arrowcamaro

iTrader: (2)

anyone put in a vafpr, i have the kit already but what else will i need to do the install? im assuming some vacuum hose and a few plastic "t"s and such, am i missing anything?

ShiftyCapone

iTrader: (7)

I have it and it was pretty easy to install. You need some vacuum line (can't remember the size sorry) and a vacuum delay valve. You will also have to drill a hole the size of your vacuum line in your spacer ring (if it is still on). The delay valve keeps the pressure up at idel without dropping to much. I got mine at napa. Once again I forget the part number. There are a couple of them you can get. Go to napa and ask for a vacuum delay valve. You will have to break off the stud in the torx screw slot to make it ajustable. Than you can use a small torx bit and adjust. I went from flush (screw head with the unit) in about 7 or 8 turns. Every 2.5 turns is one PSI increase. You drive your car and decide. Here is a pic of it installed. This is not my car but mine is literally the exact same set up.

arrowcamaro

iTrader: (2)

did you run that off the regulator to the vacuum port on the front of the throttle body with the delay valve in between?...ohh yea thanks for the help

Z28 Boy

check mine out...

http://z28boy.cz28.com/main.htm

go to "tech" then "TBI VAFPR".



there are pics and stuff on there.

-Brian

arrowcamaro

iTrader: (2)

thats why i was confused when i looked at his looked like his was running to the front port on the tb, your setup is the one that gave me the idea cause im running lean after making my motor breath better, i didnt want to bug you with a pm again thanks for your help............. both of you

JPrevost

One problem I noticed with a vac referenced fpr....it isn't really "right". Normally you'd use one when the injectors are opening into a ported runner which see's vacuum and pressure. TBI injectors (unless you're Joby) don't seem to need such a device. This is stock of course. Now obviously just by the nature of the beast it's a good idea to use it as a tuning aid. I've got to adjust my setup but it's a life saver. I've never heard of this vacuum delay hardware. I might have to check it out. I don't want any vacuum delayed with time if that's what it does, I just want a lower limit setting. The problem with a delayed or averaged value is what defeats the purpose of having it vacuum referenced. You might as well have your foot modulate the fuel pressure. Vol.ef changes quickly and your tuning tables are manifold pressure vs engine speed. To delay a signal is like slowing down your computer.

arrowcamaro

iTrader: (2)

so you dont think that the vacuum delay is needed huh, i was kinda thinking that it might be like a way of storing vacuum but im probably wrong

PaulD

The idea behind the delay is this: When you are sitting still or rolling slowly and suddenly floor it, the manifold vacuum will go from high to almost nothing. That will cause the VAFPR to immediately raise the fuel pressure. That delivers more fuel than the engine is ready for.

The delay allows the vacuum drop to effect the fuel pressure at the injectors slowly, so the engine has time to build RPMs.

I tried the NAPA delay and it didnt do crap. I have a vacuum gauge on the VAFPR line and all the "delay" did was to reduce the seen vacuum. THe same affect can be achieved with a simple line restriction.

Don't ask me why the vacuum at the gauge never "catches up" to the manifold vacuum. I thought a restriction would simply slow down the pressure changes but they remain depressed even in a steady state situation like sitting at an idle.

I eventually achieved satisfactory results with a heavier than stock spring and a vacuum line restriction.

kdrolt

To add to PaulD's comment.... the delay in the vacuum should also help when the driver suddenly gets off the WOT condition, like at the end of a drag strip run. You really don't want to suddenly make the engine see a leaner mixture instantly at high rpm and no load -- that might be a bad thing for the engine.

All L98, LT1, LS1 (and LS1 derivative engines) use vFPRs, so GM managed to get them dial-in (tuned) properly.... so I don't think it's impossible to do the same by using the big block marine-intended vFPR on a sbc TBI passenger car. That said, I don't know if those engines use a delay in the vacuum line to the FPR. I should study the one on my 94 Caprice the next time I get under the hood. FWIW.

RBob

iTrader: (1)

Just to avoid confusion the reason the L98's, LT's. . . use vFPRs is due to them being port injected. The fuel spray end of the injector is exposed to manifold vacuum. The vFPR maintains the same fuel pressure across (inlet to outlet) the injector, else the flow would change with a change in manifold pressure.

A TBI injector is not exposed to manifold vacuum.

RBob.

ShiftyCapone

iTrader: (7)

I used the extra stiff spring from Top Down Solutions. This spring is stiffer than stock but less stiff than the one that comes in the kit. Lon Salgren is his name and he and his company are a sponser at the top of this page. He helped me out a whole lot getting mine to set up and function properly.

arrowcamaro

iTrader: (2)

ok so the next question is...... how do you know that you need a stiffer or weaker spring? and shiftycapone is that vacuum line going from the regulater to the port on the front of the throttle body with the delay in between?

