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B20A5 Rebuild Plan - What are our thoughts?

 
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Old 03-08-2015, 10:32 AM
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B20A5 Rebuild Plan - What are our thoughts?

89 2.0 Si 4WS 270k and just developed a rod knock.
Ok, here is my plan. Tell me what you think, what I will need to modify and how much power I may see out of this. This is a budget build so no turbo and no transplants.
B20A5 block boared to B21A1 specs
B20A5 head decked .005-.010, with exhaust ports polished
B21A1 pistons
B16/18 rods
Honda OEM bearings
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Old 03-08-2015, 01:37 PM
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Re: B20A5 Rebuild Plan - What are our thoughts?

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Originally Posted by JirehCustoms View Post
89 2.0 Si 4WS 270k and just developed a rod knock.
Ok, here is my plan. Tell me what you think, what I will need to modify and how much power I may see out of this. This is a budget build so no turbo and no transplants.
B20A5 block boared to B21A1 specs
B20A5 head decked .005-.010, with exhaust ports polished
B21A1 pistons
B16/18 rods
Honda OEM bearings
This will raise your compression ratio, and should net you more power. But I'm not sure that anyone has ever posted the actual gains from this combination. I would think that the gains would be minimal unless you also upgrade to a tune-able ecu.

The only thing to modify is the block, and you already mentioned boring it to 83 mm. I'm not sure that you want to remove that much material from the head. I would just make sure it's true and go with that. Again, I doubt you're be able to take advantage of the increased compression without the ability to tune the ecu.

Having said that, I can't really say for sure since I've never done this myself, so I have no practical experience withe the modifications. That means everything I said is conjecture, lol. I would really like to see actual numbers on this build.
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Old 03-08-2015, 02:15 PM
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Re: B20A5 Rebuild Plan - What are our thoughts?

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Originally Posted by luzer View Post
I would think that the gains would be minimal unless you also upgrade to a tune-able ecu.
Where can I get a tunable ECU, how much do they cost and will a shop have to tune it?
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Old 03-08-2015, 02:38 PM
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Re: B20A5 Rebuild Plan - What are our thoughts?

h swap
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Old 03-08-2015, 03:38 PM
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Re: B20A5 Rebuild Plan - What are our thoughts?

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h swap
What does that have to do with the price of rice in Japan?
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Old 03-09-2015, 02:14 AM
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Re: B20A5 Rebuild Plan - What are our thoughts?

You will see a nice bump in power, on average the net power gain from that bigger displacement while keeping your stock B20a5 head will be roughly(and I do mean roughly, dyno tuning is always required) - 130-166whp with 140-156tq.
With CAMS that can increase another 20whp with proper tuning.

Currently our stock motors put down 119whp/123tq at the wheels. Average drive train power loss is about 10% to the wheels.

But this is all dependant on your build and tune.

So all in all not bad power for our low-mid power range motors.
Just keep in mind that you are pushing the service limits of the motor at this setup and I cannot say how long that kind of a build lasts.

It could last years or it could last months. I have seen on average people who build it this way last around a year or so of daily driving before something goes wrong and requires a rebuild or another motor.

And you are not going to want to use B16/18 rods because that would shorten the throw which will lose power and you will need to machine work to fit those properly on our cranks.

Now if you meant use B16/18 pistons that need the wrist pins modified to accept the pistons, then yes that can work.
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Old 03-09-2015, 02:48 AM
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Re: B20A5 Rebuild Plan - What are our thoughts?

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Originally Posted by JirehCustoms View Post
What does that have to do with the price of rice in Japan?
you can do what ever you want. i wouldn't mess with that b series when swap parts are available
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Old 03-09-2015, 06:53 AM
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Re: B20A5 Rebuild Plan - What are our thoughts?

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Originally Posted by 1funryd View Post
You will see a nice bump in power, on average the net power gain from that bigger displacement while keeping your stock B20a5 head will be roughly(and I do mean roughly, dyno tuning is always required) - 130-166whp with 140-156tq.
With CAMS that can increase another 20whp with proper tuning.

Currently our stock motors put down 119whp/123tq at the wheels. Average drive train power loss is about 10% to the wheels.

But this is all dependant on your build and tune.

So all in all not bad power for our low-mid power range motors.
Just keep in mind that you are pushing the service limits of the motor at this setup and I cannot say how long that kind of a build lasts.

It could last years or it could last months. I have seen on average people who build it this way last around a year or so of daily driving before something goes wrong and requires a rebuild or another motor.

And you are not going to want to use B16/18 rods because that would shorten the throw which will lose power and you will need to machine work to fit those properly on our cranks.

Now if you meant use B16/18 pistons that need the wrist pins modified to accept the pistons, then yes that can work.
^^ good stuff there.

Sounds like in essence if he does the basics he could have the pizazz of a nice, fresh JDM version of a B21 without the oil consumption and ring failure that plague that engine.
Then can add more zip later if his budget allows or he decides to.
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Old 03-09-2015, 11:31 AM
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Re: B20A5 Rebuild Plan - What are our thoughts?

That sounds like a nice solid build except for the rod-swap as Sean pointed out. Just make sure you port-match your intake and exhaust when they are polished to maximize the flow. Do you already have a header and/or free-flow exhaust? That will let your engine breathe and take max advantage of the modifications. You should do some research on finding some aftermarket adjustable timing wheels for both the intake and exhaust cams. This will let you fine-tune the valve timing (not to be confused with the spark timing) as the characteristics of your engine are going to change from what they were stock. Just some things to consider.

Not sure about price per horsepower in the Prelude (or even in the Import market) but with Chevy engines, $10 per horsepower is about the going rate, depending on what part you are swapping. That's just a general guideline and not a solid measurement. Maybe one of these guys know a little better.
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Old 03-09-2015, 04:23 PM
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Re: B20A5 Rebuild Plan - What are our thoughts?

Sorry, I missed the b16/18 rods part of your plan. As Sean pointed out, there will be problems using those in your engine. If you want stronger connecting rods then go with h23 rods. No modifications are necessary, as they use the same wrist pins, same crank bearings, and are the same length as b20/b21 rods.
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Last edited by luzer; 03-09-2015 at 04:25 PM.
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Old 03-10-2015, 08:44 PM
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Re: B20A5 Rebuild Plan - What are our thoughts?

Thanks for the info guys. Yes, the rod swap was probably a research mistake on my part. Thanks for catching that. No headers yet. That will have to wait for now. I had a full pacesetter exhaust Ok my last 3g and loved it. If I can put away a little money before I finish the build, I'll add that then.
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