After reading quite a few times that the 3.8 heads are better than the ones on the 3.5, and the 380 cam being the 3.5 ralliart equivalent, I was wondering has anyone done a complete 380 head and cam swap, rather than just putting in a set of cams and modifying the 3.5 heads?

If done then what results are achieved?

As far as I know no, but it seems an absolute waste. There is a much better gain to be had to use the engine COMPLETE. It does fit!

As above dont do it for the gains, the only advanatge i can see is that if you need to rebuild your heads, instead its a lot cheaper to buy 6g75 heads & its pretty easy to find them with very little ks (say 60,000) for about $500

Reasons to use the 6G75 over the 6G74

1. 6G75 has a knock sensor, this can be adapted for use on an aftermarket ECU if you choose this route
2. 6G75 runs a 10:1 CR as opposed to the 9.0:1 seen in the 6G74
3. 6G75 is rated at 175kw at the flywheel, with 3 catalytic converters! Big gains can be made from nothing more then a free flow exhaust and tune, 6G74 is rated at 155kw in "exec" trim or 163kw with "sports/vrx" (rear muffler replaced).

Changes required to fit:

- Front and rear rocker covers will need to be swapped over, COP setup removed, dizzy will need to be retrofitted and leads setup accordingly (I believe there is a cap fitted in its place on the 75)
- Engine cover will need to be removed
- 6G74 plenum, throttle body, and throttle cable will need to be fitted as the 380 uses drive by wire

Hmmm don't tempt me, I know where there a 380 motor and box for $1000 out of a s3 vrx

Fitting 6G75 heads to a "Stock" 6G74 3.5L bottom end will result in the compression dropping by a large amount.

Reason being is the 6G75 3.8L heads have a larger combustion chamber (around 60-65cc chamber volume, If my memory is correct) and this combined with the "dished" piston in the 3.5L results in much lower compression. For a reference the stock 6G74 3.5L heads have a 43.1cc chamber volume (ralliarts are approximately 44.1cc chamber volume)

Hmmm don't tempt me, I know where there a 380 motor and box for $1000 out of a s3 vrx

now you're tempting me! but i think i'll wait a few thousand km's before i do a 380 motor conversion

Hmmm don't tempt me, I know where there a 380 motor and box for $1000 out of a s3 vrx

If you don't end up buying it could you let me know the details?

Reasons to use the 6G75 over the 6G74

1. 6G75 has a knock sensor, this can be adapted for use on an aftermarket ECU if you choose this route
2. 6G75 runs a 10:1 CR as opposed to the 9.0:1 seen in the 6G74
3. 6G75 is rated at 175kw at the flywheel, with 3 catalytic converters! Big gains can be made from nothing more then a free flow exhaust and tune, 6G74 is rated at 155kw in "exec" trim or 163kw with "sports/vrx" (rear muffler replaced).

Changes required to fit:

- Front and rear rocker covers will need to be swapped over, COP setup removed, dizzy will need to be retrofitted and leads setup accordingly (I believe there is a cap fitted in its place on the 75)
- Engine cover will need to be removed
- 6G74 plenum, throttle body, and throttle cable will need to be fitted as the 380 uses drive by wire


Dean, if this is all there was to it, it'd be done in an afternoon. There's a bit more work involved than that. lol

Sump needs to be swapped. Sump also needs to be modified. Timing belt covers need to be modified or all timing gear needs to be swapped. Bosses on the rear of the block need to be ground off if going into an AWD. Alternater bracket, drivers engine mount bracket, dipstick placement, fuel rail, lower inlet manifold, water pipes, etc all need some modification/ swapping.

