5psi from SC on stock pulley with Headers and no cat?

[05SVRACER]

I've done some research and can't seem to find anything relating to this so I thought I would ask. I am only seeing 5psi full throttle in any gear. Vacuum at idle is around 15 and 20 on decel. The reading doesn't bleed off goes goes up to 5 and stays there. I have the second gen supercharger with the dynamic tensioner. I also have TRD headers, with a resonator in place of the cat with borla exhaust. Wondering if it would be normal to have only 5psi of boost or if I may have a problem somewhere...I am at 1000 ft above sea level.

About to start tuning this thing and want to make sure I don't have any issues before hand. On a side note, when I had the R4 software going looking at readings I was getting about the same. But with the engine off it was at -.8? I was just playing with it at the time and am not sure I had the settings like Gadget lists in the U-tune manual. The setting was at Vaccum/Pressure, but I hadn't messed with any of the other settings as of yet.


THanks

Steve

 

[murdarunna19]

That doesnt sound strange to me. Seems about right from what i can remember when mine was stock with sc and exhaust

 

[05SVRACER]

That doesnt sound strange to me. Seems about right from what i can remember when mine was stock with sc and exhaust

What pulley do you have now and what boost are you getting with it? I'm going to put the 2.1 on there once I install my wideband and get a chance to start tuning...

 

[05SVRACER]

Did a few runs this morning with the R4 software and the gauge. Consistantly the gauge shows 5psi where the software only shows 4.3-4.4. Plus every time the truck is off instead of showing 0 it is showing -.8. Any way to calibrate the MAP sensor in the URD computer?

 

[murdarunna19]

I have the URD 2.1" pulley. I pull somewhere around 7-9 pounds at very best. Have the coolingmist Water Meth kit waiting to go in, just need some time.

As for the URD computer I am not positive, I don't run the 7th injector or any other computer. Tons of ppl on here do and im sure will chime in.

 

[paddlenbike]

Sounds like you a leak somewhere. My boost is around 6.5 and sometimes 7 psi on a stock pulley at 200 ft elevation. But the most telling is the vacuum at idle, should be 20 in/Hg, not 15.

Check the vacuum lines, vacuum line routing and make sure the supercharger itself is torqued down and not bleeding boost through in the intake ports.

 

[05SVRACER]

I'll have to check and make sure at lunch. I wanna say yesterday after it had warmed up with the ac off it was 18-20 vacuum at idle. What way would you suggest checking for leaks?

Any insight on how to calibrate the URD map sensor?

 

[98OzarksRunner]

You might have a vacuum/boost leak, or a problem with the blower, but it might be normal.

Boost is a measure of backpressure. Anything you do to promote airflow through the engine AFTER the blower (like headers, better exhaust, porting, and cams) reduces backpressure (CAIs don't reduce backpressure), thus boost numbers fall as airflow increases (altitude and heat lower numbers as well, but that is a different matter). In fact, on my 65 Mustang (with 4.6L DOHC) I ran an Eaton blower with a 4# pulley. It would have made 12# boost on a stock Termi (03/04 Cobra) motor, but since I had better cams and exhaust, the boost peaked at 10# (but made a lot more power than the Termi with 4# pulley - it takes 14# on a stock Eaton to make the same HP I made with 10#). It would also drop to 9# on very hot days. Basically, in high performance cars, boost numbers are really just bragging rights - it's the airflow that counts, and lower boost numbers (given the same blower setup) mean the engine flows more air, and makes more power.

In short (after all that!), your headers and exhaust may be why your boost pressure is lower (but your HP is probably higher). But if your numbers are a lot lower than normal it might indicate a problem (not sure what 'normal' numbers really are on these motors).

 

[geohil]

The fact that it gets to 5 and stops makes me think faulty vacuum actuator. Had this issue on mine with similar symptoms as well. I was getting 7psi out of a URD 2.2, now I get 10.5 after replacing it. I think Texas_Ace has a write up about it over at YT. Otherwise google ways to test the actuator - most people use a modified break bleeder to create vacuum on the actuator and see if it retains the seal.
Otherwise may need to check for a leak in the intake gasket. My 2 cents.
(Just FYI - I'm running headers, but I still have my OEM cat)

 

[bikerjosh]

Could no cat being present could result in lower boost pressure, due to the lack of back pressure? Totally spit balling here.

