'93 VR4 State of the Union

[AdamVR4]

I have been eyeing that FBM fuel hat for a while. What price did you get it at if you don't mind me asking.

Paid retail after asking them a bunch of questions they promptly answered. It was like $400 vs 3sx's $500. 3sx's design really may be better. There are just so few pics of the FBM setup.

[FeaRpb]

Interesting. Hope to get an opinion from you once you get your hands on it. I was planning on modding the stock one with AN fittings that I bought, but I am also tempted to spend lots of money on shit. So if your opinion turns out good, I may just buy the FBM one.

[Chris@Rvengeperformance]

Once in a while I think about a billet hanger, but with my simple one pump setup and welded an bulkhead, I can't convince myself it matters back there under a plate what it looks like

Post some pics of the setup, maybe you can convince me.

[familyMAN]

4 month wait for an update and no pics? ....fail

[AdamVR4]

Once in a while I think about a billet hanger, but with my simple one pump setup and welded an bulkhead, I can't convince myself it matters back there under a plate what it looks like

Post some pics of the setup, maybe you can convince me.

Sounds like you're good to go so why change it? I only got it so I didn't have to salvage the stocker since I'm not exactly investing a ton of hours into the vr4.

[futurevr4man]

I got lucky and found one of the Top Gear Engineering dual in-tank hangers. Seems to be doing well... decent design. My low fuel light is on constantly though. It was fine when I installed it, then a few months later after I filled up it came on... haven't figured out that part yet. Float still works.

Outside of that - I am also running the DW1200's and have had 0 problems. I hold a 750 rpm idle even with big cams, no problem. They tune easily enough too.

I'm surprised you didn't go with a dual in --> dual out setup. I've never been fond of the loops... too nervous about starving the 6th cylinder in the loop... cylinder #6. My return line runs against the passenger side frame down along the firewall along the lip that's down there, and makes the turn where your line comes up to the fuel filter. I think it's a decent looking setup? I currently have dual Aeromotive Stealth 340's in tank, but I'll get the dual Walbro 450's if I run short on fuel in the far future. I tried to set myself up for e85... haha!

I'd like to hear some results about the transmission. My clutch is dragging as well, and I have adjusted everything correctly... no fix. Fork looks fine, etc. I can feel it wanting to lunge when in 1st and revving high. May have to try some shims aka washers behind the slave like you to give a little more throw. May not help though, idk?

If you want any pics of fuel stuff, let me know!

[AdamVR4]

I'm surprised you didn't go with a dual in --> dual out setup. I've never been fond of the loops... too nervous about starving the 6th cylinder in the loop... cylinder #6.

I almost made a thread about this.

Dual parallel walbro 255lph's will flow anywhere from ~550 L/hr @ 30 psi to ~350 L/hr @ 85 psi. They have internal pressure relief valves @ 85 psi and begin dumping volume there. If you're running 35 psi boost on top of 38 psi rail pressure, you're talking ~400 L/hr @ 73 psi.

400 L/hr or 6.67 L/min... in more useful units, that's .00011 m^3/sec. It's really not much flow and that's why people have been able to conduct reasonable fuel pump flow rate tests in their garage with a large bucket.

Assuming no pressure drop through the -8 lines en route to the rail...

Ethanol has a dynamic viscosity of ~.0011 kg/(m*s) and a density of 789 kg/m^3.

We'll assume the stock rails have a -6 AN diameter of .31" ... x-sectional area of .075 in^2... or .000049 m^2

Velocity = volumetric Flow Rate / x-sectional area =.00011 m^3/sec / .000049 m^2 = 2.28 m/s or about 7.5 feet per second.

Reynolds number = 12,900 ... turbulent

I used this calculator to find the friction coefficient because my spreadsheet was for laminar flow

Moody Friction Factor Calculator

It's reynold's number jived with mine and the friction coefficient is .0378

The stock rails and loop are about 30 inches long. We'll call it 3 ft to be conservative.

