place to mount a blow-off valve on the CA18DET is on the steel pipe section that runs between the turbo outlet and the intercooler. Ideally it should be mounted closer to the throttle body, but in this case, the rest of the inlet ducting is either plastic or simply too damn hard to get to. Here we can see my trusty comrade, Mark Tilbrook, removing the inlet tube with only the simplest of hand tools, a 10mm socket and a flat blade screwdriver.

It pays to line up the blow-off valve in the engine bay and mark exactly where on the pipe you want to mount it. If you don't do this, you may experience difficulty when it comes time to install the blow-off valve - like it butts up against some under-bonnet item you simply didn't take into consideration. This can be particularly nasty, so do what Mark did and 'dummy' the blow-off valve up against the inlet pipe and draw its position with a white marker.

Once you have done this, you can hold the inlet pipe in the vice and simply drill a one-inch hole (in this instance) which was performed using a power drill and a stepped drill bit, known as a 'tree'. To be entirely professional, Mark then 'finishes' the edges of his drilled hole with a die grinder to make sure no metal dags protrude into the inlet pipe. If you don't have such a tool, then simply use a round file and a bit of elbow grease.

A little bit of hunting was required to find a piece of one-inch steel tube, but we did find a small offcut. Any local exhaust shop should be able to supply you with an offcut for next to nothing - if you ask nicely! Once lined up with the inlet tube, Mark decided to mount it on a slightly (maybe 15 degree) angle to ensure both a smooth flow of air into the blow-off valve and also to ensure clearance of the valve to the body. You can see Mark decided on an exact position and then ground the correct angle onto the one-inch piece of pipe. Just like cleaning the original hole, you can get this angle by using a file if necessary.

You will notice by now that the inlet pipe is no longer covered in the factory black paint (powder coat?). Mark had long since removed it by using paint stripper. The reason for stripping the paint is the nasty burning effect when this type of surface is welded to - it doesn't look nice afterwards. Rather than using a MIG welder, Mark decided to fusion-weld the assembly together, which, for this application, gives a neater overall result. If you can't weld yourself (or don't have the equipment to) then another trip down to the local exhaust shop with your lined-up tube in hand will be in order. Anyone good at building an exhaust system can do this for you in a matter of minutes.

Once the welding has been completed it's time for the file again, making sure the metal surface is clean and smooth. The end result will look much better for your efforts. The shots here are of the completed pipe being painted, but remember one important step before you do this, and that is to thoroughly clean the finished (unpainted) pipe in hot soapy water to remove any traces of metal filings welding sl*g and other muck. Remember that anything you leave in your intake pipe will quite possibly make its way into your engine, which can often lead to costly time-consuming tasks, like rebuilding an engine.

Paint selection isn't too critical as the turbo outlet charge should rarely get double-check all of the hose clamps for tightness, as there is nothing more frustrating than going down the road after completing the job and having one come off. "Check and double-check," - that's the motto.

The next item you will need is a piece of one-inch inside diameter pressure hose to mount the blow-off valve. A lot of installers use a normal rubber 'heater hose,' which is not designed to take more than a few pounds of boost without splitting. Buying a pressure hose in such a small diameter, though, can be a challenge, with Mark resorting to a small offcut of 'Autac,' which is commonly used for high pressure oil lines, such as oil cooler tubes and so on. A couple of the right-sized hose clamps and the blow-off valve is securely screwed into position, but the job's not over yet.

Last but not least, will be supplying a vacuum/boost source to the top of the blow-off valve. The reason you have to do this, to keep the blow-off valve fully closed under boost. When you have boost pressure trying to push the valve open and boost pressure trying to hold the valve shut, you are still left with the internal blow-off valve spring tension as a buffer to the valve being forced open. In this instance, Mark used a small tee-piece and joined our actuator line to the fuel pressure line. Simple! Blow off valve installation is now complete. Get out there and enjoy!

DPBOV.jpg

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I have been working on a few articles for a site that I am doing, here is the article for fitting a Turbosmart BOV Kit for a 180SX.

 

Plumb Back Install Guide

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any vacuume source.

 

t piece into fuel pressure line or into vacuume line leading to throttle body.

 

 

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can any1 help me, i jus installed my blitz bov on my s15, n i jus use my original vacuum pipe but i extended to my blitz bov. but wen i drive around the car keeps on backfire wen i changes gear. do i need to connect any other thing ?? or any1 got any idea. i will very appreciate it.

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hey guys, quick question. I want to change the bov from atmo to plumb back for obvious reasons. I was planning to DIY since I thought it would be simple as putting the plumb back one in and putting the piping back into the intake pipe but after looking at a few articles on it I noticed that nearly all bovs that were being installed were on the hotpipe. The bov on my car is installed on the other pipe on the other side (dunno what its called. Cold pipe? lol) Any ideas?

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so it is better to recirculate the air back?

 

yeah thats a good question, i didnt recirculate mine back when fitting the aftermarket bov.

 

 

 

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thread is from 2002, almost 10 years old.

 

if we had an award for oldest thread bump ever this would probably get it

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