forged pistons

[the phantom]

Hey Sydneykid,

Do you use normal pump grade premium 98 with the 9:1 CR and 400rwkw in your RB31DET's, or something else...

[Sydneykid]

Oh Ghost Who Walks, we use Optimax, 1.5 bar boost, with ceramic coated piston crowns, combustion chambers, valve heads, exhaust ports and exhaust manifold. I actually exaggerated a little bit, best we have seen so far is 388 rwkw on Optimax, it made 442 with Elf LMS. But I am working on a new camshaft spec with a little more lift, which should pick up the 12 rwkw.

There are no real secrets in getting a 9 to 1 engine to make big horsepower over a useable rpm range. Keep the boost down by running the right size turbo with enough airflow to make the horsepower target, is the most important. The next is very smooth combustion chambers, with oil and water temperatures under control. Correct heat range spark plugs are essential. Back it up with sensible A/F ratios and tune the ignition timing very closely.

Hope that helps

[MattSR]

Hi Sydneykid,

"Sensible A/F ratios"

OK - for optimax, i'm assuming that this is in the 11's...

"and tune the ignition timing very closely."

Close to detonation? or do you mean listen closely for detonation?

I also read recently that the onset of detonation is always accompanied with a puff of blac smoke from the exhaust - is this how you would detect detonation?

Cheers for your help,

Matt

[T0nyGTSt]

Look at that wiseco catalog...

The CR all looks so low.

I reckon they found a whole bunch of 86-88 millimeter bore pistons from whatever cars they have in the US and modified the wrist pin connect so they fit Skylines.

ie. they aren't really Skyline pistons but some blanks that have been milled to fit the RB.

T.

[Sydneykid]

Hi Matt, firstly let me say that what I am using as an example here is a $25K engine. So I use every method I can to protect it.

As for A/F ratios, RB engines seem to make max power around 12.5 to 1, some drop off dramatically in power when you get much richer than that. Others aren't quite so sensitive, I have no idea why this is the case. So if it doesn't affect the power output too much, I target around 12 to 1, and we may have to go down to 11.5 but this is unusual. Basically we just give the engine what it wants, as each one is unique.

Moving onto detecting detonation, the car has an EGT sensor which is a god indicator, as is the fast and wide lambda sensor, the Power FC detonation detection, with the standard RB26 knock sensors, is also a huge help. But by far the best is the human ear, so I have a set of headphones with a mike and a small battery powered amplifier. It is based on the Autospeed design, you can see it here;

http://www.autospeed.com/cms/article.html?&A=1353

You can buy similar commercial/workshop equipment, I think SnapOn have one.

So when doing the ignition timing maps, we tune it on the dyno with a very close eye and an ear on the knock detectors (all of them). I also have a Datalogit system with which I review the PFC data from each run (and when we drive it in anger).

Hope that helps some more

PS, this sounds like I am a dyno tuning guru, truth is, our race team dyno guy is way better than me at this stuff. I help out where I can, as this type of thing really needs two sets of eyes and ears.

[Sydneykid]

Hi T0nyGTSt, I don't know for sure, but maybe Wiseco originally make them for RB30's which have 15% smaller combustion chambers. Perhaps that's why the comp ratio is so low when you use them with a DOHC 4 valve head. They also sell lots of stuff for VG30's in the US and they have combusion chamber volumes around the RB30 size. Who knows.

[Steve]

Do you think it is fair to compare a ceramic coated everything 25K engine that gets tuned before every race meet and has all the ecu data logged and reviewed regularly with the average guy on the street wanting an engine that can be driven in anger without problems and only gets dynoed once in a blue moon?

I dont.

[MattSR]

Cheers Sydneykid,

Just got one more question, what happens to the EGT's as detonation begins? i'd guess that they decrease due to the 'boundary layer' being destroyed thus causing more heat transfer to the metal in the combustion chamber?

Thanks again,

Matt

PS - you know you're a guru

[GTS-t VSPEC]

what would u suggest would be a better suggestion? 8.5:1?

i suggested that but was told to go lower

ill ask him y tho

I'm with Sydneykid here, either 8.6:1 to 9:1. All it really requires is a decent tuner.

[Steve]

I agree with 8.5, but really I dont think you loose that much by dropping CR to 8.5 from 9. A car may be better to drive with 9, but mine with 8.5 is absolutely fine on the road, dives very well - and detonation is very low even on 40deg day running 1.7 bar on bp ultimate - peace of mind.

If 8.5 is that bad, why did nissan use it for the GTR?

BTW Paul, how many ring lands did you smash?

[GTS-t VSPEC]

Steve, Motor is still in the car, waiting on parts to arrive before we strip it. Nothing wrong with 8.5:1, just these days with better fuels and EMS there really isn't the necessity to drop the CR too much.