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Old 07-17-2017, 08:06 AM   #1
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Default Compression difference between USDM and JDM VVT motors?

Looking for a new motor for my rotrex'd VVT swapped 90. I was on the hunt for a bp4w as they are around here in Florida and a lot of the guys recommend them. Searching the threads, it's recommend for the slightly lower compression for rotrex boost.

There's also a couple VVTs, including an imported low miles JDM motor. Days of searching I'm getting conflicting info that the JDM BPZE/BP6D is 10.5:1 and the USDM is 10 1. Can anyone confirm or deny?

If I'm strictly 93 pump gas, is 10:1 compression fine for 230ish whp for track, autox, street car? If the JDM is 10.5:1, is that safe or getting out of hand?

Thanks.

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Old 07-17-2017, 10:39 AM   #2
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I have a set of JDM VVT pistons.
Can confirm they are 10.5.
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Old 07-17-2017, 10:42 AM   #3
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The 10.5 motor won't be any weaker. Just may require a different tune. It can safely do 230whp just as well as the 10:1 motor can.

I wouldn't pay extra for one. I wouldn't pay less for one, either.
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Old 07-17-2017, 04:04 PM   #4
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Quote:
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I have a set of JDM VVT pistons.
Can confirm they are 10.5.
Thanks, did you order them or found used?
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Old 07-17-2017, 04:05 PM   #5
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Originally Posted by concealer404 View Post
The 10.5 motor won't be any weaker. Just may require a different tune. It can safely do 230whp just as well as the 10:1 motor can.

I wouldn't pay extra for one. I wouldn't pay less for one, either.
It's already a pretty good deal AND comes with a square top and warranty for $999.
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Old 07-17-2017, 04:28 PM   #6
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rotrex doesn't make torque. you're totally fine with the higher compression
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Old 07-17-2017, 05:09 PM   #7
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Quote:
Originally Posted by oregonmon View Post
It's already a pretty good deal AND comes with a square top and warranty for $999.
Sounds like a no-brainer.
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Old 07-17-2017, 10:12 PM   #8
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Thanks for the input guys.
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Old 07-18-2017, 10:34 AM   #9
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Quote:
Originally Posted by Monk View Post
I have a set of JDM VVT pistons.
Can confirm they are 10.5.
Can you please post pictures of the pistons? I purchased a JDM motor a while back and I would like know if this motor has the same pistons as yours.
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Old 07-18-2017, 07:48 PM   #10
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Quote:
Originally Posted by MX5RACER View Post
Can you please post pictures of the pistons? I purchased a JDM motor a while back and I would like know if this motor has the same pistons as yours.
This is what my broken 10.5:1 JDM pistons looked like.



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Old 07-18-2017, 09:51 PM   #11
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That looks a lot like a standard VVT piston.
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Old 07-18-2017, 09:57 PM   #12
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Quote:
Originally Posted by MX5RACER View Post
That looks a lot like a standard VVT piston.
Stock USDM 01-05 pistons do not have that third step-up in the center.
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Old 07-18-2017, 10:15 PM   #13
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Brought the pictures up on an actual computer with a real screen not an iPhone and I see the difference now. Thanks.
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Old 07-18-2017, 11:29 PM   #14
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Just leaving these here for who ever is interested.

USDM

JDM

USDM

JDM

Side by side

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Old 07-19-2017, 12:10 AM   #15
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/\ very helpful, thanks
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Old 07-19-2017, 09:08 AM   #16
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Yes, very helpful!

Placed the order for the JDM VVT with square top motor yesterday, hopefully it's not ****.
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Old 07-19-2017, 11:36 AM   #17
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Interesting that they dropped the dome away from the spark plug in the center of the 10.5:1 slug.
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Old 07-19-2017, 11:41 AM   #18
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Those are great photographs, thankyou.
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