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JAS-25T, If you want to increase the boost my first suggestion is to regap your spark plugs to 0.8mm. Doing this with the standard ECU should allow you to run about 10-11psi. After that, as others have already mentioned, "overboost protection" sets in and misfire problems occur.  

I upped the boost with a bleeder (to about 9psi) and ran into misfire problems above 4500rpm. I then regapped my spark plugs and could run 10-11psi without it being an issue. However, the real gains from the boost increase were noticed once I got a hold of a chipped ECU which has far better ignition timing than standard. Boost comes on earlier, more midrange responsiveness, and redline is acheived quicker. I can now also up the boost until the turbo goes bang :( I'm currently running 13psi.  

Regapping the spark plugs to 0.8mm can help (and is cheap i.e. $0) but better engine management is the real key.... if only the stock ECU could be reprogrammed....

this is the exact kind of answer i was looking for

thank you very much

Hi GTRman1992, sorry for the sarcasm, I couldn't resist it.

I have never tuned a Skyline that gained less than 20 rwkw (average from 4,000 rpm to 7,00 rpm) from correcting the A/F ratios and optimising the ignition timing. The more modified the car, the higher the gains from tuning. Thus far, my highest ever increase in average power from tuning alone (ie; no extra boost) was 150 rwkw. Your car would fall somewhere in between, looking at the mods you’ve listed between 30 to 40 rwkw would be my guess.

As for which ECU, standard or aftermarket it really depends on the quality of the tuner and whether or not your are going to do more mods. If you have finished upgrading then a good tuner will be able to extract the max from the standard ECU for around $800. If you have more mods to go then it will cost $350 to $450 every time it needs a retune.

In that case it would be cheaper to go for an aftermarket ECU (my recommendation would be a Power FC), cost around $1100 plus tuning $200 to $300. As you can see you get the extra expenditure back pretty fast if you have a plan of further, ongoing mods.

Hope that helps

Thanks for that SydneyKid, finally a definitive answer on the subject!

All I'm really planning to add to the car is bigger injectors (550cc to 600cc), a 600x300x97 intercooler, better intake plumbing to the air box some adjustable CAM gears (an article in ZOOM claimed 20rwkw without loss anywhere in power band - they had dyno prints).

All I'm after is around 600HP at the flywheel.

Oh yea, I also plan on adding my direct port, 3D mapped water/methanol injection system once I build it. I'm thinking of using it to get more aggressive timing as I think 20psi boost is heaps.

Hi GTRman1992, it is not really an issue of how much boost, but rather one of how much efficient (not overheated) airflow. I haven't seen anywhere near 600 bhp from a pair of turbine only, upgraded standard GTR turbos. Around 550 bhp seems to be their limit. With set of N1 (or LM) internals, they are OK for a bit over 600 (625) bhp.

Most I have ever seen out of adjustable cam pulleys only, was 40 rwkw, max at one rpm point. I didn't work out the average, unfortunately.

Hope that helps some more.

Ok, I thought more boost = less engine life. So you say more boost as long as air temp is ok. Interesting. Maybe I can aim for my original 23psi - 25psi limit.

My turbo's have an interesting background. They are genuine ex-gibson units. Back when the GTR was banned from racing, Gibson motorsport had an action and unloaded all their stuff, anyway someone I know bought a set of turbos and put then away for a special day. That day never came and he offered them to me. I had them rebuilt etc. So they should be good for 600HP at 23psi boost as that is what I think Gibson was running.

The article on the CAMS said 4deg retard on exhaust and 2deg advance on the inlet was ideal.

can i pull back this very technical (for me) thread with a biasic question? (lol)...

If i wanna take my r32 gtst from stock (10psi) to say about 14psi... what would you suggest (ps i have a BUDGET)...

I was thinking AVC-R + AFC?

or should i get a chipped ecu?

who can chip them in syd? or should i get one from a wreckers?.... doh! i'm losing myself now..... lol

Nah, i'll be putting on a nice FMIC first... but i don wanna use a bleed valve 'cause i don't want all that boost spike and crap, i want it done properly.... and when i said budget, i just meant i can't afoord a worked GTR running 20PSI like some (i think thats a strong case of jealosy there)....

riggaP:... from what i understand (please correct my errors), bleeders 'trick' the car into thinking it's still running 10psi while it's actually running, say, 12 etc.... I just don't trust something that is tricking my car... i'd prefer the car to know it was running 12psi.... sounds stupid but i'm sure you can understand what i'm tryin to say.... can you elaborate on this?... thanks.

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