Cam duration - new idea/thinking

Well I'm notsaying this is reinventing the wheel but it's certainly going against the trend...

On SF a user called Poggie (Chris) has suggested that (especially on non stock turbo'd Supra's) we stagger the cams...the other way round from normal.

Basically he is saying a 272in and a 264ex - with the intake cam opening 2degrees later than stock and the exhaust around stock timeing - you should get the most efficient intake and exhaust system. No/minimum overlap so no gas reversion and a full intake of nice pressurised air.

Basically by keeping the exhaust cam on a shorter duration the exhaust gasses should travel faster out of the cylinder helping spool. I'm getting with this setup it would be best to go for the JUN cams as they all feature the same lift (9.3mm's) (the HKS ones are 8.7/9/9.3) and you want the lift on the 264 to further enhance gas velocity.

The thread is here...

The guy's website is here...

And here is the important quote

Let say you run a very efficient turbo that will give you a pressure drop ratio over the engine of 1.4 meaning that if you boost 10 PSI the pressure in the exhaust is now 14 PSI.

 

At overlap when the exhaust cam is still open and the intake valve starts to open the minimum pressure in the combustion chamber is 14 PSI + and the intake charge is still at 10 PSI. Since the piston did not reach TDC yet and the intake charge pressure is less than the combustion chamber pressure hot combusted gases will start to move to the area with the lowest pressure which is the intake runner. Not only will this contaminate the intake charge but also heat the intake charge up. And it will keep on moving into the intake runners until the pressure in the combustion chamber is the same than the intake charge. Then only will the intake charge start to flow. This will happen when the piston is a couple of degrees past TDC. (You can not pump your tires to 30 PSI with 25 PSI pressure)

 

Open the 272 intake cam 2 degrees later and open the exhaust cam at the same time then a 272 exhaust would have open but close it +/- 2 degrees before TDC you will:

 

A: Be able to use peak cylinder pressures without a negative affect on engine performance.

B: Prevent reversion

C: Have a clean intake charge

D: Spool quicker and harder

E: Reduced Lag

F: Wider power band with good drivability.

 

I have used this cam setup with great success on many turbo charged engines and will not recommend something that I will not use on my own vehicle.

 

If done correctly good gain will be achieved.

 

Yes with stock valve springs one will most probably experience valve float but my point on the post was that the cam setup can and will allow for a very wide power band and the ability to rev the engine.

Can anyone else add any more thoughts on this? Critical or Supportive...

CW - your thoughts?

Makes sense if you think about it, will have to have a further read of his thread and site......

Intake cam with more duration and slightly retarded:

I had my old Kawasaki like this (tried several other combos and stuck to this one)

Similar timing I had on the Calibra.

So no one has tried this...would anyone consider it?

Thinking about it the Valcon system for the VVTi does this (to a degree) as it goes from 256in-272 through the rev range and with that mated to a 264ex cam you can have you're 272/264 combo.

Would love to try it...

TMC arent daft, why are the staggered the other way on the stock TT

I know, but the staggering of the j-spec was done to improve torque and spool on the j-spec as it had to produce less power.

The staggering isn't there AFAIK on the UK/US spec.

So is the stock setup completely compromised? I think so.

Not sure about that Alex. Would love to see you try though.

Think I'd need a stock head to play with...paging Mr. C lol

Alex just read that whle thread and its actually pretty interesting stuff mate.

Indeed...all the Yanks just bowed down to the guy and he sounds like a bit of a US CW...though our CW will still claim that he's a yank and won't know s**t

Open the 272 intake cam 2 degrees later and open the exhaust cam at the same time then a 272 exhaust would have open but close it +/- 2 degrees before TDC you will:

can anyone clarify what he means by the position of the 264 exhaust cam.

"open it at the same time as a 272"

assuming he's talking about the 1mm lift open time a 272 opens at 50 BBDC, 264 opens at 46 BBDC, so the exhaust cam wants retarding 4deg.

"but close it +/- 2 degrees before TDC"

a zeroed 264 will close at 2 BTDC so retarded by 4 degrees by the previous statement would mean it closes 6 BTDC

i think this is what he means??

Would be interesting to hear what CW has to say about this.

Sounds interesting and since I haven`t upgraded my cams yet could be an option if information is good.

JUN cams, hmmmmm, cossie