Heads casting

[Macj1983]

 Putting theses on( after rebuilding them) my 350 I'm building it will be .30 over idk on cam yet but are these good heads?

[rich weyand]

They're listed here: http://outintheshop.com/faq/casting/heads.html.

76cc low-compression (8:1) heads.  Not the 327/350 heads with 1.94/1.50 intake exhaust valve diameters.  Yours have 1.72/1.50 intake exhaust.

You can get good torque and good mileage with the right cam.

[Macj1983]

So the head compression is 8:1
Does the cam and piston size affect this
(Newbie and have finished reading my rebuild book yet)
I would like to put in aggressive cam with a good lope on it but just under the limit so I can rum pump gas

[rich weyand]

Cam doesn't affect static compression ratio, but will affect dynamic compression ratio.  Pistons can affect compression ratio.

You can run pump gas on 8:1 heads all day long just about no matter what you do.  The only thing to need higher octane gas for is for higher compression.

An aggressive cam won't do anything with those heads but give you a lot of theoretical horsepower at high rpms.  Surf the net a bit and read about the difference between torque and horsepower, and which is more important for street use and why.

[74 C-10 Shorty]

Something to read here..

http://www.hotrod.com/techarticles/hrdp_0401_torque_horsepower_guide/viewall.html

[rich weyand]

Good article.  "remember the end goal is always to generate maximum power within your engine's operating rpm range"

Also: "Generally the rpm range that is most important is the area between peak torque rpm and peak power rpm. The car should be geared so that you shift 400-500 rpm beyond peak power, and the engine "falls back" to just beyond the peak torque point. Assuming a similar operating range, the engine with the greater area under the power curve between the power and torque rpm peak points makes for the better combination."

This is why I say look at torque.  On another thread, a fellow is looking at engines with peak torque at 3800 rpm.  Peak horsepower (per the article) is always about a third higher, call it 5000 rpm.  So do you normally drive between 3300 and 5500 rpm when accelerating?  Get something with peak torque about 3000 rpm and peak horsepower about 4000 rpm, and your operating range under acceleration is 2500 to 4500 rpm.  That's what I did, and I love it.

[Irish_Alley]

i agree with the ideal about where your peak should be compared to operating rpm. but this also depends on your gear ratio and tire size and trans. my 79 for example when im just driving it it hardly sees anything close to 3k. i have 4.10 ratio and 38" tires and transmission is sm465. the only time it comes close to 3k is going i think its about 70mph on the highway. so peak tq at 3k and hp at 4k wouldnt do me any good mine rpm range is something like 1k-2500. not saying its the same for everyone im sure its not like rich is saying his is between 2500 and 4k. so you have to think about your setup and plans for it later.

[Macj1983]

They're listed here: http://outintheshop.com/faq/casting/heads.html.

76cc low-compression (8:1) heads.  Not the 327/350 heads with 1.94/1.50 intake exhaust valve diameters.  Yours have 1.72/1.50 intake exhaust.

You can get good torque and good mileage with the right cam.

Thanks that was a good read and full of good info.
Still have a question the 8:1 means what to me? And the 1.72/1.5 means what and what effect is it having on.my Torque or horse power

[rich weyand]

An 8:1 static compression ratio means 1) that you can run any kind of pump gas you want, and 2) there is a limit to what horsepower and torque you can get out of the engine for a given displacement.  If you had a 9.5:1 compression ratio, for example, you have more room to play with cam parameters to get horsepower, but you have to run premium.  If you have an 11:1 compression ratio, you can do a lot of crazy things with the cam, but you have to run it on unobtainium or use an additive.  This is because as you compress a gas-air mixture it wants to spontaneously ignite, not waiting for the spark.  This is called detonation, or knock.  It tries to push the piston down when the piston is still coming up, and is very hard on engine components.  Octane delays the detonation of gasoline and allows you to compress it more before you light it off with the spark.

In general, high compression ratio is more important in designing a winder.  It helps some for torque, too, but you can get a lot of torque out of low compression ratios.

