How to choose aftermarket cylinder heads?

[urbex]

The TL;DR version -

Looking to change out the stock peanut port heads on my otherwise not stock 489ci stroker BBC for some better aluminum heads (heh...as if the peanut ports are a tall bar to clear, lol). I'm trying to get a better idea of how to choose specs such as port volume, chamber size, etc., I've been reading dozens of pages on it, dozens of forum posts, and understand what the various specs ARE or how to measure them, and have tons of pages of generalizations (huge ports are bad idea on small stock motor, tiny ports will restrict high RPM power, smaller combustion chamber means higher C/R, etc.,), but not finding much on how to correlate all those numbers to my motor, and what I should be looking for.


The longer details -
About a year ago I put together a 489ci BBC for the K5, which was supposed to be a dirt cheap 454 swap to replace an overheated/seized 350...then due to my butter fingers, dropped a piston on the ground, which bent a skirt, and long story short..it became a less cheap 489 build.

I used a Scat complete balanced rotating assembly with -12cc domed pistons, Summit Racing 1789 hydraulic flat tappet cam (309 duration, .514 lift, 108LSA), Trick Flow valve springs, and reused a relatively fresh set of peanut port heads. Should be around a 9.5:1 compression, though I never CC'ed the heads to get exact numbers. I knew the heads would limit the motor, but again, was supposed to be a dirt cheap motor...I reused everything I could at the time, including factory 80's truck motor cast log manifolds with a very cobbled together exhaust that was a half-arsed combination of the factory exhaust off the '85 truck I pulled the motor from and the 2.25" dual exhaust the PO installed on the K5....though I have a set of new 2" primary/3.5" collector long tube headers waiting to go on.

Now, I'm ready to do something about those heads, but just not sure how to make sense of the bewildering array of choices out there, and don't really want to play a $2,000+ game of eenie meeny miney moe...

 

[folkenheath]

We can help narrow it down for you.

Are you planning to keep the same camshaft or upgrade to match the new heads?

What is your intake manifold? Induction system?

How much power are you looking for and what RPM do you want to turn the 489?

What about your transmission/converter?

What do you use this rig for mostly? What all do you use it for?

What gears and tires do you have?

What is your budget for this phase?

 

[urbex]

Truck details - Kind of upgrading it in stages, and accepting that it's going to be a lousy compromise way of doing things, and I'm likely to see overall performance dips along he way. Was hoping to keep this below $2,000, but I'm not sure that's a realistic number to be shooting for.

Currently running 33x12.50x15s, was planning on running ultimately running 37-40 of some flavor. Currently 3.73 gearing, will likely end up on 4.10-4.56 when the 1 tons go in.

4L80E trans, full manual (no ECM/TCM anywhere in truck). Running stock 3/4 ton converter.

I had chosen that cam thinking it was about as much as I could utilize with those peanut port heads, without getting into machine work for more lift, and I suspect that it will be the next bottleneck. Was planning on keeping it for a while, seeing as how it's still a fresh cam, but I'm not completely against swapping it out either.

Edelbrock 1406 carb on Weiand dual plane manifold, open element air cleaner right on carb, N/A now and no plans for power adders in the future. May go to a functional cowl induction hood in the future with a sealed air box under it. I'm sure that the carb will need to go bigger along with the heads, but it was a known good carb that I used for the break in miles.

Planned use is a just an all around weekend driver and off road toy - something that can cruise up state, go to the lake the back way, go camping, some easy off road trails, maybe go toss some mud after it rains. Will never be raced, outside of maybe a "for the heck of it because I'm already here" kind of pass down the mud or sand drags. I already have a full tilt rock crawler, and no desire to tear this one up off road. But it's still a straight up toy. As such, if there's an easy or not a whole lot more expensive route to more power, I'd go that way even at the cost of some street manners.

