RX Turbo Dyno Results - Playing with Fuel Pressure

[Myxalplyx]

Car: 1988 RX Turbo (Manual/FT4WD)

Mods: K&N Cone Filter

Garner Pulley

Techworks Header

GT17 Ball Bearing Turbocharger

Techworks Downpipe

2.5" Cat, 2.5" Custom exhaust, 2.5" Flowmaster

Ebay Manual Boost Controller

Ebay Rising Rate Fuel Pressure Regulator (RRFPR)

 

 

 

I attempted to play with a Rising Rate Fuel Pressure Regulator (RRFPR) I recently purchased off of Ebay. Stock fuel pressure is around 36.3psi or so (according to my Factory Service Manual). I set the RRPFR at 36psi, 44psi, 48psi and 56psi. It is now set at 56psi. Surprisingly, the difference in fuel pressure made very little difference in the amount of hp/torque I am making across the entire rpm range. I'm keeping it set at 56psi because of some unexpected boost spikes I'm experiencing lately out of nowhere.

 

I'm at a loss as to what my boost pressure is. Why? While on the dyno today, my boost gauge read 6psi. The 6psi felt the same as when I was previously at 9psi. As you'll see, on the dyno it makes about the same hp/torque as well. I did add the vacuum hose of the RRFPR on the same line as the boost gauge. I think that's the problem. The gauge isn't receiving the full amount of boost because 3psi or so is constantly going to the RRFPR. I just figured this out while typing this out.

 

Anyways, here's a dyno chart of my 2nd to last run at 52psi of fuel pressure vs my stock fuel pressure (with the stock fuel pressure regulator/Techworks setup) vs when my car was fully stock.

 

 

 

 

Max hp increase from increasing fuel pressure is 117.22hp vs 113.40hp from my previous run. Max torque increase is 126.38lb-ft vs 121.66lb-ft of torque from my previous run. So there's something to be gained depending on your setup but I wouldn't expect anything huge unless your boost is turned up. This run was done with the manual boost controller turned 'all the way down' to prevent any boost spikes that I was getting with the dyno runs I was getting. I'm keeping it this way until I get an electronic boost controller installed.

 

Notice that I have the air/fuel ratio richer than my last run(s) that I did with the Techworks setup and no fuel control. I was concerned about the air/fuel ratio below 4500rpm, especially around 2500rpm or so. It just seemed to lean. However, talking to the dyno operator, he told me that the air/fuel ratio on this dyno is usually off by 1 when you have a catalytic converter installed. With no cat, it'll read dead on.

 

For example, if you used this dyno and got a 13.5:1 air/fuel ratio across the whole rpm range, you'll actually be getting 12.5:1 because of how the cat converter is affecting the readout. If you have no cat converter and you get 12.5:1, then your actual air/fuel ratio is 12.5:1.

 

So I was trying to tune the RX Turbo to be like how the WRX/STis are on some of the boards that I read about. Usually, I see the base reading between 11.5:1-12.0:1 and then it goes as rich as 10.2:1 on the top end. So this is what I went for and it's pretty much what I got. However, I didn't get the hp/torque increase that I was expecting (10hp or more, just off the top of my head). I guess the intercooler is working as it should. It should be safer to run like this though to ward off detonation with the boost spikes.

 

Speaking of boost spikes....see next post---->

[Myxalplyx]

Here are a couple of dyno graphs to illustrate the problem I was having with boost spike. BoostSpike runs #1 and #2 I immediately let off the gas pedal when I saw it starting to go past 9psi (it was stopping at 6psi when running right). BoostSpike #3, I tried to keep the fun going by modulating my foot on the gas pedal. I was watching my boost gauge and I was keeping the boost between 8-9psi at 'Part Throttle'. The fun ended around 3900rpm when the Fuel Cut kicked in HARD.

 

Now I finally know how that feels. I was experiencing it the night before while testing on the road. Car would buck hard and a loud 'boom' sound came from the rear. Dunno if it was backfire or something else. I'm going to have to do something about this. Needless to say, even at part throttle at 8-9psi (was probably around 12-13psi), you can see the amount of hp and torque that was being made. Makes me wonder what it would've been on the top end. I'll find out......someday.

 

 

Remember, the first two boost spikes are at WOT, then I let off. The last one (BoostSpike3) was at part throttle, trying to keep the boost between 8-9psi until fuel cut kicked in. With this at 3800rpm, HP was at 106.47hp vs 80.06hp. This is a gain of 26.41hp.

 

 

 

 

The torque made at 3800rpm was 147.15lb-ft vs 110.66lb-ft (A gain of 36.49lb-ft of torque. Nice!)

