Engine width calculation

[LouisCypher]

Hi folks,

I am planning to rebuild my 914 engine and wondering how a stroker crank would affect engine width:

a 78 mm stroker cam has 7 mm more stroke than a stock 2.0 crank. The stock pistons having a comp height of 35,75 mm, I need for example KB pistons (KB 317 or KB 218???) with a comp height of 27,6 mm (1.090'') to compensate the longer stroke. Right?

OK, so I have 7 mm more stroke and 8,15 mm (35,75 - 27,6) less comp height. 1,15 mm remaining

Now, to avoid to much clearing of the case, I choose type 1 rods with 136 mm stock length, being 5 mm longer than the original type 4 rods with 131 mm.

How will this affect my engine width? Is my calculation right, that the engine will be 4,85 mm wider?


Cheers,

Louis

[LouisCypher]

sorry, I meant, 5 - 1,15 = 3,85 mm wider ;-)

[jamcleod]

realize that when you do all this, you will have to adjust the rocker arm geometry for your increased stroke. i'm not sure if it affects engine width but if it does, i'd bet it would be a headache to adjust the engine tin and pushrod tube length, etc.

[LouisCypher]

Hi,

first, I have to correct the figures again: the length of a type 1 rod is 137 mm. So according to my calculation, the engine "should" be 6 - 1,15 = 4,85 mm.


This combo seems to be very common, and somehow I cannot believe that everybody has to fiddle with the engine tin and the pushrod tubes. I believe that my calculation is only theory and that my ignorance makes me oversee something. But what?


Cheers,

Louis

[Jake Raby]

stock tin can go as wide as .300 on each side and still easily go into place..
Keep in mind that anything more than .160 sghim on each side requires custom pushrod tubes to be made. This calculation is with the OEM bored cylinders that we use, the junk cylinders on the market are .040 longer than stock so you'll knock that number down to .120 on the shim if you have them....

The combo is a favorite among many- I started working on this combo 15 years ago and since have developed 75 different configurations of it.

It is all in cam selection,cylinder heads(especially intake port shape and size- keep it small) and making peak efficiency... not just inj girth...

When you get the 2270 the best it can be, you won't need custom PR tubes, and it will go together easy.

The cam can make or break this combo.

[LouisCypher]

Hi Jake,

my calculation is correct, then? You use a similar combo (don't know the other parts, of course) for your 2270 engines. Does that mean that you use PR tubes with stock length? Are they long enough to cope with the extra width of the engine?

Regards,

Louis

[unclerichy]

Well "LouisCypher", you'll need an avitar like this....

[Jake Raby]

I have spacers made to shim the tubes from the under side (case) to compensate for the width without lengthening tubes..

I'll tell you this

with a:

crank of 78.4mm
rod of 5.398
pin height of 1.115
cylinder height of 3.602 (stock OEM rebored)
deck height of .040
and chamber volume of 58cc

you will need approximately .120 of base shim, according to the plunge cut on the cylinder head.

That will get you by with 1 of my shims under the tubes, or you can use 3 of the stock shims from the early TIV rocker assemblies....

BTW, my 3.0 is .700" wider on each side than a stocker.

[LouisCypher]

Many thanks Jake!

I slowly begin to understand. I still don't know what the stock shims of the early TIV rocker assemblies is but I will try to check out