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This Quick Test May Save Your Big Hp Engine.

STATUS

By STATUS,
in Engines & Forced Induction

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STATUS Grand Master

STATUS

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Posted (edited)

Usually on bigger HP stuff (supercharged V8's) the cars come in after being on a engine dyno so indivual cylinder mixtures were already monitored and addressed either by 8 EGT probes or 8 lambda probes in each collector. This makes tuning the engine less stressful as the tuner only needs to monitor overall mixtures (left and right on v8's or single sided on inline 6's and 4's).

With the majority of other setups the car comes in "green" pretty much the brainchild of the owner, with more empahis on cost and ease instead of result and capability so things like cylinder distribution is often overlooked and hard to monitor. This is never really an issue on stock plenum RB's etc but over the past few weeks i have had quite a few differrent plenum styles come through for final dyno tuning, some good, some bad.

Now without going into specific brands i can say that most of the established retail type products seem to work very well, and the individual shop made or cut and shut std manifolds fair far worse. One particular plenum was nice and shiny but required a 8% differrence in fuel delivery between 1 and 6, now this may not seem to bad but at idle this makes for a fairly cranky number 6 spark plug and untuned would almost certainly result in a melted piston or low knock threshhold (which was what initially alerted me to the issue).

A quick simple test is to run minimum boost in 3rd or 4th and shut the car off at the top of the pull and remove all the plugs, all colours should be equal. increase boost to your max tuned boost and do the pull again. Compare the colours and if you find the plugs get darker as you go back along the cylinders or vice versa you have an issue. The problem usually gets worse with boost and depending on plenum design can get lean as you go back or richer so make sure to lay the plugs in order. There is another culprit for poor cylinder distribution (feul this time not air) and that is the fuel rail but rb rails are pretty good and most cases ive been able to trace back to plenum based air distribution issues.

ive included some pics of spark plugs these two shots show the differrence between no cylinder compensation and cylinder compensation. These issues are easy to address in most aftermarket ecu's but if you find you need large adjusments, consider a new plenum.

post-34927-1237610117_thumb.jpg

post-34927-1237610146_thumb.jpg

Edited by URAS
STATUS Grand Master

STATUS

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something similar, any with the water inlet supplied separate tend to leak badly down the track. Just a quick note to let you know the difference in fitting a copy versus a genuine greddy plenum, we charge 250 more to fit a copy as it takes 3 times as long to fit.

W0rp3D Grand Master

W0rp3D

Posted
Posted (edited)
Just a quick note to let you know the difference in fitting a copy versus a genuine greddy plenum, we charge 250 more to fit a copy as it takes 3 times as long to fit.

lol, i wouldnt do that to you, the only other things im doing to the 33 is afm, pump, injectors (which i still havnt gotten checked yet) and tune then im selling it.

Edited by W0rp3D
unique1 Mentor

unique1

Posted
Posted

hey Trent do u have any results for rb26's running stock plenums? i run individual egt's and my results and a friend running egt's as well but with different turbo setup is showing alot different to what i have always heard stated as "fact" on this forum. number 6 is the hottest off boost and Not the hottest on fullboost by a fair bit, is this what you have found as well?

STATUS Grand Master

STATUS

Posted
  • Author
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hey Trent do u have any results for rb26's running stock plenums? i run individual egt's and my results and a friend running egt's as well but with different turbo setup is showing alot different to what i have always heard stated as "fact" on this forum. number 6 is the hottest off boost and Not the hottest on fullboost by a fair bit, is this what you have found as well?

whats number 1 and 2 doing under big boost on yours?

STATUS Grand Master

STATUS

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Trent, I run individual EGT's in each exh runner and have corrections of up to +12% and -14% depending on boost pressure.

This is on a stock plenumed rb26.....

what turbo setup, rail/inj and boost (bigger boost means bigger corrections? entry angle to plenum is also critical. We some interesting corrections on the race car but not that big. Luckily your ecu allows inj vs boost correction most dont, The 795-odd hp 2jz in the other thread needed between 6-8% in the rear 3 after 18psi, i spose i got carried away without stating that the test only takes a few mins and can save an engine, can be checked by anyone and requires no expensive gear, it should be a precautionary check taken after any plenum mods or in cases like yours after any mods. Most importantly it is not concrete but is a worthwhile test none the less.

Edited by URAS
WilYawn Enthusiast

WilYawn

Posted
Posted (edited)

URAS, did you test the air distribution on a rb25det greddy plenum? Just put a (genuine) one on my car and now you got me a bit worried :down:

/Martin

Edited by WilYawn

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