SBC Heads

I'm in the planning stages of building my next SBC 350. My question is, I'm looking for a set of heads that will give me some good street performance . I'm going with a full roller cam, nothing to big Comp 224/230 degree hydraulic roller performer rpm intake ( May be smaller ), edelbrok 600 cfm carb and headers Msd ready to run dist, 700r4 trans with 373 gears. 17" wheels.
I,m looking for suggestions on a decent set of heads that would be good for street performance, It will never see the track. Are the Vortec Heads as good as RHS, Pro Comp, etc, good for my application. I do not want to spend $1,500 on a set of heads that will not fit my needs.

you might want to try edelbrock. they have excellent products and decent prices. they can match your setup with the correct heads to use.

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Originally Posted by Jim Standley

I'm in the planning stages of building my next SBC 350. My question is, I'm looking for a set of heads that will give me some good street performance . I'm going with a full roller cam, nothing to big Comp 224/230 degree hydraulic roller performer rpm intake ( May be smaller ), edelbrok 600 cfm carb and headers Msd ready to run dist, 700r4 trans with 373 gears. 17" wheels.
I,m looking for suggestions on a decent set of heads that would be good for street performance, It will never see the track. Are the Vortec Heads as good as RHS, Pro Comp, etc, good for my application. I do not want to spend $1,500 on a set of heads that will not fit my needs.

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I would try a set of the 180 cc Dart Iron Eagle heads.
I would keep the RPM Performer.

Eric, 64 or 76 cc ?

the cc of the head chamber would have to do with the pistons you run for what you want to see for cr the iron eagles or the pbm iron heads of 180intake cc should be ok

If I went with the 64cc what are the advantages of having the larger 202/160 valves compared to the smaller 194/150 valves ?

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Originally Posted by Jim Standley

Eric, 64 or 76 cc ?

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64 cc's with the 350 engine will work fine.
A flat top piston like a Speed Prp L2256f will give you 9.75 to 1 for a comp ratio with 64 cc heads.

The valves won't make much of a difference to the performance on a street engine. At low lift the shrouding on the long side turn out of the intake runner is higher, so airflow will actually be decreased with a BIGGER valve. Big valves only help on higher lift applications or on high-RPM applications where fast, high volume breathing is required. If you're not planning to race it I would stay with the smaller valves, they also leave more material between the valves, where most head cracks appear. Chose a good chamber shape and valve seat shape (maybe try a 30° seat, good for low-lift flow), almost all of the large chamber heads have open chambers with less quench area (that's where the chamber is flat and parallel to the piston and thus squeezes mixture into the main chamber on the compression stroke, this puts off detonation. That's generally not good for performance.
But a couple of questions:
What RPM are you aiming at?
What HP do you want to reach?
Really only street?
How heavy is the vehicle?
Are you interested in mileage?
When we know this we can give you a bit of a better estimate on the heads you want to use. And don't forget, the parts most crucial to performance are heads and cam, and they have to match up nicely. It's easy to get an engine to starve at 3500 RPM, manage 8mpg and reach 200 ftlbs of torque with a set of $ 2.000 heads... But it's also possible to get 300HP out of a set of $ 50 rebuilt junkyard heads, if you match the crucial parts together nicely...
Give us some more info and we'll give you some more help :)
Max

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Originally Posted by MadMax

The valves won't make much of a difference to the performance on a street engine. At low lift the shrouding on the long side turn out of the intake runner is higher, so airflow will actually be decreased with a BIGGER valve. Big valves only help on higher lift applications or on high-RPM applications where fast, high volume breathing is required. If you're not planning to race it I would stay with the smaller valves, they also leave more material between the valves, where most head cracks appear. Chose a good chamber shape and valve seat shape (maybe try a 30° seat, good for low-lift flow), almost all of the large chamber heads have open chambers with less quench area (that's where the chamber is flat and parallel to the piston and thus squeezes mixture into the main chamber on the compression stroke, this puts off detonation. That's generally not good for performance.
But a couple of questions:
What RPM are you aiming at?
What HP do you want to reach?
Really only street?
How heavy is the vehicle?
Are you interested in mileage?
When we know this we can give you a bit of a better estimate on the heads you want to use. And don't forget, the parts most crucial to performance are heads and cam, and they have to match up nicely. It's easy to get an engine to starve at 3500 RPM, manage 8mpg and reach 200 ftlbs of torque with a set of $ 2.000 heads... But it's also possible to get 300HP out of a set of $ 50 rebuilt junkyard heads, if you match the crucial parts together nicely...
Give us some more info and we'll give you some more help :)
Max

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With the hyd. roller cam is running I would look into after-market heads based on the lift and duration.
If he runs with stock heads I would guess he would give up 30-40 hp.

