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Thread: A20 details and B20 rods/pistons thread

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    A20 details and B20 rods/pistons thread

    I would like to lay all the A20 specs out because they are a little hard to find. Some of these measurements may not be 100% accurate, I will mark those, but as far as I can tell it is good enough for a compression calculator program. Input is very welcome. The purpose of this thread is largely due to the fact that B20 pistons fit in the A20 with an overbore. B20 pistons are 84mm, but B18 pistons can come in 83mm sizes, but options are limited. This thread also assists in blueprinting the engine I am building soon and I will post progress here.

    Service manual:Section 6-3 to 6-21 (pg 49-68) Section 7-3 to 7-18 (pg 72-85) Dropbox - 1989 Accord Service Manual.pdf - Simplify your life

    Useful threads: https://www.3geez.com/forum/performa...hlight=pistons
    Is high compression on the cheap possible on an A20? (pump gas)
    A20 Head Build Thread | Honda Prelude Forum

    Useful apps: CR Calculator - Apps on Google Play
    Punch in A20 custom specs as if it were a B series.

    Head
    Cams
    Stock:
    Delta 272: .415" lift, 220 duration @.050" lift

    Intake valve dia: 30mm

    Exhaust valve dia: 35mm

    Valve stem dia: 6.6-7mm ??

    Valve OAL: 120.4mm

    Valve guide OD: 12mm

    Combustion chamber volume: 47cc ??

    Block
    Deck height: 213.25mm ??

    Bore size: 82.7mm
    Max recommended bore: 83-84mm. Most pistons come in 84mm.

    Piston to cylinder clearance: .02-04mm
    Piston to cylinder service limit: .08mm

    Service manual does not specify a maximum overbore or service limit. The cylinder walls should be strong. Bore at your own discretion, pistons can come as large as 85.5mm

    Crankshaft
    Stroke: 91mm

    Main journal min std size: 49.985mm
    Main journal max std size: 50mm

    Main bearing clearance 1, 2, 4, 5: .026-.55mm
    Main bearing clearance 3: .032-.061
    Main bearing service limit: .07mm (the only time this matter is with a min size bearing and your crank is FUBAR)

    Main bearing width: 20mm

    Main journal width:

    Rod journal min std size: 44.981mm
    Rod journal max std size: 45mm

    Rod bearing std clearance: .026-.038mm
    Rod bearing service limit: .07mm (the only time this matter is with a min size bearing and your crank is FUBAR)

    Rod bearing width (A20): 19.5mm*
    Rod bearing width (B18/B20): 18.5mm*
    Rod bearing width (B18B): 19.5mm*

    Rod journal width:

    *Not to make this confusing, but I have varying bearing widths, yet I've seen B series rods fit snugly on an A20 crank. First measurement is More Information for ENGINETECH BB2200, 2nd is More Information for ENGINETECH BB2208, 3rd is https://www.rockauto.com/en/moreinfo.php?pk=2989791. GET THE RIGHT BEARINGS!

    Piston assy.

    Rod length: 137mm

    Wrist pin size A20: 20mm
    Wrist pin size B20: 21mm ??

    Piston comp. height: 30mm ??

    Stock piston flycut depth:

    Stock ringland height:

    Rod big end width (B20): 23.7mm*
    Rod big end width (A20):

    Stock piston dish (A20A1):
    Max piston dome/height:

    *https://jhpusa.com/collections/rods/...=1655850106900

    Other

    Stock head gasket manufactured height: .0470" - .0530"
    Compressed height: ~.030" (.762mm) ??

    Stock head gasket bore size: 83.82mm (3.3")
    Careful with an 84mm bore, Cometic suggests .01" larger than your bore. 83mm bore works with stock head gasket, any larger and you will require a custom gasket or carefully scribe and cut the stock one.

    Rod/stroke ratio: 1.51:1

    B series piston list

    83mm
    CP-Carrillo SC7112 +.1cc / 10:1
    CP-Carrillo SC7013 +4.9cc / 10.87:1
    Supertech P4-H83-P6 +5.9cc / 11.07:1
    JE 338090 +3.5cc / 10.6:1
    JE 338092 +8.2cc / 11.57:1

    84mm
    Wiseco K623M84 0cc / 10.17:1
    Wiseco K594M84AP/Skunk2 316-05-0017 +8.25/8.26cc / 11.8:1
    Wiesco K567M84AP/Skunk2 316-05-0013 +2cc / 10.52:1
    CP-Carrillo SC7120 +5.8cc / 11.26:1
    CP-Carrillo SC7117 +1.6cc / 10.45:1
    Supertech P4-H84-P1R +1.4cc / 10.41:1
    Supertech P4-H84-P5 +5.5cc / 11.19:1
    JE 302413 +7.4cc / 11.6:1
    JE 302412 +3.2cc / 10.74:1
    Arias A3330521 +7.3cc / 11.58:1
    Arias A3330511 +5.29 / 11.15:1
    Arias A3330490 +.5cc / 10.26:1

