[30ONA]

I am hoping with the vast knowledge in the forum I can work my way through this rebuild.

I have a running engine in my Suzuki and a spare I picked up for $400 with a gearbox too. Planning to rebuild both and replace into my car.

The plan is to pull down the spare engine and build it back to the original specs but am considering increased compression. Before starting the build I presume I need goals and targets. What else should I know before starting?

Current goal,
1. Return the original performance to the car. Current engine is at 175PSI so I imaging another 12% will be lovely in a fresh engine.
2. Performance increases where the original ECU, fuel and ignition system will support it.
3. What else should I decide before starting?

How much additional power will the extra compression make? From my googling the CR is already 9.7-1 and it will run on 91 octane. Piston options I've seen are 9.1 (guessing stock overseas or turbo pistons) 10.1 and 11.1. I believe the H25A 8:1 pistons are good for if you want to boost. As I understand if I have 100kw new (i know its 94 but for easy numbers) , 100/9.7*10.1 will give the power with higher compression pistons? which is only 5kw and I would bother for 5kw. But I understand torque will benefit more when increasing CR, but how to calculate I don't know.

Now after the above is sorted what order do I work? As I work through each step I'll ask the finer details.

1. Block machining, bores and deck
2. crank machining and caps
3. buy pistons and associate parts to fit new machined block
4. rebuild the head to suit the new block

[Brenno]

Is 175psi within spec? I would have thought that's pretty good.

The work you are describing is likely 5ķ or more of machine work for something that can then only run on 95+ octane fuel.

Let us know what your goals are?

[30ONA]

Brenno wrote:

Is 175psi within spec? I would have thought that's pretty good.

The work you are describing is likely 5ķ or more of machine work for something that can then only run on 95+ octane fuel.

Let us know what your goals are?

175 is the lower limit 199 to 175
I want to be able to tow my box trailer comfortably and stay at the speed limit when fully loaded.
91 is getting rare I can't run on e10, so might as well go to 95. I already run 95.

[30ONA]

Brenno wrote:

Let us know what your goals are?

An engine that can do another 100,000ks and has more torque than factory and no less than equivalent hp to factor.

[Gwagensteve]

It doesn’t make any sense to spend that much money on a j20 and keep stock engine management. I doubt the management will have any idea how to deal with increased compression.

It doesn’t make any sense to up the compression and not look at head flow, camshaft profile and timing.

Increasing compression ratio a point or two will make very limited difference to torque. It won’t magically transform the engine. Adding ignition timing will also make a small difference and will force you into using better fuel. It’s pointless, in my opinion, building an engine that requires 95 octane, the difference will be too marginal.

Using stock management and relying on higher octane to deal with the increased compression is a recipe for disaster. I think J engines are knock sensed but that doesn’t mean the knock sensor is a tuning tool, it’s there for engine protection.

[30ONA]

Gwagensteve wrote:

It doesn’t make any sense to spend that much money on a j20 and keep stock engine management.

Without the CR increase it does to me.

Gwagensteve wrote:

I doubt the management will have any idea how to deal with increased compression.

I hadn't considered that. Good point. I already looked into engine management when I was looking at boost and it would be $2000-3000 min with install and tuning. So that's a no.

On the fuel note I use 95 anyway so that is a moot point.

Sticking with standard build then for the engine.

On a previous car I saw 6kw + at the wheels from a lightened crank pulley. If the same principals apply for the flywheel I wonder is there much that can be machined off that? Yes reduced fuel consumption and more engine braking.

[fordem]

30ONA wrote:

Now after the above is sorted what order do I work? As I work through each step I'll ask the finer details.

1. Block machining, bores and deck
2. crank machining and caps
3. buy pistons and associate parts to fit new machined block
4. rebuild the head to suit the new block

You want to buy your pistons (and rings) before machining the block.

[30ONA]

fordem wrote:

30ONA wrote:

Now after the above is sorted what order do I work? As I work through each step I'll ask the finer details.

1. Block machining, bores and deck
2. crank machining and caps
3. buy pistons and associate parts to fit new machined block
4. rebuild the head to suit the new block

So step one is buy bearings pistons and rings? I would have thought you need to find the worst defect in the cylinder to determine how much minimum bore then go up to the next size piston set. Or do you pretty much guarantee to get all the defects with 0.5mm as the first increment?

You want to buy your pistons (and rings) before machining the block.

[Gwagensteve]

Please take this the right way but I think you are well over your head here.

Suzuki made a GV with the power you need to do the job you want to do, and if you need more power than a H25 can provide, a H27 is a pretty easy swap.

Buying a whole H25 GV will probably cost about the same as properly rebuilding a J20, which, once you have spent all the money, still won't be enough engine to do the job.

Chasing incremental increases through compression ratio and engine management is an incredibly expensive way to try and increase performance.

