u/johnnyappleseednh

’89 Foxbody, LQ9 single turbo, 6–7 psi, 522 WHP.
I know the fuel system was underbuilt by the previous owner. When I bought the car, it had 48 lb injectors and an Aeromotive 340 pump. I’ve since upgraded to 100 lb injectors. The plan is to upgrade the pumps and go from -6AN to -8AN fuel lines this winter.

It was professionally tuned in October 2024, and I had it retuned in May 2026. Same tuner both times. This is my first boosted LS setup, so I’m still learning what’s normal and what isn’t.

Today, I started thinking more about fuel pressure after hearing a random, singular backfire during a harder highway pull. I decided to look into it and kept finding information geared toward stock/N/A applications, which obviously made me question things.

My tuner has told me the car is safe as-is for the time being. Lowest fuel pressure is around 35 psi during light cruising, but under load/WOT it comes up to around 46–47 psi. He specifically told me he only allowed me to run a small amount of boost until I upgrade the fuel system, which is already planned for this winter. This is a pretty major tuner, btw. Keep in mind this video is putting around in traffic and then a pull or two.

I sent him these videos today, and he confirmed that what I’m seeing is normal/okay.

Does anything here look overly concerning to anyone? Disregard the red/yellow sections on the handheld—they’re just adjustable thresholds.

My understanding is that the important thing is that fuel pressure increases appropriately under load/boost and that AFR stays where it should. AFR has always looked normal, and fuel pressure does rise when I’m getting into it.

Again, I’m new to boosted LS setups, so I’m mainly looking for some reassurance or a second opinion from people who have more experience with this.

Secondarily, recommendations for fuel pumps to turn up power and do more?

I bought a car with this intake and it looks like this.. briefly tried a rag and water, no clue exactly what it is.. any know what it is and if it can be cleaned off?

I have an '89 with a turbo LQ9 making 522 WHP on 6 psi. It has an 8.8 rear end, and I recently had a custom transmission mount fabricated. Since then, I've been chasing some weird noises. It may be completely unrelated to the mount, but I figured it was worth mentioning.

At highway speeds, under light acceleration, I get a humming noise that sounds similar to a bad wheel bearing, but I'm confident it isn't a wheel bearing. As soon as I let off the throttle and just coast, the noise disappears. Then, if I firmly tap the accelerator at highway speed, I hear a noticeable clunk. If I roll into the throttle smoothly, there's no clunk.

My first thought is a pinion bearing for the humming, and maybe a U-joint causing the clunk, but I'm curious what everyone else thinks.

Also, looking for recommendations for high-quality pinion bearings and U-joints that will hold up to a street car that's eventually going to be around 700 WHP? TIA

I just bought a 1989 Mustang a couple weeks back and here is the setup(some things):

6.0 LQ9 87k SBE
Holley terminator x max (professionally tuned)
Team z tubular front end
Tranny cooler
70mm turbo on3 turbo kit
Built 8.8 rear end 3:73 gears 31 spline moser axles
4180E trans built w/ shift kit b&m slap shifter
All 6AN supply and return lines E85 capable
Aeromotive 340 in-tank pump
SVE Dual 12" electric fans
SVE 3-core aluminum radiator
Holley low ram intake
102mm throttle body
Holley fuel rails
Holley fuel regulator
10AN catch can system
Holley 48lb injectors
Stage 2 BTR cam
Endless suspension work: weld-in SBFC, re-enforced and double-plated torque boxes, full-tubular from strut towards foward, etc.

I was told by the previous owner that the car made 594RWHP @ 6psi on the dyno.

I have the vehicle back at the place that tuned it 18 months ago and they did a full vehicle inspection and are addressing an oil leak(its the rear main seal). They specialize in LS builds and come highly regarded.

Here is the recommendations based off my exhaustive list of questions, some recommendations you guys put me on, and really…. mostly their findings.

