Jump to content
SAU Community

Recommended Posts

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

  • Replies 69
  • Created
  • Last Reply

Top Posters In This Topic

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

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

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!

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

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 -

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?

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • So, I put my boat on a boat. First of all, I'm going to come out and say it. Why is Tasmania not considered a holy goal, an apex that all road-legal modified cars go to, to experience? This place is an absolute wonderland of titanic proportions. If people are already getting club runs for once in a lifetime 30 person cruises to Tassy then I've never seemed to see it. It is like someone replaced the entire place with an idyllic wonderland for cars, and all of the people living there with paid actors who are kind, humble, and friendly. Dear god. After doing a lap of almost all of the place I've found that it's a great way to find out all of the little things that the car isn't doing quite right and a great way to figure it all out. All in all, I drove for 4 hours a day for a week and nothing broke. I didn't even need to open the engine bay. This is by all means a great success, but it has left me with a list of things to potentially address. I also now have a 3D printed wheel fitment tool which annoyingly hasn't got any threads in it to actually assemble it. I might be able to tape it together to check the sizing I actually want to use, but it'll likely involving pulling the shocks out to properly measure travel at least at the front, and probably raise the car while I'm at it, at least in the rear. I scraped on quite a few things and I'm not sure how else to go about it. I was taking anything with a bump at what felt like 89 degree angles. And address those 10 other tasks. And wash the car. God damn it is dirty. And somehow, the weather was perfect the entire time - And because I was on the top of Mt Wellington it turns out it was very much about to freeze up there. I did something I typically never do and took some photos up there in what must have been -10 and the foggy felt like suspended ice, rather than mere fog. If you own a car in Australia, you owe it to yourself to do it.
    • Damn that was hilarious, and a bit embarrassing for skylines in general 😂 vintage car life ey. That R33 really stomped. Pretty entertaining stuff
    • Hi, I have a r32 gtr transmission. Does any of you guys have an idea how much power it will hold with the billet center plate and stock gearset? At what power level and use did yours brake with or without billet plate? Thanks, Oystein Lovik
    • Saw this replica police car based on a Mitsubishi Starion XX parked next to a 'police box' (it's literally a box) in Hirohata, Himeji City in Hyogo prefecture the other day. It's owned by Morii-san who is a local Mitsubishi Starion enthusiast. According to a local radio station blog post, he always wanted to make a police car himself based on ones he saw in his favourite Manga comics.  As it's illegal to modify a car to look like a police car and drive on the road, Morii-san tried many times to get permission from Aboshi police station headquarters nearby. They refused initially by after they got tired of that they granted him permission. However, the car can only be displayed on private property and obviously can't be registered as long as the police livery is present. The car was completed at a cost of 1.5 million yen (US$ 10,000) in addition to the car cost. A location was chosen outside Hirohata Police box where the car can easily been seen from the street. Morii-san has two other Starion road cars, both widebody GSR-VRs.
    • Ah coolant overflow, previous discussions make way more sense now lol. 
×
×
  • Create New...