1vicissitude Posted January 25, 2014 Share Posted January 25, 2014 Have any of you ever tried fitting the greddy style rb26 plenum onto a triple weber setup? The rb26 throttles have a DCOE flange if I'm not mistaken. At first glance it looks like it could work as a nice air box for the triples, but I'm not really sure if the spacing is correct. Quote Link to comment Share on other sites More sharing options...
T-Bone028 Posted January 25, 2014 Share Posted January 25, 2014 We're you looking to pressurize for a turbo application? Pretty sure TWM still makes an airbox for triples. Personally though, with coated headers and a heat shield, my webers stay relatively cool to the touch. Quote Link to comment Share on other sites More sharing options...
madkaw Posted January 26, 2014 Share Posted January 26, 2014 http://forums.hybridz.org/topic/104821-nissan-cai-for-triple-mikunis/?hl=%2Bnissan+%2Bcai Try something like this Quote Link to comment Share on other sites More sharing options...
1vicissitude Posted January 26, 2014 Author Share Posted January 26, 2014 (edited) We're you looking to pressurize for a turbo application? Pretty sure TWM still makes an airbox for triples. Personally though, with coated headers and a heat shield, my webers stay relatively cool to the touch. Honestly, just kind of curious. The thought did cross my mind. IMO a heck of a lot nicer looking than the HKS surge tanks too. These plenums can be had on ebay for well under $200 shipped. While I haven't checked, my guess that is that is at least 1/3 the price of the TWM plenum based of past dealings with the company. I've seen instances where a well designed plenum on various N/A ITB setups actually adds horsepower. I'm not sure if this occurs from some sort of smoothing effect, cooler air, or because the under hood air flow in those cars was poorly distributed, but as example I have seen built 4age blacktops pickup 7-10whp across the range by using a well designed plenum. Decently substantial when your talking about 160-170whp engines. http://forums.hybridz.org/topic/104821-nissan-cai-for-triple-mikunis/?hl=%2Bnissan+%2Bcai Try something like this That post says he was $250 into the project all said and done. These are more affordable and actually have a smoothed airflow, like a trumpet, leading to the throttle. My assumption would be the rb26 plenum should flow much better than a cobbled together valve cover. It shares many characteristics with what I have learned to be a well designed manifold. Of course this is just an assumption, but then again it is a direct knock off of a $2,000 plenum as well. However, the rb26 manifold was designed for pressurized airflow so who knows how it will do in a N/A setup. Like I said, I'm just curious if anyone has used these before. I'd prefer not to buy a $200 paper weight. NVM the rb26 is not dcoe, adaptors would need to be made. Lame. Edited January 26, 2014 by 1vicissitude Quote Link to comment Share on other sites More sharing options...
madkaw Posted January 27, 2014 Share Posted January 27, 2014 "Cobbled together valve cover" OUCH! Quote Link to comment Share on other sites More sharing options...
1vicissitude Posted January 27, 2014 Author Share Posted January 27, 2014 "Cobbled together valve cover" OUCH! Ah I didn't mean it sucks by any means. It looks great and the idea is ingenious. I'd call anything "cobbled together" that is made out of part laying around. Quote Link to comment Share on other sites More sharing options...
Xnke Posted January 27, 2014 Share Posted January 27, 2014 If you're looking to pressurize carbs, get a box designed for it. You will need an application specific part. They are not cheap. Just slapping a plenum over some side-drafts and throwing boost at it will result in very poor drivability and very difficult to impossible tuning. If you aren't pressurizing the carbs, that plenum will likely be too small. The reasons for an airbox like that are to provide air from a cooler source, which is what i would say the HP gains come from...sucking 150F air compared to pulling 70F air. With an ITB application you need the airbox to appear "infinitely large" to the individual intake runners, so the plenum volume needs to be cylinder volume*2 at an absolute minimum and you need to be able to re-fill the volume as fast as possible to minimize disruptions to the other cylinders. The tuned-length runner system needs to see an "infinite volume" to get a well-defined discontinuity at the runner mouth, which is what reflects the induction wave back down the runner. Please keep in mind the "infinite" parts of the above are assuming we're being theoretical. The "infinite" parts need to be quite large compared to the size of the system, but not truely infinite, in actual practical installations. Quote Link to comment Share on other sites More sharing options...
1vicissitude Posted January 27, 2014 Author Share Posted January 27, 2014 (edited) If you're looking to pressurize carbs, get a box designed for it. You will need an application specific part. They are not cheap. Just slapping a plenum over some side-drafts and throwing boost at it will result in very poor drivability and very difficult to impossible tuning. I understand what you are saying, but If this manifold had worked (it doesn't without an adapter) it looks many times better than the HKS or cartech boxes. When the only application specific options are antique from the dawn of aftermarket turbo charging, surely you can't think they would have been better than this plenum had it worked? Heck, it looks a heck of a lot better than the racetep or TWM boxes as well. Edited January 27, 2014 by 1vicissitude Quote Link to comment Share on other sites More sharing options...
madkaw Posted January 27, 2014 Share Posted January 27, 2014 How are going to bolt that to the carbs? That base plate would have to be modified greatly or you will have to make something else. Even if you got the base to bolt to the webers, you might not have enough room for the plenum. The HKS type 2 plenum actually flowed well. The TMW box can't be pressurized - even at 400$$$$ Quote Link to comment Share on other sites More sharing options...
Xnke Posted January 28, 2014 Share Posted January 28, 2014 Yes, the old "ugly" HKS type 1 and type 2 and SK Compo-Turbo boxes worked MUCH better than that empty pretty thing. The cartech box is the same as this RB plenum...an empty box. They don't work well. You need to be able to diffuse the airflow into the plenum, plus you need a slightly higher reference pressure for the float bowls and you also need to be able to control the pressure gradient...so you either need to fuss with modulator rings or a properly designed dual-plenum manifold if you want to run blowthrough carbs. It's be very heavily discussed here on the forums...and both the CFD analysis AND the practical experiance agreees....the new empty plenum boxes DON'T give as good a result as the old, apparently "ugly" boxes. Like someone else here says: "But Carbs are Easy!" Quote Link to comment Share on other sites More sharing options...
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