I'm not 100% sure where to post this, so I apologize in advance if this is in the wrong place. Mods, please feel free to move this post if necessary.
I usually post my questions on Club4AG, and for the most part I get good responses, but if I mention "4AC" anywhere in my post I immediately start getting replies along the lines of, "y u no 4ag?"
Anyway, I just wanted to post here, introduce myself, and talk about my eventual project.
I have an AE86 SR5 with the original 4AC. The car has almost 140k miles on it.
I love the car. Sure, it's not fast, but it always brings a smile to my face when I take it through the corners. Thank goodness it's a manual transmission
Eventually the engine will need a rebuild, and I'm a little torn on what to do.
On one hand, I'm considering a stock rebuild, the only upgrades might be a 4AGE crankshaft and rods, and slightly oversized 4AC pistons if the block needs it. Probably get everything balanced too.
The main reason to consider a "stock" rebuild is I live in California, and my car still needs to pass smog.
My other idea is to do a 7AC build. 7AFE bottom end (probably change the pistons) plus a 4AC head. There's some math to do here, but overall it looks pretty straightforward.
Since I live in CA, there's not a whole lot I can do to the car. The intake, exhaust, and carb definitely have to stay stock. The only modifications that can be done have to be inside the engine. That means head work, pistons, and (probably not) the cam.
Even what I can do inside the engine is limited by the fact that it needs to pass smog. I don't think I can go crazy porting the head and still pass CA smog, and I'm pretty sure an aftermarket cam (unless it's really mild) would cause me to fail too.
Anyone have any tips? The only other somewhat feasible thing here would be to do the typical 4AGE swap, but that really seems like a lot of work for not that much more power.
i have no experience with 4age's but by all accounts, i think it would be a night and day different between one and a 4ac. i put a 4ac in my first tercel and honestly didn't notice any difference between it and the 3ac.
i was going to recommend you post on the 4ac-powered forum but just checked and you already did. very good. while looking up that site, i also came across this old thread on the 4ag forum. probably another one you've already seen but here it is just in case.
Most other forums are full of adolescents with rather limited understanding of combustion science. I know a fair amount about this topic, (and several others on this forum) I studied it in engineering school and also work for a factory backed fully sponsored racing team at one time. Plus almost 40 years experiance with experimenting with my own street cars.
Octane rating is a complex subject, that chart is meaningless. It is not just about CR and ignition timing but cam timing, induction shape and volume, intake air temperature, altitude, combustion chamber shape, throttle position, engine/head temperature, piston crown design, quench area and a few other complicating factors. It is not easy to predict what timing you can run, what octane you will need from a simple chart.
I have run 11.25:1 CR using pump premium (91 octane rating) without too much issue with a few tweaks to accommodate it (though I do not recommend it). theoretical Otto cycle efficiency goes up with higher compression ratio, however real world practical issues limit it to about 13 to 1 with high octane racing fuel (not legal for street use, and very costly). "Octane" is theoretical, chemically pure gasoline, and given a "100" rating in a standardized test engine with adjustable compression ratio (I have run one in our thermodynamic lab when I was in collage). You run the octane fuel and set the CR to just below audible knock, than switch to your test fuel and adjust the CR to just below audible knock. CR less than the test fuel gets a rating of less than 100, and fuel that can run a CR more than the test fuel gets a rating of over 100. That is why BTW it is properly called "octane rating", there are some other complicating test procedures that must be done, but that is how the rating is derived. It is a rather primitive one cylinder engine because the test was invented in in the 1920's or 30's.
What higher octane rating means is it has more resistance to knock or ping. There are additives you can buy, or even make yourself from common chemicals, to raise the octane rating of your fuel. some claim it is cheaper to run octane booster and run regular grade gasoline in a car that needs premium. I have done both (used home made and commercial additives), but I find making and putting in additive every fill up bothersome.
for maximum efficiency you want to run the most advance you can without knock. Higher octane rated fuel allows more spark advance, and hence more fuel economy and higher power output. It means the combustion gases reach higher pressures before the knock occurs, and you get more power out of the same amount of fuel. Knock is the presence of super sonic shock waves in the combustion chamber, they consume energy and the shocks can eventually damage head gaskets, valves and pistons. They are not just inefficient, they eventually will damage the engine. And that is why the combustion chamber shape, and the amount of turbulence in the incoming air, as well as mixture ratio, even spark plug location, will affect when the engine will ping or knock. Also, emissions tend to go off the scale if you test an engine that has a lot of knock going on during the test. IT is generally bad for all aspects of running an engine.
