I'm researching an engine build up, and trying to decide on what heads to go with. I understand AFRs are apparently the best out there, but I don't know if they're more than what I really need. (I'm looking for a 12sec daily driver.)

From this thread, "
l98 iron head project part IV (Finally) ", my stock heads could be ported to flow better than out of the box AFRs.

So is there any advantage to aftermarket heads?

I understand that there is a lot of work involved in porting heads, and the cost and flow might be comparable to just buying a set of aftermarket heads. But if they are the same, why go aftermarket? What am I missing?

 

Aftermarket castings are typically of higher quality (no core shift, no porosity) that factory castings. Core shift can lead to nasty surprises as you're working on the last port of the 2nd head and break through to oil or water - not particularly common, but it does happen.

Aftermarket castings typically have more material on the deck to reduce the likelyhood of cracking.

Aftermarket castings have runner paths that are more optimized than factory castings.

Factory castings have press-in rocker studs (limit lift capability, have been known to fail with stock lifts), stud holes that protrude into the ports (contributes to undesireable turbulence in the flow).

Some aftermarket castings eliminate the exhaust cross-over passages, which make a mess of the center exhaust ports.

Aftermarket heads typically have a better chamber design than factory heads.

Other than that, there's no particular reason not to port factory heads.

 

So unless you were going to do the port work yourself or you weren't going to port that much, you'd be better off spending your money on aftermarket heads?

When selecting heads, can you just look at flow numbers? Or are some heads better for lower/higher rpm power, etc?

 

All comes down to how deep your pockets are, what your power goals are and how inclined you are to porting.

Ultimately the AFRs will probabily make more power than a ported L-98 cast head. Their just a better head.

for a 12 sec piece a set of Pro topline heads would be all thats required.

As for choising a cylinder head to match a certain application,
You need to balance flow and port size.
For a TPI based motor that runs at relatively low rpm a small port is better. like 170 to 180cc (torque, volocity, throttle, response.)
big ports flow lots of air but need a lot of RPM to use it.
The larger the motor the better it will tolerate a larger port.
Again. 350 TPI motors are not high rpm motors as a rule.
The 180cc protopline lightning heads would be more than up to the job.

Do you have access to a flow bench to check your work?

 

No, I dont have an access to a flow bench. I think if I were to port my heads, I would get someone with more experience to do it, as I don't really even have a place I can do it on my own. (I live in an apartment.)

I'm still not sure if I want to keep TPI or not. For a few hunderd dollars more than a new base and runners, it looks like I could get a Miniram or Stealth Ram, which would have more potential. Would a 180cc port head still be okay? My car really isn't going to see and super high revs very often. But also, I'd like "enough" power down low, but not to the point of so much that it makes it horrible to drive on the street.

 

For a 350 a 180cc set of heads would be fine.

 

And for a 383? I'm still not sure what it'll take to get into the 12s, and I'm considering a 383.

 

Unless you're preparing a Stock rules class car for competition
its really iffy if it worth paying some one to port your stock heads.

It's $$$labour intensive $$$. They will need more than a little pocket port. In your case. unless you can do it your self at home I'd look at buying aftermarket heads.
The 180cc heads would be fine, they flow plenty.

It would be a good start to trash the long runner TPI setup altogether and go with a short(er), bigger runner setup like the MINI ram, LT-1 ,, style stuff.
Once you make this move a larger port head like 195-- 200cc's
get more attracktive.

But.....
A set of warmed over Vortecs with the Mini Ram III (vortec) intake would be more than enough. They work very well.
Port volume is 170cc's very snappy.
I got 245cfm -ish flow figures with modest bowl blending, guide streamlining and 2.02x 1.60 valves. on vortecs No real heavy trick porting needed. expecting 250 range at .500" lift when all finished.

You could do this in your kitchen sink......

 

Forget the stock heads. I don't see anybody justifying the time to port and flow test a set of stock heads, just so they fow as good as a set of oftbox dart, trickflows, or afr's. Then you add the other reasons that others mentioned above and you'll see that the aftermarket clearly looks like the better choice.

 

I'm confused now... how much does the port size influence things? I've gathered that the smaller port size means the velocity of the air is higher, giving better torque and throttle response correct? From that I gather at high rpms, a smaller port size starts becoming a restriction.

I see 4 possible combos for me:
350 TPI
350 MiniRam
383 TPI (not likely, but will consider it anyway)
383 MiniRam

What affect would port size (170cc, 180cc, 190cc) be for each of these for a daily driver? Are there any combos that would be really bad or I should avoid?

 

None of these will be "Bad" for a daily driver. Its not like the car will stumble and cough if you have a head with a little to much port volume.
It's all relative. the bigger the motor, the better it will tolerate a certain port volume for a certain rpm range.

Yes a smaller port will have more volocity at a certain RPM than a larger port.
A smaller port will become a restriction at high rpm before a larger port. A larger port will tend to have lower volocity at the lower rpm range and not pack the cylinders with air as much as a small hi volocity port. It won't make as much torque.
If you're planning on building hot TPI motor to run 12's
You'd want to think torque and choose a small(er) hi flow port.
like a vortec head. Because a (long runner) TPI based motor will be a relitively low rpm motor.
If you are going to build a short runner motor (mini ram) the larger 200cc+ ports will begin to show their flow advantage.
because the motor will tend to favour a higher rpm range and can use the flow of the larger head.

