Guest Anonymous Posted January 11, 2002 Share Posted January 11, 2002 well i just felt like rambling some ideas i had past your guys' ears to see if i'm on the right path. since i have decided to do the twin turbo v8 i have been reading up on them as much as i can which unforuneately isn't a whole lot since i am always runnign around doing something or other. anyway, tell me if i'm right in thinking this. i had originally thought that boost PSI was what you want to increase as much as possible to get more power. the more i read i come to find out that it isn't quite that simple. i can do a performance modifacation such as port and polishing my head and say subsequently lose 2-3 pounds of boost but still increas my power output. just from the fact that the heads flow more VOLUME of air even if it is at a lower density I.E. PSI. which means that some of those people on the street claiming 25+ PSI of boost on their fourbanger but only manage 250HP to the ground could just very well translate into meaning that they have one hell of a bottle neck in the airflow somwhere in their setup. i was just wondering if that is along the right lines or am i just taking a shot in the dark here? if i'm am going the right way here wouldn't that mean that any gain in CFM flow of the air to the motor would quantify your power gain at a given PSI level? oh i finally managed to find my maximum boost book (could'nt find that thing for the life of me) and plan on starting to read it again later tonight, and again and agian and agin till i'm am completely comfortable with the math behind the principle of forced induction. thanks for your opinions/answers i apreciate it. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted January 11, 2002 Share Posted January 11, 2002 i Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 12, 2002 Share Posted January 12, 2002 I would say that you have turned a very important corner in your understanding of forced induction. You are on the right track - boost pressure is more of a symptom than a cure. The pressure is what results from trying to force a given CFM through a given restriction. If you have less restriction, you can have the same flow at lower boost pressure. The flow is really what determines how much power you make. This is more obvious with a supercharger than a turbo, since with a turbo the wastegate controls boost pressure by modifying the flow. Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted January 12, 2002 Share Posted January 12, 2002 Give that man a cigar - he's gettin' it! Now, if I could just get about a zillion Mustang bench racers to understand this. Ever hear some of these guys talk? i'm runnin' 15lbs of boost and you're only running 10 - I'm faster dood. When you sit down and look at the pullets, what compressor they';re running, the CUBES, and other things you can find out that the 10lb guy is making WAY more power. It's just not as obvious from his boost gauge Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted January 12, 2002 Share Posted January 12, 2002 yeah for me! at least now i have a beginning of a understanding of how to get the most out of my turbo applicaion. i just have to make sure the the airflow to the cylinders is as good as i can manage to make it. and once this is acomplished i will then focus on the boost pressure level. know that i think about it if i set up the 360 as best as i can i bet that even under 20 PSI of boost will be enough to leave one hell of a skidmark stain in my shorts. its kinda funny how in a N/A motor a good port and polisha and a nice induction setup can be very benifical to its output but on a turbo the induction setup would bring very large gains if it is setup right. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted January 12, 2002 Share Posted January 12, 2002 Great thread. The basic principles of an internal combustion engine does not change whether it is NA or forced-induction. How much mass can you pack in the combustion chamber at compression? The beauty of forced induction is that you have compression in the turbo/s-charger, then that compresed mass in forced into the cylinder and compressed. Think about the actal compression ratio at that point! Can you say detonation, if you are not careful? BANG...and people are amazed that a forced induction engine can make torque equal to an NA twice its size. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted January 12, 2002 Share Posted January 12, 2002 all a motor is, is an air machine. The more air, the more power. But one thing that always puzzeled me is if 14.7 psi is all that will "push" the air into the turbo inlet, than how can so much more air be forced into the cylinder vs the same 14.7 psi pushing the same air into the carb (which has a bigger cross section opening). Especially with the sanctioning bodies that restrict the turbo inlets to less than 2". I guess it's because while the intake valve is closed, the air is still being pumped into the intake vs a NA motor that depends on the valve being open to draw air into the carb. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted January 12, 2002 Share Posted January 12, 2002 here this may help http://www.turbofast.com.au/javacalc.html http://www.m-p-c.com/engtech.htm http://www.turbofast.com.au/turbomap.html http://www.turbofast.com.au/Drag.html http://www.turbofast.com.au/TFcompB.html http://users.erols.com/srweiss/tablehdc.htm http://www.turbofast.com.au/flowmaps.html http://home.kscable.com/ssutton/miata/engine/toluene.html http://www.gnttype.org/techarea/misc/octanebooster.html http://ourworld.compuserve.com/homepag....ist.htm http://www.racepartsstore.com/pistons.html http://members.home.net/rogue15/ heres some helpful info; http://www.racetep.com/turbo.html http://www.skulte.com/turbo.html p-c.com/engtech.htm http://www.gnttype.org/techarea/engine/enginepage.html http://www.vectorbd.com/peugeot/turbo.html http://www.turbonation.com/ Quote Link to comment Share on other sites More sharing options...
blueovalz Posted January 12, 2002 Share Posted January 12, 2002 You are obviously developing a reputation for our on-line reference material coordinator. Thanks Quote Link to comment Share on other sites More sharing options...
