Guest Anonymous Posted September 17, 2000 Share Posted September 17, 2000 I have some questions about cylinder heads that I have never seen answered. Here they go. 1. If the head can flow 250+ cfm per port, that is 1000 (250 X 8) cfm right? How could the engine realize this benefit without a 1000 cfm Carb and an intake which also flowed 1,000 cfms? 2. If the head flows 250 cfm at say .500-.600 lift but less than a stock head at say .450 why is this good since the valves spend more time at less than peak lift? 3. My point is; are these heads as beneficial as the Mfgs. claims? I have never seen any published flow comparison when the entire intake track is flowed. Air cleaner to valve. And it seems to me that this is what really matters. I started this thought process when comparing Brodix, AFR, vortec, and ZZ4 fast burn heads. Please try to educate me. I am trainable. ------------------ He sent me to get the Jedi Quote Link to comment Share on other sites More sharing options...
Guest Drewz Posted September 17, 2000 Share Posted September 17, 2000 I can be long winded but this is a huge topic! Point #1 would be true if the valves were open at the same time. In real life with out of tune carbs the figures that manufacturers put out are maxed on the dyno with god knows how many techs and hours of playing. I have bolted on a set of Dart "big valve heads" and W O W!!!!!!!!! And I really mean wow. The problem with a lot of big heads is that the port is so large that there is no low end flow ergo no power ergo no torque. This is an unstreetable condition. Especially if you have no stall. Bigger is not as important as matching a combination of parts to acheive one final balanced goal. I think a few other guys on here are running the same Dart cast iron big valvers that I am. Int. 2.0477 and ex. 1.64? Not positive about the ex valve size. Old age.(LOL) Point #2 If you are running a roller cam with an agressive ramp you are spending more time at the max. adv. lift. That is why a hydraulic cam may not produce the power that a roller cam with the same spec. may provide. This gets simpler as you educate yourself BEFORE buying a bunch of parts and wondering why doesn't my car run stronger and can't idle on its own. Asking questions is the best way to try to avoid sometimes expensive mistakes. Everyone has an opinion about this that and the other but you have to choose what is going to work best with your expectations. In the end only you can do your best to build what you want. OOOOOOO I am cramping up. Can't reach beer ahhhh!! ------------------ The only stupid question is one you wanted to ask but never did!!! Drewz Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 18, 2000 Share Posted September 18, 2000 quote: Originally posted by Drewz: I can be long winded but this is a huge topic! Point #1 would be true if the valves were open at the same time. In real life with out of tune carbs the figures that manufacturers put out are maxed on the dyno with god knows how many techs and hours of playing. I have bolted on a set of Dart "big valve heads" and W O W!!!!!!!!! And I really mean wow. The problem with a lot of big heads is that the port is so large that there is no low end flow ergo no power ergo no torque. This is an unstreetable condition. Especially if you have no stall. Bigger is not as important as matching a combination of parts to acheive one final balanced goal. I think a few other guys on here are running the same Dart cast iron big valvers that I am. Int. 2.0477 and ex. 1.64? Not positive about the ex valve size. Old age.(LOL) Point #2 If you are running a roller cam with an agressive ramp you are spending more time at the max. adv. lift. That is why a hydraulic cam may not produce the power that a roller cam with the same spec. may provide. This gets simpler as you educate yourself BEFORE buying a bunch of parts and wondering why doesn't my car run stronger and can't idle on its own. Asking questions is the best way to try to avoid sometimes expensive mistakes. Everyone has an opinion about this that and the other but you have to choose what is going to work best with your expectations. In the end only you can do your best to build what you want. OOOOOOO I am cramping up. Can't reach beer ahhhh!! The things you say I understand and agree with. Thats my point. If the carb and intake will flow only X amount of CFMs, what good does it do to put on heads that will flow X +? It seems that most heads are reported to outflow the other members of the intake tract and are not the bottle neck associated with total flow. What heads did you have prior to the installation of the Dart Heads and how quick does your car currently run? What type of intake and carb are you running? Quote Link to comment Share on other sites More sharing options...
