Has anyone experienced valve float at lower rpm's such as 6K due to high boost. My last dyno, I gained power at mid rpm about 4.5k - 5k but by 6k rpm I was making the same power I made with 5psi less.

I have stock DE heads(including cams, valve springs, etc..), and assuming tuning was ideal for both boost settings (no knock, 11s afr, timing in the mid/high teens) so is it even a possibility? As for boost, I tried 15psi, then 20psi.

note: Also assuming exhaust flow out of the turbo is not restrictive and the turbo is well capable of high boost levels.

 

i would imagine the heavier spring sets available would help w this.
At least thats what i hope lol..becuase thats all i did to the top end on my build, and its a pretty high boost build.

 

Right thats what I was thinking, but is it even a possibility for vq's stock DE springs to be weak enough to have issue at 20psi?

 

Why would you think it is valve float? That would not be my first choice for not making power at +5 psi at 6k rpms.

 

https://my350z.com/forum/engine-and-...loat-mean.html

not really an issue unles super hihg rpm.


OP, if your fuel pump isnt up to snuff, youll tap out near a street map even qw race gas.. i had the same issue last week,

pump gas map at 500 whp/torque at 20 psi.. then a q16 map at 527 whp and 23 psi.. lol.. its very evident on the graph to see a steep slope that just hits a wall and trails off...
check your fuel systems capacity to move fuel.

again, im fully built w crower vavle springs tho, but i still dont think thats your issue tho.

 

What turbo kit, exhaust, and turbo?
This sounds similar to Turbonetics kit type problems.. I have seen them make less power on higher boost. I wouldn't jump too quick on valve springs.

 

Thanks for the reply guys,
Hal its a custom turbo setup, using an HX40 Holset with a BEP Bullseye .70AR turbine t3 housing (however when I ran that dyne, it had an 18cm holset housing which should be similar to an 1.00AR t3. Exhaust after the turbo is just a 3" outlet, no mufflers, resonators.

BMCCANN, I have a 255walbro and 600cc DW, if this was a fuel delivery issue, wouldnt the AFR start to lean out? In my case the afr remained flat.

Something to note, I am running VQ30 timing equipment so I do not have variable cam timing, this should not be the issue as there have been plenty of VQ30's at these power levels which the power does not drop off.

 

The T3 .70ar sounds like the problem, even the 1.00ar is small. Also what do you have feeding the turbo? Stock headers with merge pipe? If so stock headers can be contributing to your problem as well.

Fixed timing should not hurt your top end power, especially with regards to turning boost up and loss.

 

Yes I am using stock vq30 headers (no cats) feeing into a 2.5" ypipe then to the turbo. Didnt you run stock headers back in your maxima days and were fine passed 500hp? The same with Mardigra, Nealoc, etc..?

 

What do the intake temps look like when you 'max out'? Stock heads should pretty easily outflow your fuel setup. Valve float usually happens with excessive RPM not PSI.

 

I would listen to this guy .

 

i had this problem befor, it was the valve springs, i just changed them and gain extra 70whp

can u show the dyno graph

 

you really dint post a power level that it seems to be having issues but its likely not valve springs since you have already mentioned one very big restriction in the t3 hotside. the biggest t3 available isnt big enough for these engines a person should be looking at t4 hotsides thats where i would put my money being the restriction. also i imagine people are thinking you are using the manifolds from the z/g since this is a z/g forum and they are a major restriction also, the maxima ones look about the same diameters though so who knows that might be a issue also

 

Well as for power level, its approximately in the 420-430whp range, on the dyno it was with an unlocked converter so the numbers arent exactly accurate.

So from the looks of it, it might be the t3 housing then. I do not think it would be the exhaust manifold considering HAL used to have stock ones on his maxima and had 500+hp as well as other guys.

 

http://www.dynomagic.com/thefast_hlh.htm

T4 hotside it looks like.

 

So I have decided. Currently researching my options for a T4 properly sized turbo (not going to be fun finding one). 550-600whp goal (with about 15-20psi), 8.8:1 comp, 3.5L, max 6500rpm, with some kind of decent spool up. If anyone is willing to share any info or turbo spec's I should be looking for I would greatly appreciate it.

Based on my n00b calculations, pressure ratio of 2.0 with flow of 50lb/min should be my plotting points and should land me on the center island of the map of w/e turbo I go with, right?

 

I can't think of any reason why you would say "not going to be fun finding one". 6266 T4 .81 a/r:

http://i137.photobucket.com/albums/q...i20C20Dyno.jpg

600whp by 5500rpm is not bad if you ask me, and this was at about 18-19psi, pump gas. Vince felt like there was another 30whp left if he was to push it. Instead it was left as a convervative tune. That is a 75lbs/min turbo.

 

^^ That's a healthy power curve. Perfect turbo and Vince does it right.

 

cant say enough good things about the precision turbos and like sasha pointed out the 6266 has great spool as well as great power potential. precision customer service is great too, usps damaged my comp cover when i sent it in for the 66 exhuast wheel and 1.32 housing and precision replaced it free of charge saving me from dealing with usps

 

Never realized this was your issue. Glad it was resolved. You had stock springs before or JWT when you had this issue (and what did you replace with)?