Pitiful Dyno numbers on a SB 427

D

drpipes

Member
Hey man!! Just took the 67 vette to the Dynojet to see what it made to the rear wheels. It sucked bad! Despite total timing of 36 degrees and perfect air/fuel ratios I only made 300 max HP and 375 ft/lbs torque. This is a Shafiroff engine with AFR 210 heads, comp cams XE288 hydraulic roller cam, Quick Fuel 830 cfm carb, 1.6 rockers, and a Performer RPM Airgap manifold. MSD 6AL box with Blaster 2 coil and Taylor wires. Air filter is a 3 inch element on a one inch drop base cleaner. Exhaust is a set of Sanderson block hugger headers 1 5/8 primaries to Sweet Thunder baffled sidepipes 2.25 inch. Transmission is a brand new M22 Wide Ratio 4 speed. I am running AC and Power Steering along with a belt driven fan. The only thing that isn't new on the drivetrain is the differential!! Specs on the cam are 110 lobe sep, .520/.540 lift, and 236/242 duration. According to Shafiroff the engine dyno showerd 560 HP and 590 ft/lbs. Now I know that there will be substantial losses in power on the chassis but... wow... 250 HP? What should I do to get better power? Heck, if that is all I am going to get out of an 11K 427 I should have gotten a crate 350 and saved some money. :oops:
 
theres something WRONG! your usually looking at about a 20% drive train loss, putting the rear wheel hp in the 440 hp range, with a 560hp engine, that engine combos known to produce good hp/tq

whats the engines compression ratio?
did you verify each cylinders running correctly?
did you lash the valves correctly?
what was the back-pressure on the exhaust? (especially Id like to know what it was as the rpms increased, and at above 4000rpm)
(a restrictive exhaust kills power quickly, it should remain under 2 psi, with under 1 psi being better)
this looks to be rather restrictive to exhaust flow on a 427 to me!!
"Exhaust is a set of Sanderson block hugger headers 1 5/8 primaries to Sweet Thunder baffled sidepipes 2.25 inch. "

can you post dyno sheet info?

viewtopic.php?f=56&t=495
 
The compression ratio is 10.25. The engine runs like a top with no hesitation. The valve lash was just adjusted. Don't know the back pressure but I bet that is the problem. The horsepower curve was more like a straight line than a curve. Some people have told me that the 1 5/8" primaries actually partially occlude the exhaust ports on the 210 AFR's!! I will try to step up the headers to 1 7/8" but I am afraid there will be some custom work in my future!! I don't have the dyno sheet with me but I will post it later today. Thanks for the input!!
 
Here is the dyno sheet:
scan0001.jpg
 
look at the torque and power curves, both obviously fall off as cylinder fill efficiency drops after about 4000-4500rpm, your heads and cam are designed to pull higher rpms and even your intake should allow that engine to pull to at least 5500-6000rpm so it looks like the exhaust restriction is a major factor restricting performance.
Id suggest a good set of hooker headers WITHOUT the insert mufflers installed for your next dyno session


http://www.summitracing.com/parts/HOK-2224HKR/
hookerside.jpg


http://www.summitracing.com/parts/HOK-50735HKR/
hookersidep.jpg



IVE ALWAYS JUST WELDED UP A SET OF CUSTOM MADE BAFFLES INSERTS FOR MY SIDE EXHAUST SIMILAR IN DESIGN TO THIS, but the central tube had dozens of holes drilled in it, to reduce flow restriction, vaguely similar to this
preforatedtube.jpg


preforatedtube1.JPG



you can use this program and a bit of trial & error to design the baffles if you choose to get fancy
http://metalgeek.com/static/cope.pcgi


http://www.spiralturbobaffles.com/musclecars.html

TURBOBAFFLE.jpg
 
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