@ erik: 30-40 hp over the valves? That seems hard to believe... Or do you mean over the heads altogether? You're the head-expert (thanks for the PM btw), I guess you can give him an exacter estimate than me. I was only trying to save him from dishing out big $$$ ;)
Aftermarket always costs money, there are good heads out there for Street performance from World Products or Dart (or Edelbrock etc, but I wouldn't go Alum on a streeter), but I'm a firm believer that you can get tire spinning performance and good mileage out of modified GM parts. I have done so myself and my "stock" GM engine spins the tires (good grippy ones) on my 5000lbs van even when shifting into second (with a 1600 stall :toocool: ). OK, I also do have a full roller valve train with a Comp Retro roller cam, mild porting job on my 492 heads and flat tops. My cam package did cost 900$ or so, but the heads came free, just had to clean them up a bit :) :) :)
As you know, you can always combine two of the following words:
good, fast, cheap.
So you have to compromise somewhere along the line...

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Originally Posted by MadMax

@ erik: 30-40 hp over the valves? That seems hard to believe... Or do you mean over the heads altogether? You're the head-expert (thanks for the PM btw), I guess you can give him an exacter estimate than me. I was only trying to save him from dishing out big $$$ ;)
Aftermarket always costs money, there are good heads out there for Street performance from World Products or Dart (or Edelbrock etc, but I wouldn't go Alum on a streeter), but I'm a firm believer that you can get tire spinning performance and good mileage out of modified GM parts. I have done so myself and my "stock" GM engine spins the tires (good grippy ones) on my 5000lbs van even when shifting into second (with a 1600 stall :toocool: ). OK, I also do have a full roller valve train with a Comp Retro roller cam, mild porting job on my 492 heads and flat tops. My cam package did cost 900$ or so, but the heads came free, just had to clean them up a bit :) :) :)
As you know, you can always combine two of the following words:
good, fast, cheap.
So you have to compromise somewhere along the line...

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No,I meant doing a complete head change for the 30-40 hp gain.
At 400 to 425 hp I start to look at aftermarket heads.
It just makes it that much eaiser to build hp.

Yeah, but let's say he buys the cam now. Then he buys aftermarket heads. Then he might get as little as a 40hp gain. If he buys a cam that will match modified stock heads like the L31's or 492's (or 186, 041 etc.) and get a set of those heads and modify them he might see a 100hp increase for less money. Any chain is always only as strong as its weakest link, and an engine depends totally on the matching of parts. Just buying an Edelbrock carb will nominally get you a 0 HP increase. I guess for a good induction setup he'll be looking at maybe $ 1000. That would get him in the 350HP range with the short block he mentioned. Add 500 if a full roller setup is really wanted. But that should get him done "all inlcusive", gaskets and all. Maybe shop around on Ebay for some old closed chamber heads and a second hand Performer intake and carb (carb not bigger than 600, intake NOT rpm, otherwise a stall higher than 2000 or something will be required.) Roller cams can be bought used, too, provided they are in good condition, but they normally show no wear.

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Originally Posted by MadMax

Yeah, but let's say he buys the cam now. Then he buys aftermarket heads. Then he might get as little as a 40hp gain. If he buys a cam that will match modified stock heads like the L31's or 492's (or 186, 041 etc.) and get a set of those heads and modify them he might see a 100hp increase for less money. Any chain is always only as strong as its weakest link, and an engine depends totally on the matching of parts. Just buying an Edelbrock carb will nominally get you a 0 HP increase. I guess for a good induction setup he'll be looking at maybe $ 1000. That would get him in the 350HP range with the short block he mentioned. Add 500 if a full roller setup is really wanted. But that should get him done "all inlcusive", gaskets and all. Maybe shop around on Ebay for some old closed chamber heads and a second hand Performer intake and carb (carb not bigger than 600, intake NOT rpm, otherwise a stall higher than 2000 or something will be required.) Roller cams can be bought used, too, provided they are in good condition, but they normally show no wear.

