OK after looking at the dyno I was wondering why the TQ drops to about 300ft-lbs at redline. I notice between 5500-6000rpms there is a pretty significant dip in boost and HP and TQ dips down as well.....it happens again from 6200rpm and just continues dropping and you can see HP and TQ taking another nosedive. Why is this happening?

Its a 2002 Maxima SE 6speed (VQ35DE...non-revup). I have a PTE 6266 Ceramic Dual Ball Bearing Turbo with .82 A/R, Turbosmart Hypergate 45mm Wastegate with 7psi spring, Turbo XS manual boost controller, 2.5" downpipe with 2.5" intake tubing, intercooler, 3" catback exhaust, etc. I have a custom intake manifold that is twice the plenum size of the stock.

Also the boost controller was turned up ~1psi...making about 8.3psi @4500rpm and then drops and holds steady around 7.6psi...I would like it to stay that way so HP and TQ dont suffer....any ideas?

I'm thinking if boost would hold around 7.6psi then I would not have such a dramatic dropoff in TQ.....by redline down to 300ft-lbs.

Here is a pic of the dyno chart so you can see what I'm talking about:



BTW...the car runs great...I'm just nitpicking now......

 

get a good electronic boost controller that will hold boost..im sure others will have good advice for you but i beleive that would solve ur boost dip problem...

 

I was actually wondering if that would help......might just go with the Haltech boost controller since it wires right into the ECU. Those drops are just holdiing the power back and driving torque down further........

Sometime in the future I will get an electronic controller and go back to RT Tuning for another tune.....I dont like those drops.

 

it could be your turbo manifold design/wastegate placement. the greddy kits have issues like this when the wastegates are recirced (dumps back into the exhaust too close to the turbo exit and the flows fight each other). are yours recirced? what turbo kit are you running? pics could help tell the story.

 

Its a custom setup not a kit. Wastegate dumps into the air.

 

Hmm hard to say for sure. It may be your down pipe. And Your wastegate may be too far to easily control boost pressure, but I'd lean towards the bends in your downpipe.
What diameter piping did you use where?

 

does it hold steady boost all the way to redline just on wastegate springs?

 

Try what srt8 said, i bet its fine then. And based on pics you posted, it looks liek your wastegate is a bit far away from the turbo, could be the cause.

 

downpipe is 2.5" I dont think that is the cause....I seen people with 2.5" downpipes on VQ35DE and no problems.....also wastegate is not far from turbo it is within 12 inches. Who knows.....

I dont know.....let me look at the run files BEFORE they turned the manual boost controller up....

I dont know bro.....Im thinking Im just going to get an electronic boost controller that can hold boost steady.....

 

If that's a 38 mm wastegate I'd bet 12 inches of pipe is a lot, but I've never seen wastegates so far from the turbo... so I really couldn't say for sure.

2.5" could be enough but the bends are what I was concerned about.

definitely check how it did on spring pressure. throwing an ebc at it wont change anything if your kit isn't designed manage boost well.

 

45mm hypergate wastegate from Turbosmart

Actually just checked the dynos BEFORE the manual boost controller and it does the same thing....up and down around 5500rpm. I think it make be a boost leak. Have to buy one of those boost leak testers.......

 

It's your waste gate boost reference, its at the compressor housong. I bet your MAP sensor and boost gauge are connected at the intake manifold. The little nipple on the compressor cover will always have higher pressure then your intake manifold. Run a hose from IM to the wastegate and see if it hold boost better

 

you are right about my connections...so what to do about the nipple on the compressor then??

 

Are you ramping timing up as tq drops?

If you already are then the backside on the turbo is to small.

 

use those vacuum plugs they sell at autozone ,

 

it should be ok , I was running a much smaller hx40 T3 and my power didnt fall off like that, plus my torque didnt fall off almost at all.

 

Did you have a STOCK VQ35DE?? I'm running on 100% stock internals...no cams, pistons...nothing.

No, timing goes down as rpms get high. Up top is 16 degrees and about 11.8-11.5AFR. I never heard of timing increasing up top on FI applications....

OK...if I remove the hose from the compressor housing to the wastegate and connect it to the manifold to the wastegate with the manual boost controller will I need a new tune? Will this cause my car to run higher boost because of the manifold usually seeing lower boost than at the compressor? Thats a pretty long way off.....from the mani to the wastegate will be like a 3 foot hose. You think that will help?

 

I was on JE pistons stock compression with bc rods, stock cams. So not much change from oem. I did have aftermarket headers tho. But regardless this is low boost.

If you do make more boost then you will need a retune. The hose lenght doesn't matter. BP kit uses 5' of hose since the turbo is behind the transmission and manifold boost reference

 

You really don't have a clue. Get it to a qualified tuner please.

 

timing is the lowest at peak tq (midrange) and ALWAYS ramps up to redline because of the speed of the crank rotation.

also, your boost controller isn't doing anything. You need more duty cycle as the rpms go up on EBCs. Using a 7psi spring and trying to get 8psi out of an EBC is a waste. EBC won't work properly if not over 10% duty cycle. If you want the ebc to control that boost better you need a lighter spring and then use more duty cycle to bring it up to 8psi. Also a GOOD EBC (like the haltech one) will have a place to ramp up duty cycle since more duty cycle is needed as RPMs go up in order to maintain the same wastegate pressure. A static setting of % duty cycle to redline will allow the boost to slowly taper down as the rpms go up.