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Engine / 4afe build ??!
« Last post by autocrosscelica on August 16, 2024, 10:16:17 AM »Hello,
This thread is going to be following my 4afe build for my ‘91 celica st that I’ve been toying with for over 2 years now. Mostly suspension and brakes work (Had bimbos for a bit but am back on the bigger 92-93 fronts). This build is not gonna be quick as I am still in university but I have got some fun stuff planned that I don’t think has been documented that well yet.
Goals: I want to try and make power up to 6500 rpm naturally aspirated. I know what you’re thinking, that's stupid, it's just a torquey-ish economy engine. You’re right, I know that, but who doesn’t love a good challenge. If I wanted quick and easy power I would go 4age or 3s but I have accepted my fate. In typical engineering student fashion, I chronically over research everything but I am finally ready after 2 years to start using some of this useless knowledge about the 4a engines to build something. I do not have any power goals at all, it’ll make what it makes, but I am excited to go through the process and see the effects of changes in the future.
4afe History: The early 4afe (88-92 corolla/prizm, 90-93 celica) was essentially toyota throwing efi at the turd of an engine that never dies: the 4af. 1.6l, small journal bearings(40mm), small wrist pins(18mm), small valve included angle!(~22 deg) but the port slopped out horizontally to fit the injectors that were cast into the head. Not a bad engine but leaves some to be desired and can be hard to come by parts nowadays. The obd1 late 4afe is then introduced (93-95 rolla) along with the obd1 7afe (94-95 celicas, some corollas). This remodel is in every way better: journal bearings to match the 4age’s(42mm), same for the wrist pins(20mm), still narrow valve included angle but this time the injectors are moved to the manifold and the intake ports are a straight shot to the back of the valve. Bigger valves, buckets and cams as well as a pot style tps and electronic iac!!! Then finally, the obd2 4/7afe’s came around (96+ celicas and corollas). Nothing major here except having a crank position sensor and a proper cam position sensor instead of the Nippondenso CAS that doesn’t play very nicely with a standalone. I should also mention that the late 4afe and 7afe have the same head castings and components except injectors. Some claim that the 7a cams had larger lift cams, some said they were the same, idk. Out of all of these, I have found the 7afes to be the most abundant in junkyards and on FB.
The Plan: I got a cheap early 4afe on fb from a ‘92 prizm (maybe) about a year ago and have mostly sat on it till now. I plan to use this as my block because A: I already have it & B: a late 4afe has proven hard to find in the midwest. I should also mention that I wanted to stick with 1.6L because I like the bore/stroke ratio at 81/77mm for a NA ‘higher’ revving build better than the stroker 7a (lower piston speeds and little easier on the main caps which are a limitation on 7age builds). In the last couple weeks I have started collecting late afe head parts from the junkyard and some FB finds. Of those includes an awesome deal on a 6th gen celica head, so 7afe, that already had been resurfaced and the valves & valve seats recut (I tested with carb cleaner and some compressed air down the intake before I tore it down, flawless seal). The cams that were included had some slight rust. Evaporust would clear it up but the rust would come back slightly if you left it to dry (I have another set from the junkyard). This combination should be effectively a late 4afe with a slightly weakened bottom end (won’t matter for the power I’ll be at) and slightly higher lift (maybe? Conflicting answers online). All 1.6 cars had a 1.4mm head gasket but the 7afe had a .7mm HG. Things like this and shaving the head down give me the opportunity to bump compression up a little.
Wiring: I think I will end up with a Megasquirt product because there is a lot of support for it here in the US and I have a good local tuner. I also have read the documentation a couple times over the last 2 years and feel sorta confident. The microsquirt does everything I need it to but the MS3 would leave some room down the road for more inputs and outputs. I’ll price the two out down the road and make that decision. The major inputs will be the crank angle sensor from an obd2 late afe. This sensor is mounted in the oil pump so I will be pulling a CAS oil pump from the junkyard this weekend and test fitting it on my early 4afe when I make it back to the garage where the rest of the engine and the car is stored in about a week. The sensor reads teeth on the crank timing gear but the stock teeth are 36 tooth spacing with 4 of the teeth connected solid. I don’t believe MS can recognize this so I may have to get creative. I also have the option of using the stock obd2 late afe cam angle sensor in the distributor but I don’t intend on running full sequential on any outputs so I don’t think I will use it at first. The stock late afe tps is a pot style which is great and the map, coolant, and wideband sensors seem pretty straight forward. For outputs I will probably run a wasted spark setup with 2 batches. The fuel will be the same with batch fire of 2’s. I would also like to keep the functionality of the dash. If it proves too difficult I might go to a raspberry pi setup but I’ll give it a go first.
