350 mag alpha vortec head swap
10-04-2009, 05:00 PM
#11
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Ryan,
GM only went to rollers in the cars in 87, truck engines, which most of the marine engines are based on, did not switch until 1996. I am not sure exactly when Mercruiser started but I would be real surprised to see a 1987 engine with a roller cam in it. I can find out for sure on Monday at the shop.
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
GM only went to rollers in the cars in 87, truck engines, which most of the marine engines are based on, did not switch until 1996. I am not sure exactly when Mercruiser started but I would be real surprised to see a 1987 engine with a roller cam in it. I can find out for sure on Monday at the shop.
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
Thanks for the correction Bill. I now remember hearing that before but I guess it slipped my mind.
10-05-2009, 06:13 AM
#12
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you will need a vortec intake as they ae diff, a performer is the ticket, the rockers are usually different, use the felpro std style vortec intake gaskets, not the factory one peice pan/rubber stle, but you should be good to go....just did a swap like these a while back worked great and have another to do soon....heads alone worth 40hp over what you have, intake another 10 or so, good deal..Rob
10-05-2009, 09:58 AM
#13
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mrfixxal
Here is where I am not sure on things. My 93 motor is rated at 9.3:1 CR. I do not know what the pistons are (assuming they are flat top though) and I don't know what my head CC is currently. If they are 76CC heads then I am going to throw the compression up higher than I want. If they are already 64CC then I am fine for what I want to do. The 330 crate motor lists at 9:1 CR with 64CC Vortec heads, but again I don't know if the pistons are in fact the same. These are the things I really want to know before I do this. I cannot sacrifice any reliability as this boat gets used like a rented mule in the summer by my wife and kids.
I am sure I could easily pop the distributor and look for the lifter retainer, but I am not sure why I need to if I am not going to swap cams anyhow. I don't want to pop the motor out of the boat, and I don't think I can pop the timing cover without dropping the oil pan and not run the risk of an oil leak down the road.
I am sure I could easily pop the distributor and look for the lifter retainer, but I am not sure why I need to if I am not going to swap cams anyhow. I don't want to pop the motor out of the boat, and I don't think I can pop the timing cover without dropping the oil pan and not run the risk of an oil leak down the road.
02-21-2011, 12:30 PM
#14
Bringing this back.
This spring the motor is coming out of the boat. After consideration, for the extra effort, a cam swap seems well worth the modest amount of extra labor involved. I think I am also going to swap to a Holley carb as the Weber just doesn't seem to perform that well on any boat I own.
I have two cams I am considering:
Comp Cams XM 268, and the 350 mag MPI/ HT383 cam. I realize I will have to convert to a roller setup, but I have the lifters, retainers, pushrods, and rockers from the vortec motor. I think it should work fine with my bottom end.
I am going to do a spring upgrade, but I am not sure which spring I should use, and I also don't know if I will need to cut the heads to use either of these cams.
I appreciate all the input on this.
This spring the motor is coming out of the boat. After consideration, for the extra effort, a cam swap seems well worth the modest amount of extra labor involved. I think I am also going to swap to a Holley carb as the Weber just doesn't seem to perform that well on any boat I own.
I have two cams I am considering:
Comp Cams XM 268, and the 350 mag MPI/ HT383 cam. I realize I will have to convert to a roller setup, but I have the lifters, retainers, pushrods, and rockers from the vortec motor. I think it should work fine with my bottom end.
I am going to do a spring upgrade, but I am not sure which spring I should use, and I also don't know if I will need to cut the heads to use either of these cams.
I appreciate all the input on this.
02-22-2011, 02:16 PM
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I've done quite a few of these conversions. Your stock heads are going to be the large chamber with flat top pistons. So, you'll end up with compression near 10:1. However the Vortec heads are a fast burn design so it should be OK with 91+ octane fuel and 28-30 degrees of timing. The heads will only accept approximately .465 lift before the retainer hits the seal. So they must be machined for any additional lift. You should be around 330-340 HP with this setup. Limit rpm to 5000 because of the weak connecting rods/bolts. So, choose a cam accordingly.
Bob Lloyd
Full Throttle Marine
Bob Lloyd
Full Throttle Marine
02-22-2011, 04:03 PM
#16
Thanks Bob, I forgot the number where retainer to seal interference becomes a problem. Running the 14097395 GM cam, which all my research says is the same as the 350 mag mpi cam will only give me .451" lift at the valve with the factory rocker, so I should be ok with just a spring upgrade.
I may leave a little power on the table with this cam, but I think the torque should match up well with the boat and it should produce good power at 5000 rpm. A drop in comp cam spring should suffice fine for this combo.
I am leaning towards a Holley 650 to replace the weber, any thoughts on that? I just can't warm up to the manners of the carb on it now, a long crank time when the boat hasn't run for a few days, a sag on acceleration at times, and a long crank after a hot soak. All signs point to it needing a rebuild, and I would just as soon go with a new carb than try to polish that turd.
I may leave a little power on the table with this cam, but I think the torque should match up well with the boat and it should produce good power at 5000 rpm. A drop in comp cam spring should suffice fine for this combo.
I am leaning towards a Holley 650 to replace the weber, any thoughts on that? I just can't warm up to the manners of the carb on it now, a long crank time when the boat hasn't run for a few days, a sag on acceleration at times, and a long crank after a hot soak. All signs point to it needing a rebuild, and I would just as soon go with a new carb than try to polish that turd.
