| considered flow testing the manifolds before and after the EH to get a comparison? Also could do the turbine housing by itself before and after. The results of flowtesting would at least give us some indication of a percentage increase in flow - just to see how much change there is with a smoother surface. I am inclined to think that EHing the exhaust components pre-turbine wheel (manifolds and turbine housing) should produce measurable results just about entirely across the RPM band. Main reason I think this is due to the fact that the combustion process produces more gas particles than what entered the chamber on the intake stroke. This means there is a significantly greater volume of gas exiting the motor than what went into it (given same pressure and temperature) 2C8H18 + 25O2 ~> 16CO2 + 18H2O This is the equation showing reactants to products of gasoline combustion. You have 2 molecules of octane and 25 O2 results in 16 CO2 molecules and 18 water molecules. Going from a total of 27 "particles" to 34 particles within a confined volume produces an increase in pressure and temperature, which push the piston downward, but it also results in a larger volume of gases as it expands into the exhaust manifold as compared to the volume of air entering the cylinder during the intake stroke. Good old PV=nRT dictates this. If you increase the "n" (number of particles), you will also increase the PV (pressure and volume). Additionally, because the exhaust gases are significantly hotter than the intake temperature, if you increase "T" (temp), it also increases PV. Two factors here are working to increase the volume of the gases in the exhaust . Taking this into consideration it goes to show that attention to flow within the exhaust side of the system will have better probability and greater quantity of improvement. The exhaust side of the engine has to move more volume than the intake side which translates to higher gas velocities through the exhaust components. Looking at the flow area within the manifold and turbine housing, even without measuring it, you can clearly see that it is significantly less than the pipes feeding the plenum, so we are dealing with really high gas velocities. Empirically, we are all aware of the improvements seen when Z's started upgrading to SZ manifolds back in the day. Larger cross sections, reduction of sharp transitions, very smooth surface finish, all played a role there. Mike Smith manifolds further improved on this simply because when casting the part you can entirely eliminate the very sharp corners at the merging points between the log and the runners. (we've also seen the benefits of 3" exhaust vs. 2.5" :)) Given this perspective I would feel confident in saying that there would be further improvements found by going even larger in cross section, routing the duct in a manner that further reduces the hard-angle merges of port to log, even going so far as moving away from the log style and collecting all 3 runners at the turbine flange, and also extrude honing the part. I think there is still worth-while power on the table for further development of this exhaust component. Then add in more attention to the turbine housings; cleaning up the parting line flash, transitioning the inlet runner into the wastegate port, smoothing out the humps just below the inlet flange, opening up the inlet port a smidge (matched to the manifold, of course), and then EH the housing..... bound to make some notable differences, I'll bet on it. :) If you can get the company to run the EH process with the intent of opening up the runners more than just smoothing things out I'd go for it. :)
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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18:02:53 01/12/12
