TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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I've been searching for a new vafpr for awhile now and I've been having problems locating one.It seems that top down isn't selling them anymore and I can't seem to find them through GM. where can I get one?
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I have thier Bored out TBI and this regulator. I have not installed yet but they are very well made. The instructions are pretty good.
To adapt the tbi to vacuum you have to plumb the regulator body. There is a hole drilled in it already. There are a few ways you can connect it. I am going to tap it and screw in a small brass fitting I got from the plumbing isle at home depot. It is threaded on one end and has a barbed end on the other for pushing on a rubber hose.
You should be good to go. According to the instructions that came with mine all you have to do is connect manifold vacuum to the hole in the side of the regulator.
Let me know how it works out if you do connect it. Like I said I have one but have not installed yet so I would be interested in hearing your results.
If your willing to spend the money this is what I am running. The Aeromotive external regulator. I used this thread as a guideline for mine. Currently running 22 psi at idle and 28 at WOT on stock 61 pph injectors on my 350. Works great with RBobs EBL.
So these cars use static fuel pressure from the factory? What is the advantage to installing one that references vacuum to create a dynamic range? I am guessing it is a way you guys can "tweak" the fuel tables without burning a new PROM everytime you want to adjust the mixture??
On my last car, 95 monte carlo 3.1, it had a factory VFPR. I remember, i accidently pulled the line off it once to work on something else. The car ran real rich - it was nice. Smelled like an old truck or corvette coming out the tailpipe untill I realized what I had forgotten.
__________________ -Adam
1990 Firebird Formula
Bone Stock 305TBI, T5 tranny, 62k Origional
UMI subframe Connectors
if your engine requires a lot of fuel at WOT that requires a higher fuel pressure. With high fuel pressure the idle quality suffers as the pulse width cannot be small enough. The fueling goes asynch and idle gets funky. VAFPR reduces FP at idle improving idle quality. the GM unit I bought at gmpartsdirect.com a few years ago. I thought the GM-TBI application was marine 7.4L?
So these cars use static fuel pressure from the factory?
On my last car, 95 monte carlo 3.1, it had a factory VFPR.
Your Monte Carlo had a dry flow manifold with the injectors under vacuum. The FPR lowered fuel pressure while the engine was under vacuum so that the pressure difference between the fuel rail and the manifold was always the same.
Your TBI is a wet flow manifold with the injectors at atmospheric pressure. It doesn't need vacuum reference.
Your Monte Carlo had a dry flow manifold with the injectors under vacuum. The FPR lowered fuel pressure while the engine was under vacuum so that the pressure difference between the fuel rail and the manifold was always the same.
Your TBI is a wet flow manifold with the injectors at atmospheric pressure. It doesn't need vacuum reference.
why did GM decided to use VAFPR on the trucks then? they were also TBI... from what I learned the VAFPR kind of turn the static into dynamic.. its a in depth thread on FSC where this was discussed..
but i do agree with you cause you are correct, this is what HaulinA$$ on FSC had said in that thread.
Quote:
Originally Posted by HaulinA$$
For the most part, TBI systems generally do not come with a VAFPR and this is for two reasons. First and foremost is since the injectors are located pre-throttle blades, they are always referenced to atmospheric pressure, a constant fuel pressure is needed to maintain accurate volumetric efficiency. If the regulator was vacuum referenced, to make fueling constant, the VE tables would no longer represent actual VE but rather just a fudged fuel correction which can cause rich fueling issues when the Barometer falls dramatically. MPFI regulators are always vacuum referenced due to the fact that the pintle (or poppet whichever the case may be) of the injectors where the fuel is sprayed are located post throttle blades and are always subject to manifold vacuum. The second reason TBI systems generally do not use a VAFPR simply because it is not needed.
Now, notice that I qualified my statements with "generally" and "for the most part". The reason for this is because there is at least one exceptiont that I know of, possibly more that I don't know of. As was popsted, GM makes a VAFPR for TBI systems. So now the logical question is why. Well, the application for the GM VAFPR is a marine application. The catch is that the marine application is a higher performance engine with an Alpha-N ECU. Alpha-n does not use VE tables but rather uses fuel tables in relation to TPS. Most true Alpha-n systems do not use a MAP sensor. The MAP based load is calculated from RPM and TPS and in marine applications, load is pretty linear. A VAFPR can help in this application to extend the operating range and yet enjoy a smooth idle.