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I.M.O.,modified stock heads are a waste of time and money un-less you have access to a flow bench and have a lot of time on your hands.
The other problem is some of those casting numbers are over 30 years old.
I can't see putting all that money into old castings.
You can get into new Dart or World heads for around $900 complete.
To go through a set of old heads with new seats,new guides,surface,valve job,convert over to screw-in studs, bowl -blend,gasket match,etc.valves, springs, locks,retainers,you will have well over $700 to do it right.
Then you have 30 year old castings that are more prone to cracks and don't flow as well as the new heads.

Eric and Madmax, you both seem to know allot more about heads then I ever will, But to answer the questions that Madmax asked. The max RPM would be 5500 (probably not likely) I would like to achieve 375 to 400 HP. Yes street only want a good performance street motor. (I have no intentions of track racing) The car is a 55 Bel Air, 3200 Lbs. Mileage would be good but I do not want to sacrifice power. I now have a 700r4 with 2000 stall torque converter.
I do not mind spending 900.00 on a set of heads that will work with what I'm trying to accomplish. I want to be quick off the line, with a constant torque up to 5500 rpm. I just do not want to get over sized heads and valves if I do not need them. I hope this helps.:D

Yes, this helps quite a bit. From your previous post it sounded like you were trying to save money. If you have in the region of a thousand dollars to spend, then of course I would go aftermarket, too. And if you want constant torque up to 5500 RPM, you might give the Performer RPM a try. But in that HP-region I'm sure Erik can help you out better, he has much more experience than me. Just don't go for the "bigger is better" rule, especially on intake runners and chamber size. Maybe a 190cc runner and a 64cc chamber, something like the Dart Iron Eagle, or the Sportsman II form World Products. If you look into World Products, I wouldn't get anything which is stamped "SR", that stands for Stock Replacement, i.e. it's street legal, but generally won't get you 400 horses. Ask around some more, but I would think something like this is a fair price:

http://cgi.ebay.com/ebaymotors/DART-...QQcmdZViewItem

Don't be fooled by the "small" runner volume, these heads flow a lot better than the GMs right out of the box, so the runner volume isn't always exactly equivalent. Air doesn't see size or finish, it only sees flow-numbers. Or you get just a bare head and install whatever springs the cam firm suggests, which is certainly a better move than using any old springs.

Let's see what the others say...
Max

Thanks for your input Max, But I would still like to know what advantages 202/160 valve would have over 194/150 valve on a 64 cc head ?

The advantage is this:
A bigger valve has a bigger circumference and so the cylindrical area through which air can flow is bigger at the same valve lift (about 4% larger for the 2.02 valves than on the 1.94 valves). So more air can flow through the opening the valve creates in the same time. As a result of which you could use a lower lift cam for the same performance (less stress on the valve train) or you automatically get higher performance because of a bigger amount of mixture being drawn into the cylinder with the same lift cam.
Sounds good, BUT:
This is only theoretical: when valve sizes are bigger the edge of the valve is nearer the chamber wall, so the area between chamber wall and valve edge decreases (shrouding). Depending on the exact chamber shape this can even cause performance to drop with a bigger valve. One move is to deshroud the chamber somewhat, but then your compression will go down slightly. A rule of thumb is that walls which are more than a quarter of the diameter of the valve away from it aren't an impediment to airflow. This isn't possible in any two valve engine I know of, you would have to cut more material out of the chamber wall than is actually there.

So what does that mean?
If you're going to go aftermarket anyway you'll alomst certainly have 2.02 valves installed, because most performance heads have them anyway. I guess the Techs there at Dart or World did their flow testing and found 2.02 valves to be better for airflow reasons, so they put them in. I'd trust them in those things. :)
Also: the resale rate is higher because people think bigger is better :LOL: :LOL:

The bigger exhaust valves are actually more of a benefit, shrouding isn't so much of an issue here because pressures are so much higher. A bigger exhaust valve causes less backpressure. The pistons has to press the burnt charge out through the exhaust valve opening, this robs power. The faster and easier it is for the piston to push the charge out of the cylinder the more torque will be available at this engine speed. The valve being bigger it has a larger seat area and heat gets transfered from the valve to the head faster. Exhaust valves get damn hot and they don't like it :whacked:
I don't know of a downside to bigger exhaust valves except for cracking issues because the amount of cylinder head material between the valves is less, but I guess this isn't much of an issue.