 

[05SVRACER]

Awesome, ok. Last night I was doing a bit of research and came across some post on other sites recommending that. Just hard to wrap my head around lower boost from a supercharger with open exhaust. When I had my wrx with a boost controller and 3" open from the turbo back I was still running the same psi...stock manifold though. Thanks for the explanation!

As far as numbers go, from what I've read 6-7psi on stock motor at sea level is what is to be expected. So, I guess 1-2# drop at 1000 ft and open exhaust would make sense? Now I just have to figure out the URD map sensor issue. the tune can't be helping very well if it's thinking theres almost a pound less boost coming through than there actually is...

You might have a vacuum/boost leak, or a problem with the blower, but it might be normal.

Boost is a measure of backpressure. Anything you do to promote airflow through the engine AFTER the blower (like headers, better exhaust, porting, and cams) reduces backpressure (CAIs don't reduce backpressure), thus boost numbers fall as airflow increases (altitude and heat lower numbers as well, but that is a different matter). In fact, on my 65 Mustang (with 4.6L DOHC) I ran an Eaton blower with a 4# pulley. It would have made 12# boost on a stock Termi (03/04 Cobra) motor, but since I had better cams and exhaust, the boost peaked at 10# (but made a lot more power than the Termi with 4# pulley - it takes 14# on a stock Eaton to make the same HP I made with 10#). It would also drop to 9# on very hot days. Basically, in high performance cars, boost numbers are really just bragging rights - it's the airflow that counts, and lower boost numbers (given the same blower setup) mean the engine flows more air, and makes more power.

In short (after all that!), your headers and exhaust may be why your boost pressure is lower (but your HP is probably higher). But if your numbers are a lot lower than normal it might indicate a problem (not sure what 'normal' numbers really are on these motors).

 

[05SVRACER]

Cool, I'll have to look that up and test it. What water meth kit did you end up using? That's the next thing on the list

The fact that it gets to 5 and stops makes me think faulty vacuum actuator. Had this issue on mine with similar symptoms as well. I was getting 7psi out of a URD 2.2, now I get 10.5 after replacing it. I think Texas_Ace has a write up about it over at YT. Otherwise google ways to test the actuator - most people use a modified break bleeder to create vacuum on the actuator and see if it retains the seal.
Otherwise may need to check for a leak in the intake gasket. My 2 cents.
(Just FYI - I'm running headers, but I still have my OEM cat)

 

[geohil]

I went with a Snow Performance kit.
Snow Performance : Stage 2 MAF Boost Cooler?
Been a great kit - no complaints. Only regret I have is wishing I would have done the URD 7th injector kit instead of the URD 6 injector 319cc kit....too hard to tune.

 

[98OzarksRunner]

I would also check the boost bypass valve. If it's out of adjustment, it might not be closing tightly enough. You adjust it with the engine off (no vacuum) so it closes tightly. When the engine has vacuum (no boost) the vacuum solenoid pulls the valve open; when the engine has boost (no vacuum) it lets the valve close. If it's out of adjustment it might not be closing all the way. That's an easy thing to check/adjust, and if you really do have low boost, probably the most likely reason.

 

[05SVRACER]

Sounds like you a leak somewhere. My boost is around 6.5 and sometimes 7 psi on a stock pulley at 200 ft elevation. But the most telling is the vacuum at idle, should be 20 in/Hg, not 15.

Check the vacuum lines, vacuum line routing and make sure the supercharger itself is torqued down and not bleeding boost through in the intake ports.

Checked at lunch at 700 rpm fully warmed up it's a tick over 18 in/Hg at idle. Drops to 20-22 on decel. While idling I grabbed some throttle plate cleaner and sprayed around the boost port and connections at the back of the charger, around the bypass valve, around the intake manifold (hard to get to the driver's side of it under the charger though) and rechecked the torque on all the bolts. Idle didn't change at all when I was spraying the cleaner. This is how I have checked for vaccum leaks in the past on other cars, someone chime in if there's a better way...


