gruhsy

What is the displacement of a 2.7L offset grind crank with the 102mm piston used on Sid and Shawn's build?????

I'm lacking the mathy thinky for this one at the moment

The 2.5 crank equals 2.85
The 3.0 equals 3.15
The 2.7 equals ?????

Dougs951S

there is no 2.7 crank. same as 2.5.

gruhsy

Hence the 2.7 mathy thinky problem LOL

Thanks

My new project car.....RAGE2's old car has a 2.7L crank. Don't know yet if it is still good. Engine has a hole in the block by the oil filler.

David Floyd

Are you sure about the crank? one of his builds is like mine 106mm bore to yeild 2.785ltr

Dougs951S

LOL was on the phone when I responded, typing with one hand so I couldnt go into too much detail. Rage' old car was 2.8, big 106mm bore with a stock 2.5 crank I believe. Let me break it down like this.

2.5 is 100mm bore x 78.9mm stroke

2.7 is 104mm bore (3.0 block) with a stock 78.9mm stroke 2.5 crank

2.8 is 3 liter 88mm stroke crank inside a 100mm bore 2.5 liter block
Can also get 2.8 liters with a 106mm bore block and a stock 78.8mm crank

3.0 is 104mm bore x 88mm stroke

This is of course, only for factory engines/factory parts

You can also build some pretty big engines without using an offset ground crank:

2.9 is a 108mm bored out 3 liter block with 78.9mm crank

3.1 is a 106mm bore block with an 88mm crank

3.2 is a 108mm bored out 3 liter block with an 88mm crank.

The standard offset grind for a 2.5 liter crank takes the 78.9mm stroke up to 86mm stroke, almost as long as a stock 3.0 crank. The "big offset grind" starting with a stock 3.0 crank brings it from 88mm to a whopping 95mm. As stated above, you can also bore both the 2.5 and 2.7/3.0 blocks out an extra 2-3mm (and sometimes as much as 4+mm) depending on how/if its sleeved, you do the math and you can get lots of different sizes of motors, limited only by how the parts fit together.


The biggest you could "technically go" with an offset ground 3 liter crank and a bored out 3 liter block is a 3.5 liter, 108mm x 95mm. In practice though you're looking at 3.35 liters as the largest practical engine. The biggest you'd probably get using a 2.5 liter block with a 3 liter crank is a 3.2 liter. If you use a 2.5 liter block and a 2.5 liter crank, the largest you could go is a 3.0.

gruhsy

Thanks that all makes more sense.

I also went back and checked the specs. It's a N/A 944 crank...my mistaken memory had it as a 2.7 crank. Everything better with my brain now.

V2Rocket

Doug,
"mathematically" there's a way to get a 3.7L by having custom rods made with an even smaller production car journal size (40mm journal = 100mm stroke on 3L crank) but that's getting impractical for crank strength...although ACL does make such a race bearing.

Dougs951S

Some things just shouldn't exist in this world Spencer. A 3.7 liter SOHC inline 4 is one of those things...That'd be a gnaaaaarly N/A motor though with a built 8v head with some huge valves thrown in and some really nice port work, plus super high compression. 250 hp/250 lb ft?

Adonay

Great posts allot of usefull information

V2Rocket

944-4BT

H.F.B.

If you're familiar with Excel, this Excel-Sheet compressed in the Zip-File will help you. Just play around with the numbers and build your stroker...

gruhsy

Thanks for that

Got a little confused yesterday. I don't know why I thought a 2.7 had a different crank. RL is handy when your brain plays tricks on you.