small block prop/carb testing
07-06-2012, 11:13 AM
#1
small block prop/carb testing
Did some carb testing on my boat, thought I would share the results.
Boat is a formula 206, 2 people, some gear and ¾ tank of gas (about 30 gallons or so).
Engine is a 350 with scat crank, vortec heads with screw in studs and beehive springs, LT4 hotcam and rpm performer air gap. Pertronix ignition with 16 degrees initial 32 total in by 3000rpm.
These tests were done at 80 degrees, no wind, flat calm water, and no tide. I would have liked some chop because the boat is faster in chop. Speed is GPS.
This test was with a Michigan wheel Apollo 14X21:
With the 600 edelbrock:
Test 1: primary side 1 rod size rich on power mode all else stock got 62mph.
Test 2:Same except 1 step richer on the secondary, 61mph. Felt a little sluggish
Test 3:Same except 1 step leaner on the secondary, 61mph. Felt about the same.
With 750 edelbrock
First thing I notice is the idle is much better. Played with the idle mixture on the 600 and just never got it how I wanted it. With the 750 I had it perfect in just a few minutes.
Test 1: All stock except 1 rod size rich on the cruise mode to fix a little lean spot coming on plane (750’s known for this): 62mph
Test2: Same except 1 step rich on secondary, 61mph
Test3:Same except 1 step lean on secondary, 62mph
Test4: Same as Test 3 except changed prop to Ballistic 14 3/8 x 21, 63mph
I could run 63 consistently in the smooth water. I can run 64 with 3 people but in the chop. Boat runs the same top speed with a 13 3/4x23 Laser 2, the rpms come down and cruise speed Is faster.
Results/summary
-Boat is fastest with the ballistic, and with a little chop will run consistently at 63-65(especially by myself with less fuel). I didn’t write down the rpm’s but they were 5500-5600 with the ballistic 5300-5400 with the appollo and 5100-5200 with the laser 2. I really wish I had a 22 pitch prop, that would be the sweet spot. I would also like to try a mirage plus 21 because my slip is a little high and think more diameter would help
-Switching carbs and jets didn’t make a huge difference. The biggest difference I noticed is the idle and because of that I left the 750 on.
One other thing, although the ballistic is fastest, it uses more gas at cruising speed than the Apollo or laser 2.
Hope this helps out some small block guys.
Boat is a formula 206, 2 people, some gear and ¾ tank of gas (about 30 gallons or so).
Engine is a 350 with scat crank, vortec heads with screw in studs and beehive springs, LT4 hotcam and rpm performer air gap. Pertronix ignition with 16 degrees initial 32 total in by 3000rpm.
These tests were done at 80 degrees, no wind, flat calm water, and no tide. I would have liked some chop because the boat is faster in chop. Speed is GPS.
This test was with a Michigan wheel Apollo 14X21:
With the 600 edelbrock:
Test 1: primary side 1 rod size rich on power mode all else stock got 62mph.
Test 2:Same except 1 step richer on the secondary, 61mph. Felt a little sluggish
Test 3:Same except 1 step leaner on the secondary, 61mph. Felt about the same.
With 750 edelbrock
First thing I notice is the idle is much better. Played with the idle mixture on the 600 and just never got it how I wanted it. With the 750 I had it perfect in just a few minutes.
Test 1: All stock except 1 rod size rich on the cruise mode to fix a little lean spot coming on plane (750’s known for this): 62mph
Test2: Same except 1 step rich on secondary, 61mph
Test3:Same except 1 step lean on secondary, 62mph
Test4: Same as Test 3 except changed prop to Ballistic 14 3/8 x 21, 63mph
I could run 63 consistently in the smooth water. I can run 64 with 3 people but in the chop. Boat runs the same top speed with a 13 3/4x23 Laser 2, the rpms come down and cruise speed Is faster.
Results/summary
-Boat is fastest with the ballistic, and with a little chop will run consistently at 63-65(especially by myself with less fuel). I didn’t write down the rpm’s but they were 5500-5600 with the ballistic 5300-5400 with the appollo and 5100-5200 with the laser 2. I really wish I had a 22 pitch prop, that would be the sweet spot. I would also like to try a mirage plus 21 because my slip is a little high and think more diameter would help
-Switching carbs and jets didn’t make a huge difference. The biggest difference I noticed is the idle and because of that I left the 750 on.
One other thing, although the ballistic is fastest, it uses more gas at cruising speed than the Apollo or laser 2.
Hope this helps out some small block guys.
07-07-2012, 10:22 PM
#5
Registered
If we were next door neighbors I would loan you a Holley 750 Double Pumper with stock out of the box jetting and a Bravo I 23" prop. It would be interesting to get your impressions on any differences you experience.
That's the carburetor/ prop combo I am starting with on mine.
The build is twin 355's with Vortec heads, Comp HD Springs, Needle Bearing Rockers, Comp Extreme Marine Roller 272 (very close but not quite the duration as the LT4), Edelbrock/Volvo Penta Marine Aluminum brass lined high rise, Davis Unified Ignition HEI's st at 32* at 3000, Holley "Red' electric Fuel Pumps, Mercruiser OEM new style exhaust through prop. Drives are Bravo I. Dyno test with headers has 400 horse at 5200 and 435 ft. lbs at 3200...400 ft. lbs at 2000.
I figure I'll loose 20~25 hp at the top through stock exhaust and little or no torque. Boat is a Formula 255 Liberator weighing in at 5600 lbs dry...6500 lbs with full fuel/gear load plus passengers.