Really don't have a set power number or goal in mind, nor a desired RPM. Only real requirement for me is to stay within the limits of pump gas. I don't want to find myself in the middle of BFE trying to find race fuel. It would be awesome if I could keep running 87 octane in it, but I'm not against a steady diet of 91 either. I just don't want to be concerned about where to find fuel if I decide to go for a day trip in it. I'd be a pretty happy camper if I ended up with 500hp flywheel, with maybe a 5,500RPM limit. I'd probably be happy as a pig in schmitt with 600. I honestly don't see a whole lot of point in building it for high RPM, as I'm not likely to see north of 5,000 very often.

Admittedly, ever since I was a little kid, I had always wanted a K5 with a rowdy big block in it. At 40 years old, I still wanted that rowdy part, and had more of an ability to pull it off. Realistically, a bone stock 1985 K5 with a 350 in it would have accomplished everything I do with it just fine, except put that big grin on my face any time I stab the gas.

Honestly, I was OK with the stock 350 TBI for the most part, up until it overheated. Found what I thought was a screaming deal on a low mile GM rebuilt motor, then found the PO put a 350 clutch on it. Tore it down to make sure the imbalance didn't cause any damage along with a clean/paint/reseal, dropped that piston during assembly, couldn't find a single replacement that was close in weight, and found that by the time I bought new pistons then paid a machine shop to swap them, turn the crank, and rebalance everything, I was only a couple hundred short of a whole new rotating assembly.

Biggest thing is really wanting to understand why I have what I do, and not just saying "I went with blah blah parts because so and so said to".

 

[folkenheath]

600 ft-lb of torque is doable, 525 - 550 hp is doable pretty easy, and it will have over 500 ft-lb of torque through most of the RPM range, which is what big blocks do. You can easily make more power but you would need more RPM, more heads, more cam, etc.

You should stick with some oval port aluminum heads because larger rectangular port heads will have too low of air velocity at the lower RPM levels of your engine and lose bottom end. I recommend Brodix, Dart, Edelbrock, etc. They all make a decent oval port. The Edelbrock may be closest to your budget, the others will likely be over. I can get you some Edelbrock heads if you would like, I can probably get Dart too.

As for that cam, you can see that the duration @ .050" is 224 and the advertised duration is 309 with a lift of .514" and a 108 LSA.

Here's my take, the tight lobe separation makes it peaky with a rough idle. A wider lobe separation would be a flatter torque curve with a smoother idle.

The lift is fine for the peanut port heads but more lift would benefit the aftermarket heads to flow more air.

Duration sets the RPM the cam likes to work at. Also, you can see by the large difference between the duration @ .050 and the advertised duration it opens slowly. A hydraulic roller cam could open faster for more lift without needing higher RPM or a higher stall converter. For example, one of the Lunati Voodoo cams has 221 @ .050" and 272 advertised along with .575" lift. The difference is 51 degrees as opposed to 85 degrees. It also opens from 0 - .575 and back to zero again in 272 degrees, as opposed to .514" lift in 309 degrees. This faster rate of the roller lifter makes more power in a similar RPM range. I actually have the next step up in my truck 489 (282/290 with .600" lift). You will be limited with your stock converter as too large of cam will want a higher stall converter to get into the power curve.

My recommendation is to get some good oval port aluminum heads with some hydraulic roller valve springs in them. You can swap the springs with yours(you may need to shim them), and keep the hydraulic roller springs in case you upgrade the cam down the road. I can put your specs into my app ancd calculate the static and dynamic compression ratio to help you determine the correct combustion chamber size for your combination to still use pump gas.

Also, which Weiand intake do you have? Some intakes could be a major bottleneck, especially with your new heads.

 

[urbex]

Intake is a Weiand 2P 1080*, oval port. I can get the specific part number of it when I get home tonight.

My recommendation is to get some good oval port aluminum heads with some hydraulic roller valve springs in them.

