Max safe rpm for an au?

[Stav]

Guys..I am thinking about gving the wagon a new rev limit at 7000rpm.Am I mad? What gives at higher engine speeds? What will I break?Will I break anything?

[sly]

I heard years ago some mob in Brisbane were making DOHC heads for AU's (before the BA came out) and their engines redlined at 7000. I have NFI if they did anything to the bottom ends though.

[justa6]

you would have to have one hell of an angry na motor for it to be of an advantage i would think

[Stav]

I know the ba sixes damage oil pump gears start to give way around 6k. I dunno lets see what breaks...

[Stav]

Originally Posted by silverxr

you would have to have one hell of an angry na motor for it to be of an advantage i would think

I dont like to compare butmy brothers six cylinder bmw spun to 7500 no problems.It was not angry..I just want to try a few things

[Fireblade]

Do you have a built bottom end with new rods? I'd say you will probably throw a rod at those sort of revs in a AU six..

[Kryton]

Originally Posted by Stav

I dunno lets see what breaks...

get a video camera first.

[b2tf]

Rev it until it blows up then subtract 500rpm = safe limit

[private9]

Stav, mate stop clutching at straws and just boost it, or get a better base for quick times!

[66 coupe]

thats your best bet. au motors are only a couple hundred $ anyway...

You will find the rods / rod bolts will give way at those rpm. the 4.0's have a long stroke which makes piston speed very high

[Peuty]

Originally Posted by Stav

I dont like to compare butmy brothers six cylinder bmw spun to 7500 no problems.It was not angry..I just want to try a few things

I'd like to think that a BMW six would far better balanced than a Ford six. Not a fair comparison IMO

[sly]

Originally Posted by Stav

I know the ba sixes damage oil pump gears start to give way around 6k. I dunno lets see what breaks...

The BA oil pump drive is different to the AU. IIRC the AU pump is driven off the auxiliary shaft that drives the dizzy and Cam Position Sensor. The BA pump is crank-driven???

When BA production started, Ford finally conceded that the days of pushrod 6's were over, and redesigned the block that still had provision for an in-block camshaft right up until the AU was phased out!

The BA's oil pump drive is known to be fragile, I think you'll find the AU's is pretty robust. Your biggest issue would be electrical problems... due to conrods knocking the alternator or starter out of the engine bay

[EvilChief]

Originally Posted by Stav

Guys..I am thinking about gving the wagon a new rev limit at 7000rpm.Am I mad? What gives at higher engine speeds? What will I break?Will I break anything?

i think one of the biggets problems by the end of the day is the bore vs stroke issue. the AU is a square engine, meaning the bore is as wide as the stroke is long, which gives the 4l its torque characteristics. But that comes at the price of reduced revability. The problem in itself is piston speed, due to the massive amount of travel the piston has to do to complete its full stroke, the amount of friction between piston ring against bore would create emense heat. Plus ,with the added speed, the forcesthe gudgon (piston) pin would have to withstand would be nuts. i would say it would tear the gudgon pin clean out of the piston at full song.

if we look at the engine characteristics of a RB or 2J engine, basically "similar" in design, the stroke is not anywhere as long as the one of the 4l. thats what allows those engines to do the revs they do (plus the added head flow characteristics and DOHC).

Anyway while i am rambling, to overcome these issues, of course stronger internals (pistons, conrods and pins) but also blue printing and a good balance, would allow you toe rev the engine beyond its normals rev range.

BTW sly the blokes you are talking about is crocdale in Townsville, i spoke to him just after he released the prototype in his sons AU. he offered me a second head, but i didnt quite had the cash for it. it was still a 12 vakve head but twin cam, in quite refined flow design of the head and bigger valves. Same bloke was heavily involved in the twin cam head developments for the BA. from what i know he is in england now ...

[T-Pak Addict]

Originally Posted by sly

Your biggest issue would be electrical problems... due to conrods knocking the alternator or starter out of the engine bay

HAHAHAHA lmao......... classic

[Stav]

Hmm.So the blocks would go bung eh? After my first posting I had flicked through my manuals and noted that even the standard xr6t boosted cars have peak power at around 5200 rpm.The vct i6 au and hp motor peaks at 5000rpm. Without making premature assumptions it does seem these motors wont make much more power past this rpm area. Sure we can make the cars somewhat faster based on revs but then the cost of blowing an engine and fixing it seems to be a waste.

