With all that has been said about turbo or supercharging charging one of the most critical things one should do is flow test the heads to see if the gasses can pass through at the higher gas volumes produced.
Ron ----- Original Message ----- From: "Colin & Bev Rainey" <crain...@cfl.rr.com> To: "KRnet" <kr...@mylist.net> Sent: Sunday, April 11, 2004 7:27 PM Subject: KR> Cams & turbocharging > Orma & netters > At one time when I was drag racing in street and stock classes, I was studying about the feasibility of turbo or supercharging, especially when a buddy had a '56 Chevy truck with a B&M street blower or supercharger, pushing about 16# of boost according to the panel gauge. He always had a cutting out/popping back problem due to leaning out during actual acceleration. He had the hardest time understanding the dynamics of how actual acceleration involved more factors than sitting static during a burnout.. In the course of studying to understand his situation I came across a test performed by B&M where they used several different cams in the same engine and performed dyno tests to see which worked best. They found that the most dramatic differences in performance increase were made when a cam altered for the artificial aspiration, supercharging, was used. The typical long duration, high lift cams used for most normally aspirated hotrods actually performed at or even below stock cams. They reasoned that the large overlap of the valves caused too much of the air/fuel mix to be pushed out of the exhaust valve and not retained in the cylinder. The cam was designed to help overcome the lack of efficiency of the engine in order to increase its "breathing". With the supercharger this was not necessary, since the blower was providing over 100% of the CFMs capable from the engine to start with. Simply stated the cam needed to help the blower provide more power, by delaying the closing so that more air could be packed in, instead of trying to assist it in moving more air from outside. They found the best cams were cut with this in mind and were quite different from the traditional stock or performance cams. Another interesting fact they discovered was that even though the boost numbers were high with the stock and performance cams, all the pressure was remaining in the intake, not getting into the cylinder. When they changed the cam to one designed more for the blower, the boost number went down, but torque and horsepower went up. Literally more air was being packed into the cylinder, not just into the intake. > Also something to consider when selecting your turbo: choose one where the CFMs are higher, not necessarily the pressure capability is high. Especially since you are wanting to add performance over the entire range and extract more horsepower from the engine, you are best to have a turbo that can move alot of air, not one that just makes pressure. Racers have found that high boost numbers are not the whole story. Lowering the boost pressure, but increasing the volume of air delivered to the intake manifold actually puts more air into the cylinder without elevating the intake air temperature as much due to the lower amount of "squeezing". This reduces the possibility of detonation. Orma you may also want to install a blow off valve protection on the intake manifold to prevent over pressurizing, and also consider some form of spark retard at lower RPMs, while under boost, the same as the 2300 motor in the Mustang has. The engine can't tolerate these pressures for long periods in the lower RPMs and will lead to piston, rod or crankshaft failure eventually. > > Colin & Bev Rainey > KR2(td) N96TA > Sanford, FL > crain...@cfl.rr.com > or crbrn9...@hotmail.com > http://kr-builder.org/Colin/index.html > _______________________________________ > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html > >