This is exactly what I was falling on before...any of the big names make a wide variety of heads, and merely just picking a "good brand" doesn't really say/do much. Just to take say Dart as an example - I KNOW there's going to be a massive difference between the 19900010 head and the 18275070 head, besides a $3,000 difference in price (and no, I'm not spending 8 grand in the heads regardless, lol). Price aside, I'm pretty confident that a 440cc intake runner and 82cc chamber is not at all going to work well for me anyways. Granted, that's an extreme comparison, and anyone considering the Pro 1 heads isn't likely also going to be considering the Big Chief heads for the same motor.

But even with just the intake runner CCs (though I do realize there's far more to this than merely focusing on runner CCs or chamber size), I can easily find heads with oval ports that run from less than 270cc clear up through to more than 340cc. I know chamber size helps to determine compression ratio, but I've seen large chambers on relatively low compression absolutely embarrass similar motors with small chambers/high compression.

It's not that I don't appreciate the recommendations, but it's that I'm really trying to wrap my head around how the various specifications affect the performance of the engine, and getting beyond just what the cam does.

I think what I really need to do is spend some more quality time with the engine simulators plugging in a bunch of different numbers and just see how things respond to various changes.

 

[folkenheath]

Be careful with engine simulators, I like to say they are good for comparing how it affects the "curve" but the actual numbers may be way off because of all the variables. If you just want to see the effects of more duration, more lift, higher flow, that's all good and dandy. But the flow doesn't show the velocity. There can be two heads with similar flow but different velocities and they won't perform the same. You can kind of get an idea of this by looking at low lift or mid lift numbers. Peak flow is only at peak lift, the valve goes through low and mid lift twice on the way to and from peak lift.

When it comes to heads, it's all about flow and velocity. Modern heads have more efficient ports and still flow good with higher velocity than an older large port head with the same flow. And a big chief head with less valve angle requires different pistons (for valve relief & combustion chamber shape)and a lot of RPM to get the flow high enough where the velocity is there, they can make good power though, many drag racing engines are up around 1200 hp naturally aspirated on a standard bore space BBC, but you won't be driving that one to pick the kids up from school on a Friday. It's a tradeoff, too small of ports and the flow isn't there, and it will fall flat at very low RPM. Too large of ports and the velocity isn't there and you will lose your bottom end. You want to find the sweet spot for your combination that give you enough flow for your upper RPM range without sacrificing the bottom end you need. For your RPM range you would want a head in the 270-315 cc intake port range. I would say The Edelbrock RPM Oval Port, the Dart Pro1 275 Oval Port, or the Brodix Race Rite Oval Port.

It isn't about just compression or large or small chambers, it's about the whole combination, including the pistons, heads, cam, intake, carb or EFI, exhaust, ignition, timing, etc. It all has to work together to get the best results, more compression by itself isn't going to win if the cam and heads are crap or don't match up with each other and everything else.. You can read books and build engines for decades and still be learning stuff the more you do.

 

[wasted wages]

urbex,
are you definitely set on using aluminum heads?
There are quite a few manufacturers that sell cast iron heads that are equally good, or maybe even better for street use.
I know there is a weight trade off, plus the pinging issue that can be dealt with, but overall it may be worth looking into.

edit: Even the General GMPP has some decent heads that came on the 454HO. In both aluminum and cast iron.
Rectangle ports, Roller springs, decent sized valves, guide plates, good CC numbers for low to mid comp. ratios.... maybe take a look at those.

 

[6872xtc]

I wouldn't put rectangular port heads on a truck unless it is purely a race vehicle.

Aluminum heads can not only shed weight, but also dissipate heat. Just a consideration.

Great information @folkenheath

 

[wasted wages]

GMPP 454HO cast iron heads are rectangular..
The ZZ454HO aluminum heads are oval port..
Both rollers, and I think the aluminum head has a smaller chamber volume...

I run a GMPP 454HO in my buggy..cast iron heads rectangle ports... has plenty of low end torque with a dual plane and 850 cfm Jet performance stage 2 Q-jet.

I used to have a 8-71 blower on it with 2 -750 holley's... was fun in the mud, but not for crawling...

 

[6872xtc]

GMPP 454HO cast iron heads are rectangular..
The ZZ454HO aluminum heads are oval port..
Both rollers, and I think the aluminum head has a smaller chamber volume...

