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Old 11-19-2019, 10:15 AM   #1
Jrae2424
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Default Unimpressed with power gains

05 legacy gt 103000 miles. 5eat transmission

GS up pipe and crossover pipe
Cobb catted downpipe
Borla cat back exhaust
Cobb intake
AVO top mount intercooler
Cobb access port

First custom tuning brought the car to 213 whp which seemed a little low. They recommened a turbo upgrade, fuel pump, injectors and boost control.

So now

All the above with
VF52 turbo 20g rebuild
AEM high flow fuel pump
Cobb boost controller
New ngk spark plugs

After tuning and $2000 dollar the car is making 230whp at 14.5 psi

I'm looking to get to at least 280 whp a little more would be nice though. But at least 280 is my goal. They said the stock injectors are the limiting factor now. They recommened 875 side feeds, that would be the cheapest option. Under a grand installed with a retune. Question is, what more could be gained and what is the limit without rebuilding the motor?

Thanks
Jason
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Last edited by Jrae2424; 11-19-2019 at 10:25 AM.
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Old 11-19-2019, 10:34 AM   #2
shagfagon
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Why such low boost?

There's your problem.

EDIT:
NVM stock injectors. Ask him what your current IDC is. That could be why they limited boost
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Old 11-19-2019, 10:43 AM   #3
Jrae2424
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He said at around 240whp, slighlty higher boost that he was seeing 105% IDC. That's why he brought it back down.
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Old 11-19-2019, 11:04 AM   #4
shagfagon
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Quote:
Originally Posted by Jrae2424 View Post
He said at around 240whp, slighlty higher boost that he was seeing 105% IDC. That's why he brought it back down.
Well there you go. He couldn't add any more boost as he ran out of fuel.

Low boost = Low power.

Get some bigger injectors and retune if you want more.
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Old 11-19-2019, 11:23 AM   #5
Gallo2011
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So your tuner recommended higher flowing injectors, but you still haven't installed higher flowing injectors even though your post indicates you did? Or am I not understanding what "All of the above" includes?
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Old 11-19-2019, 11:29 AM   #6
shagfagon
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Quote:
Originally Posted by Gallo2011 View Post
So your tuner recommended higher flowing injectors, but you still haven't installed higher flowing injectors even though your post indicates you did? Or am I not understanding what "All of the above" includes?
He must not have installed injectors when his tuner recommended it.

Last edited by shagfagon; 11-19-2019 at 11:31 AM. Reason: reading comprehension
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Old 11-19-2019, 11:37 AM   #7
Gallo2011
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Quote:
Originally Posted by shagfagon View Post
He must not have installed injectors when his tuner recommended it.
Right. It appears he installed everything else. Properly sized injectors will solve his "low power" issue.
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Old 11-19-2019, 01:06 PM   #8
rtv900
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Quote:
Originally Posted by shagfagon View Post
Well there you go. He couldn't add any more boost as he ran out of fuel.

Low boost = Low power.

Get some bigger injectors and retune if you want more.
what was the stock boost level?
is it that much lower than 14?
why would 14psi be the point those injectors couldn't keep up?
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Old 11-19-2019, 03:07 PM   #9
shagfagon
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Quote:
Originally Posted by rtv900 View Post
what was the stock boost level?
is it that much lower than 14?
why would 14psi be the point those injectors couldn't keep up?
Because his tuner who is logging said the car was at 105 IDC.

Was it at 105 IDC and running 9.0 to 1 at idle, sure I guess I can see what you're getting at.

Sure its close to the stock boost level, but on a bigger turbo which is undoubtedly pushing more CFM at that boost level...
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Old 11-20-2019, 08:37 AM   #10
Jrae2424
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I did everything but the injectors. They said 2500$ for a top rail kit with install, 1050x injectors and tune at first which is a little more than I want to spend. They said the cheaper option would be the 875 side feeds installed and retuned for under $1000 or right around there.

Anyone with similar upgrades that could compare what they have gotten with side feed 7 to 8ish injectors vs the top rail 1050x?