Aside from tons of little repairs and quality of life changes (moving the catch can, shortening the serpentine belt as it was chewing up the lower radiator hose, creating a proper dipstick, full coolant flush, replacing lower radiator hose, replacing the rear main seal, etc).

The two biggest additions would be going to a 95lb DeatschWerks Injectors and a 3600 stall FTI converter.

The injectors was something I was hyperfixated on because I want the car to be as safe as possible. At the end of the day, this is a “fun” “ice cream getter”, not something I’m racing but something I want to be able to get in, go-fast, scare the fuck out of some family and friends and have it be as reliable as possible. It’s supposed to be a fun street car that can be reliably beat on.

That being said, I’m sure in the future.. I’ll want some more power and I know those DW injectors give me some headroom. All of the fuel trims and AFR looked okay with the 48lbers.. AFR was always pretty solid… but I know it’s not optimal.

Before I make more power, I will be upgrading the 6AN and fuel pump but not now.. as this endeavor is already at $5,000 (the injectors and converter are approx $2,200 of this) and I paid $14k for the car(clean — needs paint but spotless rust wise… tons of unlisted suspension work.

The converter replacement is a TBD. They can’t get a part # or anything off of it until they pull the trans for the rear main.. but they believe it might be undersized because it does engage in rear pretty hard(might just be line pressure, but they hypothesized it might be an undersized converter) and the two-step is a bit wonky.

I wanted to know if anyone thinks there will be any noticeable difference with jumping up in injector size and converter and just general thoughts with the plan? Am I gonna notice anything in the seat of the pants or power wise?

Entire car was built by previous owner and has about 1,200 -1,500 miles on it now.

I just bought a 1989 Mustang a couple weeks back and here is the setup(some things):

Holley terminator x max tuned by horsepower farm

Team z tubular front end

Tranny cooler

70mm turbo on3 turbo kit

Built 8.8 rear end 3:73 gears 31 spline moser axles

4180E trans built w/ shift kit b&m slap shifter

All 6AN supply and return lines E85 capable

Areomotive 340 in tank pump

Dual 12" electric fans

3core aluminum radiator

Holley low ram intake

102mm throttle body

Holley fuel rails

Holley fuel regulator

10AN catch can system

Holley 48lb injectors

Stage 2 BTR cam

I have the vehicle back at the place that tuned it doing some quality of life changes and fixing an oil leak (rear main seal... yay).

I saw lots of pushback from you guys on the 48lbs(installed by the guy who built it)… it was dyno’d at 594rwhp @ 6psi in Nov 2024. All parameters look pretty good and they didn’t have much to say about it other than me mentioning it was something I got lots of pushback in the groups for — they do agree they’re maxed but probably safe right now.

I am considering stepping up injectors while I have the car there. They’re recommending 60lb injectors(don’t remember the brand). Is that sufficient in your opinion? Seems to be from some loose internet research and they’re the tuners.. but figured I’d ask here.

Goal is a 600whp — maybe 700whp someday — street car.. that may see the drag strips once in its life. HP Farm builds some monstrous vehicles and asked me this a few times so I’ll answer it here too, lol.

Also, they have to take the transmission out to do the rear main seal and mentioned part of the reason it could be engaging in reverse hard(something I asked them about, not egregious but ya) is due to a smaller converter.

The previous owner did not tell me the stall size, and they’re trying to figure it out now.. but likely won’t be able to until they get it out. They are recommending going to a FTI 3,000-3,200 for street use, but it’s mega expensive.

Any thoughts on that?

Any thoughts in general while I have it there would be nice, I’ve had them go through it with a fine tooth comb and don’t want the bill to get too out of hand, considering I just bought the car for $14k, lol.

All in right now, I’d be at like $4-5k for the rear main seal, injectors, converter change, moving the catch can a bit, fixing the serpentine that was rubbing on a coolant hose, replacing that coolant hose, replacing serpentine belt, full coolant flush, oil change, full transmission fluid change, and re-tuning it… plus a few other things I am forgetting. Trying to not get too out hand and that’s getting close, lol.