Guest Drewz Posted September 18, 2000 Share Posted September 18, 2000 the engine was out of a 75 vette so it only had 1.94's fo rthe heads. I was running a new style 750dbl. pumper on a holley strip dominator intake with elec. ign of course. I did not do any time slips as there is no local track(3 hr drive). Too much air has never been a common problem since people still think a 650 dbl. pumper should feed a 350 easily over the 400 hp. line. Of course you need air and fuel setup properly and equally to get thew most out of the setup you are running. I think a BG. 750 holley is a great choice for most small blocks. I am now hooking up a dual TBI. tunnel ram on my 350. This should drop my low end torque and also make the dramatic statement I want to make. I am tired of the sleeper thing and want to stand out. Also My engine will and has revved out at over the 7000 rpm. range so the tunnel will be put to use. Just my thoughts and opinions. ------------------ The only stupid question is one you wanted to ask but never did!!! Drewz Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 18, 2000 Share Posted September 18, 2000 It's important to remember what flow ratings are.... They are generally flow rates at some set pressure drop. The ultimate flow will be lots higher, but there's not enough energy to pump air into/out of an engine as fast as is physically possible, so a typical pressure drop is chosen and the flow measured at that set pressure drop. Your engine can't pump enough air to get the maximum flow that is physically possible through a carb(or intake ports or air filter or whatever). Keep in mind also this leaves room for number games..... ie. company X measures the flow of their manifold/carb/heads at a pressure drop of Y, while company A makes an identical product, but they measure it at a pressure drop of B. So you have the same part with different flow ratings. Cams are often measured differently as well. Any measurement is correct if you have the luxury of defining the measurement convention! ------------------ Morgan morgan@z31.com http://carfiche.com http://z31.com Quote Link to comment Share on other sites More sharing options...
MYRON Posted September 18, 2000 Share Posted September 18, 2000 Not to sound too much like an idiot here but, I bought parts that I got a screaming deals on.. Dart heads 2.05/1.60,215cc intake runners, ported and matched to a brodix hv1 pro bracket intake. how does 800.00 bones for the set sound NEW IN BOX!! the heads also had 1.550 springs with 200lb seat pressure. I got a Crower solid roller cam and lifter set .567 lift 284 dur.. On special from Summit. A custom hp4150 carb 830cfm.. for 625.00..... I did no research on what to buy other than what I could find in my pocket... LET ME TELL YOU, THIS COMBO WORKS!!!!! The only cars that have outran me had slicks,9" rear ends with 4 links, ladder bars and alot of cubic inches. Quote Link to comment Share on other sites More sharing options...
Guest Drewz Posted September 19, 2000 Share Posted September 19, 2000 Myron are your heads cast or alum.? I am using the same one, it sounds like. These heads do add a huge amount to my engine. Sounds like a killer combo and killer price. Too bad you are not closer so we could go for dig or two. ------------------ The only stupid question is one you wanted to ask but never did!!! Drewz Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 19, 2000 Share Posted September 19, 2000 [bubafett, I hope you don't mind, I editted this message so that the quote and bold ended after DrewZ's post and before your response. Pete (pparaska)] quote: Originally posted by MYRON: Not to sound too much like an idiot here but, I bought parts that I got a screaming deals on.. Dart heads 2.05/1.60,215cc intake runners, ported and matched to a brodix hv1 pro bracket intake. how does 800.00 bones for the set sound NEW IN BOX!! the heads also had 1.550 springs with 200lb seat pressure. I got a Crower solid roller cam and lifter set .567 lift 284 dur.. On special from Summit. A custom hp4150 carb 830cfm.. for 625.00..... I did no research on what to buy other than what I could find in my pocket... LET ME TELL YOU, THIS COMBO WORKS!!!!! The only cars that have outran me had slicks,9" rear ends with 4 links, ladder bars and alot of cubic inches. Thank for the info. I know you car is fast as you have posted actual time slips. My currently runs high 7.70's to low 7.80's in the eight. My current combo is 750 holley dp, vic jr., chevy ported and polished 292 turbo heads with 2.02 valves, comp cams extreme energy cam 294 grind hyd dual pattern, 10.25 compression 1 3/4 full lenght headers and full length exaust 3000 stall, turbo 350 trans and a 3.90 r200 lincoln locker. I got a "screaming deal" last week. A 350 short block with manley flat tops, 6 inch eagle rods, a roller cam too big for me, fluid damper, and flexplate. and new Brodix track 1 heads with 2.08 valves. $1,100.00 What gears and transmission are you running? Also do you have a part number on that cam? It too seems to be working. What do you think the Brodix heads would do for my current combo? I want to put these heads and a roller cam in my car. [This message has been edited by pparaska (edited September 18, 2000).] Quote Link to comment Share on other sites More sharing options...
