olie05 Posted January 6, 2005 Share Posted January 6, 2005 Aight heres my plan: I'm going to use the flange from the webbed intake manifold since it holds itself together and bolt on some velocity stacks (since the intake is aluminum and the velocity stacks most likely won't be aluminum so I cant weld it easily) and weld together a box to seal the velocity stacks. Then I will use a 240sx throttle body and cable set up. I want to know how big this box should be, the velocity stacks i've decided should be about as long as the stock manifold (after reading the other intake manifold post). This setup would place the injectors in the stock location, would I be able to run this on the stock ecu until I decide to go megasquirt? Oh yeah, where do I get velocity stacks this long with a bolt on flange? Quote Link to comment Share on other sites More sharing options...
johnc Posted January 6, 2005 Share Posted January 6, 2005 A rough rule of thumb is that for engines in the L6 displacement range the plenum should be a 1/2 liter larger then the engine displacement. For a 2.8L engine the plenum should have an air volume of 3.3L. Quote Link to comment Share on other sites More sharing options...
olie05 Posted January 7, 2005 Author Share Posted January 7, 2005 I'll keep that in mind when I start making the manifold, but where should i get the velocity stacks from? Quote Link to comment Share on other sites More sharing options...
Drax240z Posted January 7, 2005 Share Posted January 7, 2005 Try TWM induction for the stacks. They are pricy though. Quote Link to comment Share on other sites More sharing options...
olie05 Posted January 13, 2005 Author Share Posted January 13, 2005 I did some more research and found an excellent velocity stack website : its like velocity-of-sound.com or something like that. Anyways, the stacks Im looking at would likely be made out of aluminum, and the box would probably be out of aluminum or sheetmetal... Seeing as how I have very little welding experience and this is aluminum, could I get away with getting everything to close tolerences and JB welding it up? (Mosly for sealing) -Oliver Quote Link to comment Share on other sites More sharing options...
lilj Posted January 13, 2005 Share Posted January 13, 2005 nothing beats a real weld.. jb is when you cant manage anything else.. and you definately don't want to make a performance part w/jb weld. my .02$ -Jon Quote Link to comment Share on other sites More sharing options...
Guest mongrel Posted February 15, 2005 Share Posted February 15, 2005 A rough rule of thumb is that for engines in the L6 displacement range the plenum should be a 1/2 liter larger then the engine displacement. For a 2.8L engine the plenum should have an air volume of 3.3L. A plenum of that size would seriously strangle the engine and would not perform noticably better then the stock manifold. According to Prof. Blair the plenum volume should be between 1.5 to 4.5 times the size of the engine. A lot of people build thier plenums no larger than the engine. They lose in both power and respons. Do not build a plenum for a 2.8 liter engine smaller than 4.2 liter! Unless it´s for a tractor off course... Quote Link to comment Share on other sites More sharing options...
johnc Posted February 15, 2005 Share Posted February 15, 2005 A plenum of that size would seriously strangle the engine and would not perform noticably better then the stock manifold. Funny... Jim Thompson at Sunbelt built the intake manifold for my 320hp 262ft. lb. NA engine 3L engine and he used the exact rough rule of thumb I mentioned above. I don't know of anyone that considered that engine a tractor engine... Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted February 15, 2005 Share Posted February 15, 2005 Mongrel, Who is Prof. Blair? You may be refering to boosted applications. The intake designs for NA and Boost are differant. John's formula is legitamate for NA applications. The original poster should specify his application. Quote Link to comment Share on other sites More sharing options...
olie05 Posted February 15, 2005 Author Share Posted February 15, 2005 I was recently looking into lost foam casting. If I made a manifold out of that it would be pretty cool too. Quote Link to comment Share on other sites More sharing options...
turbobluestreak Posted February 16, 2005 Share Posted February 16, 2005 Not to burst your bubble but casting is exspensive and why would you want to allow for the chance of casting inperfections when you could make a sheet metal intake that will be all smooth? tbs Quote Link to comment Share on other sites More sharing options...
olie05 Posted February 17, 2005 Author Share Posted February 17, 2005 Not to burst your bubble but casting is exspensive and why would you want to allow for the chance of casting inperfections when you could make a sheet metal intake that will be all smooth? Nah you didn't burst my bubble... It was a highly optimistic thought. I just saw a website of a guy doing it and thought it would be cool. ( I just wanna play with some melted metal! ) I have a feeling you thought about this when you were thinking of what to make the dohc heads with... -Oliver Quote Link to comment Share on other sites More sharing options...
