Hello all!

I have a couple questions regarding head work that I'd to run by anyone with more experience than me with 4a heads.

So here's the breakdown, I aquired a late model ae92 4agze (DLI, MAP sensed, small port, 8.9:1 comp, small diameter SC12 pulley) im planning on putting this engine in my 71 celica just like i did with an AW11 GZE in my 74 celica. With this one however, I'd like to try getting a little more out of it since all I've ever ran is pretty much stock 4a stuff. After some looking around and talking with friends, a buddy came upon an insane deal on a full set of Formula Atlantic valves, 2mm over sized.

Now before I go buying up a bunch of valves and whatnot I figured I'd ask some opinions. From looking at billzillas site he claims 2mm O/S valves may hurt performance with an engine under 200hp, can I have anyone else's $.02?

Ideally if I end up going this route id like some good head work done among other things (cams, good springs, etc)but are the valves going to provide any benefit if I had them machined in? I do have a megasquirt already built for when this all goes in also. So what are your thoughts?

GZE_RA21 wrote:Hello all!

I have a couple questions regarding head work that I'd to run by anyone with more experience than me with 4a heads.

So here's the breakdown, I aquired a late model ae92 4agze (DLI, MAP sensed, small port, 8.9:1 comp, small diameter SC12 pulley) im planning on putting this engine in my 71 celica just like i did with an AW11 GZE in my 74 celica. With this one however, I'd like to try getting a little more out of it since all I've ever ran is pretty much stock 4a stuff. After some looking around and talking with friends, a buddy came upon an insane deal on a full set of Formula Atlantic valves, 2mm over sized.

Now before I go buying up a bunch of valves and whatnot I figured I'd ask some opinions. From looking at billzillas site he claims 2mm O/S valves may hurt performance with an engine under 200hp, can I have anyone else's $.02?

Ideally if I end up going this route id like some good head work done among other things (cams, good springs, etc)but are the valves going to provide any benefit if I had them machined in? I do have a megasquirt already built for when this all goes in also. So what are your thoughts?

OS valve option - It depends........ to run OS valves, typically you need a custom piston because the valves diameter is now larger, there is more chance of valve to piston contact - this is especially true if you want to remain none interference.

A ported head will flow better, and can help in minimizing ping/pre-ignition. Add in careful machining, and you should be pretty happy with the results

Here is a link showing some of my work - http://ost.ebeans.ch/index.php?cat=2

First off Billzillas modified page is way outdated and has a lot of misinformation. Honestly I feel it does more harm than good reading it. I call BS on OS valves hurting performance under X hp but they will have pros and cons. With 2mm bigger valves you would need new seats with optimized throats. Throw a bigger valve in with an undersized throat and you will hurt performance.
Second you have to be careful about theory between NA, Turbo, and SC. Some theories remain the same, some change. One big thing that changes is NA will have close to the same pressure on the intake and exhaust side. SC will have higher pressure on the intake side. An optimal turbo will have about the same boost to pre turbine backpressure ratio but a small turbo can have a lot more exhaust side pressure. These things change the behavior of the motor during overlap.
Third and in this situation I believe the most important is that the supercharger is extremely ineficient. It seems silly to me to spend say a grand or more going to OS valves for the let's just say 20ish hp you might pick up when you could spend a little more on a turbo and engine management and double your hp without too much trouble. Triple it if you really wanted.

I wouldn't bother with head work/big valves = lousy bang for the buck. 16v head don't breathe worth a **** without cams n e way
gze is a nice torquey platform to build on..... inefficient SC or not
over the years, seen quite a few ae86 with 'upgraded' stock gze go 13.7s
here is a basicly stock one going 13.9. 13s is a strong running quick econobox.... from an 'ancient puny 1.6L mule'
https://www.youtube.com/watch?v=7hiLBW81TVA
u already off to a good start with standalone. Concentrate on optimum diff gearing. Get the 'right' exhaust
Tons of intercooler info on mr2oc & miata supercharging forums
Then carefully choose a cam combo proven to deliver
search!
After tweaking, I wouldn't b surprised at 13.5s with respectable near instant tq

Thanks for all the input fellas!

