6 or 7 bolt short block?

[LumpyVR4]

Next year I'll be getting a new engine built. I've decided on a 8.5:1, 94mm stroker with 156mm rods.

The only problem with this combo is in a 6 bolt I have to use an Eagle crank, Manley I beam rods (which are going to be overkill for my 400+ whp target), and Manley pistons.

If I use a 7 bolt bottom end there are several options for crank and rods. Manley makes a crank 2.5 kg lighter than Eagle, and at my power goal H beam rods would be quite adequate and are considerably lighter than I beam.

If I went 7 bolt l'd get the 6 bolt oil squirters fitted. They come off the main oil gallery rather than the crank bearing feed like the 7 bolt does, which also have check valves in their squirters that can hang open.

The main thing that has me see sawing is, for the 6 bolt some people won't touch Eagle cranks and there are 7 bolt crank options several kilos lighter, but 7 bolts can get crank walk.

Which way would you go and why?

 

[brisvr4]

7 bolt also doesn't have provision for the front engine mount.
unless you are chasing big power I wouldn't bother building an engine that spins to over 10000rpm for anything under 700whp.
It would be a waste imo.

 

[Cranked]

Stock 6 bolt crank, a decent set of pistons and rods, with some cams 400whp on 98 is easy done. I do have a 6 bolt block complete.... For sale soon.

 

[Cranked]

Or like Tim said. A decent stock bottom end with the correct head works on e85 will get there. The block mentioned above I was going to do that, so balance shafts eliminated and ready to rumble. 150psi across the board.

 

[LumpyVR4]

I want to do the stroker is to increase the off boost response, and be able to make the power lower in the band so it's more street friendly. But I don't want to do a 100mm crank due to the increased rod angle and associated wear.
I'll admit I do tend to over spec things to make sure it's bullet proof.

 

[doo doo]

You'll need 153mm rods to run a 94mm crank with 2.3 pistons (29mm compression height). Nitto do a 153mm rod for their stroker but its 7 bolt. You can always ask if they'd do a 6 bolt 153mm rod, but get the 22mm pin so you can use 7 bolt piston options. Or you could get in touch with R&R who'll do whatever custom rod you like, but getting pricey there too.

Another thought is that if you bump up the comp ratio you'll get better off boost response, quicker on to boost and more torque lower down. Proper head work will help those things too. Boost will be more limited but with the right headwork you won't need to run as much anyway to get the same power.

Oil squirters in the 7 bolt are the same as in the 6 bolt unless you get the 2g version you mentioned, which I think you'll only find on soem auto rvr's.

If you could find a 6bolt 4g64 with oem crank in it then that'd be interesting......

 

[OLDIE]

Have been running a 100 crank with no BS for 3-4 years now with a 7200 limiter and no problems to date.
Lack of $$$ prevented me from a installing 94mm crank.

Eagle make 94 mm 6 bolt cranks https://www.extremepsi.com/store/product.php?productid=21350&cat=1365&page=1

I would also get this done if the budget allows http://www.eaglerod.com/index.php?option=com_content&task=view&id=7&Itemid=27

PS IIRC you can use the 100mm stroker pistons with a 156mm rod for a better rod ratio and less side thrust on piston skirts with the 94 crank.

And when I win Lotto I will have 2 of these 1 in my motor and 1 in a glass case in my man cave, :thumbsup:

http://winbergcrankshafts.com/index.php/mitsubishi-4g63/

http://winbergcrankshafts.com/index.php/winfinish-micro-polish/

 

[bazeng]

I'm running a 6bolt 2.4L block and a 100mm eagle crank.
Long rods and short pistons.

The other engine is a 6bolt 2.0L block and 100mm stock mitsu crank.
Std length rods and short pistons.

I think for the power you are after, you will be OK with the std 2.0L block and 100mm oem mitsu / Hyundai 6 bolt crank.

Mind you the 7 bolts will be easier to find in Australia.

 

[LumpyVR4]

As stated I wanted to do the 156mm rods for the ratio, but I don't really need it. The idea of keeping a good rod ration was just giving me a warm fuzzy feeling.
If I use 150mm rods I can use Manley H beams and Manley extreme pistons (.210 9310 pin) to get the right total length. The H beams are about 125 grams lighter than the I beams and are going to be more than I need for a street tune. Plus the H beams are about $300 US cheaper than the I beams.

Once I'm bored with the power I can put on a bigger turbo and crank the boost. :thumbsup:

 

[ENGINR]

I've been running a 2.3 stroker (2.0 block with 100mm 6-bolt 4G64 OEM crank) with standard length Eagle H-Beam Rods and CP stoker pistons with 300kw atw with *touchwood* no issues sofar.

90% of the running time this engine has seen has been on the track too.

 

[blackvr]

I think you are overthinking the " less desirable" rod angle etc etc. I've built any number of 100mm stroker 6 bolts and 7 bolts. I've yet to see anything detrimental. Mind you, the long rod variants like BAZENG do rev a bit higher before falling off the power. I've got a 4G64 6 bolt with 156mm conrods, and it revs like a 4G63 88mm stroke engine . Nice torque as well ...

 

[bazeng]

I'm looking for a spare 2.4l block also if anybody has one or knows of one...

 

[LumpyVR4]

After a little more research I have settled on Brian Crower 150mm rods. They weigh 580g, which is a little heavier than Manley/Eagle, but if you compare them to these you can see extra meat around the big end and the bottom of the beam.

I also talked to Manley about the pistons and the ones designed for 156mm stroke have sacrificed some ring land meat to allow the pin to move up as far as it has, which I don't like the sound of. There is also the reality that this is my street car so it will be below 7k 99.9% of the time, so while long rods etc are nice, they aren't really necessary.