If say my power too peaks around 5000 to 5500 rpm then my current limit of 6250rpm is about right. Perhaps a slightly bigger convertor from the 2500 rpm unit to 3500 would be a wiser investment.

[Sox]

Originally Posted by Stav

I dont like to compare butmy brothers six cylinder bmw spun to 7500 no problems.It was not angry..I just want to try a few things

Stave my friend, you have your hand on your old fella yet again. :

I have a little Beemer 328i, which is a 2.8L six pack, the engine characteristics aren't even close to the 4L Ford.
The 2.8 is as smooth at 6500rpm as it is at 2000rpm, it's like a turbine in how smooth it is. The way the power builds is also different, it just continues to accelerate harder and harder as revs build, at no point does it taper off. It just begs to be revved harder.

Now my DEV5 XH was revvy for a 4L Ford, however it was on another planet compared to the Beemer.
My XH had a AU bottom end, with new bearings, and it was balanced, yet at 5800rpm it still felt like it wanted to explode compared to the Beemer.

The 4L are hirribly undersquare, that is, much longer stroke than the bore, which simply doesn't encourage high revs. The rod angle ratios are terrible, which increases side loading on the pistons.

With a standard and tired bottom end like you have, I'm surprised you haven't lunched your engine already. At 7000rpm you may as well throw a hand grenade under the bonnet.

Get the bottom end balanced, shot peen the rods, fit stronger rod bolts, better/lighter pistons, and fit new bearings, and you may have a chance.

[Stav]

Originally Posted by Sox

Stave my friend, you have your hand on your old fella yet again. :

I have a little Beemer 328i, which is a 2.8L six pack, the engine characteristics aren't even close to the 4L Ford.
The 2.8 is as smooth at 6500rpm as it is at 2000rpm, it's like a turbine in how smooth it is. The way the power builds is also different, it just continues to accelerate harder and harder as revs build, at no point does it taper off. It just begs to be revved harder.

Now my DEV5 XH was revvy for a 4L Ford, however it was on another planet compared to the Beemer.
My XH had a AU bottom end, with new bearings, and it was balanced, yet at 5800rpm it still felt like it wanted to explode compared to the Beemer.

The 4L are hirribly undersquare, that is, much longer stroke than the bore, which simply doesn't encourage high revs. The rod angle ratios are terrible, which increases side loading on the pistons.

With a standard and tired bottom end like you have, I'm surprised you haven't lunched your engine already. At 7000rpm you may as well throw a hand grenade under the bonnet.

Get the bottom end balanced, shot peen the rods, fit stronger rod bolts, better/lighter pistons, and fit new bearings, and you may have a chance.

In your opinion..what would be the optimum destroked capacity for maximum revs? Would this car make more power and torque than what we have ?

BTW ..dont go into politics...

[66 coupe]

4.1cc nitro motor, around 40,000 rpm,
obviously it doesnt have a valvetrain to keep up with that kinda rpm...

Stav, exactly what are you set out to acheive?
If you want to wind rpm, its not all about the stroke...
The valvetrain comes into account, cam, springs, and the valves themselves etc etc.

Then you have the matter of flow, spark and all the other variables.
You cant have an 11 sec car for $0

[Sox]

Originally Posted by Stav

In your opinion..what would be the optimum destroked capacity for maximum revs?

I'm not sure, I'd probably tend to leave it at the current dimensions. Just make it as efficent as possible, which you're trying to do anyway.

Would this car make more power and torque than what we have ?

It might make more power at very high revs, though it would probably not accelerate as quick in your big tank. Your car is relying heavily on low to mid range power as well because of the weight. A smaller capacity engine will only go slower at low rpm's.

If it were a pure drag car/engine, in a cortina or similar, then the smaller capacity might make sense, as spinning to 8000rpm and making 400hp but making bugger all below 5000rpm is ok in that application.

Reality is, you need to throw it on a dyno now and see where peak power is anyway. I suspect it's not over 6000rpm. In that case, it's pointless revving beyond 6300 anyway.

BTW ..dont go into politics...

Why ever not?? :

[Stav]

Originally Posted by 66 coupe

4.1cc nitro motor, around 40,000 rpm,
obviously it doesnt have a valvetrain to keep up with that kinda rpm...

