Greddy/Trust Plenum

[JimX]

Roy, good question. I'm not really sure.

The boost gauge splices into the factory line, which I think is on the plenum (it seems to go somewhere on the driver's side in the engine bay anyway). The EBC gets its boost reading from wherever. I think it gets it from before the intercooler because it's all on the left side of the engine bay.

If the above is correct then there's not much pressure drop through the cooler. I've set the EBC to 1 bar and the boost gauge reads 15psi (maybe half a hair over).

[T0nyGTSt]

Here's an idea.

Maybe we can contact a plastics fabricator and come up with a flow tested design for a rb20/25 plenum in nylon and carbon and see how many orders and prices we end up getting.

Sounds good? One of the problems with the Greddy plenum is that it is a big metal thing and it does weigh a lot.

T.

[Sydneykid]

Hi Jimx, what you are describing with spark plug colouration is typical and it is the problem. Currently based on what you have described, your car is running fairly rich on 1,2,3 and 4 with 5 closer and 6 OK. This is costing you power, the cylinders that are rich are not not running at maximum efficiency, in fact you may well have only 1 cylinder (#6) tuned for maximum power.

The problem is, if you tune 1,2,3 and 4 for maximum power, 5 will be a little lean but 6 will be way too lean. So you have a choice, less power or detonation on 5 & 6.

Now if you had a manifold that had equal flow to all cylinders you would be able to tune all 6 for maximum power. So the question is, does the front facing plenum make more power (with its poor distribution) than the standard plenum (with slightly more restriction but equal distribution)?

My experience has been that up to 450 bhp, you get more out of correct tuning with the standard manifold.

Hope that adds to the discussion

[Steve]

JimX, I think it is really hard to do a before after comparison on a plenum if you do the cooler at the same time. A decent cooler will make alot more power than the stock item so it would be impossible to be objective about the plenum.

[JimX]

Sydneykid I agree to an extent, but the difference in my plug colour is very very small. So small that between any 2 adjacent plugs I couldn't tell the difference in colour. It's only when I got 3 or 4 towards the front that I could notice the colour difference. I never checked my plug colour from the old plenum, but I would say it's just as likely that plugs 3 and 4 would be the ones running "perfectly" rather than 5 and 6 as it is now.

From my understanding of plug colours, they all seem fine to me. They range from a light brown to a slightly darker shade of light brown, with absolutely no fouling even on number 1. So yes plug 1 is running richer than 6, but I wouldn't say "rich".

I agree wholeheartedly that the standard plenum is more than adequate for 450hp+. But as I've already said, I didn't put it on for extra power. My main concern was throttle response, which has been markedly improved. My secondary concerns were easier servicing of plugs and injectors, and thirdly just the neater "custom" appearance.

[JimX]

Steve, the cooler I had before wasn't the factory item, it was just a smaller front mount with fairly long piping back to the factory plenum. So I think the comments on throttle response are valid. Bigger cooler plus shorter piping equals better throttle response than small cooler with long piping back to factory plenum.

[Steve]

Fair enough then, sorry I thought it was the stocky:D

definately worthwhile comparison then. What size were your before and after coolers? What plenum are you using?

Just be careful with number 6, one bad batch of fuel or hot day and you may have problems. Are you using stock injectors? Might be worth getting your injectors flowed and then putting richest to 6 - leanest to 1 as a safeguard.

[JimX]

Plenum is a home-made job I bought off GR8NES.

The old cooler was around 500x300x50 I think. The new one is 600x300x70. The old one had bad angular end-tanks as well, which is another reason for the upgrade.

Still running stock injectors, but I have a set of RX7 injectors ready to go in, which have been flow tested and I'm definitely putting them in the proper order

It's running ok for now with the stockers, I'm contemplating saving up for a PowerFC before I put them in. Or at least replacing the dump pipe with a 3" one to help with the surging/dipping in upper revs.

