^^^ nice! i think i like this idea the best so far, good work :beer:
any testing done yet? and do you have anymore detailed pics on devalving the pprv?
any testing done yet? and do you have anymore detailed pics on devalving the pprv?
Frps
- Thread starter 03yellow
- Start date
Yea, I've done a bit of testing and found that the PPRV function may be a bit more complicated than the public believes. I thought that the PPRV was simply a couple valves consisting of a check valve and a blow off valve. I'll try to illustrate with the following pictures.
What I believed is that the PPRV had 2 simple functions: (1) with the use of a check valve, maintain fuel pressure for quicker restarts, and (2) with the use of a blow off valve, bleed off any excessive fuel pressure. Using the picture above, the check valve allows for flow in the red arrow direction, the blow off valve allows flow in the blue arrow direction, and the green arrow represents a chamber in the PPRV which allows excessive pressure to move to the blow off valve (I'll call this the output chamber). However, I find the PPRV is not as simple as that.
If you notice in the above pic, the lower green arrow represents a second chamber where fuel is allowed to flow from the PPRV's inlet right to the small nipple on the left (I'll call this the input chamber). Think about that for just a second. Fuel, coming from the pumps, is allowed to enter the PPRV, head towards the small nipple via the input chamber, and exit that small nipple. The only regulatory device is the fact the small nipple actually has a very small hole. Now, that function kinda baffles me. Why would the engineers design a part that is basically a controlled leak (based only by the hole's size) for the fuel system? At all times, a small amount of fuel is allowed to come out of that nipple regardless of engine operation.
Let me run this scenario. Car is at WOT, rail pressure is 39psi + actual boost. That means pressure in both chambers is roughly rail pressure with the nipple blowing off some fuel. Now, foot is off the gas, injectors close, pumps run for a short period of time longer, and fuel pressure spikes. What I though occurred was that the blow off valve of the PPRV expelled the excessive pressure out the small nipple (as represented in the 1st picture) even though the pumps were still pumping after the injectors closed. However, I don't think that's the case. With the PPRV as described in the 2nd picture, rail pressure will only begin to come down when the pumps are slowed down or shut off. This would occur because the pumps are not pumping fuel into the PPRV, and therefore the blow off valve would expel excessive pressure into the input chamber (as represented by the lower green arrow) when pressure in the input chamber is lower than the output chamber. Excessive pressure is not simply expelled out the small nipple when pressure exceeds 67psi. (I hope this makes sense.)
Let me put it in other words........as designed, the PPRV only reduces rail pressure after the pumps are commanded to reduce pressure. The PPRV does nothing to protect against pressure spikes to begin with. This means, if the pumps were allowed to continue much after the injectors are shut off, pressure would spike beyond the ~67psi blow off amount.
I'm still waiting for another PPRV I bought from another member to make sure this is the case. I didn't confirm the operation of the PPRV before trying to modify it. If what I think is true, the size of the hole in the nipple plays a significant role of the whole function of the PPRV. A modified PPRV may entail more than just removing the check valve. It would also include blocking the path of fuel from the input opening to the small nipple (basically, sealing the input chamber).
I really wish I could pick the brains of the engineer(s) that designed this part.
What I believed is that the PPRV had 2 simple functions: (1) with the use of a check valve, maintain fuel pressure for quicker restarts, and (2) with the use of a blow off valve, bleed off any excessive fuel pressure. Using the picture above, the check valve allows for flow in the red arrow direction, the blow off valve allows flow in the blue arrow direction, and the green arrow represents a chamber in the PPRV which allows excessive pressure to move to the blow off valve (I'll call this the output chamber). However, I find the PPRV is not as simple as that.
