Head ID 3917215

[thirstybob]

I was surprised to see these on my truck. Can anyone tell me whether or not there is any benefit to having these heads on my '74 C20/454? The engine runs really well, nothing fancy.
The casting numbers are 3917215. I understand they are from a 68-69 396/427.
Closed chamber (I don't know what the means)
Are they beneficial for performance or no?

[geezer#99]

More performance is possible due to the increase in compression ratio.
But that depends which pistons you have.
Here’s a thread that will help explain things.

https://www.hotrodders.com/forum/dif...ads-62689.html

[thirstybob]

Good info. Thanks for the reply.

[thirstybob]

Would you happen to know if I should try and increase the valve size? If so, how big can I go? I understand that close port heads have the ability for increased compression which is good? Will larger than stock valves be of any benefit?
My goal is to get as much respectable performance as possible in a low budget kind of way, working with what I have.
Currently, Edelbrock 1407, Performer manifold, true duals, stock exhaust manifolds, stock 14 bolt FF, TH400.
My next purchase is headers, H pipe and complete exhaust.

[geezer#99]

Likely not worth the time and expense!
If your motor spent most of it’s time over 5 grand it might help. Then better flow needs a bigger/better cam.
Headers can be the biggest hp adder for a bbc.
Many years ago a buddy and I built an L88 for a 72 nova. Had to use stock cast cast iron manifolds. No room for headers, even 1 7/8 inch ones.
We did a sub frame swap to a front steer 76 nova set up. Had lots of room then. 1 7/8 headers added 50 easy horses. Going even bigger to a custom built set of 2 1/4 inch headers added another 50 horses.
BBC luv headers.

[geezer#99]

What’s you un for timing on your bbc?

[thirstybob]

Originally Posted by geezer#99

Likely not worth the time and expense!
If your motor spent most of it’s time over 5 grand it might help. Then better flow needs a bigger/better cam.
Headers can be the biggest hp adder for a bbc.
Many years ago a buddy and I built an L88 for a 72 nova. Had to use stock cast cast iron manifolds. No room for headers, even 1 7/8 inch ones.
We did a sub frame swap to a front steer 76 nova set up. Had lots of room then. 1 7/8 headers added 50 easy horses. Going even bigger to a custom built set of 2 1/4 inch headers added another 50 horses.
BBC luv headers.

Ok, cool. Would you suggest a bigger cam? At this stage, I'm only interested in my butt dyno so there will be no "serious" tuning going on, yet.

[geezer#99]

depends What cam you have now.
If it’s stock it’ll run out of breath at 4500 rpm. Good for torque and mileage though.
A bit tricky swapping cams though. The bbc is known for eating cam lobes. The other problem you might have is a different cam may need piston mods to clear the lift.
Headers are the biggest bang for the buck.
Second best bang is timing curve. Especially at your elevation.

[thirstybob]

Originally Posted by geezer#99

what’s you un for timing on your bbc?

14 btdc

[thirstybob]

Originally Posted by geezer#99

depends What cam you have now.
If it’s stock it’ll run out of breath at 4500 rpm. Good for torque and mileage though.
A bit tricky swapping cams though. The bbc is known for eating cam lobes. The other problem you might have is a different cam may need piston mods to clear the lift.
Headers are the biggest bang for the buck.
Second best bang is timing curve. Especially at your elevation.

Gotcha. I believe it has an RV cam but I don't know for sure. I have a fair amount of low end torque.
Do you think 3" exhaust all the way back would hurt anything?

[geezer#99]

I’ve never been one for big pipes.
2 1/2 inch is adequate if you limit the bends.
Depends a lot on room for bigger pipes and budget.

[thirstybob]

Originally Posted by geezer#99

I’ve never been one for big pipes.
2 1/2 inch is adequate if you limit the bends.
Depends a lot on room for bigger pipes and budget.

Thanks Geezer, for taking the time to share your knowledge. I'm sure I'll have more questions at a later time. I do appreciate you.

[68c10owner]

With flat top pistons those heads usually give about 9.5:1 compression which is perfect. The smaller valves were great in engines like this. Once you start running more camshaft and winding it up higher you might see a increase in performance. Stock is 2.065/1.72 and the factory big valve heads use 2.19/1.72 on the closed chambers and 2.19/1.88 on the open chambers. You would possibly see a difference with some mild pocket porting and bowl work but stock they will perform well

[thirstybob]

Originally Posted by 68c10owner

With flat top pistons those heads usually give about 9.5:1 compression which is perfect. The smaller valves were great in engines like this. Once you start running more camshaft and winding it up higher you might see a increase in performance. Stock is 2.065/1.72 and the factory big valve heads use 2.19/1.72 on the closed chambers and 2.19/1.88 on the open chambers. You would possibly see a difference with some mild pocket porting and bowl work but stock they will perform well

Thanks for the input. It runs really well but I think it can do better with some minor messaging. It is (or I thought it was) bone stock and complete. No leaks, no smoke. Compression is 160, give or take, across the board with a constant 15 vacuum. I'll eventually tear it down and do some nasty mods but for now, headers.
You guys are a great help! Stay safe and healthy!