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F20B Pistons & Rods

Hi been searching on here and other sites for info about piston and rod combo's
I want a high revving 9000rpm motor and want to keep it as close to 2 litre as possible with an Evo 5 turbo
Don't want to sleeve the engine as it has iron sleeves stock

F20B
Bore x Stroke: 85 x 88mm
Compression Height: 31mm/1.221
Pin Diameter: 22mm/.866

The complete F20B rod specs are with common engine matches:
Length: 145mm (5.709") - no engines
BE Bore: 48mm (1.809") - D16, B16A, B17A, B18A, B18B, B18C, B20
BE width: 23.75mm (0.935") - B16A, B17A, B18A, B18B, B20, F22, H22, H23
Pin Bore: 22mm (0.866") - F22, H22A, H23A
Pin Width: 23.875mm (0.940") - F22, H22A, H23A

Considering 4G63/4G64 pistons 28.7mm comp height, K20 pistons 30mm comp height & custom made 31mm com height
Problems will be valve-relief piston pockets clearances and rotation of motor, will need to rotate them 180 degrees to align valves / (and k20 offset pin)

What is the boring limits of the stock iron sleeves ?

What pistons 9.0:1 will work ?

What H beam rods can I use ?

Thanks in advance

Re: F20B Pistons & Rods

1. Normally 1mm over

2. Use the h/f compression calculator and use the piston specs from different pistons with the same bore and wrist pin size.

3. Do this along with step 2. So you get the correct compression and all that fancy shit your looking for. Use this guide.

F/H series bore, crank, piston and so much more! [Archive] - Honda Prelude Forum : Honda Prelude Forums

Re: F20B Pistons & Rods

thanks h22god

So have decided on wiseco pistons K631M86 K20 86mm 9.55:1 30mm compression height, 50.5 cc head on k20 from amazon $419.72usd is that ok ?

Do I just deck the block 1mm to get them setting at the correct 0 deck height because stock pistons are 31mm compression height ?

Using the H/F compression calc decking block 0.026 (1mm) will it be ok/need to to shorten head bolts 1mm, also will it affect valve / ignition timing etc ?

k20 head has a 50.5cc head combustion volume vs f20b 53.8cc = lower cr I worked out 9.38:1 ?

Do the k20 pistons need the exhaust valve pockets machined bigger to match the h22a intake valves or work with no mods ?

What head/manifold is best for 86mm bore x 85 stroke h22a with bigger valves or f20b ? what head gasket works with 86mm bore ?

Interesting that the stock turbo civic 2015/16 K20C1 uses 9.8:1 CR, 86 bore x 85.9 stroke @306 hp

Cheers

Re: F20B Pistons & Rods

Quote:

Originally Posted by B20MTR (Post 50888607)

thanks h22god

So have decided on wiseco pistons K631M86 K20 86mm 9.55:1 30mm compression height, 50.5 cc head on k20 from amazon $419.72usd is that ok ?

Only way to know is to get them. This is what "customization" is all about. If it were that easy to answer, more people would have the F20B already, so don't sweat it. If you're installing it, it'll all be on you whether or not we agree with the choice :shrug:

Do I just deck the block 1mm to get them setting at the correct 0 deck height because stock pistons are 31mm compression height ?

No. I wouldn't. Just deck enough to make the block straight. Don't try to get specific number of millimeters.

Using the H/F compression calc decking block 0.026 (1mm) will it be ok/need to to shorten head bolts 1mm, also will it affect valve / ignition timing etc ?

k20 head has a 50.5cc head combustion volume vs f20b 53.8cc = lower cr I worked out 9.38:1 ?

Do the k20 pistons need the exhaust valve pockets machined bigger to match the h22a intake valves or work with no mods ?

This all is going to have to be determined when you get the pistons. I understand you're looking for guidance at this particular build, so that you can get every part right the 1st time, but be honest with yourself; no one is going to be an advocate for this build more than you. If that means that you have to clay the engine in order to answer these questions, (Which is exactly what will help answer them) then that's what you'll need to do, bottom line. These calculators online only give best guess. Don't be surprised, as a lot of what makes math and science what it is, is best guess

What head/manifold is best for 86mm bore x 85 stroke h22a with bigger valves or f20b ? what head gasket works with 86mm bore ?

No one can answer that really, but I'm sure it's narrowed down to the K20 /H22 family. There's probably no best manifoldeither. There's what exists in the market, and what you're willing to fabricate or alter.

As for the Gasket, I'd see about using an OEM one first. Take your original head gasket and try to compare it with the H and F series to see about commonalities in the OEM world for a match, or find another original one via the part number (if possible), and perhaps Golden Eagle has something similar that they can modify in the OEM world to fit that bore. If you did find another OEM one, you can send it to them and see if they can bore it to what you need.

Worst case scenario is that you can make a template of the original gasket out of cardboard or construction paper and mail it to Cometic for analysis and creation.(I did this with an Escort Cosworth engine a couple of years ago. It took about 2 weeks, but it was worth the wait. I ordered 2 just to be safe once they confirmed the matchup.) It may cost a bit more than you wanted, but this isn't a cookie cutter build anyway.

Interesting that the stock turbo civic 2015/16 K20C1 uses 9.8:1 CR, 86 bore x 85.9 stroke @306 hp

What makes that particular fact interesting?

Cheers

Re: F20B Pistons & Rods

Quote:

Originally Posted by B20MTR (Post 50887202)

I'm planning on using an f20b as well. You can get forged f20b piston 86mm from bisimoto for 500 a set. As far as rods, f20b specific rods are expensive, I was contemplating using an h22 crank, and h22 eagle h-beams which together are cheaper and easier to find, the larger stroke crank only bumps the displacement up to less than 2.1liters. The bisi slugs at 11:1 on h22 crank and rods drops the comp ratio down into the 10's. Should be ok, on lowish boost and a good tune for fast spool and good power.