Anthony Posted July 31, 2012 Share Posted July 31, 2012 Trying to take a slightly more scientific approach to my engine build, I've been reading up on airflow and volumetric efficienciesMy thinking is, if I can calculate my engines maximum airflow I can then estimate its maximum power potentialFrom this, I can then identify the bottlenecks and restrictions in the system and improve on themThis will help the engine work more efficiently, and free up more power with less stressesDoes anybody have any airflow figures for various engine components?Maximum engine flow?Cylinder head flow?Inlet manifold flow?Carburettor flow? Link to comment Share on other sites More sharing options...
Anthony Posted August 1, 2012 Author Share Posted August 1, 2012 Some initial assumptions.....100% VE (volumetric efficiency) can be calculated as follows.....100%VE = (Cubic Inch Displacement X RPM) / 3456100%VE = (122 x 7000) / 3456100%VE = 854,000 / 3456100% VE = 247CFMSo, a standard 2.0 litre engine will flow 247cfm at 7000rpm if volumetric efficiency could be made to be 100%I've heard and read that it takes approximately 1.5cfm to produce 1hpSo, if1.5cfm = 1hp247cfm = 165hpSo, these very rough calculations show a 2.0 litre engine will flow upto 247cfm, and can produce 165hpSince these engines don't produce this power they obviously provide less than 100% volumetric efficiency, and have bottlenecks/restrictions in the systemWho's worked out where and what these restrictions are, and how they can be overcome? Link to comment Share on other sites More sharing options...
esxefi Posted August 1, 2012 Share Posted August 1, 2012 unless you have countless hours on a free flowbench i would go with recomendations from this and other forums,any engine will only produce its maximum potential at a given rpm with a combination of the correct parts(intake system,head mods,cam choice and timing and exhaust system.this is not exhaustive though so s'cuse the pun)it is widely regarded that to obtain over 80hp/ltre from a 2 valve engine is a good result.'freeing up power with less stresses' is a contradiction in that to produce more power the engine will be under more stress.these engines like many others were a compromise of power over tractability and fuel consumption so by design they are what they are.100% ve is not the ultimate goal,with carefull modding and matching of components you can obtain more than this but at the price of driveability,do you want an engine that produces high power at say above 5500rpm or slightly less power but more torque through a wider rev range?even some of todays modern? 2valve engines only produce around 75hp/ltre,the latest ls v8 series in the corvettes is around this,although emissions play a big part in the final power output.how often are you going to be driving at 7k rpm? :) Link to comment Share on other sites More sharing options...
rotoflex Posted August 1, 2012 Share Posted August 1, 2012 Sheesh, I just put the screws back where the pictures in the books said they were supposed to go. Link to comment Share on other sites More sharing options...
Anthony Posted August 2, 2012 Author Share Posted August 2, 2012 I've heard that a 150 stromberg will flow upto ~84cfmSo, fitting three of them would provide a maximum of 252cfm, meaning they would no kinder be the restrictionBut, I've read that the manifolds aren't very efficientAlso, I've heard people say the firing order of the 6 cylinder engines isn't good for triple carbs, as the intake pulses wouldn't be evenly spaced outie;Firing order 1,5,3,6,2,4Would give carb pulses atFront, Rear, Middle, Rear, Front, MiddleI can see that's not evenly pulsing, but it is an issue of any kind?I note the Jags have the same firing order, and they use triple carbs Link to comment Share on other sites More sharing options...
Saltddirk Posted August 2, 2012 Share Posted August 2, 2012 Anthony,Whatever it is you are having, i'll have 2 kg please ;D ;DYou have to get your 252CFM of uncompressed air to the engine, not easy if you take into account all the restrictions you have under the bonnet, Try to have a unrestricted even flow of laminated air without turbulences to the carbs would be your first priority.Dirk Link to comment Share on other sites More sharing options...
Anthony Posted August 2, 2012 Author Share Posted August 2, 2012 ;D I get a little carried away at timesWhat would you recommend to get air to the carbs?What's wrong with the original airbox as a starting point?Turbulence, restriction, or both?Obviously I couldn't use that with triple carbs, but I could use that as a basis Link to comment Share on other sites More sharing options...
Mr Elsie Posted August 2, 2012 Share Posted August 2, 2012 1903 wrote: ;D I get a little carried away at timesWhat would you recommend to get air to the carbs?sDriving it down a country lane, windows open Link to comment Share on other sites More sharing options...
Saltddirk Posted August 2, 2012 Share Posted August 2, 2012 The lemans cars, more out of necessity because they used the longer webers, took the air from inside the wheel well.Have a look under the bonnet and try to imagine how the air has to travel to reach the carbs when you are traveling forward. Obviously you want to try getting the air from the front where it is helped by the car speed and you want as little obstructions as possible. A nice straight ducting will do. Turbulence eats up energy and thus slows down the air, with a result of less reaching the carbs.It is a bit like a low grade turbocharger really.Original air filters are also an obstruction, the air has to travel upwards first then sideways before it can enter the carbs, you can improve this by different filters and or ram pipes...Not easy but all little things help, CheersDirk Link to comment Share on other sites More sharing options...
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