280rwkW at 1.2 Bar

[whatsisname]

But if you don't have ANY cams how are you going to attach the cam gears?

[Nightcrawler]

fark you too for good measure .... damn wiseasses ....

[whatsisname]

Back to being serious for a sec, the downside in doing SR20DET cam gears is it's a labour intensive process Rocker cover off, timing chain and so on... I still reckon it's worth doing though mate. Of course you'll have to put your cams back in to fit the gears to them

[MattR]

So im my car is due in the next 10000k for timing chain might as well go new cams:) and gear at the same time???

[whatsisname]

Sounds like good plan to me Matty.

[MattR]

Or just build another sr20 with NA cams and everything else then put it in when its done???

[Martin Donnon]

We've made cam timing adjustments to my motor twice (the original motor and the built motor) on both occassions there have been noticeable mid range and top end rwkw gains with nil loss down low (retarding ex cam for mid/top power).

While that may be your experience, common physics would tend to argue with that. Think for a moment of whats really happening when you change cam gears, rather than the shiny gear itself.

Effectively you change the LSA (Lobe Separation Angle) of the camshafts, and alter the opening/close valve events of the exhaust camshaft. You would need to have a look at the real effects this has on camshaft timing using a degree wheel. What you would find if you did this is an effective shortening up of the exhaust time for the camshaft when you dial 5 degrees into the exhaust (and thats a lot).

The bottom line here is that for a power gain to happen from this modification at the top end of the rev range, you will essentially have to lose cylinder pressure and response through the 0 - 4000rpm mark. This can however be effectively made invisible during dyno testing with a combination like yours due to selected dyno ramp rate, or turbocharger response. On the road? Its a whole different story.

Remember the simple principle with this cam timing process you describe, that being there is no magical gain to be had, rather you are equipped with the ability to effectively move the powerband of the engine around the rpm range....within limits.

.....All of which is why the correct solution, rather than the 'nickel & dime' solution is to pick the correct camshaft profiles for the application in the first place.....Try something like a 262 inlet with a 256 exhaust installed at 114ICL on your engine, and your eyes will drop out of your head!

[Steve]

Icl?

[whatsisname]

All very true Martin. I should have clarified that the 'nil loss down low' was a dyno observation and not a on-road seat of the pants test.

The minor trade-off in cam gear adjustment to achieve top end gains is acceptable to me. As when I compare my power curve to other similarly modified RB25DET combos it still has very good bottom end and mid range power/torque.

My camshafts will be upgraded as soon as I have the funds.

I might see you out there on Sunday mate?

edit: Forgot to add... thanks for the cam selection recommendation!

[Freebaggin]

Martin/Matt, yep, there has to be a trade off across the rev range for sure.

However with mine, I'm lucky in that I think the better flowing manifold and definately the better tune (both off and on boost) has more than hiden any power loss below 4000rpm and it feels better everywhere on the road.

Martin is ICL the same as LCA? Lobe Centre Angle, it governs/determines overlap I have read.

I was going cams with this latest upgrade as it is was the next logical step but went the half way option for now as I'll have a few months of enjoyment until the next upgrade. I like to do things in stages to see what happens for myself, however I pay for it in the end with more labour costs I spose.

But yeah, bring on the cams. Myself, Whatsisname and Grepin are due in the next few months, should be interesting, start to give Steve a run for his money.

Any of the RB30 R32 boys going aftermarket cams??

[Martin Donnon]

[Cubes]

I'm going to see how the stockers go first then possible slap a set of 256dur inlets and 264 exhaust. I want to try and keep a bit of economy. Maybe the smaller duration exhaust will do this (as per Martins suggestion)?

According to the Engine Dyno Sim the RB30 will pick up bottom end torque up until a 260duration cam then over that it will start to drop it with little gain up top. It appears the larger exhaust cam is what gains the best top end power and prevents torque dropping off in the higher rev range.

Martin? Could you explain a little better why you suggested basically the opposite to what the Engine dyno sim suggests?

[whatsisname]

That's exactly what I was thinking Martin

[Bl4cK32]

yer same as Joel. 256 inlet and 264 exhaust. Still deciding on lift though...when the GT35/40R goes on the cams should be going in the same time Just stockers (rb25de) for the run in though....

[EnricoPalazzo]

did u think of tomei poncams that SK always recommends.

[Martin Donnon]

Think outside the square for a minute, and put down the keyboard and engine simulator. They are great for a ballpark reference, but are based on the same - what I believe to be outdated - principles, and old wives tales that hampered traditional V8 camshaft selection for years. Now these same rules of thumb are making their way into DOHC circles. In nerd talk, GIGO.

Now step into the real world and have a look at the engines that are making truly huge horsepower, and running enormous trap speeds. Worry not of their inlet duration, claimed exhaust numbers, or even lobe separation. These are rough, rule of thumb figures that give and indication of the camshafts design, rather than tell the whole story. The true power comes from the actual valve events that take place in reference to crankshaft rotation. Then theres the lobes themselves. No duration figure will explain the ramps. If you have a basic understanding of this discussion, and knew the sorts of camshaft numbers I am talking about, then you would be awestruck. There is no theoretical simulator or text book in the world that would recommend you use them. But, they work.

My recommendations? Concentrate on the inlet more than the exhaust, after all, this is where the exhaust energy comes from. Ask most of the gurus around the traps about this, and most of them will simply shake their head "nup, cant work". Then ask them how a camshaft actually works, and they will give you a blank look. Twiddling around with an adjustable gear does not instantly convey understanding.....Unfortunately for 99.9% of camshaft selections in Skyline engines, picking an old fashioned profile out of a book is as technical and sophisticated as it gets. Sure they work, BUT they could work MUCH better. There is only one LSA ICL and ECL that works perfectly for any given engine and turbo combination. The closer you get to that, the more power and torque you make.

[Steve]

Martin you tease...

This is why I just picked HKS catalogue items, all the research in the world was just giving me headaches - too many different ideas on what works and what doesnt.

I chickened out and went the combo that allowed me to run the largest cam, under 9mm lift, that still allowed me to use VVT - after all it is a street car (and having a HKS turbo, HKS cams seemed a good choice:p).

And for those who are wondering, the car is alot crisper with the VVT connected than disconnected, so it must be doing some good.

Martin, what sort of combos do you recommend, that you have seen work well, for street and/or strip?

[Martin Donnon]

Look Steve for a mild mannered road car like yours, you havent done the wrong thing. Most off the shelf Jap cams are extremely mild though. Like the 256/256 HKS sticks I put in my Soarer made like 10rwkw for $1000. Nice. Not. Im writing about maximum effort engines rather than roadies, however, if you have the tuning ability then unconventionally large camshafts can be made to run sweetly. Heard Keirs engine idle? Put an exhaust on it, and the thing would sound almost stock.

As an aside the Japanese aversion to large camshafts would more than likely be due to their lack of tuning tools to make them run correctly. Ie. the same reason they change GTRs from six throttle bodies to a big single, when the single has less cross sectional area than the stockers.

[BOOSTD]

.....Try something like a 262 inlet with a 256 exhaust installed at 114ICL on your engine, and your eyes will drop out of your head!

How about a tomei poncam with VCT 264 inlet and 256 exhuast... what lift are you referring to?

If I'm thinking right this setup will increase exhaust velocity throughout the entire rev range....is that correct?

Have you seen this setup used, if so can you provide us with some results

cheers matt