Hey guys.

This is the situation. I have 2 broken 6g74 motors both suspected piston damage. 1 of them is my original ralliart motor. I am currently running a standard 3.5 from a TL in my ralliart and was hoping to swap parts to make it ralliart spec.

I would like to know from those who have the knowledge, what are the exact differences.
I know the cams and valve springs are much better but is there any thing else?.
If it is just the cams how hard and costly would a swap over be. I know a few members have swapped cams form stock to ralliart or 380 cams so any input would be great.

Things that were different:
-Cams
-valve springs
-pistons

Cheap sets of ralliart pistons sometimes go on ebay if yours were damaged.

The heads were improved quite a bit, if you want to rebuild to Ralliart spec you'll need to have your Ralliart heads rebuilt and installed, and install Ralliart pistons, although if I were you I'd go oversize 10:1 pajaro pistons instead for a nice jump in power.

The heads were improved quite a bit, if you want to rebuild to Ralliart spec you'll need to have your Ralliart heads rebuilt and installed, and install Ralliart pistons, although if I were you I'd go oversize 10:1 pajaro pistons instead for a nice jump in power.

Thought headwork was a rumor.

Im not looking for improvement on power to the ralliart engine as i have a supercharger for that. I just noticed straight away the difference between the ralliart motor and the stock motor. It does not rev as freely at high end revs which i liked with the ralliart.
I am going to strap the blower back on this motor i was just wondering if it would be worth the time to give it that bit more kick at high end.

Would swapping the cams get me closer to this or is it just not worth it.
My plan is to rebuild the ralliart engine so i have the original motor for the car and eventually build something stupidly powerful with the other busted engine.
In the mean while I will supercharge this engine and see how things go. It only has 60xxx k's on it so i though i might improve it a bit before hand if practical.

The cams alone expand your powerband to about 6000 (stock dies off at 5500). If you are boosted I'd consider dropping a set of forged pistons with TH rods in though or its just going to go bang again.

If you have the cams its worth the swap, anything else would probably just be money and time.

Valve shroud is also increased over a stock exec, verada, vr-x 3.5lt

The cams alone expand your powerband to about 6000 (stock dies off at 5500). If you are boosted I'd consider dropping a set of forged pistons with TH rods in though or its just going to go bang again.

Not true, before tune my ralliart was dead at 5600 lol

I have a list of differences I found from multiple sources.
If any of this is incorrect, please let me know...

http://www.aussiemagna.com/forums/group.php?do=discuss&discussionid=17


Increased Compression (9.0:1 to 9.4:1)
Modified cylinder head combustion chambers to reduce valve shrouding and improve breathing at small valve openings.
High-Lift Camshafts (additional 10% lift)
Nitrided valve springs with a unique cross-section
Pistons - Anodised crowns and top compression ring land

Thanks for the help guys. I am in the middle of pulling the ralliart engine down to diagnose what happened.

I have a list of differences I found from multiple sources.
If any of this is incorrect, please let me know...

http://www.aussiemagna.com/forums/group.php?do=discuss&discussionid=17

Well I have a stock 3.5l with 380-ralliart cams. I haven't seen a ralliart do a quicker time than me. I reckon the only real gain was the ralliart cams witch u should swap over and you'll have your top end power back.

Depends what the problem is with the current engines though. The heads should be ok to spare over even if there is valve damage. Just get some off of another engine that he has laying around.

I've read the pistons are cause of the higher compression ratio as they have a shallower bowl. Despite a bit more of the combustion chamber missing on the ralliart heads.

Best just take the engines apart and see what's broken.

Well I have a stock 3.5l with 380-ralliart cams. I haven't seen a ralliart do a quicker time than me. I reckon the only real gain was the ralliart cams witch u should swap over and you'll have your top end power back.

But there is something about your car, it might be light or something.

Well found the problem. Yep piston all the way lol. Valves on the heads look ok so i may swap over.
Other than the pistons is the ralliart different from a stock motor in the block?.

Apparently bosses on the block are different. Shoot Madmagna a pm about that as he did a few of them and would know

The supercharger is your problem...

You'll keep blowing pistons until you have a set of forgies put in. How much boost are you running?

if you guys can get me VIN's I can get you part codes for each... (through ASA)

The supercharger is your problem...

You'll keep blowing pistons until you have a set of forgies put in. How much boost are you running?

told him that :/

Trust me i am well aware of the risks and strength of these engines lol. I will be rebuilding the ralliart motor to stock and ralliart spec just so i have it there if needed. Then i will forge build the other block. I hope to get enough knowledge and experience to do a lot of the work at home. As i am so far into this car now it would be stupid to quit now lol. Again all information on these engines will be greatly appreciated.

