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It's Back - 3.7 Content *Now With Prelim Results*

You're such a tease, Baz :hand:

Good info as ever, though.

Seems like the longer my engine keeps going (perfectly), the bigger the replacement displacement! will be :grin: :Cops:
 
I'm planning on a prophylactic rebuild at around the 80ish thousand mark for my engine - and yes, I know what thread I'm posting in, and that I'm clearly lacking moral fibre etc etc, but I'd rather it be done and out of the way as it were. I had a chat with a chap from Hartech (not Baz) a month or so about it and the 3.7 litre option (I've a 1998 3.4) certainly seems to make sense.
 
I'm going to wait until I've also done 1/2 million Km's until my 3.7 build.
 
bazhart said:
I can confirm that extra mid range is quite significant. We are currently road testing a 996 3.4 converted to 3.7 (100mm pistons), a 996 3.6 converted to 3.9 (different 100mm pistons) and a 997 3.8 converted to 3.9 (same pistons as the 3.6) - all with Nikasil alloy cylinders.

We will also be building a 3.2 Boxster S into a 3.7 and Cayman S 3.4 etc using many common parts for our oversized engine range (just need to finish testing the others before moving them on so we can get in the other models we intend to offer in the range).

All testing is going well and we hope to be taking orders later in the year.

Although it is theoretically possible to change the 3.2 and 3.4 engines right up to 3.9 (or more) to do it reliably would require many more parts to be changed and updated at significantly greater cost for relatively little extra performance and after all that you would question the brakes and suspension etc - so for now we are limiting our future conversions to those ranges.

Also in build a Gen 2 - 4 litre car - something for next winter perhaps?

Baz

Great news for the smaller engine cars, but owning a 3.8 - I would hope (and I am sure I am not alone) for at least 4.0 or 4.1 - wouldn't that be the sweet spot? :)

I think people will at least feel they are getting an upgrade, rather than spending so much money on a "repair" - this definitely the way to go Baz :thumbs:
 
The problem is that although the same basic parts and design of the smaller engines are also in the 3.8 - it is the model we repair the most of and as such too big a capacity increase may be reflected in unreliability.

Our capacity increases are largely for people who need a repair anyway and therefore will be offered more or less as a benefit for very little extra cost.

The Nikasil alloy cylinders will take bigger pistons and more power but the crankshaft journals from the 3.8's do show wear sooner than smaller engines and we are intent on preserving reliability combined with extra performance.

Once we have got some miles under our belts with the present range - depending on how they perform - we may well try a further capacity increase but probably with a new crankshaft and rods (as we perceive this to then be the probably Achilles' heel) = more cost - by which time owners may well be more prepared to pay for such an upgrade.

We always test our products for long periods and high mileages before offering them to the public and although this may be frustrating for some (as it actually is for us) we regard it as a responsibility we have to fulfil.

Baz
 
poppopbangbang said:
Dammit said:
Great news, did the rebuild come in according to your budget?

Yes no surprises or dramas. Autofarm were great to deal with, as they always have been in my experience. I think we were a bit under budget in the end.
Agreed Autofarm are a great company to deal with. :thumb:
 
Preliminary Results

So with around 1200 miles on it now I thought it was time to see where we were in terms of power compared against the previous engine. Now the below is fairly accurate, even when compared to what a direct measure would be, but it's very reliant on the figures you are plumbing into it. It's really a system we use to monitor how the engine health is doing over life in a racing car but it does provide repeatable results and obviously having some 200K miles of data to compare it against is the important thing for measuring a gain. The below is based on linear acceleration over time to determine the wheel power developed to move the specific amount of mass with the specific amount of aero drag at the measure rate of acceleration.

