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Discussion Starter · #1 ·
Salutations everyone. I'm posting this while at work so hello from The Home Depot. Anyways, after my last post about the VTEC Killer setup, I've decided against it in favor of doing high compression. As such, I have a couple of questions as I look into this route of modification.

NOTE: all of these pertain to a mild, daily driven street build on a K24A4. not looking to push the engine past 7000 RPM, if even that.

Onto the questions:
1. what is the highest compression I could run on 93 octane fuel? I'm not going any higher

2. would it be necessary to replace the connecting rods on this mild of a setup? if so, which ones would be appropriate?

3. this is kind of a more general question, but would I begin to run into interference issues with higher compression pistons? if so, would the stock 25 degree VTC gear be enough?

4. it is worth the price difference to get new, aftermarket pistons, or will a used one work just as good (in terms of seal and compression)?

5. I'VE NEVER PULLED APART AN ENGINE LIKE THIS BEFORE. despite this, I am fairly skilled with car modifications as it is and have friends that have pulled apart engines before so I should be ok. that said, what other components should be replaced when I do this, like crank bearings and such? also, is there any advice you would give to someone doing this particular job?

Thank you for any input you may have; I look forward to learning from my contemporaries!
 

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I am also at work and will write more later but here is a good starter for taking the engine apart.
You can reuse bearings if they measure out correctly and aren’t damaged but while in the engine that far it is advisable to spend the extra but and do new rod bearings at least. The rpm is what will kill the rods if you’re staying 7k or under the a4 ones are fine I would say.
 

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Another .02 a friends engine is running 13.5 wiseco pistons on pump 91. It needed a little bit of timing retard but it’s doable. Ideal is 12.5:1 for balance of power and safety for pump gas in my opinion
 

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Discussion Starter · #4 ·
I am also at work and will write more later but here is a good starter for taking the engine apart.
You can reuse bearings if they measure out correctly and aren’t damaged but while in the engine that far it is advisable to spend the extra but and do new rod bearings at least. The rpm is what will kill the rods if you’re staying 7k or under the a4 ones are fine I would say.
Another .02 a friends engine is running 13.5 wiseco pistons on pump 91. It needed a little bit of timing retard but it’s doable. Ideal is 12.5:1 for balance of power and safety for pump gas in my opinion
Wow, I wasn’t expecting to be able to go that high. about how much power would a jump from say, 9.7 to 12.5 achieve?
 

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Wow, I wasn’t expecting to be able to go that high. about how much power would a jump from say, 9.7 to 12.5 achieve?
It’s hard to say without knowing the rest of what the engine has done to it /bolted onto it but on a stock k24 I would expect 10-15whp from bumping compression alone. It has more of an effect when paired with larger cams and larger manifolds. It also depends on the tuner being capable as well. Most people will tell you a 13:1 engine is impossible to run on pump fuel. The higher you go in CR the harder it is to keep detonation out of it with low quality fuel.
 

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Discussion Starter · #6 ·
It’s hard to say without knowing the rest of what the engine has done to it /bolted onto it but on a stock k24 I would expect 10-15whp from bumping compression alone. It has more of an effect when paired with larger cams and larger manifolds. It also depends on the tuner being capable as well. Most people will tell you a 13:1 engine is impossible to run on pump fuel. The higher you go in CR the harder it is to keep detonation out of it with low quality fuel.
This is pretty insightful honestly, I’ll probably keep it under 13:1 then. Do you think the power difference between used tsx 11:1s and say wiseco 12.5:1 would justify the price difference? All of this is being done on a very conservative budget (I’m still in high school)
 

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This is pretty insightful honestly, I’ll probably keep it under 13:1 then. Do you think the power difference between used tsx 11:1s and say wiseco 12.5:1 would justify the price difference? All of this is being done on a very conservative budget (I’m still in high school)
You can do a lot with the tsx pistons (06-08 RBB are 10.5:1, the 09+ RL9 are 11:1 ) and a good head/set of cams. If it were my engine I would use the oem pistons and spend the money saved on the cylinder head/intake manifold/header.
 

