BC

Try shortening the headers in software and see what happens to the hp and to lines. Leave them big bore, but just shorten the primary sections.

slate blue

Pipemax is basically a header or exhaust program and it only details what it says is the correct range of length for a particular engine configuration. It does also provide the amount of flow both for the intakes and the exhaust side. It is very widely used and respected.

I did last night while I was using the Pipemax program, I did work out the peak intake speeds at the respective volumetric efficiencies of 110% and 115% The speeds are 315 and 333 FPS. These air speeds occur at 8,000 RPM.

Now David Vizard's book Developing Functional Heads, says that for 3,4 or 5 valve per cylinder engines have the following speed ranges.

Production unported heads have a range of 300 to 310 FPS
Production fully ported have a range of 300 to 360 FPS
Nascar heads (2 Valve) would fall into a range of 340 to 360 FPS
and F1 Style have a range of 380 to 420 FPS

TexasDude74

Finished bore will be 4.285 inches, just shy of 109mm which will give 427 ci. I've been considering using a gapless second ring, even though a lot of old school hot rodders I know recommend against them.

I plan on running the car on E85, best hot rod fuel out there. In early discussions about this engine with Todd we kicked around the idea of 15:1 compression to explore the limits of this fuel. We also talked a bit about a 3.6 or 4.2 liter twin screw which I still think would have been fun regardless of the hoodline. But, with these sorts of things, in order to actually get them built compromises do get made and a big bore, normally aspirated, high compression itb motor is really what I wanted.

I agree with your machinist about dialing back the rpms a tad. It's amazing how much more effort and expense is required in the entire vehicle to chase that last thousand revs. He's also right about the dog box as well.

slate blue

Hey TD, I didn't think there would be a 109 mm piston, so that makes sense. I wouldn't mind using that size too. What sort of cam are you looking at? Street or race? I am thinking about 260 degrees on the intake and 255 degrees on the exhaust. Were going to port the exhaust at the flange to 46.5 mm. The inco pipes for the start of the primaries turned up today. Don't know what flow we can get on the exhaust but obviously going for the maximum. To achieve a big power number we need to get exhaust flowing around 300 cfm, That seems to be a big challenge.

G.G.

slate blue

TD, thought you might find this interesting, went back to the trans place and again he said, good that you have revised down the revs, keep going, keep going until 6,500 rpms where I can guarantee you'll be able to shift. Urrghh

When I said I saw on youtube a F-body firebird with a T-56 shifting well at 7100, he said they are different, the TR trans has many more dogs and that they are very fine and this creates the high rpm problem.

So, again he warned to be careful and consider all the options. So he is certainly not in a big hurry to sell me something. I suppose if you have a good business you don't need to con people and they just don't need the hassle.

He also said, we don't know what the new Z06 will have and thinking about that, it may well have the new double clutch 9007

http://www.tremec.com/anexos/File/TR...R-9007.DCT.pdf

It has plenty of torque capacity and the input shaft speed is a maximum of 10,000. It has a wet clutch which means no need for the normal clutch in the 928. My car is going to run on CAN for the major functions such as brakes differential, engine etc existing gauges and controls will run conventionally. If the Z06 comes with a standalone controller for the trans this may be feasible. Not that I am expert in CAN but everything I have asked the regarding functions and connecting to the CAN seems to be no trouble. Happy to here if this is not the case but I think if you have all the sensors that is required for inputs and the relevant controls for the outputs why shouldn't it work?

The aftermarket also always comes up with solutions to these things too. So I am putting the decision on the gearbox on hold and will do all the other work, of which there is plenty!

TexasDude74

On the cam I was thinking of pretty much reusing Mike's original specs. I would be hesitant to increase duration much past 250° @ .50 to keep from pushing the torque curve and shift point too high.

That's awesome that Tremec is working on a dual clutch, although I have zero experience working with those things. I have driven 5 or 6 GTR's and was not impressed with that dual clutch transmission at all. They make all kinds of inexplicable noises and I was convinced I must have broken the first one I drove. I later learned they're all just like that. If you're a car guy that listens and pays attention to what your car is doing a GTR would drive you crazy with its clunks, thuds and vibrations. You'll constantly be thinking something must be wrong. I would much rather have a traditional manual.

