[WolfPlayer]

I've been waiting to make this post until I had completed enough testing using the same environmental conditions. Why do tuners recommend installing a Walbro pump on a simple Stage 2 setup. It is not necessary and does nothing.

Car: Basic Stage 2 STI w/ custom tune running 18.5psi midrange and leaned out to 11:1 AFRs. Specifically, the car is a 2005 STI with an APS 3" TBE w/ cat, modified intake (+ the rest of the mods in my sig).

Injector Duty Cycles before Walbro install were 104.5% @ 6500rpms. This was with the car was at operating temp with coolant and oil temps stabalized at normal (coolant = 185F, oil = 195F). The outside temperature was 34F. The MAF voltage at the data point above was 4.72v (with approximately 16.24psi boost).

After installing the Walbro pump the injector duty cycles are 103.6% @ 6500rpms. This was with the car was at operating temp with coolant and oil temps stabalized at normal (coolant = 185F, oil = 195F). The outside temperature was 34F. The MAF voltage at the data point above was 4.72v (with approximately 16.25psi boost).

For the record, I could have easily fudged data to show that the Walbro makes a difference on a Stage 2 setup. All I would have had to do was to test the car in warmer conditions or with a hot engine bay, etc. In fact, I can easily compile logs that I could use to try to convince n00bs that a Walbro makes a difference. However, I was striving for EQUAL environmental conditions with the same tune on the same road. Done. Walbro didn't do anything. IMHO, 0.9% IDC is well within the norm of error.

I'll continue to monitor things on my end and you can bet that I will be the first person to report back if I see something that shows it makes a difference on a stage 2 setup. However, IMHO, using like data, the Walbro doesn't do anything on a standard Stage 2 STI. This actually AGREES with 2 very reputable tuners whom I trust: Quirt Crawford (Crawford Performance) and Christian from Cobb Tuning. Quirt has used the stock pump with aftermarket injectors on a setup making 425 crank horsepower with no problems. Christian has tuned many STIs and has reported that a Walbro doesn't do anything on a Stock Stage 2 car and, in fact, the stock pump is good on upgraded turbo setups (he didn't specifically give a rating on lb/min turbos for when a walbro is needed). So, the ultimate question still remains: Why do people say to put a Walbro on a simple Stage 2 setup.

I went into this thinking that a Walbro wouldn't make a difference on a Stage 2 setup because theoretically it should not. The only way for Injector Duty Cycles to reduce is if the actual Base Pulse Width (BPW) gets lower. The car is in Open Loop at WOT and not monitoring AFRs. At WOT (Open Loop) the car does not use the O2 sensor for adjustments. Thus, there is no way for the BPW to lower. Good thing too because the stock O2 is extremely inaccurate.

t

[stituner420]

Interesting! Thanks for the info Wolfplayer, I was still debating on whether this was necessary on my Stage 2 setup.

[Rexinre]

Good stuff! What size injectors come with the STI stock?

[Brahmzy]

Great test - my tuner advised against it as well.

[WolfPlayer]

Originally Posted by Rexinre

Good stuff! What size injectors come with the STI stock?

This is another topic in itself. I have heard ratings of 480cc, 520cc, 540cc, and 550cc. In fact, APS and Cobb and Gruppe-S originally claimed that the stock injectors were 480cc. Perrin claims 550cc. Individuals have had their stock injectors flowed and there are RC Engineering documents that show anything between 520cc and 540cc. Peter from APS offered to flow one of our US injectors given this discrepancy. The new test showed 520cc. He said ...

"I'm not sure why we now have a discrepancy between the original STI injectors tested in July 03 and the current STI injectors tested in Oct 05 as all STI injectors 03,04,05 all have the same part number according to a Subaru dealer. These current STI injectors are 520cc (we measured all 4 injectors and the flow was virtually identical on all 4 injectors) as measured on our injector test machine as of today, 10-24-05. "

Very weird.

I'll be able to lend evidence relatively soon. I intend to have my stock injectors flowed after I get my new injectors installed. I have a set of Nismo 740cc injectors at WitchHunter getting cleaned, flowed, and latency tested. Call my crazy, but I hate driving around with > 100% IDCs even though there has not been a single failure due to lack of fuel. Plus, I'm building my way toward a 3" 20G .

t

[IslandSTILE]

Originally Posted by WolfPlayer

I went into this thinking that a Walbro wouldn't make a difference because theoretically it should not. The only way for Injector Duty Cycles to reduce is if the actual Base Pulse Width (BPW) gets lower. The car is in Open Loop at WOT and not monitoring AFRs. At WOT (Open Loop) the car does not use the O2 sensor for adjustments. Thus, there is no way for the BPW to lower. Good thing too because the stock O2 is extremely inaccurate.

I totally agree with this statement. I can't see how upgrading the fuel pump alone can reduce IDC significantly. IMO the only you can lower the IDC without changing out the Injectors is installing a Fuel Pressure Regulator and even that may not be as effective.

