350 sbc HP, old vs. new question
01-25-2012, 09:10 PM
#1
350 sbc HP, old vs. new question
OK, a bit confused on HP ratings for the mercruiser 350's.
My 1986 - 272 Formula came with 260 HP 350's. Now the basics of the short blocks look pretty similar for all the gen 1's in this group. But this older one was a non-roller cam, that had around 212 duration @.050 on I and E. Lift is listed at 0.440 on both also. The flat tappet is supposed to limit how fast you can open the valves so you get a less agressive profile than the roller cams.
No Vortec heads, just the poor cast iron production heads of the day with 76cc combustion chambers I believe.
Cast iron intake with a carburator and standard Merc exhaust.
Now you go forward to a newer 350 from the late 90's and HP is now up to 295.
Roller cam now available. Standard marine cam is .450 lift and duration is 197/207 @ .050 similar lift but the timing is a bit more conservative. Should be better than the old tappet cam.
Also have the Vortec heads now which are a dramatic improvement. I have heard that the Vortecs are worth 35 to 40 hp alone, maybe that is with a better aftermarket intake. Not sure. But the vortec heads are one reason for the additional horsepower due to shape, burn and the 64cc for higher compression ratio.
Add fuel injection and such on the newer ones and it seems like 295 to 300 HP is not that great an improvement over the old 260HP mercruiser of old. Were the old engines just over rated some? New ones under rated? Any feedback?
The reason I ask all this: I am installing newer motors in my 272. Going 350's, 4 bolt, 1 piece main seal cranks so roller cam, vortec heads, and edelbrock performer intake. Right now I have one of the stock marine cams (GM#14097395) and need to find another. All of this seems to be a more dramatic increase in performance than the 35 HP that mercruiser seems to indicate. Is the stock marine cam limiting and should I consider a hotter cam? is it worth the additional $400 it will cost me for two new cam verse one more marine cam? I am fine with 295 to 300 HP a side if that is what I get, just don't want to leave any obvious HP on the table. Looked at Sprink's new engines and specs, his dynoed at 365 Hp at 5k. I believe roller rockers and better springs help with the higher RPM's, does it add much HP below 4800? Port work and matching also helps. carb's can be changed later on if I want to. Seems like a vortec like I am putting in would be 310 to 320 HP? What am I leaving on the table?
Also need to find someone to look at my carbs and go through them and make any changes that may be needed unless it is worth going with new ones.
Brian
My 1986 - 272 Formula came with 260 HP 350's. Now the basics of the short blocks look pretty similar for all the gen 1's in this group. But this older one was a non-roller cam, that had around 212 duration @.050 on I and E. Lift is listed at 0.440 on both also. The flat tappet is supposed to limit how fast you can open the valves so you get a less agressive profile than the roller cams.
No Vortec heads, just the poor cast iron production heads of the day with 76cc combustion chambers I believe.
Cast iron intake with a carburator and standard Merc exhaust.
Now you go forward to a newer 350 from the late 90's and HP is now up to 295.
Roller cam now available. Standard marine cam is .450 lift and duration is 197/207 @ .050 similar lift but the timing is a bit more conservative. Should be better than the old tappet cam.
Also have the Vortec heads now which are a dramatic improvement. I have heard that the Vortecs are worth 35 to 40 hp alone, maybe that is with a better aftermarket intake. Not sure. But the vortec heads are one reason for the additional horsepower due to shape, burn and the 64cc for higher compression ratio.
Add fuel injection and such on the newer ones and it seems like 295 to 300 HP is not that great an improvement over the old 260HP mercruiser of old. Were the old engines just over rated some? New ones under rated? Any feedback?
The reason I ask all this: I am installing newer motors in my 272. Going 350's, 4 bolt, 1 piece main seal cranks so roller cam, vortec heads, and edelbrock performer intake. Right now I have one of the stock marine cams (GM#14097395) and need to find another. All of this seems to be a more dramatic increase in performance than the 35 HP that mercruiser seems to indicate. Is the stock marine cam limiting and should I consider a hotter cam? is it worth the additional $400 it will cost me for two new cam verse one more marine cam? I am fine with 295 to 300 HP a side if that is what I get, just don't want to leave any obvious HP on the table. Looked at Sprink's new engines and specs, his dynoed at 365 Hp at 5k. I believe roller rockers and better springs help with the higher RPM's, does it add much HP below 4800? Port work and matching also helps. carb's can be changed later on if I want to. Seems like a vortec like I am putting in would be 310 to 320 HP? What am I leaving on the table?
Also need to find someone to look at my carbs and go through them and make any changes that may be needed unless it is worth going with new ones.
Brian
01-25-2012, 09:31 PM
#2
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Why don't you save yourself all the guesswork and trouble and just drop in a new GM 5.7 HO at 330 hp for $2800 a piece? Runs on pump gas, just throw an aluminum intake on it, move over your ignition and carb and be done. It isn't crazy money and you jump up abt 70hp with all new parts. Just my .02 though
http://www.jegs.com/i/GM-Performance...ductId=1231165
http://www.jegs.com/i/GM-Performance...ductId=1231165
01-25-2012, 10:02 PM
#3
mainly because you are talking $6,400 del. with intakes to put into a boat that I paid less than $5k for in "running condition"! This is just a for fun project to let us know if we will use a boat or if I should just walk away from it until we are empty nesters.
That and I already have the engines at work!
Good link though, very comparable setup to what I have sitting at work right now except for the cam difference. Still, this makes me more impressed that they used to pull 260 hp reliably out of the older engines.
Brian
That and I already have the engines at work!
Good link though, very comparable setup to what I have sitting at work right now except for the cam difference. Still, this makes me more impressed that they used to pull 260 hp reliably out of the older engines.
Brian
01-29-2012, 01:44 PM
#6
already did that in another thread. Transom is perfect, and I mean looks like the day it was assembled! Center stringer needs some help along the bottom and the first bulk head, those are very common also and I will start on both of those this week.
Brian
Brian
01-29-2012, 02:00 PM
#7
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350 chevy is cheap and simple to make decent power. If your using the vortec heads look for some gm alunimum intakes, they make similar power to something like an edelbrock performer and people usually discard them or sell them cheap as they do not realize that these intakes perform pretty good.
Look at one of the comp extreme marine cams. Cheap enough and you do not need to go roller. And you will not need an exhaust upgrade if you pick one of the more conseervative grinds.
You should quite easily be able to make 350hp on a tight budget.
Look at one of the comp extreme marine cams. Cheap enough and you do not need to go roller. And you will not need an exhaust upgrade if you pick one of the more conseervative grinds.
You should quite easily be able to make 350hp on a tight budget.
