Rb 25 Inlet Manifolds. When Do They Cause A Restriction

[klh6686]

For those of you that experience a loss in power when switching to a greddy IM need to retune your engine.

Greddy Intake on Stock-ish RB25DETs

We put a Greddy Intake on a stock turbo, SII RB25DET, and along with a FMIC, we gained 70rwhp at the same boost level (8 psig). We were using a tuneable stand alone ecu as well.

After talking to quite a few guys that have put the Greddy intake on stock-ish RB25s, it seems like most of these guys are very unhappy with the results. After some thinking, I realized the reason is that they are running stock ECUs. On the stock ecu, the power band will seem really high with the Greddy Intake, and it could actually run slower at the drag strip.

If you plan to get the Greddy Intake Manifold, you better have a way to change the fuel AND the timing. The Greddy intake moves the peak torque up almost 1500 rpm. This is not a bad thing, if you can take advantage of it. Taking out fuel and adding a lot of timing on the lower end, will make the bottom end a lot less soggy, and make it feel a lot more "snappy".

Another thing that we are finding is that the RB25 responds very well with increased timing all throughout the rpm band, especially when not in the boost.

__________________

AEM Trained EMS Tuner

This is done w/ a rb25 in a usdm 240sx running an AEM EMS.

[discopotato03]

That quote from the post above makes the all important mention of tune with aftermarket - programmable computer .

From Nissans point of view the factory inlet manifold was designed to be a good all rounder but as R31Nismoid points out its capable of passing 370 odd Kw 's worth of air . This is not too foul for a system designed for what - 184 ?

Realisitically a T04Z compressor (in Garrett form) can pump ~ 75 + lbs of air so I'll say 750+ Hp or 560+Kw potential . I really don't understand why anyone would try to run it to its limit without an RB26 head and inlet system . I can understand why some people dont like the std T/B being high and pointing back across the cam covers (IC plumbing issues) but is the 120 deg pipework really that bad ?

I would be more inclined to adapt the six throttle inlet system to an RB25 head than buy any aftermarket inlet manifold , but as has been thrashed to death the other benefits of the RB26's head/valve train are pretty essential to survive the revs required reliably at this power level .

I'll be brave and say I think the RB25's (R33 anyway) hydraulic buckets would be more of a power limiter than its inlet manifold . If I really wanted big power reliably and be even vaguely streetable an RB26 head/inlet system is the go , otherwise I can't see how you won't paint yourselt into expensive corners .

For those who want to hot up a street RB25 I reckon there's better ways to go about it than non std inlet manifolds .

Only my 2c worth , Cheers A .

[R31Nismoid]

For those of you that experience a loss in power when switching to a greddy IM need to retune your engine.

This is done w/ a rb25 in a usdm 240sx running an AEM EMS.

50rwkw on 8 PSI?

Thats a bit rich... but then its in the US and stange things happen all the time.

I think its EMS taking people for a bit of a ride.

[infected flow]

because there is money to be made.

some companies sell plenums, some sell wheels. you can buy aftermarket wheels and make your car look worse... but the company still made money didnt they?

now that's a stupid response!....there's money in everything..geez u might as well say why upgrade your turbo or why are they selling them..to make money duh!... lets just do research for the sake of it...hahahahhahaha.....ffs...

[infected flow]

50rwkw on 8 PSI?

Thats a bit rich... but then its in the US and stange things happen all the time.

I think its EMS taking people for a bit of a ride.

lol hahahaha... just take it on the chin...hahahaha or the forehead---the sphincter of the universe slap for you ..ahahhaha

[SLIMVLT]

i dont c that the lifters will be that much of a problem when there are plenty of high powered rb20/25/30's making plenty of power with them

i just want the truth about the plenums b4 i go and waist $xxxx on a gredy plenum or whatever when some1 else's plenum is way beter, or works the same as a gredy 1.

[slo-a31]

its a bit of playing around but i like the idea of rb26 plenums.

flow better than a greddy plenum (from what i've read) and still has really good low/mid range,2 throttlebodys close to your valves for good throttle response...i dont see a downside apart from the effort its taken to put it on.

[whatsisname]

The old Zoom VR (maybe VS?) Commodore that was mentioned earlier in this thread actually had an RB26DETT plenum adapted to fit the RB20DET head (it was NOT a GReddy unit), totally different runner design, totally different throttle arrangement and most importantly the engine in question was well below the kind of power level were a plenum/inlet manifold was required - no wonder it was a big step backwards! The only thing I can't recall is whether the Zoom Commodore retained the RB26DETT multi-throttlebodies or switched to a single unit?

Would you fit a T51 on a basic SR20DET package and expect it to become a brutal power house? Of course not. The 'package' needs to be modified so that everything is working together.

