RPM limit for AU bottom end?

**Stav** · 24-12-2006, 08:43 AM

Does anyone know what rpms the bottom end is good for on the au six ?

INJECTED_250 · 24-12-2006, 08:56 AM

i have an au bottem end in my eb, With gas theres no rev limit, it see's 6500 (needle on dash) a fair bit and hasnt broken yet.... been trying to kill it

**Stav** · 24-12-2006, 09:35 AM

Cool. I am getting some stiffer valve springs so hopefully its duty will get me to 6200 rpm.I am planning to have a bit more power at 5900-6100rpm.

NeishaXR8_347 · 24-12-2006, 10:08 AM

Theres always a little more that can be found hiding somewhere lol, N/A i think they would handle 6500 easy, with the cross bolted mains and all its fairly ridgid, The only thing i dont like about these AU 6's is the crank is a very heavy item but is counter weighted to suit. After playing around with them a bit even tho they dont give much trouble i can see a failure occuring on a conrod bolt eventually, ive measured them once they have been stripped and they are like an egg shape usually ranging between 0.0005" to anywhere around 0.0015". If something goes bang just get another one i guess.

Shaun

**Stav** · 24-12-2006, 10:22 AM

Thanks man. I am looking at rev limt raised to 6200 rpm.My hopes are that this exhaust I am thinking about kicks very hard at 5800rpm and up. It should be just what the doctor ordered.

EvilChief · 24-12-2006, 03:45 PM

i used to run my AUI6 around the 6000rpm mark on standard injection and high lift cam without too much trouble using the XR springs. never had a hickup

blackers10 · 24-12-2006, 04:45 PM

what real benefit would there be from making the VCT I6 rev harder??
would you need some specific extractors and cam profile to make real use of the new higher rev limit?
what about tail shaft and gearbox issues especially in the LWB models with increasing the RPM at which it spins all?

im guessing a bigger fuel supply would be needed?
would we need a bigger fuel pump or will the standard one suffice for the limit of our motors?

hope thats not TOO many questions. but it is pretty much on topic

FS5 · 24-12-2006, 09:00 PM

Quote:

Originally Posted by useless

Does anyone know what rpms the bottom end is good for on the au six ?

you can be the guini pig mate , if it all holds together ,i reckon there will be a few following suit.

afer rebuilding one ,they are definately built to handle a rev or 2 .

xr8ute · 24-12-2006, 09:05 PM

I think it would be the top end (valvesprings, and HLA's) that might restrict rpm more than anything else...

But rpm is pointless if the cross-section of the intake is too small, making the air speed in the ports too high to the point where it cant turn corners anymore (referred to as "sonic choke", "velocity choke", or "power limiting port area").

So...the hardware has to support it, and the airflow has to support it.

xr8ute · 24-12-2006, 09:09 PM

Quote:

Originally Posted by blackers10

what real benefit would there be from making the VCT I6 rev harder??

More revs, means it can pump more air....more air means a bigger bang...more hp

Quote:

Originally Posted by blackers10

would you need some specific extractors and cam profile to make real use of the new higher rev limit?

Both would need to match the amount of air the engine wants to move at the intended rpm range

Quote:

Originally Posted by blackers10

what about tail shaft and gearbox issues especially in the LWB models with increasing the RPM at which it spins all?

Tailshaft speed is relative to car speed, not engine speed.

Quote:

Originally Posted by blackers10

im guessing a bigger fuel supply would be needed? would we need a bigger fuel pump or will the standard one suffice for the limit of our motors?

Fuel system would certainly need to support the hp potential of the engine. I dont really know what the stock gear is good for?

FS5 · 24-12-2006, 09:37 PM

Quote:

Originally Posted by xr8ute

But rpm is pointless if the cross-section of the intake is too small, making the air speed in the ports too high to the point where it cant turn corners anymore (referred to as "sonic choke", "velocity choke", or "power limiting port area").

.

very good info.

**Stav** · 25-12-2006, 08:57 AM

The wagon occassionally does see 6000 rpm already without any dramas provided the car is warmed up.My rev limit is at 6000 currently. Dave shhh your giving everyone ideas...heheeh. Sonic choke is an interesting topic but the size of the port is not the only limiting factor. My ports are alot bigger on my new cylinder head. However there are other limiting factors which determine power band cutoff.

EvilChief · 25-12-2006, 09:42 AM

Quote:

Originally Posted by xr8ute

More revs, means it can pump more air....more air means a bigger bang...more hp

hehe in simple terms, spot on

Quote:

Originally Posted by xr8ute

Fuel system would certainly need to support the hp potential of the engine. I dont really know what the stock gear is good for?

stock gear is good for light turbo applications. I have seen figures as high as 300HP at wheels with simple FPR upgrade on a stock fuel system (injectors and pump)

there are camshaft designs out there, where the theoretical optimum rev range go as high as 6500 rpm. Matching these requirements through thorough porting of the head, as well as modification to the intake manifold are not too hard.

Biggest worry i would have is the bottom end. Due to the fact that the 4l is already a stroker from a 3.2l engine, the bore and stroke is square or close to. Looking at the RB engines, which are very rev happy, you will find its and undersquare engine, which due to its characteristics is safer to rev higher (do a google on this). The AU aready has a good main bolt and main cap design, which reduces risk of bottom end failure, however a good set of main bearing and checking the condition of rings and bores, may help to reduce the risk bottom end failure at higher stress levels.

Merry christmas

NeishaXR8_347 · 25-12-2006, 10:00 AM

My major concern wouldn't be the bottom end it would be the crappy 2 piece valves they use from factory with heavy springs behind them. If your worried about the bottom end i would get a BA or BF bottom end as they also have a mains girdle fitted which would help keep it all ridgid.

Merry Christmas.

Shaun.

EvilChief · 25-12-2006, 10:08 AM

Quote:

Originally Posted by neishaxr8

My major concern wouldn't be the bottom end it would be the crappy 2 piece valves they use from factory with heavy springs behind them. If your worried about the bottom end i would get a BA or BF bottom end as they also have a mains girdle fitted which would help keep it all ridgid.

Merry Christmas.

Shaun.

in that case u may as well use the complete bottom and top end .. 4 valves to play with

FS5 · 25-12-2006, 08:38 PM

Quote:

Originally Posted by useless

The wagon occassionally does see 6000 rpm already without any dramas provided the car is warmed up.My rev limit is at 6000 currently. Dave shhh your giving everyone ideas...heheeh. Sonic choke is an interesting topic but the size of the port is not the only limiting factor. My ports are alot bigger on my new cylinder head. However there are other limiting factors which determine power band cutoff.

go for it stav , its only $595 to replace if it goes bang and thats for a sub 100k donk .
trust me if mate you don't ,i'll be testing the bounderies early next year.rest asured you'l be the first to know .

have a most excellent holiday all.

**Stav** · 25-12-2006, 09:27 PM

Hahah good on you Jake. I will be spinning the wagon to 6200rpm before too long ..not a worry.Hopefully it will all come together properly the first time.