V2Rocket

I am starting to plan out my next engine build and am looking for thoughts and experiences related to my dilemma.

I want to increase the displacement of the engine, period. As a daily-driven car in a hilly area grunt at low engine speeds is a must. This engine will be supercharged and perhaps turbocharged eventually if the SC doesn't keep me satisfied in power terms.

What I have currently is a 2.5L block, steel-sleeved and needing to be clean-up bored. The bores are way worn out and it's likely the next biggest size to get good bores would be 4.00" or more.

I need new pistons of course, thankfully the sleeves make that less of a challenge to find good options. I also have a nice set of Carillo rods from this engine.

There is a 3.0 crankshaft for sale near me for the standard price and some others available online. I could buy the crank and off-the-shelf pistons for ~$1500 and the rest of the engine would go together as normal.

Or, I could grind a spare 2.5 crank ala Sid/Shawn, buy new rods and pistons to match, and have a similar displacement engine (slightly smaller) for ~$1100 plus seals etc.

So the 3.0 crank route would be slightly larger displacement but more expensive, but no special crank work needed. I would use the michaelmount rod bearing service if I go this avenue. It would also give me a 3.0 crank to offset grind down the road if I get really crazy.

Fueling will be Rogue-tuning stuff, on E85 or pump gas 91 in a pinch.

I would like to see around 400HP out of this engine, yes I know it's doable on a 2.5 as standard but the extra grunt is very attractive.

Ideas?

refresh951

You know what I think

blade7

Sell the rods you have and offset grind the 2.5 crank.

Meine44

It all depends what options are available for pistons.

V2Rocket

With the bore and pin heights for the stroke options there are several off the shelf options within a few thousandths of being at deck height. That raises some questions regarding quench area though... How much is enough or too much on a 944?

V2Rocket

re-visiting this...
pretty sure i've got my paws on a 3.0 crank needing some rod work.

im debating some options now...some are slightly unorthodox

can build an alusil-bore 3.0 with 10.5-11:1 cr...104x88mm (definitely not a boost engine, but would be a hoot NA)
(pistons + rods + machining ~$1100)
can build an alusil-bore 2.8 "classic" stroker with 8.4 cr...101x88mm
(pistons + rods + machining ~$1600)
can build a steel-sleeved 3.1 hybrid stroker...any cr i want...102.362x94mm
(pistons + rods + machining ~$2000)
can build a steel-sleeved 2.9 stroker...any cr i want...102.362x88mm
(pistons + rods + machining ~$1000)

all these are prices are just for the major hard parts, in addition to the other standard costs of engine rebuilding (gaskets and stuff)

is 0.2 L worth an extra ~$1000 in machining and parts cost?

gruhsy

I vote 2.9 for a thousand

Xaerran

will the 2.9 be just as reliable as the 3.1?

The longer stroke may offer more torque a bit earlier... but that claim is not really dyno proven yet. An extra grand may not be worth it...

Raceboy

2.5 crank based motors have better rod ratio.

V2Rocket

is this really relevant on a 6000rpm engine?
I thought the rule was "run the longest rod you can fit between your crank and piston"...I know there are some differences like piston speed, tdc dwell time but is it that significant to worry about?

stock 2.5 is 1.9 which is nice
stock 3.0 is 1.7 (mine would be like 1.65)
95mm hybrid strokers are under 1.6 and seem to do ok.

ford 302w is 1.7 (5.1" rod/3" stroke) but the 351 can be taken to a 427ci which has a rod ratio of under 1.5:1 and they get spun up pretty hard too.

Humboldtgrin

Just an idea. I'm building a 2.7 turbo big block base engine. 2.7 head breaths better,.2 more displacement, good rod ratio still at 1:9, and a full knife-edge 2.5 crank not cross drilled, machined 2.7 stock pistons to look similar to the 2.5 turbo piston but looking for 7.5:1 compression. Super 53 turbo to top it off. Should spin up pretty fast with a lightweight flywheel also. No need for harmonic dampener or dual mass flywheel to take up the 3.0 cranks harmonic vibrations. And cheaper then building a 3.0. Or sleaving a 2.5.

V2Rocket

will be interested to see your setup.
for the high-cr 3.0 i was thinking 2.7 pistons with shorter other-brand rods on a modded 3.0 crank, also considered getting the dishes machined a bit bigger to bring cr down.

Raceboy

I am running my 2.5 16v turbo at 7000 and for the peace of mind at least it makes a difference
Of course, my project has been sort of a budget build in a manner to use as many stock components as possible to have a replacement easy to find if needed. That means no offset ground cranks, sleeved blocks etc. So far it has been holding on very well at ~500hp and you can be sure it sees WOT at least half of the time
Just my 2c.

blade7

It wont be cheap if the pistons melt, still I have a spare set under my bench I could sell you cheap .

Humboldtgrin

I was thinking about the Pistons melting as well. So I called North America Mahle and asked them for a quote for forged 2.7 stroke 104 mm bore 7.5:1 compression and they said about $1000. I'm thinking I might just go with them and not machine mine. Just that piece of mind is worth the $. And I want to boost to 18psi. So yea your right the machines ones may melt. Best get ones that are made for the purpose intended for sure.