New VR6 Piston Questions

[redsamuraidragon 0]

I have a 92 Slc that took a dump on me recently after 173k miles. Its a distributor 12 valve vr and im looking to rebuild this motor asap with upgraded crank pistons rods cam and head.

Im told reboring the cylinders over 83mm is unsafe as the wall of cylinder number 1 becomes thin.

Im looking to run on Supreme pump gas. I have intentions of having my new cylinder head milled ported and polished.

The big valve head that is. I have heard of putting a mark 4 mls head gasket to further lower the compression on the vr6 but im wonder about clearance issues with the high compression pistons.

Ive been told 10.5:1 is high as I can go. Should I be expecting problems if I put 10.5:1 pistons in the car and then mill the head further? I dont mind adding additive to pump gas. I just want a motor that I can get 170 k out of and still produce 225 horses or better. Im not having any luck with places online to buy pistons. Anyone know of any places?

Also, im taking recommendations for band names to buy, and ones to stay away from. Any websites would be a big help.

 

THanks

[dukest 0]

discussed a fair bit here recently...

 

viewtopic.php?f=1&t=27844&p=742904&hilit=wossner#p742904

[chazrad 0]

I'd pm Corozin on here. He's just had his VR rebuilt in a simialr way you are talking about. Its a good job and he's now a wealth of advice. I think he's running 11:1 comp ratio and Wossner pistons. He'll give you the lowdown.

 

Also, FourseasonsTuning.com are a good source for parts. They're your side of the Pond too. You'll find them if you Google them.

[Philmo 0]

Chazrad

 

Notice you run 288's with FI - is this a recommended combination? [like 263's?]

 

Who makes 288's? :?

 

Regards

 

Phil

[Supercharged 2]

I think the 288 refers to the diametre of his brake discs dude!

[pete_griff 0]

hey philmo - don't want to sound patronising but chazrad is talking about his 288mm brake conversion - not 288 degree cams - that would be truly wild with forced induction!

[Philmo 0]

Of course!

 

Can't you just tell I'm a rookie? :?

 

Thanks & regards

 

Phil

[corozin 0]

@redsamuraidragon

 

If you're based in the USA or Canada (as I assume you are) you might want to consider contacting Bildon Motorsport as they can source you not only a wide range of piston sets (including Wossner's new 13:1 compression ABV pistons) but also all the piston/ring sizes up to 83.5mm. I'm running the 12:1 set and the quality of the componants is top-shelf (see pic)

 

In addition they can also advise you (and provide service) on all the other things you need to do depending on what type of rebuild you're planning, and can provide the head/porting service you seek.

 

Regarding the rebore the AAA/ABV block is 100% safe to 83.5mm and that conversion has been around for ages. I'd actually be wary of anyone who tells you that it's not. Ditto the 10.5:1 advice provided you use decent octane fuel and get your ECU mapped properly. There are guys who've gone out as far as 85mm but this requires the throw to be shortened to avoid things smacking into each other at the bottom of the vee (if you open the engine block up you'll quickly see the issue).

 

What I would say (based on recent experience) is that what you're planning is not necessarily the most cost effective way to replace a failing AAA block with a big power replacement. A 24v lump makes more sense financially, but if (like me) you're attached to the 12v experience and want to do something really unusual then it's worth considering. Certainly I'm not regretting it (yet).

 

Hope this helps

John

[Kevin Bacon 5]

Im told reboring the cylinders over 83mm is unsafe as the wall of cylinder number 1 becomes thin.

 

It's not 'unsafe' as such, the engine just won't last as long. It's not a question of the machine shop's ability to build the engine, but as a business they shouldn't be telling their customers that they can expect 100,000+ miles from an 83.5mm block with forged pistons.

 

You are wise to be wary of exceeding the bore size on the VR6.

 

The cooling jackets around 1 and 6 are the smallest and is where the block casting is thinnest, so consequently they are the hottest running cylinders.

 

You are then asking these bores to remove the heat of a more powerful, hotter combustion stroke with less wall thickness. My maths isn't great, but 2.5mm less metal over an area of 90.3 x 83.5 must be significant on these fragile bores. Not a problem for bores 2, 3, 4 & 5 as they have more meat and bigger cooling jackets.

 

If you're running sequential injection, you can of course trim cylinders 1 and 6 with a little more fuel but it's a workaround rather than a cure for a lack of cooling.

 

83mm is plenty imo. Going from your stock block to 83mm gives you an extra 139cc. Going from there to 83.5mm gives you an extra 36cc. Having experience of both 83.5mm and 83mm engines I can tell you that 36cc difference makes bugger all difference..... but the initial jump from 2792cc to 2931cc does.

 

You only have to look at what happens to ABV engines to see the effects of increasing the bore from 81mm to 82mm. Cyls 1 and 6 can ovalise prematurely. It's a risk we take and personally I'd excercise some damage limitation and go no higher than 83mm.......but it is of course your money and your decision ;-)