SmallPort vs Bigport HEAD 4AGZ/TE power figures

[nick.parker]

Hi,
I currently use a bigport low compression (8:1) 4AGZE in my SC14'd AW11, it makes 150hp at the wheels and goes pretty well at all RPMs (except really low because of Wade 267 cams).

I have a smallport GZE in the garage and got to start thinking about how it might improve the low/mid range torque if I was to swap this head onto my car (and for that matter the 8.9:1 block!!!) But for now I just want to talk about the head.

Surely it couldn't be any worse than my bigport TVIS manifold (no TVIS, but 8 small holes so probably same area as the small port anyway...!) But before I do anything rash, I want to hear from people who have made some good power with the smallport manifold, or from anyone who has used both and what their opinions are of each. Ie what is the crossover point power-wise for switching heads etc....I imagine with my relatively low horsepower that the smallport might actually be a favourable option? WDYR?

Cheers, Nick

[oldcorollas]

from memory, the difference between them in port size (in circle equiv) is 40 vs 43mm.. not a huge amount really... (well.. 43mm is 15% larger area...)
with not so much boost, higher compression will also help everywhere, esp off boost.
as for head flow... ni, just kicking off topic with port size but i think you couldn't go wrong with the small port for th epower levels you are talkign about.

[Starfire]

i really wouldn't think that it would make much difference at all for your particular application. For the time and effort involved you would really be better off getting the existing inlet manifold ported a little.

[Ben Wilson]

You're running a high boost, SC14ed ZE with a programmable ECU and you're after more bottom end and midrange?

May I suggest a tractor motor?

[Nim]

That's a good question, how much boost are you running?

[The Witzl]

may i second teh tractor suggestion?


.... but.... if you are stubborn and wish to stick with a 4A....

# The best head for all applications in MY OPINION is the smallport.
# The best bottom end is the smallport.

Smaller ports = greater flow velocity.

velocity is a very good thing, it makes turbos build boost faster, gives massive improvements in low-midrange performance... and just generally makes things GOOD.

That said though, FLOW VOLUME is also important. Without the ability to flow the volume of air, then you cannot make teh powahz.


The key element is to achieve the perfect balance of flow and velocity.
Why do you think Toyota went from bigport TVIS heads to smaller ports and no TVIS on the 3S-G, 1G-G, 4A-G engines?
.... did they want to give you LESS performance??

NO.


In short, my belief is that the smallport 4A-GE 16 and smallport 4A-GZE (AE92, not AE101) are the best of all the 4A series engines, for so many reasons.
I'll list a few for you:
# higher compression
# stronger block
# the strongest crank of all 4As
# best performance
# oil squirters
# crank scraper and windage tray design
# lack of debilitating TVIS plate
# smaller pulley on SC12 (more boost)

[myne]

You call the tvis debilitating, but surely when you're after max power, the bigport is better?
Even with the minor restriction of the tvis plate, it's still a much larger port, allowing more flow.

[Nim]

A lot of car manufactuerers re-design engines to give you a better torque curve, make them more reliable, cheaper, or more economical. So they don't neccissarily want to give you more top end power. They also don't tend to plan for modifications. There must be some point where the bigport is better for forced induction, but it may well be above the boost level and power output that nick is after.

How much power are you chasing nick.parker? If you are happy with your top end (and you seem to be) and just want more low and mid range, then yeah, smallport is probably the go.

[Nim]

You call the tvis debilitating, but surely when you're after max power, the bigport is better?
Even with the minor restriction of the tvis plate, it's still a much larger port, allowing more flow.

I hear forcing too much boost against the TVIS butterfly can losen it, an utlimatly rip it free. Any confirmations on this would be handy.

After a certain point, you'd just remove your TVIS. It'd just start getting in the way. I know you do with an N/A build bigport.

[Valkyrie]

Hi,
Have you thought about installing the TVIS?

I would hazard a guess and say that would cause the less amount of hassle.

If you went smallport, then you are going to have to swap inlet manifolds.

I'd look at the simplest option first, but I'm lazy.

Cheers

[wiso]

That's a good question, how much boost are you running?

15psi iirc

[The Witzl]

You call the tvis debilitating, but surely when you're after max power, the bigport is better?
Even with the minor restriction of the tvis plate, it's still a much larger port, allowing more flow.

Did you miss me saying this....

The key element is to achieve the perfect balance of flow and velocity.

....???? I wass stating that the balance was much better struck with the smallport against the bigport.
This should be blindingly obvious when they've had to incorporate a system such as TVIS to compensate for the failure of the bigport head to work anywhere near effectively below 3000rpm.

Do you know what the flow differences are between the two, and at what level a smallport would start posing a restriction over a bigport?

... and in what application (beyond dyno competition) do you want max power only?

There must be some point where the bigport is better for forced induction, but it may well be above the boost level and power output that nick is after.

Yes there would be, but i'd suggest that point is well beyond what any of us would ever reach in a STREET setup. It would also probably only improve at that last 5% or so of your engine's performance range..... for what percentage of time do you think you'd spend in that range going down the 1/4 mile, or around a race track, or on the street even?

How much power are you chasing nick.parker? If you are happy with your top end (and you seem to be) and just want more low and mid range, then yeah, smallport is probably the go.

Nick, if you have the whole engine, then put the whole engine in your car. bigport gze is about 20% down in power against a smallport gze.



Remember: what i say is only what i think. If you think differently, im all ears to hearing why with good constructive discussion and reasoning

[takai]

Do you know what the flow differences are between the two, and at what level a smallport would start posing a restriction over a bigport?

Around 190hp of NA power. And even then some. The mildly ported (about 1mm dia) smallport head which i have is pushing 170hp at the fly, and i have seen better ported smallports do a lot more.
I think the delineator is around 190hp though.

Hell of a lot more with 15psi of boost being pumped into it.

[Dimitri]

i get to see alot of race engines being built through being friends with a mate whos dad build/specializes in porting them.

very close to always the port volume is DECREASED once he is finnished. he uses epoxy in the ports to achieve this.

shape is another thing to consider.

but back on topic. smallport is pretty much a better motor in all ways, including the points you wish to improve upon.

[myne]

Well, while we're on the topic, I've had a theory about tvis.

What if you ground all the non-tvis inlet cam lobes to say 260* and all the tvis lobes to say 300*
Theory is, at lower revs it'd act like an 8valve. As the revs pick up, it becomes a pretty decent 16v and winds a bit further out than a plain 260* cam would allow.

Expected advantages :
Near normal idle
Good midrange
Decent top end.

Sorry to sidetrack a bit...