VR4 pistons compression ratio drivebility?

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sucka
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Re: VR4 pistons compression ratio drivebility?

Postby sucka » Fri Apr 15, 2016 11:41 am

fugazi wrote:Take a look at the SOHC non-turbo pistons... do they have flat (-er) top w. reliefs?


The problem with any sohc pistons aftermarket or otherwise, is the 2mm thick compression rings and oil control grooves weaken the pistons in the ring land area.

Dohc pistons have thinner compression rings and oil control holes rather than slots which result in a much stronger piston than the sohc version. The down side is that the dohc pistons don't have valve reliefs in the right spot for the sohc head. If you use atmo dohc pistons you will have to fly cut them to prevent contact with the valves

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Re: VR4 pistons compression ratio drivebility?

Postby Nosaki Faki » Fri Apr 15, 2016 2:00 pm

I don't actually want to run a flat top, was just curious.
I will most likely go down the road of the wiseco's with the 10cc dish.
Or supertech with 9cc the supertech don't appear to have reliefs other than the twin cams.
The Wiseco's may or may not I haven't been able to confirm this yet.
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Re: VR4 pistons compression ratio drivebility?

Postby fugazi » Fri Apr 15, 2016 4:40 pm

sucka:
I didn't mean "put em in" just "take a look" at the reliefs in them to see how much is needed if going flattop and "standard" cam...
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Re: VR4 pistons compression ratio drivebility?

Postby quest » Fri Apr 15, 2016 5:40 pm

Do "weak" factory SOHC pistons fail on MPI setups as well ?
I'm wondering if TBI fuel distribution is to blame

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Re: VR4 pistons compression ratio drivebility?

Postby Nosaki Faki » Mon Apr 18, 2016 4:13 pm

I have ti sorted I actually ended up going with SRP pro pistons 4032 alloy in the later type 22mm pins.
9.8 cc dish so with a slight cleanup of the head and block I should be 7.8 - 7.9:1.
Eagle hybrid H beam rods and got some ACL race bearings while I was at it.
I will have the bottom end balanced, still debating whether to remove the balance shafts.
Turbo will be a small 16g as I already have it, Is there any point going to large 16g? looking to run 10-12lb boost.
Head has been ported and will be running TBI for now. Need to start saving money again for MPI.
Can anyone tell me what sort of numbers I should expect from this setup?
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Re: VR4 pistons compression ratio drivebility?

Postby fugazi » Mon Apr 18, 2016 5:01 pm

Don't see any need for a "big" 16g... the small will probably spool a tiny wee bit faster, but...
I'd say about 220hp with a good IC too go with it.
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Re: VR4 pistons compression ratio drivebility?

Postby Nosaki Faki » Mon Apr 18, 2016 5:08 pm

Oh yeh i forgot to mention the intercooler, already fitted.
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Re: VR4 pistons compression ratio drivebility?

Postby redzone » Thu Apr 21, 2016 7:20 am

quest wrote:Do "weak" factory SOHC pistons fail on MPI setups as well ?
I'm wondering if TBI fuel distribution is to blame


Yes they fail with mpi too. It's a legit design fault.
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