I will also conservatively neglect fuel sprayed into the cylinders that would reduce pressure drop to cylinder #6 for simplicity. I may explore this further later.

I'm getting 1.3 psi pressure drop across 3 feet at these flow rates. Jives well with available calculators like this one: https://www.lmengines.com/fuel-line-calculators/

Differential pressure across injector #1 is 38 psi

Differential pressure across injector #6 is 36.7 psi ... or 3.4% less... Seems significant, right?

If you assume my 1200cc injectors flow that at 38 psi (a slightly conservative assumption) and plug the differential pressure numbers numbers into RC Fuel Injection

That 1.3 psi pressure difference only amounts to 11 cc/min or less than 1%.

For reference, my current 6x 780cc injectors flowed a maximum of 744cc/min and {*edit* a minimum of} 734cc/min... or a totally acceptable 10 cc/min deviation.

That and... The #6 cylinder gets the least air flow simply due to our throttle body location and intake manifold design. I want less fuel @ cylinder #6.

[futurevr4man]

That and... The #6 cylinder gets the least air flow simply due to our throttle body location and intake manifold design. I want less fuel @ cylinder #6.

I almost made a comment about that in my post as well. But meh. When everything is under pressure, I have a hard time believing there is THAT much of a difference, but I haven't seen any models of it, or the numbers they used in said models.

I will also conservatively neglect fuel sprayed into the cylinders that would reduce pressure drop to cylinder #6 for simplicity. I may explore this further later.

Maybe I am being ignorant here, idk, but I don't think neglecting fuel sprayed is being conservative. There would be an inherent pressure drop at each point, every injector taking it's piece of the pie right? Sure, they fire for just, what? a ms? (don't want to calculate that out right this second), but at 7000rpm, or a rotation ~every 10ms, they are firing QUITE a bit. Am I just totally looking at this wrong?

The last thing I would want to happen is starve an injector for even a few ms, and get a lean spike in your injector firing. Create quite the hotspot pretty dogone quick.

And to be clear - I don't think you have a bad setup going at all. I am simply asking questions out of curiosity. You're smart enough that you know what you're getting into. A nice discussion is a rare thing to have

[FeaRpb]

[AdamVR4]

I almost made a comment about that in my post as well. But meh. When everything is under pressure, I have a hard time believing there is THAT much of a difference, but I haven't seen any models of it, or the numbers they used in said models.

I'd be impressed if there's only a 1-2% difference in air flow from runner 1 to 6 through our asymmetrical intake manifold... How good was the CFD in 1990? How about the CFD of anything aftermarket for a 3S? haha

Maybe I am being ignorant here, idk, but I don't think neglecting fuel sprayed is being conservative. There would be an inherent pressure drop at each point, every injector taking it's piece of the pie right? Sure, they fire for just, what? a ms? (don't want to calculate that out right this second), but at 7000rpm, or a rotation ~every 10ms, they are firing QUITE a bit. Am I just totally looking at this wrong?

8000 rpm's is 133 rev/sec... my 1200cc injectors @ 92.5% IDC will dump 1.11 L/min or .0185 L/s or .000139 L per revolution. There is .0487 L of fuel sitting in a 1 m long fuel rail... Each time an injector opens it draws a negligible 0.2% of the available fuel.

Also, the 6.67L/min parallel walbro flow rate I assumed in my last post is exactly what 6x 1200cc injectors @ 92.5% IDC would need.

The last thing I would want to happen is starve an injector for even a few ms, and get a lean spike in your injector firing. Create quite the hotspot pretty dogone quick.

Thanks to the fuel pressure regulator, the only way that happens is if you run out of fuel pump, right?

And to be clear - I don't think you have a bad setup going at all. I am simply asking questions out of curiosity. You're smart enough that you know what you're getting into. A nice discussion is a rare thing to have

Thanks for asking. This was something I'd started to do a few weeks ago and blew off. Glad the math worked out! haha