I run a GMPP 454HO in my buggy..cast iron heads rectangle ports... has plenty of low end torque with a dual plane and 850 cfm Jet performance stage 2 Q-jet.

I used to have a 8-71 blower on it with 2 -750 holley's... was fun in the mud, but not for crawling...

Ok, but you bought crate engines, correct? If you are shopping for heads, then why not look at ones which are more in line for the engine and use of the truck? And @urbex already has an oval port intake, so that would be a consideration.
I would guess that it's possible to get identical chamber and runner volumes in aluminum and cast iron, would you want identical specs?

Mine has oval ports, and the torque and power was pretty good at the 2K RPM which the dyno started recording. ( considering how mild mine is)

Obviously, the weight of the truck and gears will have an influence, too.

 

[urbex]

Biggest reason for looking at aluminum is having to heave those stupid heavy hunks of iron out/in the truck...I popped a head gasket on one last weekend (99% sure I forgot to retorque the head bolts after a few heat cycles. Blew out the fire ring, and a chunk of gasket literally parted ways with the engine), and nearly killed myself heaving it out of the truck. NOT a fun time when you're on a 9 inch lift.

To a lesser degree, because I can, lol.

Also, I know for most people "drives on street" means they want/expect it to be able to idle in bumper to bumper traffic for hours, to have a factory stock smooth idle while still sounding mean, to have instant tire shredding torque right off idle, etc etc etc. That's not my expectation nor need...if it was, I would have just did the same LS swap that everyone else does. This is truly a weekend toy for me. It doesn't need to get me to work. It doesn't need to go get groceries. It's not going to go take the kids to school. I'm not going rock crawling with it...I already have a full tilt trailer queen rock crawler, with 4 links/coilovers, deep gearing, engine swap, full hydro steering, spooled front/rear, etc etc...I don't need/want another crawler.

Yes, I KNOW there's LOT more than just compression, just as I said a few times, and the whole reason I started this - I'm trying to find the resources to learn more about how it ALL intertwines and works together. I get that most people really don't understand how to make the choices themselves, or just call X head company's tech line for their recommendations, and that's fine. This is also why I didn't ask "what heads should I buy?" I can copy some other company's or builder's engine just fine. But copying their specs doesn't do much for helping me understand WHY those parts were chosen to go together.

 

[folkenheath]

So in selecting heads there are several parameters as you are aware of. I will try to summarize "how" to select them. I usually would select them before I do the short block, because the heads and cam really decide how much power you are going to make and at what RPM range. And then the intake and short block components need to be selected to withstand that power and RPM. But if you change stroke or cubic inches that changes the head port requirement again and possibly the RPM range depending on if you want it to move, so it all has to work together. Also the pistons, head and cam all have to match for the proper RPM range and compression ration for the fuel you are using.But since you already have the short block done the thought process for upgrading heads is slightly different.

- material, if you can afford aluminum, get it, it's better in pretty much every way(except cost). Lighter, conducts heat faster, doesn't rust, etc.

- port size, as we mentioned before, this is selected based on airflow requirements. Airflow requirements are based on engine size and RPM. To large of port will lose velocity and bottom end, too small of port will lose top end. For your RPM range you will want to stick with an oval port head in the 270 - 310 cc range for a BBC. When you switch heads, volume numbers change because of different port lengths. So I wish they would lists heads by port cross sectional area instead. Its an easier way to calculate air velocity from CFM too and it would be more comparable across different engines. If you think you might switch to a solid roller cam for racing someday then you would use a rectangular port with larger ports and more flow to sustain the engine at higher RPM.