If I feel enthusiastic one weekend I might just put them in anyway and see how they go, then swap them back again on the same day, but I'll need some advice on how much fuel to cut from the S-AFC to make it run the equivalent of before. The front-facing plenum makes this a viable experiment, because I'm stuffed if I would bother removing the whole intake just to swap the injectors in and out for something to do

[benm]

You aren't running a 3" Dump pipe?

Geeeeze i'd be using a 3" dump before using a drivers seat if i did mods all over again.

Guaranteed 10rwkw and much better flow.

[JimX]

Well, it's 3" from the front pipe back (including cat) so I'm not so sure a 3" dump is going to give me that much of a power increase. But if it did nothing other than smooth out the power curve in the upper rev ranges it'd be worth doing. I'm saving my pennies as we speak

[Sydneykid]

Hi HJimx, if you can see a colouration difference in the spark plugs then there is alway more than 0.5 A/F ratio difference (oil usage not withstanding). By moving an RB25DET from 11.5 to 1 to 12 to 1 A/F ratio you pick up 25 to 30 rwkw. So if you have 1 cylinder at 12 to 1 and 5 at 11.5 to 1, then you are loosing 20 to 25 rwkw. Remembering that this is the minimum, a noticeable colouration difference could easily be 1.0 A/F ratio which is closer to 40 rwkw.

Now I have worked on over 20 X RB20/25's and have never seen one that shows any consistent spark plug colouration differences on 3 and 4. I have seen it on differing cylinders but this is usually traced to lower flowing injectors or other factors. It certainly is not airflow related with any consistency.

To others, I believe introducing discussion on inlet systems for 1,000 bhp drag cars is not really relevant to this thread. In these cases with Motec ECU's, uneven airflow is easily compensated for by tuning individual cylinders. We measure A/F ratios and EGT's at each cylinder's primary exhaust runner, and tune that cylinder accordingly. This compensates for any uneven airflow as well as combustion temperature differential due to the engine's water flow characteristics.

But that is in the heady area where power is everything and money doesn't matter, I don't think that is the purpose of this thread. Here it's value for money and, in my ever humble opinion, aftermarket or fabricated front facing plenums are bad value for money on RB20/25's until you start to modify the internals. Then the costs can be justified.

Hope that adds some more to this interesting thread.

[JimX]

Sydneykid, I don't think there I am losing anywhere near 40rwkw. If I was then it would be making less power at 1 bar than it did at 0.8 bar before. At present I'm making 215rwkw @ 1bar, when it was 166rwkw before at 0.8 bar. Both these figures after the S-AFC was tuned by the same guy on the same dyno to around the same AFR, possibly even a little more conservative now than before.

If I got a linear power increase from the same boost increase (which I know isn't so, but just for argument's sake) then in theory I should only be making around 208rwkw at 1 bar boost. But I'm making almost 10kw more than this, and this is with something strangling it in the upper revs.

If the front-facing plenum has cost me 40rwkw, then the cooler upgrade and shorter piping has gained me over 50kw. I don't believe this is true for an instant.

[Sydneykid]

How much more boost?

[JimX]

1 bar boost=215rwkw with front-facing plenum and bigger cooler.

0.8 bar boost=166rwkw with factory plenum and smaller cooler.

If it was a straight 20% power drop from decreasing boost by 20%, I should have been making 172rwkw at 0.8 bar.

[Sydneykid]

Thanks JimX, let's see if I can do some numbers. Based on our experiences with RB25 boost up, you get 22 to 28 rwkw for each 0.2 bar of extra boost (let's say 25 in your case). Intercooler upgrade should net 15 to 20 rwkw (say 18 in your case).

166 rwkw Boost = 0.8

25 rwkw Boost + 0.2

18 rwkw Lower restriction in intercooler

= 209 rwkw

That leaves 6 rwkw for the manifold and the pipework.

Now this assumes (dangerously) that the car is just as well tuned (ie; close to the limit) as it was before and after. If it is better tuned after, then the gain from the manifold is even less.

