Badtoon

LOOKING FOR SOME SMALL BLOCK HELP. I HAVE A 5.7 VORTEC HEAD MERCRUISER. WOULD I PICK UP HP BY SWITCHING TO THESE HEADS
http://www.gmpartsdepot.com/store/pr...Category_ID=57

AND 1.6 ROCKERS

I STILL HAVE THE STOCK CAM (TO BE CHANGED AT FIRST REBUILD) STAINLESS MARINE EXHAUST, SWITCHABLE MUFFLERS, 650 DP MECH SECONDARIES CARB, MSD IGNITION

WETTE VETTE

I would venture to say just changing heads will hurt low end perf and probably not pick up much on top. Go to a different cam, intake, carb and headers and twist the motor 6300-6500 RPM and there will definately be a benefit to the larger runners.

rmbuilder

They(Bowtie Vortec small port 175cc/ Bowtie Vortec Large port 206cc)are a much-improved design compared to the standard Vortec small block head. They are standard with 2.00”/1.55” stainless valves compared to 1.94”/1.5” for the original head, 65cc chamber fast burn combustion chamber design vs. 64cc, 175cc rated intake runner (actual 185cc) vs. 170cc and a 65cc exhaust port. They come standard with screw in studs vs. press fit, large valve pocket machining, and will accommodate up to a .530” lift without any additional cutting vs. .475” max lift on the original, and will accept both center and perimeter bolt valve covers. The runner size and cross section are ideal for your application making more power above 4000 rpm where the std Vortecs begin to nose over. Both small and large port cross sections have been worked extensively to maintain velocity. The flow #'s indicate that the small port flows nearly as well as the Fast burn to .500" and the Lg port exceeds the flow of the FB heads with the exception of the exhaust port on the Lg port head above .500". That will be corrected shortly. If you need an iron head for a marine application these are viable options especially for the price.
Intake Vortec...... Small Vortec BT........ Fast Burn.. .....Large Vortec BT
.100" 62............ 67............................ 65............................ 63
.200" 133.......... 136.......................... 133.......................... 133
.300" 179.......... 182.......................... 183.......................... 182
.400" 218.......... 223.......................... 225.......................... 228
.500" 211.......... 251.......................... 254.......................... 258
.600" 213.......... 240.......................... 244.......................... 255
.700" 217.......... 240.......................... 248.......................... 261
Stock
Exhaust Vortec...... Small Vortec BT........ Fast Burn.................. Large Vortec BT
.100" 47............ 53............................ N/A.......................... 50
.200" 99............ 100.......................... 98............................ 100
.300" 128.......... 128.......................... 129.......................... 134
.400" 139.......... 145.......................... 150.......................... 154
.500" 143.......... 152.......................... 171.......................... 168
.600" 143.......... 164.......................... 179.......................... 168
.700" 145.......... 166.......................... 184.......................... 169

Port Size 170 cc...... 175 cc...................... 202 cc...................... 206 cc
N/A..........64 cc........................ 78 cc........................ 77 cc

rmbuilder

The bottom numbers are posted left and are exhaust port size not combustion chamber size.
Bob