lukevl

Just wondering if the Rb20 and R25 lower intake manifold runners are the same? Because the Rb25 ones dip down in the middle two for equal length. I was wondering if the RB20 ones were all in-plane to make it easier to cut down. Thanks

Don't murder me but I'm pretty sure as the Rbs got newer, Nissan closed the lobe centres up. The early models ran very wide separation angles (Just like the VL turbo) but with newer models they closed them up gradually and increased overlap. By what you guys are saying the gains are had by retarding the exhaust cam- is this right? If so then you are doing what nissan did with the later model hence less power increase because they have already moved them to a lesser extent.

See through all this bickering, a lot of good points have come out. You just have to sift through some people's crap first

13_devil - No I would say that someone is doing just that. Posting stupid things directly slandering and challenging the other whereas other people question opinions instead of starting fights. Trust me mate, when you get far enough down the track you can tell who is something and who is nothing. JasonO - Someone is always going to give you different answers, and if people didn't bicker, maybe you would have an answer by now. Would it be the right one but?

Haha! Okay I'll have a go. First of all purely by visuals - the Greddy plenum has a lot more volume than the GTR plenum. So straight up I go for the GTR plenum because oversize plenums are so overrated. Look at the Cosworth stuff from the DFV days. Then if you go multi throttles its all about lag time people. Problem solved. You can just close the thread now guys

Hahaha! I've converted him! Viewers at home - I understand your concern about the arguing between these two fellas. It seems like its getting old etc. I can understand that you want the right answers to your technical answers and thats all. But face facts - you are never going to get just that on an internet forum. There are too many bandits out there thinking they know all. So what do you do? Well when you get to a point where you know a considerable amount more than the average Joe (Technical - automotive) these arguements get quite interesting because the people argueing are forced to bring out their real beliefs and open up, which really helps you decide wether they know what they are talking about or not. You have to do this for every user on every forum but once you figure out who knows what - the forums are quite useful. So basically after seeing 3 or 4 threads of these two its easy to tell which one knows something and which one starts fights to try and make it look like they are all conquering.

Agree with discoepotato. Very good statement about Nissan. So true as well. A lot of people think that aftermarket stuff is the be-all and end-all of car developement. None of these guys would have any idea what its like behind the doors of an OEM facility.

Trust me - it will work and work fine. You can tune the car to suit so I am not worried. I have heard flow test results from both plenums and I'll take the GTR one thanks. Have you ever heard of a GTR plenum flowing unevenly? No I don't think so. Q for Steve - Yes Zoom magazine found that it lost power in most areas, but can you tell me how that RB20 test applies to my motor? 3lt with modified cylinder head and GT35 0.82 housing? I'll give you a hint - there is no comparison.

Thank you for your opinion Steve. However I want multiple throttles and a front facing plenum that is not too large in capacity. Going for the Rb25 plenum and single throttle will reduce my throttle response not to mention the extra intercooler piping. Oh and it doesn't matter what you are doing - you have to look good doing it.

Yes Steve, but how do I get multiple throttles onto a Greddy plenum for my Rb25? Either way I'm going to have to do some fab. And I know the GTR plenum works well as a unit. Not sure about the capacity of the Greddy ones either. My car isn't being built for outright power but more so for low down torque/boost response.

i am getting rid of it. I have a GTR plenum and throttle bodies because the original plenum is one of the ugliest things around and I want multiple throttles really bad. It was either that or a Greddy plenum.

Theres positive feedback for you

hey SK- I have an early model Skyline Pump (Nose diameter and flat distances are the same) but the one concern I had was that ther wasn't enough overlap between the flats on the pump gear and the crank (RB30 crank). Have you ever seen these fail from this problem? Also what is the nose diameter difference (and distance between the flats) between the early and late 26 cranks? I assume its a few millimeters at least?

RPM is irrelevant- to a degree. They will bleed down easier with less oil pressure hence low rpm, but I don't think it will make that much difference. They will bleed down becuse they can't seal. SK - Totally agree about the seat height. I recommend CCing all chambers to check they are the same. Different CR = pain in the shfincter.

SK - What are those bends in the photo? They look Mandrel bends. I take it they are aluminium? Whats the deal they look alright.

Being a bucket type motor, the profile will be exactly thre same regardless of base circle size (to a certain degree. It makes effectively no difference.) If the base circle is still in the hydraulic range, then there is absolutely no problem grinding the camshafts. The reason camshafts are hard-faced is so they retain an almost standard base circle (About 0.25mm down in diameter) and they can go back in without any mods to the valve heights and followers. There is nothing wrong with a small grind like I suggested on the GTR cams to make them hydraulic. Nothing at all. Its safer than a lot of other options out there. I dare say that there would be no reduction in hardness of lobes either so its as good as OEM because after all they are OEM cams. Joel - Spring seat tension is set by the valve height and retainer design only. The 'stops' in the system are the valve on the seat and the retainer and collets.