Thanks Al,

As Al has stated, there is a lot more than rocker covers and a few bits, I have done a few of these now and while it is not a hard job, for someone who has not dont this before it would be an interesting thing to watch

Also, there are other issues such as transport department. I have had mixed reactions from Vic Roads, they have told me it would need to be engineered, when I argued the point that the capacity and power gain falls within the limits of the Vic Roads rules and the engine will bolt in WITHOUT mods to mounts etc they then told me that it would be registered as is. They really dont know what is going on to be honest and I would think you would find the same thing no matter what state yo are in

I would expect as the 3.5 gets harder to get the 3.8 will become a standard bolt in approved replacement in most places for our cars as often happens

The 3.8L i built for the people in WA that was put into there KJ verada said they didnt have any issues with the motor reg... They just filled out a engine number change form (which had a section for engine capacity) and submitted it, it was processed there and then with new rego papers issued with the new number noted on it.... Much the same as the 3.5L i fitted into a TE magna a few years ago here in SA

what about engine management? use 6g75 ECU?

what about engine management? use 6g75 ECU?

Use the 3.5L computer... You basically have to cos your "retro" fitting all the 3.5L external parts (eg distributor, TB etc)

Plus the 3.5L ecu is remappable, the 3.8L ecu is not

Question - Why does the sump need to be modified, and what gets in the way using the standard 75 sump? I'm guessing headers, would pacemakers overcome this?

As for alternater, could you not use the 380 one?

What is different on the drivers engine mount?

And I can understand inlet manifolds, but why water pipes and fuel rail?

The sump sits lower with the 75 compared to the 74, the 74 headers will not clear a 75 sump without modification.

Question - Why does the sump need to be modified, and what gets in the way using the standard 75 sump? I'm guessing headers, would pacemakers overcome this?

As for alternater, could you not use the 380 one?

What is different on the drivers engine mount?

And I can understand inlet manifolds, but why water pipes and fuel rail?

The 380 uses a returnless fuel system whereas the magna has a return line from the fuel rail back to the petrol tank.. Hence why the complete 3.5L lower inlet manifold and fuel rail is used.

Sump needs to be modified internally as well as it wasn't designed to hold the 3.8l internals.

Fuel rail is different.

Alternator bracket is different.

Bracket holding engine mount is different.

In short, you use the 380 block and heads and EVERYTHNG else from the 3.5

it looks original, it all works, it all bolts up fine then as well

The sump is different, there is a minor internal mod to be done and a couple holes in the block to be re drilled

The water cross over pipe is different and you have no facility for the water pipes to the TB as well as the heater hoses are in a different location

What sort of minor internal mod to the sump?

Buy a Engine and send it to Mal :) problem solved

What would Mal charge for the work to be done?

What would Mal charge for the work to be done?
Ask Mal.

Fitting 6G75 heads to a "Stock" 6G74 3.5L bottom end will result in the compression dropping by a large amount.

Reason being is the 6G75 3.8L heads have a larger combustion chamber (around 60-65cc chamber volume, If my memory is correct) and this combined with the "dished" piston in the 3.5L results in much lower compression. For a reference the stock 6G74 3.5L heads have a 43.1cc chamber volume (ralliarts are approximately 44.1cc chamber volume)

Out of curiosity I tried calculating the CR based on the 65cc chamber volume for the 6G75 heads.

For the standard 9:1 6G74 pistons, I got 7.1:1. With the 10:1 6G74 pistons, 7.7:1...

Doing the calculation the other way, to get 9:1 with the 6G75 heads would require pistons that attained 12.5:1 with the 6G74 (43cc CV) heads...

6G75 heads and then turbo ? :)

With a 7.1:1 CR it would be lag city but when it hits you better hold on!! :shock:

Twin turbo?

With a 7.1:1 CR it would be lag city but when it hits you better hold on!! :shock:

on standard 74 pistons? yeah you'd hold on for a short time on minimal boost before something melts

;1318320']on standard 74 pistons? yeah you'd hold on for a short time on minimal boost before something melts

I was simply referring to the driveability.

I've just got 6G75 heads and injectors installed in my 6G74 engine. At the moment, all I can say is its smoother than before when accelerating. However, as the seals are still new, I can't really test the setup until the seals bed in.

Will let you know later.

I've just got 6G75 heads and injectors installed in my 6G74 engine. At the moment, all I can say is its smoother than before when accelerating. However, as the seals are still new, I can't really test the setup until the seals bed in.

Will let you know later.

I'd like to see a dyno result from this. I have a feeling it will be <100wkw. Are you planning on boosting?

Anyone Else in Aust played with this? (bump)