Getting more power from 6g74

Post by **hokey** » Mon Mar 20, 2006 1:37 pm

G'day,
my dad's mate has just blown the big end on No 6 in his pajero. he is getting the engine rebuilt and was wondering if you guys would know of some common mods to increase low down. just mods that make it better in the bush.
Cheers, Calvin

Post by **-Scott-** » Mon Mar 20, 2006 3:26 pm

From my limited experience with modified motors, to increase torque:

Increase compression (obviously, don't go too far.) If you shave heads/block it will alter the cam timing, which then needs to be corrected.
Port matching can help, but I don't know how pedantic you should be.

Do Not:
Lighten the flywheel.
Increase your valve overlap.
Install larger valves/larger lift.

Theoretically, increasing intake air velocity is good for low-down torque (something to do with better turbulence/mixing in the chamber.) Blocking one intake valve at low revs is supposed to be good, because the other port then gets higher velocity - I'm not sure how you'd do this.

Otherwise, the generic "blueprint and balance" is probably worth it, as is a decent dyno tune (based on Frank's experiences.)

Cheers,

Scott

Post by **hokey** » Mon Mar 20, 2006 3:46 pm

Thanks for the advice. you pajero drivers seem to leave your engines pretty stock. i guess they have pretty good power in stock form. anyone else with first hand experience with these engines? are these engines run interfernce heads? could someone tell me what stock compression is? maybe just some work on the ports and shaved head for higher compression.
Cheer guys

Post by **Adomw** » Mon Mar 20, 2006 4:23 pm

Increase your exhaust 1/4' and fit a high flow cat

Fit a bored throttle body from RPW

The stock comp is 1:9.5

And it's a free spin (non interferance motor)

Ado

Post by **hokey** » Mon Mar 20, 2006 5:04 pm

cool thanks for the tips Adomw

Post by **DougH** » Mon Mar 20, 2006 11:52 pm

Adomw wrote:Increase your exhaust 1/4' and fit a high flow cat

Fit a bored throttle body from RPW

The stock comp is 1:9.5

And it's a free spin (non interferance motor)

Ado

Since when was a 3.5 a free spin. The 3.5 DOHC is NOT, I repeat NOT a non interference engine. I have the bent valves to prove it.

Post by **hokey** » Tue Mar 21, 2006 10:06 am

alright thanks for the info doug. i guess if you have the bent valves you must be more correct

Post by **DougH** » Tue Mar 21, 2006 12:43 pm

hokey wrote:alright thanks for the info doug. i guess if you have the bent valves you must be more correct

I have the DOHC, it may be that the SOHC version in NI, but I never heard that.

The 6g73 is non interference as long as you don't over mill the heads, but as far as I know the 6g74 is not.

It makes getting the timing right more involved. Can't leave the crank at TDC because if the cams slip with lining up you will hit a valve into a piston when it turns under valve spring force.

I actually bent my valves by trying to turn the crank with the cams lined up... took out the two #3 intake valves. Do not turn the crank like the directions state. They must have fawked them up bad when translating from Japanese to Engrish.

Post by **NLShorty** » Tue Mar 21, 2006 1:22 pm

Put a supercharger in it

Post by **hokey** » Tue Mar 21, 2006 3:09 pm

he doesn't want to go FI. too much work involved. if he does shave heads we will just do a dummy fit to make sure everything clears

Post by **-Scott-** » Tue Mar 21, 2006 6:33 pm

Doug, please forgive my ignorance, but what's the 6G73? I'm only familiar with the 72 and 74.

Cheers,

Scott

Post by **Bitsamissin** » Tue Mar 21, 2006 7:17 pm

It's a typo Scott.
3.0 6G72 - 12 valve SOHC = free spinner
3.0 6G72 - 24 valve SOHC = interference
3.5 6G74 - both DOHC & SOHC 24 valve = interference

Post by **Adomw** » Wed Mar 22, 2006 10:55 am

Guys this free spin thing has got me

I have a 6g74 (stock) and I'm sure it's a free spinner

I know this as I have done full rotations of the crank with the belt off and I've rotated all the cams with the crank at TDC on number one pot with no clashes

My local service centre's belt source has huge red warnings on the packageing of interference belts and the one for mine has no such warning

But I'd rather err on the side of safety and assume that I was dreaming and assume that the motor is an interference type

Ado

Post by **Zute** » Wed Mar 22, 2006 9:30 pm

this may be a little off topic, but do the 24valve motors and 12valve, have flat or shaped piston tops ?
Can you fit 3ltr heads on a 3.5ltr block ?

Post by **DougH** » Thu Mar 23, 2006 1:01 am

Zute wrote:this may be a little off topic, but do the 24valve motors and 12valve, have flat or shaped piston tops ?
Can you fit 3ltr heads on a 3.5ltr block ?

Sorry typo 6g72...

You might be able too but I am not sure. The coolant and oil passages are different on the heads, I was comparing the head gaskets the other day.

The 3.5 pistons have small valve indents but they are more flat in comparison to the 3.0 pistons.

Post by **hokey** » Mon Mar 27, 2006 4:18 pm

NLShorty wrote:Put a supercharger in it

did you have a supercharger for sale atm??

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Getting more power from 6g74

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