The only reason I held off initially was that I told the shop owner where I wanted to be and he said that should be doable with the turbo, fuel pump, and boost controller with the other mods that were done.

Well I'm looking to have the injectors done in a about a month so I need some input or suggestions on injectors and if the side feed will be good enough to reach at least 280, and is it true that at a certain point a 1 psi increase in boost adds roughly 10 hp?
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Old 11-20-2019, 12:30 PM   #11
gt58
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dont bother going big side feed. switch to top feed if you decide on upgrading.
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Old 11-27-2019, 09:05 AM   #12
svynx
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Top feed. 1k or a variant of that (the 1050x are good). That will wake things up. And, if you have it around you, you can go to corn fuel.
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Old 11-27-2019, 10:13 AM   #13
awfulwaffle
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Sounds like you're getting upsold hard, someone forgot to check fuel pressure and just rescaled the stock injectors to compensate, injectors are super clogged, or your tuner has a very low reading dyno. I assume your fuel trims are good?

You can and should be able to get near 280 WHP on the stock sidefeeds with a VF52 and the supporting mods you described in your original post.

Check out user Max Capacity on Legacygt.com. He's got a 280whp/300 wtq dyno'd 05 LGT, on a VF52. He's still running OEM sidefeeds, though very near their limit.

Before I dropped a new motor/turbo into my current 05 LGT, it made 260 whp/ 280 wtq on a stock VF40 running 17 psi. Injector duty cycle was around 80% there, on the factory yellow sidefeeds with 170k on them and just a downpipe. Street tune on that one, done by Horsepower Techs in Clinton, MI. VirtualDyno power values, but they've got correlation to their actual Dynocom dyno so stated confidence is about 10%. Even if you pull out 10%, that's still 234/252 on stock injectors at 80% IDC and a stock VF40, which is apparently close to what your guy was able to get on a modded VF52 with maxed out injectors. Something's up.

I would, as a first step, verify fuel pressure is good. Then, check injector signal if you have a scope, and maybe find yourself a cheap set of known good side feed injectors to swap in, if you want to stay with sidefeeds and make 280.



All of that said, you definitely no longer have enough injector to get the most potential out of your new turbo, so if you're already that far down the rabbit hole I guess some might say that you might as well bring it home.

If you happen to be around Michigan, I have the sidefeeds off my LGT that you could try swapping in quick to troubleshoot. Doable in a parking lot, and if they help it'd be immediately apparent from a big negative shift in fuel trims.

Last edited by awfulwaffle; 11-27-2019 at 10:33 AM.
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Old 12-01-2019, 12:12 PM   #14
ThinWRX
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I was able to pull around 300whp and tq with the vf52 and a completely stock fuel system. After I upgraded everything it was around 350whp on e85.
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Old 12-01-2019, 02:26 PM   #15
2slofouru
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I have some FiveO 1000cc side feeds for sale, relatively cheap. Made 340whp on a dyno dynamics running a stx20gr turbo. Pretty sure my injectors were for 04-07 side feed style, had to buy some adapters to make them fit my V3 side feed rails.
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Old 12-06-2019, 05:20 PM   #16
Jrae2424
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Went with the 875s, but now I need a rebuilt. Developed rod knock at 18.5 psi, 241whp and 236tq. Literally the last run of the tune, he said if it didn't happen there it would have happened relatively soon.
This was on a mustang dyno which I've heard and they even said reads lower than others.
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Old 12-08-2019, 12:07 PM   #17
Sour_K
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Quote:
Originally Posted by ThinWRX View Post
I was able to pull around 300whp and tq with the vf52 and a completely stock fuel system. After I upgraded everything it was around 350whp on e85.
same same.

I'm at 300 WHP and 315 TQ on a p&p VF52. I also did intake, IC, and turbo back, but stock fuel and stock internals. Also tuned on a mustang. 215 seems pretty low considering. Didn't realize the Legacy injectors were that much smaller.
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