small valve vs. large valve after porting

Depending on how much cam you are adding, it is certainly worth it. A lot of cars run in the mid, and low, 11's with good porting, but still iron intake and exhaust. At least go for some good bowl work, as discussed above.

 

Bottom line in my opinion is spend your money on pocket porting rather than stepping up to larger valves....assuming your valves are good. I picked up .3 just porting my small valve heads and a .490 lift cam (118). As stated the velocity off the seat is better with the small valves. That said if you are going with a cam over .500 lift I'd go with the Stage 1 valves

 

An advantage of larger valves is that it gets you back to virgin metal when the seats are ground.

Otherwise, you're sinking the valves deeper into the head when the original-size seats are re-cut (unless you install seat inserts.)

 

Wow, there is a lot of mis-information in this thread. What are you building? I dont mean what size motor-can be a 400/430/455, does not matter. What I mean is what do you expect the motor to do? Stock rebuild? Perf plus? Sleeper big power? If it's a true perf build, big valves all the way. Forget the "it's loses torque/velocity" etc BS. More air is more power. Now, doing the big valves without bowl porting is a waste, so if you do one, do both. There is way more to this discussion, but short version is bigger valve is bigger power.

 

The bigger valves don't lose the port any velocity anyways, and yes...not porting them can be detrimental.

 

I'm still himming and hawing and trying to figure out the way to go. Initially wanted all iron but aluminum heads are very interesting. I want a street/strip vehicle, power breaks and steering too. Quadrajet carb. 2.5" exhaust. Got Jims 2800 stall in it a couple weeks ago. Thinking I'll keep the air conditioning as well. I don't want it sounding too thumpy either. Was thinking mid 400s and up for hp. Pump gas for sure.

 

For mid 400hp the aluminum heads are overkill.
If you want them and don't mind the cost, cool.
Plenty of things affect the 'lumpiness' or perceived streetability of any engine, neither head choice would drastically affect that.
Ported factory heads with either valve size tends to tame whatever cam you use. The faster avg velocity and smallish port cross sectional area keeps things responsive and tame. Not porting any of these heads makes the cam 'lumpier'.
The flow numbers everyone displays give NO indication to this. It's simply a port speed based on area and how well the port is functioning type of thing.

 

Go alum, you wont be sorry. Put all your $$$ into the best heads you can afford. They are the basis for building power. I like the E-brocks for a lot of reasons, but the TA's are just as good, just valvetrain. You'll have every bit of $800-1200+doing your iron heads and they are still iron.

 

we will know shortly, my 70 gs all #s matching motor, had a botched attempt at converting the factory small valve heads to stage one seat diameters, so im using a virgin set of small valve heads with a stage one cam