I have a 1994 corolla as a cheap daily i got a while ago, during its tenure as my beater it always drank oil at a decent rate. eventually it became severe enough to become annoying. Between the cost of oil and the smoke it produced, i debated whether to get rid of the car or to fix it. Eventually i settled on fixing it properly.
The main issue here is of course myself, i have been working in the technical industry, including aviation and automotive for 10+ years now, and always like to tinker more than is likely good for myself or my cars.
I decided if i was going to yank the head on the old 7A-FE to replace the rings and valve seals id better see what could be done to improve it while i was in there. this resulted in a few months of research, measuring various parts, contacting people at dealerships, and general technical investigation. the result of which is now is far too much time and effort on a daily but entertaining to me all the same. and hopefully entertaining and useful to others in the process.
The first step to the work was sourcing new pistons and rings along with everything else to freshen up the engine, initially i was going to go for the original 7A-FE hardware with new rings. However i decided to see if there was a cheap option for bumping the compression without having to go for 4A-GE or GZE parts which were more than i was willing to spend on a beater. after a lot of looking i found the second gen 4A-FE pistons are the same compression height pin size and valve relief pattern and depth while having a dish of around 6.9-8.3cc as measured across the 4 i purchased. the stock 7A-FE dish is 11.2-12.9cc across the 4 from my engine. the chambers on my head were all around 34.5-36.2cc in volume, and all had pitting and sharp edges in the casting that could prove an issue for detonation, thus i spent a while evening them out and adjusting each to match its respective piston to put my static comp ratio at 10.46:1. the stock HG measured in at 0.61mm thickness compressed while the new nippon reinz gasket i ordered was 0.56mm thick compressed. the 4A-FE pistons sit the same 0.6mm below deck as the 7A-FE.
The variance across the piston volume and chamber volume in the head was rather severe across the castings, which made me interested in the potential for easy gains in the head from smoothing out core shift in the port castings and removing bad casting flash. upon removing the valves i found a lot of easily fixed issues in the second gen FE head casting. the valve seats were shifted from the port center line by up to 2mm in places, and easily brought in line without exceeding 80-85% in the throat to valve head ratio, combined with some bad casting flash and general casting issues gaining a solid 5-10% from the head with a few hours of work was easy. a 30* back cut on the valves further helped and showed a 4% gain on the flow bench.
After finishing the head work i moved on to the manifolds. the stock intake on the non egr manifold, while better than the egr intake is not great. there is a great deal of flash and sharp edges and awkward geometry directly in the air stream limiting flow into the ports and dropping velocity. as the goal was to gain port velocity and maximize torque at low rpm to help with efficiency in daily driving i didn't change the cross sectional area of the ports much at all, however there is plenty of meat in these castings to go further if someone were looking at building a more performance oriented motor. overall with a bit of smoothing and working on the lower port entrance plus plenty of radiusing it showed a sold gain that while not massive will add on to the other work done so far. The exhaust was a bit more involved. the ports of the FE head are rather compromised by the included valve angle and the requisite drain back ports for the oil. i managed to get them close enough to each other to satisfy myself, but i don't doubt there would be significant gains to be had for someone willing to spend a lot more time reshaping them properly. as for the manifold it was a simple 4-2-1 header swap. the original had a large crack in the main body near the o2 sensor bung, and thus had to be replaced anyways. i may take the time to log the back pressure in the exhaust system to see if there was any appreciable improvement due to scavenging from the header, but i doubt it would be more than a scant few percent.
i still have a few parts im finishing up on the testing side for BSFC improvement currently, but after wrapping it up and firing it off for the first time is showed a noticeable improvement in throttle response and acceleration. it can easily follow traffic and the improved throttle response allows for much smoother downshifting. it does slightly slip the clutch at WOT now however, but it was due for one anyways so that and a few other things will be the next order of business for work to be done.
The main issue here is of course myself, i have been working in the technical industry, including aviation and automotive for 10+ years now, and always like to tinker more than is likely good for myself or my cars.
I decided if i was going to yank the head on the old 7A-FE to replace the rings and valve seals id better see what could be done to improve it while i was in there. this resulted in a few months of research, measuring various parts, contacting people at dealerships, and general technical investigation. the result of which is now is far too much time and effort on a daily but entertaining to me all the same. and hopefully entertaining and useful to others in the process.
The first step to the work was sourcing new pistons and rings along with everything else to freshen up the engine, initially i was going to go for the original 7A-FE hardware with new rings. However i decided to see if there was a cheap option for bumping the compression without having to go for 4A-GE or GZE parts which were more than i was willing to spend on a beater. after a lot of looking i found the second gen 4A-FE pistons are the same compression height pin size and valve relief pattern and depth while having a dish of around 6.9-8.3cc as measured across the 4 i purchased. the stock 7A-FE dish is 11.2-12.9cc across the 4 from my engine. the chambers on my head were all around 34.5-36.2cc in volume, and all had pitting and sharp edges in the casting that could prove an issue for detonation, thus i spent a while evening them out and adjusting each to match its respective piston to put my static comp ratio at 10.46:1. the stock HG measured in at 0.61mm thickness compressed while the new nippon reinz gasket i ordered was 0.56mm thick compressed. the 4A-FE pistons sit the same 0.6mm below deck as the 7A-FE.
The variance across the piston volume and chamber volume in the head was rather severe across the castings, which made me interested in the potential for easy gains in the head from smoothing out core shift in the port castings and removing bad casting flash. upon removing the valves i found a lot of easily fixed issues in the second gen FE head casting. the valve seats were shifted from the port center line by up to 2mm in places, and easily brought in line without exceeding 80-85% in the throat to valve head ratio, combined with some bad casting flash and general casting issues gaining a solid 5-10% from the head with a few hours of work was easy. a 30* back cut on the valves further helped and showed a 4% gain on the flow bench.
After finishing the head work i moved on to the manifolds. the stock intake on the non egr manifold, while better than the egr intake is not great. there is a great deal of flash and sharp edges and awkward geometry directly in the air stream limiting flow into the ports and dropping velocity. as the goal was to gain port velocity and maximize torque at low rpm to help with efficiency in daily driving i didn't change the cross sectional area of the ports much at all, however there is plenty of meat in these castings to go further if someone were looking at building a more performance oriented motor. overall with a bit of smoothing and working on the lower port entrance plus plenty of radiusing it showed a sold gain that while not massive will add on to the other work done so far. The exhaust was a bit more involved. the ports of the FE head are rather compromised by the included valve angle and the requisite drain back ports for the oil. i managed to get them close enough to each other to satisfy myself, but i don't doubt there would be significant gains to be had for someone willing to spend a lot more time reshaping them properly. as for the manifold it was a simple 4-2-1 header swap. the original had a large crack in the main body near the o2 sensor bung, and thus had to be replaced anyways. i may take the time to log the back pressure in the exhaust system to see if there was any appreciable improvement due to scavenging from the header, but i doubt it would be more than a scant few percent.
i still have a few parts im finishing up on the testing side for BSFC improvement currently, but after wrapping it up and firing it off for the first time is showed a noticeable improvement in throttle response and acceleration. it can easily follow traffic and the improved throttle response allows for much smoother downshifting. it does slightly slip the clutch at WOT now however, but it was due for one anyways so that and a few other things will be the next order of business for work to be done.
