Guest Simon Posted August 1, 2002 Share Posted August 1, 2002 Hi all, I am putting a RB25det into my Z and just after some information. Because of the clearance problem would it be hard to make up a new plenum and have twin throttle bodies etc.. then there is no intake going over the top of the motor, the plenum will not hit the top of the bonnet. and i can have a better flowing intake. i have heard that a larger plenum is can add power? any info would be good Cheers Simon Quote Link to comment Share on other sites More sharing options...
RB30-ZED Posted August 1, 2002 Share Posted August 1, 2002 Hi Simon, yes a bigger plenum can give you more power, but only if it wasn't correct to start with. We all seem to think the factory get it wrong , but the truth is the RB25DET plenum is not to bad at all, it may look like the RB20 but there are some differences. The RB26 style manifold would make it an easier job and help keep some heat from the inlet plumbing. The Standard manifold will fit under the bonnet, ive got about 15mm clearance at the closest point. There are photos of the manifold in my home page link . Good luck with the project. Steven Quote Link to comment Share on other sites More sharing options...
Guest mongrel Posted August 1, 2002 Share Posted August 1, 2002 On plenumsize prof. Blair advices that the size should be within 1.5 to 4.5 times the engine displacement. Going smaller will result in power penalties and larger will result in exessive spoolup and bad throttle response. The idea behind plenums is that it shall even out the pulses traveling up the primaryintakerunner and create a smooth flow through the secondary intakerunner and airfilter. Thats why it needs to be of considerable size. For good flow velocitystacks should be used, they will improve flow through the ptimary intake runner with up to 18%. Velocitystacks is, I think, the best way to improve any intake, provided thay can be fitted, that is. Quote Link to comment Share on other sites More sharing options...
RB26DETT Posted August 1, 2002 Share Posted August 1, 2002 Hi all, it will depend on how you make your engine mounts and sump that will determine if the factory RB25DET will fit under the bonnet. a forward facing inlet manifold will make the job of plumbing the intercooler easier if you are using a GTR style I/C. I noticed that you're in western australia, there is a guy who is currently selling a RB25DE (non turbo but still twin cam) with forward facing intake, modified sump,5 speed gearbox and simplified wiring, all for $1200 (drop me an email if your interested and I'll pass you the contacts) If you are making an intake you need to have it at least the volume of the engine (2.5 litres) and also be careful not to starve or favour certain cylinders of air, alternatively you can get an aftermarket GReedy intake to suit an RB25DET. Good luck and all the best!!! Quote Link to comment Share on other sites More sharing options...
stony Posted February 28, 2003 Share Posted February 28, 2003 A complaint we often hear when people install a bigger cam(s) in their Japanese engine is that they don't get the power increase they were looking for or actually seem to loose power on a stock engine. Have you ever wondered why Japanese engines have such a high power to displacement ratio? It's because they have a high volumetric efficiency, or VE. The intake manifold, throttle body, and everything else for that matter, are perfectly matched for the engine they're used on. The intake mani is designed to flow air at a certain velocity at a certain engine speed for that particular engine to maintain an overall balance between low, mid, and high rpm performance. The only way to truly get substantial power out of high performance Japanese engines is to flow more air. Not try to increase the VE. If the engine already has a peak VE of better than 90% from the factory, you have to move the rpm point at which the engine achieves peak VE (peak torque) up in the rpm band. Higher duration cams do this, but if the intake mani is designed to flow best with the stock engine, it'll stall (choke) in the higher rpm range you're looking for. The system will be unbalanced and you will not gain the full potential of the cam(s). At Motorworx, we build intake manifolds to match each individual engine. This is the only way to ensure that your manifold will compliment the rest of your system. There are a few high volume manufacturers making intake manifolds for Honda's and what not, but they only make one manifold for each type of engine. They claim horsepower gains on the stock engine just by changing the manifold. Yes, you may gain 10 horsepower or so, but you will loose some torque and your car will be slower. Toyota, Nissan, Honda, etc. spent a ton of time and money developing the intake manifold on your car. For best all around performance with a stock engine, there is no better intake than the stock one. The after-market manifolds may work well with a cam(s), but which one? What is the rpm range on the manifold? Look in any high volume manufacturer's catalogue for small block chevy intakes. There are hundreds of manifolds made for this engine. They list the rpm range where the manifold works and from there you can determine the size cam that works best with it. There is no "one size fits all" with any part of the internal combustion engine that affects airflow. If you are going to buy a pre-made after-market intake manifold, make sure to ask the manufacturer what it will do for your setup. Don't be fooled by "horsepower" claims. Horsepower is just a number. Ask how much quicker or faster it will make your car. taken from my friends site in okinawa ... motoworx Quote Link to comment Share on other sites More sharing options...
Guest sooley Posted March 6, 2003 Share Posted March 6, 2003 i am fitting a custom plenum to my RB25DET converted 240z. Its a 6ltr and Im using an XF Falcon Throttle body. Its going to make the job of plumbing a breeze. I priced the Trust brand plenum and at $2500 I thought I go a custom joby. $800 if you want one. Will take a while to make though Quote Link to comment Share on other sites More sharing options...
BRAD D Posted March 8, 2003 Share Posted March 8, 2003 You could just run a cowl hood like Scottie GNZ, or mod your stock hood. Just an idea. Quote Link to comment Share on other sites More sharing options...
fl327 Posted March 9, 2003 Share Posted March 9, 2003 you guys talk like the old haynes 240z repair manual. Quote Link to comment Share on other sites More sharing options...
Tony240ZT Posted March 10, 2003 Share Posted March 10, 2003 Where can I purchase velocity stacks for an okay deal? Has anyone found a creative alternative than buying them new from a performance shop? Possibly forming them out of fiberglass? I'm sitting here looking at a carbon fiber 90 degree ram tube on http://www.speed-technology.com/ I can't find a price, but I'm betting these are more than $30 a peice. If I could take a chunk of that craft stiff spunge stuff that you stick floweres into, form the inner part of the ram tube fiber glass it up, put flanges on the bottom to bolt it up then I could probably have them for pretty cheap, if I sit down, take the time to do it. If I can get a set of aluminum velocity stacks ready to weld in for $60 or so I'd probably go for it though. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.