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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 02-19-2013, 12:28 AM   #61
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Ok, so I found myself a nice cast begi and am on the verge of getting som h beam rods. I have a question about appropriate cr ratio. Based on using stock pistons I have a choice of 8.8, 9.0 or 9.5. If my goal is smooth linear power with very fast response, at the expense of top end hp, am I right in thinking 9.5 would give better low down power, understanding this might limit my ability to run lots of boost ?

Thanks for you're advice
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Old 02-19-2013, 02:57 AM   #62
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Quote:
Originally Posted by TheV's View Post
Based on using stock pistons I have a choice of 8.8, 9.0 or 9.5.
Where are you finding stock pistons with these various compression ratios? Are you talking about using stock Mazda BP-T, BP05, BP4W and BP6D pistons? Drink less beer or don't go out to eat as much for a couple of months and just buy a set of Supertechs in your desired ratio. If you are going to go through the trouble of building a motor, do it right the first time and spend the extra $450 on a decent set of slugs.

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Originally Posted by TheV's View Post
If my goal is smooth linear power with very fast response, at the expense of top end hp, am I right in thinking 9.5 would give better low down power, understanding this might limit my ability to run lots of boost?
From what I understand, its more an issue of spark advance than compression. You can run something like 20 psi on a 10:1 engine but your spark table is going to be miserably retarded. More compression will make it "peppier" down low but more prone to detonation ("more" is a relative term.) Less compression will give you more knock resistance and let you squeeze out more power with ignition timing and the expense of that minor low end loss.

To try to understand more, read this thread as its full of sex and magic: https://www.miataturbo.net/ecus-tuni...actices-56374/

After not understanding any of it, search Google until you recognize the terms and read it again. Then do a search for "MBT" here on MT. In the threads you find in your search, pay close attention to Andrew, Trey and Emilios comments.

Your "linear response" is going to be more dependent on the turbo than anything else. What sized turbo did you end up going with?

I'm sure someone will come in here and correct me if I'm wrong, but I hope some of this helps.
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Old 02-19-2013, 07:48 PM   #63
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Thanks for the hints, a lot to read up on ;o). Plan is for something small and responsive, I have committed to a t25/t28 sized flange, but am open to options for the turbo, srd20 or gt2560 or gt2554r or ....goals are not huge power, response and predictable are most important for driving on the loose stuff.

I'll do some reading and no doubt return with some more q's
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Old 02-19-2013, 07:52 PM   #64
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