    If you would like dished pistons see SpeedFactory's site
    Or RealStreet

    Compression ratios based on 47cc combustion chamber and 213.25mm deck height

    Rods
    Skunk2 306-05-1130
    Speedfactory SF-02-104
    Manley 14025-4
    Manley 14412-4 I beam
    Supertech CR-HB20B-H137
    Eagle CRS5394A3D
    CP-Carrillo HN-B18>-65394H-4
    CP-Carrillo HN-B18>-65394S-4
    Speedmaster PCE274-1108 I beam... but cheap?
    Crower B93728B-4 I beam
    Callies C22103
    Saenz SS-HB18B-A00-T
    Saenz PS-HB18B-A00-T I beam
    K1 015BR16137
    Brian Crower BC6019
    Brian Crower BC6029
    Scat 2-5394-1771-935-827

    My Parts
    Intake valves: Supertech HIVN-1102
    Head Diam: 31.00mm (+1)
    Stem Diam: 5.48mm
    Length: 118.50mm

    Intake valve springs: Stock exhaust valve springs

    Intake valve retainers: Manley 23100

    Intake valve lash cap: Supertech LC-55 Required due to shorter valve than stock

    Intake valve guides: B18C

    Intake valve seals:

    Exhaust valves: Stock

    Exhaust valve retainers: Stock

    Exhaust valve guides: Stock

    Exhaust valve seals: Stock

    Cam: Delta 272

    Pistons: Arias A3330511

    Rods: Skunk2 306-05-1130

    Rod bearings: King CR439AM

    Main bearings: King MB5168AM
    Last edited by ShiRen; 04-27-2021 at 11:24 AM.



  2. #2


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    Re: A20 details and B20 rods/pistons thread

    Honda A engine - Wikipedia

    some of the specs are here and there is a "3geez' wiki also floating around someplace in internet space.
    1988 Lxi owner since August 1995
    336k miles running strong!
    Now running E85.

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    Re: A20 details and B20 rods/pistons thread

    Quote Originally Posted by Oldblueaccord View Post
    Honda A engine - Wikipedia

    some of the specs are here and there is a "3geez' wiki also floating around someplace in internet space.
    3geez wiki

    Neither of those really have much to offer... I'd love to get a good measurement of the combustion chamber size, mine won't be perfect
    Last edited by ShiRen; 04-22-2021 at 06:42 AM.

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    Re: A20 details and B20 rods/pistons thread

    Is high compression on the cheap possible on an A20? (pump gas)

    you can paw thru the numbers on this one.
    1988 Lxi owner since August 1995
    336k miles running strong!
    Now running E85.

    Oldblueaccord

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    Re: A20 details and B20 rods/pistons thread

    I had low expectations for that thread until page 2 lol. Cygnus said he measured his stock head at 47cc, I'll take that with a grain of salt if a welded head is 44cc though. Its a start though, gets me a decently accurate compression ratio. I am going to be careful of milling the head or block, but I will do what I have to, I'm just wary about flycutting a new set of pistons. I am going to make a list of 83 and 84mm pistons that are in the reasonable compression range. I am not chasing any number, not welding the head, just probably somewhere around 11:1, a 10cc dome is asking for trouble.

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    Re: A20 details and B20 rods/pistons thread

    Hes a reliable source for whats its worth...and I think the 44cc Open loop number is also creditable.

    Doubling checking everything is important.

    For pistons I would just have them made to what you want from one of the big piston makers.
    1988 Lxi owner since August 1995
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    Now running E85.

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    Re: A20 details and B20 rods/pistons thread

    I'm just saying its old info and it seemed like an off the top of the head answer. I assume the head was roughly 45-50cc. I can't visualize how big a cc is, I just figure that huge quench zone would be more than 3cc. A b16a head is 2.3cc smaller than a b18b head and I doubt there is a ton of difference in there and I can't visualize a cc with my brain.

    I updated the post with a list of pistons and rods. I should be pretty good unless I need an 83mm with a really small dome. I think I can find some dished pistons though. There are several Arias part numbers I was unable to list because I can not find anything on them... I hate that everyone advertises pistons with a compression ratio instead of piston cc. Its really confusing because they list the same things under B18 LS non-vtec and B18 LS vtec but just change the compression. I shouldn't have to do math to guess the cc. Only Speedfactory lists Arias though and they lean heavily towards boosted applications, so I assume they are dish, one might be really close to flat.

    Doesn't really matter what dome you go, 84mm bore will boost compression and increase displacement to 2011cc, very likely it will be considerably more spicy than an 83mm bore.
    Last edited by ShiRen; 04-23-2021 at 12:23 PM.

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    Re: A20 details and B20 rods/pistons thread

    The Open loop head and motor was at the time the most horsepower made NA. Old 3gee lore.

    The chamber was welded to reduce the CC and increase the compression.
    1988 Lxi owner since August 1995
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    Now running E85.