If you notice in the above pic, the lower green arrow represents a second chamber where fuel is allowed to flow from the PPRV's inlet right to the small nipple on the left (I'll call this the input chamber). Think about that for just a second. Fuel, coming from the pumps, is allowed to enter the PPRV, head towards the small nipple via the input chamber, and exit that small nipple. The only regulatory device is the fact the small nipple actually has a very small hole. Now, that function kinda baffles me. Why would the engineers design a part that is basically a controlled leak (based only by the hole's size) for the fuel system? At all times, a small amount of fuel is allowed to come out of that nipple regardless of engine operation.
Let me run this scenario. Car is at WOT, rail pressure is 39psi + actual boost. That means pressure in both chambers is roughly rail pressure with the nipple blowing off some fuel. Now, foot is off the gas, injectors close, pumps run for a short period of time longer, and fuel pressure spikes. What I though occurred was that the blow off valve of the PPRV expelled the excessive pressure out the small nipple (as represented in the 1st picture) even though the pumps were still pumping after the injectors closed. However, I don't think that's the case. With the PPRV as described in the 2nd picture, rail pressure will only begin to come down when the pumps are slowed down or shut off. This would occur because the pumps are not pumping fuel into the PPRV, and therefore the blow off valve would expel excessive pressure into the input chamber (as represented by the lower green arrow) when pressure in the input chamber is lower than the output chamber. Excessive pressure is not simply expelled out the small nipple when pressure exceeds 67psi. (I hope this makes sense.)
Let me put it in other words........as designed, the PPRV only reduces rail pressure after the pumps are commanded to reduce pressure. The PPRV does nothing to protect against pressure spikes to begin with. This means, if the pumps were allowed to continue much after the injectors are shut off, pressure would spike beyond the ~67psi blow off amount.
I'm still waiting for another PPRV I bought from another member to make sure this is the case. I didn't confirm the operation of the PPRV before trying to modify it. If what I think is true, the size of the hole in the nipple plays a significant role of the whole function of the PPRV. A modified PPRV may entail more than just removing the check valve. It would also include blocking the path of fuel from the input opening to the small nipple (basically, sealing the input chamber).
I really wish I could pick the brains of the engineer(s) that designed this part.
wow about 75% of that just went over my head lol
so what kind of setup could we put together to keep the benefits of the pprv and only get rid of the shift hesitation?
so what kind of setup could we put together to keep the benefits of the pprv and only get rid of the shift hesitation?
That's hard to say. I've given this topic a lot of thought (too much, actually). I think the ultimate answer would be a combination of a redesigned PPRV (with the small nipple removed and the blow off valve set to ~30psi) and the fuel tables optimized. One could run a FPR, like the one I pictured earlier, and a check valve in parallel. It would take up more space than a purpose-build PPRV.
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Very interesting research you've done. Still confusing but I also noticed before that when the pumps run a steady stream of fuel would always come out of the nipple. I didn't know what to make of it though. Sounds like you on to something. I like to see something work properly.
I have a theory that the small hole is designed so that the pumps are incapable of generating an excessive amount of pressure. I tried using a small air compressor to check and it could only generate ~30psi with the small hole open. I'm assuming with stock pumps @ ~13V pumping gasoline, the pressure would peak around 75psi. It may also be something like a KB FRPS disc, a small hole used to soften or slow down pressure spikes. I'm almost tempted to make a rig to check. Anyone want to donate a couple stock Cobras pumps in the name of science?
If this turns out to be true, a simple fix may be to enlarge the hole very slightly.
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Good Work Black306.
Subed,Interesting read on this page.
good work black306, it's very interesting. it's people like you that get the refined fixes for these kinds of problems thought up. i don't have any cobra pumps to donate but we could start a small donation fund to further your research
Definitely want to sub in on this discussion! Very interesting theories!
any more news on this black306?
Unfortunately, the PPRV I bought has been delayed and I dissected my original already. So I haven't done anymore research. If anyone wants to send me another PPRV, I wont mind.
