R33 Gts-t Throttle Response Issues

[Kustom20]

Hi All, I wanted to share this with you to get your thoughts on any issues which some of you may have encountered before. I will try to be as brief as possible and include as much detail.

Subject Vehicle: 1995 GTS-T RB25DET NISSAN SKYLINE

Vehicle drives great when under soft accelaration, when I increase accelaration too hard I need to back off because it starts surging, when I back off the throttle until I find that point where it runs great and then continue to accelarate, more noticable when car is under load 40km 4th gear throttle increased - it does this in all gears when throttle increased too much.

Current Spec:

Apexi Power FC V5.10 ECU

Stock Hitachi Turbo - High Flowed - running dual stage Low 7psi High 12psi

Stock AFM

Stock Injectors

Stock Fuel Pump

Stock FPR

Stock Dump Pipe

Stock Coilpacks

Large Front Mount Intercooler

Aftermarket Air Filter (Pod)

Twin Kakimoto Exhaust Cat Back

The vehicle does this in either low or higher boost setting - it just appears that it is getting too much air not enough fuel for that throttle position - I have never had the throttle past half way without it doing this.

1. Early next week I will be putting a wideband in to see what AFR readings I get when this occurs.

2. I wouldnt have thought fuel flow and pressure would be an issue running such low boost - stock is 43.5psi with additional 12psi to accomodate boost load which is only 55.5psi that the fuel pressure needs to be when at full boost.

3. Last night I logged the current ECU maps and tested in various load ratings and throttle positions and also logged the data, I cheked this in replay mode but I couldnt see anything major jumping out at me when this surging was occuring.

Any constructive thoughts would be great

[Ben C34]

Has it ever run right?

I'm going with the tried and tested boost leak is the cause of your problems. Pressure test to rule out.

[Kustom20]

Hi Ben,

No from the moment I purchased the vehicle it has always had this issue. I presumed it may have been from the small modifications and not having a re-tune to allow for these mods.

I have maintained hosing and connections from the turbo outlet to intercooler to the manifold inlet - but never actually tested any additional manifold area's where it could leak.

I'll check this out.

Thanks Ben

Edited November 17, 2015 by tuning_vs_hardware

[89CAL]

Coilpacks good? Spark plugs good (and gapped properly)?

[Kustom20]

Hi Callan,

It doesn't misfire or appear to have any spark issues, no backfiring type problems when the surging happens. Im presuming coil pack or spark failure would tend to show signs of backfire issues with excess unburnt fuel, which would cause some form of firing issue.

New plugs not too long ago - Gapped to 0.9 - Never changed the coilpacks

I'm in the middle of upgrades now and just wanted to try and teeth out this issue before these upgrades. Which also consists new plugs and coil packs as well

After reading some other forums - what Ben mentioned about boost/vacuum leak almost sounds like what the issue could be. Not noticeable by ear when driving but obviously when the car ramps up I wouldn't hear it anyway. So I will run some pressure tests to see.

Car in neutral would rev to limit with no issue's - I don't free rev to the limit but just an example of how it behaves in free rev - only under increased load and throttle position it has this surging.

I'll check the pressure in the system and see for leaks - then post an update on findings

[Kustom20]

Has it ever run right?

I'm going with the tried and tested boost leak is the cause of your problems. Pressure test to rule out.

Hi Ben, I have started to pull the engine down for the new upgrades and noticed some issues that I was not aware of, I guess this is the difference between just having general maintenance and not doing thorough tests.

The pressure test between the turbo to the intake manifold passed with no issues.

However when I started to pull the engine down removing the intake and exhaust manifold

I found that one vacuum hose was split right at the fitting about halfway through the hose.

The second one was where the boost gauge Tee's into another vac controlled sensor with a small little crap plastic Tee fitting which was too small for the hose it was into in the manifold - you could basically grab this without any resistance and was a very sloppy fit into the intake hose.

1. 2 x very noticeable vacuum/boost leaks

So I guess this was the issue over time as it slowly got worse the leaks were getting worse - hence the bad throttle response.

The other issues I found was the - Exhaust manifold had a large split right down the centre front face just beside where the turbo mounts. I noticed this is common

Currently have the cylinder head off and ready for the build up of the top end.

1. Aftermarket Plenum

2. 80mm Throttle Body

3. Z32 AFM

4. Top Feed 650cc Injectors

5. GTX3582R Turbo

6. Steam pipe Manifold

7. Cometic VRS

8. 45mm Turbosmart Hypergate Waste gate

9. 340LPH Fuel Pump

10. High Flow air intake

11. Ditching any performance plugs as they are a waste of money and sticking with ngk bkr6e plugs - The copper plugs are more heat resistant at higher boost plus can close the gap up on them all to aid and stop miss fire under boost

Already has Large Front Mount, Apexi Power FC, Twin Kakimoto Exhaust Cat Back

Looking forward to the new additions and some tuning/mapping to bring it all together.