 

 

Man, this car just begs to be making more hp/torque. I'm going to take my time and try to do things right. I'll still concentrate on fueling (possibly bigger fuel pump and cleaned or slightly bigger fuel injector) and a better boost controller. My boost gauge needs to be reinstalled somewhere else as well so I get a truer psi reading. That's all for now.

[WJM]

Coolness.

[ballitch]

so by upping your fuel pressure by almost 20 pounds you made and extra 4-5 hp and 4-5 ft lbs of torque, sounds good to me.

 

 

 

 

 

~Josh~

[calebz]

Kevin.

 

Upping the pressure doesn't really change how much is coming from the injectors.. It may help to push them closer to max output, but UNfortunately, I have a feeling you were pretty much already there.

 

As far as differences in boost.. Humidity, temperature play a huge part in how high your car will boost.. 3 psi difference in different types of weather isn't really anything to worry about.

[Myxalplyx]

Kevin.

 

Upping the pressure doesn't really change how much is coming from the injectors.. It may help to push them closer to max output, but UNfortunately, I have a feeling you were pretty much already there.

 

Are you sure about this Calebz? I ask because the more I turned up the fuel pressure, the richer the car ran on the dyno according to the dyno's wideband air/fuel ratio. This would mean more fuel is being sprayed from the fuel injectors. Maybe I'm misunderstanding what you are saying. :-\

[nkx]

i think hes trying to say your injectors are still opening the same distance, and staying open for as long as they were before you upped your fuel pressure. youll see more of a performance increase if you install new injectors which are rated to flow more fuel.

[Do It Sidewayz]

dude..you know your WAY too lean

 

you should be running someplace in the mid 11's for Air Fuel ratio on a Wideband.

 

In the 12's is danger zone!

[Vanislru]

At the level's of air you are moving those injector's are on basically 100% duty at max boost, you could up the fuel pressure more but it'll run like crap off boost if you raise it too much. Are you thinking about fuel management and larger injector's? melted pistons really suck. With that turbo and decent fuel metering .

[Do It Sidewayz]

it definately looks like he's at 100% duty cycle.

 

 

The way that it's way lean in the mid-range, then get's richer at high RPM's gives that away.

 

From the look of this curve....Melted pistons aren't far off..

 

 

I think Will is prolly due....as he's making 50 more hp!!!!

[The Scooby]

ya hate to tell you but upping your fuel pressure that much wont show any gains BECAUSE, your ECU is what controls the length of time the injector stays open, not the fuel pressure. if you want to see some hp/tq gains put in some lerger injectores and run about 7-15psi higher then STOCK, and that will be plenty, putting that much pressure on your stock injectores will most likly just blow the seals in it.

 

they are made to operate at a certain psi, along with your fuel rails/fuel lines, and pushing that much pressure on a car that old with the stock components (most likly) just isnt smart.

[Subarutex]

What boost controller are you running?

 

I'm guessing your boost spikes are because of a sticky wastegate or perhaps a ************ty boost controller.

 

I would never run with a boost controller in but not adjusted... just seems like that is asking for trouble, i'd bypass it and see if the spikes go away.

 

Fuel pressure is an intergral part to tuning an engine. By upping the pressure you are going to increase the flow up to a point. I don't think anyone knows what that point is on our injectors, it could be that Kevin is close to it. Or, he may not be.

 

I am not arguing that bigger, higher flowing injectors are not the right way to do this, because they are.

 

See this link for several handy calculators: http://www.megasquirt.info/manual/minj.htm#size

 

I think everyone here agrees that 180cc/min is what our stock injectors are (or close to). For the sake of this calculation, we need to convert that to lbs/hr. There is a handy dandy calc. for that on the above link.

 

180cc/min gives us 17.1lbs/hr of flow. Our systems run about 36psi of fuel pressure I believe. On the link above there is a calculator to calculate the expected flow of upping the fuel pressure. Lets do that.

 

17.1lbs/hr at 36psi

 

at 44 psi it gives us 18.9lbs/hr of flow

48psi = 19.7lbs/hr

56psi = 21.3lbs/hr

 

Using the cc/min to lbs/hr converter tells us that 21.3lbs/hr is 224cc/min. That is a pretty big increase in theoretical fuel flow.

 

There is a point at which an injector will not flow anymore, it just isn't possible, but none of us here know where these injectors hit that line.

 

Drivability could be affected by the bigger injectors... but also see he's running a different turbo. We have no idea what it flows compared to stock (hell, we don't even know what that flows!) so maybe the high fuel psi and the different turbo make up for eachother. Which then would mean upping the fuel pressure is working, and he's not causing any damage. His AFR's are good enough, I think this was a good step. I would go even farther to say that if he cleaned up his boost and ran say... a steady 9-10psi his AFR's would still be in check.

[WJM]

it definately looks like he's at 100% duty cycle.