Dan W

If I get what you are saying, you want more fuel pressure than what you are running at idle but less than the regulator is giving you?

If thats the case you might be able to install a bleader valve in the vacuum line to the diaphram... similar to how an adjustable waste gate on a turbo system works... or ATI's FMU. It wouldnt be quite the same becuse you are not seeing more than atmospheric pressure but it would have the effect of raising your pressure at idle while keeping it the same at wot... just adjust your base pressure down to compensate and your wot pressure should come down where you want it.

ShiftyCapone

iTrader: (7)

This is a long post but bare with me and it should answer a lot of questions that people are having about this. I will post the instructions and testing that I read at the bottom of this post.

Quote by arrowcamaro

"ok so the next question is...... how do you know that you need a stiffer or weaker spring? and shiftycapone is that vacuum line going from the regulater to the port on the front of the throttle body with the delay in between?"

First you are correct on the location of the vafpr. I goes from the regulator, through the spacer ring, into the delay valve, and onto a vacuum port on the TBI. I used the port that you plug when you installed your open element and dissabled your thermac devise.

Now on the srping itself,
From what I have been told and what I did is this.

The spring that comes with the GM vafpr kit is way to stiff and will increase the pressure way to high even at the lowest setting. Using the stock spring is way to weak and you have to have the regulator cranked all the way, and this will not supply enough pressure. So the guy I mentioned before sells a spring that is right in the middle of the two. It is like 5 bucks after shipping so I would buy it. They have done all the testing on a 1991 305 with full exhaust and an LT1 cam. There should be a write up on it if you click on the link at the top of the forum page.

Now on the delay valve. Once again I was told and read stuff on this so it may or may not be true but it seems to work great for my car. If no vacuum delay valve is used the car will come to an idle and run to lean. The valve keeps the vacuum slightly higher to make a smoother idle without affecting WOT pressure.

Here is what I have read and what I was sent to help me tune my car with the new spring, delay valve, and GM regulator kit.

Tips for setting the GM TBI P/N 17113186 regulator
(vacuum-adjustable fuel pressure):
Background: The GM TBI P/N 17113186 regulator Top-Down Solutions has tested the
spring (orange in color) that came in the GM TBI vafpr (GM P/N 17113186) and found it
measures approximately 18 lbs/in. TDS found this spring rate was too high. We were
unable to adjust the fuel pressure below 18 psi at WOT (Wide-Open Throttle) with this
spring. Swapping this spring for the stock spring (tan in color) that came in the nonadjustable
fuel pressure regulator wasn’t acceptable either. This spring tested at
approximately 8 lbs/in. This was found to be too low of a spring rate. We were unable to
adjust this spring beyond 13 psi at WOT.
The new spring you have purchased (TDS P/N 105290) is rated at 15.5 lbs/in.
This spring will give you an adjustment range from 12 psi to 20 psi at WOT.
Tools needed: Torx T10 & T15 tips.
CAUTION: Before attempting to turn the center adjustment screw you MUST break off
the pin in the center. This is a TORX-T10 security screw. Do not try and adjust it using a
Torx security tip. Or you’ll wind up buying a new one as we did. Use a small flat head
screwdriver or chisel to break off the pin, then use a standard Torx T10 tip. We have
found that adjusting the screw from flush 7 turns in will give 8 psi at idle and 15 psi at
WOT. Turning the adjustment screw in 2.5 turns raises the fuel pressure by 1 psi.
Turning it out by 2.5 turns will lower it by 1 psi. For some applications the 8 psi at idle
may be acceptable. But for our test engine, the air fuel ratio was a bit lean and it
wouldn’t idle well. We used a Distributor Vacuum Control Valve (aka Spark Delay Valve)
by NAPA/Echlin p/n 2-1010 (cost between $10-$12) available at most auto parts stores.
This was put in-line from the vacuum source (at the TBI base) to the vafpr. This raised
the fuel pressure at idle to from 8 to 11 psi. It didn’t effect the pressure that had been set
for WOT.

BlackBird89-350

vapfr? Ok, so some of you have it in. Does it work?

The next question is (JPrevost you there?) if you have already done a custom chip or are planning to add one, how will the vapfr effect a custom chip tables? (if at all)

I've been sratching my head about adding this vapfr to my set up as well, thanks for the good question and the responces as well... good info.

lonsal

iTrader: (2)

FYI, I sold the last TDS 105290 spring I had in stock this week. I've ordered more and will modify them to my specs. They will be ready to ship Saturday. For some reason my web site adds too much for S&H. The spring is $4.50, S&H is $2.50.