Ozark
I'll see about checking that after work. I assume the adjustment method is pretty obvious with the bypass valve?

geohil
That was my initial debate was using a AEM piggyback with all new injectors or the URD. Seemed like the URD 7th would be a bit easier and maybe more reliable in the long run. I've looked at the Aquamist kit, but can't see what benefit double the price of the AEM would be. Haven't really looked at snow performance yet...

 

[Swimmerboy2112]

I am running the stock pulley on a factory setup around 450ft above sea level. At max boost, I'm at 7psi.

 

[geohil]

I don't think the old carb cleaner trick would work if the leak is on the other side of a diaphragm inside the actuator. Here is the test I was talking about earlier:
https://www.youtube.com/watch?v=bQU45XEFKYw

Question - how does the sunpro read boost? Where did you connect the line to?

The 6 injector kit is such a PITA to tune I gave up and left the stock URD map alone. I use the meth kit to supplement in weak spots, then added back timing until AFR stuck to 12.1 across the board. The Snow Performance kit reads the MAF sensor to ramp up the spray so it seems to be a good combo for the linear build of boost from the S/C.
Make sure you upgrade the valve body of your transmission before you go to the 2.1 inch pulley. The 2.2 in mine darn near toasted my trans until IPT did the mod.

 

[05SVRACER]

I don't think the old carb cleaner trick would work if the leak is on the other side of a diaphragm inside the actuator. Here is the test I was talking about earlier:
https://www.youtube.com/watch?v=bQU45XEFKYw

Question - how does the sunpro read boost? Where did you connect the line to?

The 6 injector kit is such a PITA to tune I gave up and left the stock URD map alone. I use the meth kit to supplement in weak spots, then added back timing until AFR stuck to 12.1 across the board. The Snow Performance kit reads the MAF sensor to ramp up the spray so it seems to be a good combo for the linear build of boost from the S/C.
Make sure you upgrade the valve body of your transmission before you go to the 2.1 inch pulley. The 2.2 in mine darn near toasted my trans until IPT did the mod.

Cool, thanks man...no youtube at work, so I'll have to check that on my phone in a bit.

As far as the sunpro I tappped into the line going from the back of the supercharger (fuel rail vaccum) where I already had it tapped for the URD Map sensor line, just tapped it again using vaccum hose instead of the ridiculously cheap plastic line that the gauge comes with.

So by measuring off the MAF how does it know the boost, or does it just go off airflow calculation? Mines a 5speed so no tranny worries here, already have the TRD clutch in want to get the diff that speedy has eventually....

 

[geohil]

Lucky - wish I had the 5-speed. Just could never find the 5-speed with e-locker (maybe I'm just not that patient).
Yes, the ECU for the meth system reads the volume of air passing the MAF and adjusts the flow on the pump accordingly.

I think I may have to add a Sunpro now. I've got a PLX Devices R-500 (junk) that is failing sensor by sensor so I've been having to hook up my laptop to read boost.

Out of curiosity - how did you get your down-stream o2 sensor to not throw codes when you swapped a resonator for your cat?

 

[05SVRACER]

Lucky - wish I had the 5-speed. Just could never find the 5-speed with e-locker (maybe I'm just not that patient).
Yes, the ECU for the meth system reads the volume of air passing the MAF and adjusts the flow on the pump accordingly.

I think I may have to add a Sunpro now. I've got a PLX Devices R-500 (junk) that is failing sensor by sensor so I've been having to hook up my laptop to read boost.

Out of curiosity - how did you get your down-stream o2 sensor to not throw codes when you swapped a resonator for your cat?

The sunpro was like $12 on amazon too...just wanted a cheap gauge to try out, apparently most people are pleased. Nothing fancy, but it's accurate...

So far it hasn't thrown a code, just did it Saturday. Going to order the rear O2 emulator from URD though. Still waiting on a reply from my email about the Map sensor calibration.