I've got a custom 3" exhaust and a FMIC, and I have not been able to get my stock turbo to hold 10psi to redline, let alone seeing 12psi. I've installed an FPR and I'm getting AFR of 11.5 to about 5500rpm then the whole setup gets as rich as 10.2 after 5500rpm, pressure drops to about 6psi by redline. Is the stock turbo really limited at that pressure or is there something wrong?

I've got an HKS EVC III controlling boost.

 

Limitations of the stock turbo...live with it.....however that is really stinking rich at the end...that might not be helping.

What are you using to control fuel?

James

 

news to me, are the S5 wastegates really that unreliable at controlling boost?

 

It has nothing at all to do with the wastegate, the compressor just can't keep up with the engine when you increase the total airflow with exhaust and intake mods.

 

Sounds like it's time to visit www.bnrturbos.com

 

That's kind of the problem... Because of the pressure drop, and my only source of fuel control being a pressure regulator I don't see any way to keep it from being that rich. If I had more air through the rev range(consistent with the 10-11psi before 5500rpm) I'm sure it would maintain the 11.5 AFR to redline.

 

i have the same prob. except my turbo has many miles on it...they just cant do it IMO...

 

my TII would hold solid boost up to the redline with only custom TID and full exhaust (FCD, walbro and cleaned/flowed injectors) - but it still had the TMIC....the extra volume of the front mount might be where you're losing charge in the higher rpm rnage

 

I don't think the money on the FP reg was well spent...you really don't need it. You should get your self SAFC or look at an rtek. Thats great you have a wideband...but that is really a two thing purchase (wideband/something to change fuel).

You need something to alter fuel. What other fuel mods do you have besides the FPR?

 

my tii s4 with just a FPR and intake/exhaust sure as hell could not hold to redline. top mount has nothing to do with it. the turbo is not designed to hold like that anyway.

 

that turbo is not designed to hold like what?(geuinely asking) maybe yours was just worn?

because if it isn't then I have some magical Hitachi HT-18...mine would hold consitent 10-11psi right on up to 7,000 any day of the week in any gear except 1 and 2

 

ahh i didn't notice he had an FMIC, that would explain it.

 

If the turbo is in good shape it should hold till you shift. Mine worked very well for a while, without boost controller, just racing beat exhaust, it would hold boost 11psi for a long time. After a while it started only holding 7 from like 6 to 7k, then after a while more everytime I let off the gas from boost, huge cloud of smoke, installed a rebuilt turbo and it holds again, no smoke, probably only for a while though...they are just not made to do that, they are only designed to work at 6.5 psi anyway.

 

hmm...maybe the fact i considered redline the 8k mark....

 

hehehe, didn't the BEEEEEEEEEP give you a head's up - hehe...

The S5 TII of my friends used to see 8k regularly, but even he would only experienec MINOR drop off between 7 and 8...drop from 11-12psi to 10-9psi over the 1000rpm span...

 

What was the altitudes of these runs? I have had a number of different variants of stock turbos on my car back when it had a TMIC. NONE of them were capable of maintaining 12 PSI to redline. These runs were at 3000 Ft ASL

There are too many other variables to consider then just making blanket statements that "All HT-18s will make 12 psi out to the end", because the fact is, you are the exception not the rule.

 

An fpr is more tuneable than 720cc injectors. You put those in and hope that the combination of timing, compression and boost will give you the right afr. With the FPR, I turn it up all the way, set my boost as desired, then turn down the fuel pressure until I get my desired AFR at the boost that I've set. Also, my car is an S5, so I don't have the RTEK available.

Even with the RTEK, it's good to be sure that your AFR are within a reasonable range and not just trust that everything on a car is in proper working order.

 

Does the stock rubber inlet restrict enough air to actually make this happen?

 

If anything, the stock rubber inlet prevents CREEP, but it shouldnt restrict 12 PSI out. The turbo simply cant do it.

 

What kinda fuel pressure under boost did you settle on?

James

 

with a 3 inch turbo back and no cat and a 3 inch tid i could hit 14 psi and hold 12- 14 to redline it even crept up to 17psi once i can take a pic of the peak setting on my profec b i had a large streetport too tho so who knows ill see how high i can get it on stock ports soon

 

In my experience, most stock turbos boost fade after 6k rpms. For some reason a stock turbo'd car of mine would make 13+psi til 8500rpms. I have datalogs from several years ago floating around the 2nd gen section of nopistons if anyone wants to see for themselves...

 

You know, this is probably a lame answer, but here it goes. "Enough"

I don't have a fuel pressure gauge, but I was able to watch the results of my adjusting the fuel pressure on the AFR meter. To me, it didn't matter how much fuel pressure I ran as long as I was getting the AFR that I wanted. So when I say "Enough", I mean enough to get the 11.5 AFR that most people say is ideal.

 

Well... as Carlos Mencia would say DE DE DE!!!

I just double checked my boost controller hoses... one was cracked. WIDE OPEN. I think the curve will look a little different now.

Luckily, I'm not racing my car on PINKS or I'd be pretty screwed at 7psi