85mm pistons in a VR?

885 Views 16 Replies 9 Participants Last post by [email protected], Feb 9, 2002

CorradoCam

Discussion Starter · Feb 7, 2002

Will it work? I figure if I am going to do this I might as well go all out.
If anyone has ever fit a set of 85mm pistons in a vr6 where there any fitment problems? I read an article in EC about a guy who fit 86mm pistons in his VR but he had some major clearance issues due to the narrow angle v6.
I e-mailed matrix motorsports and they said they had a set of 85mm JE forged pistons in stock. If these will fit with no major problems I will place my order today.

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vwmotorsports

· #2 · Feb 7, 2002

Re: 85mm pistons in a VR? (CorradoCam)

The Matrix 85mm pistons drop right in. They don't have any clearance problems. I should know, I've ridden in 3 or 4 of their 3.1's

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CorradoCam

Discussion Starter · #3 · Feb 7, 2002

Re: 85mm pistons in a VR? (vwmotorsports)

anyone else running these?

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VWpowa

· #4 · Feb 7, 2002

Re: 85mm pistons in a VR? (CorradoCam)

What do you think for the 3.1 ?? Good value ?? Do you think there are any problems down the road as far as possible failures??

Slayer

· #5 · Feb 7, 2002

Re: 85mm pistons in a VR? (CorradoCam)

i thought that 83-83.5mm was the max?

[email protected]

· #6 · Feb 8, 2002

Re: 85mm pistons in a VR? (CorradoCam)

quote:[HR][/HR]anyone else running these?

[HR][/HR]

We have a few customers with them but unfortunately they're not Vortexers.
We spent a great deal of time and money engineering the 3.1's. We haven't seen ANY problems.
We use 83.5mm(3.0) as the largest piston for FI. 85mm(3.1L) for NA.

HTH,
Jeremy

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kingofA2`s

· #7 · Feb 8, 2002

Re: 85mm pistons in a VR? ([email protected])

what comprsion are u guys useing on the 85mm pistons?11-1?

Bundaho

· #8 · Feb 8, 2002

Re: 85mm pistons in a VR? (vwmotorsports)

quote:[HR][/HR]The Matrix 85mm pistons drop right in. They don't have any clearance problems. I should know, I've ridden in 3 or 4 of their 3.1's

[HR][/HR]

Dont you have to bore out the engine to fit them in??

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vr6Cop

· #9 · Feb 8, 2002

Re: 85mm pistons in a VR? (Bundaho)

Any bump in piston size requires boring the cylinders. The clearance issue comes in on the bottom end, where the wrong pistons will slap each other and lock up because of the narrow angle of the VR6.
Jeremy, I'm not doubting you at all, so please don't take it this way, but: have you seen any problems with the cylinder walls being much thinner with the 85mm pistons? I was always under the impression that the pistons are so close together that the 85s would thin the walls too much.

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Bundaho

· #10 · Feb 8, 2002

Re: 85mm pistons in a VR? (vr6Cop)

Thats what i thought. I dont know why people say drop in pistons, when you have to take out the engine and rework it.

[email protected]

· #11 · Feb 8, 2002

2

Re: 85mm pistons in a VR? (vr6Cop)

No worries. The static CR is 10.5:1, you DO have to bore the block as well as some special machining in the block for clearance. On the 85MMs vs wall thickness we sonic check all our blocks. Wall thickness is not an issue.

quote:[HR][/HR]Any bump in piston size requires boring the cylinders. The clearance issue comes in on the bottom end, where the wrong pistons will slap each other and lock up because of the narrow angle of the VR6.
Jeremy, I'm not doubting you at all, so please don't take it this way, but: have you seen any problems with the cylinder walls being much thinner with the 85mm pistons? I was always under the impression that the pistons are so close together that the 85s would thin the walls too much.

[HR][/HR]

[Modified by [email protected], 11:13 AM 2-8-2002]

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CorradoCam

Discussion Starter · #12 · Feb 8, 2002

Re: 85mm pistons in a VR? (CorradoCam)

So Jeremy,
You are saying that the 85mm pistons won't fit in the block without some special machining?
What needs to be machined? The pistons?

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need_a_VR6

· #13 · Feb 8, 2002

2

Re: 85mm pistons in a VR? (CorradoCam)

Stock pistons are 81mm, therefore the hole in the block is only slightly larger. 85mms will require machining of the bores, and apparently additional maching, though I can't figure what (int shaft?).
When you were a kid, ever try to fit that big peg into a hole that's just too small?

Were you the kid that got out the hacksaw and fixed it? I was

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[email protected]

· #14 · Feb 8, 2002

Re: 85mm pistons in a VR? (CorradoCam)

The pistons will fit without any trouble. Our propriatary JEs have the proper clearancing for bores this big. The block needs to be machined by a very experienced machinist though. Make sure they have a torque plate too

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need_a_VR6

· #15 · Feb 8, 2002

Re: 85mm pistons in a VR? ([email protected])

Yeah, don't go to the guy holding the hacksaw

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CorradoCam

Discussion Starter · #16 · Feb 9, 2002

Re: 85mm pistons in a VR? (need_a_VR6)

I just thought of something else...
What do you so for a head gasket?
A stock one will be too small

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[email protected]

· #17 · Feb 9, 2002

Re: 85mm pistons in a VR? (CorradoCam)

We are using copper gaskets for now. We may have a run of 3 layer metal gaskets made though......

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