Ok..

This is going to sound dumb, but I was thinking about what lines get pressurized when we boost. The first thing that came to mind is our brake booster and that fat ass line that runs from the intake manifold to the brake booster.

I decided to go out to Autozone and buy a simple check valve that wont allow the brake booster to be pressurized, but still allow for its vacuum needs. Be careful when you install this or you might find yourself without brakes.

Let me tell you, the response is a little different (boost response). The turbo seems to spool quicker and reach max boost faster. Ill be doing more tests to confirm this but Im pretty sure its helping the system simply because you aren't waiting to fill up the brake booster and line with pressurized air.

James

Originally posted by siueclipse
Ill be doing more tests to confirm this but Im pretty sure its helping the system simply because you aren't waiting to fill up the brake booster and line with pressurized air. James

I can confirm this. I did the same thing using a check valve from AutoZone a few months ago.

mmm, I might be just misunderstanding you or I'm just not as mechanically inclined yet, but I know the booster line from the intake to brake booster has a check valve in it. What would be the purpose of putting another check valve in the line when one is already doing the job of allowing vacuum, and blocking pressure?

Originally posted by DSMRoadster
mmm, I might be just misunderstanding you or I'm just not as mechanically inclined yet, but I know the booster line from the intake to brake booster has a check valve in it. What would be the purpose of putting another check valve in the line when one is already doing the job of allowing vacuum, and blocking pressure?

there is no check valve inline. mitsu never thought the intake manifold would see positive pressure..

ahhh

lets get a writeup with part numbers and instructions, stat!!!

Yes this sounds great. Please show some pics and give us more info if you can.

ive talked with a few people who say the 97's have a check valve inline.. i dont get it.. ill take some pics and shit in a day or two.

james

I'm one of the persons he spoke with. I know my car has a check valve inline, because I replaced my brake booster a couple weeks ago. ExtremeRS and I determined that we have an inline check valve.

I have a 97 and mine originally came with a check valve in it. I noticed a difference when I replaced my booster line with a silicone line w/o the restrictor. I think some cars came with it and others without. :shrug

are there any other lines you could add check valves to + expect any benefit?

I have a check valve inline also and my car is a 99. I noticed it when i was gonna replace with some other line and noticed it didnt have the check valve like my stock one did. Maybe i was just one of the lucky ones that got it.

pictures of this check valve perhaps?

Pictures of what?!? It's a check valve. It's in the brake booster line. Go check under your hood, there's only about 12" where it could be. It looks like any other inline check valve.

Originally posted by dougie2
Pictures of what?!? It's a check valve. It's in the brake booster line. Go check under your hood, there's only about 12" where it could be. It looks like any other inline check valve.

lol i didnt say i didnt know what check valve is, but if you have one on and are ranting about it why not go snap a picture? i looked and there is no inline check valve...i have a 96 :shrug

not for nothing but I looked under my hood to see if there was a check valve and there wasn't.So it leads me to ask, if one is installed on and for your turbo applications and there wasn't one there will it hurt the booster to to hold pressure at a constant rather than fluctuate.Also if the check valve is put right(flow in) its only allowing unused pressure to stay in the booster but your turbo vac will still have to charge the system because it's vac into the booster on the check valve. So would it really help? Also braking and boosting don't don't go hand in hand so by any chance if you need to hit the brakes hard would there be enough pressure in the line to make the stop or would that split second that it took for the check valve to open and allow pressure to the booster give you brake failure when you needed it the most.Maybe I'm seeing it wrong but spooling time vs safety.

correct me if I wrong...but doesn't the booster "store" vacuum..therefore already has a check valve built in :shrug

I need to verify this, but there's a vacuum line that runs back to the fuel tank on 97-99's. I had a boost leak and similar weird evap CEL's from the back of the car, but never investigated. Once the car kicked fuel out the fill cap at me. This might be another place to put a check valve.

Originally posted by micyek
correct me if I wrong...but doesn't the booster "store" vacuum..therefore already has a check valve built in :shrug

I guess?is there a purpose to even add it?

Vacuum From The Engine

Engine intake manifold vacuum is used for augmenting the foot's braking power in vacuum assisted power brakes. This vacuum is created by the pistons as they draw downward, sucking air into the cylinders. When you push the brake pedal down, the vacuum control valve lets the engine draw a vacuum in the front section of the booster unit. The atmospheric pressure on the other side of the diaphragm provides significant additional braking force.

In a vacuum booster type system, pressure on the brake pedal pushes forward a pushrod connected to the pistons within the master cylinder. At the same time, the pushrod opens the vacuum-control valve so that it closes the vacuum port and seals off the forward half of the booster unit. The engine vacuum line then creates a low-pressure vacuum chamber. Atmospheric pressure in the control chamber then pushes against the diaphragm. The pressure on the diaphragm forces it forward, supplying pressure on the master cylinder pistons.

As far as I know, every brake booster has a check valve, either external, or internal, to keep vac in the booster in case of the engine dying at speed. This gives you a few pumps of the pedal for brake assist. A wild guess here would be that the 95-96 cars have an internal valve, and the 97+ has an external check valve.

As for the EVAP thing...I've put in a check valve in the line that goes from the top of the throttle body, that connects to that hard plastic line that finnally runs along the passenger frame rail, which leads to the EVAP solenoid. If for some reason, the EVAP solenoid is engaged, and you are boosting, it will send pressure back to the gas tank, or more specifically, that certain valve that has a rubber diaphram in it, that can rip internally if it sees boost pressure. When that happens, it trips the CEL for a "gross leak detected" code.

Originally posted by XtremeRS
A wild guess here would be that the 95-96 cars have an internal valve, and the 97+ has an external check valve.

That may be so. I know that my brake booster assembly doesn't have a check valve built in because when I replaced my booster line with a straight silicone hose, I would build up so much pressure in the brake booster that my brake pedel would rise and decrease my ability to brake. I could feel tons of pressure built up. When I ran an automatic tranny, from a stop, in drive... I could rev the engine and the pressure builing inside the booster would force my pedal up despite me putting all my weight on it. Also, without the check valve... I can hear and see boost leaking. I'm not sure what my point is here but just thought I'd add what I know.

Also, my factory check valve was installed INSIDE the brake booster line... you couldn't see it without looking inside the hose. Just FYI.

the check valve is INSIDE the booster vac line. i have a 95 and it is a small cylinder jammed into the hose so you cannot see it from the outside. this may be different on the 97-99's

lates
james

nope, this is exactly where my brake booster check vavle is.