 

 

The way that it's way lean in the mid-range, then get's richer at high RPM's gives that away.

 

From the look of this curve....Melted pistons aren't far off..

 

 

I think Will is prolly due....as he's making 50 more hp!!!!

 

nnnnnnnNNNNNNNNNNNNNOOOOOOOOOOOOOOOOOOOOooooooooooooo!!!!!!!!!

[Do It Sidewayz]

well...we did blow up 2 engines on the weekend.

 

 

One had a #3 piston which was melted to crap. Another...we blew the head gasket on #3.

[sheppie62]

Who makes the gt-17 turbo, and does it come off any particular vehicle?

[Vanislru]

Upping the fuel pressure will help deliver more fuel no doubt, but it'll run very rich low-mid rpm range off boost[read sputter like crazy cause your plugs are fouling, probly bung up any cat you may run too]. Larger injector's will be the same prob.. To do things right[read not melt stuff and blow HG's] fueling needs to be addressed, maybe go with another injector boost activated or go with one of the many other fuel management options[ you'll be able toforget all about fuel cut too ].

I was doing the high boost thang on my lifted wagon for awhile but I don't have the $$$ for better fueling so I'm back down to 12 psi for now. I have spare blocks ready to be thrown in but the thrill of an extra 10 or 20 hp for a month or two is not worth the time to swap in another motor. After I've finished installing the hybrid tdo4 I will be steppin up to ? ... something better than this stock pos fuel setup.

[Vanislru]

Drivability could be affected by the bigger injectors... but also see he's running a different turbo. We have no idea what it flows compared to stock (hell, we don't even know what that flows!) so maybe the high fuel psi and the different turbo make up for eachother.

The prob with larger injectors is the ecu still determins the duty cycle of the injector relative to how much air the maf see's so... maf sees x amount of air and tells the injector to open for x period of time, with larger injector's you'll be rich all the time wether you are boosting or not. The turbo has nothing to do with the fuel issues, flow issues are related to heat and efficiencies. This really has nothing to do with the turbo he's running, yes it spools fast and flows more and is waaayyy more efficient:slobber:, but that doesn't mean much to the computer it just measures cfm and fuels accordingly.

[Subarutex]

You are correct Vanislru... that is up until the ecu goes into a a no feedback loop reading. If I understand how our ecu operates.... once the boost light comes on, it goes into a non feedback loop. Thus relying on the preloaded maps in the ECU to determine how much fuel it needs. This is where larger injectors will help compensate for the "more effecient" turbo.

 

For instance, I run a TD04 on my RX. It has different flow, and different effencies compared to a stock turbo. I'm also running higher fuel pressure (42psi).

 

Off boost the ECU seems to be able to dial back the fuel (because its in a feedback loop) to keep the AFR close to what i was seeing before the turbo and fuel mod. To further help the ECU i also have an SAFC which i use to help trim back the fuel in off boost conditions.

 

At times, the idle is wavy... idle up, idle down, idle up, idle down (i attribute this to my externally vented BOV and the higher than stock fuel pressure)

 

Once on boost (and the ecu in the no feedback mode) the higher fuel pressure has helped me keep my AFR's close to what they were before the turbo and fuel mods.

[Myxalplyx]

Thanks for all the responses. I just want to point out a few things. I'm not agreeing nor disagreeing with anyone. There's a reason why I did what I did and I'm not sure I was clear initially.

 

I chose to go with the air/fuel ratio that I did because after installing the Techworks header, the car had a leaner air/fuel ratio curve than I wanted. Even when the car was stock, the air/fuel ratio went leaner than it did when I previously did a baseline dyno run and I truly did not like the curve of that air/fuel ratio.

 

If some remember, I dyno'd the RX turbo after I had the Garner pulley installed. The dyno reported I lost hp/torque but I don't know if I could attribute that to the pulley (I'm keeping it on). But if some remembered, my air/fuel ratio curve was LEAN.

http://www.ultimatesubaru.org/forum/showthread.php?t=27996&page=1&highlight=dyno

 

http://home.comcast.net/~thomasck/GhettovsKandNHP.jpg

 

It stayed pretty much flat in the 13.25 - 13.75 range throughout the whole dyno runs. This was without an intercooler on 93 octane. The car didn't ping or show any signs of detonation or timing being pulled. The dyno curved showed that since it was pretty smooth. What this mean is that despite the 200F+ temps the car may have experienced at stock boost, everything was cool. We know how hot intake temps can get with no intercooler from All_Talk's previous thread on this subject.

http://www.ultimatesubaru.org/forum/showthread.php?t=15554&highlight=intercooler+temps

 

Then I installed an intercooler while the car was still on the dyno. The curve stayed the same but the air/fuel ratio still lingered in the 13.25:1 range and leaner without pinging or detonation issues.