For tj's question i am running 7psi with a water air cooler system it also runs a 7th injector. I thought the car should handle this as it was fine the whole time i was running a sprintex kit on the car. This may have been a cause to the engine failing this time also haha. it made around the 200atw mark which i am more than happy with so now i just want that power with ease and no risk of damage. I'm not looking for 400hp just somewhere between 270 and 300 is more than enough for a reliable and practical daily thrasher.
I couldn't imagine 400+hp on a front wheel drive car but i know there are members with that power here and all i can say is HANG ON lol.

how are you logging knock?

Those pistons would be fine if you got the ecu's ignition map tuned to suit the supercharger, get bigger injectors, so you can get rid of the 7th injector.
A quick fix maybe to run standard 3.5 9:1 pistons, that may cover the fact that you have way to much ignition timing.

Cheers Dave

Dave TJ i also thought the pistons should be fine but in this case and in many other cases on this forum it just was not to be haha.
Just a quick question guys.
As i said i found the piston that was damaged lucky for me the cylinder has no marks what so ever and the ring seal looks in good order. However when i pulled the heads off i found metal on both front and rear sides. How is it possible for metal to travel from 1 side to the other?. This may be a simple answer its just im learing as i go here lol.

I have pulled apart the standard broken 3.5 also and found nothing wrong with the top of the pistons so i will use that as my practice engine to go right into the block and see whats what. Again before this time last year i barely new how to change a spark plug so all advise is welcome :D.

Oh yeah what do you guys think of these? http://www.ebay.com.au/itm/Forged-ROSS-Pistons-suit-6G74-3-5L-Ralliart-specs-/280839075168?pt=AU_Car_Parts_Accessories&hash=item4163503560#ht_1661wt_140

They shoot up through the valves, and then get sucked into another cylinder, every time vie cracked a piston, it ends up in my intake manifold
Dave TJ i also thought the pistons should be fine but in this case and in many other cases on this forum it just was not to be haha.
Just a quick question guys.
As i said i found the piston that was damaged lucky for me the cylinder has no marks what so ever and the ring seal looks in good order. However when i pulled the heads off i found metal on both front and rear sides. How is it possible for metal to travel from 1 side to the other?. This may be a simple answer its just im learing as i go here lol.

I have pulled apart the standard broken 3.5 also and found nothing wrong with the top of the pistons so i will use that as my practice engine to go right into the block and see whats what. Again before this time last year i barely new how to change a spark plug so all advise is welcome :D.

Oh yeah what do you guys think of these? http://www.ebay.com.au/itm/Forged-ROSS-Pistons-suit-6G74-3-5L-Ralliart-specs-/280839075168?pt=AU_Car_Parts_Accessories&hash=item4163503560#ht_1661wt_140

Great thanks for that

The cams and the headers were the only thing's that really made a difference with the Ralliarts. I'm not sure what the purpose of the pistons were considering they're good for maybe a 3kw gain. The cams gave Ralliarts about another 500rpm of useable power, but were still small enough to provide torque down low at the expense of losing all power after 6100rpm. I could wind my manual Ralliart to 6700rpm but there was little point.

You should try being the first person here with a high compression, boosted magna. See how long you can get a 6G74 to last with Pajero pistons and 7psi on 98RON.
You'd make damn good power before it goes bang, and who knows - maybe the pajero pistons will respond better to boost than you'd expect.

The cams and the headers were the only thing's that really made a difference with the Ralliarts. I'm not sure what the purpose of the pistons were considering they're good for maybe a 3kw gain. The cams gave Ralliarts about another 500rpm of useable power, but were still small enough to provide torque down low at the expense of losing all power after 6100rpm. I could wind my manual Ralliart to 6700rpm but there was little point.

You should try being the first person here with a high compression, boosted magna. See how long you can get a 6G74 to last with Pajero pistons and 7psi on 98RON.
You'd make damn good power before it goes bang, and who knows - maybe the pajero pistons will respond better to boost than you'd expect.

You do realise high comp with boost is extremely harsh on pistons. highest you can go in a magna in 10:1 with boost and only person as far as i know who pulled other off is rodney with 6 psi, everything else is experimental. tzaboy apparently blew up forgies with 10:1 comp and 10psi??

You do realise high comp with boost is extremely harsh on pistons. highest you can go in a magna in 10:1 with boost and only person as far as i know who pulled other off is rodney with 6 psi, everything else is experimental. tzaboy apparently blew up forgies with 10:1 comp and 10psi??

