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......

 

I would start with the easiest cheapest thing 1st, start by checking for boost and exhaust leaks

 

There are none. RT Tuning went over the car when it was in Lansdale. The tuner said it was the Wastegate opening and closing trying to regulate boost. I'm thinking an electronic boost controller would hold the boost better because of the electronics constantly being able to open and close to hold boost steady at 8psi......If I can get boost to hold then TQ wont drop off as much in the high rpms.

 

that might have been the case but car has since gone thru a few heat cycles and some stuff could have come loose. There maybe no leaks but it would suck to buy a ebc when the solution to the problem was just a turn of the wrench.

Another thing I ever had nor has anyone I know had a ebc and when boost hits it holds steady less they have a boost spike then it will shoot up then fall back down to where ever boost it set too

btw does haltech has the ability to control boost

 

with an electronic boost controller the Haltech can control boost. It says that it can hold boost more steady than a manual boost controller and it can also change boost depending on rpm and vehicle speed....pretty neat....

 

hell yeah that's great for the track

 

Could be the wastegate or the (turbo vs the engine) did this all of a sudden just happen or you always hold full boost to the redline?

 

just had the car boosted for about 2-3 weeks only. Its been happening since the car was dynoed. Perhaps its the 2.5" downpipe??? Dont know.....small boost leak?? TQ nosedives up top though from 393ft-lbs @4500 rpms to 300ft-lbs @6700rpm...almost 100 ft-lbs drop....WTF?? Could this be the downpipe?

 

Wouldn't this be because of NA cams?

 

Make sure your downpipe is tight and your tq is going to drop at the high rpm that seems normal to me. Did you try raising the boost level to see if you get more than 8psi?

 

I dont know......but 100ft-lbs drop still dont sound right....I expected a drop but not that much.....even with NA cams.

Downpipe is tight...Vband. If I raise boost then peak going to do up but still will have same drop....might go to 410ft-lbs and still have 100 drop down to 310ft-lbs this time.....

 

when you coming down to see RJ, maybe I can check the car out then

 

That is a possibility. Your turbo is a 700+ hp maker, so it's probably like "Wtf dude, only 8psi? Pssshhh...."

What wastegate do you have, btw?

 

Perhaps the 2.5 downpipe is causing this, at that power 3" would b ideal, maybe an electric cutout even. Where is the wg getting boost reference from? The boost controller u have might have a checkball inside, it cuts flow while out of boost to speed up spool up and once opened the controller uses its vent hole to keep Ur set boost, this means Ur initial boost may be higher. What I did was remove the checkball and spring so right away the controller is venting for the desired boost; spool up might not be hurt with the bad *** turbo you have.

 

Honestly I dont know when Im going to be able to come down there. I have this surprise baby shower for my wife this month then next month we perform at the musikfest (salsa dance team) then I work some weekends in Aug. September is when the baby due.....dont know...lol. I'll try to make it down there and I'll let you know.

That turbo is laughing at 8psi, but have nothing to do with wastegate though. Turbosmart Hypergate 45mm wastegate.

I dont know whats inside. Its a Turbo XS standard manual boost controller, not the high performance one.

I just figure Im going to enjoy the car this year and next year perhaps TOM can fabricate me a 3" downpipe and then I'll get an electronic boost controller and then go get a little more aggressive tune.....running anywhere from 12.1-11.8 AFR at 16degrees. I know the TQ can hold a lot better than that.

 

try a 38mm wastegate, 45mm is a little big for the power. it maybe bypassing a little too much exhaust

 

or try the .63 ar housing if available for a quick test

 

That's a good idea. Noticing the GN in your sig you're probably familiar with his situation.