Limitations to Power: If you’re not aware, the afe heads are able to achieve this narrow head because they use a slave cam setup (the two cams are geared together and driven by one cam gear). Modern engines use roller rocker cams(cough cough 2ar-fe I love this engine) but the slave cam was still pretty cool for its time. Although we lose some adjustability, I think we can follow the footsteps of all the d series guys and still make some power. The lift of the 7afe cam I think will be sufficient to start actually (and being safe with shim over bucket) but where it lacks is in duration. Sitting around 220 deg stock, there is hardly any overlap at about 8 deg. I am curious if a regrind with a little bit longer duration and subsequently overlap would allow this head to scavenge and breathe a little better at higher rpms. But I plan to have the first iteration use a stock cam and then go from there. For compression ratios (9.5:1 stock) we can do about anything we want and reach the limitations of pump gas at about 12:1 (shell 93 is gold) without doing anything too crazy. 4age pistons are dropped in on a late 4/7afe bottom end and since the 4age has a larger combustion chamber volume than the afe’s have in the head, the piston is taller to compensate. So, 4age pistons + afe head = easy high compression. The valve reliefs in those pistons wouldn’t be perfect, but I think we could get creative if this build got that far. The manifolds on the other hand may be the end of me. The stock exhaust manifold just shoves all the ports together as fast as possible and although the stock intake is a cool 2 piece design, the runners are rather small. There is a mythological oem exhaust sold in certain European markets for a late 4afe head with a 4-2-1 design that might actually scavenge well but I can’t imagine the pain of tracking one down and shipping it over here. I have found one aftermarket header that looks okay but would be coming from Australia. And for intakes I am pretty sure there is only one aftermarket option and it is an overpriced billet unit that doesn’t even take advantage of the intake port angle. So we may have to get our thinking caps on for that down the road. I do have some experience with itb’s but that would be a last ditch hail mary option. Albeit awesome, it is very involved and can be very finicky. But it would give us a plethora of powerband tuning opportunities.
Updates will probably be infrequent due to me having very limited space to work on these projects while in school, but I will update as I start to test fit components. If you’ve made it through this blab fest, you’re awesome. Feel free to share about input, suggestions, and/or experiences with the 4a platform to keep me motivated
Also how the heck do you post an image on here ?! haha
This thread is going to be following my 4afe build for my ‘91 celica st that I’ve been toying with for over 2 years now. Mostly suspension and brakes work (Had bimbos for a bit but am back on the bigger 92-93 fronts). This build is not gonna be quick as I am still in university but I have got some fun stuff planned that I don’t think has been documented that well yet.
Goals: I want to try and make power up to 6500 rpm naturally aspirated. I know what you’re thinking, that's stupid, it's just a torquey-ish economy engine. You’re right, I know that, but who doesn’t love a good challenge. If I wanted quick and easy power I would go 4age or 3s but I have accepted my fate. In typical engineering student fashion, I chronically over research everything but I am finally ready after 2 years to start using some of this useless knowledge about the 4a engines to build something. I do not have any power goals at all, it’ll make what it makes, but I am excited to go through the process and see the effects of changes in the future.
4afe History: The early 4afe (88-92 corolla/prizm, 90-93 celica) was essentially toyota throwing efi at the turd of an engine that never dies: the 4af. 1.6l, small journal bearings(40mm), small wrist pins(18mm), small valve included angle!(~22 deg) but the port slopped out horizontally to fit the injectors that were cast into the head. Not a bad engine but leaves some to be desired and can be hard to come by parts nowadays. The obd1 late 4afe is then introduced (93-95 rolla) along with the obd1 7afe (94-95 celicas, some corollas). This remodel is in every way better: journal bearings to match the 4age’s(42mm), same for the wrist pins(20mm), still narrow valve included angle but this time the injectors are moved to the manifold and the intake ports are a straight shot to the back of the valve. Bigger valves, buckets and cams as well as a pot style tps and electronic iac!!! Then finally, the obd2 4/7afe’s came around (96+ celicas and corollas). Nothing major here except having a crank position sensor and a proper cam position sensor instead of the Nippondenso CAS that doesn’t play very nicely with a standalone. I should also mention that the late 4afe and 7afe have the same head castings and components except injectors. Some claim that the 7a cams had larger lift cams, some said they were the same, idk. Out of all of these, I have found the 7afes to be the most abundant in junkyards and on FB.