I know you didn't, but if you had paid $1,500 for a Greddy manifold, I would consider that bad value for money. For the same cost I could get a set of Tomei 256 Poncams that would give around 20 rwkw max power increase. That's better than twice as good kw per $.

Now what if I could tune it better because of the distribution issues not prevalent in the standard manifold. maybe another 10 to 15 rwkw.

Hope that better explains my position

[Steve]

JimX, can only agree with you, as BOOSTD was making close to the same figures you are quoting with 1bar and stock plenum (also indicates to me that you have one of these freak 95ecus?), so even 20kw difference would not allow you to be making that sort of power, as it would imply with a stock plenum you would be making 235rwkw at 1bar.

i wouldnt bother trying to change the injectors until you are getting it tuned. I used powerfc and upgraded to 550cc - resulted in running rich even with correction.

To work out your correction as a percentage, just divide 370 (stock injectors cc) by the upgraded injector size, then multiply by 100. So if using 550cc injectors, the correction would be 0.67 (or just a bit over to be exact).

[Steve]

Originally posted by Sydneykid

18 rwkw  Lower restriction in intercooler

= 209 rwkw  

That leaves 6 rwkw for the manifold and the pipework.

Would this still be the case if he is already running an aftermarket cooler? I was under the impression that a cooler upgrade from stock could be worth around 20rwkw?

Still, at 1 bar, you would expect around 215-220rwkw, if you stubract the 20rwkw (you indicated this to be his loss due to running rich on front cylinders), you are saying he would be making 235-240rwkw with the stock plenum and turbo at 1bar. I doubt it. Didnt the GCG (Ben Ellis GT-T) highflow make around 230odd at 1.2bar?

[JimX]

Originally posted by Steve

To work out your correction as a percentage, just divide 370 (stock injectors cc) by the upgraded injector size, then multiply by 100.  So if using 550cc injectors, the correction would be 0.67 (or just a bit over to be exact).

My main problem is I don't know how to work the S-AFC. I don't know if the numbers (I think it's -10 to +10 or something?) specify adding/subtracting fuel or air. Like, is setting a positive number adding in more fuel, or telling the ECU that there is more air going in than there really is?

Also, I'm guessing that you would change the -10 to +10 scale into a 0 to 20 scale, otherwise you'd get some funny results (ie, how would you add/subtract 0.67 on anything on the middle baseline of 0?)

I'm only going to do this IF I feel motivated and bored enough, mostly so I can see how smoothly it will run with the bigger injectors. I guess worst case scenario I will just leave the tuning as-is and just drive it straight to the workshop for tuning thereafter (whether S-AFC or PowerFC by that stage). That is if it will even fire running that rich.

[Steve]

http://www.apexi-usa.com/documentation.asp

they have downloads of the manuals there, might help.

[Sydneykid]

Hi guys, I seen plenty of R33 GTST's with standard turbos, FMIC's, PODs, 3" turbo back exhaust, standard inlet manifolds and tuned properly that make 205 to 210 rwkw. So I have no problem saying JimX is getting somewhere between 5 & 10 rwkw from his inlet manifold and shorter/better pipework.

I am not saying that there is no power increase, just that to me a Greddy plenum (which shows the same result) is not good value for money. I could get twice that much for less cost. Cams for one or if I spent slightly more I could get 3 times that much out of a hi flow. Which is the result Steve is talking about on the R34 GTT, which ran out of injector flow at 230 rwkw.

Don't get me wrong I am not against front facing inlets, I have gone to great expense to have a GTR one on the RB31DET, but they need to be thought of in terms of what else you can do for the same cost. As usual it is a matter of priorities, and I believe a front facing plenum should not be that high on the list. Certainly it should not be placed before a Power FC and a set of cams in an R33 GTST.

Plus Steve, if you want to use Ben's car as an example, it still has the complete standard inlet system at 290 rwkw. Even at that power (470 bhp) it still hasn't reached the top of his priority list.

Hope that clarifies some more.