Will 272/272 Cams Idle Different To 272/264

[jet_r31]

the camshaft plays a role in allowing 10,000rpm..but so does the back end of a turbo..272 won't make power to 10..i doubt your

turbo will either before it chokes on its own backpressure.

Ive never built anything like that and never will, but id be thinking 290+duration and GT47 T6 frame turbine would be in some form of ballpark

To the thread starter., ill try again..so these cams are reverse staggered..ie 272 inlet 264 exhaust....

YOUR NOT WORRIED ABOUT THE REVERSE STAGGERING?,., not at all?, just the idle

cheers

darren

[JH32]

Lift is volume, duration is overlap, both have different effects on engine and turbo charistics

Manual or auto ?

Capacity ?

Turbo?

Do you have a thread of your own ?

He's got about 80 threads of his own, all asking the same question or a variation thereof.

[MJTru]

Yes I started like two threads on the topic of cams and preparing my cylinder head. Sorry if this one seems to have more replies than mine. I have not made 80 plus threads on this topic. Lol

Ok how about I list what I have done to my cylinder head and then each of you can give me some insight on cam selection or use oem set up. I wanted to do 10k off the line but its obvious thats not going to happen without a serious learning curve. Whats funny is the only reason I even entertained the idea is because I have a r33 with just a lot off bolt on parts and launch that at 9200rpms. With stock internals. But I do know its not good to do and the power will drop off. I also know that its way more stress to raise the rpms than to raise the boost at lower rpms. Rpm's kill straigh up.

Well as for the cylinder head the first mod I did was clean up the bowls under the valaves. In doing so I followed instructions from couple of head guys that menstioned the same things. There was even a step by step procedure I found with photos and all. It was about just Not opening the ports more about cleaning up the machining marks and making the air have less turbulence under the valves. So I did so I made nice transitions in the bowls and removed the ridges that factory machining left behind. Next I removed the humps in the exhaust ports. This took a while to figure out if there was enough material left in the walls. Every drag guy I spoke to said if im running custom turbo manifilds to get rid of them. To make sure I had an old rb26 head and chopped it in pieces. Theres more than enough material left over. About the same as the opposite side with no hump. Next I went with supertech springs and titanium retainers. The specs on the springs are as follows. Well ill just take a photo of the specs. I also got the titanium retainers to match. Next I should mention thats its a brand new cylinder head. I did the valves my self no to mention there all oem valaves. now that im thinking of it 10k was ambitious from my part.

So now that you guys know my head setup which in the past I've never done anything to the heads and made good usable power. What you think what should I do. Im going to drop the cams I know this much.

Edited June 9, 2014 by MJTru

[MJTru]

Oh and I spent like a day shimming the head. It was a fun process and would love to do it again. All of this is from information I got from this site. And there isnt to much guys that uses and do as well as update there progress that I know of on this site. In depth of course. I never could have post photos without a big hassle. This app makes it so much easier.

[XKLABA]

10k isn't a hard ask providing everything is up to the task, as for cams, get a set of Tomei 280 x 11.5mm super highs, will give you the velocity to run those RPMs as well as the volume to make a puck load of power while your up there, this cams will be a pig down low for general driving and make the turbo lazy between gears so better suited to auto application

The 260 x 10.8mm will go to 10k but that would be the end if there range, they will make the car better lower in the rev range and between gears and still good power for most of the rev range

I remember one of your threads now, I believe it started with " I'm a street racer " or something to that effect and which point I moved on and so would a lot of the people on here who know something as street racing over here is very much frowned on and anyone that would get on a open forum stating that must be a dumb arse

[MJTru]

Kml. I know what you mean, I wouldnt state it if I could have gotten in trouble. But to brake it down for you. I actually live in the states but race in the Bahamas. Over here we get all the RHD cars that I like. racing here in the bahamas isnt as strict as the states not even close. Shit over here we can even drink and drive not saying its a good thing to do now. All im saying is its way easier to managae the risks as everyone knows everyone.

As for your help with the cams setup ill try the 260 with 10.8 mm lift after I research it a little bit more. The cylinder head is a new area for me and as these guys keep bring up topics its becoming more clear to me. My experience with it like everything else I will just have to learn through my actual setup. I hate having to try setups without having an idea of how it will work. I usually think up of a solution and see how it comes out.

Thanks mate.

