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hi all, soon i will attempt to build a 6a13 mivec na. at the minute i have a 6a12 mivec in a mirage hatch chassis but picked up a 6a13 2.5L engine. I've read a little about this hybrid build but couldn't find much info.

i know the compression ratio will be low but does anyone know if the 4G92 (1.6L mivec) pistons will fit my rods? both are 81mm bore, a cheap way to raise the compression if it works. also I'm sure the 6a13 block is a little taller too or the mivec heads are taller so timing belt will be a problem? if anyone has info or experience with this build your info would be greatly appreciated thanks

We wish you good luck

Hi Craig,

The 4G92 and 4G93 pistons will fit. The wrist pin is 19mm in all of them.
I've spoken to someone who used 6A13 pistons in a 4G93 turbo and it worked but the compression ratio was unusual (can't remember what it was).
However there are many 4G9X series pistons available stock so one of them will likely give a relatively good compression ratio.

As for the timing belt, my research has suggested that a Honda NSX timing belt will fit.
Alternatively you can use spacers to lift the pulley that holds the timing belt between the two heads.

The drawback to all this is that you will need to customize the intake manifold and exhaust manifold (or at least the Y pipe).
Additionally, the MIVEC valves are smaller than the 6A13TT valves (both intake and exhaust). Which mean a far easier, cheaper, straight forward and more powerful option would be to just rebuild a 6A13TT with high compression pistons and use the 6A12 DOHC non MIVEC camshafts (if you really want to remain NA).

If you got to www.ozvr4.com there is a build thread thread for a 6A13TT MIVEC by user "6A13TT TYPE S":
https://www.ozvr4.com/threads/adams-99- ... vec.13822/

You can see what he did (with plenty of pictures) and he is also active so you can IM him with questions.

If you do find more info in this, do post it back here, perhaps someone in the future will look at it and do his own build.

Another thing to keep in mind is the 6A13 block has a taller deck height so it is unlikely that the stock hood will shut over the engine.

Anyway, as you can see this is doable but the costs keep piling which is why no one has really done this, because in the end there are just cheaper and faster alternatives.

Which state are you in?

Hi Spetz,

Wow thanks for the info that was really helpful! I’m in Ireland , iv done Honda hybrid builds before b20/k24 but not this one it’s unusual and I was guessing it would make decent power towards the 6a12 mivec unit , il follow the link you gave me too and if I find any more info il keep you posted! Thanks

Can we have a forum sub section for things that will never happen?

Hi Caig, no problem.
Are you documenting this build on any forums so that we can follow it?


I am not sure how much power this would make, as to make the most of it you would need to do lots of head work as well custom grind cams.

In the end the cost of all this is so high which (I believe) so far has deterred anyone who's considered this (myself included)

spetz wrote: ↑Fri Jan 17, 2020 1:04 am As for the timing belt, my research has suggested that a Honda NSX timing belt will fit.

NSX belt doesn't fit. The tooth spacing is a lot wider and makes for a much longer belt.

Vectose wrote: ↑Sun Feb 16, 2020 10:35 am

spetz wrote: ↑Fri Jan 17, 2020 1:04 am As for the timing belt, my research has suggested that a Honda NSX timing belt will fit.

NSX belt doesn't fit. The tooth spacing is a lot wider and makes for a much longer belt.

Are you sure?
From memory it was the same, the only difference being that the NSX belt was 28mm wide rather than 30mm but I could be wrong.

Either way the timing belt isn't an issue here as we see the idler pulley in the V valley can be lifted up with spacers to accommodate the extra deck height

spetz wrote: ↑Thu Mar 12, 2020 7:51 pm

Vectose wrote: ↑Sun Feb 16, 2020 10:35 am

spetz wrote: ↑Fri Jan 17, 2020 1:04 am As for the timing belt, my research has suggested that a Honda NSX timing belt will fit.

NSX belt doesn't fit. The tooth spacing is a lot wider and makes for a much longer belt.

Are you sure?
From memory it was the same, the only difference being that the NSX belt was 28mm wide rather than 30mm but I could be wrong.

Either way the timing belt isn't an issue here as we see the idler pulley in the V valley can be lifted up with spacers to accommodate the extra deck height

Yup, I've got one here.

Hi all, built this engine eventually. But stuck on a timing belt to use. The 6a12 mivec timing belt is too small (252 teeth). what belt have people used doing this before? Honda nsx one don’t work and the 6a13 belts i have researched all have 177 teeth. waiting on my local motor factors to get back to me.

Well considering both teeth count you mentioned are wrong I would suggest further research.

CraigMirageV6 wrote: ↑Wed Feb 03, 2021 11:02 pm Hi all, built this engine eventually. But stuck on a timing belt to use. The 6a12 mivec timing belt is too small (252 teeth). what belt have people used doing this before? Honda nsx one don’t work and the 6a13 belts i have researched all have 177 teeth. waiting on my local motor factors to get back to me.

What someone did on a VR4 is they used spacers on the pulley in the valley of the V between the two banks to lift it up and just use a standard 6A12 MIVEC belt.

Let us know how you progress

spetz wrote: ↑Thu Mar 12, 2020 7:51 pm

Vectose wrote: ↑Sun Feb 16, 2020 10:35 am

spetz wrote: ↑Fri Jan 17, 2020 1:04 am As for the timing belt, my research has suggested that a Honda NSX timing belt will fit.

NSX belt doesn't fit. The tooth spacing is a lot wider and makes for a much longer belt.

Are you sure?
From memory it was the same, the only difference being that the NSX belt was 28mm wide rather than 30mm but I could be wrong.

Either way the timing belt isn't an issue here as we see the idler pulley in the V valley can be lifted up with spacers to accommodate the extra deck height

Here we go. Pulled out the NSX belt. Showing the wider tooth profile as well as the length difference.

Thanks for clarifying.
According to some parts catalogue the tooth profile was the same.

In any case what others have done is add spacers underneath the middle idler gear (in the V valley) to lift it up by the require amount and then run a 6A12 MIVEC belt

spetz wrote: ↑Sun Jan 02, 2022 9:38 pm Thanks for clarifying.
According to some parts catalogue the tooth profile was the same.

In any case what others have done is add spacers underneath the middle idler gear (in the V valley) to lift it up by the require amount and then run a 6A12 MIVEC belt

Wrong again. You use the 6A13TT 234 tooth belt.