http://www.ultimatesubaru.org/forum/showthread.php?t=27996&page=1&highlight=dyno

 

After having the Techworks parts and turbo put on, the car ran leaner still, especially on the low end. The whole air/fuel ratio changed dramatically up to about the 5k rpm range.

http://home.comcast.net/~thomasck/TechWorksHP-TQ.jpg

 

All I wanted to do was richen the air/fuel ratio to at least where the stock air/fuel ratio was (which showed it was ok, even with hotter non-intercooled intake air). At the most, I wanted to richen it to where I've read about the WRXs and STis run on some of the dyno charts I've seen. The RX is running around these air/fuel ratios now. No detonation or pinging.....Yet!

 

All I'm trying to say is that the car is running richer throughout the whole powerband (on 93 octane), with an intercooler (cooler inlet temps) on the same boost (manual boost controller turned all the way down...piece of s***). The car is running great off and on boost. The richer curve may be saving my arse with the spikes. It has a full tune-up

 

I'm aware that the fuel injectors may be at 100% but really, no-one knows for sure. If I drop my car off for wheel bearing repair this weekend, I'll request for the injectors to be removed so I can send them off to RC Engineering. I remember one person here saying he had his injectors done at RC Engineering and they got around 190ccs from them doing a slight mod to them.

 

All in all, the car seems to be running well except for the fun and nasty boost spikes.

 

Here's some food for thought on the injector size. I know the XT6 has 185cc injectors since I sent a set of injectors out to RC Engineering. GrossGary here got the same result recently. Some of us know that the XT6 is basically a 6 cylinder version of an 4 cylinder EA82. If the 6 cylindered XT6 is basically a 4 cylinder EA82 with 2 more cylinders, they should have the same injector size (185cc). With this reasoning, why would Subaru go to a lower sized injector (180cc), lower the compression and add a turbo to make 25hp more on an EA82T?

[Myxalplyx]

Oh BTW: (I can't shaddup) I know raising the fuel pressure is basically a band aid for getting larger fuel injectors and tuning with an aftermarket ECU. Using the RRFPR just happens to be the most convenient (and cheapest) way for me to reach my goal right now. I'd get some larger fuel injectors and get my ECU reflashed by ECUTune like them SVX folks if I could. Plug-n-play is cool! We just don't have that option right now.

 

As soon as you mention MS&EDS around me, you can actually see chicken feathers fall from under my shirt. I'll wait on the sideline on that one until more testing is done.

Have fun!

[JWX]

has anybody sent out some 82T injectors yet?

[Vanislru]

Here's some food for thought on the injector size. I know the XT6 has 185cc injectors since I sent a set of injectors out to RC Engineering. GrossGary here got the same result recently. Some of us know that the XT6 is basically a 6 cylinder version of an 4 cylinder EA82. If the 6 cylindered XT6 is basically a 4 cylinder EA82 with 2 more cylinders, they should have the same injector size (185cc). With this reasoning, why would Subaru go to a lower sized injector (180cc), lower the compression and add a turbo to make 25hp more on an EA82T?

I don't understand :-\.

[Myxalplyx]

I don't understand :-\.

 

What you read was based on this thought.

 

I think everyone here agrees that 180cc/min is what our stock injectors are (or close to).

 

My statement wasn't directed at Subarutex however. There are other posts mentioning that the EA82T injectors flow about 180cc. LIke this one for instance........

I'm not sure if I asked on this forum, but I know I did on the NASIOC. If I were to upgrade my fuel injectors from 180cc's to let's say, ummmmm....

Patrick

http://www.ultimatesubaru.org/forum/newreply.php?do=newreply&p=240871

 

What I'm saying is, since the XT6 has 185cc, it's safe to assume that the EA82 (N/A) engine has 185cc also. If this is the case, why would Subaru go to lesser flowing injectors (180cc) for an EA82T turbo if it makes more power than an EA82 (N/A)?

 

My assumption that an EA82 (N/A) has 185cc injectors could be flawed though since I believe the XT6 has a slightly higher compression ratio (9.5 vs 9.7).

 

Ahh...this is meaningless. Somebody hasta get these things flow tested.

 

To sum it up, yeah the fuel injectors may be maxed out but it may run ok like this for a while. I just hope I don't blow anything. I'm taking 'Scrappy' to work tomorrow. 4-8" of snow is expected (Translated: 6-12").

[Vanislru]

That's a good point.

[The Scooby]

no offence but no matter what pressure your running, the ecu will see that pressure and back off the time in milliseconds that the injectors stay on, we did this on a car at school today to help to prove the point i was making, it doesn't matter what pressure your running it will always come down to the ECU to control the amount of fuel entering the cylnder.