But still a good 170cc port is all you really need to make the power nessessary to run mid 12's even with a short runner intake design.
On a 350 the smaller port cross section will make noticably more torque and will give up very little or nothing in top end.
Especially with a TPI and a smaller cam.

Big ports = lots of rpm ( bigger cam) or more cubic inches or both.
Small(er) ports = lots of torque, efficiently and volocity better for a smaller motor in the same rpm range.

The stock low flow TPI intake and runners will be the biggest problem, not the heads.

 

Thanks for the excellent info! So for me, I should lean toward the smaller ports, 170cc or possibly 180cc if I want some more "potential", whether i go with TPI or the Miniram, 350 or 383.

 

No ya got it twisted. the bigger ports have more "potential" because they flow more air.
But......

The idea is to pick a port volume that flows enough air, but has the right volume and cross sectional area to get a nice fat torque curve too. All relative to the cubic in size of the motor.
The "potential" of a large port is wasted if not carefully matched the rest of the motors components and intended rpm range.
The smaller port is more efficient and "torquey" as long as it has enough peak airflow to get the job done.
The available big(er) port heads really only flow more air at very high valve lift when compared to good smaller port heads.
If your only planning on say a .500+/-" lift cam you won't see the benefit of a big race port head. especially on a 350.
I'd tend to lean towards the smaller 170/180cc port sizes
for that kind of hp (mid 12's) on a street driven 350 or 383.

If you look at some of the working sucessful combinations by people like Linkenfelter and TPIS and Arizona Speed and Marine you'll get a good idea of what it takes to get there.

A 350/383ci GM RamJet crate motor with a upgrade to a GM Hot Cam is more than enough to do the job.

You'll need some sticky tires ....

 

I think I understand what you were staying, I just wasn't clear with what I meant.

I was thinking if I went with 180cc (which is more than I need for my current goals), then if my goals changed and I wanted to go with a bit more top end I wouldn't have to get new heads. *shrug* I dunno... is that thinking too much? I understand it's a matter of matching everything else too (especially cam).

 

Here is a link to a article on a successfull combination
using the Mini ram III.
On a 350 based motor ;

I think a set of warmed over 170cc L-31 Vortec heads with their
smaller ports and more than equal flow (when ported) would make just as much power and fill in the torque curve to boot.
Less cost too.

Same goes for 180cc Protopline lightnings.

the Protopline Vortec "906" with its upgraded ports and machining would be near ready to go out of the box.


Mini ram street efi

 

Cool, thanks for the link. And for all your help.

 

Actually by the time I got to the stage 4 and 5 porting of the heads, you're well over the cost of the afr's unless you can do ALOT of work yourself, even then if its your first attempt you probably won't get the port shapes right. Also the walls were VERY thin in places, so you sure wouldn't want to use them if you were gonna be looking at boost. I would still use the afr's over the ported stock pieces just for piece of mind. I think I even said that the only reason to go that far with the stock heads is if you ABSOLUTElY have to have the stock part numbers for a specific racing class or something. If i didn't I should have, but i'm to lazy to go back and look.
John

 

Yeah, I didn't have my heart set on porting the stock heads. I could see that the cost of getting someone to do them would be as much as new aftermarket heads. It's just with the flow numbers you got, I was wondering why more people didn't do it.

As for me, I think I'm going to concentrate on either Vortecs or the Pro Toplines. I'll play around with Desktop Dyno as well and see what does what.

My biggest worry is coming up with something that's just too squirelly on the street.

 

Posted by camaroejoe



I'm a relative rookie when it comes to Car Crafting, & I'm in the middle of porting a set of stock 083 heads. I started in May, I think, and am about a week or two away from finishing. When I finish, I estimate that I will have about 100 hours in them. I haven't really kept up with the time so I'm really guessing. Knowing what I know now I could at least cut the time in half. I'm also doing some flow bench testing to guage my progress, and compare to others, though the flowbench I'm getting this done on doesn't seem to compare too well. I'm not expecting to get AFR numbers or equal the flow of high performance heads, Vortecs, etc. Just some self education.

If all I wanted to do was 12seconds and have a daily driver, some experienced racers told me not to touch the ports, but have a performance valve job done, keep the stock valve sizes (1.94-1.50), use Manley Race Flo Valves, get an LPE Cam, match the torque converter to the cam, and get it to hook, and 12s shouldn't be a problem.

I'm in a position where learning to port my heads will pay big dividends in the future. For anyone not in my type of situation, I wouldn't recommend doing anything but basic cleaning of the ports and a valve job if that's all your engine needs. Otherwise buying new aftermarket heads is the best way to go...

I've broken three carbide bits, bent another, lost one in a Craftsman Grinder I exchanged...and have spent a lot of time (not just porting). I know what these heads smell, feel, look, and taste like now.

Depends on the purpose

 

Having said all that, even the AFR's i'v eseen have needed some basic port work out of the box, just smothing some transition areas and stuff. The biggest area is smoothing aroudn the valve seat and throat. The main advantage is they have the meat to do it. I've been able to get another 20 cfm out of them with less than an hour of work of blending. No real increase in volume, just in velocity. (aluminum also cuts ALOT faster than cast iron so be careful). I heartily recommend the pro-flow or megaflow valves, they really boost low level flow and cylinder filling.