Edited September 1, 2006 by whatsisname

[R31Nismoid]

thanks for the replys guys.

yea i relised that replacing the manifold could net gains but its a cost v's gain thing that is the problem.

if its going to produce a good gain, or help with the way the thing drives then i will do it, but if its all about wank factor and looks then im not sure it will be worth it. its $1000+ that i can put into something else.

r31 nismod thats great power with the std inlet. so do u beleive that your setup could realy gain from a aftermarket inlet even though your against it, would it help.

just re-read it... missed that part

We didnt go for more power/boost as ignition was breaking down at anything more.

Had that problem not arisen... we could make more we think.

Im not against it, i just think the $$$ was better spent elsewhere... and really, i didnt have another $1000+ to throw at it all based on someone "thinking" that it "might" be better when i was more than happy with what i had for what it cost me

As i said, if you have the coin spare, get one, if you dont, then dont really.

Worst case, put it all together without one, then fit one later on if you feel its robbing you

[SLIMVLT]

cool, yhea thats what i thought....

problems with the rb25 is that so manny ppl are suposabley making xxx rwkw on what they say is no mods or with just a cam gear or whatever u get the drift and its hard to seperate the bs from the truth and the ppl who are arnt real informative at time's. its not this forum so dont worry guys.

1 thing i have found is u guys will help other forum members.

also r31 nismo do u have cams ect or any other major work done.

[ISL33P]

no one has yet to prove when they become restrictive because the two have never been compared so no one will be able to answer the question. i have offered a plenum* in the past to anyone making 300rwkw with a standard one to help prove a point but no-one has taken up the offer.....yet.

the magic 300rwkw (400rwhp) mark is always mentioned but also unsubstantiated, just a myth waiting to get busted (i love that show). surely the car can continue to make power, and which car wouldn't, as long as the turbo will support it and you keep on pushing more boost into it.

just one thing to say, efficiency is the key when trying to make the most of what you have and with that you will see the benefits.

again, thanks Ben for the vote of support. from when you took me for a drive, lag is almost extinct considering the turbo size and i have also noticed this on a rb25 equipped with a gt35/40 with one of my plenums.

this is just my 2c worth

ps - watch this post get deleted

[R31Nismoid]

also r31 nismo do u have cams ect or any other major work done.

Stock Cams

Stock Inlet Plenum

Stock Head

[Young GT-R]

I bought a second hand subzero plenum for my RB25.

My main reason was for the piping.

I had 204rwkw @ 12psi before.

I plan on running 16psi so the new power figures won't help but I think it's $600 well spent.

R31Nismoid.....You got that power out of an RB25 with a stock head and cams? That's insane! What turbo did you use if u don't mind my asking?

[R31Nismoid]

GT30 600hp or whatever the largest one at the time was.

sunoco 104, 24psi and lots of timing

it had made 330rwkw and day prior on a different dyno without any of the timing adjusted and so-on... using the same pressure/fuel

stock head and cams

There have been others who have had valve issues, so in that respect i think i was lucky... the head was pulled apart and checked when rebuilt and it was in excellent condition so we didnt touch it and see what it would do

[ISL33P]

any ideas what it runs on pump fuel ? so how does that power relate to pump fuel ?

not many people get around on sunoco fuel on a day-to-day basis. allows more boost, timing and fuel compared to pump fuel. not knocking it, just trying to put things in perspective for other who dont run sunoco.

[R31Nismoid]

Yeah nah thats cool... i didnt drive it much for a while so i could run whatever fuel i wanted... i never did try the really expensive stuff though hehe

It was 270rwkw on 17psi on the PULP tune when it was being daily driven. And casting my mind back it was around 4200/4300rpm/17psi without the fuel.

I think INASNT made similar PULP numbers on the same turbo, with the rest almost the same as me... or maybe his was the 550hp GT30.

If he sees this he will clarify

Both cars were different workshops too but very very similar results, but my car looked better

[Taffy]

50rwkw on 8 PSI?

Thats a bit rich... but then its in the US and stange things happen all the time.

I think its EMS taking people for a bit of a ride.

This was on my car. All dyno tests were done on the same dyno as well. 50rwkw is hard to believe, but the dyno does not lie.

The increase was using the Greddy Intake and a 4" core FMIC. Before, it had the stock RB25 side mount and stock intake manifold. It would have made more power, but the turbo was out of steam. It held 10 psig all the way to about 6K, but then fell to 8 psig all the way to 7500.

I am not advertising the AEM EMS, in fact, I would rather no one buy one. Their quality assurance program is non-existant, and they customer support is useless when it comes to any real questions.

[R31Nismoid]

So its 10psi and not 8psi now eh?

Which version of the story are we to believe?

But you are in the US remember, the figures are somewhat "higher", your 50rwkw is around our 30, which then (going to 10psi/management) is whats expected

[bigcarl]

i recently had a gt3040 600hp garrett high mount set up put together onto my rb25 running tomei poncams but stock plenum and pulled 305rwkws first run running rich afrs at 21 psi!! stock plenum is good . the only thing i modified was 3inch pipe into plenum. only thing stopping me producing more was a got severe valve float with stock springs over 7000rpm with higher lift cams. this will be rectified shortly.

[SLIMVLT]

what cams u runing mate????