The H23A Vtec Blue Top "The Mystery Motor"















I started this due to the amount of Questions I get daily about this motor so thought I would but all the information here.  I started a thread about this motor back in 08 ish.  Above the picture is the link to a thread on Honda-Tech in the Prelude Section.  WIth over 400K views it was easy to say a lot of people were interested in this topic.  I first started toying with the H22 motor back in like 03ish or so.  Was going to do H2B way before the craze.  Ended up doing a Full H swap in the Crx and that is when things took off for ESP.  I love the peppiness of the motor and the torque compared to the B series.  Some semi built B series will never reach the torque out of the box of an H swap.  I drove it for a couple years stock made 185 whp and 155 trq.  With a spoon chipped p13 and a couple bolt ons and stock header.  I then did bolt ons with it Header etc and got it up to 200 whp and 158 trq.  Then I came across the H23AVtec Blue Top motor.  No one really knew much about this motor.  This was back in like 05ish.  I purchased one happen to be a 2000 PDE version.  They came out of the SIRT wagons from 98-02.  All were Automatics and few were actually AWD.  What caught my eye was at first glance the Horsepower claims from Honda was around 197 hp to the FLYWHEEL and 163 ft lbs of torque.  Now the Type S/Euro R was around 217 hp to the FLYWHEEL and 163 ft lbs of torque.  What caught my eye at the time was the H23AV Blue Top was Auto... there for RPM was much lower around 6200 peak with Auto ECU and Auto low RPM shift points etc.  So in theory I new the motor being a 95mm stroke versus H22 90.7mm there might be more power in this puppy and being severly UNDERATED.  Sure enough mated to a manual transmission and a tunable ECU with a higher than Auto redline and fuel maps.  The thing came alive.  When I did the swap into the Crx same bolt ons I had on the JDM H22 but with Euro R intake manifold (Rosko) and 68mm throttle body (PP) the thing made power.  Believe was 218 whp and 178 ft lbs of torque with same M2B4 jdm lsd transmission.  The torque was impressive.  From then on did some research on the Motor.  Then soon after took the Motor out of the Crx and Fully Built it and Turbo Charged it.  It made some impressive torque with the 95mm storke.  From then on really never went back to a normal H22.  H23AVBT from then on.  That is when I gathered the knowledge of below.  Below are some specs and information on the motor.

H23AVtec Blue Top 98-02 Motor:

2 Versions PDE and P13 heads.  PDE is known to be associated with the Euro R and Type S H22.  They have slightly smoother Intake casting runners.  The Intake Manifold is also altered on the PDE like a Euro R/Type S is far as injector nose area etc.  The valve seat was re-adjusted from 60 to 45 degrees.  The P13 version came with a PGMFI logo on the intake manifold plenum.  The PDE did not was smooth.  The PDE had the IACV in the back like a EuroR manifold.  The P13 version had in the front.  It seems all the PDE versions were only from 00-01. 98 and 99 were P13.  The injectors on the PDE were slightly different angle like the EuroR and small diameter.  Similar to s2000 injector size.  The next myth was the Blue Tint on the cams.  At the time it was only thought to be the EuroR/TypeS cams.  Turns out the Blue Tint was a magnesium coating put on for wear purposes.  This was common in all 98-02 P13 and PDE versions as well as all F20B Auto and F20B Manual and Euro R and Type S.  It also trickeled down to some of the JDM OBD2 H22 Black Tops in those year ranges.  Turns out the cams Part numbers were same as JDM H22.  The valve springs/retainers in both P13 and PDE were also cross referenced to JDM H22 OBD2 as well as the valves.  The only way to 100% identify EuroR/TypeS cams is to Mic the vtec lobe to measure it.  I later went to swap F20B Manual Cams which are same as EuroR/TypeS same with the matching Valve Springs into another H23V Blue Top it made 210 whp and 174 trq with Power Steering.  So the investment in time may not of been the best.  However I believe it will see its gains with boost.

The Bottom End Story:

The Bottom End is same on both versions 98-02. Feature same old FRM cylinders and is OPEN DECK.  It does not have Oil Squirters in it like an H22.  Mainly because like most back in the Day when doing Frankenstein H23A1 internals into H22 you had to slightly massage the oil squirters in the way.  So obviously Honda new when Blue Top cam around this would only create a Hassel.  The Oil Squirters were designed to lubricate the cast pistons more at higher RPMs.  Then again the Auto H23AV Blue Top was going to be spinning much RPMs at 6200 rpm peak on Auto ha.  Either way it is still not worth the effort to install them for higher rpm securities. 

