Hoffman5982
03-04-2015, 02:21 AM
So I just picked up a spare DOHC KA that, so far, seems to be in excellent shape. My current KA, which I picked up for $60, has been the best engine I have ever owned. I have wanted to do a high comp build for a while now as I am extremely happy with the power I already have, especially after the recent 248/232 cam install(Seriously, if you're NA and haven't done this, you need to get on it). I drift the car, but it's nothing more than a hobby. I'm not trying to kill myself over it, and I'm not trying to make a bunch of power and waste a bunch of tires. I can do literally any track or spot I want to do with no issues with the power I have. It's very important to note that this is not strictly a track car. While I do have a daily s14, I actually drive this car quite a bit. Sometimes it is more of a daily than my actual daily, go figure.
I have been wanting to build a high comp KA for a while, but I don't dare tear into my current motor and mess with its juju. Obviously we all know that dropping SOHC pistons in will bump the compression up to ~10.5:1, but I had a few questions about my build ideas.
First, tuning. If I just do a basic overhaul(gaskets, bearings, etc), what will I need to do about the ECU. I highly doubt it's as simple as run 93 octane and go, but if that is miraculously the case then great! I have a Nistune board that I can send back and have reflashed for the KA base map if needed. I have a friend trying to convince me to trade that for Nismotronic and run ITBs. I'm not totally opposed to this idea as that would be the ultimate NA motor.
Second, piston brands. Now I know the '89 and early '90 pistons had no dish, and therefor bump the compression even higher. Unfortunately, all OE replacements are the same as the later pistons and have a tiny dish. So I ask, should I look for used OEM pistons or get OE replacements like NPR? Are the OE replacements good? I drive the car pretty hard. I don't bounce off rev limiter constantly, but I have at rainy day events. I want my motor to be as reliable as I can make it.
Third, injector size. This may be a dumb question, so bear with me. If tuning is required, would I be able to squeeze any more power out by dropping in, say, SR 370cc injectors? Also, and this could have been asked along with the tuning, I assume I will be running 93? race gas is not an option with how much I drive this car. I run iridium plugs if that makes any difference. Everyone said you HAVE to run 93 with the 248/232 cams and advancing the distributor toe 25*, but I accidentally added a little over a quarter of a tank of 87 octane to the quarter tank of 89 octane and haven't had the first sign of detonation.
Fourth, Head gasket. Can a FelPro head gasket handle this application? I ask because I don't necessarily want to have a bunch of machine work done. I'm not trying to go bankrupt here, although I will gladly spend money where it should be spent. IF I do buy an MLS head gasket, what thickness should I get? Also, since we're on the subject of raising the compression even further, I have heard that S14 heads will bump it up a tiny bit higher. I could easily attain one, but should I?
Fifth, machine work. I have never used the DIY cylinder hone tool. Should it stay that way? If I run a FelPro gasket and therefor have no extensive machine work done, should I have a shop at least hone my cylinders or would doing it myself be ok? Be honest here, please.
And last, I would love for anyone with any experience in building a high compression motor to give any tips or tricks and some advice on my plans:
I'd like to keep the build relatively simple. I already have a new oil pump/front cover and timing component kit. I'll be replacing all gaskets, bearings(most likely Clevite) and obviously the pistons. If I do run a MLS head gasket I will have the block and head decked(I assume I want as little as possible taken off if I want to be able to run 93?) and hot tanked, cylinders honed, and crank polished. Tuning would be through nistune, or nismotronic. I will keep the current 248/232 cam setup, and may run an MSD coil just to get every last drop of power out.
I think that about covers it. Hopefully I didn't bore people with too many words. Maybe this thread can eventually serve as a good source of info for those wanting to do the same in the future. All I've found in my searches are backyard builds with no actual info. Thank you so much in advance.
I have been wanting to build a high comp KA for a while, but I don't dare tear into my current motor and mess with its juju. Obviously we all know that dropping SOHC pistons in will bump the compression up to ~10.5:1, but I had a few questions about my build ideas.
First, tuning. If I just do a basic overhaul(gaskets, bearings, etc), what will I need to do about the ECU. I highly doubt it's as simple as run 93 octane and go, but if that is miraculously the case then great! I have a Nistune board that I can send back and have reflashed for the KA base map if needed. I have a friend trying to convince me to trade that for Nismotronic and run ITBs. I'm not totally opposed to this idea as that would be the ultimate NA motor.
Second, piston brands. Now I know the '89 and early '90 pistons had no dish, and therefor bump the compression even higher. Unfortunately, all OE replacements are the same as the later pistons and have a tiny dish. So I ask, should I look for used OEM pistons or get OE replacements like NPR? Are the OE replacements good? I drive the car pretty hard. I don't bounce off rev limiter constantly, but I have at rainy day events. I want my motor to be as reliable as I can make it.
Third, injector size. This may be a dumb question, so bear with me. If tuning is required, would I be able to squeeze any more power out by dropping in, say, SR 370cc injectors? Also, and this could have been asked along with the tuning, I assume I will be running 93? race gas is not an option with how much I drive this car. I run iridium plugs if that makes any difference. Everyone said you HAVE to run 93 with the 248/232 cams and advancing the distributor toe 25*, but I accidentally added a little over a quarter of a tank of 87 octane to the quarter tank of 89 octane and haven't had the first sign of detonation.
Fourth, Head gasket. Can a FelPro head gasket handle this application? I ask because I don't necessarily want to have a bunch of machine work done. I'm not trying to go bankrupt here, although I will gladly spend money where it should be spent. IF I do buy an MLS head gasket, what thickness should I get? Also, since we're on the subject of raising the compression even further, I have heard that S14 heads will bump it up a tiny bit higher. I could easily attain one, but should I?
Fifth, machine work. I have never used the DIY cylinder hone tool. Should it stay that way? If I run a FelPro gasket and therefor have no extensive machine work done, should I have a shop at least hone my cylinders or would doing it myself be ok? Be honest here, please.
And last, I would love for anyone with any experience in building a high compression motor to give any tips or tricks and some advice on my plans:
I'd like to keep the build relatively simple. I already have a new oil pump/front cover and timing component kit. I'll be replacing all gaskets, bearings(most likely Clevite) and obviously the pistons. If I do run a MLS head gasket I will have the block and head decked(I assume I want as little as possible taken off if I want to be able to run 93?) and hot tanked, cylinders honed, and crank polished. Tuning would be through nistune, or nismotronic. I will keep the current 248/232 cam setup, and may run an MSD coil just to get every last drop of power out.
I think that about covers it. Hopefully I didn't bore people with too many words. Maybe this thread can eventually serve as a good source of info for those wanting to do the same in the future. All I've found in my searches are backyard builds with no actual info. Thank you so much in advance.