Edited June 9, 2014 by MJTru

[MJTru]

10k isn't a hard ask providing everything is up to the task, as for cams, get a set of Tomei 280 x 11.5mm super highs, will give you the velocity to run those RPMs as well as the volume to make a puck load of power while your up there, this cams will be a pig down low for general driving and make the turbo lazy between gears so better suited to auto application

The 260 x 10.8mm will go to 10k but that would be the end if there range, they will make the car better lower in the rev range and between gears and still good power for most of the rev range

I remember one of your threads now, I believe it started with " I'm a street racer " or something to that effect and which point I moved on and so would a lot of the people on here who know something as street racing over here is very much frowned on and anyone that would get on a open forum stating that

must be a dumb arse

Do you think the valve spring that I choosed will work with the 260 at 10.8mm lift cams. ?? Tomei mention that ill need to use there lifters with that cam setup. Which is no problem.

[XKLABA]

Super tech springs are fine at that, IIRC they are happy till just after 11mm

Tomei Procams have a 30mm base circle so the buckets they say you need to run have 1mm added to the top of them making them thicker where the lobe hits so you don't have to run to thick of a shim

[MJTru]

Super tech springs are fine at that, IIRC they are happy till just after 11mm

Tomei Procams have a 30mm base circle so the buckets they say you need to run have 1mm added to the top of them making them thicker where the lobe hits so you don't have to run to thick of a shim

Ok sounds great so far. Ill place the order tomorrow but start the car up and see how the cams I have right now works untill they arrive. Then do a comparison of the two. Ill order the 260 -10.8 mm lift cams for both intake and exhaust. Then the lifters as you mentioned. Next ill have to reshim the head so measure and order shims accordingly, But before I install them ill double check if the springs will suit the setup. Im planning on running the oem gear box but making arrangements to install a dog engagement gear set from PPG. This should also help with gear changes and turbo spool. I want to keep the 4wd system and dont know of any companies that can beef up the stock oem transmission for drag racing.

Thanks for you help mate. I have so much money in this damn motor it would be a shame and by no means will I give up until im happy. Im looking for a 10s pass.

Edited June 10, 2014 by MJTru

[XKLABA]

Contact Unigroup Engineering, they have a set of 260 x 10.8 cams that are stock 32mm base that use the factory buckets and only require shimming, have you had the head relieved for high lift cams ?

Don't fark around with a replacement gears set, just get a sequential, you'll be glad you did in the long run and will make car faster

[MJTru]

Contact Unigroup Engineering, they have a set of 260 x 10.8 cams that are stock 32mm base that use the factory buckets and only require shimming, have you had the head relieved for high lift cams ?

Don't fark around with a replacement gears set, just get a sequential, you'll be glad you did in the long run and will make car faster

Wow I have alot to learn. No I haven't gotten the the head relieved and as your saying this its making sense in my mind. When you say that you're meaning that the bigger cam lobs on the camshafts are going to hit the aluminum on the head before it comes in contact with the lifters right????.

Damn. Ill have to pull the head off again to do that. I wounder if there a cam setup thats a little bit easier than the 260 at 10.8 lift. IIRC the max lift without relieving the head is 9.5mm

So what setup would you recommend using with what I have? using stock buckets. Keeping in mind I just want to drag race the car. But im limited to the lift. ????

I wouldnt mind dropping the rpms eather.

Edited June 10, 2014 by MJTru

[GTSBoy]

One of the reasons for the Procams to have a smaller 30mm base circle is that you can get more lift without having to relieve the head (as much - I don't know where the limit is). The tip of the lobe is not as far away from the centreline of the camshaft as it would be on a stock base circle.

[XKLABA]

Right, smaller base circle means lobe doesn't extend out as far, I have always believed 9.5 and in my experience with 26 is what I have found but very recently someone I know tried Poncams with 9.15 lift and they fouled

I have Type R poncams in my RB2630 and made 460kw @28psi at all 4 and ran 10.8 in a full weight R34 (1661kg + 105kg for my fat arse ) with 24psi, but I don't rev past 7200rpm cause that's where the cams end and the rear housing become a restriction

Tomei make a 260 x 10.25 with a 30mm base which would just clear but IMO its too much duration for the lift, 30mm is the diameter so 2mm less base give 1mm more clearance

[MJTru]

Wow ill have to pull the head to use a fly cutter to relief the cylinder head. From what I have heard the max lift is around 9.5 all depending on the cams base circle.

So let me understand somthing here. The duration of the cam alone wont make power so matching the duration and lift is the science. ?? A cam with lots of duration but not enough lift will not move as much air killing the turbo. So matching of the two is whats important.???

Now as the duration and lift providing match right can lead to more rpms and power production with sustainable hp higher in the rpms. Keeping in mind you will loose a bit down low as the duration and lift you goes up. ???

In saying this how does the stock oem gtr heads stack up?? Whats the max power and rpms that oem head would do before you loose power. RPM and power. ???

This is a great discussion.

Edited June 10, 2014 by MJTru

[GTSBoy]

You need increased duration to support operation at high revs. You need increased lift simply just to get more air into the engine at any revs. Operating at high revs gives less time for air to flow in each cycle, hence why you need more duration - but it also means more lift helps too.

As I said in my PM to you, setting up a head is in fact a very scientific process - or at least it should be. Set your targets, then work out what has to be done to make those targets happen. The serious guys will work out the required cross section of the ports to get the velocity right, will size the bowls and work out whatever porting changes are required to get the air to flow nicely across the valve head. They'll work out whether they need high lift or not to get the flow they need and will design the ports and seats to work with that decision. They will even take into account the expected boost level as that will affect density and hence velocity.

The cam does not specifically affect port velocity except that a higher lift cam will reduce the pressure drop across the valve, enabling more air to flow and hence lifting the port velocity. What you actually do is size the port to the flow you want (as I said above) then select the cam to achieve that flow goal. Remember also that peak flow rate and velocity is not the same thing as the average or total flow for the inlet event and depends on the cam profile and how well the valve bowl flows at low lifts vs how well it flows at high lifts.

[Ben C34]

You need increased duration to support operation at high revs. You need increased lift simply just to get more air into the engine at any revs. Operating at high revs gives less time for air to flow in each cycle, hence why you need more duration - but it also means more lift helps too.

As I said in my PM to you, setting up a head is in fact a very scientific process - or at least it should be. Set your targets, then work out what has to be done to make those targets happen. The serious guys will work out the required cross section of the ports to get the velocity right, will size the bowls and work out whatever porting changes are required to get the air to flow nicely across the valve head. They'll work out whether they need high lift or not to get the flow they need and will design the ports and seats to work with that decision. They will even take into account the expected boost level as that will affect density and hence velocity.

The cam does not specifically affect port velocity except that a higher lift cam will reduce the pressure drop across the valve, enabling more air to flow and hence lifting the port velocity. What you actually do is size the port to the flow you want (as I said above) then select the cam to achieve that flow goal. Remember also that peak flow rate and velocity is not the same thing as the average or total flow for the inlet event and depends on the cam profile and how well the valve bowl flows at low lifts vs how well it flows at high lifts.

That post is way too helpful and intelligent.

I liked this thread more when it was about lumpy idles......

Edited June 10, 2014 by Ben C34

[MJTru]

Hmmmm. I think for me to start working things out in increments GTSBoy how does a stock rb26 head stack up. Whats the max rpms before power drops off. I think we need a thread for people to compare there results using different head setups. It would be hard.

Seems to me like rb26 bottom ends can spin really fast to 10k and stay with in safe mean piston speed even better with forged internals. 5000 fpm is what most guys say is the rule of thumb to be safe. At 10k the block is about 4800 fmp. It seems like the real potential is in the head. For this reason I wont stop until I get at least some more rpms. If not 10k at least 9. Lol

[MJTru]

Also ill have to send the head out have it ported. I really try to do most things myself. and never thought about opening up the ports. I always though with forced induction I could just pack the air in there. Lol.

Im coming across sites that sells complete heads and setups for quite some cash. I guess I need to start somewhere. Now I understand that I wont get it right the first time, but I've build so mush rb motors, but always left the heads stock. Now it's time I start learning the tricks or what the heads needs. So I know all the duration and lifts on the stock cams that will be my base line. Ill try a few things using what we speak about here. Them I feel this will pave my path to understanding how to make more power above the stock rb26 redline.

I really try to stay away from major machining work other than valve angle jobs and so forth. Sending the head out to have the ports machined wont probably happen at this time.

But ive always appreciate guys that can take a certain condition and extract the most out of that given condition. It kind of separate the guys that just read the stuff and the ones that have true understanding of how these stuff works. Its kind of like having knowlage about somthing and having no experience which can be call wisdom. By no means am I being disrespectful here. Just explaining myself. I will have to start out slow at this head science, and learn as I go. I just wish I could find the optimal setup for what I have done so far. Cause it seems like when I go all out ill just find something more to do. Lol.

Thanks for all your input. Its way better than a lumpy idle.

Edited June 10, 2014 by MJTru

[GTSBoy]

Yuh, don't port anything until you are absolutely sure that you a) need to, and b) really really know what you want and how to achieve it.

[MJTru]

Ok. That sounds like a plan. I was interested in higher rpms. But i think I should stick to my 600hp to 4 wheel goal and if I can get that at a reasonable rpms then do so. Which means these cam still have to go. Can stock rb 26 cam sustain 600hp. I also upgarded the rod bolts and piston pins like you said so if I wanted a little bit more power I would be on the safe side. A little bigger cam may help at lest say like 252- 9.15 I can do the relief myself. Or just stick to the stock cams.

Edited June 10, 2014 by MJTru