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Porsche 996 Fast Road / Track Car - Oversize Build

Hi Ned, I think the factory figures for the 3.4 are 257ft/lb at 4600rpm, but the curve is more of a peak at this value sloping away above and below. The 3.6 has a broad shelf near max torque from 3800rpm to 6100rpm. I took the car out again this morning for a spirited run through the Scottish Borders in the warmer, drier conditions and actually - contrary to my previous statement - it pulls hard right to the redline. My tendency is to shift up at 6500-6700 simply because I am unfamiliar with the 6MT box in the car and the throw seems a bit long (and dare I say, imprecise!?) for my liking. If you shift a bit earlier (6000-6500rpm) it gets you back into that really strong mid-range punch which almost feels like it's got a light-pressure turbo. This is a certainly a good way to make progress in any gear/situation but maybe not quite as characterful as the 3.4?

BTW I think you can be amazed at your dyno figures tbh. I bet your car flies if you keep it in the power band. Have you weighed it recently?
 
Interesting thread. I have just started a similar project on a 2nd engine. I am still at the research stage and collating material and figures on where to go. Have the paper written by Barry at Hartec on oversizing and will likely take this route. My aim is not to build a track focused car, but to build some reliability in to the M96 and enjoy the car for the next decade or so on road trips & the odd track.

Thanks for sharing your figures as this at least seems testing various setups shows pro/cons. Whilst many knock the m96, it shows that Porsche had spent some time developing the basic package and 'bolt-on' mods hinder performance - unless of course you have very deep pockets.
 
dc2100k said:
Hi Ned, I think the factory figures for the 3.4 are 257ft/lb at 4600rpm, but the curve is more of a peak at this value sloping away above and below. The 3.6 has a broad shelf near max torque from 3800rpm to 6100rpm. I took the car out again this morning for a spirited run through the Scottish Borders in the warmer, drier conditions and actually - contrary to my previous statement - it pulls hard right to the redline. My tendency is to shift up at 6500-6700 simply because I am unfamiliar with the 6MT box in the car and the throw seems a bit long (and dare I say, imprecise!?) for my liking. If you shift a bit earlier (6000-6500rpm) it gets you back into that really strong mid-range punch which almost feels like it's got a light-pressure turbo. This is a certainly a good way to make progress in any gear/situation but maybe not quite as characterful as the 3.4?

BTW I think you can be amazed at your dyno figures tbh. I bet your car flies if you keep it in the power band. Have you weighed it recently?

I hadn't looked much at the curve compared to a standard one tbh. I must do that. This car is my only experience of a 911 and the exhaust was on it when I bought it so I can't compare how it is to a standard one.

I'm on a little weight saving mission atm but it's not going to be too drastic
 
Crash can you pm me a number about the flywheel? For some reason my messages aren't sending
 
This is a great thread (maybe some more pictures please?). How did you lose 100kg from the interior? I reckon that 350bhp from the 3.4 is a great effort. :thumb:

It seems to me that a lot of the real action and good ideas these days is in the 996 arena, whereas people are scared of driving (let alone modifying) their 997s (despite Phil997s best efforts!) and are all just existing on a scale that starts with worried and goes to paranoid. :wink:
 
Firstly, great thread!

Any chance you could post part numbers or even year etc of Zamora the electric pump comes off of? I feel like this might be something I'll be tackling in the future so I'd like to buy up the bits.
 
It's nice to see how owners are beginning to enjoy modifying their M96/7 cars to increase their enjoyment while protecting their longevity. It is clearly starting to provide a lot of interest as well.

Information about power and torque figures are always going to be subjected to variables that can confuse results, however it is a fact that EU legislation has changed the way manufacturers rate their engines and this has altered comparisons between older and newer cars.

The practice of elevating power outputs in some models in the Porsche range and down rating others to rank then in the preferred order between 911's and other models has gone on for years (mainly started with the 924S) and as a result we find older models of the M96/7 usually produce less than claimed in standard form with newer models closer to what we find.

Power outputs recorded from braked inertia runs don't usually follow the same graph plots as the manufacturers versions either and so between all the various different methods of testing engines and manufacturers claims and EU regulations the picture has become extremely confused and variable.

What is probably better to consider is the differences changes can make after modifications rather than trying to link them to other claimed figures and results.

Torque is what accelerates a car (and rear wheel torque at that) and not BHP which only benefits performance if the gearing exploits changes in the maximum torque range. Gearing down a car built to max at over 170 mph (that you will probably never use or experience) will always increase rear wheel torque from the same engine output but if you cannot gear down the final drive, it is better to exploit the range of gearing you are stuck with and as the cars are overgeared from standard - the best way to do this is to increase the mid-range torque, which increasing the capacity does beautifully.

These engines are built to do this anyway (for the same reasons) and variable cam timing and valve lift enable the engine to breath a lot of air at peak revs while trapping more at the bottom to mid range and overall increase the torque you experience when accelerating through the gears.