The best bang for your buck would be to regear the diffs to 5.12. You'll gain more performance than any N/A engine work could provide and take load off the engine. The next step would be to buy a H25 GV.

Pulling apart a cheap engine that isn't broken doesn't make any sense.

[30ONA]

Thanks Steve. I'm doing it. The op did not ask if I should. I'm asking for guidance through the process.

[fordem]

30ONA wrote:

So step one is buy bearings pistons and rings? I would have thought you need to find the worst defect in the cylinder to determine how much minimum bore then go up to the next size piston set. Or do you pretty much guarantee to get all the defects with 0.5mm as the first increment?

No - step one is to disassemble the engine and "mike" or measure the bores with a micrometer to determine the extent of the wear and ovality, once you've determined the oversize you need, you purchase the pistons & rings and then bore the block.

[30ONA]

fordem wrote:

30ONA wrote:

So step one is buy bearings pistons and rings? I would have thought you need to find the worst defect in the cylinder to determine how much minimum bore then go up to the next size piston set. Or do you pretty much guarantee to get all the defects with 0.5mm as the first increment?

No - step one is to disassemble the engine and "mike" or measure the bores with a micrometer to determine the extent of the wear and ovality, once you've determined the oversize you need, you purchase the pistons & rings and then bore the block.

Ok thanks. That's kind of what I meant. Can I do that by just removing the head and moving the pistons down or do you need to remove the pistons too to measure?

[Gwagensteve]

Unless you own the appropriate micrometers and know how to use them, this is a job for your engine builder. I suspect that any reputable engine builder would re measure the block regardless of what you’d already bought, measured or supplied.

[Urbex]

I think part of what OP is missing here is that, despite "standard" overbores frequently being mentioned in build sheets, the exact amount being machined out needs to match the diameter of the pistons you're using. I don't know what your overbores typically are in millimeters, as I am in the USA, but for us it's usually 0.030" or 0.060". I can grab 10 different sets of pistons labeled as 0.030" overbore pistons, and get 10 different diameters on each set as they're manufactured to a particular tolerance that may or may not be exactly 0.030" larger than the factory.

Thus, you buy your pistons first and supply them to the machine shop doing your engine work. They measure the pistons, then bore your block to match them, to meet the piston to bore clearance spec. This will vary based on your piston selection, but will be a small amount somewhere likely in the area of 0.25mm. If you end up with pistons that are slightly larger than the listed overbore, and your machine shop bores the cylinders to the exact overbore amount, you'll end up with an engine that has a lifespan measured in hours when the pistons seize in the bore.

However, as others noted - the block needs to be disassembled first to accurately measure your existing bores to determine if you need the 0.030", 0.060", or even larger pistons, or you may find that one or more cylinders in the block are so worn that it won't have enough material to be bored enough to bring it back to a round condition and is now considered scrap metal.

Yes, the block needs to be completely disassembled to do it properly. You need to take multiple measurements in each cylinder, at the top, middle, and bottom of the cylinders. The bottom will be a problem with just pulling the heads and spinning the crank over, as you need measurements in the same place that the piston will be occupying at the bottom of the bore.

Rebuilding an engine is FAR more than just buying the appropriate parts, and assembling them. Get any of this stuff wrong, and you've just spent a LOT of money on something that will become a block of scrap metal in a few hours.

[30ONA]

Gwagensteve wrote:

Unless you own the appropriate micrometers and know how to use them, this is a job for your engine builder. I suspect that any reputable engine builder would re measure the block regardless of what you’d already bought, measured or supplied.

Thanks will do. I'm removing all the accessories and timing gear. If like to look in the cylinders before I send the head and block. If Iopen up the head that's not going to cause them any issues is it?

[Joe]

As gbanger said if ya want performance upgrades swap in some 5.12 diffs, want more torque swap in a h25/h27 otherwise I think you'll be left feeling pretty disappointed trying to get more power from a j20.

[Gwagensteve]

Talk to the engine builder. If I was going to rebuild a customer engine I wouldn’t want them to have touched it at all before I got to it.

[USMC5811]

Did you guys have the Aerio with the 2.3? Easy bolt in

[Gwagensteve]

USMC5811 wrote:

Did you guys have the Aerio with the 2.3? Easy bolt in

No, we had the J24 in the Kizashi but it's far from a straightforward swap.

[USMC5811]

Gwagensteve wrote:

USMC5811 wrote:

Did you guys have the Aerio with the 2.3? Easy bolt in

No, we had the J24 in the Kizashi but it's far from a straightforward swap.

Yeah, the 24 is a whole different animal, the entire drive train.

[30ONA]

How do I remove the crank pulley? Left ir right thread and do i need an impact gun?

[fordem]

It's a standard right hand thread, and an impact would probably be easiest, assuming you have the space to get it in there.