big bore 930 options?

[b930]

Hi,
I am in the process of collecting parts for a big bore build of my 930. I have carerra heads with a high flow valve set up (from Turbokraft) that are twin plugged, 3.2 inlet, full bay IC etc. Will be using Rarlyl8 1.625" equal length header, twin gates, T4 split / twin scroll GT3582R with 1.07A/R. Will also be looking for 964 cams.

My initial thoughts were to use slip fit 100mm cylinders for 3.5L, but I also understand that if I machine the bore registers to 106.5mm I can use 102mm nickies (for 3.7L?). In doing this, and using the stock 930 crank, are there any major other issues to be aware of? Not sure how much meat gets left between the head stud tapped holes and the case register bore diameter, but I have not seen much in the way of this level of big bore conversion so just looking for guidance.

Thanks

[JV911SYDNEY]

regardless of displacement, machine-fit cylinders are a better option than slip-fit

[b930]

better maybe, but worth the cost when going 3.5L?.

I have heard of numerous projects running slip fit 3.5L that hold up fine. Splitting cases and machining bores adds a significant cost so why would you not just go 3.7L with 102mm jugs??

[b930]

I was wondering if anyone here has used the LN 102mm cylinders on a 930 set up. Advice from LN that this is not really done, but they never said why. I guess cylinder wall thickness starts getting a little low, and maybe not enough to flame ring it?? If you open up the case bores to 106.5mm they should work.

I was wondering about the excessive flat caused by the smaller head sealing diameter and maybe issues with piston domes etc but nothing a small machined shallow angle taper from the dome to the sealing flat could not fix.

I really like the idea of a 3.7, running say an 8.0:1 CR with twin plugs and a carrera manifold, full bay cooler. I have my motor out now and stripping it down but am having a hard time finding the 102mm cylinders in stock anywhere.

[Flat6pac]

Buy a 3.6 engine and with your crank and rods, that will open to 3.8 and you still have a 930 turbo case that hasn't been modified, remembering the factory still uses the 964 case on all the most powerful engines they build.
Bruce

[JFairman]

Originally Posted by Flat6pac

Buy a 3.6 engine and with your crank and rods, that will open to 3.8 and you still have a 930 turbo case that hasn't been modified, remembering the factory still uses the 964 case on all the most powerful engines they build.
Bruce

That sounds like the best idea. The 3.6 engines have a different chain tensioner design that looks simpler and better too.

[KTL]

Send your SC cams (your signature says you have these in your engine) to Dougherty Racing Cams and he'll regrind a 964 profile on them for $385

[Robert Espeseth]

Most cost efficient option is to take a 3,6 engine and replace the Crank and Rods with them from a 3,0.

This requires machining of the Rods small end from 22 to 23mm diameter...keep the original pistons.

Gives a SS 3,3 liter medium CR which easily cranks out lots of HP...and you keep your valuable 930 motor as is.

Displacement is less important on a boosted engine...just boost more to get there

[b930]

never really thought about the value of leaving the case original. Sounds like many would not machine case bores becuase of this. I guess this is why the slip fit 100mm 3.5L is so attractive, decent capacity increase but original cases.

I already have some nice 964 cams so the SC cams will be going for sale.

Cheers.