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Old 11-18-2013, 04:23 PM   #1
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Default Noob question - 1.8L compression reduction

Noob here.
I'm considering a 94-95 1.8L Miata as a turbo project. I've done several other Megasquirt projects and turbo setups, the Miata seems like an inexpensive way to have a little fun.

Although I've read that the Mazda motor does just fine with stock compression and a turbo - is is possible to open up the combustion chamber a bit to drop the compression? Other vehicles I've worked on often have CNC options for making those changes.

If this isn't the usual method - other than pistons, how do you lower the compression a bit on these things?
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Old 11-18-2013, 05:16 PM   #2
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Stock compression is fine for the amount of power you can make on stock rods.
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Old 11-18-2013, 06:47 PM   #3
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Thanks for the reply. Being a noob and all, I have to ask:
How much power is that?


The other variable that's in play is that I'd like to run on pump gas. Can I max out the stock rods on pump gas with stock compression? Just beyond that - can you drop the compression on the Miata without swapping pistons - via the head cc enlargement that I'm talking about above?
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Old 11-18-2013, 06:52 PM   #4
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Quote:
Originally Posted by cb1000rider View Post
Thanks for the reply. Being a noob and all, I have to ask:
How much power is that?


The other variable that's in play is that I'd like to run on pump gas. Can I max out the stock rods on pump gas with stock compression? Just beyond that - can you drop the compression on the Miata without swapping pistons - via the head cc enlargement that I'm talking about above?
Yes you can.. most of us are running pump gas and stock compression.

You can get Forged rods that youll never max out for $300-$400. Thats the weak point of our motors... Those and the ECU
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Old 11-19-2013, 09:45 AM   #5
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Thanks. I understand that proper tuning is required - I'll be doing Megasquirt.
What is a safe level of power on those stock rods, assuming pump gas?
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Old 11-19-2013, 10:04 AM   #6
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General rule of thumb is 200-250. Beyond that, you'll bend them.
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Old 11-19-2013, 10:05 AM   #7
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Quote:
Originally Posted by cb1000rider View Post
Thanks. I understand that proper tuning is required - I'll be doing Megasquirt.
What is a safe level of power on those stock rods, assuming pump gas?
ALLOFIT!!!! as long as it doesnt exceed 250tq.
But you can do forged rods for about $300.... JUST DO IT! lol

And, depending on your end goals, while you are already in there, you may as well do Pistons/rings, All ARP bolts and studs, MAYBE a billet oil pump, and replace all the seals...
But, that all depends on your "endgame" at the least do the rods, and call it did

Last edited by supercooper; 11-19-2013 at 10:26 AM.
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Old 11-19-2013, 01:38 PM   #8
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Thanks guys... My experience with aftermarket turbo setups is that if you keep the power reasonable, things will last a long time. 200-250 ft/lbs in a Miata will be enough for round one...
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Old 11-19-2013, 01:56 PM   #9
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When choosing a miata, I would say go with the 94 over the 95. For sure it will be OBDI and have the oil feed port on the driver side of the engine. Long term they can make things slightly easier depending on where you live and such.

You will want either a gt2554 or a gt2560 is you are on a budget. Both will spool quick and won't grenade the engine. The gt2554 will top out at about 220hp at the wheel, the gt2560 can top out around 300hp at the wheels.
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Old 11-23-2013, 02:27 AM   #10
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The turbo i ran on stock block on 1.6 did 220 whp and 200wtq all stock with 91 octane. Good tune. So the 94 is good for 250whp good tune daily driver. Needs coolant reroute to be safe and upgrade radiator. A cool engine is your friend
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