OST - im definitely interested in some of your head work when the time comes. I think a little port work could be beneficial to the setup, and anything less prone to pinging is a plus in my book! Sounds like OS valves would be pretty expensive for not so much gain, probably money better spent elsewhere.

Yoshi - I appreciate the info also, i was starting to question some of billz info as it does seem a bit dated. Im always happy to get a second opinion and I'm glad you chimed in. I realize the SC12 isn't the most efficient forced induction system but I kind of like it despite the draw backs. I realize that many modern turbos can provide near instant boost, but damn that belt driven linear torque is nice. Granted I've never driven a turbo 4A, I was not terribly impressed by my friends twin scroll BB turbo WRX. I understand the application is much different in my celica as opposed to his subaru, but the sudden surge of power from the turbo spooling i found somewhat unpleasant, but the low end grunt from the GZE was very satisfying in my 74 celica. i just was wondering how to get a little bit more out of this ae92 gze and get my feet wet in engine tuning/modding also. That's why I decided I would be best off starting with a stand alone computer but was curious where to go next.

Jinx - I do very much like the GZE, it's a sweet little setup for a stock motor. I will most likely end up going with a nice pair of cams with good lift and valve springs to suit, and based on what im hearing ill probably pass on the OS valves. I do have a pretty badass setup in the works from weir performance for my rear end, im keeping the stock 4.30:1 ratio with chromoly gears, 28mm chromoly axles, solid pinion spacer kit, all new bearings and seals, and a KAAZ 1.5 way LSD. Should be a nice package with my W58 transmission!

Thanks for all the info guys! Its nice getting other opinions, if anyone has anything to add please keep them coming!

4.3:1 ratio fine for low tq revvin na 4age. Boosted motor far better off with taller gearing, in general
Not only et better on the clock, but improves the daily drive..... keeps the motor in its 'sweet spot', less shifting, etc
Same reason oem may run 4.10 on the n.a., but 3.7:1 on the turbo model of the same car

Hmmm interesting food for thought, I ran the stock GTS diff 4.30 gear in my last AW11 GZE celica after switching from the stock celica rear end that had 3.73 gears. I must say I really liked the 4.30 compared to the 3.73 gear, but that could have been partially to do with the 3.73 being open and the 4.30 being LSD. I'll have to consider making a change, the options I have are 3.91 4.11 and 4.30 which would you go with? Thanks for the input btw!

If anyone has any opinions, I'd love to hear them.

jinx wrote:4.3:1 ratio fine for low tq revvin na 4age. Boosted motor far better off with taller gearing, in general
Not only et better on the clock, but improves the daily drive..... keeps the motor in its 'sweet spot', less shifting, etc
Same reason oem may run 4.10 on the n.a., but 3.7:1 on the turbo model of the same car

agree completely.... I'm running a 3.9 in my car because there is enough power to warrant it.

I must say I really liked the 4.30 compared to the 3.73 gear, but that could have been partially to do with the 3.73 being open and the

4.30 being LSD. I'll have to consider making a change, the options I have are 3.91 4.11 and 4.30 which would you go with?

if u preferred the 4.3 with your previous gze, then that may be your answer. Sure u can swap in a gze and just "be happy" with it
Of those choices, I'd go 3.9(with a 195/50-15).... seeing as w58 ratios comparable to t50. Don't forget final tire diameter also
Wouldn't want you to dump a load on a nice rear end with a less than ideal ratio
Best way I've found is to experiment with some cheap used tall tire. You can figure your ratio out from there
Gearing often overlooked causing many swaps not to realize their full potential - acceleration, driving pleasure, economy, etc..

this UZ(+6spd nissan box) rolla owner was actually looking for gearing even taller than the 3.73 for his toyota 7.5 diff
http://www.dorikaze.net/showthread.php? ... ild/page26

here is an excellent thread of an RZ swapped rolla.... similar tq to a gze
http://www.dorikaze.net/showthread.php? ... d-3RZ-AE86
Notice how even before supercharging, the 3.73(vs the 4.10) make or break the swap. Tremendous effect he says
useful supercharging water injection info detailed there too

after the swapped settled in, then start "tweaking".... like cams, mild head cleanup/manifold match
it's the details that make a standout.... all about the combination

jinx wrote:

I must say I really liked the 4.30 compared to the 3.73 gear, but that could have been partially to do with the 3.73 being open and the

4.30 being LSD. I'll have to consider making a change, the options I have are 3.91 4.11 and 4.30 which would you go with?

if u preferred the 4.3 with your previous gze, then that may be your answer. Sure u can swap in a gze and just "be happy" with it
Of those choices, I'd go 3.9(with a 195/50-15).... seeing as w58 ratios comparable to t50. Don't forget final tire diameter also
Wouldn't want you to dump a load on a nice rear end with a less than ideal ratio
Best way I've found is to experiment with some cheap used tall tire. You can figure your ratio out from there
Gearing often overlooked causing many swaps not to realize their full potential - acceleration, driving pleasure, economy, etc..

this UZ(+6spd nissan box) rolla owner was actually looking for gearing even taller than the 3.73 for his toyota 7.5 diff
http://www.dorikaze.net/showthread.php? ... ild/page26

here is an excellent thread of an RZ swapped rolla.... similar tq to a gze
http://www.dorikaze.net/showthread.php? ... d-3RZ-AE86
Notice how even before supercharging, the 3.73(vs the 4.10) make or break the swap. Tremendous effect he says
useful supercharging water injection info detailed there too

after the swapped settled in, then start "tweaking".... like cams, mild head cleanup/manifold match
it's the details that make a standout.... all about the combination

Wow, what an incredible build on that corolla. Although i do think the RZ is much more torquey than the GZE ever will be, especially with the extra displacement, and that super charger in his case.

Based on that and the recommendations of Spence, ill probably go with the 4.1 gears. I think it'll be a nice in between, the gears in the w58 are just a tad taller than the t50 also so I think it will be a nice setup.

That Canadian RZ 86 definitely got me interested in water/meth injection though, seems like a fantastic way to milk some more efficiency out of the not-so-efficient SC12. One thing I realized though..... and anyone who knows megasquirt better please chime in.

I ordered a DIYPNP kit for the 87-89 AW11 4AGZE, when i stated earlier that I had a computer built that's what i was referring to. I didn't realize till i started looking at the ae92 4agze ecu in more detail that it's a 64 pin ecu instead of a 52 pin like the aw11. Which makes sense seeing as how it has more and different features. Is there any way I'd be able to retrofit the 52 pin ecu to the 64 pin harness? The ae92 64 pin harness has 20 blank pins and the aw11 52 pin has 4 blank pins, seems like there might be a way to utilize the factory ae92 harness?

I should know more about megasquirt but my aw11 gze became unusable before I had a chance to install the megasquirt computer and mess with it.....

Thoughts?

u don't have to guess at your final diff ratio at all. As I did/mentioned, boro some old 240sx rim with a tall 15", or somethin
ez to calculate your ratio like that
another rwd gze-gearing thread.... note the tire diameter comment too
http://www.rollaclub.com/board/topic/60184-diff-ratios/

jinx wrote:u don't have to guess at your final diff ratio at all. As I did/mentioned, boro some old 240sx rim with a tall 15", or somethin
ez to calculate your ratio like that
another rwd gze-gearing thread.... note the tire diameter comment too
http://www.rollaclub.com/board/topic/60184-diff-ratios/

I'm not guessing, I used an online final drive ratio calculator based on 4.1:1 FDR, 195/45/15 tires, and all my w58 gear ratios. I'd rather speculate based on a calculator than run around trying to find or borrow second hand wheels and tires anyway.

Then again I suppose we got a little off topic here and i may have failed to mention that the engine isn't even in the car yet. This was originally just too get an idea of performance tweaks for the GZE before I install it in my celica. The diff is currently being rebuilt though so even if i wanted to experiment i couldn't physically move the car under its own power.

Thanks to everyone, especially jinx for all the help and advise! I'll be sure to let you know how it turns out.