5m crank in a 7m, or just go 5m?

[suprarich]

The deck height is the same between the 5m and the 7m, the 5m crank with the 5m rods is a direct swap, this is why I kept asking how much power they will hold .
You would use the 7m pistons on the set up as they fit directly on the 5m rods. 2j, 7m, 5m all use a 22mm pin diameter, You can adjust the comp height with the head gasket. Did this all once before many years ago, abandoned the project due to lack of money.

 

[bigaaron]

I was only assuming the rods would be custom (or a from a different application) because I don't think anyone makes aftermarket 5m rods.
I would like to get upgraded rods just because of the fact that I don't know how much I will eventually push this engine and the stock rods are really the only weak link in the 7m I have now. I am going to take 5m and 7m cranks, pistons and rods to our machine shop and take precise measurements of everything. Then they have application books and it is just a matter of looking at rods that have the right specs. As mentioned earlier, there are v8 rods that sell for ~$250 for a set of 8! I can't see spending $700-900 for the same damn thing just because it was intended for an import engine.

 

[turbodhbar]

I didn't think that the would have different rod lenghts. I quess I'm use to sbc's all having the same rod lenght. all their gen1 no matter what displacment execpt the 400 had the same rod they just moved the pin placement on the piston.

 

[bigaaron]

Toyota likes to get as much mileage as possible (no pun intended) out of their block castings. They usually change other parts that are easier to manufacture like rods and pistons.

 

[turbodhbar]

Thanks guys I learned something here today. the discussion has been good and knowledge exchanged without ego's getting in the way or stepped on . if you can destroke a 7m with said parts then you can also stroke a 5m doing the reverse right? opens up some options for those with mkII's and 5m's .

 

[ma71supraturbo]

if you can destroke a 7m with said parts then you can also stroke a 5m doing the reverse right? opens up some options for those with mkII's and 5m's .

Toyota did it for you (it's call the 6m). That's why early 7m engines have crankshafts that say "6m" on them...

 

[suprarich]

Toyota did it for you (it's call the 6m). That's why early 7m engines have crankshafts that say "6m" on them...

You right about that, 6m is a 5m block and 5m 2v head with a 6m crank in it. 3.0l.

P.S - Don't forget to give me a call Arron!

 

[suprarich]

I was only assuming the rods would be custom (or a from a different application) because I don't think anyone makes aftermarket 5m rods.
I would like to get upgraded rods just because of the fact that I don't know how much I will eventually push this engine and the stock rods are really the only weak link in the 7m I have now. I am going to take 5m and 7m cranks, pistons and rods to our machine shop and take precise measurements of everything. Then they have application books and it is just a matter of looking at rods that have the right specs. As mentioned earlier, there are v8 rods that sell for ~$250 for a set of 8! I can't see spending $700-900 for the same damn thing just because it was intended for an import engine.

Hey Arron, one good thing about the 5m crank is that you will find that all the rod journals are the same size. 7m #3 IIRC :biglaugh:

 

[bigaaron]

No way! He should put it in his Ford Ranger.

The Ranger has already had more Toyota engines in it then any Ford ever! (in the bed) :biglaugh:

Hey Arron, one good thing about the 5m crank is that you will find that all the rod journals are the same size. 7m #3 IIRC :biglaugh:

So did they sell the good crank machine and then buy a cheap one to make the 7m cranks? :biglaugh:

I like this idea. Do a 2mm bore on the block, and have an 85x85 square bore setup. Oh snap, that's awfully close to another engine I can think of

That sounds like a winner! My oldschool JZ :love:

85mm pistons with 85mm stroke would probably put it back to almost 3.0L, yes?

 

[bigaaron]

This is pretty cool!:
Engine Displacement Calculator


85mm (3.346") bore and stroke would make it a 2.89L engine.

7m with 91mm X 83mm would be 2.95L. I guess there is a little extra volume from the head also.

Here's the 7M guru question of the week:
How many CC's are there in a 7M head?

 

[Doward]

If nobody has it on hand, tomorrow I'll CC the spare head I've got holding my bed up

I don't know if you will be able to find forged 5m rods - but if they are indeed 6.1" rods - well, there you go! Seems the 7m's rotating assembly was a stroked 5m, (aka 6m) with shorter rods to keep the pistons in the block.

If that is the case, you may find the 7m and 5m pistons are physically identical, with the exception of the 4 valve reliefs vs 2.

In which case, I'd see how much machine work would be needed to use GM rods in there! LS1 rods, not Gen1 or GenII rods - you need GenIII

6.1" scat forged rods, you'll be getting forged pistons anyway, right? Have them use a .927" pin instead of Toyota's .866" pin.

Pauter lists the 7m rod as having a .975" big end width. Those $250 scats are listed as .940" width. So you've got a .035" gap to take care of

 

[soapra]

I was looking at some of the Vegas dyno sheets and I looked at 5MGE mk2's Vs 7MGE mk3's and for some reason all the 5M's were making more power then the 7M engines (GE'S). There's good ideas in here. We are going to have alot of fun!

 

[tig321]

How many CC's are there in a 7M head?

I've only read the end of this thread, so I'm not sure if I've missed something. If your talking about the combustion chamber volume, stock is 40cc's. I just measured mine this evening.

I've always wondered about destroking a 7m. It sounds like a very cool Idea. It would make for a more resposive/quick revving engine wouldn't it? That would be awesome.:naughty:

 

[ma71supraturbo]

7m with 91mm X 83mm would be 2.95L. I guess there is a little extra volume from the head also.

But displacement is only the volume occupied by the moving piston. A larger combustion chamber just lowers the compression ratio -- it doesn't increase displacement.

Here's the 7M guru question of the week:
How many CC's are there in a 7M head?

I believe its around 40cc

 

[soapra]

resposive/quick revving engine wouldn't it? That would be awesome.:naughty:

You Sir are right!

Some of us always seam to get lost in torque and displacement. Response plays a big roll on how power comes on and how a turbo spools.

 

[bigaaron]

But displacement is only the volume occupied by the moving piston. A larger combustion chamber just lowers the compression ratio -- it doesn't increase displacement.

Engine displacement is defined as the total volume of air/fuel mixture an engine can draw in during one complete engine cycle. If you bore the cylinders larger for larger pistons then you are increasing the displacement, and you would use a thicker headgasket to keep the compression ratio the same.


We see a lot of 7M pistons with excessive wear on the sides of the piston skirt parallel with the pin, which is also visable on the cylinder walls. I think that less stroke with longer rods would cause less friction and wear since the maximum angle of the rod would be less.

 

[drjonez]

heh. good to see someone is finally going to do something w/my idea....

 

[suprarich]

I believe its around 40cc

You are correct sir,

stock head is 40cc
piston is -16
stock hg is .056 or 1.2mm

 

[suprarich]

drjonez heh. good to see someone is finally going to do something w/my idea....

HKS did this back in the 80's with their 7m mk3 dragcar and I did this very project like 4 years ago!:naughty:

Engine displacement is defined as the total volume of air/fuel mixture an engine can draw in during one complete engine cycle. If you bore the cylinders larger for larger pistons then you are increasing the displacement, and you would use a thicker headgasket to keep the compression ratio the same.

That is a good point that you bring up Arron, most people don't realize that an increase in displacment squeezed into the same cc head will result in higher psi.

 

[turbodhbar]

Are all 5m cranks forged ? Since they have the same rod journal dia. and or 6mm shorter stoke they would have 3mm more overlap between the crank pin and the rod pin which would be a stronger crank ? If the crank is stronger and the throws shorter would it not be easier to balance and have less harmonic vibration? this would allow for higher rpm operation?