"Tuning" Vortech kit with FMU discs- question

[nicholase]

I have a stock 90 GT other than a full exhaust. I installed a Vortech kit . I am using the included FMU, BTM, and Trex w 255lph HP intank pump. I'm getting around 7lbs of boost. I did install a UPR power pipe and mounted the stock MAF in the fender well.

I am using AEM boost/ AFR and FP guages to "tune".

I started out with the standard 12:1 disc for the 19lb injectors.

The AFR guage reads:
Idle 14.7
Cruise 14.5
WOT dips to 12 and steadily drops to 9.0. This seem pretty rich.

I installed the 10:1 FMU disc
The AFR guage reads:
Idle 14.7
Cruise 14.5
WOT dips to 12 and steadily drops to low 10's.

I'm wondering if I should try the 8:1 disc? I'm not wanting to lean out and melt anything. I'm not trying to extract every bit of power. I also don't want it so rich that I'm washing down the cylinders and covering O2's and wideband in soot.

Is there anything I'm missing here? I'm thinking to try discs until I get around mid 11's at WOT full boost / max RPM. Does that sound right?

I don't want to make any rookie mistake here. Thanks for any info.

 

[Noobz347]

Yeah, try giving your base timing a little tickle. Just a degree advance.

 

[nicholase]

Thanks for the reply. Right now I'm set at 10° base and using the BTM at 1. I checked it with a pressure tester. So I should be running 19° total advance at WOT near redline. Which I'm figuring to be safe. I'm not hearing any detonation at all.

Mostly just worried about using an 8:1 disc (which is suggested for 24lb injectors) with my stock 19's. Maybe Vortech calibrated the discs for the stock pump and Trex? When replacing the stock pump to a 255lph and using the Trex it's more fuel than they are calibrated for? I dunno.

I'm assuming I just use whatever disc combination that gets me in the mid 11's as I near redline at max boost, which is 7psi currently. If I'm off on this line of thinking please let me know.

Thanks for any insight.

 

[Noobz347]

There are multiple ways to affect AFR in any given range.

It can also be affected by the robustness of your ignition system.

The point is that the AFR ratio is not the only way to 'adjust' AFR in your circumstance and the possibility also exists that you may not be able to get it 'perfect' without a digital tune. The issue there is that if you're going to go [that] far, you may as well ditch the FMU, the in-line pump and do it all up with larger injectors and a high volume in-tank pump.

If you're hyper focused on the just the FMU disk tho... Let us know what you come up with.

Another wrinkle in the whole mess is the inadequate power supply to both, the fuel pump and coil through the entire useable rev range. It is not consistent.

 

[AeroCoupe]

Fuel pump voltage can be solved with a 30amp relay mounted in the trunk with a 10 gauge wire from the battery for the power supply to the relay. Use the old pump 12V supply for the trigger wire. This will ensure you have enough amperage and the voltage will be much more stable. I did this on my Coupe and it’s loads better.

 

[nicholase]

There are multiple ways to affect AFR in any given range.

It can also be affected by the robustness of your ignition system.

I think my ignition should be pretty solid. All the connections are clean. I put in a new Motorcraft TFI and I'm using the MSD6BTM (6Al, BTM combo), Performamce Distributors Screaming Demon coil, and 10.4 mm livewire plug wires. I gaped the plugs to .35 but then raised it to .40. Maybe I should bump that up more as it holds up fine to the rev limiter. See if that makes any difference in the AFR?

The point is that the AFR ratio is not the only way to 'adjust' AFR in your circumstance and the possibility also exists that you may not be able to get it 'perfect' without a digital tune. The issue there is that if you're going to go [that] far, you may as well ditch the FMU, the in-line pump and do it all up with larger injectors and a high volume in-tank pump.

If you're hyper focused on the just the FMU disk tho... Let us know what you come up with.

I'm hoping to get through the summer with it as is. It's just a weekend toy I take out on nice days. Then debate over the winter if I want to go deeper. I did find a reputable tuner about an hour away so that might be an option if I want to do a HCI and other things.

It actually runs great. But the low 9's richness under boost with the 12:1 disc was blowing soot and I had some gas smell in the oil. I changed the oil and swapped discs to the 10:1 and it definitely got better.

At this point I'm not really looking for a perfect tune and I realize the FMU / BTM is old school. Just wondering how close I can get and not wanting to burn anything up.

