boost jump?

[rs73]

Hey guys... I just got a boost valve installed in my R33 and put the car on dyno...

1st prob: What happenned was that even the boost was set at 10psi, the boost only stays at 8psi, then suddenly at around 5600rpm the boost frees up and jumps up to 10psi in a rush for the last 1000 rpm or so before rev limiter kicks in... Thats when the car produced about 150kw at rear wheel. (Standard exhaust, Standard turbo, standard ic, standard air filter)

Was the sudden boost jump due to the fact that my standard exhaust being restrictive, or is there anything else missed? At first it was set at 11psi and power curve was all over the place, so it was lowered to 10psi, but still the same jump occured....

2nd prob: Also when the car was tested on 1st gear (this is an automatic gearbox) a/f ratio is fine, on 2nd gear there's quite a big area of flat spot as the car running too rich there, and on 3rd gear or Drive position, it's fine again.... Is this normal for cars with auto gearbox or something else??

I have also the S-AFC installed but due to problems above no correction setting has been set on the unit. I still have to bring the car back in again on Monday and tune it again. I was thinking to try it on 9psi only, since some cars on last dyno day made it better when the boost was lowered down a bit.

But meanwhile, if anyone knows/have any suggestion to possible cause/solution to those situation above....?

Thanks!

[meggala]

you exhaust is the biggest problem once you fit a bigger exhaust it should be better. bleed valves aren't the best way to increase boost they are unreliable,becuase of boost spikes autos should be tuned in 2nd gear on a dyno. and the a/f ratio change cause you arent running stock boost.drop it to 9 psi this should help.

meggala

[rs73]

Thanks Meggala, I know you'll come to the rescue

so my suspicion on my standard exhaust causing this is right... I may need to invest in a higher flow exhaust and probably an electronic boost controller...

In the meanwhile, I'll try drop the boost back to 9psi.

Thanks.

Rianto

[Cubes]

I've been running a bleed for the last say well since I got the car almost and what i realise now it used to spike quickly to around 16psi which would bring power on really hard then back off and settle around 15psi then over 5500rpm it would drop to 12psi.

I've just fitted the boost controller and well honestly boost feels a lot smoother but it doesn't get that hard kick like it used to but it does kick then it holds that kick then you get the rush of 15psi up top.

I've still got a bit of tuning fuel/timing etc.. to do as i replaced my cam belt and found out the crank was 1 tooth retarded.

Timing on the CAs is now totally different. and I think the ecu now works in retarding the timing as when I set it to high i don't hear pinging (probably due to it running rich) but i do feel flat spots.

Also when I had the std exhaust i could not run any more timing than std as it would ping like hell.. Replace the exhaust and it wouldn't ping with 25degrees timing on 98 ultimate.

hrmm got a bit off track didn't I.... Oh well hope something i wrote helped you out

[adam 32]

im using a GFB bleed valve and have had no problems with boost spikes etc. its being used on an external wastegate if this makes any difference?

maybe check the setups cos ive heard from alot of people that bleeders are fine and some use them on very big hp engines!

[Cubes]

What I mean by a boost spike is that when you first put your foot down it will spike to say 16psi then up top over 5000rpm it will slowly start to drop off back to 12psi.

Technically it probably is a boost spike but apparently all turbo's with a bleed setup do this..

But yes maybe an external wastegate makes a difference.

[Gradenko]

rs73, how have you hooked up the bleed valve? The R33 stock boost control solenoid is set up to provide 2 levels - low boost below 5600 and high boost above. To get rid of 2-step boost, don't hook up any pressure lines to the solenoid, but leave it plugged to the wiring harness.

I agree with meggala about your exhaust. Its hurting your turbo if you run higher than stock boost without getting a bigger exhaust. The factory airbox in R33s is a huge restriction too, I got an extra 1 psi just by changing to a k&n pod.

[Cubes]

I'm thinking of possibly changing over to a pod filter.

Sorry to get a bit off track with the subject but..

Gradenko.. Any other +'s from the pod. Boost comes on a little lower or smoother ?!?!

[meggala]

Joel; dont change to a pod to many cop hassles with them

meggala

[Gradenko]

Joel, I was having a problem with a fuel cut at 5000rpm in hot weather. After much testing, it turned out that the stock airbox was limiting airflow to the point were the engine was running dangerously lean in warmer weather (lower O2 density than cold air). Moving to a pod let the engine rev freely to 7000rpm and also brought boost on sooner.

From what I've read, the R32 and all GTR airboxes are no where near as badly designed, so you may be just as well off with cold air ducting.

Meggala may be right about cop hassles, we're lucky in WA that it isn't as much of a police state as some others. Pod filters are fine here, k&ns get passed through pits all the time and no cop has ever complained about mine.

[rs73]

Is there a place where you can engineer-tested a pod filter installation and get it papered as street legal?

[raist60]

Two things.

1. Dry, unoiled pods are not illegal. Thats comin for a victorian TOG member.

2. Boost dropping off is not really-ish a problem with the bleed setup it is more because of the turbo itself. Standard turbo just will not flow that much to feed the motor at the higher revs.

The electronics can make em hold boost cos they are increasing the amount that gets vented. But it aint good for the turbo. Bye bye wheels

Aftermarket turbo with bleed setup should not have MUCH boost drop as far as ive heard. Anyone confirm or disagree?

[adam 32]

the t04e on my car holds 0.9bar perfectly

[Gradenko]

Originally posted by raist60

2.  Boost dropping off is not really-ish a problem with  the bleed setup it is more because of the turbo itself.

True for the stock R32 gts-t turbo, not true for the stock R33 gts25t turbo. With intake and exhaust done, I have no problems holding boost. They work OK unitil you try and push them out of their envelope.

[raist60]

Joel be really careful. Detonation in skylines is damn quiet. By the time you can hear it its really bad. Just reading your post you say you can hear no detonation, that doesnt mean it aint detonating.

BTW... Majority of timing lights do not read the RB25DET pulse wire correctly and generally show double the timing that they are really running.

Ie. If the timing light reads 30dBTDC it is most likely around 15dBTDC

[raist60]

Im talking bout the R33 man. Its happening to my car right now. Run a valve setup. Hits 14psi then drops back to around 11/12 at 7000

Was told by Racepace this is due to the turbo being too small.

[rs73]

Originally posted by Gradenko

rs73, how have you hooked up the bleed valve?

It's hard to explain, however will try to get a photo & post it here so that you guys can see & tell what you think.

I agree with meggala about your exhaust. Its hurting your turbo if you run higher than stock boost without getting a bigger exhaust. The factory airbox in R33s is a huge restriction too, I got an extra 1 psi just by changing to a k&n pod. [/b]

That's why next I'm thinking to get exhaust, but want something that's not too loud & not attract too much attention. My work area has cops around at all time! Pod maybe not, as cop hassle with it, maybe just aftermarket panel filter once my stock air filter is too dirty & need replacement. I'm not really ambitious on chasing top end power, but want a little bit more mid-range where I drive the car most.