blow off valve on draw through IMPCO

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jono
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blow off valve on draw through IMPCO

Post by jono » Mon Oct 21, 2013 8:25 pm

:( been a while since I visited or askled a question ....

I have a shiny new valve to install - said to be part of my troubles when I am high revs, shift up a gear to get almost no power until things settle.

I have flat 4 1800 cc Subaru (ca 1985) running IMPCO 200 feeding my turbo, rather than the turbo feeding the mixer as it does not work due to odd intake pulses - despite what IMPCO and a few others say ....without all sorts of clever tinkering mods.

I intend to tap into the pre throttlebody pipe to add the blow off/recirculation valve to and let the pressure off as it chooses. I got a Bosch style metal unit that came with 3 springs and 2 shims to finer tune pressure dump settings.

QUESTION is : is it going to be OK and safe to vent these boosted vapours back to post mixer/pre turbo or should it go to pre mixer ?

Unhippy
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Re: blow off valve on draw through IMPCO

Post by Unhippy » Sun Oct 27, 2013 7:32 am

if you ported it in pre mixer you would get a double strength fuel mix when the 'blown off' mixture passes thru the mixer again

ported post mixer the only thing i can see being a real problem would be if you got a backfire intake fire making its way thru the BOV, the engine would stall out pretty quick but it makes a mess of the ends of any vac lines you have hooked to the intake....

i had an intake fire after a backfire once many years ago on my EJ subaru due to an old dizzy cap crossfireing with a new high output coil hooked to it...lol since then i've always made sure my vac lines have enough extra length that i can cut a fried end off and still have enough line to plug back on...and taken a bit more notice of the condition of the cap, rotor and leads :lol:
petrol hedonist by nature... LPG cheapskate by necessity

jono
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Re: blow off valve on draw through IMPCO

Post by jono » Sat Nov 02, 2013 7:15 am

at last !! - someone cares about me enough to comment :) Where is everybody ?

I think you have put the words right - the blow off has got to go somewhere. Atmosphere is out for safety and pollution reason, pre mixer will increase richness for a moment but also subjects the air box to no protection of the vapours for any event and post mixer I guess it will act as another source of mixed vapours, so like an air leak yet with fuel :)

That is the way I am going to go - having found a nice spot to place the BOV and its exit should fit directly into the silicone T pipe I have. Maybe flame proof vacuum hose to add to the equation.

C3H8
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Re: blow off valve on draw through IMPCO

Post by C3H8 » Sat Nov 02, 2013 1:46 pm

It's not that no one cares. We love the unusual questions as they spice up the interest, however, that being said. There are a limited number of members with TC experience. This means a limited number of responses. My experience is quite limited to this subject except with mostly large industrial engines. The only other experience I have was in the late 80's where our company was involved in converting a cat diesel to 100% propane. It had a TC and no paid any attention to the blow off valves until the driver complained about a frequent odour of raw propane. Digging into it the engineers/techs realized this model had spring loaded BOV's that dumped excess pressure directly out of the intake manifold and under the hood. A nice recipe for disaster. It was re-engineered to an exhaust waste gate system.

In your case you have essentially the same issue. The BOV will be releasing a fuel air mixture. Dumping it will be an issue no matter where you do it. If you have aggressive fuel control it might work but the method you are considering is going to create a very rich mixture during the venting process no matter where you dump it. Since the mixer adds fuel strictly based on air flow it will continue to put in fuel at the same rate no matter how much fuel is added ahead or behind the mixer. This is where I defer to the guys with experience as it is the limit of my knowledge on small turbo's and BOV's.

jono
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Re: blow off valve on draw through IMPCO

Post by jono » Sun Nov 03, 2013 5:18 pm

Thanks C3, just teasing .... :) Guess this happened since Franz retired ??

I don't believe from my head theory , that if i supply the bleed off vapours to post mixer will be any richer, be just like running an extra mixer with the engine breathing in its air fuel supply from somewhere just this somewhere is a mix that has been by-passed and recirculated, and thinking the amount will be so small for such a short duration that the blow off will simply be sucked in by the turbo. I think I was concerned a pressure from the blow off will tickle the mixer from underneath.