There are some that maintain that adding a VAFPR where there was none helps to increase WOT performance and smooth out the idle and to my suprise there are a bunch of misinformed people on this board running VAFPR's on TBI. If you tune your OWN chips, adding a VAFPR can be helpful and make a hot setup run at WOT and idle smoothly but a fair amount of tuning is required and a WBO2 is almost a must but this is a bandaid fix and there will be issues though they can be minimized through tuning. Lastly, having said all this, there is a proper way to run a VAFPR on TBI. If you reference injector pulse width to engine vacuum with the proper values that emulate spring pressure in the FPR, it will work and maintain accurate VE throughout the operating range. The EBL setup comes to mind. It incorporates this feature. HTH
but i still wonder why GM used VAFPR in their trucks.. ?
Thanks. That really helps alot. I never actually thought about it in-depth and realized that MPFI injectors are under vacuum, which would help draw the fuel out.
I still think this would be a neat toy to have. Do you know if it is possible to use one like roadmaster's in place of the stock one? Im not really sure where the stock one is - or how it is hooked up.
Even for nothing else, roadmaster's looks sweet, and you can have a really easy to see guage showing the current pressure. No more threads about "well go rent a FP guage at autozone to know if the fuelpump is working right." Also I plan on getting an EBL setup in the next year, so that would be sweet to have adjustablilty.
One reason I am kinda "partial" to these things is, I have seen one used before. This kid in my town built a early 90's Honda Civic, he did it right tho. Used the good head, headers, cams, all that stuff. Posi in the FWD too. Then he sold it to my buddy dan.
Dan was telling him how it was running one day, and mentioned it was running rich because the puffs of black smoke. Dre was like, I can fix that right here for you. He used a screw driver, and adjusted the fuel pressure right there on the spot. After a few test runs, the thing was running much better.
__________________ -Adam
1990 Firebird Formula
Bone Stock 305TBI, T5 tranny, 62k Origional
UMI subframe Connectors
I dont know of any TBI cars or trucks that use VAFPR? Not sure is there was a GM performance parts engine for car-truck that used one years back? I think marine 5.7L-7.4L was the application.
robertfrank, did you ever end up hooking up the vacuum on that AFPR from XtremeEfi and make it work? I'm running a TBI setup with 90 LB injectors at 22 psi constant pressure and idle sucks. In the market and this looks like a direct fit bolt-on (easy as hell).
Wondering if you were able to test its functionality? They advertise -5PSI at idle and "richern up top end" but dont really describe the full range of pressure vs vac.
I haven't yet, now that I've gotten into tuning I've not quite needed it like I thought. I know once I put the ZZ4 heads and cam in I might go ahead and modify the FPR to a vacuum referance. I'll let you know how it goes.
__________________
The ZZ5.0 is in full effect!!!
Check out my Cardomain!!! The Future Ultimate source for TBI performance. http://www.cardomain.com/ride/3869220
Forgot to add, I have 16psi at idle and 23psi WOT. Also had it at 17-24psi, looks like 7psi would be the adjustable range with a 94 Fbody LT1 cam and topdownsolution's spring.
Does anyone else have first hand experience with the xtremefi AFPR with vacuum compensation connected? From the literature it mentions a ~5psi drop at idle. I just purchased one and am trying to figure out appropriate values in the EBL BPC table.
The only way I can think of is to log the fuel pressure for the full range of vacuum and then graph it to see where to set my BPC. rBOB has a spreadsheet with built in formulas that ships with the EBL, but the values there appear to have a much larger range in pressure where I only have about 5PSI sway.
I was just lucky. I found a member with almost identical engine /vehcile as mine and just borrowed his table. We both use the same VAFPR(Aeromotive). Important thing here is he did it correctly. I am uncertain of exact procedure but it involves placing a VAC on the AFPR and noteing the resulting FP resulting. Then you calc the BPC for that VAC area. This is done with a devise called a Mighty Vac(?). I think it sells for about $70. During logging I went over 100 in VE tables so I needed to increase the BPC at that VAC and retune a few times. It was close.