Michael Posted September 19, 2000 Share Posted September 19, 2000 My understanding of the flow measurement techniques is that cylinder head flow numbers are always obtained from tests on a flow bench, never on a running engine. On the flow bench, the head is subjected to a fixed pressure drop. Generally that number is 28†of water, which corresponds to approximately 1.0 psi. Each port is tested individually. The valve is held open at a set opening height, and flow volume measurements are taken for a sequence of opening heights. Generally, the intake manifold and engine block are missing; they are “modeled†by plastic pieces which attempt to approximate inlet and exit conditions at the cylinder head ports. And this is all done at steady state conditions and room temperature. So there is no combustion going on, no valve motion, no port-to-port crosstalk, etc. It seems to me that flow rate numbers are only useful as a relative comparison between different heads in the same catalog, and not as an accurate guide of what a particular head will flow in a particular engine. For instance, for my streetable big block, I can choose an “oval port†head that is rated to flow 140 cfm (intake) at 0.200†valve lift, 270 cfm at 0.500†lift, and 290 cfm at 0.800†lift, or rectangular port heads that flow 120 cfm at 0.200â€, 280 at 0.500â€, and 400 at 0.800â€. My cam tops out at 0.504†intake lift, so the rectangular port head’s high flow numbers at 0.800†are useless. But the oval port head’s better flow at low-lift will hopefully – hopefully! – increase low-end torque and throttle response. On the other hand, recent experience has shown that 450+ ft-lbs in a 2700 lb car and 3.27 first gear does not call for a lot of low-end torque. Probably the OEMs have the capability to measure flow in the ports while the engine is running; for example, by laser-doppler velocimetry. Otherwise they’d have a tough time designing such things as intakes with variable length runners. But I would be greatly surprised if any of the aftermarket manufacturers had comparable imformation. Making guesses is a big part of the hot rod hobby! Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 19, 2000 Share Posted September 19, 2000 Knowing flow rates is not necessary for making tuned intakes/exhausts. Flow rate does not matter, only engine speed and configuration matters(To determine patterns and time between events) as far as tuning intake/exhausts is concerned. ------------------ Morgan morgan@z31.com http://carfiche.com http://z31.com Quote Link to comment Share on other sites More sharing options...
MYRON Posted September 19, 2000 Share Posted September 19, 2000 BUBAFET, You did get a "screaming deal"!!! those brodix heads are awesome. My buddy has some that were massaged to flow 335cfm.. His 383 Camaro runs 6.50's in the 8th, It pulls the wheels off the ground without the juice... My cam is a solid roller .567 lift with 1.65 ratio rockers. I am running a 3.54 diff with a stock converter.. I have a big stall 10" B&M converter and I hated it for street driving so i too it out.. When you put that combo in your car, be carefull because that will be tons of power that the ujoints will have a hard time holding up to. Myron [This message has been edited by MYRON (edited September 19, 2000).] Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted September 20, 2000 Share Posted September 20, 2000 Here's a chart to convert all measurements to the same pressure head: http://www.centuryperformance.com/afrconversion.htm Quote Link to comment Share on other sites More sharing options...