The Plan: I got a cheap early 4afe on fb from a ‘92 prizm (maybe) about a year ago and have mostly sat on it till now. I plan to use this as my block because A: I already have it & B: a late 4afe has proven hard to find in the midwest. I should also mention that I wanted to stick with 1.6L because I like the bore/stroke ratio at 81/77mm for a NA ‘higher’ revving build better than the stroker 7a (lower piston speeds and little easier on the main caps which are a limitation on 7age builds). In the last couple weeks I have started collecting late afe head parts from the junkyard and some FB finds. Of those includes an awesome deal on a 6th gen celica head, so 7afe, that already had been resurfaced and the valves & valve seats recut (I tested with carb cleaner and some compressed air down the intake before I tore it down, flawless seal). The cams that were included had some slight rust. Evaporust would clear it up but the rust would come back slightly if you left it to dry (I have another set from the junkyard). This combination should be effectively a late 4afe with a slightly weakened bottom end (won’t matter for the power I’ll be at) and slightly higher lift (maybe? Conflicting answers online). All 1.6 cars had a 1.4mm head gasket but the 7afe had a .7mm HG. Things like this and shaving the head down give me the opportunity to bump compression up a little.
Wiring: I think I will end up with a Megasquirt product because there is a lot of support for it here in the US and I have a good local tuner. I also have read the documentation a couple times over the last 2 years and feel sorta confident. The microsquirt does everything I need it to but the MS3 would leave some room down the road for more inputs and outputs. I’ll price the two out down the road and make that decision. The major inputs will be the crank angle sensor from an obd2 late afe. This sensor is mounted in the oil pump so I will be pulling a CAS oil pump from the junkyard this weekend and test fitting it on my early 4afe when I make it back to the garage where the rest of the engine and the car is stored in about a week. The sensor reads teeth on the crank timing gear but the stock teeth are 36 tooth spacing with 4 of the teeth connected solid. I don’t believe MS can recognize this so I may have to get creative. I also have the option of using the stock obd2 late afe cam angle sensor in the distributor but I don’t intend on running full sequential on any outputs so I don’t think I will use it at first. The stock late afe tps is a pot style which is great and the map, coolant, and wideband sensors seem pretty straight forward. For outputs I will probably run a wasted spark setup with 2 batches. The fuel will be the same with batch fire of 2’s. I would also like to keep the functionality of the dash. If it proves too difficult I might go to a raspberry pi setup but I’ll give it a go first.
Limitations to Power: If you’re not aware, the afe heads are able to achieve this narrow head because they use a slave cam setup (the two cams are geared together and driven by one cam gear). Modern engines use roller rocker cams(cough cough 2ar-fe I love this engine) but the slave cam was still pretty cool for its time. Although we lose some adjustability, I think we can follow the footsteps of all the d series guys and still make some power. The lift of the 7afe cam I think will be sufficient to start actually (and being safe with shim over bucket) but where it lacks is in duration. Sitting around 220 deg stock, there is hardly any overlap at about 8 deg. I am curious if a regrind with a little bit longer duration and subsequently overlap would allow this head to scavenge and breathe a little better at higher rpms. But I plan to have the first iteration use a stock cam and then go from there. For compression ratios (9.5:1 stock) we can do about anything we want and reach the limitations of pump gas at about 12:1 (shell 93 is gold) without doing anything too crazy. 4age pistons are dropped in on a late 4/7afe bottom end and since the 4age has a larger combustion chamber volume than the afe’s have in the head, the piston is taller to compensate. So, 4age pistons + afe head = easy high compression. The valve reliefs in those pistons wouldn’t be perfect, but I think we could get creative if this build got that far. The manifolds on the other hand may be the end of me. The stock exhaust manifold just shoves all the ports together as fast as possible and although the stock intake is a cool 2 piece design, the runners are rather small. There is a mythological oem exhaust sold in certain European markets for a late 4afe head with a 4-2-1 design that might actually scavenge well but I can’t imagine the pain of tracking one down and shipping it over here. I have found one aftermarket header that looks okay but would be coming from Australia. And for intakes I am pretty sure there is only one aftermarket option and it is an overpriced billet unit that doesn’t even take advantage of the intake port angle. So we may have to get our thinking caps on for that down the road. I do have some experience with itb’s but that would be a last ditch hail mary option. Albeit awesome, it is very involved and can be very finicky. But it would give us a plethora of powerband tuning opportunities.
Updates will probably be infrequent due to me having very limited space to work on these projects while in school, but I will update as I start to test fit components. If you’ve made it through this blab fest, you’re awesome. Feel free to share about input, suggestions, and/or experiences with the 4a platform to keep me motivated
Also how the heck do you post an image on here ?! haha