I should probably leave the 10:1 disc and get through a few different weather patterns. It's hot as balls right now. Might get leaner when the humidity and heat calm down. Maybe with this old school FMU 10's at max boost / rpm isn't a terrible thing. It is in the 11's for most of the pull.

If you're hyper focused on the just the FMU disk tho... Let us know what you come up with.

Will do.

Thanks again for the feedback.

 

[nicholase]

Fuel pump voltage can be solved with a 30amp relay mounted in the trunk with a 10 gauge wire from the battery for the power supply to the relay. Use the old pump 12V supply for the trigger wire. This will ensure you have enough amperage and the voltage will be much more stable. I did this on my Coupe and it’s loads better.

Thanks for the info.

I'm running a 130a PA performance 3g alternator and it seems to output pretty well. I did a few things different than the vortech manual. I passed on mounting the relay in the trunk and using the cigar lighter fuse as power. I put the relay under the driver's seat next to the factory fuel pump relay which I used as a trigger for the TRex pump relay. I also mounted my guage relay there. I ran 10ga power and ground from the battery to the relay and then back to the TRex.

The factory fuel pump bracket conveniently has places for a couple more relays. Just have to drill a hole in it, slide a clip nut over the hole and bolt the new relay to it.

 

[Noobz347]

Just for reference and informational purposes:

When I initially installed my Kenne Bell, I fought 'gremlins' in the AFR vs. RPM for a time.

I eventually solved the issues with two things:

Kenne Bell Boost-a-Pump - This is nothing more than an adjustable voltage regulator specifically for the pump. It keeps the pump at a constant voltage regardless of current draw over my 38 year old wiring and electrical signal. [Side Note: I do not use their boost pressure switch. I just keep the pump saturated at a constant voltage]

Kenne Bell Boost-a-Spark - Same thing only, it keeps the coil saturated.

Other manufacturers make similar components. Air On/Off, Lights On/Off, etc... doesn't matter to those two components anymore.

 

[Cheapskate207]

I love that you’re using some old school tech with good results. I considered doing that with my first gen lightning and kinda regret not.

FWIW I had my HCI 7 psi vortech car dyno tuned and the (reputable) tuner was happy with 11:1 afr.

There’s probably a million cars with the same setup as you running the 12:1 disc so it’s probably fine, especially with the 10:1. If it were me I’d likely try the 8:1 and see how it works. Back out if it’s lean, put the 10:1 back in and enjoy it indefinitely.

 

[Noobz347]

I ran a similar setup with my KB when I got it. The [tweaks] that I employed to get it right are not tweaks that I would prefer to relay over a forum.

On a side note: The 19 lb injectors used in this setup are being pushed way beyond spec and it is a [really] good idea to have them all flow tested and adjusted so that they all squirt the same.

It only takes one weak injector to throw the whole damned thing off.

 

[nicholase]

I love that you’re using some old school tech with good results. I considered doing that with my first gen lightning and kinda regret not.

FWIW I had my HCI 7 psi vortech car dyno tuned and the (reputable) tuner was happy with 11:1 afr.

There’s probably a million cars with the same setup as you running the 12:1 disc so it’s probably fine, especially with the 10:1. If it were me I’d likely try the 8:1 and see how it works. Back out if it’s lean, put the 10:1 back in and enjoy it indefinitely.

I tried the 8:1 and I feel it was too lean. It hung in the 12's initially and pulled down to high 11's when I got close to peak RPM/ Boost. I just did the one pull and didn't want to push it.

A 9:1 would probably be perfect. I put the 10:1 back in and I'll just run with that. It was a little fat, but it leaves some room for error.

All in all the car runs great and it's got considerably more balls than it did before. That's all I was looking to do.

I'm really happy with the drivability FMU / MSD BTM. Seems to be a good option for a pretty much stock street car.

 

[nicholase]

When I was doing the Vortech install I noticed how sad the factory radiator looked. Besides being 35 years old it's pretty scrawny. So I ordered a DeWitt pro series 2 row. Tool a while for them to make it. Just got it last week. Seems really well made. It's quite a bit bigger than the original....

For it to clear the supercharger pulley I had to relocate the wiring harness between the rad and condenser and move a few other things. While I was in there I replaced the condenser with a parallel flow and replaced all the A/C lines.

Nice looking rad. I like the stamped tanks.

This week I'm taking it to the rear end specialist. Getting 3.55's. Looking forward to that.