As a result - increasing the capacity has a bigger affect on the amount the mid-range increases than the top end so an oversized engine by say 9% might increase the mid range torque by nearer 15% but the top end by nearer the capacity increase (because at those revs the engine is reaching its breathing limit).

This increase in torque also makes the cars more responsive and easier to drive especially coming out of corners.

But there is much more that can be done to increase performance. Acceleration is proportional to torque/resistance so increasing torque has the same effect as reducing weight and the two together double the benefit.

Inlet and exhaust systems that increase air flow at the top end will also increase top end power but may slightly reduce that mid-range torque making it necessary to spend a lot more money for minimal increases in overall performance. The increase in capacity combined with weight reduction is therefore a very cost effective way to get a lot more performance than chasing revs and top end air flow especially if the engine needs a rebuild anyway.

Lots more on this topic is available in a long technical report on our oversized engines from our Sharon on [email protected] but it requires a lot of stamina and some technical knowledge to get through it all, a few days to cover it fully, a few whiskeys to recover from it - and is not for the faint hearted. It will however explain a lot for those interested enough to work through it slowly enough to understand the difficult issues covered because they have been mis-represented for so long many no longer understand the subject as they could.

Baz
 
That's very interesting baz. Do you find that the grunt at the top end dies off as the oversized engine dosnt want to rev the same as the smaller capacity? Or is that more of a stroker problem?

I had an impreza p1 that I stroked to 2.15 litres. Awesome job for torque. The turbo spool was on a different level.

Also one that I've been interested in, lowering the gearing. Do you offer a lower final drive?
 
Hi Ned, I'm not sure what info Baz may have for you, but I think you can fit a 997 gearbox in more or less a straight swap, apart from new shifter cables and take advantage of the shorter gearing in that transaxle. The G97 gearboxes seem to be cheaper second hand than the G96s too.
 
Martin I was thinking of just simply the diff. My lsd has had it and I was thinking if there was a different ratio option, it might be worth a look. I've always found the gearing to high for my liking but coming from the rally bred stuff, I'm used to short sharp blasts. It'll probably just be something I'll get used to I suppose.
The budgets not really plush enough for a new lsd just atm
 
I'll try and keep answers as short as possible (most are more fully explained in our report on oversized engines available from [email protected]).

(1) when you change gear you accelerate from the revs the nest higher gear starts at to the peak revs you change up again at. As the revs rise the rear wheel torque accelerates the car. If the increased torque is greater just when you change gear than at the top far end of the rev scale just before you change up again then you will not feel as much of a surge as the revs rise - but feel it most just after you change up. However you will be going faster. Unfortunately human sensory reaction feels the rate of change of acceleration (jerk) more than a more steady acceleration through that rev range so a slower peaky engine might feel faster but a more torquey one will ACTUALLY BE FASTER).

(2) Yes they rev the same to the same peak revs. in fact the power increase through the extra capacity is about the same as the capacity increase at the very top end of the rev scale. This is because the higher the revs the shorter time there is to breath in air so at peak revs the extra capacity only breaths in a similar amount near the engines breathing limit. But the burn then is applying pressure to a greater piston area and therefore more power.
Lower in the rev range there is more time for the valves to be open and the extra capacity can then breathe in more air AND the resulting burn pressure is still pushing down on a bigger piston and as a result the mid range torque is often almost twice as much as the increase in capacity.

(3) Most engines driven on track to peak revs between gear changes run with falling torque as the revs rise and this helps lap times because driving out of corners as fast as possible is all about traction control and an engine that produces a smoother falling torque delivery can apply it more than one that is always trying to spin up the rear wheels as the revs rise from a slower less powerful initial power delivery.

Furthermore a wider usable power band allows more tolerance of unsuitable gear ratios for particular corners by enabling them to be driven out in a higher gear at lower revs with the same or even more acceleration for a longer period as the corner unwinds - so can be very beneficial.

However the cars are all over geared for track use (rare to exceed 135mph anywhere and often down to 120 mph on some shorter circuits) so 6th is rarely - if ever used and sometimes only up to 4th - which have bigger rev drops in lower gears (benefitting form wider power bands).

Lowering the final drive ratio will increase rear wheel torque and therefore acceleration.

As I used to make my living many years ago making different gears for racing motorcycles I understand the benefits only too well but it would be expensive to make the final drive lower - possibly easier and cheaper to change some internal gears.

Perhaps I need to look into this as owners seem more prepared to pay more to develop these cars as they age and become more fun to tune up.

You still need a low 1st gear to get off the line (or drive on the road) and still need a high top gear (if also using on the road) but a change to 2nd, 3rd and 4th (possibly 5th) would improve track performance.

For Porsche Club events a winning car may have those ratios checked so quite rightly gear box changes would not be suitable in those events.

The tooth profiles used in the gearboxes are not standard Imperial or Metric gear cutting shapes and this prevents just changing the number of teeth on one gear in a pair and would require both changing to a new matched std profile or a special set of cutters being made (which would be very expensive).