Lon Salgren
Top-Down Solutions

steve8586iroc

Hey guys, let me throw a wrench in on the subject. What happens when you add a lumpy cam into the equation? With less vacuum at idle whats the vrfpr going to do other than add more fuel as well as the ecm trying to do the same thing.

Steve

RBob

iTrader: (1)

The vFPR reduces fuel flow everywhere except WOT. How much depends upon the manifold pressure (inverse of vacuum). Lets say you have 100#/hr injectors at 16 psi. With a cam that idles at 850 rpm, 60 Kpa (~ 12 " vac). Right now the PW is 1.1 to 1.2 msec at idle, not alot and difficult to control.

So you vacuum reference the regulator and it happens to be a 1:1 ratio (1 psi vac = 1 psi fuel press change). At the 60 Kpa idle pressure (manifold) the change in fuel pressure will be:

102 (baro) - 60 (idle) kpa = 42 Kpa.

42 Kpa * 0.14503 = 6.1 psi.

16 psi (at baro press) - 6.1 psi = 9.9 psi fuel pressure at idle

Fuel flow is reduced:

78.7#/hr = 100#/hr * sqrt(9.9 / 16)

So you can see that the injectors are now flowing 78.7#/hr at idle allowing for a larger PW, ~2.2 msec. The larger PW is easier to control with less of a flow change due to all the other factors that come into play.

RBob.

snflupigus

nice

steve8586iroc

Rob, I thought as vacuum increased fuel pressure decreased. So If I have a stock cammed 350 that has 18 to 19in of vac at idle the vrfpr would bring the fuel pressure down. Then when wot was applied and low vacuum of 0 to 3in occured max pressure would be seen.

Now if you have a lumpy cam that only makes say 11 to 13in at idle is added into the equation, wouldn't you have a overly rich condition. I realize with chip tuning a lot of this can be overcome if not all of it. Some people talk about a hunting idle problem due to the low vacuum signal where the iac can not compensate.

Did I miss something or am I just lost without hope?

Steve

snflupigus

you would just use a weaker spring with a lower vacuum signal.

your vacuum would still go to 0 at wot so the spring would keep the diagphram closed and let less fuel back to the tank, increasing pressure at wot.

what spring? you would have to figure that one out.

arrowcamaro

iTrader: (2)

well i ordered the spring today from top down sol. should be here around wednesday so ill keep you guys posted on any difference thanks to all of you for all of your help:hail: :hail:

RBob

iTrader: (1)

Yes, an increase in vacuum (which is a decrease in manifold pressure) will decrease the fuel pressure. The key to what fuel pressure to run (the max pressure) is based on how much fuel the engine requires.

Once that is set then it is time for tuning via changing the cal tables in the EPROM (in the ECM). Vacuum referencing the FPR is just another aid for tuning. It does make for screwy VE tables that's for sure. But it does work.

A hunting idle can be caused by many things. The idle SA control seems to help in that regard. Folks running the '747 won't have this idle SA control and may run into a hunting or rolling idle condition.

RBob.

JokerRS

I ran a vafpr with a "top down solutions" spring and had good reasults with it, as far as fuel tuning goes. I had a LT1 cam with headers and full exhaust, ultimate tbi mods etc. and was able to use a stock chip. It took care of my rich idle condition. Looking back, I wish I would have gotten into chip tuning instead. The reason is that the stock chip timing sucks big time. I could have had bigger gains with this settup had I tuned the chip to the cam. A vafpr is a band aid for not having a proper chip.
Some people don't have the time to mess with chip tuning, or the money. A vafpr may be the answer all though its a compromise. If after you change cams your air fuel ratio is off you need to tailor the timing curve also to get the full good out of your cam.

As far as chip tuning with a vafpr, it adds one more variable to chase. example, as you add timing you will gain power up to a point. As you gain power at a given rpm you need less throtle opening to maintain the same mph. Less throtle opening = more vac which changes your VE (fuel) table. Timing changes afect the fuel table with out a vafpr. I think adding one would make it harder to tune a chip, all though I'm sure it could be done. It would just take longer.

When I went to my pressent combo, I dissabled the vac feature and tuned it in the chip.

BlackBird89-350

Thanks Joker, that was what I was wondering......

Z28 Boy

just in case anyone cares...i picked up the mysterious "vacuum delay valve" from the dealer today. after this weekend, i should have he car all put back together, so i can see how it works.

ill let everyone know how i make out.

by the way...it only ran like 9 bucks at the dealer.

-brian

PaulD

Brian,

Did you get the NAPA part? Do you have a vacuum gauge to watch whether it actually delays or simply reduces the vacuum? As mentioned above, I didn't achieve a delay, as I was hoping for. I'm very interested in how you make out. Please post results, the more detailed, the better.