3rd Generation Honda Prelude Engine Stats

[synthoova]

B20A5:
Engine cc: 1958.14
Cylinder cc: 489.535
Deck cc: 13.885
Head cc: 47.3
Cylinder cc + Head Gasket cc + Head cc: 550.7200
Deck cc + Head cc: 61.185
Compression Ratio: 9.0:1

B21A1:
Engine cc: 2056.03
Cylinder cc: 514.0075
Deck cc: 10.191
Head cc: 51.0
Cylinder cc + Head Gasket cc + Head cc: 575.1985
Deck cc + Head cc: 61.191
Compression Ratio: 9.4:1

B20A5 block with B21A1 Head:
Engine cc: 1958.14
Cylinder cc: 489.535
Deck cc: 13.885
Head cc: 51.0
Cylinder cc + Head Gasket cc + Head cc: 554.4200
Deck cc + Head cc: 64.885
Compression Ratio: 8.545:1

B21A1 block with B20A5 Head:
Engine cc: 2056.03
Cylinder cc: 514.0075
Deck cc: 10.191
Head cc: 47.3
Cylinder cc + Head Gasket cc + Head cc: 571.4985
Deck cc + Head cc: 57.491
Compression Ratio: 9.941:1

[3livs]

This is great info, and would like to know if you have built a b21 with the b20 head, and if so can you give details.

Thanks, 3livs

[synthoova]

I've never personally put a B20A5 head on a B21, but many people have successfully done this.

The heads themselves are very similar, so you don't have to do any special modification to get everything to bolt up. If you have a B21 block and a B20A5 head, just get a head gasket (for a B21) and bolt the B20A5 head to the B21 block.

There are several advantages to doing this, the first of course being the increase in compression ratio. The final compression ratio will vary slightly depending on your head gasket thickness, but in the end you'll come out ahead of the stock B21 head.

This head swap also creates some nice little squish zones (a good thing) in your cylinder due to the slightly smaller bore the B20A5 head is machined for.

I don't have any official documentation, but many people also claim that the B20A5 head flows slightly better than the B21. If you're attempting to do a naturally aspirated build up, using the B20A5 head makes sense.

We'd love to help you more. If you're planning a particular project, feel free to ask some detailed questions so we can better assist you. Also, feel free to start a seperate thread with your questions so that we can deal with your topics individually.

Thanks for visiting; we're glad to have you here.

[spiffyguido]

More great info....

Engine tune up specs.

Year Engine Spark Plug Gap Ignition Timing (manual) Ignition Timing (auto) Fuel Pump (psi) Idle Speed
(manual) Idle Speed
(auto) Intake
Clearance (In.) Exhaust
Clearance (in.)
1988 A20A1 0.039- 0.043 24B 15B 3.0 800- 850 700- 800 0.005 - 0.007 0.010 - 0.012
A20A3 0.039- 0.043 15B 15B 35 750- 800 750- 800 0.005 - 0.007 0.010 - 0.012
B20A3 0.039- 0.043 20B 12B 2.5 800- 850 750- 800 0.005 - 0.007 0.010 - 0.012
B20A5 0.039- 0.043 15B 15B 35 750- 800 750- 800 0.003 - 0.005 0.006 - 0.008
1989 A20A1 0.039- 0.043 24B 15B 2.6 - 3.3 750- 850 680- 790 0.003- 0.005 0.010- 0.012
A20A3 0.039- 0.043 15B 15B 33 - 39 700- 800 700- 800 0.005- 0.007 0.010 0.012
B20A3 0.039- 0.043 20B 12B 2.5 800- 850 750- 800 0.005- 0.007 0.010- 0.012
B20A5 0.039- 0.043 20B 15B 1.3 - 2.1 750- 850 700- 800 0.003- 0.005 0.006- 0.008
1990 F22A1 0.039- 0.043 15B 15B 36 650- 750 650- 750 0.009- 0.011 0.011- 0.013
F22A4 0.039- 0.043 15B 15B 36 650- 750 650- 750 0.009- 0.011 0.011- 0.013
B20A3 0.039- 0.043 20B 15B 36 750- 850 700- 800 0.005- 0.007 0.010- 0.012
B20A5 0.039- 0.043 15B 15B 36 700- 800 700- 800 0.003- 0.005 0.006- 0.008
B21A1 0.039- 0.043 15B 15B 36 700- 800 700- 800 0.003- 0.005 0.006- 0.008
1991 F22A1 0.039- 0.043 15B 15B 36 700- 800 700- 800 0.009- 0.011 0.011- 0.013
F22A4 0.039- 0.043 15B 15B 36 700- 800 700- 800 0.009- 0.011 0.011- 0.013
F22A6 0.039- 0.043 15B 15B 36 700- 800 700- 800 0.009- 0.011 0.011- 0.013
B20A5 0.039- 0.043 15B 15B 36 700- 800 700- 800 0.003- 0.005 0.006- 0.008
B21A1 0.039- 0.043 15B 15B 36 700- 800 700- 800 0.003- 0.005 0.006- 0.008

Torque Specs.
All numbers are in ft. lbs.
See note below for * and ++
Year Engine Cylinder Head Main Bearing Rod Bearing Crankshaft Damper Flywheel Manual Intake Manifold Exhaust Manifold
1988 A20A1 49 48 23 83 76* 16 23
A20A3 49 48 23 83 76* 16 23
B20A3 49 48 23 83++ 76* 16 23
B20A5 49 48 23 83++ 76* 16 23
1989 A20A1 49 48 23 108 76 16 23
A20A3 49 48 23 108 76 16 23
B20A3 49 48 23 83++ 76 16 23
B20A5 49 48 23 83++ 76 16 23
1990 F22A1 78 52 34 166 76 16 23
F22A4 78 52 34 166 76 16 23
B20A3 49 48 23 83 76 16 23
B20A5 49 48 23 83 76 16 23
B21A1 49 48 23 108 76 16 23
1991 F22A1 78 52 34 159 76 16 23
F22A4 78 52 34 159 76 16 23
F22A6 78 52 34 159 76 16 23
B20A5 49 48 23 108 76 16 23
B21A1 49 48 23 108 76 16 23
*Flywheel for automatic transaxle is 54lbs.
++Fuel injection 108
Spark plugs are torqued to 13lbs. on all models.
Lug nuts are torqued to 80lbs (stock wheel) on all models

Engine Specs.

Engine Class Displacement
Liter (cc) Fuel System Net HP @ RPM Net Torque @ RPM Bore x Stroke Comp. Ratio
A20A1 2.0 (1955) 2 bbl 98@5500 109@3500 3.25 x 3.58 9.0:1
A20A3 2.0 (1955) EFI 110@4500 114@4500 3.25 x 3.59 9.3:1
B20A3 2.0 (1955) Dual Sidedraft 100@5500 107@4000 3.19 x 3.74 9.1:1
B20A5 2.0 (1955) MPFI 135@5500 127@4500 3.18 x 3.74 9.0:1
B21A1 2.1 (2056) MPFI 140@5800 135@5000 3.27 x 3.74 9.4:1
F22A1 2.2 (2156) MPFI 125@5200 137@4000 3.35 x 3.74 8.8:1
F22A4 2.2 (2156) MPFI 130@5200 142@4000 3.35 x 3.74 8.8:1
F22A6 2.2 (2156) MPFI 140@5600 142@4500 3.35 x 3.74 8.8:1