6/26/22 9:00 p.m.

hello everyone.. super newbie here..

we are building a track car that will hold for sprint and endurance races with a regulated target of no more than 150hp.. we have a 1995 miata 1.8 and tuned it with haltech 550.. it made 109whp.. but we need to reach close to 150hp.. i think it was in this forum that suggested to put in a vvt head and that would solve the 150whp target.. and we obliged.. 


after a vvt head, exhaust headers, adjustable exhaust cam gear and an itb from a toyota silvertop.. new dyno is at 120whp.. we did a compression test and its 160psi.. everything looks good.. something must be wrong.. an 11whp gain doesnt add up.. 2 knowledgeable tuners has tried.. but no one seems to be able to figure it out.. philippines is honda country.. hahahahahahahahaah


we are definitely doing something wrong.. is there a miata guru who we can hire (video call or something) to sort this problem out?  or can this forum at least help me out please.. 


tell me if you need more information.. 


thank you everyone and be safe

Rodan SuperDork
6/27/22 10:04 a.m.

150hp is on the high end for a fresh BP6D (NB2 VVT) engine with bolt ons and a good tune (and probably E85).  I would not expect to see that with a VVT head on a BP05 short block.  I'm getting 135hp from a BP6D with no internal work, flat top manifold, header and tuned on MS3.  The type of dyno and dyno settings are also a factor.  IMHO you're in the ballpark for what you've got.

Here's some info you'll want to read, lots of other good tech info there as well.

BP power levels

BP power recipies



mdshaw GRM+ Memberand HalfDork
6/27/22 11:23 a.m.

I'm not a Miata motor expert but isn't 160psi low? The easy fix would be more compression. My D16Z6 is 230psi. Needed re-tuned but runs great on 93 octane. 

don1207 New Reader
6/27/22 12:39 p.m.

In reply to Rodan :

thank you for the reply sir and info.. really appreciate it..

i use 97ron (100 octane) gasoline.. 

calteg SuperDork
6/27/22 12:40 p.m.

150whp on a VVT engine is definitely doable with mods, mostly due to the higher factory CR.  Slapping a VVT head on a lower CR bottom end will net you approximately the gains you already have. Don't forget you'll need a way to control the VVT solenoid (either a standalone  VVTuner, or MS3 natively supports this function).

don1207 New Reader
6/27/22 12:44 p.m.

In reply to mdshaw :

sir.. thank you as well..

my mechanic said its alright.. not the best.. but its alright.. i am getting a second opinion though and let you know..

be safe

mdshaw GRM+ Memberand HalfDork
6/27/22 2:46 p.m.

In reply to don1207 :

Why would it need 100 octane with only 160psi? 87 would be fine at that wouldn't it?


jwagner (Forum Supporter)
jwagner (Forum Supporter) GRM+ Memberand Reader
6/30/22 1:52 a.m.
mdshaw said:

In reply to don1207 :

Why would it need 100 octane with only 160psi? 87 would be fine at that wouldn't it?


I think octane requirements depend on how aggressive the timing tuning is.  100 octane does seem like overkill for a stock compression Miata 1.8 though.  You might consider using 93 octane premium and watching for pinging.  I assume the Haltech ECU would do this.  I don't think E85 is much help on this engine with a 9:1 (IIRC) compression ration.  Compression of 160lbs seems OK for this motor, I think a fresh one would be at about 180psi, so that's probably some of the HP loss.

The supermiata page that rodan links corresponds to my experience.  A fairly fresh '96 1.8 with a '99 head and mazdaspeed cams, intake, header + exhaust, megasquirt and dyno tune ended up at 141hp, and the tuner was surprised it was that high.  The OP's setup sounds pretty similar, I would expect similar output HP if everything is in good shape.


Schmidlap Dork
6/30/22 10:33 a.m.

The OP is in the Philippines so their 97 RON octane is similar to 93 octane in the US, I think.

Paul_VR6 (Forum Supporter)
Paul_VR6 (Forum Supporter) SuperDork
6/30/22 10:46 a.m.

I would be less worried about the absolute hp but the gains vs what you did. If it's all on the same dyno with no other drivetrain changes (like wheel dia/tire weight). 

Check to see what other vvt engines compression test at, if vvt is retarded at idle it would be lower than you may expect. What size ITB and header? You can go a few wrong directions there by over/under sizing. Same thing with the cam gear, make sure you start at stock position. Generally I only fool with this for clearance with big cams as it's a smaller knob for power.

oldeskewltoy UberDork
6/30/22 12:41 p.m.

having now built two 160+whp Miata engines.... 150whp would be maxed out on stock parts.

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