RickSE
05-30-2000, 11:46 AM
A while back I had a post on changing my 96 2-barrel 350 to a 4-barrel, http://206.150.187.82/ubb/Forum1/HTML/000160.html. The change over is now done and I’ve had the boat out two times. Here are some results if anyone is interested.
Parts used:
Holley 4-Barrel #0-80599, 650 CFM, 4150 Double Pumper.
Edelbrock Performer Intake #2104 for pre-Vortec heads.
3-blade 19P Quicksilver SS prop.
4-blade 21P Revolution 4 prop.
4-blade 19P Revolution 4 prop.
Best performance with the 2-barrel and a 19P Quicksilver was 4600 RPM, & 53-MPH w/full trim, at 3700-ft elevation. My first ride out with the new carb I left on the original 19P Quicksilver prop. I could really feel the extra power in the mid and upper ranges, motor ran up to about 4900 RPM, close to 45-MPH. I changed to the new 4-blade 21P prop expecting to drop to around 4500 RPM. Nope, instead of seeing the expected 200 RPM/inch pitch change I saw 400 and dropped to 4100 RPM. Mercury says to expect between 200-400 RPM change for each inch of pitch change. 200 seems to work if you stay in the same family of props, but 400 seems to be the number when changing from 3-blades to 4-blades.
So what now? I came home and ordered a 4-blade 19P. My thought was that the 19P 4-blade should drop the engine speed 400 RPM’s irt. to the 19P 3-blade.
We went out this weekend with the 19P & 21P 4-blades. I also advanced the timing to 10 deg. and leaned the secondaries in the carb from 74 to 72 and then 71 on the water. Here are the results.
19P 4-blade: 4600 RPM at WOT & 56 MPH, 75-80% trim.
21P 4-blade: 4200 RPM at WOT & 56 MPH, 75-80% trim.
The only thing I am curious about is what a 21P 3-blade would run. I would expect to see 4600 RPM’s, but could I get more speed??
I think the old 2-barrel cam is really holding back the potential of the 4-barrel, so I’ll probably be putting in a new roller cam soon.
So about $900 and 3 MPH, $300/MPH. I hope future speed increases come cheaper.
Parts used:
Holley 4-Barrel #0-80599, 650 CFM, 4150 Double Pumper.
Edelbrock Performer Intake #2104 for pre-Vortec heads.
3-blade 19P Quicksilver SS prop.
4-blade 21P Revolution 4 prop.
4-blade 19P Revolution 4 prop.
Best performance with the 2-barrel and a 19P Quicksilver was 4600 RPM, & 53-MPH w/full trim, at 3700-ft elevation. My first ride out with the new carb I left on the original 19P Quicksilver prop. I could really feel the extra power in the mid and upper ranges, motor ran up to about 4900 RPM, close to 45-MPH. I changed to the new 4-blade 21P prop expecting to drop to around 4500 RPM. Nope, instead of seeing the expected 200 RPM/inch pitch change I saw 400 and dropped to 4100 RPM. Mercury says to expect between 200-400 RPM change for each inch of pitch change. 200 seems to work if you stay in the same family of props, but 400 seems to be the number when changing from 3-blades to 4-blades.
So what now? I came home and ordered a 4-blade 19P. My thought was that the 19P 4-blade should drop the engine speed 400 RPM’s irt. to the 19P 3-blade.
We went out this weekend with the 19P & 21P 4-blades. I also advanced the timing to 10 deg. and leaned the secondaries in the carb from 74 to 72 and then 71 on the water. Here are the results.
19P 4-blade: 4600 RPM at WOT & 56 MPH, 75-80% trim.
21P 4-blade: 4200 RPM at WOT & 56 MPH, 75-80% trim.
The only thing I am curious about is what a 21P 3-blade would run. I would expect to see 4600 RPM’s, but could I get more speed??
I think the old 2-barrel cam is really holding back the potential of the 4-barrel, so I’ll probably be putting in a new roller cam soon.
So about $900 and 3 MPH, $300/MPH. I hope future speed increases come cheaper.