It is something we will return to and look at again if demand increases, meanwhile I think there are lower crown wheel and pinion sets available but I don't think they would be as suitable for all round uses as internal ratio changes.

Baz
 
Nice update - thanks.

I know I will get slaughtered for promoting what we do but after reading through this again several points emerged and it occurred to me that they might just be worth repeating here.

(1) We also found add-ons generally reduced performance.

(2) You can only really compare a before and after dyno run on any car to assess changes.

(3) Engine dynos (that manufacturers used to use) are usually run at fixed revs in steps and allow time for the unsteady gas flow to stabilise - increasing results. Braked inertia runs on rolling road or rear axle dynos reproduce the breathing closest to the performance when accelerating your car and therefore offer more accurate comparisons.

(4) If you work out (or observe) the "rev-drop" from when you change gear to the revs it starts the next highest gear at - then for maximum acceleration you need the maximum torque in that rev band.

(5) As you go to higher gears the rev drop usually reduces (except perhaps into top gear) but if you never (or rarely) drive flat out in say 5th (or even 4th) most of the driving you want your car to be really fast is in gears that have quite a large rev-drop.

(6) At 3,500 rpm there is twice as long to fill the engine with air (and expel it again) than at 7000 rpm which with variable inlet cam timing (and in later engines a choice of two switching cam lobes) and lift - these engines are designed to produce good performance in the mid-range where you will need it for most of your fast road or track work.

(7) An oversized engine can exploit this by filling the engine even more in the mid range than the proportion of the increase in capacity. When peak revs are reached - by then the breathing is becoming strangled so the increase is less and usually around the same as the increase in capacity.

(8) The most significant point that came across was what great value for money increasing capacity is. Less than many of the bolt ons that actually reduce performance and with the standard auxiliaries provide a really significant increase in performance (especially if you need a rebuild anyway, fancy a pre-emptive rebuild or want to keep the car but have a change).

(9) Finally - we do have several examples of our increased capacity cars at Hartech and by appointment will be happy to allow existing owners of the same models to test the increases for themselves if they are seriously interested in a conversion (nothing to hide and very confident in the outcome - as have the clubs, individuals and magazine drivers that have already done so - been).

Finally Phil - the 4.0 litre gen 2 PDK is going really well - absolutely resonates on full power and surges forward like a rocket - really enjoying it - when are you coming up for a test drive?

Baz
 
crash7 said:
Plenum, I fitted an IPD competition plenum with a 997 GT3 82mm throttle body, linked to the standard airbox, with a resonator delete and BMC panel filter. – If the internet is to be believed this is a solid setup and should produce gains, this is where it got interesting.

The car was dynod, the results were deemed to be sub-optimal, so various items listed above were systemically removed and replaced in various combinations and the car again dyno'd immediately after to compare the results and this is what was discovered..,

IPD Plenum with 997 GT3 throttle body, reduced engine output and left flatspots and holes everywhere in the curve, apparently down to the lose of exhaust scavenging effect.

Resonator delete airbox with BMC filter, produced less bhp & torque than a standard airbox with a standard filter. - The rational, in deleting the resonator the airflow is more turbulent, the MAF doesn't like this and winds things back, standard filter flows more than enough air.

The optimum solution for the most bhp & torque was, standard airbox with resonator, standard air filter, standard throttle body and a 997S plenum.

Hi Crash7,
I was re-reading this thread being in bed with fl, on lockdown, and thinking about the roadmap for improvements on my 996.
Re: the 997s plenum, do you have a part number by any chance? If i look for it all that comes up in my search is the IPD plenum.

How is the car coming along? Have you been driving it much?

I've had lots of headaches with the geo and finally found someone local that has fixed my toe and am really enjoying my car again. Can't wait for the next track day. In the meantime also thinking about futur improvements so the plenum is on the list.

Thanks
James
 
crash7 said:
I've not update this for a while, I will get around to adding images etc eventually, in the interim I found this which shows a 996 on a rolling road and the effect of a performance air filter.

https://www.youtube.com/watch?v=GK329_MhMuM&feature=youtu.be

In essence it mirrors what was found with mine.


Yep Wayne Scofield of Chip Wizards always advocates the standard airbox.
I wouldn't bother with a different panel in the std box. Worst of both worlds. No extra power (maybe even less) and no big sound benefit.

Cone filters are a different kettle of fish though. I'll take the extra sound over the possibility of losing a few BHP any day, as the sound you get adds way more to the experience than a few HP does.

My old C2 had a K&N cone on it. My GT3 has the std airbox. The C2 screamed more. Spine tingling at high revs. My GT3 is good but muted in comparison despite the full Cargraphic exhaust system.

My first GT3 had a cone and it was amazing. Almost Ferrari good.

So the first mod this year will be a Cargraphic Cup filter for the GT3. To hell with a few bhp which I've never ever felt were lost anyway.

:thumb:
 

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