You will get early knock or ping with more spark advance, lower octane rating fuel, with high compression, with leaner fuel mixtures, with higher engine and air intake temperatures and with higher engine loads. That is why you will often hear knock or ping when going up steep hills on a hot day, particularly when lugging the engine (high engine load, wide open throttle).
By "7AC" I assume you will putting a 3ac or 4ac head on a 7a engine short block? your piston tops will not match the head, but if you have adequate valve clearance you should be okay. Also, eight tiny valves with those tiny intake ports will limit the amount of power you can get out it, though you should have great low end torque.
If you clean up the ports, and remove all of the sharp corners out of the combustion chamber that should add some power and perhaps help reduce ping. You should also cut in combustion chamber grooves in the head, this will greatly reduce knock. you can see pictures of it on my 3ac build over in the repair guilds section under "head gasket replacement: petros method". You should also use that procedure, and the recommended mods to install the head on your engine. the 3ac head does not cool evenly, tweaking it for more power makes it even worse and with poor head gasket reliability. I have not had that problem with my current 4ac installation, the head is similar but there are some differences. So I suggest using the 4ac head on your 7 a block. If you have the budget, you should also install larger valves and seats, to improve performance. but that is a costly upgrade (unless you can do it yourself and have access to a machine shop), I would do a full 16 valve engine swap before I spend the money to install larger valves in a 4ac head.
With the 3ac/4ac combustion chamber with the factory carb and intake manifold I have found that you can get by with running pump premium fuel with a max of about 10.5:1 CR. Though personally I would try and keep it around 10:1 for running on hot summer days and allow to run about 8 or 10 deg spark advance.
The factory 5 deg advance was to reduce the peak pressures in the combustion process to reduce NOx emissions, but it also harms efficiency. But far worse is that it means you have much hotter exhaust temperatures (the fuel is still burning when the exhaust valve opens), making the exhaust valves run very hot. eventually the exhaust valves will break up and cause a lot of damage, I have had it happen, and have seen it even on fully stock 3a and 4a engines. the exhaust valve head will break off and get crunched up between the piston and the head in a few milli-seconds, usually doing heavy damage to most of the rest of the engine (turning it all into scrap metal). I would only run the factory 5 deg to pass your annual emissions test, and than run 8 or 10 deg the rest of the year. it does not save the environment nor reduce pollution to keep sending engines to the scrap yard. BTW, this is why sensor controlled fuel mixtures and spark timing is such a vast improvement in both efficiency and emissions, and really engine longevity too. Win-win-win on all levels. Curious California does not allow switching to a more modern EFI engine without a lot of hassle, do they really want people driving around old cars with carburetors and mechanical spark ignition? stupid bureaucrats, they should encourage it and have a simple process to approve it.
In summary, I suggest doing the head and gasket mods over in my head gasket installation thread, limiting the CR to about 10:1, use pump premium fuel and run 10 deg spark advance (back off to 8 during the summer if you get knock or ping). You should be happy with that arrangement.
BTW, you want to do everything you can to get even fuel and air distribution by cleaning, and evening up the intake and exhaust ports, and balancing the combustion chamber volume in your head build up. Also, use new exhaust valves, the best quality you can find (made in Japan or USA only). also, lighten the flywheel and balance all the moving parts, these will improve throttle resonance and help it run smoother.
Good luck. let us know how it all works out. Some pics of the build would be nice too.
dlb wrote:I was going to recommend you post on the 4ac-powered forum but just checked and you already did. very good. while looking up that site, i also came across this old thread on the 4ag forum. probably another one you've already seen but here it is just in case.
Yeah, I've been posting everywhere online looking for answers. I think I did find that Club4AG post you linked to, but it has been a while; thanks for reposting it!
Petros wrote:Welcome to the forum!
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Good luck. Let us know how it all works out. Some pics of the build would be nice too.