Stav, exactly what are you set out to acheive?
If you want to wind rpm, its not all about the stroke...
The valvetrain comes into account, cam, springs, and the valves themselves etc etc.

Then you have the matter of flow, spark and all the other variables.
You cant have an 11 sec car for $0

Just wanting to find out what is doable and if it is worth the effort. I like to find the boundaries. If revving the car harder to 7000 rpm will or will not make it faster with more power .This was my question.

[Stav]

Originally Posted by Sox

I'm not sure, I'd probably tend to leave it at the current dimensions. Just make it as efficent as possible, which you're trying to do anyway.

It might make more power at very high revs, though it would probably not accelerate as quick in your big tank. Your car is relying heavily on low to mid range power as well because of the weight. A smaller capacity engine will only go slower at low rpm's.

If it were a pure drag car/engine, in a cortina or similar, then the smaller capacity might make sense, as spinning to 8000rpm and making 400hp but making bugger all below 5000rpm is ok in that application.

Reality is, you need to throw it on a dyno now and see where peak power is anyway. I suspect it's not over 6000rpm. In that case, it's pointless revving beyond 6300 anyway.

Why ever not?? :

I think I will put my last round of mods into improving the power in the rev range I have.

[66 coupe]

if you had the bottom end setup to withstand 7000 rpm, you would have to get a cam suited to that rpm range, and springs, and valves that are strong enough to withstand that amount of rpm with those harder springs. Which would also mean you have to do away with the hyd HLA and go solid. Then you would likely need to upgrade injectors to support the fuel at those rpm providing the bottom end infact does hold together. Once you've got past those few hurdles, then you would probably need to alter the serp belt setup, so its not boiling the power steering fluid, cavitating the water pump, and spinning the alt too hard. Then you will probably find a rod will kick out anyway. There is a lot that comes into play, and i doubt anyone has had a 4.0 which they could reliably, if at all wind up to 7000 rpm.

[Stav]

Well...I have found myself withno other questions after all these years Thanks for the input.I think I am nearly ready grass hopper

[Sox]

Originally Posted by 66 coupe

if you had the bottom end setup to withstand 7000 rpm, you would have to get a cam suited to that rpm range, and springs, and valves that are strong enough to withstand that amount of rpm with those harder springs. Which would also mean you have to do away with the hyd HLA and go solid. Then you would likely need to upgrade injectors to support the fuel at those rpm providing the bottom end infact does hold together. Once you've got past those few hurdles, then you would probably need to alter the serp belt setup, so its not boiling the power steering fluid, cavitating the water pump, and spinning the alt too hard. Then you will probably find a rod will kick out anyway. There is a lot that comes into play, and i doubt anyone has had a 4.0 which they could reliably, if at all wind up to 7000 rpm.

Yup, what he said. :

[sly]

Originally Posted by Stav

After my first posting I had flicked through my manuals and noted that even the standard xr6t boosted cars have peak power at around 5200 rpm.

The XR6T's power delivery is carefully "managed" though. There was an article some time ago where the mag got hold of the SCT/CAPA tuning software and had a look at the BF's tune, in both a NA and turbo car. They found that up to 5000rpm the cam phasing settings chased power as revs rose, then between 5000 and 6000 the cam phasing went into reverse, tapering power off again.

This is why it's easy to pick up extra power in a BA/BF through a flash tune. Just keeping the cam advance (and overlap in a BF) steady from 5000 to 6000 keeps the power increasing up to redline.

[EvilChief]

Originally Posted by sly

The XR6T's power delivery is carefully "managed" though. There was an article some time ago where the mag got hold of the SCT/CAPA tuning software and had a look at the BF's tune, in both a NA and turbo car. They found that up to 5000rpm the cam phasing settings chased power as revs rose, then between 5000 and 6000 the cam phasing went into reverse, tapering power off again.

This is why it's easy to pick up extra power in a BA/BF through a flash tune. Just keeping the cam advance (and overlap in a BF) steady from 5000 to 6000 keeps the power increasing up to redline.

yep, not only the cam phasing plays a huge part in that but also the torque control through the TB controller. threy actually use cam retard as a primary rev limiter and ignition cut as a secondary limiter