It's fairly simple stuff, firstly we calculate the power absorbed moving the car through the air at the current speed which we can do by knowing the frontal area of the car and the drag coefficent along with the speed in metres/second. Once we have this value we can then calculate the wheel power of the car (it's important we know aero drag or the resulting figure would be vastly different for a given RPM in first gear vs 6th gear due to the greater vehicle speed), to do this we need to know the mass all up (so with fuel, driver, additional kit etc.) which I have from time spent on the corner weight scales along with the linear acceleration of the car - linear acceleration being essentially the rate of change in velocity. For the sake of accuracy we are using a 10hz GPS to determine the start and end velocities and validating this with a longitudinal G measurement i.e. to accelerate from X to Y speed in a certain time has to have yielded an average accelerative G of Z so if our measured G is vastly different at one point or our measured average G between the points doesn't match our calculated average then we disregard this measurement as flawed. To get to flywheel power from wheel power we use a simple formula based on a known measure of wheel power against a known OEM SAE corrected engine dyno result, in this case what my car made as a standard 100 and a bit thousand mile car vs Porsches 300PS no aircon, no PAS, engine dyno rating. It's a sliding scale based on torque produced but at peak power the total loss between flywheel and tyre contact patch is about 14.8% by my math.

It might all sound a bit math heavy but with a decent logger you can do this live on the box and it's pretty much the same system we used in pro motorsport in the days before we had reliable and long lived drive shaft torque sensors.

So here is where we have ended up from testing today. This is an average across 12 runs with 6 in each direction to account for the slope of the runway:



According to this it's making 363.2bhp at 6250RPM and a peak torque of 318.8ftlbs at 4750RPM. What's nice is that it makes over 300ftlbs from 3500RPM to 6200 and a bit RPM. It is quite clearly all done by 6.5K and torque drops away rapidly here to the rev limiter at 7200rpm.

Lambda is fairly good considering the ECU calibration is pretty much standard. There is something odd going on at mid RPM in low gears where the ECU is winding the throttle down during 100% PPS which is likely to be the result of a torque limiter somewhere being exceeded (not surprising all things considered!) and performance could clearly be found by going richer below 4500RPM, at the moment the ECU is staying in closed loop mode until this point to keep the cats happy (which is fairly pointless as mine hasn't had cats since 2013).

Gains wise when compared against the old engine (and that is compared using the same math as determined this engines performance so it is a good comparison!) this engine is about 30ftlbs and 25bhp up on it when the old motor was at its best with considerably more torque at lower RPM - indeed the additional low RPM torque is far more than I would have thought would be gained by going up a relatively small amount in capacity, it's likely there are some improvements in cylinder filling at lower port velocities/engine speeds as a result of the larger bore/swept capacity.

For those interested the full spec of this engine is:
- Autofarm 3.7L castings.
- Autofarm cylinder heads
- CP Pistons in standard C/R with reduced size skirts for friction reduction.
- Standard size inlet and exhaust valves.
- Standard Cam Shafts
- Variocam fitted and working.
- Cams timed to Autofarms spec for 3.7L
- FVD Equal length exhaust manifolds
- Cat delete crossover pipes.
- No name perforated tube stainless silencer boxes (I think these are the same as D911, Porscheshop etc. sell).
- 996 GT3 Throttle Body
- Slightly hooky IPD plenum to suit the above
- 997 Airbox
- Large diameter silicone hose to suit the above joint to the GT3 throttle.
- No Secondary Air System
- No Air Con Compressor.
- ECU Calibration is essentially standard but with lower fan on temps etc.
- FVD Large Capacity Sump (not that this really has any effect on power)
- Low Temperature thermostat (as above)
- Metal impeller water pump (12 months life) (as above)
- Roller bearing IMS (as above)

It will go on a dyno at some point in the near future as it's very clear there is more to be had from some engine calibration development (not least solving the torque limiter problem that rears it's head when launching the car hard) and the instant 30 second feedback a chassis dyno provides when doing this does rather minimise the time required. It's also pretty clear the cams that are in it are probably too soft for an out and out performance engine as the additional low RPM torque could be traded off for high RPM power, however as my car is 99% a road car and the lower the revs the longer the engine life I'm quite happy setting the last shift light at 6.5K RPM :D

For those interested in how I'm logging this data the car has an AIM EVO5 logger onboard with two LCU-One wideband controllers, a GPS08 GPS/Glonass receiver and a GS-Dash (with motorsport cable tie mounting!). It takes basic data from the car via OBD2, RPM from the tach signal at the OBD2 connector and oil pressure on a dedicated sensor.

To sum up - I'm rather pleased with how the old girl goes now and it would be interesting to see where we are vs a 996 Mk1 GT3 :D
 
:bow: :bow: :bow: :bow:
 
:agree: Wot he said, I think I want one of those engines.