My guess would be waiting on that development could set your project back at least two years. I would think that it would be easier to control than the 6l90e which is a pain to get to shift right without talking to the engine.

I know the TR6060 can handle shifting in the 7-7500 rpm range, they get iffy beyond that and need some upgrading. If you're looking to be rolling in the next 18 months that's probably your safest bet.

I'm sure there are a lot of guys around here that would to see a dual clutch 928 stroker though!

slate blue

Interesting about the noises from those DCT boxes, that's crazy, I certainly wouldn't be entertaining this option if I wasn't worried about the outcome. I can't spend the kinda dough and fail, although there is always a chance of failure when push you the boundaries.

I believe the Z06 will have this box and that will be unveiled in the next 6 months. The same time it would take if I waited for the close ratio 7 speed manual. Maybe it wont be a 7 speed manual but the DCT? I know they flash tune the current BMW DCT in the M3 and I couldn't imagine the same flash tuning not being developed for a car like the Corvette. It would certainly make the car fast! However I do understand why people don't like them.

slate blue

So the update is about the transmission, I abandoned the plans for the TR6060 or TR6070 on the basis of advice provided the the transmission shop which I can tell you is RPM transmissions. They have a very good name and you have to say lost a sale by telling it how they saw it, that is advising that I would be disappointed in the end result given the application.So cudos to them.

However it appears it may be GM to the rescue, the new Z06 will not get a DSG gearbox but an automatic, a auto that will shift (they claim) as fast as Porsche's PDK. It has seven performance ratios and one economy ratio. Also this is the big break, I believe I will be able to use the factory ring and pinion. So no extra cost of approx $9K USD for bespoke parts. I will only need to change the adaptor plate and machine or fabricate a new output shaft. The torque tube is entirely carbon fibre. The trans will be 20 kgs heavier than the existing manual and I will make a new automatic alloy flywheel and this will greatly benefit weight balance and bring it to the optimum balance of 45/55%. The other parts which add weight to the rear will be the PSD and the variable ride height pump. Not good to add weight but it will go into the correct areas including the correct side of the car. My engineer is a big one for weight distribution which he says is all about contact patch.

Regarding the auto, I bought the SAE paper which contains the ratios, six gear is one to one and eighth gear is 0.65 to 1. It will have a separate module to control the shifts and pressures. I know there will be time involved in tuning it but I will use a GM throttle pedal switch and I may use the GM wheel speed setup. I think it would be easier to get working then any DSG setup. The variocam will help with idle and low speed operation given it seems the car will be automatic. The one question hanging over this choice is what will be the max input speed. The 6L90 has a max shift speed of 6,500 rpm however a huge amount of development went into the balance of the parts including doing away with circlips which are inherently unbalanced. The housing for the clutches to reduce mass are alloy. If there was a high speed problem I suspect it would only be in sixth gear and this would require short shifting. Remembering that it is one to one you would be doing around 200 mph at 8,000 depending on the rear end ratio. So with this trans there won't be a bang rattle clang either.

Also some more exhaust parts turned up. I love these Burns lightweight mufflers, there is 4 of them plus the custom built most rearward mufflers. So at this point 6 mufflers will be implemented and I hope that will be enough.





The large mufflers (17") weigh 1.45 kgs and the shorter 12" version weighs 1.1 kgs I figure the whole system will be around 25 to max 30 kgs versus around 70 kgs if I didn't use lightweight parts. So at least a 40 kgs saving.

slate blue

Some other interesting parts turned up, with our custom software these parts will adjust the ride height for many purposes. To assess the rake angle of the car for downforce produced, to getting over speed bumps. Once the rake angle has been worked out, settings can be made to run on the street to then different settings for track work and high speed runs. They are fitted to all four dampers.






I am employing the Eibach ERS system, this will give some compliance given the main spring rate will be 1200 front and 500 rear. This compliance will be relatively small and is achieved by double springing. I am hoping the tender springs will compress at speed and lower the ride height to further increase the downforce. Given the ground clearance at that point will be in the 70 mm range, the springs need to be pretty stiff. I am concerned that 1200/500 is too light but......I wont be able to tolerate anymore and nobody will want to ride in the car. The tender springs haven't been worked out yet but may well be front 300 rear 150.