Other option is to use the Micro Excel calculator and place in your specific values(cylinders,CID, FP,injector size, # of inj) and it will calculate for you the BPC vs VAC for table. I can send it tou you if you like.
FYI I am at 20 lbs FP 0 VAC and idle am at 11 lbs FP at 60 (62 in log) area of VAC table.
Obviously the strength of spring will affect the drop in FP. Not all equal.
Modifying a stock FPR to VRFPR, will require some soldering. I doubt you can make it externaly adjustable without leaking issues. Best will probably be to stack shimms untill desired FP.
I'm using RBob's excell formula and it works wery well.
well, I put the xtremefi AFPR with vac (VRFPR) with a spring that advertises 15-30 adjustable. Set at 20psi its only providing about a 3-4 psi drop at idle. I did, however, learn that at idle, I dont produce as much vac as when I give the pedal a quick stomp and let it wind down. When I do that I get 5-6 psi reduction. Might be the cam, not sure.
Anyway, Im looking for alot more than a 3-4 psi drop at idle. If my logic is right, I need a much "softer" spring to achieve this. Anyone successful in getting this style of FPR to produce a 7 psi drop?
Ronny, I see you mentioned a 1-20 psi spring... I'll try to find one.
One other thing is that when I got close to 20 psi adjustment range, if I turned the screw a touch more, it would jump to 60 psi or more. I guess the spring reaches a point where it acts like a solid block?
Not sure if this will work but topdownsolutions offers one that is stronger than stock but not as strong as the one that GM offerred in their VAFPR(36 lbs?). Designed for GM TBI reg. My aeromotive spring may be different in size(width/lenght) and may be inappropriate choice.
Thanks Thomas... I now see post #20, my bad. I'll keep working on my setup.
As for the stock FPR, if you are looking for pics of how I modified that, I"d be glad to post or email them. It was really easy and the only catch was that its really hard, if not impossible, to adjust while on the TBI. I had to take the injector pod off and plumb the fuel to it and then use the key-on/key-off method a few dozen times to get the pressure set just right. Let me know if the modification of the stock setup is what you are looking for. I even have a few laying around that I can dissect and take pics of.
Thanks Thomas... I now see post #20, my bad. I'll keep working on my setup.
As for the stock FPR, if you are looking for pics of how I modified that, I"d be glad to post or email them. It was really easy and the only catch was that its really hard, if not impossible, to adjust while on the TBI. I had to take the injector pod off and plumb the fuel to it and then use the key-on/key-off method a few dozen times to get the pressure set just right. Let me know if the modification of the stock setup is what you are looking for. I even have a few laying around that I can dissect and take pics of.
Its very hard to get to. I ended up using a piece of allen key cut down to half inch length and cutting a groove around it wrapping it with a small piece of safety wire and securing it into regulator with heat shrink. Then I picked up a small flexible nutdriver from harbor freight that just barely reaches in and stays on it for adjustments. Nice thing about the Holley TBI is they put it on top.
ah, ok, so I think there is some confusion. I bought the xtremefi regulator with the 1/8" vacuum hole and used a 1/8 piece of copper tubing with epoxy to seal it. I did not modify the stock FPR for vac assist, however it would be really easy now that I've see the concept first hand. A small piece of sheet metal over the outside and a tig welder would seal up the stock fpr. Then just grind back the tab on the spring base plate so that it is still long enough to stop the base from spinning, but not long enough to drag on the sheet metal you weld in. If I had known how simple the vac FPR was, I would have done this from the strart but never fully understood it until I held the aftermarket one in my hand.
ok, got the Top Down Solutions 15.5 psi spring. Installed and the range of pressure is better now. Still only about 5psi between WOT and idle, but I blame the cam for poor idle vacuum. Anyway, thanks for the help here guys!
If your VAFPR is maxed out at 15.5psi, you can stack some shims under the spring. I have used 4 of topdownsolution's FPR spring's and all could hold 24psi without problem.
I have noticed that best is to set the initial pressure 1psi over desired because all FPR I have set up have dropped 1psi after the first week.