Wow Petros, thanks for the detailed and prompt reply! Looks like you started your reply before I edited the title and content of my post (I decided to make it more broad.)
Yeah, you can't upgrade from carbs to EFI here in CA.
My main fear is spending $ building a 7AC, and then not having it pass smog. At that point I'd be kinda SOL.
Then again, spending the $ on a stock 4AC rebuild seems like a potential waste. Anything too expensive and a 4AGE would probably be a better option.
Regarding head porting and smog, I noticed oldeskewltoy has built a couple CA heads, and his port work is minimal. Then again, that was on a 4AGE head, not a 4AC.
Regardless, I'm glad to be here on the forums. There is a lot of stuff I still need to research and it seems like there is a lot of info on here
opening up the ports should not affect emissions much, it allows more airflow at full throttle (hence more hp at the high end). The emissions test is not run at full throttle, mixture and combustion are not changed at lower throttle settings.
If you want the max power out of the 4ac and still be smog legal this is what I would do:
compression ratio of about 10:1, go max overbore the block will allow (0.040" over-sized likely), Delta Cams mild performance street grind (available from Delta Cams, Tacoma WA), ported and polished head and intake manifold, balanced and grooved combustion chamber. lightened flywheel, fully balance all moving parts. And either a header if it is legal, or go with 2"+ sized cat back exhaust system (should be legal in CA). You can also port out the exhaust manifold, but that is hard work on cast iron, might be worth cleaning up the sharp edges and seams however. If you have the budget have larger valves installed too, it will not affect smog and will give you some more hp at the top end. and run 10 deg spark advance except when you go in for an inspection and smog test. Also running 5wt synthetic oil might gain you an hp or two, only do it on a fresh rebuilt engine however.
With these changes you will pass both the inspection and the dyno smog test. And you will be happy with the results as well, not a big increase, but it will be noticable, and still be "legal".
I do not know what you hope to gain by switching to the 4age crank and rods. the 4ac and 4age cranks are identical in the early 4age, and heavier in the later 4age, but geometrically identical, and offer no performance advantage, it would just add weight. You would also have to have a costly custom 8 bolt flywheel made (the 4ac has a six bolt flywheel, 4age is 8 bolt). The stock 4ac crank is plenty strong, you will NEVER fail it with 4ac engine no matter how much you build it up. Save your money for more important up grades.
I am not sure if the befit vs. the cost, and the risk of going 7ac would be worth it. What are you gaining? 175 ccs? Less with a .040 overbore in the 4ac. That engine block is physically larger, taller, heavier and does not look the same on the outside, so if you get an observant inspector it may not pass muster. you may not be able to get it to fit without a lot of chassis mods, which will also tip off the inspector. I do not think I would do it.
There is possibly some benefit in going to a "performance" airfilter/induction system, but none of the aftermarket system actually do anything, most are a waste of money. It might be possible to develop your own low drag induction system from junk yard parts off of other cars, but likely you would have to switch it back to the factory air filter assembly for the test. If you can install it and make it look "stock" (not slapped together with sheet metal screws and duck tape) and consider that the inspector does not know the car well enough to recognize it as a non-stock intake system, it might even pass the inspection.
You gain power by only a few basic ways: larger displacement, higher compression ratio (which has limits because of fuel quality), improve efficiency by reducing friction and pumping losses. intake and exhaust system mods lower air pumping losses and imprve the amount of air that gets into the combustion chamber, synthetic oil reduces friction losses, the cam changes reduce intake loss with larger lift, and moves the power curve higher up on the rpm band (so you get more power at the high end). You can also switch to an electric radiator fan if you do not already have one to reduce the fan belt loss. but that is about it. you are limited to the improvements you can do on the 8 valve head, consider that putting a 16 valve 4af head on it gains you 20 or so hp because of the improved breathing (lower pumping loss, more air into the combustion chamber).