 

[General karthief]

rear end specialist

Awh, too bad, that could be a winner

 

[FastDriver]

Like you, I'm more conservative with fuel, but I wouldn't be happy with an AFR that drops to low 10s. I agree that a 9:1 FMU sounds about right for ya.

I would run the 10:1 FMU, but pull some base fuel pressure back. Nothing crazy, though... say 3 psi, which should be enough for the EEC to compensate for. Then monitor AFRs closely and listen for detonation in the part throttle ranges. I usually run 15-15.5:1 AFR at cruise, and ideally a 14.5-15 at light-moderate throttle. You're running there at cruise and idle; so, I think you have some wiggle room.

Assuming you're running stock 39psi, that should lean it out a few tenths across the board.

This is probably the type of tweaking Noobz wasn't keen to post about.

 

[Monkeybutt2000]

Firstly, NICE car that is one clean Fox. I wouldn't be concerned with high 11's at your boost level. Did you go to a colder plug?

 

[nicholase]

Like you, I'm more conservative with fuel, but I wouldn't be happy with an AFR that drops to low 10s. I agree that a 9:1 FMU sounds about right for ya.

I would run the 10:1 FMU, but pull some base fuel pressure back. Nothing crazy, though... say 3 psi, which should be enough for the EEC to compensate for. Then monitor AFRs closely and listen for detonation in the part throttle ranges. I usually run 15-15.5:1 AFR at cruise, and ideally a 14.5-15 at light-moderate throttle. You're running there at cruise and idle; so, I think you have some wiggle room.

Assuming you're running stock 39psi, that should lean it out a few tenths across the board.

This is probably the type of tweaking Noobz wasn't keen to post about.

Thanks for the feedback. That's something to ponder. I wasn't sure if the FMU overrides the fuel rail FPR. As in if it blocks off the return (or mostly) I was thinking regardless of the base FP the FMU would over ride it. I'll have to think about that suggestion some more. My base FP reads between 39-41. Looks to have the factory FPR.

I do have the bleeder on the FMU which can bleed off pressure to the disk to fine tune it. However I'm leary of messing with that too much because my BTM is tied into that vacuum source. So if I bleed off pressure to the FMU I'm also doing it to the BTM, which doesn't seem like a good idea. Also introducing a vacuum leak intentionally also doesn't seem ideal.

Looking at the FMU discs I'm thinking any quality machine shop could spin off a few in between sizes. Might be worth investigating.

 

[nicholase]

Firstly, NICE car that is one clean Fox. I wouldn't be concerned with high 11's at your boost level. Did you go to a colder plug?

Thanks! It's just as clean underneath. Tough to find em like that, especially up here in the North East.

I wish I could find a link to a tune and see what AFR is suggested at various RPM's and boost levels. I really have no idea and don't want to do something stupid. In the one pull I made with the 8:1 it really didn't dip into the 11's until I was at about 5500. It sounded fine. Pulled hard. Just seems a little on the edge for me.

What Noobs was saying about the injectors being pushed got me thinking if one was wasnt flowing as much as the others that could be a problem.



I'm running the factory plug. That's what was suggested in the manual. I did tighten up the gap a bit.

 

[FastDriver]

You should run a step or two colder on your plug, IMO.

Based on your description, I'd run the BTM off of a different vacuum source, and tune from the bleeder, then. You definitely want to be able to tune the timing separately from the AFR.

 

[Noobz347]

Super Simple Diagram of what's going in your fuel system and why it works the way it does:

The [red] lines are pressure lines and the [blue] is the return line.

The FMU is at the end of the row and when it closes off, the fuel has nowhere to else to go. Pressure will increase to the limit of the pump to make it until enough fuel volume is relieved to outrun the pump or the FPR.

 

[nicholase]

Super Simple Diagram of what's going in your fuel system and why it works the way it does:

The [red] lines are pressure lines and the [blue] is the return line.

The FMU is at the end of the row and when it closes off, the fuel has nowhere to else to go. Pressure will increase to the limit of the pump to make it until enough fuel volume is relieved to outrun the pump or the FPR.

Right. That's why I was wondering if lowering the base fuel pressure would make any difference under boost. Say you managed to lower the base pressure by 10psi with an adjustable FPR on the fuel rail (by reducing the restriction to the return) the FMU is restricting the return after the FPR and would still raise the pressure to max pump pressure I believe?