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The nippon pistons are a great choice for a budget build and you don’t really want to trust the original 87mm bore it’s rare that when you take the pistons out for the first time that the bore is “in round” still. The engine would benefit most from an 87.5 bore and new piston to ensure long life and good sealing on the rings. Yes you can just hone the original bore sometimes but to be sure you would want to take the block to a shop or someone who can measure and confirm whether you can use a 87mm piston
 

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Discussion Starter · #9 ·
The nippon pistons are a great choice for a budget build and you don’t really want to trust the original 87mm bore it’s rare that when you take the pistons out for the first time that the bore is “in round” still. The engine would benefit most from an 87.5 bore and new piston to ensure long life and good sealing on the rings. Yes you can just hone the original bore sometimes but to be sure you would want to take the block to a shop or someone who can measure and confirm whether you can use a 87mm piston
i'll definitely be looking into these. in regards to the bore issue, what happens if the bore is less or more? this is my daily and only car so its not like I can wait on a machine shop to sort it out. i've never had to think about these kinds of issues so this is all new to me
 

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Discussion Starter · #10 ·
You can do a lot with the tsx pistons (06-08 RBB are 10.5:1, the 09+ RL9 are 11:1 ) and a good head/set of cams. If it were my engine I would use the oem pistons and spend the money saved on the cylinder head/intake manifold/header.
thank you for everything you've taught me so far. if it helps, I already have an RBB manifold which will be installed, and I plan to do a full exhaust but I'm still unsure about headers. in regard to the cylinder head though, i would need to swap the pistons anyway because of the design of the k24a4 pistons specifically, which with any other head will make contact (or so i've heard). the only other reason I wouldn't want to is because I plan to run the stock transmission and don't stupidly long gears (6 speeds are expensive). my planned rev limit is 6800, and this is only because I want to use actual redline on the tach (and for the gear ratio reasons); its honestly just a quirk of mine. hopefully this will help you understand what i'm trying to accomplish
 

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I understand. The bore size won’t be smaller , just could be slightly out of uniform in some or one area if any part of the piston wasn’t wearing evenly. It may be better to junkyard a block from an element or accord so that way you can make sure you have a perfectly round bore. Otherwise the engine could burn oil and/or wear the cylinder walls out excessively. Most of the time if you find a car at the yard that still has the valve cover and coils on it that’s a good sign.there was a member who had a jdm tsx engine with only 60k or so and when it got taken apart the machinist advised going to .25 over because the cylinders weren’t perfectly round.
 

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thank you for everything you've taught me so far. if it helps, I already have an RBB manifold which will be installed, and I plan to do a full exhaust but I'm still unsure about headers. in regard to the cylinder head though, i would need to swap the pistons anyway because of the design of the k24a4 pistons specifically, which with any other head will make contact (or so i've heard). the only other reason I wouldn't want to is because I plan to run the stock transmission and don't stupidly long gears (6 speeds are expensive). my planned rev limit is 6800, and this is only because I want to use actual redline on the tach (and for the gear ratio reasons); its honestly just a quirk of mine. hopefully this will help you understand what i'm trying to accomplish
You are right about the a4 /a8 pistons. I would use oem tsx or nippon pistons over a set of wiseco and put the saved money towards a k20 or tsx cylinder head is what I meant. However you go about it just be sure you aren’t taking apart something that won’t go back together. If you found a good set of tsx pistons (or crv k24a1) and they were nice and clean and you got a nice hone on your block technically there’s nothing stopping you , it just may not last as long as the original motor put together by Honda would of.
 

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Discussion Starter · #13 ·
I understand. The bore size won’t be smaller , just could be slightly out of uniform in some or one area if any part of the piston wasn’t wearing evenly. It may be better to junkyard a block from an element or accord so that way you can make sure you have a perfectly round bore. Otherwise the engine could burn oil and/or wear the cylinder walls out excessively. Most of the time if you find a car at the yard that still has the valve cover and coils on it that’s a good sign.there was a member who had a jdm tsx engine with only 60k or so and when it got taken apart the machinist advised going to .25 over because the cylinders weren’t perfectly round.
at that point it would probably just make sense to get the bore measured, but this still helps
 

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Discussion Starter · #14 ·
You are right about the a4 /a8 pistons. I would use oem tsx or nippon pistons over a set of wiseco and put the saved money towards a k20 or tsx cylinder head is what I meant. However you go about it just be sure you aren’t taking apart something that won’t go back together. If you found a good set of tsx pistons (or crv k24a1) and they were nice and clean and you got a nice hone on your block technically there’s nothing stopping you , it just may not last as long as the original motor put together by Honda would of.
ok so I have just a few more questions: when you talk about the head, I understand that some heads are better flowing than others, but it would be nice if you could shed some more light on this (like which would be the best choice for me). also, could I transplant the stock cams and lifters if I wanted to, or would that just negate any power gains? The only reason I ask is because I still would like to retain some gas mileage, though I’m willing to sacrifice some in the name of more power.