Mike
 
PPBB - what do you think the power and torque would look like if you had standard throttle body/manifolds/catalytic converters still in place?

I know that you moved all of this over from the old engine, but wondering what the delta would be for a stock 3.4 to 3.7 conversion.
 
Dammit said:
PPBB - what do you think the power and torque would look like if you had standard throttle body/manifolds/catalytic converters still in place?

I know that you moved all of this over from the old engine, but wondering what the delta would be for a stock 3.4 to 3.7 conversion.

I'd have thought 30bhp or so, there is a pretty good example in that the standard 3.6 is rated at 320bhp (okay they generally make a little less than that on a dyno but it's a good figure to work from). In my experience of my car the major restriction is in exhaust/emissions bumpf and then throttle/airbox. This seems to be corroborated by the Cayman guys making 340bhp odd with low loss exhausts, inlets and larger throttle bodies/plenums on 3.4L cars. The real plus point of going larger bore appears to be the increase in low RPM torque, roundabout exits for example can now be dealt with in third with no loss in pace :D

I think a capacity increase is really only sensible when it's engine rebuild time. You'd be fairly mad to do it for the sake of it when the gains are relatively small - it is after all only an 8% or so increase in capacity. The biggest bang for buck is definitely decent exhaust manifolds, removing the cats and fitting a larger throttle body. On my car they were worth the same as the capacity increase in headline figure.

Having said that it's a nice feeling to have GT3 poke from an M96 powered Carrera :D
 
Good stuff PPBB; keep the updates coming 8)
 
So a further update now we're nearing 5 figures in.

The engine has loosened up a little from when it was built and feels very settled now. No leaks, no worries and it now uses less than 25ml of oil per thousand miles which is fairly impressive but then it is vs half a million KM old rings and valve stems that were in the old one!

Performance is very impressive for a "slow" 996, obviously the fact the car is a bit lighter than a standard one helps but it quite happily pulls on a current M5 for example. I'm fairly gobsmacked at how much of an improvement there is over what was in there.

I've also (finally) swapped to a Lithium battery, specifically a Super B 20P which saves another 4KM over what was in there. I've kept my old Redtop/Helicopter battery for the time being whilst we see how the Super B holds up but I don't expect any major issues as they last well in the race cars!

20P_hr.jpg


I've got some planed maintenance coming up, mainly regreasing the coffin arm ball joints and swapping the ARB drop links as the sphericals on these are approaching end of life. I've made some new ones ready:



I'll also replace the fuel filters for the rail and aux tank at the same time and give it a general once over. We're getting near the point of needing to do some bodywork maintenance too as the level of stone chips and general rat look is getting a bit high, to be fair it does spend a lot of time chasing things like this:



So it's to be expected but I like to at least make the effort....... or maybe I just wrap it in full prototype camo as generally that avoids some bother on the continent!

I've also got to sort the dash pack out as the bubbles on the white dials are jamming the needles now! I've got a spare black dash pack so should just be able to swap the clocks over and leave the LCDs in place from the original. I also need somewhere to mount the AIM dash as I can't really leave it cable tied in front of the clocks!



Either way the old girl continues to be utterly brilliant at being a car and the engine freshen up has really made it feel fresh again :D
 
Nice update Poppop,
You've done 10k miles already. Wow.

Is the super B replacing an Odyssey 680 or voltfreaks battery? I have a bracket for a 680 but am holding off fitting one until the car sees more regular use as I'm not sure of how it'll hold with infrequent use. I'll have it on a conditioner though.

How do you measure 25ml of usage? Just a case of what comes out vs went in? Or some fancy race car measuring equipment?

Anyway good pics. I'm loving that LMP looking thing. :thumb:
 
Love it love it!

Rebuilds are fine......., but hard to justify a £11,000 bill to put a £12,000 car back to standard again........ but spending £15,000 ish on a significant upgrade, turns the car into something special and in my eyes seems to make sense.

Ie the difference between a recon engine, and a rebuilt and upgraded bit of quality is only* £4,000?

* I appreciate this is still significant wedge!

Keep going with the updates. Inspirational stuff. Ta
 

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