    Oldblueaccord

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    Re: A20 details and B20 rods/pistons thread

    A20 motor build threads.

    I been trying to put motor builds up on the sticky if you find any others floating out there. I think I added the Open loop build to it what little is left on the internet.
    1988 Lxi owner since August 1995
    336k miles running strong!
    Now running E85.

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    Re: A20 details and B20 rods/pistons thread

    Man I should have paid more attention to the threads you linked there, makes me want to do more to the head. I'm going to link a few in my post once I get a chance.

    A20 Head Build Thread | Honda Prelude Forum In this one though he has an a18 bottom end. He listed the deck height in there and it was about a mm shorter than my estimation, but same length crank, pistons and rods as our a20s, is that right? I was kind of skimming because I'm on my phone and I didn't see if he shaved the block.

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    Re: A20 details and B20 rods/pistons thread

    yeah thats a great thread and looks like some missing pictures are back up. The head cut aways are really cool.

    I have and xtra head I just never found any body local worth a shit on Honda heads that would run it on a flow bench for me and rework the valves.
    1988 Lxi owner since August 1995
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    Now running E85.

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    Re: A20 details and B20 rods/pistons thread

    I've ordered about everything for my head except intake valve guides, I think, no big deal I need another set of exhaust valve springs. I think I picked out my pistons and rods, everything is in the top post. So depending on how much the head and block needs skimmed, I am looking at a 11.19:1 cr, I'll check valve and piston dome clearance, but if its skimmed a mm it'll bump the compression into the 12s, I don't want to go more than 12.5:1, so combustion chamber cc needs to be around 41.5cc minimum with a stock height block and 44.5 with half a mm off the block (212.75mm)

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    Re: A20 details and B20 rods/pistons thread

    The two big unanswered questions for me are:

    1. how far can you safely bore out an A20 block....and that means sonic checking the cylinder walls.... not checking FB 27 times in an hour.

    2. How much does our head flow...never hear a word on this even on the facebbook pages. Thats the answer on how much power we can make. The answer always come back to the head flow.

    Those two questions cant be answered unless you have a good engine machine shop and so far I have not found one close enough for me to really fool with it.

    I dont think any one ever settled in on the deck height either...and thats not the piston height.

    One thing with your pistons is the compression height and ring pack. With our rod ratio the numbers I did for the piston speeds at RPM over 8000? were higher than any engine produced at the time,Type R Ferrari etc. Ring position and ring pack would be critical to keep the motor from jamming a piston ring which is what I see on Rjudeguys engine pictures.
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    Re: A20 details and B20 rods/pistons thread

    I will probably bore the block first thing once its pulled and if the shop has any concerns I will have them call me. As far as sonic checking it, I don't think I will go that deep, but I'm not adding boost. I might be able to get the head on a flow bench... might...

    What happened to Rjudeguy? I don't think I've heard of him. I can't do much about the pistons unless some of the ones that cost twice as much do a little tweaking... I will probably not spin it over 7750. I mean he made 180hp at 7250.
    Last edited by ShiRen; 04-26-2021 at 11:23 AM.

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    Re: A20 details and B20 rods/pistons thread

    The quarter mile time mph and the power don't add up. Not sure if a dyno in Mexico is considered a gold standard.

    You want the block final hone to match the Pistons size so make sure that your machinist has them.

    Sonic check is to make sure the thickness supports the bore. It's more important to have a strong cylinder wall then max bore.
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    Re: A20 details and B20 rods/pistons thread

    I just looked at his dyno to see where it made peak power, it carries on good a little passed 7500, but even he stopped before 8k.

    84mm should be about the limit, I've at least got another block if I "learn anything" after some track time. If anybody can do a sonic test I will have them do it.

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    Re: A20 details and B20 rods/pistons thread

    I should add his 13.2 at 106 mph is over 200 wheel hp especially on a front drive car.
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    Re: A20 details and B20 rods/pistons thread

    Nothing says the dyno numbers aren't low lol

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    Re: A20 details and B20 rods/pistons thread

    Whats that song we learned as a kid "one thing doesnt look like another"

    Not trying to spend your money but those Supertech pistons are made in Argentina im pretty sure and the company is in Cali. thats two strikes in my book.
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    Re: A20 details and B20 rods/pistons thread

    My second choice would be the CP-Carrillo +5.8cc pistons, but my wallet would probably force me to buy the Skunk2s, which are Wiesco, so that's nice, but only +2cc. Supertech is a fairly reputable brand, they aren't the nicest pistons, but I don't have much of an issue buying them.

    Edit: Found some more pistons. The JE 3.2cc and the Arias 5.29cc would also be a good choice, but they're in a higher price bracket. Found some more for 83mm but nothing spectacular, to compete with 84mm they'd need to be in the ballpark of 6.5cc
    Last edited by ShiRen; 04-27-2021 at 07:12 AM.

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    Re: A20 details and B20 rods/pistons thread

    I think I am actually going to go with the Arias 5.29cc

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