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Originally Posted by MadMax

The advantage is this:
A bigger valve has a bigger circumference and so the cylindrical area through which air can flow is bigger at the same valve lift (about 4% larger for the 2.02 valves than on the 1.94 valves). So more air can flow through the opening the valve creates in the same time. As a result of which you could use a lower lift cam for the same performance (less stress on the valve train) or you automatically get higher performance because of a bigger amount of mixture being drawn into the cylinder with the same lift cam.
Sounds good, BUT:
This is only theoretical: when valve sizes are bigger the edge of the valve is nearer the chamber wall, so the area between chamber wall and valve edge decreases (shrouding). Depending on the exact chamber shape this can even cause performance to drop with a bigger valve. One move is to deshroud the chamber somewhat, but then your compression will go down slightly. A rule of thumb is that walls which are more than a quarter of the diameter of the valve away from it aren't an impediment to airflow. This isn't possible in any two valve engine I know of, you would have to cut more material out of the chamber wall than is actually there.

So what does that mean?
If you're going to go aftermarket anyway you'll alomst certainly have 2.02 valves installed, because most performance heads have them anyway. I guess the Techs there at Dart or World did their flow testing and found 2.02 valves to be better for airflow reasons, so they put them in. I'd trust them in those things. :)
Also: the resale rate is higher because people think bigger is better :LOL: :LOL:

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Max,is this very well written.
I am sure there are people who have done dyno testing to see at what point and time you start to benefit from the larger valves.
Never forget that the port shape is also very important to flow numbers along with the intake being an extension of the port.
One area I have noticed a lot better flow numbers is going to an 8mm valve stem.
The 8mm is just a little smaller than the 11/32 which tends to help the flow a lot around the guide area.

To be exact, there is of course more to it, than I wrote in my previous posts. If you want the more or less full story behind the valve size and flow characteristics of a head, here goes:

You have to make a compromise between flowing speed and flowing volume.
The reason is this:
Flowing fluids and gases have certain physical properties:
(1) flowing speed and internal pressure are indirectly proportionate
(2) speed and mass are directly proportionate
(3) high pressure enhances condensation, low enhances atomization
(4) port area perpendicular to the flowing direction is indirectly proportionate to the flowing speed (i.e. it is directly proportionate to the pressure, see (1))
(5) a high pressure difference from one end of a tube to the other causes high flowing speed
(6) a large perpendicular area lets more gas pass at the same pressure difference

Directly proportionate means that when one size is increased, the other is increased by the same amount, so if you double the flowing speed you automatically double the flowing mass per second.
Indirectly proportionate means that when one size is increased, the other is decreased by the same factor, so if you double the speed, the pressure will be only half of what you had before.
Perpendicular area is the area, through which the flowing takes place at a ninety degree angle
I think the other things are clear. These simple physical relationships are almost all you need to calculate the flowing numbers if you know the mathematical function of the port shape. As this is unknown I will not go into it any further, but will try to stay "unmathematical" :)

Now I would like to join a few of these statements together to make sense in a cylinder head:
The ultimate goal is to get a certain amount of evenly distributed mixture into the cylinder in a short time. The way an engine does this is by moving the piston down the bore on the intake stroke, thus causing a pressure drop, and the "missing" air wants to be replaced by something else. The pressure drop is always the same because the same amount of air is missing on every stroke (an eightth of the engines displacement). But at WOT the "vacuum goes down", because the throttle blades are open and a lot of air can pass through them (6) (high speed => low pressure).

In a race engine you want to cram as much mass of this mixture into the cylinder as you possibly can, so the perpendicular area of the whole port has to be large (reason (6)). There is then a lot of mixture in the engine, the correct ratio of which is what is important. You don't always get the same amount of mixture into the cylinder per stroke, at WOT the cylinder draws in much more than at small throttle openings (reason (2) also applies to the throttle opening, which is where your intake runner starts: Small opening keeps the flowing speed down, so less mixture per time unit is sucked through it).
In a truck engine you want maximum efficiency, so you don't always want a lot of mixture in the cylinder, you just want it to burn as well as possible, so a fine distribution of the fuel molecules in the air is required. The fine distribution is enhanced by the low pressure (3), which is to be achieved through high flowing speed (known as port velocity, which you have probably heard of, this would be reason (1)), and this high flowing speed is achieved by making the runner area smaller.