Not that it really matters but for general info, the balance pipe links the wastegate feeds to help make sure both wastegates see the same pressure/flow whichever is more important. Better boost control and ensures one turbo doesn't spin a lot harder than the other. Thats my understanding of it. Good looking manifolds BTW

Niiice browny. Think of a profile as a series of radii corresponding with angle. If you lay a bigger profile over a cam, and start grinding the base circle grinds first and the last part to clean up (usually) is the nose of the cam. And like browny said, with the smaller base circle you have more lift. This is accentuated by the removal of ramps which instantly gives you 0.5mm more lift without taking the base circle down at all.

Don't be silly SK. You know how they work. they hold their position for a while but do leak thats why they need constant oil supply. Being a mechanical seal -Just two bits of steel with maybe half a thou (excuse my units of measurement) of clearance diameter- they leak oil slowly. No meachanical seal is perfect. But this is an important aspect of the lifter, they have to be able to bleed off some of the oil to accommodate valve growth. Also the force pushing on the lifter is spring pressure, but the force holding the lifter up is oil pressure x lifter internal bore area. Geez Louise, you have to be careful how you write things around you SK! :Oops:

If I don't get much interest soon, I will make my own manifold as I am pressed for time. Any of you boys out there keen?

You won't be able to noticeably linish the ramps off the lobe. One option is to get a light cam grind on them to make them hydraulic. If you did do that you would be able to improve the GTR profile by about 0.5mm in lift and 10 degrees or so at 0.050". It would be a goo dimprovement and the base circle would still be like 31.50mm or more depending on how similar the profiles are. This way you could run a hydraulic profile on the lifters and have a larger profile than GTR cams and they would have a new rubbing surface. All on the same hydraulic lifter with no mods. (I am assuming the hydraulics will pick up on 0.25mm travel) Before you ask, it would cost around $320 Inc. Tax. (Retail).

Theoretically they don't reduce in height. However they do, it just takes a while. So it doesn't matter what size the base circle is, they will not hold the valves open on the base circle. Thats why I said that it will hold the valves open after an over rev, but they will bleed down after a minute or so. Say a lifter has about 2mm or travel in its hydraulic range, you could have 4mm difference in base circle diameter and the valve timing and operation would remain unchanged.

Okay someone deleted the last one for some reason so heres the newy. 304 stainless steel, 6-1 style of extractors, 3mm wall thickness, high mount position, tail external wastegate monting flange (cut off and weld on your own adaptor), stainless flanges. The downsides I can see are: Not tuned length (No big drama for us lamo street boys) Wastegate does not merge into gas flow Looks like the turbo will sit very close to the rocker covers I haven't seen one myself so I don't know what the welding is like and how it looks in terms of positioning. I also don't know the diameter. On the plus side they are only $580 if we get 10! Extra $200 if you get 321 stainless (aircraft quality material). Luch, can you please fill us in on the diameter and the chances of getting a different style of wastegate pipe that doesn't require the gas to do a 180 in the flow to control boost?

I have seen a picture of this manifold and it looks quite good. The only issue I can see is the wall thickness. I prefer 1.6mm wall. BUt i am keen to do a group buy on this. Do I still have 10 people? $580 for 304 stainless.

How do you know they used GTR camshafts? You can't tell by looking at them so I am intruiged to find out where the verification was. Think about this - Lobe centre lines are the crankshaft position at maximum lift (essentially for a symmetrical lobe). This varies from a minimum (tight lobe centres) of about 100 degrees before/after TDC to a maximum of 120 degrees if its a stock V6 holden. For the RBs you wouldn't want to go out of the 102 - 114 range. Thats a total movement of 12 degrees. The ramps are in the viscinity of 80 degrees long total. How can 12 degrees compensate for such large ramps? HERE WE GO - Hydraulic lifters. The theoretical operation of hydraulic lifters is that they can increase their height (tip of valve to cam rubbing face) but can not reduce their height. They use a one way valve to let oil in and not out. This means that no matter how you prepare the lifters for installation, they will end up being the right height so they just touch the base circle (smallest radius on the lobe) after a minute or less depending on how good the lifters are. This means that they run ZERO tappet clearance hence no need for ramps. The lifters adjust their height accordingly to suit valve growth. So if you give your car a big over-rev and get valve bounce, the lifters will adjust to a point where the valves are slightly open and the car will run like a wrx for a minute or so until the lifters settle back down. Yes they leak oil, but only slowly. Anti pump up lifters (old school) leak fast and this is their purpose. I said theoretically because they do squash, but only by the amount i mentioned earlier as specified by the SAE. I dare say it is actually less because those figures are old and relevant to pushrod lifters which run higher spring pressure. So in short, how you prepare the lifters makes no difference to the cam operation. If you put too much oil in the lifters, they have a chance of snapping the cams. I have seen a few broken RB cams from installation. I prefer to only put a small amount of oil in because the oil pressure will take up the clearance quick enough anyway. Wow, i can't believe i got back into this arguement. Pardon my spelling, I didn't proof read it.