grumpyvette

one of my pet peaves is rigged results from testing, in magazine dyno results, as most of the experianced guys know the engine is a SYSTEM of parts that must match in the rpm range and air flow/ horse power levels they need to run at to get valid results
anyone can take a nearly stock 350 chevy engine designed to run at 3500rpm or lower most of the time and show a marked advantage on a dyno for the use of a dual plane intake and 650 cfm carb, especially if the dyno run only goes to 4500rpm, yet theres not a thing wrong with the single plane intake, the opposite result would be shown on a 350 engine equiped with a cam, high compression pistons, open headers and cylinder heads designed to run 7000rpm especially if the dyno testing started at 3500rpm and pulled to 7200rpm

I just got thru reading a DYNO test on oval versus retangle port heads on a bbc engine in one of the magazines, now the results they got while valid, for the tested engine combo, they were not a fair comparison, and any engine builder with experiance would have picked up on the fact that the DYNO test was set up so that only one result was likely.

in the article they first matched results on a 454 useing rectangle then oval port heads, the results was 407hp (R) versus 419hp(O) N/A
then 558hp(R) versus 563hp(O) SUPERCHARGED
now thats fine UNTILL YOU LOOK AT THE OTHER COMPONENTS USED
in the first test a cam was used with only 220/220 duration and .500/.500 lift,and the dyno was only run up to 5700rpm. now any engine builder knows that the advantage of the rectangle port heads will not show up untill a cam designed for rpm ranges of about 6000rpm and lifts in the .550 plus ranges are used, MOST ENGINE BUILDERS WILL TELL YOU THAT CORRECTLY SET UP OVAL PORT HEADS ARE THE BEST CHOICE ON THE STREET, AND THEY ARE CORRECT! but in this case a look at the dyno torque curve shows very clearly the CAM started causeing the engine to run short on air at about 4300rpm. this ment the rectangle port heads had no chance at ever reaching the rpm range they were designed to run in. in the second test a supercharger was used on both heads, but it was a HOLLEY 174 power charger DESIGNED for efficient low rpm street use,but a supercharger that not designed to feed a 454 at 6000rpm, and again the same cam severly limited power potential at over 4300rpm
if your going to compare the results fairly to take ADVANTAGE of the STRONG POINTS OF BOTH HEADS, a larger CAM and a LARGER SUPERCHARGER would need to be used, I would be VERY SURPRISED if the results still favored the oval port heads if both cylinder heads were tested with a cam like the CRANE,
http://dab7.cranecams.com/SpecCard/D...1=Display+Card with a N/A dynamic compression ratio of about 8:1
or the HOLLEY, 871 supercharger driven at 1:1 engine speed ratio and spun up to 6000rpm was used on both engines with a lower compression matching the supercharges boost curve
http://www.holley.com/HiOctn/ProdLin...-71_14-71.html
btw DD-2000 guesses at a 190hp plus advantage to useing the larger port, larger valve rectangle port heads on a combo like that ! THE POINT IM TRYING TO MAKE CLEAR HERE IS THAT ALL PARTS IN AN ENGINE BUILD MUST MATCH THE INTENDED USE FOR THAT ENGINE FOR THE PARTS TO WORK CORRECTLY IN THE INTENDED RPM RANGE AND AT THE INTENDED HORSEPOWER LEVEL, ANY PART NOT MATCHING THE THE REST OF THE COMBO CAN BE MADE TO LOOK BAD ON A DYNO TEST. you can match the best flowing intake, and high rpm roller cam in the country for example to a corvette engine with a very restricted stock cylinder heads, exhaust and low compression and youll be WAY DOWN on POWER

CentralCoaster

TTT