You can get the car to pass CA ASM dyno emissions test with the Delta regrind cam (I have the 260 grind cam in my car). Even with a stock CR engine NOx emissions tend to get high during the test, so you must make sure the EGR system is working properly and you have a healthy amount of vacuum going to the EGR vac modulator. Raising the CR above 10:1 will likely make it difficult to pass the NOx part of the test, although it's likely to pass if you retard the timing to 3 degrees BTDC (max allowed is +/- 3 degrees) and you have a good catalytic converter. You can avoid all of these headaches if you either live in a basic inspection area or you can borrow someone's address who lives in a county that participates in that program since then you'll only have to pass an easier two-speed idle test. First, a 2500 rpm test and then an idle test, which would be easier to tune the idle emissions to pass and 2,500 rpm should not be hard to pass as long as the feedback system is working properly and you have a functioning EGR system (meaning it stalls when you apply vacuum to the EGR valve) for that part of the test. I've been wanting to build a 10.3:1 CR 4A-C for sometime so I've been thinking of ways of addressing the emissions concern when the time arrives. I believe it's possible to squeeze close to 100 hp out of the 4A engine, in Japan there was a special 4A-E 8 valve SOHC fuel injected version of the 4A-C and it made almost as much power as a 4A-FE did, which means with fuel injection and the proper intake and exhaust system enhancements one should be able to increase the stock output by over 20%.
2015 Honda Fit EX "Malachi"
2001 Toyota Corolla CE "Eugene"
Man, I am loving this forum; these replies are fantastic!
Alright, let's see if I can reply with some helpful info
Petros,
Regarding the 7AC, I think it is worth it, and probably not as much of a gamble as you'd think. A few people have done a 7AC before. No custom fabrication, just 1 water line needs to be cut and clamped with hose:
That's FR specific, and you could probably do a little work to make that look more "factory".
The other "hurdle" is the 7AFE uses a 2 piece oil pan. That's a dead giveaway you've got a different engine in there than stock. However, I believe you can use a 1 piece 4AFE oil pan, that looks the same as a 4AC oil pan:
With those 2 hurdles out of the way, the only giveaway is the "7A" stamped on the side of the block in place of the "4A".
My problem is with any sort of mods, be it to a 4A or a 7A, there's still a smog gamble. At least with a 7A, you could likely sell off the internals to a guy wanting to build a 7AGE if things don't work out. You figure you'll have a bored and balanced 7AFE bottom end; might only require different pistons to be suitable for a 4AGE head.
Here are some of the best 7AC builds I could find. I've got more links on my home computer though (and still need to search for more):
I still think cost is important here. Spending too much and you'd be better off going 4AGE. The biggest thing is probably the porting. Any recommended books on porting? I don't mind investing time (over my money) to do it myself.
tercel4wdrules,
I just smogged my car a few weeks ago and there were some numbers that barely passed. Then again, my car has always "barely" passed smog ever since I bought it nearly 4 years ago. I've got all my smog results to help troubleshoot.
I think my car needs: a carb rebuild, an EGR cleaning, and a new catalytic converter. While I'm doing the carb I should also probably replace all the vac lines under the hood.
I've read a lot about Delta Cams with the 4AC; did you do a regrind or a weld and regrind? I've read the latter is better, although it's a little more expensive. Can I ask how much it cost? I don't see pricing on their site. I've also read that a more aggressive cam helps "bleed off" compression; I want to say that's dynamic compression, not static though.
And yeah, I'd love to smog my car in a less strict area, but I'd rather it pass smog in my area. And I've read about the EFI'd 4AC; too bad CA won't let me install it!
Finally, if you're registered at 4AC Powered you can view a thread I posted about 7AC compression ratio calculations using A-series Toyota pistons:
the Delta Cam regular regrind is a great bargain, only $59 plus shipping, with exchanging your old cam (or they return a deposit after you deliver your old cam). The weld and regrind would give you a more aggressive profile, and more power, but likely it will not pass emissions and it will affect your fuel economy as well. It will also have a high rough idle, the normal street grind gives a nice smooth idle. At least in the TErcel4wd, I do not want all my power way up above 6000 rpms. Snider also makes a performance am, but it peaks at around 7000 rpms, runs like crap at the low end (I can not imagine what they were thinking, those eight tiny valves can not delevier enough air for it). It is also quite costly.