Here in Australia we used to have a performance lpg website with quite a few experienced with LPG and turbo - site folded or gone to cyberspace for some reason :)

storm
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Re: blow off valve on draw through IMPCO

Post by storm » Sun Nov 03, 2013 7:53 pm

jono wrote:Here in Australia we used to have a performance lpg website with quite a few experienced with LPG and turbo - site folded or gone to cyberspace for some reason :)
That wasa good site, only ever saw it a couple of times but the info was brilliant. Been considering creating another one like it and hoping the old timers would join and share again.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

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Steptoe
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Re: blow off valve on draw through IMPCO

Post by Steptoe » Mon Nov 04, 2013 2:45 am

It's not that no one cares. We love the unusual questions as they spice up the interest, however, that being said. There are a limited number of members with TC experience.
It is interesting to simply follow many applications out of interest....Imagine if all of us who follow threads quietly had to say we are only watching because its out of our legue :shock:
My Spelling is Not Incorrect...It's 'Creative'

C3H8
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Re: blow off valve on draw through IMPCO

Post by C3H8 » Mon Nov 04, 2013 6:54 pm

You bring up an interesting hypothesis on that. The venturii vacuum to lift the diaphragm in an IMPCO mixer is generated by the airflow passing through the mixer as it flows over the gas valve. Introducing a blast of air/gas, when the BOV activates, just below the mixer could cause the valve to close, stabilizing the mixtures or even worse it could cause a sudden leaning and a momentary lag. Hard to tell without trying it. Introduce it ahead of the mixer and there should be less impact as the same amount of air is flowing through the mixer and as you suggest the impact on mixtures may be minor as the BOV will only activate at high RPM along with the max pressure being reached. After consideration I lean towards the pre-mixer.

Steptoe: Not quite sure what you meant on the last post. I'm not sure if you were indicating a lot of people read the post and don't respond and this is a good or bad thing. Also I want to be careful not to get off the topic and lead it astray by sidetracking jono's original post.

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Steptoe
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Re: blow off valve on draw through IMPCO

Post by Steptoe » Mon Nov 04, 2013 11:26 pm

Steptoe: Not quite sure what you meant on the last post. I'm not sure if you were indicating a lot of people read the post and don't respond and this is a good or bad thing. Also I want to be careful not to get off the topic and lead it astray by sidetracking jono's original post.
Confirming most of use follow these unusual interesting projects but dont comment as out of our league, which is where Jono was under the impression we where not interested...
Back to the interesting subject.
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jono
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Re: blow off valve on draw through IMPCO

Post by jono » Thu Nov 14, 2013 3:51 pm

See if thisa draws a response, rings any bells ....

Image

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Not yet in use, not yet finished install but does show where the diverter valve fits in :)

franz
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Re: blow off valve on draw through IMPCO

Post by franz » Fri Nov 15, 2013 9:36 am

From what I can see in the image, the BOV is mounted downstream from the mixer. If so, it wont work, as both sides reference the same pressure. It needs to vent outside. PLUS, and I mean a BIG PLUS, is the BOV in this position will vent air and fuel, and is a terribly combustible mixture. The BOV should be mounted upstream from the mixer body where it will vent air only.

As for me retiring, I did, from my day job that paid the bills for more than 4 decades. Everyone who has retired also knows that it is really a short vacation and that I quickly found projects to keep me busy. My wife and I live on a small ranch that keeps us busy plus I have calls quite often to teach classes and review projects. Some are classified and I really cannot discuss, while others are fun to play with. The income isnt bad either.

I am not on the forum as frequently as I used to but its not because I'm not interested. I just have more than one pan on the fire.

Best!

Franz

jono
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Re: blow off valve on draw through IMPCO

Post by jono » Fri Nov 15, 2013 4:33 pm

Franz, thanks for looking in :) Apologies everyone, for the trick photography - even did it without Photoshop ! I think I have given the wrong impression of the set up :( sometimes pics don't speak enough words !
Image

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This picture should reveal the path a litttle better. I notice from the first pic it looks like the mixer is feeding same component the diverter valve is coming off !
The 200 has sucked in fresh filtered air and supplies the mix to the turbo not seen here but is below the darker blue duct. Compressed mix then comes up from the turbo to the alloy casting (emblazened with SUBARU 4WD TURBO :) ) before it gets to the throttle body which is located just below the O of TURBO in casting .

