1999 Miata ITB Dyno. Stock Bottom End. No Porting. 172 WHP

Head is not ported at all, just shaved .060". Supposed to be around 11.5:1 compression now, but I am not sure if it was actually raised that much.

Engine:

2002 Block 10:1 compression
Cams are 264 / 264 10mm Lift Maruha's
Supertech Single Valve Springs
Supertech Titanium Retainers
Mazdaspeed SUBS
Toda Adjustable Cam Gears
New OEM Valve Seals
OEM Head Gasket
TWM 45mm Individual Throttle Bodies
36 lb Fuel Injectors
ITG Sausage filter and backing plate
Hondata Intake Manifold Gasket
Adaptronics Standalone ECU
Maruha VP Race Header
Racing Beat Resonated Race Pipe 2.375"
Jet's Integral Kobe Muffler 2.375"
Garage Star Alternator and Waterpump Pulleys
6.2 lb Spec Billet Pressure Plate
7.1 lb Fidanza Flywheel
1.3 lb Clutchnet Unsprung Street Disk
Golden Eagle Vacuum Manifold
Chikara Motorsports Oil Catch Can
Koyo 52mm Radiator
Koyo 1.3 Bar Radiator Cap
Mishimoto Slim Fan
Samco Radiator Hoses
Flyin Miata Oil Cooler Kit
Beatrush Radiator Cooling Panel

This stock 02 block at 10:1 compression, tested at 200-205 psi in each cylinder with the stock cams in previously. With the new cams creating more overlap and the head shave at .060" supposedly 11.5:1 compression, it tests at 205-210 psi in each cylinder. So with stock cams in the head creating less overlap it would most likely test much higher compression on the gauge. Honda's F20c at 11:1 compression on the non-VTEC lobes compression tests around 230-240 psi depending on the gauge.

With a .060" shave and 10:1 factory pistons, there is still a good 1-1.5mm of clearance in the reliefs. My friend/tuner was telling me to shave .080", but I was scared because the highest I was told I can go was .030", and I asked a lot of the big name Miata guys this too. I should have done .080". If the head ever comes off, I am going to shave it again to .080".

The results of all of this? Here are before and after comparisons of both the corrected dyno numbers and the uncorrected (what car was actually making at that very point in time). We fiddled with the cam gears on the street and on the dyno as well. These engines are not very sensitive to timing changes. Changing the cam and ignition timing yielded very little results. We advanced and retarded both the intake and exhaust cam quite a bit, but nothing significant changed. When we originally baselined the car it made 168 whp and 124 ft/lb's. We were however able to pick up a good chunk of mid-range power and settled with both the intake cam advanced about 6-7 degrees and the exhaust cam advanced about 3-4 degrees. We spent some time trying to get that funky dip out at 2600 rpm, but were only able to flatten it a little. We think it is just the nature of the cams and maybe the combination of them, the ITB's, and the header as well.

So there you have it. The idea behind this build was to avoid getting into costly bottom end work or head work and making the setup easily reproducible. Literally the only machine work required if the motor were to fail worst case would be shaving another head for 135.00.

[TheSlipAngle]

You are talking about motors that have much more efficient heads and capabilities to spin rpm much higher than this engine where shorter runners can be taken advantage of. The F20c is an incredible engine. I wish Mazda's motors could have been half as good as Honda's. I still envy how smooth and light the F20c is when I hop out of this into my stock AP1. The difference is noticeable, even though this is now slightly faster, but most of that is due to the weight advantage.

[TheSlipAngle]

The heads on these motors do not breath well enough to make good top end power. Don't forget that compression on this engine is ~11.5:1 now with how much was shaved off of the head. The block is stock, so it is still a 1.8 liter. Shorter runners almost always yield more top end power at the cost of low end. Cam timing, intake lengths, exhaust manifold lengths, etc. all move the powerband around.

[schrizzox]

Read your writeup in one of the ITB threads on one of the Miata forums. Really nice car!

[nmed]

What did this end up costing in the end? I remember hearing you say that you were trying to keep costs lowish as one of your goals for the build. Great car; very inspirational to start my own build!

[BF]

damn you've had this car for this long 😂 crazy

[zacharybsmith]

Impressive stock bottom no boost numbers right there.

[edgestr]

From your parts list it looks like this build was around 10 grand, is that about right? I'd really like to replicate it.
Also, please make a video of your exhaust. I just looked up some videos for the sound. Even on a stock engine that thing sounds great. Also, do you idle <1k? I'd really like to keep the idle as low as possible.

[jamiegonzalez]

I was curious on the clutch setup ! Is it the "kush lock" or the "fiber-carbon pro"? I won't be making as much power, so I feel like the setup here is definitely sufficient. Thanks !

[mitchellrg]

Where did you get the head shaved and what ITB are you running?