With 750 horse power and 850 ft lbs in the water behind 6000 lbs...it should be fun. My goal is 55~60 cruise in the 4000~4500 RPM range with a top around 65~70 at 5200~5300 RPM. If I figure a 15% prop slip...according to BAM Marine's on line calculators...a 23" at 4500 puts me at 55 MPH and 5300 has me at 65. If the little Vortecs handle it well enough as twins...25" props give me 60 at 4500 and 71 at 5300.
It's all going to be about a flat torque curve and the most efficient prop with minimum slip.
Thanks for the info.
That's the carburetor/ prop combo I am starting with on mine.
The build is twin 355's with Vortec heads, Comp HD Springs, Needle Bearing Rockers, Comp Extreme Marine Roller 272 (very close but not quite the duration as the LT4), Edelbrock/Volvo Penta Marine Aluminum brass lined high rise, Davis Unified Ignition HEI's st at 32* at 3000, Holley "Red' electric Fuel Pumps, Mercruiser OEM new style exhaust through prop. Drives are Bravo I. Dyno test with headers has 400 horse at 5200 and 435 ft. lbs at 3200...400 ft. lbs at 2000.
I figure I'll loose 20~25 hp at the top through stock exhaust and little or no torque. Boat is a Formula 255 Liberator weighing in at 5600 lbs dry...6500 lbs with full fuel/gear load plus passengers.
With 750 horse power and 850 ft lbs in the water behind 6000 lbs...it should be fun. My goal is 55~60 cruise in the 4000~4500 RPM range with a top around 65~70 at 5200~5300 RPM. If I figure a 15% prop slip...according to BAM Marine's on line calculators...a 23" at 4500 puts me at 55 MPH and 5300 has me at 65. If the little Vortecs handle it well enough as twins...25" props give me 60 at 4500 and 71 at 5300.
It's all going to be about a flat torque curve and the most efficient prop with minimum slip.
Thanks for the info.
07-08-2012, 08:09 AM
#7
Registered
Play around with these...
http://www.go-fast.com/Prop_Slip_Calculator.htm
http://www.go-fast.com/boat_speed_predictions.htm
...gives you an idea of what we're up against to get there.
07-09-2012, 06:37 AM
#8
Powerqrudy,
before the build I had a 290 horse replacement engine in the boat. It would run 56 with the same conditions that I tested the props/carb (2 people, 3/4 fuel, normal amount of gear in boat).
Keith, running edelbrock air gap rpm intake and stainless marine exhaust.
Sprink, thanks for the offer, I would like to try a double pumper. what bravo I 23 prop are you using? Bravo props are only even pitched? Those are great torque numbers. they should push your formula nicely.
I was thinking of cleaning up the intake and cleaning up/little port work on the exhaust on the vortecs this winter since the vortec head kind of suffers on the exhaust side. Not sure I will but would be interesting to see if it made a difference.
before the build I had a 290 horse replacement engine in the boat. It would run 56 with the same conditions that I tested the props/carb (2 people, 3/4 fuel, normal amount of gear in boat).
Keith, running edelbrock air gap rpm intake and stainless marine exhaust.
Sprink, thanks for the offer, I would like to try a double pumper. what bravo I 23 prop are you using? Bravo props are only even pitched? Those are great torque numbers. they should push your formula nicely.
I was thinking of cleaning up the intake and cleaning up/little port work on the exhaust on the vortecs this winter since the vortec head kind of suffers on the exhaust side. Not sure I will but would be interesting to see if it made a difference.
07-09-2012, 09:06 PM
#9
Registered
Gonna chime in here on my experience with the lt4 cam and vortec heads. I'm running a 350 with the lt4 cam, forged flat tops, performer rpm intake, 1.6 roller rockers, 650 BG demon carb with mechanical secondary (#70 jet in primarys, #78 jet in secondarys), stock merc exhaust manifolds and risers. I'm running a thunder bolt IV ignition with a v6-14 module. Timing is 21-22 degrees at base, 31-32 degrees all in by 2500 rpm. Boat is a 1987 20' Concord Magnum II. My lake is 3000 ft above sea level. Runs 61 mph and best I've seen is 63. Turns a 21 pitch laser II to 5000-5200 rpm depending on outside temp and humidity. Going to upgrade to stainless marine exhaust this winter and have o2 bungs put in the risers so I can run an A/F ratio gauge for tuning the carb in a little better. Hope this helps some folks as well.
Last edited by 87MagnumII; 07-09-2012 at 09:11 PM.
07-09-2012, 10:55 PM
#10
Registered
Gonna chime in here on my experience with the lt4 cam and vortec heads. I'm running a 350 with the lt4 cam, forged flat tops, performer rpm intake, 1.6 roller rockers, 650 BG demon carb with mechanical secondary (#70 jet in primarys, #78 jet in secondarys), stock merc exhaust manifolds and risers. I'm running a thunder bolt IV ignition with a v6-14 module. Timing is 21-22 degrees at base, 31-32 degrees all in by 2500 rpm. Boat is a 1987 20' Concord Magnum II. My lake is 3000 ft above sea level. Runs 61 mph and best I've seen is 63. Turns a 21 pitch laser II to 5000-5200 rpm depending on outside temp and humidity. Going to upgrade to stainless marine exhaust this winter and have o2 bungs put in the risers so I can run an A/F ratio gauge for tuning the carb in a little better. Hope this helps some folks as well.