This would also explain why bigger valves generally flow more air: The perpendicular area is larger. High lift also achieves this, but the physical reason behind this is also (6). Shrouding, too, is a direct effect of there being too little area between the valve and the chamber wall, through which the flow is slowed down (smaller area => slower flow => less mass per time).

An interesting effect with bigger valves is: the valve throat is then bigger than the nominal area of the rest of the port: So right before the valve the pressure goes up and the mixture forces itself into the cylinder (4). In an optimal engine this effect would be timed when the piston is actually already moving upwards again. As you know, air has a mass, so it has momentum, and the flow in a certain direction doesn't stop immediatley the suction from the cylinder is gone. It continues for a short while to travel in the same direction of its own accord. So if the pressure rise is experienced in this time you can close the intake valve a good deal later than otherwise, thus having a higher mixture amount in the cylinder as would normally be possible.

This immediately shows one common misconception: A large port will actually keep power down at low RPMS, because the flowing speed isn't high enough (because of the bigger area the speed goes down) to keep the mixture finely atomized (because the pressure is high). So the mixture won't burn smoothly (only the outside of the droplets of fuel in the mixture is burnt, so the smaller the droplets the better). And there wont be much charge in the engine at low speeds, because the pressure difference occurs slower, so less air is drawn into the cylinder. Only at high RPMs these big heads come into their own: When the engine turns faster the pressure drop becomes more abrupt and pulls on the mixture harder, so it will flow through the big port at high speed, so it also gets well distributed. But only at high engine speeds. A small port is better for low RPMs because the mixture is drawn into the cylinder fast, so it's finely atomized and will burn smoothly. But at high RPMs this small-port-engine will "starve", because of (6) - the flow area simply isn't big enough to get a lot of air through the port at the pressure drop we have. Because you don't need a lot of mixture in the cylinder in a low-RPM engine you can save the chapter about the bigger valves pressing mixtur into the cylinder after the pistons has passed BDC.

That about sums it up I think. It's still quite physical I'm afraid and rather long, but I think it gets you in the ballpark when choosing cylinder heads, even if I have added no exact numbers: I specially didn't want to do this, as the only numbers air is really concerned about are the flow numbers, a port with a different shape might flow worse at a bigger volume than a small one, depending on the exact shape funtion it has. So the question is not : do I want 190cc runners or do I need 230cc ones? The question should be: do I need 230cfm at .200 lift or more like 260cfm?

BTW, "swirl" and "tumble" are fine words, but they're all included in the port shape, generally at high flowing speeds you will get more tumble and swirl (imagine running through a tight tunnel with a million other people. It's much more difficult to go in a straight line then as if you were only walking slowly. In fact, this is pretty exactly what happens in "port-reality"). This also keeps the abolute speed of the mixture up: The molecules don't only move straight towards the cylinder, they also move in all sorts of other directions, all adding to the overall speed, keeping pressure down and atomization up, so you get a nice, efficient burn even at low engine speeds, which is what you want in a daily driver. (btw, "swirl polish" doesn't get you anywhere at all, as the air doesn't know what finish you put on your valves, hardly any of it ever touches the valve...).

Right, this is the end. :LOL: :LOL: :LOL:

OK, not quite: I like the following quite precise analogy:
Imagine you have a 20ft rope lying in front of you. Give it a slow pull of 2 ft (one slow swing of your arm). What happens? The rope has travelled 2 ft in your direction, it is still straight. Now give the rope a sharp tug of the same length, but much harder. With luck the whole rope will be lying tangled up at your feet. This is what race engines rely on: At high engine speeds the pistons pulls so hard on the air, that more than a cylinder load is pulled into the cylinder and this is well disordered.
But when you combine these fast engine speeds with a lot of "rope" being in your cylinder you can easily understand that the amount of rope you need goes up. So does the amount of fuel you need.

This is it now, finally :LOL: :LOL: :LOL:

Max, that's allot to absorb. Thanks for the time you put put into writing it. I'll print it out so I can go back and read again when I have a laps in memory. Thanks for the information. :cool: