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Rb25det With A "real" .82 A/r Gt3076r

Lithium

By Lithium,
in Engines & Forced Induction

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huddy Veteran

huddy

Posted
Posted (edited)

yes RB24DET

Tomei pistons, GTR crank, rods etc...

hence with the way rb20's and rb25's flow gasses differently, i'm after some sort of assistance in trying to figure out best setup for my car. also assumin my 20 based engine will rev more, also after opinions, that is why i would like peoples opinions on my questions.

thanks for the links, i have spent time reading them, and in mafia's thread he is relating to RB25... but i will have another look at them

thanks

-Matt

Edited by huddy
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Cubes Grand Master

Cubes

Posted
Posted

If you stroke out the bottom end and leave the head untouched it will make its peak power earlier in the rpm and nose over earlier. in other words rev less.

Your going to have to get the head breathing better with a set of cams.

Dale FZ1 Veteran

Dale FZ1

Posted
Posted
Stock ECU that dip is normal, its the rich/retard kicking in most of the time... plus average mapping i would suspect.

PowerFC/Tune = gone.

I have to say that I've seen that mid range dip more than a few times. Ignoring any stock ECU that's going into rich+retard, it's more with unopened engines but uprated turbo specs and with a new ECU. I see that Lithium has a Link setup.

Which area of mapping should be used first to attack the problem? ie fuel or ignition? If it is fuel (and assuming that the AFR in that area is a "nice" repeatable value, should it be leaned off?

Simon-S14 Grand Master

Simon-S14

Posted
Posted

i too have seen that dip in plenty of RB25 dyno's... and thats with aftermarket ECU's, stock bottom ends and supporting gear with decent turbo's... any idea what the cause is there??

Huddy: the prob with making 300 rwkw with your set us is you have the bottom end support to do it... but the head is still an rb20 head... it just wont flow the air to support the big numbers... no matter what turbo you run.

Lithium Grand Master

Lithium

Posted
  • Author
Posted
I have to say that I've seen that mid range dip more than a few times. Ignoring any stock ECU that's going into rich+retard, it's more with unopened engines but uprated turbo specs and with a new ECU. I see that Lithium has a Link setup.

Which area of mapping should be used first to attack the problem? ie fuel or ignition? If it is fuel (and assuming that the AFR in that area is a "nice" repeatable value, should it be leaned off?

The fuelling on mine was nice and consistant, and the timing is all fairly sensible though we / he didn't play with the VCT point. The tuner is a very accomplished tuner, he tunes some NZ GTR who went over to Australia last year and turned a few heads.

1400r Veteran

1400r

Posted
Posted (edited)
i too have seen that dip in plenty of RB25 dyno's... and thats with aftermarket ECU's, stock bottom ends and supporting gear with decent turbo's... any idea what the cause is there??

Huddy: the prob with making 300 rwkw with your set us is you have the bottom end support to do it... but the head is still an rb20 head... it just wont flow the air to support the big numbers... no matter what turbo you run.

time to buy Blinkies head then

Mach Go Go style 405rwkw on low boost

rb20 head

http://www.geocities.jp/akfw1_rbx32/free/car.html

rb20 head 3lt bottomend 600ps hmmm list it as a 25 head in specs?

http://www.eonet.ne.jp/~7thmeister/2003914zen.htm

2.2lt rb20 272 cams 500 ps http://www.dragster.st/dragster/mizo/mizo.html

Edited by 1400r
R31Nismoid Grand Master

R31Nismoid

Posted
Posted
I have to say that I've seen that mid range dip more than a few times. Ignoring any stock ECU that's going into rich+retard, it's more with unopened engines but uprated turbo specs and with a new ECU. I see that Lithium has a Link setup.

Which area of mapping should be used first to attack the problem? ie fuel or ignition? If it is fuel (and assuming that the AFR in that area is a "nice" repeatable value, should it be leaned off?

Dunno, i didnt tune the car, i leave that to my tuner/builder.

But there must be something people arent looking at/changing as no car i know of that gets tuned has a problem and a few RB25s have been done there.

I dont think its bottom end related as that largely has no effect IMO.

Dale FZ1 Veteran

Dale FZ1

Posted
Posted

I guess it comes down to what the budget will stand, and whether you can feel a difference on-road.

VCT change point on a mechanically standard engine can have marked impact, but usually in a negative way if you alter it a long way from standard. But + or - a couple hundred rpm might be worth a try.

I've seen using an adjustable cam gear also work well in terms of smoothing the torque curve - but no actual increase in my case. Just minimised the peaks/troughs so it was evident the engine was running in a happy mechanical zone.

With that slightly saw-tooth appearance, I'd think that the ignition map might be worth a look. If it was mapped to the best output without knock, some columns will take less timing, meaning that as you advance through the rpm range the map is not moving smoothly through a curve. Can give the up/down appearance I'd commented on.

None of this is a smart-arse commentary, just looking to see how the end result came about and whether it's possible to improve with comparatively little effort or $$. I like to know the how/why rather than just leave it to a tuner.

The fuelling on mine was nice and consistant, and the timing is all fairly sensible though we / he didn't play with the VCT point.
series2r33 Collaborator

series2r33

Posted
Posted

Shit hey, i had just ordered the GT3082r with the .63 the day before i posted my question. Now i read u guys reckon it'll be crap and i've got it! I hope your all wrong lol. I'll post the dyno results when i get it all fixed up.

SilverECR33 Veteran

SilverECR33

Posted
Posted (edited)
I have to say that I've seen that mid range dip more than a few times. Ignoring any stock ECU that's going into rich+retard, it's more with unopened engines but uprated turbo specs and with a new ECU. I see that Lithium has a Link setup.

woudlnt this have something to do with the Profiles on the cams?

Edited by silverbulletR33
Dale FZ1 Veteran

Dale FZ1

Posted
Posted

I'd say probably, yes.

He should be in a position to work with what he's got though. I posted a few ideas on #51.

Changing to non-standard cams may well just move the characteristic (I won't call it a problem) around and upwards. The saw tooth torque curve I would think is the bigger issue to address. And there are things that can be done that cost more in the way of time than anything else.

Again though - Lithium has got a generally good result. I'd just like to see something done to make it "happy".

woudlnt this have something to do with the Profiles on the cams?
Lithium Grand Master

Lithium

Posted
  • Author
Posted
Changing to non-standard cams may well just move the characteristic (I won't call it a problem) around and upwards. The saw tooth torque curve I would think is the bigger issue to address. And there are things that can be done that cost more in the way of time than anything else.

Again though - Lithium has got a generally good result. I'd just like to see something done to make it "happy".

Yeah me too. For what its worth, you really can't feel any of it on the road. All passengers etc perceive it as just building up and having strong power all the way through, the only "weakness" is that the thing doesn't go straight to 15psi and hold it. If it did that it'd be so much more solid, nonetheless there are definitely gains to be had by removing that slight dip.

The plan is next year to go to a built motor etc and then give it some boost and revs, this tune was just to get it safe and fun to drive - not to hunt every last hp :thumbsup: For what its worth, I gave it a run on a rolling road dyno for fun and the dip wasn't anywhere near as extreme.

  • 2 weeks later...
huddy Veteran

huddy

Posted
Posted (edited)

did you guys get custom lines made up to suit? just got my 3076r... :)

LITHIUM

-i cant see pics of your dump, can you please post up, mine phsically looks the same as yours with the antisurge front, and same stye rear exhaust housing.

-how did it go for standard intercooler piping to the top of the turbo? (well maybe not standard, as mine had previously been modded for the hks turbo...)

-was there any difference noticably with the change in manifold? (even noise??)

cheers

-Matt

Edited by huddy

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