I do alot of cruising day to day, which would make something like vtec killer on a2 cams (my original plan) fairly detrimental while cruising at speed, or at least I think it would be. If you have any input on this then that would be great. I don’t try to hypermile but it would still be nice to stay efficient when I want to be, which is why the stock camshafts would be nice
 

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ok so I have just a few more questions: when you talk about the head, I understand that some heads are better flowing than others, but it would be nice if you could shed some more light on this (like which would be the best choice for me). also, could I transplant the stock cams and lifters if I wanted to, or would that just negate any power gains? The only reason I ask is because I still would like to retain some gas mileage, though I’m willing to sacrifice some in the name of more power.

I do alot of cruising day to day, which would make something like vtec killer on a2 cams (my original plan) fairly detrimental while cruising at speed, or at least I think it would be. If you have any input on this then that would be great. I don’t try to hypermile but it would still be nice to stay efficient when I want to be, which is why the stock camshafts would be nice
gas mileage= gone with vtec killer. The 3 lobe system is much more fuel efficient. Any of the 3 lobe cylinder heads will flow better than the a4 by far. The RBB being the “worst” performer out of the set. The k20a2/z1 PRB head is revered as being the best available to US market. The k24a4 only has vtec on the intake cam and uses a single lobe exhaust cam so if you are swapping the cylinder head you need the rocker assembly and 3 lobe cams to go with it. All the camshafts are interchangeable between the RSX 02-06 ,civic si 06-11 and the tsx 04-08. 04-05 tsx k24a2 cams will be the cheapest. 06-08 k24a2 will be the most expensive. If you can find 05-06 rsx type s cams (k20z1) those are pretty much the same as type R. If you give the engine real vtec and tsx pistons or similar CR you will not lose mpg, but gain mucho performance. If you go past oem CR for the tsx you’re looking at consuming more fuel. The RBB intake is just fine to use and will benefit the TQ down low -mid range.
 

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building an engine takes a little bit of time, especially if you don’t have routine and all parts ready to go.
Just measuring all the clearances and ring gaps takes a few hours.

May I suggest you source a cheap k24a2 or k24a3, high milers should be cheap and rebuild that.
Once that engine is fully build and ready, you swap out your current engine.
This takes a lot of time pressure out of the build. And things build in a hurry = issues.
Once done, you can always sell your current engine and end with much of the same expense, but you have a car to drive while doing so.
 

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What lotus suggested is the route I am taking as it is the least stressful. Leaving the stock engine running nice in the vehicle until the spare motor is done is never a bad idea. I remember my first gsr build it was Friday we were taking it apart and I had work on Monday morning with a bare block on the engine stand 😂 it ended up working out ok, but I’m sure I would of had a better time if I could build the motor on the stand at my own pace.
 

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Discussion Starter · #18 · (Edited)
building an engine takes a little bit of time, especially if you don’t have routine and all parts ready to go.
Just measuring all the clearances and ring gaps takes a few hours.

May I suggest you source a cheap k24a2 or k24a3, high milers should be cheap and rebuild that.
Once that engine is fully build and ready, you swap out your current engine.
This takes a lot of time pressure out of the build. And things build in a hurry = issues.
Once done, you can always sell your current engine and end with much of the same expense, but you have a car to drive while doing so.
the one issue with an engine swap is having a place to put the other one, but i'll find a solution to that.

i do have one question though: say I had all the parts on hand to build the current engine to basically turn it into a k20/24. I do you think that it would be cheaper to do it that way? or to just pull and engine from a junk yard? I only ask this because I at one point found a 08-12 tsx at a yard with the k24z3 I believe. it was auto so, first off, would my current 5 speed work? also if I could go back and get that engine do you think it would be worth it?
 

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Discussion Starter · #19 ·
how easy do you think it would be to sell the current engine once it's done? this is a big factor since I don't think my parents will be very happy with an engine just sitting around (they WILL shoot this down). other wise I honestly was considering an engine swap but the trans would also have to be made to work as well, but that's honestly not that big of a deal anyway.

In a pinch I could probably leave the engine with a friend that has the land to spare so maybe I will end up going this route, but Idk. for this amount of work I might as well just turbo the car lmao
 
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