- valve size, larger valves flow more with lower velocity, and vice versa, just like port size. Typically head manufacturers match the correct valve size for the corresponding port size. Sometimes you have a couple options for the same port size. This comes down somewhat to RPM, but more so bore size. Smaller bores, especially in a big block, will not only shroud, but also literally collide with too large of valve in a bbc head, the combustion chamber is commonly larger than the bore itself, especially on anything smaller than a 4.5" bore. So if you have a 489 with a 4.28" bore a 2.19 or 2.25 valve would be fine. Some actually machine a taper in one portion of the top of the bore in the block to unshroud the valve and match the chamber (I do this). But you can't go to deep it or will get into the top ring at TDC.

combustion chamber size - this dictates your compression ratio and some combustion chamber shapes are more efficient than others, particularly when the valves are rotated more vertical. Compression can be calculated in a few different ways for engine building. Static and Dynamic. There is also "effective" compression if you are building boost but that doesn't apply here. Static compression is just the ratio of the volume in the cylinder at the bottom of the stroke vs the top of the stroke. So at BDC it's the cylinder volume plus the gasket volume plus the combustion chamber volume. And then at the TDC its just the gasket volume plus the combustion chamber volume. Now, the actual combustion chamber volume can also be affected by the piston dome and also the exact depth of the piston in the hole. In the app I wrote it will calculate this for you.

Dynamic compression takes it a step further and calculates the compression ratio only after the intake valve closes. This more closely resembles what the engine actually sees. The connecting rod length slightly effects this, but the main effect is by far the camshaft which determines when the valve closes. You typically want to stay around 8, sometimes 8.5 with pump gas and aluminum heads as the fuel just can't take much more cylinder pressure without detonation. This is a little more complicated as you need to calculate the exact depth of the piston in the hole at the point the valve closes, but nothing too difficult, my app will calculate this as well. I am going to show you a screenshot of a 489 with a dif, and your 489 with your cam (assuming the same heads and gaskets, rods, etc., I already know you have the same piston dome. You'll notice because of the slow ramp rates the flat tappet cam bleeds off a lot more compression as the dynamic is more than a full point lower than that roller cam profile with similar duration @ .050. But if you switch cams someday you have to plan for that.

So if you leave all else equal and just heads (combustion chamber size) and cams (intake valve closing) you can watch how it affects your static and dynamic compression.

I hope this helps you understand, I could write for days about this stuff I enjoy it so much, but I don't have that much time and I don't really like typing. FYI, if you move to a 119 cc head static drops to 9.5 and dynamic drops to 6.55:1.

 

[folkenheath]

I am going to add this here for more reading on the subject...

https://dartheads.com/cylinder-head-fundamentals-materials-options-and-terms-explained/

Also, if you need me to run a number for you in the app let me know, I could do that for you if it helps you decide which head you need.

 

[urbex]

Thank you! Now we're getting towards more of what I was looking for. I wasn't looking for spoon fed hand holding, attempting to become a big time engine builder, or any thing like that. Rather just some nudges towards some resources that I can use to learn more about what I'm doing, and how to make better parts choices. Just as the Dart page said - "Choosing a cylinder head is one of the most important decisions you will make when it comes to building a performance engine", but finding the information on HOW to choose the appropriate heads is very difficult beyond "call Dart/AFR/whoever and have them tell you what head to get", but that doesn't help me better understand the why.

I _thought_ I did OK based on constraints that I placed on myself when I built this motor initially (largely total cost related) and actually changed my mind on various things a couple dozen times, lol. Once I got it going, it definitely didn't end up how I thought it would, despite knowing I was going to be taking a hit with the peanut port heads and relatively small carb, though I also believe the stock cast exhaust manifolds and lousy exhaust pipes are also choking it off, which is why I have the new set of headers sitting here waiting to go on this weekend.

Not so much in a disappointing way (I had nightmares that I was going to get it fired up, find it sounding like a stock 1985 V6 with massive exhaust leaks and making about as much power), but also not making as much power as I thought it would. Now, I want to have a better understanding of where I went wrong, whether it was on the side of poor parts choices, poor expectations, poor tuning, or a combination of all.

But at the same time, I want to understand and learn WHY part X or part Y was maybe a bad choice, beyond just hearing "you should have used this cam/piston/heads/carb/crate engine/whatever".