I'm going to be honest, my engine does not make much low end torque. What is my plan to change that? Replace it with a smaller engine that revs higher and makes even less low end torque of course! More on that later. My actual plan to increase low end torque is to install an intake manifold spacer from a 2005-2006 Acura MDX. The manifold spacer shifts the torque curve to lower rpms so I should get more usable torque for my usual low rpm driving. These spacers cost $50 brand new, but since i'm cheap and want this to be able to pay for itself i'll look for one in a junkyard. Unfortunately, the spacer is too tall stock, 1.5", so I will have to mill it down to about 1". Luckily my dad has a mill!
People on Driveaccord have reported improved low end power, and in some cases better mpg, both good things. I have high hopes for this mod.
Okay, as for the engine swap plan...
I discovered a while back that I did not actually have the smallest J series engine Honda made, they made an even smaller V6, the J25. That's a whole half liter smaller than my J30! And no, before you suggest it I am not swapping to the 4 cylinder. I like my V6s, and I also like having a tall geared 6 speed manual. The J series transmissions do not fit on the K series 4 cylinders. Back to the J25, it was made from 1998-2003, IN AMERICA! Unfortunately it was only sold in Japan.
However, there are plenty of J25s being shipped here with low miles for cheap, because, Japan...I found one such example of a J25 for $399! But it was in New York, so that's that...The J25 shares some features that my J30 has, like a variable intake manifold, and VTEC, yo! However, it also features something different...Direct injection...
Honda has a habit of implementing new technology and not advertising it before they know it works. Case in point: SH-AWD. NO ONE talks about the direct injection in the J25, I really thought that the new earth dreams engines were the first Hondas to have direct injection, guess not. This direct injection makes me a little nervous. If it was in the original car I would be absolutely fine with it, but it won't be. My plan for this engine was to swap my J30 out for the J25, hook up everything like normal, and enjoy better fuel economy. The car wouldn't know the difference. However, with direct injection, I don't think this would be the case. If I plug everything in like normal, assuming the injector connectors fit each other, I think the DI would fire early(comparatively) and cause pre-detonation. The other thing i'm worried about with this engine is the compression ratio, I can't find any info about it, so I have no idea what it is. Does it run on regular gas? I have no idea. What I will probably end up doing is swapping the heads from the J30 to the J25, just to make everything guaranteed to work, and just leave it at that. The car wouldn't know the difference, the engine will just have a shorter stroke.
I don't JUST want to swap to a J25 for better fuel economy, I also want to enjoy the ability to rev to 7200 rpm, instead of 6800 like the J30. However, If I swap the heads over and just plug it into the car I fear it will still be limited to 6800. And I doubt the Honda Inspire ECU is compatible with my accord, so I would probably have to resort to a tuning software to raise the rev limiter.
I really want to leave the original J25 heads on, and make everything work, since DI should have a fuel economy benefit. But without hooking up an Inspire ECU I just don't see how I could get it to work. The J25 was made back before Honda integrated the exhaust manifolds into the heads, so that means the possibility of running some nice tuned headers, but again, I don't think I will be able to get the stock heads to work. Another problem with that is emissions compliance, will I get a check engine light? Do the J25's exhaust manifolds have O2 sensors in them? Does it have pre-cats like my J30 does? Do the headers hook up to my stock J-pipe? I have no idea.
So since I have little confidence in the DI system working on my accord ECU (honestly I wouldn't even want to test start it, cause it might blow itself up), I have three potential solutions:
1. Most realistic solution: Swap the J30 heads onto the J25, the car WILL NOT know the difference.
2. The solution I want to work: Keep the stock J25 heads on, leave the direct injectors in place and swap all the J30 hardware onto the J25, ie: Intake runners, manifold, fuel rail(assuming the fuel injectors plug into the runners, and not the head), injectors.
3. The solution that won't work but I wish it could: Sprinkle some unicorn dust onto the fuel injectors and injector connector plugs, cross fingers and hope it doesn't explode
My current questions regarding the J25:
What fuel economy benefit does it offer? It seems to get 10% better fuel economy than the J32 according to one site, still looking for user feedback.
Fuel system questions:
Can my fuel pump supply the correct pressure for the DI system? No Idea.
Will my fuel rail bolt up to the DI system? Probably not.
Will my accord's ECU work with the DI in the J25? Probably not.
Will the ECU limit the engine to 6800 rpm instead of 7200? Probably.
Can the Inspire ECU work on the accord? Probably not.
Will the engine run on regular gas? No idea.
Will it be emissions compliant with stock heads? No idea.
Mechanical questions:
Are the mounting holes the same? Apparently all J series blocks are the same so they should be.
What type of oil to use? No idea.
Will my J30 flywheel fit on the J25? Probably.
Will the engine mounts be in the same places? Probably.
Will the heads have to be swapped ? Most likely.
Will the accord J pipe fit the manifold on the J25? Doubt it.
Is the throttle body compatible with the J25? It will be if the manifold from the J30 is swapped over!
Is the intake manifold the same on the J25? From the pictures, it doesn't look the same, however it still has a variable intake function.
Also on my engine mods to try list: I kind of want to try adjusting the valve clearances on one intake valve each to give an intake swirl effect like in the i-VTEC engines. I found the valve lift to be about 10mm on a performance K24, its probably similar on a J30, and it looks like when in low lift mode a i-VTEC engine lifts one of the intake valves about 40-50% of the height of the normal lobe. I fear it may be bad for the valves if I do this, and I am sure it would be very noisy. What I am not sure of is any benefit offered by this. Also, my engine would be unable to revert back to normal lift for both valves when I need to step on it, so I don't know what that would do to the engine.