DanG

Hey guys. I don't frequent this part of the forum very often, as I'm still putting along in my non-boosted 944. I do however, own a turbo car, actually a pair of 89 Dodge Daytona Shelbys. You can read about one in this months Grassroots Motorsports magazine, I placed 5th... from last in the $2004 challenge.

I bought the car to learn how to crank up the pressure on turboed cars while making mistakes on engines that cost $300 or less to replace. I'm on my 4th (after shooting the #4 rod out of the block on my second pass at the Challenge)


Why do any of you care? You probably don't. However, there is a bit of interesting "technology", if you could call it that, in the turbo Dodge world. It comes in the form of a sewage flapper valve...



The part is simply an oversized check valve, allowing positive pressure flow in only one direction. Those crazy turbo Dodge guys figured out a pretty good idea for this.

They plumb it so that in situations where the turbo side of the throttle body sees vaccum, this valve will open just before the throttle body allowing atmospheric pressure in at that point. TD cars use a MAP, but on an MAF equipped car like the 944, you'd just have to be sure the "atmospheric" side of the valve pulled its air from after the MAF.

What it does is bypass the turbo and IC in vaccum/no boost situations and allow everything to spool much faster, and greatly improve throttle response. Air rushes through the valve, combusts, and generates more exhaust gases to build boost. The valve closes automatically as soon as pressure equalizes and remains closed even up to a tested 30 psi.

If I had a 951, I'd try it. But I don't. The valve is only $10 and is carried by Home depot in their drainage aisle.

Enjoy.

toddk911

Well, the LBE/Reliaboost are supposed to d othe same thing i.e. stay shut until X amount of boost is reached, then open.

This seems like an extra check though to ensure no boost is bled early.

Interesting.

Did anyone ever report any overboosting with this??

toddk911

So it would go after the IC right before the throttle body?

B951S

Reliaboost etc is not the same. THis system allows the inlet air stright into the throttle body (bypassing the IC, turbo etc) under no boost conditions. It will automatically close when boost hits. Reliaboost etc controls the signal to the wastegegate on the turbo. Sounds like a feasible idea, not sure about the rubber flapper in those things standing up to regular abuse.

DanG

todd, this device doesn't control or modify boost whatsoever. It only operates during a vaccum, which would be at low/no throttle position and lower RPMs. So with the car at idle, you mash the throttle. Intake plumbing drops into vaccum as it tries to pull air through the turbo and IC (aka spool). At this point the engine can combust air faster than the stock intake can supply it. So this valve bypasses the restriction and everything moves faster. Ok, now your turbo has spooled up and begins providing more air than the engine is pulling (aka boost). The valve shuts, as air would now want to reverse flow and blow back to the low pressure zone before the turbo.

You'd have to plumb an alternate route for air from imediately after the map to immediately before the throttle (essentially the path that a non-turbo intake makes). When there's vaccum in the intake track, this valve opens and allows atmospheric pressure to bypass the turbo and intercooler.

toddk911

Ok, gotcha.

Well, the guy on that site uses it as a daily driver with lots of 1/4 runs, on 20+ psi!!!

Dan, do a lot of owners of those cars run 20+ psi ???

toddk911

OHHHHH, ok, got ya now.

Ok, I'm going to Home Depot!!!

toddk911

So on our cars it would plumb in right after the K&N cone?

Assuming you would be running a cone, or a cone with MAF/MAP.

DanG

B951S, the idea has been around since 2001, and the general consensus is that the flappers are fairly reliable, both in life and in the ability to seal against boost.

However, the valve is not automotive grade, and there is a possibility that the rubber in the valve could tearoff, ending up (most likely) in the turbo/IC and (unlikely) the engine (due to much greater pressure differential on boost than at vaccum). I have not heard of a single failure like this, but only the possibility of it happening.

DanG

20 psi is what the wimpy guys run. 30 psi is about the max the stock components are good to. I had a recalibrated computer set to think 18 psi was "stock" and was going to take things in my own hands from there. Unfortunately even just 18 psi was too much, as the engine I dropped in two weeks before the event had rod knock from the start.

There are lots of 11 and 12 second turbo dodges driving around, kindof scary when you think about it!

http://www.thedodgegarage.com is the mecca of all things turbo dodge if you're interested, pretty good ideas in the "turbo database".

Here's a 10 second PLYMOUTH RELIANT built by the guy that made the site...



todd, I'm not 100% sure what the order of the 951 intake track is, but I'm guessing its:

filter
MAF
turbo
IC
TB
engine

If this is the case, you'd want one hose T'd off of the plumbing between the MAF and the turbo, and the other between the IC and TB. Join these hoses and connect the D Valve with flow pointing towards the TB. Also, be sure to do some measures to retain the hoses on the valve. Its smooth pvc or similar plastic and hoses blow off easily unless you carve/grind ridges or something else on the ends.

JDeitz951

On the Dodge website the guy mentions the need for an addtional air filter, but it looks like that would not be needed on the setup you describe for a 951, correct?

This seems too good to not try!

Wormhole

If I understand your example correctly then this is already being accomplished by the stock BOV in a 951. Under vacuum the BOV pulls air directly from the MAF inlet and bypasses the intercooler and turbo.

Dal Heger

Wormhole is correct. The stock bypass/recirculation valve does exactly this.

Dal.

DanG

The BOV still has to overcome the force of the sealing spring. There's three pressure zones in a BOV, the top which is at manifold pressure, the middle at "just after the MAF" pressure, and the bottom at "before the TB" pressure. So in low rpm/high vaccum situations, the TB is wide open and zones 1 and 3 are essentially equal. Zone 2 is higher pressure, so the valve opens only propotionally to the amount of mismatch in area between the top diaphram and the bottom MINUS the spring force keeping it shut.

The short response is that yes, the BOV opens under vaccum. But it doesn't provide the kind of flow that a valve like this does. This valve provides nearly zero restriction in the correct direction of flow.


Deitz, you're right. Dodge guys don't have to replumb to be sure the MAF is counting all the air. So they can just slap a filter on the end and be done with it.

Laust Pedersen

As I understand it, this check valve is intended to provide a faster manifold pressure change from vacuum to 1 atm abs.
In that case I find it hard to improve on what is already there.
Try for example to stomp the gas pedal from cruising (vacuum) and the manifold pressure immediately jumps to 1 atm abs (on an aftermarket boost gauge).
Above 2500 rpm our turbos already pressurize the ducting (including the IC) between the turbo and TB, making the manifold pressure jump above 1 atm abs when the pedal is stomped.