boost drop

[nickdutch]

i just dynod my r32 gtst and i got 235whp and 232 torque it was runing 14psi but then the boost starts to decreas slowely at 3500rpm and gose doun to 10.5 psi at 5500 rpm whare ime makeing the power i have a rb25 turbo i am just woundering why it drops to 10.5 can the turbo just not keap up or is my waset gate leting go? ime runing a boost control tee and hks mushroom intake yelowe jaket coil packs full 3inch apexi exost and the rb25 turbo and a good aftermarket fuel pump and gtr injecters

[amnash]

what year is your gts-t?... isnt 230hp less then what the gts had out of the factory?? lol

[quadracer111]

^^ r32 gts-t's had 215 or 216whp from the factory.

[nickdutch]

its a 91 r32

[Prophetic]

My manual boost controller is set to like 15psi but it settles at 13.5 or so from what I remember when I had it dyno'd. Dunno if that would be your problem or not since it's a pretty big drop?

[nelsonmxmarc]

^^ r32 gts-t's had 215 or 216whp from the factory.

Actually, it had around 180whp from what i have heard. I believe the stock RB20 is something like 210 crank based on factory spec?

At any rate, that is a pretty hefty drop in pressure.

1 Thing to look at is your manifold pressure on your dyno chart. From this you can see where the boost is seeping off..

You'll see one of 2 common things;
1. sporadic spiking; high frequency of up and down curves of various pressures
2. a very gradual slope decreasing in boost pressure

The former is often due to a turbo being pushed to its maximum potential, and by the looks of your hp numbers, that's highly unlikely.
The latter is often due to, from what im told, a TIRED turbo. If the boost creep is enough to exceed 2 psi and your slope takes a pretty nasty tumble at the end of your curve, it's could very well be a leaky seal. CFM's increase as a function of RPM, as more exhaust gas passes through the exhaust turbine, the faster the turbo spools, if oil is being pushed from the bearing cavity, you're going to increase heat, and oil will cause a disturbance in air circulation and pressure, slowing the turbine.

Of course this is your worst case scenario, and i surely hope you've noticed if your car is eating that much oil..

Otherwise you may have a small leak somewhere.. ? lol.

It could be as simple as a tear in a gasket, that after a certain rpm begins to seep.


Check for symptoms of oil leaks or a on-the-outs turbo, and do a boost leak check.


Also, what kind of boost controller? If its electronic and not properly set up, maybe your "caution" values are set too low and your bouncing off that.. Pretty honest mistake, if you neglect to read manuals :P

[nickdutch]

hmm ya ime not loosing eny oil and its just a stedy drop in presher no big drop as soon as it peaks at 14 at 3000rpm it starts slowely going doun but the hp is still going up at the same rate

[amnash]

If its electronic and not properly set up, maybe your "caution" values are set too low and your bouncing off that.. Pretty honest mistake, if you neglect to read manuals :P

hey if you guys have user manuals, post em up!

http://forums.gtrcanada.com/general-skyline-tech/44631-user-manuals.html

[Skym]

Reasons why boost level drops -

1.) Turbo out of puff (as mentioned above)
2.) Lean A/F ratio
3.) Leaking BOV
4.) Stuffed stock internal wastegate actuator (usually hear rattling sound on back of turbo, as spring inside bulb has failed)
5.) Intake airleak (as mentioned above)

Most common one with mild mods is leaking stock BOV, especially when engine has a bigger turbo installed. It leaks after 10psi. Blocking hole (boost feed, helps BOV to release properly at lower boost levels) next to main valve on bottom of BOV is a temporary solution, but it makes a flutter/surge sound (flutter/surge sound from podfilter). After fitting a proper aftermarket BOV (Synapse BOV), I wouldn't recommend the stock BOV mod.

[nickdutch]

hmm could be my bov it is apexi but i got it with the car and it looks kinda old and it spuders sum times insted of a solid blowe off

[Skym]

BOV might be set too tight (not releasing enough pressure inside intake piping between turbo, engine) if makes a flutter sound from podfilter.

Next would be checking ECU tune (A/F ratio) via wideband and monitor fuelpressure at same time on dyno.

My car was roughly around 160kw / 214.56hp (UK hp) at flywheel (when you take into account drivetrain losses) when stock on roller dyno. That's exactly factory hp figures. Around 111rwkw or 148.851rwhp (UK hp). US hp seems to be lower?? or higher?? (can't remember) and is exactly the same as Germany, Japan that use ps.

With stock RB25 turbo, should be producing around 255rwhp at 13.5psi. I know one car has produced 255rwhp at 14.1 psi on roller dyno with stock RB25 turbo. So rwhp figures seem low for that setup.

Also it could be that turbo is tired (doubt it) or intercooler is restrictive (possible if it's a cheap intercooler, as can be very restrictive, bad at cooling and causing high intake temps, knock. Then ECU protects engine by switching to knock maps).

[nickdutch]

hmm ya thanx for all your hellp ime geting a new intake and intercooler soon and i might as well replace the bov at the same time then hopefully my numbers will go up a hole bunch ime geting a frunt faceing manifold and a new throtel body came with a fancey looking fuel rail kit as well should be good

[quadracer111]

Actually, it had around 180whp from what i have heard. I believe the stock RB20 is something like 210 crank based on factory spec?

Woah really?

I know the r31 rb20's had quite a bit less hp than the r32 rb20's. But I didn't think even the rb20's in the r32's were that low.

[fast316]

That's more than 100hp per litre, out of a turbo charged engine built in the early 90's, from factory, sounds like pretty good stock numbers to me.

[Skym]

They say R31 GTS-R (RB20DET-R) with stock T3/To4E turbo, stock FMIC and stock equal length exhaust manifold has 210ps or 210 hp (US).

R32 RB20DET has smaller turbo, less aggressive intake cam, short runner exhaust manifold, small SMIC and produces similar ps.