Guest 75Turbo Posted February 21, 2005 Share Posted February 21, 2005 Here is a really odd idea that I had to try... I realized that my old N/A motor was in need of a better manifold. The Datsun runners were to short (according to my math their torque peak was around 7500RPM), to small diameter (I think around 3000 RPM TQ-peak), and the plenum appeared to small. I bought a used manifold and cut the injector portion off leaving approx 2" of factory manifold. Went to Home Depot and bought PVC tubing. Yep, PVC. The I.D. was very close to what I wanted... approx 2" for the runners and 4" for the plenum. I made the runners as long as possible while still allowing room for the plenum. Used regular PVC glue to assemble the plastic parts and JB weld to glue that to the factory piece (that mounts the injectors). There was a very noticable improvement in power at almost all RPM's. Much better mid-high range. I built the PVC version just to test my theory of runner size/length with no intention of keeping it. To my suprise, the manifold held up extreemly well and didnt seem to have any problems until a lean tuning error caused a backfire. That created a very lean condition (large hole in plenum). I then used the dimensions of the PVC manifold to build an aluminum copy. I cant remember the math for the length/size torque calculations, but could probably find it if your interested. Happy fabricating! Quote Link to comment Share on other sites More sharing options...
olie05 Posted February 21, 2005 Author Share Posted February 21, 2005 Cool info, 75turbo! I think I'll try that first before I do aluminum and sheetmetal. What did you use for the plenum? When you started talking about the pvc runners and plenum it sounds like you used a 4" diameter pvc pipe as the plenum... is that correct?! It would be very cool if you could post the dimensions of your project. Maybe pictures too! -Oliver Quote Link to comment Share on other sites More sharing options...
(goldfish) Posted February 22, 2005 Share Posted February 22, 2005 Suprising as it sounds some of the newer Merc. Cougars have plastic intakes. My dad's buddy was kinda bummed when he reported that he cracked it. of course I'm not saying they're made of pvc.... Quote Link to comment Share on other sites More sharing options...
olie05 Posted February 22, 2005 Author Share Posted February 22, 2005 I've seen pictures of 914 type IV engines and some of the fuel injection ones look like they have pvc runners from the heads to the throttle body, sooo... it can't be that bad right? -Oliver Quote Link to comment Share on other sites More sharing options...
mtcookson Posted February 22, 2005 Share Posted February 22, 2005 supposedly pvc is very bad to use on an engine... something like fumes are created from the heat that go into the engine and are bad for it or something along those lines. Quote Link to comment Share on other sites More sharing options...
Guest 75Turbo Posted February 22, 2005 Share Posted February 22, 2005 Ok, found some math... For runner length (which includes length of intake port) RPM=108,000/length OR Runner lenght=108,000/RPM 108,000 = 2nd resonance 97,000 = 3rd resonance 74,000 = 4th resonance 54,000 = 5th resonance The first resonance is too long to be feasable in a normal engine configuration. The manifold would have to be approx 30in long. The earlier the resonance, the stronger the signal. So tuning for the second resonance would give much better results than tuning for the 3rd or 4th. Runner diameter calculations - Cross Section = (RPM x Cyl volume)/88200 OR RPM = (Cross section x 88200)/cyl volume The math I used was for a 3.0 liter (diesel crank). The factory runner diameter is 1.25 which would be a peak torque of 3600RPM. I dont remember the lenght, but I believe it was around 9in (including 3" of intake port) which essentially means there is no resonant tuning being used. The 2nd resonance tuning is somewhere around 12,000 RPM. The 4th resonance is useable at 6000 RPM although its a very small gain by the time your at the 4th resonance. Something like a 10% improvement in torque for 1st resonance, down to 1% for 4th. My intake was 1.90 ID = 5500RPM and 13.5 in which made resonances at 8000, 7200, 5500 RPM. The overlaping of the 5500 RPM tunings mad a noticable "hit" at 5500 RPM and (I believe) the increasing strength resonances at 7200 and 8000 allowed the engine to rev extreemely well (it pulled to 8200) Hope some of that is usefull Quote Link to comment Share on other sites More sharing options...
Deep Posted February 22, 2005 Share Posted February 22, 2005 From what I've gathered, the manifold should be 1.5 X displacement for an N/A application and 2 X engine displacement for turbo or supercharger. Longer runners will help you more if you need low end and shorter runners will benefit you in higher rpms. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted February 22, 2005 Share Posted February 22, 2005 Longer runners will help you more if you need low end and shorter runners will benefit you in higher rpms. I hate this statement as it is untrue as written. (sorry Deep a pet peeve, nothing personal) Given the same diameter a shorter tube has a higher resonance frequency than a longer tube. This usually manifest itself as a power gain at specific rpms corresponding with the resonant frequency. Longer tubes also tend to have more laminar flow when approaching the head than short tubes do. The more turbulant flow in shorter tubes can benefit carb'd cars in particular in keeping the fuel suspended. All this info and a lot more is on this site somewhere in old posts, I know because I wrote it! As for plenum volume, there are lots of rules of thumb out there that are good to follow, but you need to get into your calculations in depth to come up with a hard number. Most rules of thumb aim for good throttle response based on a single TB design. ITB's have much more flexibility with their plenum sizing. Quote Link to comment Share on other sites More sharing options...
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