Forged_G

iTrader: (10)

Great thanks! i just called but they didn't answer.. its like 9 there.. ill try back after lunch.

Hexxum001

iTrader: (3)

I'm running the 2.87 pulley on a conservative tune and I am just under 400whp (and about 330tq) and usually run between 9-10psi (10psi on really cool days). It's all about the tune bro. You don't necessarily have to switch back to the 3.12 to get less power and less boost.

Forged_G

iTrader: (10)

I see.. well i guess that is something i can discuss with my tuner.. i mean if i can keep PSI's down and make 400+ on 3.12 i will be happy. Would prefer 8-9 psi. THe 2.87 i have now is maxing at 13

Dont want to push it too much.

So now that i have headers and HFC's coming.. u think stay with 2.87? and hope to see what kind of #'s at what PSI?

binder

iTrader: (8)

actually you do, that's how a s/c works. Boost is rpm dependant and it's directly related to pulley size.

You can pull a lot of timing to theoretically make it safer but you'll increase combustion chamber temps by decreasing timing too much.

3.12 most of the time yields 8-9 psi. If you are at 9psi then you're fine but the question is why are you only at 9psi with a 2.87? Don't say free flowing exhaust because i have a full built engine, ported heads, cams, test pipes and large true dual exhaust...i have the most free flowing you can get and i'm still seeing 12psi with my 2.87.

Forged_G

iTrader: (10)

LOL. 3.12 it is! hahaha

i rather be at 400+ at 9 psi.

Hexxum001

iTrader: (3)

Forged G - 13psi??? Wow, that is definitely too high for a stock block. I see in your sig that you dyno'd at 440rwhp. What mods do you have? (Sorry I am being too lazy to look back at the other posts and it is kinda busy here at work too. )

binder - Yeah I know that boost is dependant on rpm. The kit for the revup engine comes with the 3.12 (3.33 on non-revup kits) pulley which is good for 8-9psi right out of the box. I went with the 2.87 pulley, MD spacer, 600 DW injectors, Walbro fp and initially was hitting 10psi with my stock cats and HKS exhaust. Then I switched to Fast Intentions HFC's and Fast Intentions exhaust and I went back to GTM for a follow up tune. I lost one psi of boost but I gained power and more importantly, I gained even more torque. So even though you said to not say a freer flowing exhaust, that's the only things I changed. I am also running HKS FCon iS which allowed for a little bit finer tuning by Sam as opposed to the SS box or Unichip. I could have easily been over 400whp but because this is my DD we went with a conservative tune.

jccalzada

Hi everybody.... I have a question for you all, maybe you can help me out since im struggling with this issue for about 2 weeks now. I have a 350z non-revup with vortech sc running 3.12 pulley. Before I changed to this size I was making 350whp with the 3.33" pulley, however, when I changed to 3.12 and 550 injectors I made 315whp....so we checked basically all the kit again...ordered a repair kit and changed all bearings, seals, etc....when we checked boost, it was doing around 3psi... with the repair kit installed, the car was doing around 5-6psi with the 3.12" pulley...it's still to low, somewhere along the way we are still missing aroung 3-4 psi right? Anyone with any ideas? I also notice that if we check boost before throttle body is around 6psi, but the boost inside the plenum or after the TB is max 3psi...im serioulsy running out of ideas here. I also have AAM plenum spacer, motordyne lower plenum, injen catback, HFC's, etc but im really getting frustrated here since since I cannot get more psi thus more hp...

help please, someone!?

Thanks for taking your time and read my question by the way....

binder

iTrader: (8)

hmm....that still seems low if people are getting 8-9 psi wth a 3.12. You should get more than just 1 psi increase with that change in pulley.

i would assume a boost pressure test was done but if not i would do it. i would expect minimum 2 psi gain from a pulley change.

but anyways, that's another story. the story for him is a 2.87 is 13psi as he sits now. If he moves down 1 pulley size he's only going to drop 2-3 psi so that puts him at 10psi.

there is no other way to reduce boost on a fixed system like a supercharger except for changing a pulley (taking into consideration the same engine configuration).

binder

iTrader: (8)

hmm, i'm not sure how you are getting different boost readings in the plenum and before the throttle body. When you are WOT the throttle plate is open so the pressure is the same from teh supercharger all the way to valves of the engine. The only time there would be a pressure difference is if the throttle plate was closed which would stall the engine at any rpm except idle.

sounds like you have serious leaking issues. impossible to diagnose online truthfully

Hexxum001

iTrader: (3)

Actually, I agree. I didn't realize at first that he was hitting 13psi with the 2.87. That is definitely too high on a stock block. The 3.12 should get him back down to acceptable/safer levels.

jccalzada

Well, we still have to check the intercooler tonight, maybe we have some leaking in the intercooler....what about the bypass valve? is there a way to determine if there's something wrong there?

By the way, this boost difference that I told you was made with the car parked, just accelerating, could that vary the readings or it would be basically the same?

Hexxum001

iTrader: (3)

Check your plenum spacer. Sounds like you might have a serious leak somewhere and many times plenum spacers are the culprits. Besides that, it's kinda hard to say but hopefully that is the problem. Good luck bro.

05Z33

iTrader: (11)

Check to see if your bypass valve is stuck open. Also make sure your belt is on tight enough.

binder

iTrader: (8)

there is supposed to be an oring on the BPV to seal it. I woulnd't think it would cause that huge of a leak to be down half of hte psi you should be but you never know. easy to find out if hte oring is there. Either 2 bolts to remove the BPV or you can try to open it and look inside the port.

the car won't boost while parked. It has to have a load on the engine.

- bigc -

iTrader: (18)

also check the vacuum tube between the bypass valve and the plenum (or FMU)

Forged_G

iTrader: (10)

Rev-up kit, 2.87 pulley, 92 7/8 belt, Deatschwerks 650 injectors, Walbro 255 fuel pump, stillen cat back exhaust tuned on Cobb AP. Put those #'s down on a dynotjet.

Hexxum001

iTrader: (3)

Wow, very similar to my setup. My numbers are also on a dynojet but your psi and hp numbers are much higher than mine.

Forged_G

iTrader: (10)

IDK.. maybe the guy was wrong?

What are your #'s?

binder

iTrader: (8)

numbers can vary greatly between 2 cars with teh same mods even on the same dyno.

numbers are really only comparable between the same car on the same dyno with the same tuner and correction factors.

Once you start throwing different cars on there all bets are off no matter how exact each car is setup. Use your numbers as just a base of comparison but don't expect them to be the same as another. Therefore if they are lower, don't feel bad.

Hexxum001

iTrader: (3)

I understand that. Different shops, different tuners, different cars. But guys with the Si trim haven't put up numbers that high on a stock block and no head work. It's just kinda suprising to see numbers and psi this high on the 2.87 pulley.