project:b20a7 pistons

[davke]

hi guys! i am planing to get b20a7 pistons from hp3 engine. the reason is the compression ratio: 10.1. my engine b20a1 has 9.5. so i guess these pistons will ad me some hp, etc? what do you think? what parts i need to complete this project? is it worth?

[MessyHonda]

everytime you raise the compression you make more hp....are you rebuilding the whole engine or just swaping the pistons?

ps....the compression is 10.5 on the b20a7

[davke]

im thinking about swaping pistons, but do i need rods and/or pins?

[thegreatdane]

Get the rods too. As far as I remember the piston pins are different sizes, plus it is much easier to install them with the pistons still mounted on the rods.
And yes, B20A7 is 10.5:1 compression ratio.
Have thought about doing it myself too.

[davke]

will the rods with the pins fit from b20a5? is there 22mm width too?

[thegreatdane]

b20a1 piston pins are 20mm, i dont remember if b20a5/7 is 21 or 22mm. But the crankshaft ends of the rods are the same as B20a1, and so is the lenght of the rod.

[davke]

today i checked, b20a5 rods have 22 mm pins too. what about fuel injection system? and why people aren't doing this swap? it looks quite easy and not expensive

[thegreatdane]

Yes it is quite simple. If more people on here had B20 engines I guess there would be more who would do this swap.
Be sure to get the B20A7 pistons and not the B20A5 though.
You can also take the distributor, exhaust cam sensor and the igniter from the B20A7, that way you can use the ecu from the B20A7 too.
To be able to use the correct EACV (electronic air control valve (electronic idle)) you will have to swap on a B16A intake manifold though.

[davke]

but b20a7/b20a5 has obd1?! then i need 02 sensor, egr, etc. at this moment there are no 02 sensor, egr... i have distributor, ex cam sensor from b20a5 and they fit mechanically but wiring is different

[carotman]

B20A7 pistons should be a nice upgrade!

[thegreatdane]

but b20a7/b20a5 has obd1?! then i need 02 sensor, egr, etc. at this moment there are no 02 sensor, egr... i have distributor, ex cam sensor from b20a5 and they fit mechanically but wiring is different

B20A7 engines shouldnt have either egr or O2 sensor. And yes you will have to do some wiring to swap it in. It's more of an OBD-0.5 engine really

[davke]

today one guy explained me that too:no egr and o2 sensors at all !! thats cool, so i need b20a7 ecu and ... the main wiring? or i can just upgrade my wiring?

BUT: will the b20a7 ecu and others electrical components give to my car performance?

[thegreatdane]

Who knows no one has used a B20A7 ecu yet. Maybe the pistons alone will do the difference.

[Honda_Quaalude86]

why dont you guys skim the head a bit to bump compression?

[snoopyloopy]

so wait, b20a7 ecu is an upgrade from the ph3 ecu?

[thegreatdane]

so wait, b20a7 ecu is an upgrade from the ph3 ecu?

dont know, as I said no ones tried it yet afaik. but you'll get rid of the egr and oxygen sensor if that's a route you'd like to go.

[Nafs Asdf]

Would b20a7 pistons fit directly in a b20a8? And how hard would his be to do, and is there any other work that would be required for it to be worth it?

[thegreatdane]

Yes they fit directly in a B20A8 engine. The hardest thing will be pressing the piston pins out and in. Or you can just let the B20A7 pistons stay on their rods and swap both.
Of course you have to be aware of rod bearing clearances if you swap rods. If the new rods have the same number as the old ones stamped on the big ends of the rods you can reuse your old bearings (assuming the old bearings arent worn out). If the rod's dont have the same numbers (the numbers represent the big end bore size of the rod) then refer to the bearing selection chart in the shopmanual.
Another thing you have to watch out for is the piston to cylinderwall clearances, since there are two different sizes of standard pistons. An A and a B size. The size is stamped on top of the piston. The new pistons should have the same letters as the old ones to maintain proper clearances.
And then there's the rings. You can do it the cheap way and use the used rings from either of the pistons or you can do it the more expencive and proper way and buy new rings and get the cylinder walls honed at the same time.

I would probably do it the cheapest way otherwise it wouldnt justify not to just buy new pistons with slightly higher compression ratio than the B20A7's since 10.5:1 isnt all that much anyway if you want to make some good power.

Oh yea you will need a new headgasket and a new oilpan gasket as a minimum for this operation. Perhaps you might also decide to check on your main crank bearings, and possibly find out that those might need replacing as well.
But as always there's the proper, thourogh and often expencive way of doing things and then there's the faster and cheaper ghetto way of doing things.
Which way you choose depends on your budget and expectations from the final result.

Welcome to 3geez! 2.0i-16's are a rare find!

[Nafs Asdf]

Thanks for the welcome! =)
And yeah, everyone on here keeps telling me how rare this thing is...
I think mine's extra rare tho As far as I know all the finnish models have the b20a2.

Thanks for the info on the pistons, sounds like it might be a fairly cheap upgrade. Am I right assuming the a9's are the same?

Don't know if I'll try doing it, but I was curious if it'd work... And maybe if I learn enough to feel confident about taking an engine apart I'll try it.

First on my list is just getting it through inspection, then CAI and a new exhaust system if I can afford it.