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Best place to source mild cams for the RB25det quickly and cheaply

rev210

By rev210,
in Engines & Forced Induction

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Sydneykid Grand Master

Sydneykid

Posted
Posted
OK so the longer the duration the later power will be in the rev range and a lumpier idle. Is there any disadvantage from going higher lift ?? 8.5mm on my 264's seems abit low. Would there be much advantage from going to 9.5mm lift? Without upgrading springs that is. Power comes on very hard at 6000rpm with the 264's. I wouldn't want it any later. My head is also majorly ported. Is higher or lower lift better suited to a ported RB25?

Sorry for all the questions but Julian's 21st Century Performance book doesn't help much.

Hi Boosted, I posted thsi a while ago and I think it answers your questions....

-------------------------------------------------------------------------------------------

Hi guys, it's been a while since we had a thread on camshafts. Camshaft upgrades need to be considered, not for the max power increase they give at one single rpm point, but for the improvement in average power over the rpm range that you intend to use. A few rules of thumb that I use;

If you intend to use 7,000 to 9,500 rpm, something around 272 to 288 degrees would be the go. For 5,500 to 8,000 rpm, around 260 to 272 and for 4,500 to 7,500 rpm then 248 to 260 is the go. That's a simplification, but you get the idea.

I should point out that you need to be realistic in your rpm choice, most people grossly overestimate their rpm usage and then are disappointed with the result.

So much for timing, now moving to lift. I have a personal philosophy that says go for the highest lift you can get with the timing as per above. You need to be aware that anything over 9.5 mm may require machining of the head to clear the lobes. It’s not a big job, a couple of minutes per lobe with the die grinder is all it takes. Can be done in the car, if you are careful with the swarf. In my opinion, anything over 10 mm will require upgrading the valve springs and changing to solid lifters in RB20/25’s.

Lastly, I never use camshafts that have a smaller PCD than standard, they put too much side load on the buckets. You can get offset followers, but why go to the expense when you can get standard PCD camshafts that don’t need them.

--------------------------------------------------------------------------------------

Hope that helps

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BOOSTD Mentor

BOOSTD

Posted
Posted
each wheel should be 360 degrees with 7.5 degrees per tooth.

Each cam wheel turns twice in relation to the crank....so 720- I am so confused. If each tooth is 7.5 degrees than 4 degrees retard relates to ~4mm, but if each tooth is 15degree than ~2mm is 4 degrees.

Someone please give me a definate. Going off the HKS Cam gear markings. 2mm(two marks) equals 4 degrees, But, on my OS cam gears 2 marks equals 4mm..........Ahhh So this 4 degrees retard equats to what... I read from another thread warpspeed said that 15degrees per tooth was correct.

help pls

BOOSTD Mentor

BOOSTD

Posted
Posted
Hi Boosted, I posted thsi a while ago and I think it answers your questions....

-------------------------------------------------------------------------------------------

Hi guys, it's been a while since we had a thread on camshafts.  Camshaft upgrades need to be considered, not for the max power increase they give at one single rpm point, but for the improvement in average power over the rpm range that you intend to use.  A few rules of thumb that I use;

If you intend to use 7,000 to 9,500 rpm, something around 272 to 288 degrees would be the go.  For 5,500 to 8,000 rpm, around 260 to 272 and for 4,500 to 7,500 rpm then 248 to 260 is the go.   That's a simplification, but you get the idea.

I should point out that you need to be realistic in your rpm choice, most people grossly overestimate their rpm usage and then are disappointed with the result.

So much for timing, now moving to lift.  I have a personal philosophy that says go for the highest lift you can get with the timing as per above.  You need to be aware that anything over 9.5 mm may require machining of the head to clear the lobes.  It’s not a big job, a couple of minutes per lobe with the die grinder is all it takes.  Can be done in the car, if you are careful with the swarf.  In my opinion, anything over 10 mm will require upgrading the valve springs and changing to solid lifters in RB20/25’s.

Lastly, I never use camshafts that have a smaller PCD than standard, they put too much side load on the buckets.  You can get offset followers, but why go to the expense when you can get standard PCD camshafts that don’t need them.

--------------------------------------------------------------------------------------

Hope that helps

Hi sydneykid, thanks for the info. What in essence exactly would going from 8.5mm to 9.5mm lift on the same duration cam make to power. Would it make no difference to off power band? How much extra power would be expected?

Cheers matt

Craved Grand Master

Craved

Posted
Posted
Each cam wheel turns twice in relation to the crank....so 720- I am so confused. If each tooth is 7.5 degrees than 4 degrees retard relates to ~4mm, but if each tooth is 15degree than ~2mm is 4 degrees.

Someone please give me a definate. Going off the HKS Cam gear markings. 2mm(two marks) equals 4 degrees, But, on my OS cam gears 2 marks equals 4mm..........Ahhh  So this 4 degrees retard equats to what... I read from another thread warpspeed said that 15degrees per tooth was correct.

help pls

sorry boosted

i think i may have been confused last night- and still am.. now i wanna know for sure..

so we've got each wheel which will have a total of 360 degrees...

after just having the engine apart, i noticed that the wheel on the crank is much smaller than those on the cams... so when taking into consideration the stages of the engine you would need one revolution of the crank to activate the inlet side cam.. then another to activate the exhaust side... which would mean that the crank has 2 revolutions to the each cam gears one..

so it looks to me now that you were right with 720 crank degrees for each cam...

conformation will definately be appreciated!

Sydneykid Grand Master

Sydneykid

Posted
Posted
Hi sydneykid, thanks for the info. What in essence exactly would going from 8.5mm to 9.5mm lift on the same duration cam make to power. Would it make no difference to off power band? How much extra power would be expected?

Cheers matt

Sorry Matt, I am not sure I understand the first question, "Would it make no difference to off power band?"

Let me guess, you are asking about off boost performance. Well we have an RB25DET in an R34 GTT that makes more power EVERYWHERE from installing Tomei 260 Poncams (they work with the VVT). On boost, off boost, even at idle, it makes more power.

As for the second question, the average power increase from 4,000 rpm to 7,000 rpm was 30 rwkw with a max power increase of 18 rwkw. It starts to build boost 500 rpm earlier and reaches full boost (1.3 bar) 300 rpm earlier. The car feels alive to drive, it responds quickly to throttle inputs whether on boost or off.

I have never back to backed 8.5 mm versus 9.5 mm lift cams, but what I can say is the higher lift extends the high rpm power without decreasing the low rpm. The result is you end up with a wider power band, so average power is probably up 10 to 15 rwkw, but max power is maybe 5 to 10 rwkw up.

Hope that helps

Sentric dancer Collaborator

Sentric dancer

Posted
Posted

hey sydney kid,

Iam looking for cams and camshafts for my rb25det soon. Is it ok if i pm at the time and ask you for advice. Iam marvelled at your indepthness into modifying cars ( i have spoken to you before. )

Thanks

Sentric -

BOOSTD Mentor

BOOSTD

Posted
Posted
Sorry Matt, I am not sure I understand the first question, "Would it make no difference to off power band?"

Let me guess, you are asking about off boost performance.  Well we have an RB25DET in an R34 GTT that makes more power EVERYWHERE from installing Tomei 260 Poncams (they work with the VVT).  On boost, off boost, even at idle, it makes more power.

As for the second question, the average power increase from 4,000 rpm to 7,000 rpm was 30 rwkw with a max power increase of 18 rwkw.  It starts to build boost 500 rpm earlier and reaches full boost (1.3 bar) 300 rpm earlier.  The car feels alive to drive, it responds quickly to throttle inputs whether on boost or off.

I have never back to backed 8.5 mm versus 9.5 mm lift cams, but what I can say is the higher lift extends the high rpm power without decreasing the low rpm.   The result is you end up with a wider power band, so average power is probably up 10 to 15 rwkw, but max power is maybe 5 to 10 rwkw up.

Hope that helps

Thankyou Sydneykid, that helps alot. Were the 260 Poncams 8.5mm lift?

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