See if a normal 4ac oil pan will work on the 7a block, if it can be modified to work than that might be best way. likely the externals of the engine are similar enough with a 4ac oil pan no one will notice. It does weight more, but at least the crank still uses the 6 bolt flywheel so there should not no issues putting your flywheel on it.
Before you replace your cat converter, I saw somewhere that someone took their cat out, soaked in warm soapy water overnight, rinsed it out, than blew it out with compressed air, and than it worked again. Lots less costly than buying a new one, might be worth a try.
I haven't contacted Delta Cams yet, but do they do a numbering system for their cams? I know Schneider has a number system (260 - 300), and tercel4wdrules mentioned the 260 regrdind specifically. Which Delta Cam(s) are you familiar with Petros?
And yeah, the oil pan swap makes it a bit more appealing to me; I doubt anyone would notice it's a 7A*, and not a 4A*. I'm not sure on the difference in capacity between the oil pans, but the 7A at least looks larger. Which then brings me to the question of using a 4AC or a 4AG oil pump:
Once I get my brain around everything I'm hoping to get a "parts list" together to confirm with the community that I've got everything right. Then start calculating what all this will cost me...
I think they only have one grind for the 4ac. Not a lot of call for getting more performcance out of a 35 year old economy 8-valve engine. they have a web site with information about the cost, terms and cam shafts.
I am not familiar with the 4ac, but all of the 3a/4a oil pumps are almost the same and can be interchanged.
Delta probably offers different cam regrinds, but the mild street one is the 260 one. It shifts the powerband a bit higher up in the rpm range, which I figure probably moves peak torque past 3000 rpm, probably as high as 3400-3600 rpm. Peak hp seems to occur closer to the redline as the engine seems more happy to rev past 5000 rpm, but you have to really pay attention to notice the change. It will idle ok as low as 650 rpm, but it seems to idle better closer to 900 rpm. Schneider cams has a slightly more mild cam regrind they apparently don't advertise on their site, a forum member here inquired about it. It's called the 256-260 grind (the intake and exhaust have different duration with this cam) and it's the "torque" regrind. I personally believe that the mild regrind cam would work best with a higher compresssion ratio. I can really tell the engine wakes up when I advance the distributor well past 10 degrees BTDC. I paid about almost $100 for the regrind cam, core, and shipping fee to CA. These cams are a regrind, meaning they reduce the base circle of the lobes to obtain the desired duration. Supposedly this is not the best way to go since you're technically changing the geometry of the valve train, but it works out fine. Someone on the 4ac powered forums posted an informative article about how the cam regrind works if you'd like to see the specifics behind this. The best way to go would be to start with a new cam and grind it to the desired specs, but last time I reached out to Schneider they told be they sold the new cams they had and have not sourced any more. Bummer.
As for the smog situation, I had a Tercel in the past I put a fresh cat converter in and it passed ok, even with a fully plugged EGR valve! I didn't know about this until later on I removed it and found that it was clogged shut with some nasty carbon deposits. Worst case scenario you can always run a water injection system if you can't get it to pass the NOx part of the test, but chances are it would be ok with a good cat converter.
I drive a Prizm that has a 7A-FE engine and I really like the torque characteristics of this engine. It gets great mpg and has loads more torque at low rpm than the 3A-C engine. I wish the Tercel had come with 1.8L engine, even if they had left the crappy 8v SOHC cylinder head on it. I have contemplated building something similar to what you want to build, but I want to avoid the clearance issues installing a taller block would create. A compromise would be perhaps finding out if the 7A-FE connecting rods and crank could be made to work in a 4A-C block or perhaps use the 7A-FE crank but get custom connecting rods made to fit the 4A-C to increase the displacement to at least 1.7L or so, the end result being a longer stroke and thus increased torque and overall power.
2015 Honda Fit EX "Malachi"
2001 Toyota Corolla CE "Eugene"
I'll have to consider Delta's 260 "mild street" regrind; sounds like a great deal!
Yeah, I'm thinking with a clean EGR (no idea what state mine is in now; it barely passes smog) and a new / cleaned CAT (once again, no idea how effective it is; I haven't tested with a laser temp gauge) it'll probably pass.
No idea on if a 7AC would fit in a Tercel, but the block is only 15mm taller or something. Lower motor mounts would be able to compensate for that.