  It features a stouter big brother H23A 95mm stroke 55 mm mains crank.  I feel it is a lot stouter piece than the smog motor H23A1 in the OBD1 years.  The Crankshaft is also the lightest out of all F/H crankshafts.  It weighs in at 34 lbs.  The next up is the F20B at 36 lbs, then the H23A1 at 38-39 lbs, then H22 at 44 and 46 lbs.  This is kind of neat.  So lighter in theory little more REV happy. The Crank pulley is a Alternator ONLY Crank pulley same as what you see on the Euro R and F20B since they are all Accord Motors and 98-02 Accords used Electronic Power Steering not Belt driven. The Rods are interesting as well. They use a decent rod bolt not a press in.  Similar to s2000 style. Which seems to be stouter.  The Rods are roughly 20k shorter in height than a H23A1 rod.  It is all by its self in height.  This was done to be able to use a H22 type comrpession height piston.  So swapping the pistons for tiny bump in compression with Euro R/Type S pistons is possible.  The H23AVBT pistons may not have the deepest valve reliefs as the H22 and may be more similar to H23A1 piston.  It seems the piston is more deck level 0 than like a normal H22 motor which is roughly 6k in the hole.  Some have issues with big lift cams and hitting the valve reliefs.  To fix that I think simple thing is either 35k or 40k thick cometic head gasket to give a little more Valve to Piston room.  Yes this will slightly bring down compression ratio tiny bit.  

On the Average Setup H23V Blue Top produces 8-15 more whp and 12-20 more ft lbs of torque over a H22.  It wil outperform out of the box a EuroR and TypeS motor.  Just a given :)


I have built a few of these motors for Boost.  Darton MID sleeves, forged pistons and rods.  What has worked is I use a forged H23A1 rod yes it is longer than the H23VBT by 20k roughly.  I then use H22 forged piston.  I then compensate with the piston sticking out of the hole by getting a thicker Cometic MLS headgasket.  60k thick.  My compression of a 9-1 piston now becomes closer to 9.6-1.  So roughly 1/2 point compression ratio increase.  I did this route before when custom forged piston options on different compression heights were spendy.  Now you can use the H23A1 rod and just alter the compression height (have the wrist pin up 20-22k) to have the piston sticking in the hole or deck height.  This option does create a wait time of atleast a month and is only about $100 over a shelf piston cost with some of the manufactures.  Then can use a stock headgasket thickness with this option.

H23AV Blue Top Head and Bottom uses all replacement parts of 98-01 H22A4  Water Pump, Oil Pump, Headgasket, Timing Belt, Balance shaft belt, Auto tensioner, Rod and Main bearings and thrust washer, Rings, Complete Gasket Set Head and Bottom.

Oil Pan and Oil Pickup/Strainer is a F23A1 same part numbers.  Which is interestng because the Pan is metal like OBD1 and is roughly 3/8 of an inch longer in heigh only in the pickup area not header area.  The pickup is also longer.  You can also use the H22 OBD1 metal pan and H22 pickup.  You HAVE TO MATCH PICKUP TO PAN using.

I get this a lot too on which Cams are the best for my stock H23A Vtec bottom end.  My answer is kind of long. To start it is believe that the pistons sit almost deck height 0 which most H22s are 6k in the hole.  Which may equate to why some kiss the valves to the piston on larger lift cams.  Easiest solution as stated above would be to go to a thicker head gasket 35k-40k thick.   For a street/strip setup most Cams out there S2 Tuner Series 1 and 2 or Crower Stage 1 cams are not ideal for the amount of power versus dollar your putting in.  EuroR/TypeS cams spec wise are almost similar to S2 tuner 2s so why spend double?  Most cases a stock bottom end you will loose mid range power and torque.  Even in some cases Pro1s etc. have lost torque.  Google DDtech cams he seems to have a good solution for the power and keeping the torque up.  In most cases will need his matching valve springs and retainers.  For the average person daily car the peppyness of the factory internals is all you need.  Another question get a lot of is what is a decent header on the market far as power?  Highend or H22 Tri Y Headers flow great they are cheap as well.  They make power even up to 240+ whp builds.