3781147 Heads on Low Perf. 348

[60 Nomad]

I have a 348 low performance car engine with stock pistons and cam. I know the 3781147 high performance heads will fit on my engine, but will the valves hit the pistons. Will this work with the low performance pistons or does it have to have the pistons like this description below. Maybe it just means you have to have this piston with these heads to get this horsepower. Might be a dumb question but if you don’t ask you will never know. I already have new stock LP pistons installed. I have too much invested in this engine to blow it now just because of too much pride to ask for help. Does anyone out there have this head on a low performance block setup or know the answer?

Heads I would like to use:
Head# 3781147
Year used: 1960
Model: Passenger car
Engine: 348
Horsepower: 320,335
Intake Valve Size: 2.06
Exhaust Valve Size: 1.72
Notes: This cylinder head was introduced 4-1-60 for all special high performance 348's for 1960 and early 1961 until head #3795586 was released. This head is identical with head #3758379 except it has larger valves and hardened shank rocker arm studs. The pistons used with this head had larger relief notches for the valves, increased metal thickness in the rib on inside of skirt and additional reinforcement at the lower edge of the skirt.

My engine block is:
Block# 3755011
Year used: 1960
Model: Passenger car
Engine: 348
Bored .30 over

My Original Heads were: (both cracked)
Head# 3758379
Year used: 1960
Model: Passenger car
Engine: 348
Horsepower: 250,280
Intake Valve Size: 1.94
Exhaust Valve Size: 1.66
Notes: This cylinder head is the second design. Major design differences from the first design 1958 head #3732791. Water cooling passages have been added around the spark plugs. This head is distinctive as there are cored cooling slots visible at the spark plug relief area.

Thanks for any help.

 

[Ronnie Russell]

60 Nomad, There is no such thing as a dumb question. If you dont have valve spring compressor and checking springs, use play dough in the valve reliefs to check clearance. Use used head gasket or no head gasket and install head (no need to tighten head bolts) If you use no head gasket, then you can figure an extra .030 clearance to your measurment. Lifters and pushrods in the one
cyl.. you are checking. Set valve lash, then rotate crankshaft several times. Remove head and you will know where you stand. Most people use .100 as minimum clearance for intake. I believe you will be okay, but like Ray said, it depends on valve lift. This is a simple procedure and will give you "peace of mind" for final assembly. Ray, fantastic picture!!!! That looks like something out of an assembly manual. First class!

 

[Ronnie Russell]

Forgot to mention that you must use solid lifter for vpc check.

 

[60 Nomad]

Thanks guys for the advice. The more the better. Seems to me that a stock cam would have less lift and less chance of hitting the pistons. Here is one more thing I was wondering. Without machining the seats to a larger size, can hardened seats be put in, thus reducing the valve size to the same size as the Low Performance heads? This it seems would prevent the chance of hitting the pistons and allow me to burn unleaded gas? They probably don't make a seat to do this. Like I said, the more information I can get the better. Still would like to hear from someone with a stock Low Performance Engine, stock cam, stock pistons, and 348 High Performance heads.
Thanks again for advice, I'll use it all.

 

[Ronnie Russell]

60 Nomad, There has been much discussion already about hardened valve seats. I think if you searched "unleaded gas" in the 348-409 engine section you could get much info. As far as your valve seat decreasing valve size, I didnt understand the question. The stock cam is only .403 lift and has little duration, so I dont see a problem, however that is only an opinion and there is too much at stake to gamble, hence the vpc check to make sure. You might also search 817 heads because of the same size valves you are using. Im not sure you will hear from anyone using that combination. Most people upgrading to bigger valves usually go with bigger cam. I think that if you spend time searching old threads you will find a lot of useful info. Good luck

 

[60 Nomad]

Thanks for the input. Just trying to get as much information as possible before using the 3781147 Heads. I need them Magnafluxed before I know if they are good anyway. If not then I have another set of Lo Perf. 379 heads someone is having checked out that I might purchase. I have already read the threads on the 817. I think the 147 heads will work. I just don't have the heads yet to do a VPC check. The question about the hardened seats, (you don't have to reply to this) was could a machinist install hardened seats in the 3781147 head to reduce the size from 2.06 & 1.72 to 1.94 & 1.66 (like the 379 heads) if the 147 heads have a VPC problem. Probably not. I can imagine the look I'll get from my machinist when I ask him. I know most people want larger valves not smaller. See, there is such a thing as a dumb question. Thanks again for the advice. Have patience with me; I’ll get there.

 

[SS425HP]

Heads

First of all, be very careful about trying to put hardened seats in 348 or 409 heads. Most I have talked to say not to do it. You are very close to water, and might go through to the water jacket. Then you have junk.
As to valve sizes, The diameter of the valve will have very little to do with the valve to piston clearance ( VPC ).The only way that could be a problem is if the piston relief for the valve isn't big enough. That's the notch in the top of the piston. I would doubt that .030 difference in diameter would be a problem. Like Ronnie said, set a head on the block, with modeling clay on top of the piston, and roll the engine through at least 2 revolutions. Then remove the head and see if there is a problem. You are looking for the thickness of the clay at it's thinnest point. That will be your VPC.
There are no dumb questions. Dumb is when you do something that causes a problem that a question would have answered. And, I'll bet we have all done that, too!!!!!!!!!!!!!!!!!
Keep asking. Better to find out now than too late.

Fred

 

[SteveD409]

I'll trade ya a set of 379s for your 147s! Fix your problem.

SteveD

 

[gearhead409]

60Nomad

i've been reading the answers to your questions for the past two days. the truth is with the cam and pistons you are using, any W head with any valve size will bolt on your engine without fear of piston/valve contact. anything bigger than 817s or 1147s would be a waste, your engine combo wouldn't need that much air. Hard valve seats? i don't think you will need them. i would use new stanless steel valves and let your machinist do his magic.

 

[60 Nomad]

gearhead409,
That makes me feel more positive about the 1147's working out. I was thinking that the stock cam would not have enough lift to cause me a problem. Good to hear it from someone with experience with the "W" motors. If the heads do check out ok, just to be safe, I'm going to do a vpc check for my own peace of mind. I feel like I have a better understanding of what I need to do now. Thanks everyone. I'll let you all know how things work out.

SteveD409,
I would rather have the 1147’s than the 379’s. But if I have a problem with the clearance, I will let you know.