X51 but no carbon fibre box...

seeforez · 3 Feb 2017

when i was looking for my last 997 i was advised that x51 were more prone to engine issues as they run hotter and the additional rad is of little use...is this really the case
if not i am thinking i may start to gather parts to upgrade mine?

tims1959 · 3 Feb 2017

If this car hadn't lost its original airbox I think it might have been a potentially good buy (subject to inspection etc).

But an X51 car only works properly with an X51 airbox - the carbon fibre is purely for looks but the MAF sensor housing is bigger than on the standard airbox. So the MAF sensor input to the DME will conflict with the O2 sensor inputs and the engine will run with the wrong air-fuel ratio. And the airflow at high revs will be worse and a bit of power lost, thanks to the missing snorkel as GT4 pointed out.

The K&N kit would've introduced the same issue (not to mention hot air and a restrictive u-bend that belongs on a camper-van toilet). Maybe the car got a remap to compensate, who knows.

From the picture it also looks as if whoever put the 'wrong' airbox on also put on a matching non-X51 oil filler hose (or maybe that was fitted along with the old K&N kit). And I've no idea how they managed to bodge the intake hose (made for 76mm throttle body) over the 82mm throttle body...

J Holmes, agreed on the retrofit but as a prospective buyer I'd want to see an OPC receipt for the retrofit work if X51 wasn't on the VIL. With factory X51 engine numbers, the fifth digit from the right is a 4, whereas retrofits have an 'S' stamped to the right of the last digit.

I don't know the cost of an X51 airbox today but I'd be very wary of extrapolating from a 2007 price. OPC spares prices are reviewed annually and I know firsthand that they can and do rise way above inflation, especially for oddball parts like this. The 997.1 has been discontinued for nine years now so these 997.1 X51 parts are no longer in production.

I suspect the cost of restoring an X51 airbox to that car could be 10% of the asking price of the car.
Used ones don't come up for sale very often but when they do they're hardly a bargain either.
In theory a 997.2 airbox (easily available and a better design than the X51) would fit, but would need some clever one-off intake hose plumbing and a bespoke remap (MAF sensor housing again).

tims1959 · 3 Feb 2017

tordofm said:
I am impressed, :worship: not only can you provide photos of the build process but you have also met the previous owner. So it sounds like it is a car that has had a lot of money spent on it but has since had the K&N removed, a non X51 air box added and then given to a dealer that has no idea about the basics. 12 wheels indeed :floor:

Thanks Marc

This was a good find, well spotted! Hopefully the thread will help 911uk members with some useful info and not just about this particular car.

The odds are that the seller's unaware of the airbox issue (they did run out of fingers on the wheel count!) and that someone will buy this car and drive it around in blissful ignorance of the wrong airbox and other mods not declared in the ad, like the Milltek exhaust (hence the dodgy tailpipes) and the lightweight flywheel - until an OPC or a good indy gets it in for a service.

tims1959 · 3 Feb 2017

seeforez said:
when i was looking for my last 997 i was advised that x51 were more prone to engine issues as they run hotter and the additional rad is of little use...is this really the case?

Hmm I don't think there's any real grounds for that advice. I've not seen or heard of any X51 997.1s failing due to bore scoring or IMS issues.

It's true that the 997.1 X51 kit does nothing to strengthen the bores or the pistons. Mechanically it only changes the intake and exhaust systems to to allow more airflow, including intake and exhaust ports on the cylinder heads, which do also have more durable exhaust valves that can take higher temperatures.

Also true that the X51 kit comes with the third radiator (as already fitted to tipronics) which will keep the engine cooler under heavy loads in hot weather but paradoxically hotter under light loads in cold weather :?

But by all expert accounts (most notably Hartech) the risk of bore scoring seems to be less about high revs (where the X51 kit actually makes a difference) than about low revs/high torque and maybe also production quality variations in the lokasil material in the cylinder bores.

So while there's no good reason to suggest X51 cars are generally less prone to engine issues I don't think there's any good reason to suggest the opposite, certainly not for a manual as opposed to a tipronic.

Then again there are very few X51 cars about and maybe more of them have rev-happy owners that know to warm them up properly, hence a lower failure rate in practice?

Lastly all the usual preventative measures like LTT have the same effect with X51 cars as standard ones.

seeforez said:
if not i am thinking i may start to gather parts to upgrade mine

Not a bad idea but could be a very long term project

Best starting point is X51 exhaust manifolds.

If (big if) you're ok to do without the OPC warranty then you can get close with aftermarket intake parts like a BMC/K&N filter element and Helmholtz resonator delete, 82mm throttle body and plenum, and then 200cpsi cats and a good remap.
I'm sure Phil will agree :lol:

Performance-wise I think a strong-engined non-X51 car will go just as well as an X51 car with a slightly sub-par engine - there isn't a lot in it.

A bit of gratuitous information about the cylinder heads: unlike the 996 X51 kit with its (GT3-like) properly ported/gas-flowed tracts, the 997.1 X51 heads are cast with slightly more open tracts, but otherwise not reworked/ported at all. So the 997.1 X51 cylinder heads probably don't add that much to the package in terms of power increase.

GT4 · 3 Feb 2017

seeforez said:
when i was looking for my last 997 i was advised that x51 were more prone to engine issues as they run hotter and the additional rad is of little use...is this really the case
if not i am thinking i may start to gather parts to upgrade mine?

If anything they run cooler (due to third centre rad)

At any given power (ie constant 70mph), a Carrera 3.8S and a Carrera 3.8S X51 will be producing identical excess (waste) heat, whilst the X51 will have 30% more rad area (cooling).