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i would send you mine but it's still in my car :shrug:
we could start a thread asking for people to send you theirs. im sure shipping couldn't cost more than a couple bucks and if they already have it out of their cars, i can't see why they'd need it?
we could start a thread asking for people to send you theirs. im sure shipping couldn't cost more than a couple bucks and if they already have it out of their cars, i can't see why they'd need it?
I posted a couple threads where I wanted to buy a PPRV on a couple sites and only 1 actually contacted me (that's the one I'm waiting for). I think anyone that has already pulled the PPRV couldn't care less about a modded PPRV and would rather simply throw it away than bother mailing it out. I believe it's only a select few that are truly interested in my modded PPRV idea, and these are the people that will hold on to their PPRVs to see what I come up with. The rest are happy with a typical PPRV delete, so long as it doesn't damage their FRPS (people experiencing damaged FRPS' seems to be the minority).
In light of my more recent discovery on how the PPRV works (ie no actual "blow off" function), I think the easiest solution that will satisfy most people would be to go with a PPRV delete, tweak the fuel tables to minimize pressure spikes, and increase the duration for the pump cycle at key on/engine off to help with startup. If my theory is correct that the small hole in the nipple is a pressure limiter or pressure spike reducer, and someone is still popping FRPS' after optimizing the fuel tables, then simply drilling a tiny hole in the "Y" fitting should do the trick.
Eh, but we'll see. I'm still interested in what will happen with a stock PPRV.
PS. On a side note, I personally don't understand how people can feel comfortable with the use of 3/8" hose for a PPRV delete. First, the nipples on the pumps and hat are closer to 5/16", and the bends the hose must make actually start to kink 3/8" hose. So, people risk having the hose ends come off or leak at the pumps and/or hat, and a kinked 3/8" line would probably flow as much, if not less than an unkinked 5/16" hose. Even without the problems of fitment and kinking, there should be no significant advantage of going with 3/8" hose instead of 5/16" hose. The restriction in either case would be the fuel filter and fuel line leading to the rails. If someone were going through the trouble, or had a need, to replace the filter with a high-flow version and modify/replace the restrictive fuel line, a Fore hat would probably be the better route anyway. My suggestion, use H209 30R10 5/16" hose and a "Y" fitting from McMaster-Carr (part# 2653K19) or LFP.
OK, time to get off the soap box. :laugh:
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i'll ask around
In regards to increasing the pump priming duration, I was told by my tuner that it wasn't possible. Do you know otherwise?
I haven't done it personally, but I've heard that it could be done. I may be mistaken though. Might want to ask RWTD, RET, Amazon, or any other reputable tuner.
O.K. So if I get all this right. The main cause of FRPS failure is due to a pressure spike during release of the throttle after WOT. I have an idea. What about a tee installed in the fuel line in the tank with a small piston backed by a spring in the side leg. The spring could have a specific tension and be adjustable by a set screw for prototype adjustments of pressure release. A hole could be drilled in the side of the tee's leg and when the fuel pressure gets to a certain point. The piston would compress the spring, letting the piston slide back to the point of exposing the hole and releasing fuel pressure. Basically an exposed, low-tech regulator in the tank to quickly bleed off pressure spikes. Just like a blow-off valve for a gas cylinder or air compressor.
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Yup, you've got the idea. Unfortunately, easier said than done. I've tried looking for a PPRV replacement piece that is essentially a blow off valve, but I haven't had any luck. I thought I found it with this piece:
However, I contacted the manufacturer and they said it would not work for what we needed. Since I don't have my own CNC machine, I can't make a pretty, small, and effective piece similar to the one above. I do have an idea in my head for a blow off valve that would attach to a "T" fitting made out of a brass fitting, steel tube, ball bearing, and a spring. But I'll leave that for later. Instead, my thought are geared towards a blow off valve we all already have....the PPRV. I'm thinking about modifying it and attaching it like so:
Instead of a cap (which would be the wrong way to do it), I'm going to cut off the inlet half exposing the valves. Then I'll probably JB weld the check valve shut leaving the blow off valve exposed.
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