Cheers

[Dose Pipe Sutututu]

plugs too hot and injectors are gay

would go 7 heat range and at least 1150cc injectors.

[scotty nm35]

With a GTX35 I would be going iridium 8's personally, gapped to .5mm. Each to their own, there are many ways to modify cars, some better than others. You only find out if the advice you have been given is correct by putting your engine on the line.

Most of your shopping list isn't required to max out a GTX35, such as plenum, exhaust manifold large throttle etc, but I would be going larger on your injectors for when you inevitably have to go e85.

[Dose Pipe Sutututu]

For E85, 8s are boarder line too cold.. 7s are fine.. depends on how much boost you're making.

Stock manifold is a restriction, they glow bright red on heavy load... even on E85. I'm in the process of getting a stock manifold modified venting the exhaust pressure/gases from there.

[Gcjosh]

Sorry to hijack thread but why do people always say you need minimum 1000cc injectors?

A simple google search of a calculator tells always that 800cc injectors are plenty good enough for 500 crank hp... Is there something I'm missing? And that's not 100% duty cycle

And yes that's on e85

Edited November 23, 2015 by Gcjosh

[Dose Pipe Sutututu]

always good to have headroom, and also the 1150cc are cheap, stainless and newer than the likes of your sards, nismos, RC, etc.

[scotty nm35]

When your tuner sets up the parts of the map you should never see, as in when something goes wrong (too much boost, etc) he will want to dump fuel into the map for protection. If you don't have enough overhead (20% or more) it becomes dangerous.

Seeing most injectors around that size are a similar price, and most modern injectors tune up nicely at idle/cruise regardless of size there is no real reason to limit yourself with flow. You don't want to have to buy another larger set down the track if your goals change.

As Johnny said, the newer stainless internal injectors are the go these days, don't be fooled by the flow numbers, every brand test them at a different pressure so the 900cc Bosch stainless long tip injectors are called 1000's, 1050's, 1100's and 1150's, but they are all the same injector with the same flow.

[Kustom20]

plugs too hot and injectors are gay

would go 7 heat range and at least 1150cc injectors.

Thanks for the advice,

I have 3 other choices for injectors sitting here - 850cc 1000cc and 1200cc

Chequered Tuning will be mapping the ECU and have been working close with 2 other tuners

If I am only looking for around 330KW 650cc should suffice - this was advised by a performance injector supplier - but either way when we get closer to fitting I will take everything on board as constructive comments from you guys and also the tuners to see which will be better suited. Obviously we dont want to use something that we dont need to.

Thanks Johnny

[Kustom20]

With a GTX35 I would be going iridium 8's personally, gapped to .5mm. Each to their own, there are many ways to modify cars, some better than others. You only find out if the advice you have been given is correct by putting your engine on the line.

Most of your shopping list isn't required to max out a GTX35, such as plenum, exhaust manifold large throttle etc, but I would be going larger on your injectors for when you inevitably have to go e85.

Thanks Scotty, when I pulled the engine down I noticed the stock manifold had a large crack right across the front face just beside the turbo mount position, so we opted for the top mount steam pipe manifold arrives this friday. It was 3 choices buy stock again a crap 1.6mm chinese stainless which have issue's or pay an extra amount for a quality manifold, which to me is a great investment. Many people have issue's with costing on these manifolds, when you way up the cost vs quality and the amount of work that goes into these manifolds then I think well worth it.

Thanks again

[Kustom20]

Sorry to hijack thread but why do people always say you need minimum 1000cc injectors?

A simple google search of a calculator tells always that 800cc injectors are plenty good enough for 500 crank hp... Is there something I'm missing? And that's not 100% duty cycle

And yes that's on e85

Josh,

I think some people like to be on the higher side, nothing against those wanting to say I have 1000cc injectors or 1600cc injectors. It comes down to basic formula and knowing what target hp or kw one is intending on getting out of there application. And the extra percentage headroom is always great - we dont want to stay borderline

Thats right with injector sizing and duty cycle - for 6 cylinder 450hp @ flywheel only need 492.2cc injectors running @ 80% duty cycle the calculations are endless based on sizing type of engine hp duty cycle and so on, and then bring this all together with mapping and tuning

We have chosen the 650cc for our initial sizing and have 3 higher variances to choose, that being 850cc 1000cc and 1200cc

650cc are good for about 595hp @ flywheel for 6 cylinder running @ 80% duty cycle 43.5psi - 62 lb/hr - 0.5 B.S.F.C

Should be fine come the day of tuning and mapping as we have the variances - and like the guys said especially when the time comes to go e85

Cheers Josh

Edited November 25, 2015 by tuning_vs_hardware

[Dose Pipe Sutututu]

you're going to regret putting in the 650cc injectors

[Kustom20]

you're going to regret putting in the 650cc injectors

Hi Johnny, thanks for your advice on this we have the other available sizes here on the shelf. No doubt I will be sending you a message advising we have used the 850's or 1000's - maybe we can list the top feed 650's for someone upgrading an SR20 or RB20