|Posted on Sunday, September 13, 2020 - 09:26 am: ||
So, I have a small ball-and-spring pop-off valve. It's adjustable. I'm trying to find a way to build a rig, so I can set it's release pressure.
Basically, I'm "bleeding" pressure off a MAP sensor for one of my turbo cars so it stops seeing what the computer calls "overboost". I want it as close to 10psi as possible, so the MAP runs as much injector pulsewidth as possible, without going over 10psi and causing shutdown. When the MAP sees "overboost", it shuts fuel and spark to the engine, which is more than a little jarring (and annoying, when trying to build more power). I've run more boost through this engine in the past, with a custom computer...but that computer has taken a dump and I no longer have my programming software. This is a relatively quick way to override the overboost circuit. In the past I was running HIGH boost - over 30psi. Now, though, I'm not looking to really push it - it's a collectible car - I just want to run 15, maybe 20psi through it. I know I have enough fuel - I have a boost-referenced fuel pressure regulator on it (more boost = more fuel pressure), and I run a digital air/fuel gauge and the moment it starts leaning out, I'll pull back the boost.
What I need to have happen is, the ball comes off the seat and starts to bleed pressure, around 10psi.
I have the valve; I have the ability to fit it up to just about any size hose or tube to feed the pressure to it. I have construction-type air compressors. I'm trying to think of a way to build some sort of reservoir that I can set for my 10psi goal, hook the valve to it, and adjust it until it just cracks open. I don't think my compressors will allow me to set them for such a low pressure, though.
|Posted on Sunday, September 13, 2020 - 11:27 am: ||
what about something like a tire deflator for airing down offroad? some can be set to a specific pressure. maybe a nipple on the reservoir....
|Posted on Sunday, September 13, 2020 - 11:33 am: ||
Have one of these feed a Portable Air Tank that is also connected to your valve?
|Posted on Sunday, September 13, 2020 - 12:32 pm: ||
Something like this?
|Posted on Sunday, September 13, 2020 - 02:25 pm: ||
What you have now is a 1 bar MAP sensor.
10psi? Get a "2 bar" MAP sensor, they are made for exactly that purpose.
|Posted on Sunday, September 13, 2020 - 02:52 pm: ||
Yes, but without the software, changing the sensor does no good.
I have a 3bar sensor for a Grand National on one of my other turbocars...but it has the software to match.
|Posted on Sunday, September 13, 2020 - 03:33 pm: ||
Adjust pressure in your air compressor by bleeding it down to 10 psi as measured with a tire gauge. Adjust your relief valve until it bleeds. Repeat until you’re confident with the adjustment. Or, bleed the tank using the adjustable bleed valve while monitoring tank pressure with a tire gauge.
|Posted on Sunday, September 13, 2020 - 05:50 pm: ||
An aftermarket ECM that can handle boost is very easy to install and cheap! and you want to double the boost on your "classic" using ONLY fuel pressure for tuning???? Good luck my friend.
This is what you're asking for:
But static pressure isn't your issue. any one of those is pre-set to 10psi.
FLOW is your issue, you aren't bleeding a static pressure tank down to a pressure, you need to bleed a pump (turbo) down to that pressure
So you need to bleed enough FLOW to reduce pressure to the MAP to stop at 10psi.
So, the whole manifold will be at that pressure,
meaning 10psi of manifold pressure
A pop off valve with that much flow looks like this:
But you have one on your car already to control the boost.
Your solution will be found on the electrical side not the pressure side. Still use a 2 bar map so it can physically take the pressure, and modify the electrical signal to stay at the 10psi signal max to the stock ECM. Like a rising rate resistor:
But I didn't tell you that.
(Message edited by shoggin on September 13, 2020)
|Posted on Sunday, September 13, 2020 - 06:23 pm: ||
This method works. I've been running this exact car for nearly 30 years - I bought it brand new in 1991. The turbo flows MUCH more air into the manifold - and cylinders - than this small tube sends to the MAP sensor. This is a pinhole in a garden hose - a tiny reference signal, for the electronics. For a primitive system, it is amazingly adaptive.
I don't need proof of concept - again, I've been doing this for decades and I have friends who do the same thing, who've run 8s in Shadows and 10s in Aries sedans (my friend Pat's car - the Scaries, which has run 10.96 - is here: https://grassrootsmotorsports.com/articles/meet-sc aries/ ). The one that started it all is Gus Mahon's minivan, here:
15.1 in a minivan (!), with nothing but this type of MAP bleed and 13psi of boost. Eventually, Gus went on to bigger turbos, bigger intercoolers, more injectors, more boost...and 13.1 ETs.
In a van.
All I need is some ideas how to build a reliable rig to test the pop pressure for this valve. I'll buy some gauges and figure it out. I may just do the "trial and error" method. I'm not looking to push huge boost...I just want the damned cutout to quit, when the weather cools off and the air gets dense.
|Posted on Sunday, September 13, 2020 - 06:29 pm: ||
And a blowoff valve does not control boost. A wastegate controls boost.
A blowoff valve is designed to prevent "stacking" - when you are on the throttle under boost, the turbo is spinning, forcing air through the throttle body and into the engine. When you step off the throttle, the throttle plate closes - and now the boost has nowhere to go. It "stacks" - you get a pressure wave reflection that goes backwards through the charge air system (intercooler, hoses, etc), and back to the turbo impeller.
Which is still spinning, and trying to make boost.
That pressure wave damages the turbine, by shaking it in its bearings.
A blowoff valve is mounted between the turbo and the throttle plate, and has a post-throttle reference hose. When the throttle blade closes, boost behind the blade goes away - when boost goes out of that hose, the blowoff valve opens, and the residual boost in the plumbing, is vented to atmosphere instead of stacking back into the turbo.
|Posted on Sunday, September 13, 2020 - 07:24 pm: ||
Joe, you could use Water column to get darn close:2.24/ft./psi.
|Posted on Sunday, September 13, 2020 - 08:44 pm: ||
"pinhole in a garden hose"
That is a great analogy to understand the problem is not static pressure. You even said "bleed off air" in your OP??
The manifold line of the MAP sensor (the garden hose) will need a calibrated orifice bleed (the pinhole) for the 10psi max you need at the 1 bar MAP you have (in the "pinhole" line, not the "hose"). Not a pressure switch.
But the rate of climb will be affected, affecting your OE computers 'tune'
Or buy a switch thats already set at 10psi from the link I gave you and connect it to a line* that keeps exactly 10 psi at the 10psi switch exhaust side. Too small and the pressure will still rise, too big and the MAP won't like your pop-off buzzing away under your hood. It takes a drop of a few psi to get them to close again so your MAP will see 7-10-7-10-7-10psi and your stock ECM won't like that either.
Thats why an aftermarket ECM or electrical solution is better for you. A circuit that lets .5-4.7V through and stays at 4.7V max should be easy to find/make and would solve this part of your issue except a 1 bar MAP doesn't like to be overpressurised so keep one in the glove box. And you still need to totally guess at enrichment tuning by fuel pressure alone.
Sorry you got offended. Have fun, go fast, good luck.
*To calibrate it, you will need to have it hooked up to something running at the same CFM as your turbo is, using the same length and diameter line that feeds the MAP.
(Message edited by shoggin on September 13, 2020)