Many of you have seen this project car. we built this about 4 years ago, Started life with a JDM NB2 engine and our Big Grip Kit. Later got a 1.9L Whammy engine, CNC head and C30-74 JR Rotrex kit. Later we pulled the Rotrex off and ran N/A for a while. Now it is time for Vtec. Yo.

Starting a new thread to focus on the engine. It's going to be enough of a different car than the original 95R build that it really needs it's own thread to keep folks from getting too confused.

I decided on a K20 because I like to rev the snot out of it. Often. The planned usage for the car is much the same as before. Giving walk-in customers rides to demonstrate Xidas and 9's. Ride-a-longs at big track events like MRLS, MazdFest, etc. The occasional Miata Challenge TT event, some wekeend canyon runs and the occasional CnC. It'll run on pump gas, or what passes for gasoline here in Cali. I also want it to idle so no vtec killer hardware and 10k redline for me. Hytech in Irvine, CA is building the engine. They have done some amazing things with the K series and really kno wtheir way around the platform. Our plan is a relatively lightly modded build, compared to what they build for some customers. Rev limiter set at 8800 with accidental over rev protection into the 9's. Based on the many dynos John showed me, we should make around 260whp without too much trouble. Stage 2 cams, custom RRC intake manifold, stock TB, some tweaks to the KMiata oil pan for increased capacity, some cleaning up of the head, custom 12.0:1 CP pistons, ATI small diameter damper and a few other shiny bits.
Hondata will set us up with a Kpro4.

Drivetrain will remain as is, 6s pd x 3.9 with SuperMiata tuned OS Giken, SPM Sport clutch cover on 13.6# KMiata flywheel. We're now running our 11.75/10.9 BBK with 1" master. Love these brakes.

Here is the cruddy looking salvage yard engine on the stand at Hytech this afternoon. Paid $1500 shipped off ebay so I wasn't expecting gold. Probably paint it gray or orange after it's tumbled clean. Valve cover is getting PC'd orange.



This is where the vtecs happen.. I think


This is an empty block John loaned us to install for the header, intake manifold and oil pan packaging. KMiata oil pan held on with two bolts just for measuring stuff. Steel Moroso KMiata pan is only 2lbs heavier than aluminum OEM pan. K bare block with head and girdle weighs about what a bare Miata block weighs by my uncalibrated arm scales.




soon, my little orange friend

 

very cool. keep the awesome pictures coming, I'm sure many will thank you for em

 

Exciting!

 

In for win. It will be interesting to hear your preference on powertrain once you have driven this for a bit. I know you say the BP with the Rotrex is the most cost effective HP gain wise, but I don't live anywhere near competitive racing, so my build and mods are just for fun.

 

Subed. This should be good.

 

Subed!

This is going to be awsome!

 

BP + Rotrex more cost effective for big power regardless. If big N/A power is the goal, K then probably LFx then LSx. Big N/A power and lots revs are exciting to me. Plus, as an engine geek, the K20A2 is just amazing. Kinda like the guys that love rotaries (poor souls), it goes beyond rationale, just passion. IOW, its not just about the cost/whp ratio.

 

Subscribed!

This car will be a beast, glad to see our kit being put to such good use.

 

I guess it will be "custom" fitted or do you use an existing swap kit like "kmiata" ?
This is one of my favorite Swaps for a Miata
Once the Turbo Na is finished i will eventually go the same Route for a DD
Let's see if i get it street legal here (would be the first in Germany)
Emissions are way better than a b6 but that's the only good thing ,everything else will be a huge Problem.
Subscribed!!

Edit: i have just seen you use a kmiata kit

 

Slightly unrelated question... What's the pinch weld height on this Miata?

It seems really low on the track, wasn't sure what it's set at.

 

Well . . . I guess the writing is on the wall for my next project . . . . Have to Emulate Emilio you know.

 

^^^ Hurry up and paint/vinyl your Miata orange, already!

 

Miata Race alignment

 

Why the k20a2 over the k24a2?

I'm gonna have a hard time not cleaning up my K engine as much as yours. Probably shouldn't check this thread once the engines done...

 

I like the higher revs the K20 is capable of. Besides 260whp on pump gas is plenty in an HPDE car with no aero on street tires. To me running a long stroke, under square rev limited engine (K24) even though it has that fabulous k series head would be too much like sticking a fancy BP in it. Running a K20 get to all the honda goodness. The only thing more hi revving would be an F20 and realistically the K is a better platform anyway.

I know someone is going to jump in and talk about an 11000 rpm K24 but we are talking about a reasonable cost to build here, not a $15,000 oval track or drag racers time bomb.

 

What's your expected service life of a K20 of your choice? 100, 150, 200h?

 

And what are the running costs? Most of us know what it will costs us if a B6/BP grenades, what happens with a K20?

 

I wrote detailed replies twice and the friggin site logged me out before I could post it, maybe 5 minutes later. Annoying as hell.

I asked John for a 100hr motor and wanted to rev to 9k. He said 880 would be the limit if I wanted to retain vtec. It’s interesting to me that he was so specific. Most engine builders will round off to the nearest thousand. Hytech’s recommendation comes from hundreds of hours on the dyno. They have an in house engine dyno they built that almost always has a K series on it. Some of the prep he specified to meet my goals:

Custom Hytech CP pistons
Carrillo H beam rods with Carr bolts
OEM Honda bearings
DLC coated Wrist pins and rocker shafts
ST valve springs running about 100# seat pressure (wow)
Hytech custom ground cams

I asked about the chain tensioner. He laughed and said something to the effect of ”most shops don’t really know how the valve train works”. I’m paraphrasing here to encapsulate a 25minute conversation on valve train life. He’s run the OEM tensioner way past 10k and never had a failure once they identified how to make the entire system work together.

There are endless little conversations about each little aspect of the motor. It’s clear to me that he has literally forgotten more about these motors than most shops will ever know.

So yeah, sounds like 100 hours.

In the US “running costs” would be consumables, i.e. fuel plus a little oil now and then. I assume though, you are simply asking what the engine costs to build. Not including a $1000 Kpro4, it looks like the core, build and a few ancillaries will cost around $8k for 260whp on pump gas. That same money including the $5k for Kmiata swap kit and Hondata, spent on a BP N/A would net you about 190whp on pump gas and not last quite as long. 200whp if running ITB’s. That same money ($13K) spent on a BP+Rotrex would net you about 370whp on pump gas and last about as long. 400whp if running race gas or E85. This last bit is not conjecture. We have a good customer that has way over 50 race hours on a 400whp BP build (race gas) that was built for a lot less than $13k. He made 440whp but it was undriveable on the big end and broke the driveline too often. At 400whp it was just the occasional halfshaft wearing out.

FWIW, we ‘murricans don’t bother with the B6

 

Thanks for sharing

So $8k (counting a rebuild from major kaboom) every 100h gives $80 per hour, a really low figure (That's Volvo red engine country over here, with Evo heads).
Rebuild before kaboom (by keeping an eye on things) makes things a lot cheaper.

Hmm, $80 per hour, doesn't race gas cost more (pump gas is close here)?

 

It's not likely ever to go kaboom though. We generally don't ever grenade engines here. Only 3 out of maybe 40 that we have had our hands on and then only on crazy experimental stuff. When the compression drops, we rebuild them. This one won't cost anywhere near $8k to rebuild and it might go way past 100hrs. Probably more like $2000 to rebuild.