On a race track, the non-X51 will have boiled dry at the X51's performance envelope.

In any case, fit an LTT to any and all Carrera derivatives.

I've just done mine today!

seeforez · 3 Feb 2017

thanks tims i already have done most of the stuff on that list except Helmholz resonator which doesnt do much IMO or the remap which i think has negligible benefit on these cars.

And agreed GT4 on the track etc and under load it will probably be better, i suppose it was just the logic that in the instances where borescoring (supposedly) occurs e.g off the lights - would the greater BHP mean hotter quicker?

And how did your LTT fitting go GT4 - i hope you read your guide first and followed it to the letter?

CarreraMonkey · 3 Feb 2017

It needs a label similar to this. Without doubt.

Phil 997 · 3 Feb 2017

tims1959 said:
seeforez said:

when i was looking for my last 997 i was advised that x51 were more prone to engine issues as they run hotter and the additional rad is of little use...is this really the case?

Click to expand...

Hmm I don't think there's any real grounds for that advice. I've not seen or heard of any X51 997.1s failing due to bore scoring or IMS issues.

It's true that the 997.1 X51 kit does nothing to strengthen the bores or the pistons. Mechanically it only changes the intake and exhaust systems to to allow more airflow, including intake and exhaust ports on the cylinder heads, which do also have more durable exhaust valves that can take higher temperatures.

Also true that the X51 kit comes with the third radiator (as already fitted to tipronics) which will keep the engine cooler under heavy loads in hot weather but paradoxically hotter under light loads in cold weather :?

But by all expert accounts (most notably Hartech) the risk of bore scoring seems to be less about high revs (where the X51 kit actually makes a difference) than about low revs/high torque and maybe also production quality variations in the lokasil material in the cylinder bores.

So while there's no good reason to suggest X51 cars are generally less prone to engine issues I don't think there's any good reason to suggest the opposite, certainly not for a manual as opposed to a tipronic.

Then again there are very few X51 cars about and maybe more of them have rev-happy owners that know to warm them up properly, hence a lower failure rate in practice?

Lastly all the usual preventative measures like LTT have the same effect with X51 cars as standard ones.

seeforez said:

if not i am thinking i may start to gather parts to upgrade mine

Click to expand...

Not a bad idea but could be a very long term project

Best starting point is X51 exhaust manifolds.

If (big if) you're ok to do without the OPC warranty then you can get close with aftermarket intake parts like a BMC/K&N filter element and Helmholtz resonator delete, 83mm throttle body and plenum, and then 200cpsi cats and a good remap.
I'm sure Phil will agree :lol:

Performance-wise I think a strong-engined non-X51 car will go just as well as an X51 car with a slightly sub-par engine - there isn't a lot in it.

A bit of gratuitous information about the cylinder heads: unlike the 996 X51 kit with its (GT3-like) properly ported/gas-flowed tracts, the 997.1 X51 heads are cast with slightly more open tracts, but otherwise not reworked/ported at all. So the 997.1 X51 cylinder heads probably don't add that much to the package in terms of power increase.

Yes Tim I agree , I have the x51 stainless headers from NHP in the States also 200 cell cats gt3 throttlebody and plenum and bmc sports filter with a remap and its about as close to an X51 as you can go without actually retro fitting the whole thing from an OPC as mines a tip it has the 3rd rad and fitted a LTT.
The std airbox will handle the 83mm TB and a bmc will ensure more than enough cold air, especially as the aerokit creates more of a ram air effect as the intake vents on the lid point forward.

The X51 airboxes are usually around £1500 used when they come up

It does look someone just tried to put it back to some sort of standard as it hasnt even got the smooth silicon pipe and res delete which would assist with increased airflow. I think for 3k you could turn it into a very nice car but it would still only be worth early 30k so the buyer needs to get the 3k off the price which wont be easy given a non Porsche enthusiast wouldnt know what was missing and would see it as a reasonable buy. :thumb: :grin:

GT4 · 3 Feb 2017

seeforez said:
And how did your LTT fitting go GT4 - i hope you read your guide first and followed it to the letter?

Very well thanks.

The sun was out, I had the music on and I was lying on my back under a 911.

What could be better?*

Write up to follow.

*no such thing as third time lucky: It would have been nice if the hose retaining clip hadn't corroded and the release tabs snapped, requiring an angle grinder, but hey, it's just another excuse for power tools!

Phil 997 · 3 Feb 2017

As coincidence would have it this is for sale in the for sale section, would solve everything :thumb:

http://911uk.com/viewtopic.php?t=118379

GT4 · 3 Feb 2017

Very cool.

Don't let him see this, or he might have to raise his price!

tims1959 · 3 Feb 2017

Phil 997 said:
As coincidence would have it this is for sale in the for sale section, would solve everything :thumb:

http://911uk.com/viewtopic.php?t=118379

Abracadabra! :worship: :grin:

tims1959 · 3 Feb 2017

GT4 said:
Very cool.

Don't let him see this, or he might have to raise his price!

:?: "I suspect the cost of restoring an X51 airbox to that car could be 10% of the asking price of the car.
Used ones don't come up for sale very often but when they do they're hardly a bargain either."

"£3.2K to you then guv, cheap at half the price" :bandit:

:coat:

KJD · 3 Feb 2017

"Also true that the X51 kit comes with the third radiator (as already fitted to tipronics) which will keep the engine cooler under heavy loads in hot weather but paradoxically hotter under light loads in cold weather "

Can I ask why the 3rd rad causes the engine to run hotter in cooler weather at low speeds :?:

GT4 · 3 Feb 2017

:shutup:

X51 but no carbon fibre box...

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