I thought Maggie did that? hahaha

I thought Maggie did that? hahaha

Haha my point is still valid

Whoa, people have done boost with 10:1s before?
Damn, i thought the highest anyone boosted was the standard Ralliart ones.

Well there you go, 10:1 and, say, 5psi through a supercharger and it should be fairly reliable.

Whoa, people have done boost with 10:1s before?
Damn, i thought the highest anyone boosted was the standard Ralliart ones.

Well there you go, 10:1 and, say, 5psi through a supercharger and it should be fairly reliable.

but 5psi through a supercharger? you will have maybe 200kwatw at the most. If you are spending 6000 on a charger setup i'd make use of it. Drop the compression to 9.4:1 or 9.0:1 and run 7-10 psi with forged pistons and either balanced rods or th rods and it should be reliable everyday.

CR of 9.0:1 and 10 psi boost is effectively 15.1 compression ratio.

http://www.jegs.com/s/tech-articles/superchargers.html&title=Superchargers+-+Blowers+-+Roots+Type+-+Centrifugal

NOTE:
"Note that for most street applications with 92 octane pump gas, you should keep your effective compression ratio below about 12.0:1."

Higher octane only, I guess. lol

It's not a matter of "I spent a lot of money on this supercharger, so I'm going to crank it up." It's more a matter of keeping the engine from detonating itself to death first time it sings in anger. But what the hell, what do I know? And it's not my engine, so go for it!

CR of 9.0:1 and 10 psi boost is effectively 15.1 compression ratio.

http://www.jegs.com/s/tech-articles/superchargers.html&title=Superchargers+-+Blowers+-+Roots+Type+-+Centrifugal

NOTE:
"Note that for most street applications with 92 octane pump gas, you should keep your effective compression ratio below about 12.0:1."

Higher octane only, I guess. lol

It's not a matter of "I spent a lot of money on this supercharger, so I'm going to crank it up." It's more a matter of keeping the engine from detonating itself tth first time it sings in anger. But what the hell, what do I know? And it's not my engine, so go for it!

Are you being a troll again or what?.. if it was equil to 15:1CR every supercharged car wouldn't work... even 98 octane is only good to serve around 11:1 compression give or take. Hence cars having knock sensors.

You do realise high comp with boost is extremely harsh on pistons. highest you can go in a magna in 10:1 with boost and only person as far as i know who pulled other off is rodney with 6 psi, everything else is experimental. tzaboy apparently blew up forgies with 10:1 comp and 10psi??

Jason was running 15-16psi with the kenne bell charger for a few weeks and it was fine. Jase put a larger pulley on to drop it back to 10psi to be safe. Tell you what, it romped. Easily spun the wheels in second if you were up it. Compression was still the same AFAIK

Are you being a troll again or what?.. if it was equil to 15:1CR every supercharged car wouldn't work... even 98 octane is only good to serve around 11:1 compression give or take. Hence cars having knock sensors.

I'm simply providing a source of information that tells me that a CR of 9.0:1 and 10 psi boost is not going to be too reliable. I wouldn't put too much trust in the ability of the knock sensor to pull the ignition timing back enough to protect the engine under those conditions.

CR of 9.0:1 and 10 psi boost is effectively 15.1 compression ratio.

http://www.jegs.com/s/tech-articles/superchargers.html&title=Superchargers+-+Blowers+-+Roots+Type+-+Centrifugal

NOTE:
"Note that for most street applications with 92 octane pump gas, you should keep your effective compression ratio below about 12.0:1."

Higher octane only, I guess. lol

It's not a matter of "I spent a lot of money on this supercharger, so I'm going to crank it up." It's more a matter of keeping the engine from detonating itself to death first time it sings in anger. But what the hell, what do I know? And it's not my engine, so go for it!

Some good reading thanks for that :)

Jason was running 15-16psi with the kenne bell charger for a few weeks and it was fine. Jase put a larger pulley on to drop it back to 10psi to be safe. Tell you what, it romped. Easily spun the wheels in second if you were up it. Compression was still the same AFAIK

Yeah not with 10:1 though.

I'm simply providing a source of information that tells me that a CR of 9.0:1 and 10 psi boost is not going to be too reliable. I wouldn't put too much trust in the ability of the knock sensor to pull the ignition timing back enough to protect the engine under those conditions.

That's bullcrap. 9.0cr with 10psi isnt insane at all.

Yeah not with 10:1 though.

Sure was. Even without the blower it was toey as all hell and certainly had some get up and go

That's bullcrap. 9.0cr with 10psi isnt insane at all.
It is when it's an engine that was never designed for boost.

