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Adjustable Cam Gears, 1 or 2?

Steve
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Steve Grand Master

Steve

Posted
Posted

Hi,

Just after some thoughts, what do people thing of the pros and cons of 1 cam gear (exhaust) versus 2 cam gears on an RB25DET.

Would be especially interested to hear comments from anyone who has done the exhaust side first and later done the inlet side, but any ideas/experiences/thoughts are very welcome.

I am looking at making upto about 600bhp. What will be the affect of loosing VVT with a higher hp engine? What will be the gains.

Also are there any thoughts on what cams would optimise the use of cam gears, bearing in mind that I am after torque, not peak hp, and this car will be a daily driver capable of handling heavy traffic as well as the more spirited stuff.

All ideas are welcomed, thanks for your time

Steve:)

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rev210 Grand Master

rev210

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Posted

steve,

The exhaust cam gear is all you can do if you retain variable valve timing on the inlet (ie: you have a stock ecu with a S-afc or such).

I recently did mine (exhaust) and retarded it 4deg.

The exhaust cam is the better of the two for power adjustment on a turbo, not to say the inlet has no benifit. The overlap and duration of the exhaust side of valve control gives turbo cars extra zing if done right. The inlet cam will allow some extra advance, for peak power at the expense of mid range.

As for aftermarket cams:

They are usually designed with a 0deg install in mind, on a 'perfect match' engine, the one they were designed to work with. The cam gears then allow such after market cams to be propperly 'dialed in' to suit your engine characteristics. So its not a case of 'cams optimising the cam gears' it's the other way around.

If you want 600HP with bottom end torque you might want to look at a 3litre conversion and/or a supercharger.

Sydneykid Grand Master

Sydneykid

Posted
Posted

Hi Steve, I'm with the rev (210), we typically adjust the inlet camshaft 1, maybe 2 degrees, but on the exhaust 4 is very common.

I would keep the the VVT but you need to be careful with camshaft selection to allow for the VVT. ie; choose a camshaft designed for VVT, not one designed for an RB26 or RB20 with no VVT.

For example Tomei make a set of 256 degree ones that worked great on the two RB25DET engines we have seen. Both have around 250 rwkw (400 bhp) on hi flowed standard turbos and are very driveable, daily. Do mid 12's for the 1/4, strong mid range and good throttle response on the circuit. Altogether a very nice combo.

Hope that helps.

Steve Grand Master

Steve

Posted
  • Author
Posted

Thanks for the replies, all sound good. so go the exhaust side adj cam gear and leave the VVT in place.

Rev210, I am seriously considering going to a 3L when the bottom end dies, and supercharger/turbo combo - just for something different. this will also mean the removal of the VVT.

For now I want to optimise what I have and then move on. I have been considering too many directions at once of late I think, so I just want to get the top end sorted first. And see where things take me from there.

Cheers

Steve

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