[Rexinre]

Originally Posted by WolfPlayer

This is another topic in itself. I have heard ratings of 480cc, 520cc, 540cc, and 550cc. In fact, APS and Cobb and Gruppe-S originally claimed that the stock injectors were 480cc. Perrin claims 550cc. Individuals have had their stock injectors flowed and there are RC Engineering documents that show anything between 520cc and 540cc. Peter from APS offered to flow one of our US injectors given this discrepancy. The new test showed 520cc. He said ...

"I'm not sure why we now have a discrepancy between the original STI injectors tested in July 03 and the current STI injectors tested in Oct 05 as all STI injectors 03,04,05 all have the same part number according to a Subaru dealer. These current STI injectors are 520cc (we measured all 4 injectors and the flow was virtually identical on all 4 injectors) as measured on our injector test machine as of today, 10-24-05. "

Very weird.

I'll be able to lend evidence relatively soon. I intend to have my stock injectors flowed after I get my new injectors installed. I have a set of Nismo 740cc injectors at WitchHunter getting cleaned, flowed, and latency tested. Call my crazy, but I hate driving around with > 100% IDCs even though there has not been a single failure due to lack of fuel. Plus, I'm building my way toward a 3" 20G .

t

Wow, thanks for the reply... I did a little search and came up with a few different answers that is why I asked the question!

Sorry about the off topic question!

Mitchel

[siusti]

You can only flow as much as your injectors allow without comprimising the spray pattern on the injectors which will do more damage than good.

[Nixlimited]

Hmmm, I have a new Walbro for my GT30R, hope it was a necessary purchase.

[VSGTS14]

^the walbro is necessary for upgraded turbos/injectors.
he's stating the fact it's not really needed on the stock turbo/injectors because it doesn't quite do anything.

[WolfPlayer]

Originally Posted by VSGTS14

^the walbro is necessary for upgraded turbos/injectors.
he's stating the fact it's not really needed on the stock turbo/injectors because it doesn't quite do anything.

Exactly. I updated the title and content to specifically refer to a stage 2 car. The stock pump can support a stage 2 setup. C'mon, I am pulling 4.72 MAF volts. That's pretty good airflow. Rumor also has it (Quirt and Christian) that the stock pump can actually support MORE than just a stage 2 setup (i.e. small turbo with upgraded injectors). A GT30R though ... holy crap. I imagine a Walbro is definitely needed for that.

t

[Irishsti]

Doug from Topspeed recomended it for the PRO-tune, he has gotten some great numbers from some of the cars he has tuned from the northeast, now I do not know how much of a difference it could have made, but seeing the results I will be doing it anyway.

[sciolist]

My understanding is that the OEM fuel system is limited by the VF39. My understanding is also that once you have a TBE, the VF39 is essentially octane-limited. This is to say that additional hardware is useless without upgrading the VF39.

If you are working with the VF39 according to SCCA rules, then even porting is not an option.

[WolfPlayer]

Originally Posted by Irishsti

Doug from Topspeed recomended it for the PRO-tune, he has gotten some great numbers from some of the cars he has tuned from the northeast, now I do not know how much of a difference it could have made, but seeing the results I will be doing it anyway.

That's weird because I have seen Doug say on a number of occasions that a pump is NOT needed. Furthermore, they don't have the pump as part of their TS310 package (Stage 2).

t

[Cicio]

Doug from Topspeed recomended it for the PRO-tune, he has gotten some great numbers from some of the cars he has tuned from the northeast, now I do not know how much of a difference it could have made, but seeing the results I will be doing it anyway.

Like WolfPlayer said, Doug does NOT recomend a fuel pump for a tune.

Here is his quote on all the generals concerning a tune.

Originally Posted by TopSpeed

I believe I have said it before but I will say it again, the stock intake and inlet pipe is more than enough for the stock turbo, only thing I would recommend doing if your runing the stock turbo is get a highflow drop in airfilter. Now that is not saying if you have an intake your car will make less power, that is not true. On my dyno intake usually gain around 2-3hp, that is not much imho and not worth the cost vs hp factor. Secondly the stock fuel pump will work fine with the stock turbo, again its not neccessary to replace it. However if you would like to run a larger fuel pump like the walboro that will work too. Again its not going to hurt anything having a fuel pump that flows more fuel. Now onto headers.. there is alot of talk about headers making any power. I personally have yet to see any make huge gains on the dyno. Most cause an increase in lag, loss in tq down low for a mild gain up top. The only header I have ever seen make a noticable gain were the Fujitsubo but again the gain wasn't worth the cost. I have made 600hp Sti's with the stock cast manifold's. It would be my opinion to keep the stock headers as long as possible and keep your low end tq.

Doug

Don't mean to post anything off topic wolfplayer, but I felt it was related.

Great info by the way, very informative!!