6M and 7M differences???

[fatboy13]

I'm currently undertaking an engine conversion in my MS55 Crown, and i was putting in what i thought was a 7MGE and have found out that it is actually a 6M block with a 7M head on it... just wondering if there are any differences between a 7M and 6M block? and would having a 7M head on a 6M block have any advantages?? power wise or otherwise...

thanks alot

Ben

[thechuckster]

not much difference except castings near where cranks counter-weights swing by.

there are differences in the position of counter-weights in 7M cranks as well

(persons more with more knowledge might chip in here)

[CrUZida]

Early 7M's use a 6M crank
Late 7M's use an unstamped crank.

Mid/Late 7MGTE's have oil squirters.

The blocks are pretty much identical, except for almost everything that bolts to them.

Are you sure its a 6M block? (obviously stamped 6M 00xxxxx)
It would have to have 7M pistons/rods in it.

Wouldn't matter either way though.

[hamgatan]

correct me if im wrong someone, but doesnt the 6M have the same compression ratio as the 5M (9:2:1), only that its stroked out to 3 Litres instead of 2.8.. theyre the same head anyway.. 6MGE is literally a 7M Bottom end with a 5M top end. Which means 12 Valves off memory..

however the compression ratio in the 7M is the same (except on GTE its less..) and its a 24 Valve head to boot.. Thus there shouldnt really be any major difference in the 7M/6M hybrid you have now since the 6M was basically a 7M bottom end anyway..

I cant understand why they would have put those two together either.. doesnt make sense..

[CrUZida]

I cant understand why they would have put those two together either.. doesnt make sense..

The 7M block probably had a rod thrown through it at one stage, and he happened to have a 6M block just lying around.

Its about the only explanation I can think of.

[fatboy13]

so in other words i have a pointless hybrid... how unfortunate i hoped it may be some super engine or something exciting like that... though it would be interesting to find out why.... its definately a 6M block... so are the counterweights different does anybody know??? and theres no other differences anyone can think of???

[hamgatan]

The 7M block probably had a rod thrown through it at one stage, and he happened to have a 6M block just lying around.

Its about the only explanation I can think of.

Or had a warped head at some stage and decided to go with a 7M head thinking that 24 valves would make a major difference.. well, it would make some difference, but not the kind of difference a GTE would..

on a side note, dyno the engine after you put it in. it would be interesting to see the power output you're getting over a stocko 6M.. if any. the dyno will tell all..

[fatboy13]

so should i expect somewhere around the power output of a 7M maybe a little more?? it will prolly get dynoed at the next dyno day... not this weekend... nooooo chance haha....
should i worry about anything due to the differences???

[hamgatan]

the only thing i can think of is that if a thicker MHG or something has been fitted it would throw out the compression ratios..and would need to be tuned accordingly but other than that no, it should perform very similar to a stock 7MGE.. only marginally different.

[CrUZida]

If the previous owner has used a stock 6M block with the stock 6M pistons, then who knows what will happen.
They both run the same static compression, but that was relative to their respective combustion chamber volumes, which may or may not differ.

If the previous owner has replaced the 6M rods/pistons with 7M items, then for all intents and purposes it will perform as per a stock 7M

[fatboy13]

should be interesting to find out the results.... if anyone else can shed some light on things it would be much appreciated...

[CrUZida]

Shine a light down the spark plug hole and see if you can see 2 or 4 flycuts.