103 mm bore x 71 mm stroke engine., Anyone tried this? Options

[Charles Deutsch]

The Scat (what a name!) catalog has a 103 mm big bore kit for the 914. Could I use these pistons & cylinders with my 2.0 case without any machining? What kind of hp and torque curves would this combination produce with a street cam optimized for mid-range power and torque? If it's well balanced, it should be a free-revver considering the stock stroke is retained, no? Btw, what are some of the bore/stroke numbers for the flat-six motors?

Thanks

[URY914]

That is a lot of questions!
1. 103's require case and head machining.
2. HP? easy question-many answers.
3. Yes
4. Don't know

[Charles Deutsch]

I wonder what kind of engine dyno simulation software Jake Raby uses - it would be interesting to plug some numbers in and see the corresponding hp and torque curves. A few years ago, I read about the software that BMW bought for designing their engines - I wonder if it's dropped in price in the mean time. (IMG:style_emoticons/default/laugh.gif)

[tat2dphreak]

here's the answer to the last Q:

http://www.pelicanparts.com/911/technical_...hassis_info.htm

[Jake Raby]

Going with a bore that big and a cast iron cylinder is asking for trouble....Some of this trouble is:

Head leaks- those darn out of round non square cylinders leak like a sieve and need 5-6 studs to keep from it...

Oil temperatures- The bore size is increased 9mm over stock thats a whopping .360 about 3/8 of an inch!! Cooling that oil takes alot of work..

Head studs- the TIV has a non square stud pattern, it does not like a huge bore......Also the studs are 2 different lengths from top to bottom, and that makes for uneven expansion rates...uneven expansion warps the cylinder and even the heads and starts head leaks!

heads- After you get them sealed off, you have to flow the air that a piston that big can move....not happening cheaply or easily!

I felt so strongly and had so many problems with those pistons (actually anything over 100mm) that I REFUSE to use them any further. Every 100mm+ bored engine I build gets LN Engineering Nickies, or I won't put my serial # on it...simply too risky!

alot of guys disagree with this, and thats fine....I can make 180 ponies from a 96mm bored engine with some stroke and correct cam and head selection and do so for 80-100K miles....I have seen 103s last 10% of that time before they have a head leak or worse.

They are simply not needed, and until we correct some issues with cylinder heads and borespacing, they are a simple waste of money.(in my opinion)

As for my software, I use Engine Analyzer Pro, coupled with old fashioned trial and error...

[Charles Deutsch]

Thanks for the great information, Jake. I've decided that I'm going to just rebuild my 2.0 to stock specs (using the Euro pistons and cylinders) and build, or buy, a big-four sometime in the future. I'm going to do a web search for the software now but I'll probably get "sticker shock".

[Charles Deutsch]

For anyone who's interested, you can download and try a demo version (beta) of the latest Engine Analyzer Pro software but you have to phone Performance Trends and ask for an unlocking code everytime you want to use it.