jeffp Posted October 15, 2009 Share Posted October 15, 2009 what you guys need to be looking at is the swept volume of the cylinder/piston assemblies. That will tell you exactly what air will flow into the cylinder under normal conditions. That is why the longer stroke and over bore are popular. For a N/A engine that is the key, so going with this wild cam and wild set of heads wil be not such a good fit to the lower rotating assembly. Now that was the basics for all of the combinations. The other things you need to look at is the volumetric efficiency of the engine, and this is where you will be able to make additional gains from the engine. The use of a tunnel ram intake manifold will help you out with this. You can push the VE of the engine over 100% provided you select the correct cam, intake and carb. Also keep in mind all of your efficiency will depend on the rpm's of the engine as well. John Lawlor has a book the engine math book that would really be beneficial for you to read, and just a good read for anyone and as a reference book so you don't have to remember all of the formulas. It sufices to say to install a 650 double pumper on a SB engine that really will only injest 600CFM is a waste of money and efficiency as example. There are some really cool parts out there at good prices, but if you don't have the lower rotating assembly to support the components then again you are wasting your money on parts that will not perform as well to components that are properly sized/designed for the complete build. Engine building gentlemen starts at the mathematical level and the engine is then designed around your math computations. Most of the really trick big port/valve heads are much better suited to forced air induction, and boy you can really make some power that way. Myself, I don't like guess work, I never have approached an engine build that way, decide what you want for power and build accordingly. Bigger is not always better, design on the other hand will always be the winner. Quote Link to comment Share on other sites More sharing options...
Drewz75t Posted October 15, 2009 Share Posted October 15, 2009 9 years ......... Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 15, 2009 Share Posted October 15, 2009 jeffp wins "Search Button User of the Year" award! Quote Link to comment Share on other sites More sharing options...
DeepV Posted October 15, 2009 Share Posted October 15, 2009 wow... back from the dead! Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted October 15, 2009 Share Posted October 15, 2009 (edited) I have some questions about cylinder heads that I have never seen answered. Here they go. 1. If the head can flow 250+ cfm per port, that is 1000 (250 X 8) cfm right? How could the engine realize this benefit without a 1000 cfm Carb and an intake which also flowed 1,000 cfms? the ports only flow that, rated flow at MAX cam LIFT and only a single cylinder pulls air from the plenum at any one instant, in most cases if your select a carb thats about 2.5 times the max port flow rate youll have, more than enough flow to feed the engine http://forum.grumpysperformance.com/viewtopic.php?f=52&t=322 http://forum.grumpysperformance.com/viewtopic.php?f=52&t=333 2. If the head flows 250 cfm at say .500-.600 lift but less than a stock head at say .450 why is this good since the valves spend more time at less than peak lift? IT MAY NOT BE, it depends on the rest of the parts in the combo and the, cam, gearing etc. [/b 3. My point is; are these heads as beneficial as the Mfgs. claims? I have never seen any published flow comparison when the entire intake track is flowed. Air cleaner to valve. And it seems to me that this is what really matters. I started this thought process when comparing Brodix, AFR, vortec, and ZZ4 fast burn heads. Please try to educate me. I am trainable. ------------------ He sent me to get the Jedi LOOK THRU MY DATA BASE, its there, as a resource to answer questions http://grumpysperformance.com/ http://forum.grumpysperformance.com/viewtopic.php?f=55&t=858 Edited October 15, 2009 by grumpyvette Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted October 16, 2009 Share Posted October 16, 2009 (edited) you might want to keep in mind that carbs are flow rated at 1.5 inches of mercury, heads at 28" of water and that anyone who has ever watched a vacuum gauge, will tell you the readings fluctuate rapidly, under most conditions and vacuum tends to vary with the cam,used the rpms the engines running,throttle blade angle, displacement and intake design,exhaust scavenging,ETC. in most cases there factors are at least, mostly or on occasion, partly understood well enough that theres formulas and charts that can be used to define probable results, that parts selection will result in to a reasonable degree. Edited October 16, 2009 by grumpyvette Quote Link to comment Share on other sites More sharing options...
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