94AWDcoupe

iTrader: (125)

I have not been a fan of long rod motors. The theoretical gains are not worth the effort in my opinion. The biggest drawback to making rod longer is increased dwell time at TDC. This gives detonation more time to happen. so short rod ratios are are good thing in turbo motors.

The stock 4g63 rod length is 150mm. The 4B11 stock rod length is 143.75mm!

Migsubishi

iTrader: (38)

Hmm very interesting...

bluedevilx

never realized that good info

KX250Fmotoracer

Don't forget the 4B11T's stroke is also shorter.

a 150mm rod in a 88mm stroke 4G63T = 1.70 rod ratio
a 143.75 rod in a 86mm stroke 4B11T = 1.67 rod ratio

So its not as big of a difference as it seems

94AWDcoupe

iTrader: (125)

The rod ratio didnt change much. but still begs the question why they went shorter and not longer.

Aby@MIL.SPEC

iTrader: (161)

on the flip-side to that, 1 can also believe that cylinder scavenging would be enhanced with a slightly longer dwell @ tdc....which would lead to a better / cleaner environment for the next firing event.

discopotato03

The bore and stroke are 86mm and I think Mitsy would have tried to make the engine as light and as compact as possible . They've gone up 1mm in bore and down 3mm in stroke so together with the slightly shorter rods lost some rotating and reciprocating mass .
I think one of the shortcomings of the 4G63 is the 85mm bore and not much chance of increasing it significantly because of the close bore centers .

I think flow dynamics would be tightly controlled by the continuous VVT in 4B11T engines .

A .

wreckless969

iTrader: (11)

I think the fact that the 4g63 is as old as it is and as over engineered as it is means we shouldn't be so critical of it's "short comings" in terms of comparison to the motor that was designed to replace it...

Teal2nnr

iTrader: (7)

^^ I think its just an observation, since LR motors are gaining popularity.

wreckless969

iTrader: (11)

I was more refering to the post speaking of the 4g63's "shortcomings".

discopotato03

I'm not saying they are garbage just comparing what they have to what the later engine has .

A .

R/TErnie

iTrader: (32)

Just a guess...

The 4B11T's cylinder head is taller and therefore they had to make the deck height and block more compact in order to fit it under the hood? Not to mention they run the charge pipe over the head. :P maybe an idea. I've seen stuff implemented at the OEM level for faaaar less reasonable things.

Ted B

iTrader: (6)

We have a winner.

Dimensions like bore spacing, deck height, etc. are all seleced by OEMs with packaging considerations at the top of the priority list.

KX250Fmotoracer

You really think they went to a square bore because of that?

wreckless969

iTrader: (11)

I kinda agree going to a square bore for that seems a little ridiculous. Considering the bore was pretty much predetermined long before prototype X back when the block was called the world engine and it was in development with Hyundai and Chrysler. I doubt the Mitsu engineers were like "Well lets give it this bore so we can have this stroke so it fits onto this head that hasn't even been designed yet."