BC

Air pressure. Nice. Does that fit on a normal Bilstein tube?

Rob Edwards

Dummy question from a dummy- what is the magnitude of the change in downforce achieved by tilting the whole car up and down vs. just sticking an actively adjustable bigass rear wing on it, a la Chaparral 2C?

slate blue

Not air but hydraulic pressure, if it was air you would get uncontrolled movement. The ID is about 55 mm. The damper I am using has a OD of 48 mm but the way I am fitting them, they are not part of the unsprung mass. So they are not being attached to the damper body. The unfortunate aspect of the fitment is the weight penalty of approx nine kgs. Five kgs is the pump which is similar to the PSD pump.
As mentioned the bulk of the weight is rearward which is the only positive of the additional weight.

slate blue

Quote:

Originally Posted by Rob Edwards

Dummy question from a dummy- what is the magnitude of the change in downforce achieved by tilting the whole car up and down vs. just sticking an actively adjustable bigass rear wing on it, a la Chaparral 2C?

Initially we won't put a wing on the car nor the larger front splitter, we are in the concept stages for the bodywork and a artist is drawing what the various pieces will basically look like. So the downforce harvesting will be concentrated in more discreet areas such as the floor.

The rake angle needs to be optimized as every car is different and there is not one best angle. So by doing straight line aero tests with suspension sensors we can see how the rake angle effects not just downforce but the aero balance, that is front to rear downforce.

There is a good article here and it explains a fair bit of theory,

http://www.auto123.com/en/racing-new...id=130054&pg=1

We may well run the exhaust exits at the rear axles which is legal in Australia for the 928. I have ordered super alloy exhaust valves to be able to cope with the extra heat the retarded ignition and extra fuel will create. Along with a very exotic copper alloy for both the intake and exhaust valves and the exhaust guides, (we are using 6 mm stems on the exhaust) as we need to get rid of as much heat there as possible to prevent damage and pre-ignition due to hot exhaust valves. This material has better heat transfer than copper beryllium.

slate blue

Just returned from overseas, I bought home with us the exhaust for the car, the pipes you can see are the (small pipe) header pipe off the head 2 1/8" and then the pipe after the headers 3 1/2". The header pipe is a bit thicker in wall thickness at 0.9mm and the 3 1/2" is only 0.7 mm and is made from heat stabilised stainless grade 321. It is extremely lightweight. The header pipe off the head needed to be thicker to support the weight of the system. at the first primary step it goes back down to 0.7mm.





So for the sake of some pointless comparison, the header pipe is the same size as the standard engine pipe that comes down to the cats. The new engine pipe is that 3 1/2" pipe. However the engine pipe section again will be a bit thicker at 0.9mm. Have some other interesting pieces like the Burns Stainless lightweight mufflers (4) I might post some more info later on the engine bearings I have found for the mains. They are harder slightly smaller in diameter have 180 degree grooving versus 220.and will fit into the tunnel at low cost. My estimate is less than $500 for conversion. I still may look at the 140 degree grooving but I may try these bearings in the intermediate engine I am building

slate blue

So the bearing comparisons, you will see that the new bearings have the same length as the thrust bearing for the 928 which is approx 21 mm. The other main bearings in the 928 are approx 24 mm. The groove in the 928 bearing is around 8 mm wide and the groove is approx 220 degrees. The new bearing is 180 degrees but the groove is only 3.5 mm wide leaving the nett area in the upper bearing with an increased length. The new lower bearing is totally ungrooved and is of course 21 mm wide. There is a slight difference in diameter 68 mm versus 70 for the 928. The bearing material is much harder in the new bearing. So the nett difference in load area is about the same but the new bearings should lower friction by increasing dynamic lubrication.





I propose to groove the 928 thrust bearing from hole to hole creating around 160 degrees of grooving. This main bearing will remain stock. I will use the undersize version but this main will be a Porsche size to keep things simple. I am also looking to find a set of 140 degree bearings which should be better still. These bearings come from an engine of large capacity and power similar to strokers.