blueovalz Posted January 12, 2002 Share Posted January 12, 2002 I can't speak to port volume, but the smaller cams appear to be better for a forced induction motor rather than a larger one. And I believe your premise about the less effecient ports holds as well. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted January 12, 2002 Share Posted January 12, 2002 just for your info, on a naturally asperated engine the port flow max,s out at a valve lift of about 1/3 of the intake valves dia. so having a port the has a cross sectional area the is much larger than the valves max flow area only serves to slow the intake port air velocity, thats why huge port sizes tend to loose low and mid range torque but because supercharged engines do not use or need high port velocitys dependant on the negitive pressures of the piston moveing down into the cylinder and the draw caused by the rapidly departing exhaust pulse in the header tube from the previous fired cylinder the larger size ports help to funnel more fuel air mix into the cylinder with less restriction/back pressure. now this also means that because the cylinder filling is accomplished by mechanically forceing the air into the cylinders the exhaust valve must close earlier to trap that charge before its pushed out the exhaust and the exhaust must open earlier to give more time for that extra cylinder voluum to blow down so as not to fight the intake charge when the intake valve opens.this change in valve timeing also applies to the intake valve in that because the charge need not wait for the cylinder to start drawing the intake valve can open earlier and close later to max the cylinder filling but to avoid pushing excess fuel out the exhaust the LSA (lobe center angles)are spread wider (112-116degs) on blower cams as opposed to (105-110)on most non-blower cams or put another way dedicated supercharged engines need huge ports and valves wide LSA cam timeing and relatively mild valve lift and durration numbers. BTW cams designed for use with nitrious normally work well with supercharged engines, heres more info, http://www.blowerdriveservice.com/tech.htm http://www.procharger.com/ http://www.paxtonauto.com/ http://www.vortechsuperchargers.com/ http://www.turbotechnologyinc.com/ Quote Link to comment Share on other sites More sharing options...
Guest super280z Posted January 13, 2002 Share Posted January 13, 2002 Blueovalz one of the main reasons "big" cam's dont work as well is that in the upper rev's where a N/A motor would make power because of a longer valve dwell time, a FI motor is going to loose that precious cyllinder pressure because of the length of duration on the bigger cam. cyllinder pressure has just about everything to do with your powerband. (does that even come across??) V8zfreak, you're right. CFM in any FI setup is one of the KEY elements to make good power. keep up the good work and let us know how the setup progresses. BTW Grumpy you are the man, happy rodding everyone, Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 13, 2002 Share Posted January 13, 2002 quote: Originally posted by blueovalz: But one thing that always puzzeled me is if 14.7 psi is all that will "push" the air into the turbo inlet, than how can so much more air be forced into the cylinder vs the same 14.7 psi pushing the same air into the carb (which has a bigger cross section opening). My take on this is that although you are correct in stating that ~14.7psia is available at either a carb inlet or a turbo inlet, the actual pressure differential across the carb is not 14.7 psi. On the contrary, for a carb at WOT, the manifold pressure is very close to atmospheric (zero vacuum), so the resultant flow through the carb is only due to maybe 1 or 2 psi of pressure differential at most. My guess is that the compressor blades cause a much higher pressure differential at the compressor inlet, hence the higher airflows. On the big cams thing - the assumption that long overlaps don't work well because of the fuel/air mix getting 'blown through' only holds for supercharged engines. With a turbo, the opposite happens, because the exhaust manifold pressures are almost always higher than the intake manifold pressure. This is due to the backpressure produced by the turbine. The problem with long overlap cams and turbos is actually due to exhaust reversion. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted January 13, 2002 Share Posted January 13, 2002 heh in light of my newfound angle on this forced induction thing i have decided that i might want to try my hand at designing my own intake setup. let me brake down my current idea so far. i will take a 4 foot length of 4" round aluminum tubing then cut it in half cap off a end on each one, then weld a flange on to the opposite side of the tubes, and drill it to mount, say a 5.0 throttlebody. then i will take those two tubes lay them parallel to each other and weld in smaller tubes to connect my "plenums" together. i figure this way that if on turbo ends up pushing a bit more than the other on it will still even out once it gets to the plenums. kinda like a H pipe on exhaust setups. then from each plenum i will have four runner tubes come off of it and connect to another flange meant to connect to my heads. do you understand what i'm getting at? i'm not too sure if i was clear enough. but i think the twin throttle bodies should make it nice since there cheap, plentiful, easy to get a hold of, and since i run two of them it will flow more. it will be a royal PITA to work up some throttle linkage between them though i'm sure. Quote Link to comment Share on other sites More sharing options...
pparaska Posted January 13, 2002 Share Posted January 13, 2002 Scottie, all, I've been wondering, is port flow (as measured on a flow bench as much as a factor when you have forced induction? It'd seem that having large volume ports that don't flow extremely well on a flow bench wouldn't limit power/torque as much as they might on a NA engine (both with FI, to take carb signal out of the picture). Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted January 13, 2002 Share Posted January 13, 2002 look here http://www.hogansracingmanifolds.com/ http://www.wilsonmanifolds.com/smform2.html either company custom makes those type intakes all the time (btw adding a pressure/flow ballance tube between the two feed plenums in your design will help hp output Quote Link to comment Share on other sites More sharing options...
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