02-23-2011, 06:07 PM
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Good call on the carb. Just make sure it's a marine version, and I'd opt for a double pumper. More money but much better response.
I used the old Crane part # 104224 cam (214/220 deg @ .050 .452/.465 lift)in a lot of builds. It's the same cam spec as used in the Merc 6.2L engines. They had a great spring package that increased the retainer clearance. Unfortunately none of that is available since Crane went under.
The stock cam is pretty small. 197/207 deg @ .050, .430/.450 lift.
Bob
I used the old Crane part # 104224 cam (214/220 deg @ .050 .452/.465 lift)in a lot of builds. It's the same cam spec as used in the Merc 6.2L engines. They had a great spring package that increased the retainer clearance. Unfortunately none of that is available since Crane went under.
The stock cam is pretty small. 197/207 deg @ .050, .430/.450 lift.
Bob
Thanks Bob, I forgot the number where retainer to seal interference becomes a problem. Running the 14097395 GM cam, which all my research says is the same as the 350 mag mpi cam will only give me .451" lift at the valve with the factory rocker, so I should be ok with just a spring upgrade.
I may leave a little power on the table with this cam, but I think the torque should match up well with the boat and it should produce good power at 5000 rpm. A drop in comp cam spring should suffice fine for this combo.
I am leaning towards a Holley 650 to replace the weber, any thoughts on that? I just can't warm up to the manners of the carb on it now, a long crank time when the boat hasn't run for a few days, a sag on acceleration at times, and a long crank after a hot soak. All signs point to it needing a rebuild, and I would just as soon go with a new carb than try to polish that turd.
I may leave a little power on the table with this cam, but I think the torque should match up well with the boat and it should produce good power at 5000 rpm. A drop in comp cam spring should suffice fine for this combo.
I am leaning towards a Holley 650 to replace the weber, any thoughts on that? I just can't warm up to the manners of the carb on it now, a long crank time when the boat hasn't run for a few days, a sag on acceleration at times, and a long crank after a hot soak. All signs point to it needing a rebuild, and I would just as soon go with a new carb than try to polish that turd.
02-23-2011, 09:42 PM
#18
Looks like I will be on either a 600 or 750 carb, no real 650 double pumper in a marine carb. With a 5000 rpm limit I think a 600 will suffice just fine and give me better response. I was going to go with a double pumper anyhow and of course it will be a marine carb.
Looking at cams, the Comp XM 256 H seems very close to the Crane you listed, although it is still a flat tappet. The Comp XM 262 H appears to make about 10 more horse at peak power and more average hp and torque according to Comp's cam quest program. I am pretty sure Comp makes a drop in beehive spring that will increase retainer clearance also. The price they are getting for Comp roller grinds is hefty compared to flat tappets. I suppose if I use the factory roller lifters I have it won't be too much more, but is there that much to gain converting to a roller on a small block that is limited to 5000 rpm?
I appreciate the input I am getting, it is really helping me figure out the details of the motor conversion.
Looking at cams, the Comp XM 256 H seems very close to the Crane you listed, although it is still a flat tappet. The Comp XM 262 H appears to make about 10 more horse at peak power and more average hp and torque according to Comp's cam quest program. I am pretty sure Comp makes a drop in beehive spring that will increase retainer clearance also. The price they are getting for Comp roller grinds is hefty compared to flat tappets. I suppose if I use the factory roller lifters I have it won't be too much more, but is there that much to gain converting to a roller on a small block that is limited to 5000 rpm?
I appreciate the input I am getting, it is really helping me figure out the details of the motor conversion.
02-23-2011, 10:11 PM
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I would definitely stay with a roller cam if you already have one. Even if you don't it would be money well spent. The roller lifter conversion kit is pretty cheap. My biggest concern is the durability of a flat tappet cam with todays oils. I've seen several failures. You also can get a more aggressive lobe profile with the roller, which will pick up power at all rpm levels.
Bob
Bob
Looks like I will be on either a 600 or 750 carb, no real 650 double pumper in a marine carb. With a 5000 rpm limit I think a 600 will suffice just fine and give me better response. I was going to go with a double pumper anyhow and of course it will be a marine carb.
Looking at cams, the Comp XM 256 H seems very close to the Crane you listed, although it is still a flat tappet. The Comp XM 262 H appears to make about 10 more horse at peak power and more average hp and torque according to Comp's cam quest program. I am pretty sure Comp makes a drop in beehive spring that will increase retainer clearance also. The price they are getting for Comp roller grinds is hefty compared to flat tappets. I suppose if I use the factory roller lifters I have it won't be too much more, but is there that much to gain converting to a roller on a small block that is limited to 5000 rpm?
I appreciate the input I am getting, it is really helping me figure out the details of the motor conversion.
Looking at cams, the Comp XM 256 H seems very close to the Crane you listed, although it is still a flat tappet. The Comp XM 262 H appears to make about 10 more horse at peak power and more average hp and torque according to Comp's cam quest program. I am pretty sure Comp makes a drop in beehive spring that will increase retainer clearance also. The price they are getting for Comp roller grinds is hefty compared to flat tappets. I suppose if I use the factory roller lifters I have it won't be too much more, but is there that much to gain converting to a roller on a small block that is limited to 5000 rpm?
I appreciate the input I am getting, it is really helping me figure out the details of the motor conversion.