The size of the valves is one factor determining how much mixture you can flow through the engine, which is one of the limits to horsepower.  Basically, the power you get out of an engine depends on how much fuel you can move through it.  Bigger valves and cams that facilitate flow give more power.  The issue is that the cam setup that increases power at higher rpms, cuts it at lower rpms and vice versa.  A torquer down low will not have as much horsepower as a winder up top, but it will have more horsepower and torque at the lower rpms where you drive.  It will run out of breath sooner as the engine speeds up, and at higher rpms the winder will have more horsepower an torque.  So that's why you pick the cam to match the kind of driving you do, and for most people concentrating on high-end horsepower is the wrong choice.

[Macj1983]

An 8:1 static compression ratio means 1) that you can run any kind of pump gas you want, and 2) there is a limit to what horsepower and torque you can get out of the engine for a given displacement.  If you had a 9.5:1 compression ratio, for example, you have more room to play with cam parameters to get horsepower, but you have to run premium.  If you have an 11:1 compression ratio, you can do a lot of crazy things with the cam, but you have to run it on unobtainium or use an additive.  This is because as you compress a gas-air mixture it wants to spontaneously ignite, not waiting for the spark.  This is called detonation, or knock.  It tries to push the piston down when the piston is still coming up, and is very hard on engine components.  Octane delays the detonation of gasoline and allows you to compress it more before you light it off with the spark.

In general, high compression ratio is more important in designing a winder.  It helps some for torque, too, but you can get a lot of torque out of low compression ratios.

The size of the valves is one factor determining how much mixture you can flow through the engine, which is one of the limits to horsepower.  Basically, the power you get out of an engine depends on how much fuel you can move through it.  Bigger valves and cams that facilitate flow give more power.  The issue is that the cam setup that increases power at higher rpms, cuts it at lower rpms and vice versa.  A torquer down low will not have as much horsepower as a winder up top, but it will have more horsepower and torque at the lower rpms where you drive.  It will run out of breath sooner as the engine speeds up, and at higher rpms the winder will have more horsepower an torque.  So that's why you pick the cam to match the kind of driving you do, and for most people concentrating on high-end horsepower is the wrong choice.

Thanks rich that helps a lot. Yeah I rather have a " torque motor" I will be driving it Down the hwy but like you said i rather have my power coming in around 2k-3k rpm let me ask this what would you recommend for a cam then
So the motor will be .30 over
Heads are 8:1 and cam? I would like a good sound lope idk if that's would match what your saying
Thanks again

[rich weyand]

A loping idle generally means the engine doesn't want to run at low rpms, it's cammed for high rpms.  Most torquer cams have a roar when you get on them, but they idle very smoothly.  Basically, if you pull up alongside me at a light with a loping idle, it means I'm gonna smoke ya.

I decided on the Comp 12-300-4, and am very happy with it.  The torque comes on very early and strong, but it runs out of breath about 4600 rpm, which isn't an issue for me.  Torque peaks at 3000, hp peaks at 4000.  You can go to www.camquest.com, enter your engine parameters and run a dyno simulation on it and others.

[Macj1983]

Thanks that's what I need to hear going to check out that site now

[jaredts]

Those heads have the same size combustion chamber that most stock sbc's have:  76cc.  If you are building a bottom end and boring it .030" over, you will be buying pistons anyway.  Choose the pistons that give you the compression ratio that you want.  8:1 is not what I would choose if I was building a complete engine.  I don't think I would choose those heads either.  1.72 intake valve is small and limiting.

[rich weyand]

Agreed on the 1.72 intake valve.  The other 76cc heads have a 1.94 intake valve.  While the heads are off, one way to bump the compression ratio is to mill the heads down a touch.  Not sure what you can get away with.  I think .015 is OK, .030 might be.  Google it on the net.  If I had my heads off for some other reason, I would probably trim them down a bit. A set of 1.94 intake 76 cc heads can be had cheaply.  Not sure I would go to real performance heads, because they entail other changes, maybe more than what you want to do, and would appropriate for high-end horsepower.  You can still get a lot of torque out of a low compression engine.

[Macj1983]

Those heads I listed came with the block and would need to be rebuilt but if I can get better heads and not rebuild buying new ones is fine with me to
The motor is being striped and completely rebuilt
So what heads would u do?