The diverter valve is mounted to take it between the turbo and throttle body - exhausting the excess pressure mix to below / downstream of the mixer.

My concern is maybe the exhausted mix's pressure vented under/below/downstream of the mixer might confuse the diaphragm signals to the converter ?
Yet , the very same thing may be ocurring in there with the forces trying to back-pedal the turbo anyway - the very thing I am attempting to resolve !

I really did not want to vent combustible mix to upstream of the mixer as it would not be what I would regard as safely contained and would also richen the mix momentarily.
My thinking was that a decelerating engine would simply draw it through, using it up in a safe manner ???

I initially forgot instructions to set this engine up as TURBO DRAWS THROUGH MIXER and followed the IMPCO US & AUS verbal instruction that all turbo lpg needs to be turbo blows through mixer - it was not driveable due to eratic? intake pulses of a 4 cylinder turbo (maybe add boxer to the equation?) I was able to 'drive' as such but would not do anything beyond the idle circuit, no load, no acceleration - had to get some speed up on the flat so I could return up slight incline to my driveway and shed ! Explored all the different ID's of balance line differences first, gaining improvement with smallest ID of 4 or 5mm ?? when stated 200's must have 3/8" !

Page C5 of my IMPCO service manual (ca 1980's) says :

b. " the mixer may may be remotely mounted,as upstream of a turbo charger with the throttle body still mounted on the the intake manifold"
c. "the complete carburettor may be mounted upstream of the turbocharger"
d. "the complete carburettor mounted on the intake manifold may be turbocharged through the IMPCO carburettor"

I believe the term "mixer" used in b. above is the complete IMPCO carburettor minus the throttle body

I tried d. first, then went for option b. :) Happy to see that allowed in the manuals :)

Once set up as turbo draws through mixer it has been great, faultless over 50,000 miles except when shifting at higher revs in a hurry - get a fluffy pedal and momentary no go, think the turbo trying to spin backwards ! Another lpg , turbo and Subaru (but not all in one experienced) tuner suggested the diverter valve idea as he had done same on same engine (just not the potent fuel ! ) Now, he is backing out of the idea ( ONYA Greg !

Everything on the install is still containing all fuel in all stages to comply with current safety standards - all the vacuum control devices get boosted vapours in minute amounts for a small moment :!

Just trying to work out engine spinning, throttle closed, is it actually drawing air in as vacuum is created, O2 fuel burn readings lean out to maximum ????

Will find out eventually but may need a few spare clamps, ducts and mixer in the boot :(

Also, currently, the exhausting side of the diverter/blow-of valve where it will re-enter the stream is not a fully open 1" ID hole - two metal sleeve tubes almost butt up against each other and have the possibility of creating a baffling of the exhausted blow off until I open the hole up completely by cutting half moons from each sleeve. Wondering if i should retain a baffling effect on the return air/fuel mix for coyrtesy of the diaphragms ?

jono
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Re: blow off valve on draw through IMPCO

Post by jono » Fri Nov 15, 2013 5:47 pm

storm wrote:
jono wrote:Here in Australia we used to have a performance lpg website with quite a few experienced with LPG and turbo - site folded or gone to cyberspace for some reason :)
That wasa good site, only ever saw it a couple of times but the info was brilliant. Been considering creating another one like it and hoping the old timers would join and share again.

This is another one like it, just wish they'd been able to find it here and build on it ! There was lots of photos, turbo LPG of all types, rotaries included, drag cars, a lot of helpful advice ,the odd BS I suspected too. You'd swear the odd member was a little aggressive also ! Safe to suggest in here ?? Maybe some guys exploring their female side :-)

storm
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Re: blow off valve on draw through IMPCO

Post by storm » Fri Nov 15, 2013 5:54 pm

The difference betwen it and this place was it was very specifically Australian from what I saw. No need to read through material that, while excellent information, was not relevant to or legal in Australia.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

jono
Posts: 347
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: blow off valve on draw through IMPCO

Post by jono » Sat Jan 18, 2014 9:17 pm

Well, it is on the road, done a 2 mile trip to shop and back. Driving very gingerly until near cheapest towing times and locations - past the driveway of one towie in particular may be best :D

The female tennis player exhalation noise between gears is almost but gone, something must be working :)

More updates later

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