XR6T Falcons - those things with the engines that are proven to last to at least 500,000kms all the time? You know, the 1000hp supporting blocks and head ones?
6psi @ 8.7:1.
Reliable w/ 15psi @ 8.7:1 on 98RON providing it has F6/late BF internals.

RB26s?
10 to 14.7psi @ 8.5:1


If it was equil to 15:1CR every supercharged car wouldn't work... even 98 octane is only good to serve around 11:1 compression give or take. Hence cars having knock sensors.
Except is IS equal to 15:1. What's a turbocharger?
It's just an air compressor. So you're pushing compressed air into the engine, which is increasing the effective compression ratio.

Atmo is 14.7psi (ish). Pushing 14.7psi through a turbo means you're doubling the atmosphere pressure, and basically doubling the compression ratio.

See here:
http://www.gtsparkplugs.com/EffectiveCompressionCalc.html

7psi @ 9.0:1 = 13.3:1 effective compression.

double post.

Rb26, boxer turbos and Evos can all run.20psi on stock pistons.

It is when it's an engine that was never designed for boost.

XR6T Falcons - those things with the engines that are proven to last to at least 500,000kms all the time? You know, the 1000hp supporting blocks and head ones?
6psi @ 8.7:1.
Reliable w/ 15psi @ 8.7:1 on 98RON providing it has F6/late BF internals.

RB26s?
10 to 14.7psi @ 8.5:1

Except is IS equal to 15:1. What's a turbocharger?
It's just an air compressor. So you're pushing compressed air into the engine, which is increasing the effective compression ratio.

Atmo is 14.7psi (ish). Pushing 14.7psi through a turbo means you're doubling the atmosphere pressure, and basically doubling the compression ratio.

See here:
http://www.gtsparkplugs.com/EffectiveCompressionCalc.html

7psi @ 9.0:1 = 13.3:1 effective compression.

9.0:1 is a RATIO, not a value for pressure. You cant add the two together like that as it makes no sense. A normal NA 6G74 engine has a PSI value of around 130.

9.0:1 compression means atmospheric air at 14.7 psi is compressed 9.0 times as the piston rises, which means at TDC just before ignition the pressure in the combustion chamber is (9.0 X 14.7 = )132 psi.

If you add 10 PSI boost, the effective atmospheric pressure with the piston at the bottom of the compression stroke is 24.7 psi and at the top the pressure goes up to 24.7 psi X 9.0, which is 222 psi.

To get 222 psi with a NA engine, you would need a compression ratio of (222 / 14.7 = ) 15.1:1

That's how it is worked out.

http://blog.1aauto.com/wp-content/uploads/2010/01/Piston1.jpg

http://www.sdsefi.com/piston17.jpg

Nice pics there max!

Just a bit of trivia - Mazda's new Skyactiv engines have a CR of 14.0:1. Rumour has it this could be even higher for the next generation. Weak rods and pistons need not apply! The next Mazda 3 SP model will be dropping back to 2000cc because of this.

http://www.mazda.com/mazdaspirit/skyactiv/engine/img/skyactiv-g_img_03.jpg

Piston out of a skyactiv engine . . . .

http://www.mazda.com/mazdaspirit/skyactiv/engine/skyactiv-g.html

http://www.mazda.com/mazdaspirit/skyactiv/engine/img/skyactiv-g_main_ttl.jpg

9.0:1 compression means atmospheric air at 14.7 psi is compressed 9.0 times as the piston rises, which means at TDC just before ignition the pressure in the combustion chamber is (9.0 X 14.7 = )132 psi.

If you add 10 PSI boost, the effective atmospheric pressure with the piston at the bottom of the compression stroke is 24.7 psi and at the top the pressure goes up to 24.7 psi X 9.0, which is 222 psi.

To get 222 psi with a NA engine, you would need a compression ratio of (222 / 14.7 = ) 15.1:1

That's how it is worked out.

This.
9:1 compression means the cylinder volume with the piston down is 9 times what the volume is when its all the way at the top.
If you run boost, the air is already partially compressed inside the cylinder when its all the way at the bottom, so if you have 14.7psi atmospheric pressure, with a further 14.7psi of boost on top of that, when fully compressed the pressure would be equal to if you were running an 18:1 normally aspirated engine, e.g. "effective" compression ratio.
So if you fit internals to give a lower compression ratio, you end up with a car that has a more managable effective compression ratio, if the intake air is at higher than atmospheric pressure.

Cams for boost and cams for NA engines are different. In a boosted engine the air is partly sucked in by the downwards movement of the piston, partly blown in by the compressor. On an N/A engine its all the downwards piston movement pulling in the next charge. If you want to run higher boost, you might want to look into cams designed to work in a forced induction setup.

There is also a lot more to it than that.