2.0L a20a3 max overbore (.080)? rjudgey, anyone?

[bobafett]

hey guys, i have a situation here, and i need some feedback asap hopefully.

im getting custom pistons and rings, and i need to step up to .050 bore (84mm) in order to get the nice rings that will hold up to boost. at that point i have to get a cometic copper headgasket custom made for my motor.

my QUESTION, is would it be safe to bore the motor .080, that would bring me to bore size of 85mm...

my shop thinks it will work, and thinks there will be room, but we are unsure about the overheating factors. i will have forged pistons and rods and so it will be tough, but i dont want to deal with overheating issues constantly...

does anybody know if .080 is a death sentence? the highest i have heard of is .040, but the smallest amount i can do is .050, but since im into the realm of custom pistons, rings, and headgasket, i might as well go as big as possible to gain some displacement.

[bobafett]

well the motor is pretty wild in general.. i just want to make sure if 85mm bore is a totally lost cause. it "looks" like there is room.. but you never know...

i have heard of lude guys putting a a18 to .080 or even .130 i think... but that a18 can be bored out to 2.0 no sweat, then they are just looking at a a20 lol...

from what i read on 3geez, .030 or .040 is the MAX people are comfortable... even rjudgey said 1mm bore is the most he would go... which is just under 84mm.... i need at least 84mm to even be compatible with the rings that i need.

what would you consider, "not too wild"?

[bobafett]

ok, im sticking with .050, i dont want to be the first guy to go .080 and have my motor explode the first time those walls see boost. :)

hopefully .050 gives me a noticable gain in displacement though.

[bobafett]

i should. i know the intake side will flow nice. i am using stock sized valves, thats the only bad thing, but i do have valve grind, and port matched manifolds. :)

84mm bore should bring me to 2017cc

84x84x91x.0031416 = 2017

[bobafett]

2065 if i went with .080 (85mm) bore, which would effectively get to me 2.1L

[Oldblueaccord]

have to have the block sonic checked for cylinder wall thickness and start from there. Most engine places do it now days.

I m thinking the 84 mm is the popular piston size for hondas so that might help you with the cost of custom piston/rings and all.


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[bobafett]

oh yeah, i know, we got the block checked, and its fine, other than some scarring and pitting we need to get rid of :)

84mm bore = i can find the good rings = .050 over standard bore. i think thats what imma stick with. :)

[wprocomp]

you should only as much as you need to get rid of of old scarring and pitting,if it takes .030 or .040 thats fine unless you wanna go stroker motor mmmm stroker A20 lol,but i wouldnt worry that much about .050 boba that should plenty of strength in the cylinder walls np

[rjudgey]

The rings can be gapped to go down to 83.5mm it's only half a mm or even down to 83mm i use Peugot 205 GTI rings from GOETZE which are 83mm then i gap them down to 82.75 and that way i get the best possible gap end clearance to really get the best possible Compression

[bobafett]

yeah... i just finalized the order for everything

pistons 84mm bore = 3.305" = .050 over STD.
rings = 1.2 1.2 2.8 power adder compatible

pistons rings pins and locks are 524 + shipping

gaskets are gonna be 80 ish from cometic. :) but its all in motion now...

[bobafett]

i get 2017... but either way, it will be a slight boost in displacement, but more importantly, i have sweet rings and low compression, so its gonna boost hard! :)

bore (mm) X bore(mm) X stroke(mm) X (pi/1000) = cc displacement on 4 cyl motor

(84mm x 84mm x 91mm x .0031416) = 2017cc.... or thereabouts....

[rjudgey]

Are the pistons forged?
you know the bore spacing is only 90mm? If you have 84mm forged pistons you need more room to breathe the bore size may have to go upto 84.25 maybe even 84.5mm that will leave you 5.5mm inbetween the cylinders for the gasket to try and seal not too mention the bore walls will be super thin not sure how much boost you could run before you blow out the cylinder wall, if it's a race engine and your only going to be running for short periods should be fine but if this is going to be a road car i think your sacrificing to much mechanical reliability. The biggest weak point would be the head gasket to begin with make sure that Cometic make a few spares or maybe look at solid copper gasket.

