​Hummelink- Modifications 1.6 ITB screamer

(20 December 2021)

End of 2021 this high revving 1.6 was built and tested for my personal Miata. Take a closer look at the build process!

End of 2020 Hummelink-Modifications offered the first billet 4A-GE ITB adapter online. I ran this ITB adapter on a slighly modified 1.6.

To get full advantage of the ITB kit I started building a high revving 1.6 with all the bits needed for a naturally aspirated machine. To keep the cost down I chose to get as much out of the stock components as possible, which I had loads of.

Despite that, many of the stock parts simply can't hold up once revving above the stock redline.

For the rotating assembly the rods and bearings were upgraded. Stock rods simply stretch too much, and eventually fail at higher RPM's.

The stock cast iron Miata oilpump tends to crack and shatter to pieces with increased harmonic vibrations. A Boundary oilpump and ATI crank damper were used.

The stock pistons were re-used but needed some modifications.

The new rods where slightly longer, and together with the decked block surface this caused a 0.45mm deck height. (piston sticks out 0.45mm above the deck surface). This was a good thing as the compression would be slighlty higher, although the crown of the piston had to be machined to clear the head, the overall height of the piston still resulted in higher compression.

After modifying the pistons the complete rotating assembly was weight balanced.

To further raise the compression the head was skimmed 0.5mm, and a 0.8mm Maruha headgasket was used. This combo ended up with a 11.3:1 compression ratio and 0.85mm squish.

The valvetrain was upgraded with arround 40% stiffer Volvo valvesprings, Mazdaspeed shim under bucket lifters and Kentcams Competition camshafts while remaining the stock valves and retainers. A lot of valvetrain weight was removed after switching from hydraulic t solid lifters. The valves clear the piston safely with close to 1.5mm of clearance just before TDC. The >2.5mm lift at TDC on both the intake and exhaust cam makes up for a nice overlap.

The intake and exhaust ports were modified and portmatched with the ITB adapter to further gain airflow.

To aesthetically please the engine it has been repainted, aluminum has been glassbead blasted, it has been fitted with a 323 valvecover and all hardware has been freshly zinc plated. The Hummelink-Modifications ITB's and coil on plug kit definitely make the engine stand out aswell.

This setup made 165 HP and 168nm on the first dyno day and showed up to 172hp and 180nm with different velocity stacks.

Check out the dyno test blog to see the impact of various runner lenghts here: ITB Plenum Test

Complete spec list of this engine:

1.6 NA engine stock stroke/bore

-Forged rods

-King racing bearings

-0.5mm skimmed deck

-0.5mm skimmed head

-Modified pistons, crown got milled to clear the head.

- 0.80mm Maruha head gasket

This combo ended up with 11.3:1 compression.

-Weight balanced pistons and rods

-Fresh hone/piston rings

Head modifications:

-4A-GE ITBs with Hummelink-modifications ITB adapter.

-70mm velocity stacks

-Modified intake and exhaust ports.

-3-angle valvejob

-ITB adapter portmatched with head

-Volvo valve springs

-Mazdaspeed SUB lifters / Supertech shims

-Kentcams competition camshafts 278°

Supporting mods:

-Boundary oil pump / ATI damper to keep it safe at higher RPMs

-ARP head studs / rod bolts

-Hummelink-modifications coil on plug kit

-Full stainless steel exhaust / cat delete

-Dual feed fuelrail

-1.8 VVT fuel injectors

-ME221 ECU