[bobafett]

they are forged pistons.we are going for a final bore of 3.30500 inches = 83.94700 millimeters

so my pistons will be slightly smaller than 84... i guess i wasnt being clear... but yeah the pistons are being built to fit into a ALLLMOST 84mm final bore.

hopefully im not pushing my luck too far with this motor, it will be driven a lot... as for boost, im shooting for 8.5:1 compression, so i want to run AT LEAST 10 psi, probably more like 15... (not daily like that though) street driven maybe 6-9 psi...

[bobafett]

hahah i know i do too, but ill start breaking stuff i think after about 12psi tuned

[AccordEpicenter]

i personally wouldnt go over .020 overbore for a big boost setup. Cracks can develop between the cylinders...

[bobafett]

yeah... well im gonna try it out at .050

if it turns out you are all right, and that was wayyyy too much, i always have my 'old' block and i can just bore it less, and order another set of pistons and rings. i can transfer alll my other parts over, so it wont be the end of the world.

[Oldblueaccord]

What where your sonic numbers before?



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[bobafett]

honestly not sure... the shop tested the block, and other than the scarring in the cylinder walls, they told me it was fine... but im not positive on any specific numbers at this point...

[jigga89SEi]

I'm not sure of the safety... But I'm goin up to 85mm on one of my blocks in a couple weeks, to accomidate the 4th gen turbo pistons I have... I'm gonna finish my N/A build first...

I Don't know the physics of it... But I believe it will hold and so does my manager... And he's been doin this for a while... Plus u can get a block from pick n pull for $100...

[bobafett]

awesome jigga! .080 on an a20 block, please keep me posted how it goes...

as long as i dont explode my block at 20psi im ok! cause i know all of the rest of the parts are going to hold together. whats the specs on your builds man?

[jigga89SEi]

I don't have everthing set in stone right now... But this is what I'm doin for short term...

http://www.3geez.com/showthread.php?t=47582

[bobafett]

cool! its good to see more and more people working on these motors! :) keep me posted on the results as it gets further!

[Oldblueaccord]

honestly not sure... the shop tested the block, and other than the scarring in the cylinder walls, they told me it was fine... but im not positive on any specific numbers at this point...

im think you need about .200 cylinder walls. But thats a general number I couldnt find a hard fast number for Honda. that sound close?

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[88Accord-DX]

I'm not sure what the over-limit bore in on this engine, but I think you should be o.k. with .050 thousandths of an inch. It looks like you ordered everything, but wanted to mention something. If you could have ordered a milimeter size bigger rings, you can file the rings down to end gap specs.(like .010 or so) I noticed rings that come with aftermarket pistons don't have the closer end gap needed. I beleive they do that cause they don't want to be responsible for the rings binding up with excessive heat in the cylinders. As mentioned, closer end gap gives you higher compression ratio.

[bobafett]

yeah... the pistons i ordered are coming with the 'right' size rings, i assume they still need to be filed for perfect fitment though. ??? we will see... :D

[Oldblueaccord]

I'm not sure what the over-limit bore in on this engine, but I think you should be o.k. with .050 thousandths of an inch. It looks like you ordered everything, but wanted to mention something. If you could have ordered a milimeter size bigger rings, you can file the rings down to end gap specs.(like .010 or so) I noticed rings that come with aftermarket pistons don't have the closer end gap needed. I beleive they do that cause they don't want to be responsible for the rings binding up with excessive heat in the cylinders. As mentioned, closer end gap gives you higher compression ratio.

There forged pistons they 'll grow is why. Forged pistons can be a little noisy on start up. The skirt design also has something to do with it.

Follow the piston manufacture specs there a reason they got them set that way. A bunch of people wrecked motors when KB's hypertectics came out cuz they didnt want to follow there recommended piston gaps.

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[bobafett]

well the piston diameter is 3.3030" and the bore is intended to be 3.3070" which leaves .004" of clearance or 'gap' for the rings to make up.

thank god im having my shop do all this, cause it seriously makes me nervous... heheh

[Oldblueaccord]

well the piston diameter is 3.3030" and the bore is intended to be 3.3070" which leaves .004" of clearance or 'gap' for the rings to make up.

thank god im having my shop do all this, cause it seriously makes me nervous... heheh

yep

let them match the pistons to the bore exactly.


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