thehelix112

From what little I can tell, the point of an exhaust manifold is to provide as little resistance to the flow of hot exhaust gases as possible, in order to deliver them to the turbine housing/wheel. The housing/wheel are a restriction to the flow, but thats how you extract the energy to drive the compressor. A stock manifold has lots of fugly restrictions BEFORE the flow gets to the turbine, this restriction is entirely wasted, contributing nothing to the energy extraction for driving the compressor, and only to increasing exhaust manifold pressure, and decreasing the efficiency of the engine. At least thats how I understand it. There is a reason you don't see log manifolds on cars aiming for maximum HP. Dave

Looking good Myron! My question is, have you fixed that lovely header/exhaust join you had going on a while back? Dave

Tis true that horsepower is perhaps not the most important thing in determining lap times (on tight twisty circuits at least). I am not entirely sure where you are getting your information about turbo cars `falling off' between shifts. I would suggest that every race car worth its salt uses flat-shifting, in which case the `fall off' (I presume you are referring to boost drop?) is less than neglible. Dave

It seems to me that the benefit of moving the engine rearwards cannot really be to improve the static weight distribution. As others have noted, reportedly the zed approaches 50/50 anyway, especially with driver/fuel? However moving the engine backwards, in conjunction with moving the fuel tank forwards (like beside the driver in an approved, enclosed space), could maintain the nice static weight distribution, whilst lowering the Polar Moment of Inertia (the cars resistance to turning if you like). Regardless of this, it seems to me that you can potentially get a usable amount of power from most engines that will fit in a zed bay (like: any?), so the choice is entirely up to you and can be made based on: personal preference, bore configuration and its contribution to chassis design, drivability requirements, etc etc ad infinitum. Good luck, Dave

Justin, Fuckyou my friend. Sideways. Dave

Cary, It was me who mispoke, I apologize. I understand that RCs move, my point about them moving `magically' was that it doesn't appear that you are drawing the lines that people use to identify them, but rather have just decided that its somewhere else? I'm not saying you're wrong, I'm just saying its not something I've seen before, and doesn't really make sense to me. BTW, Ortiz's latest article is again, about this very topic: three wheeling in NASCARs. Dave

Cary, I only just noticed you replied, sorry. Thats a very interesting theory, about the roll centre moving to the outside wheel. It seems to me that what we're not considering, is the longitudinal weight transfer. During turn-in, you are going to have more than 500lb sitting on the front inside, so it will take more lateral load, hence roll, before it lifts, because the height its rolling from has been reduced. During exit you will have less than 500lb, so the suspension will be close to full droop anyway, hence you see cars lifting the inside front. I need to do some work, but maybe food for thought. The idea of the RC magically changing is a bit far fetched for me, but I try to remember that RCs, ICs, and all the lines people draw all over their chassis sketches are just there to try and help us understand how things work. They don't actually exist. Dave

Yes. No doubt. The weight of the lexan would surely by sfa. It wouldn't have to be very thick given its slight convex shape (increased strength). I assume that you cut the upper window track out for some reason? If it were me I'd be installing a tight plastic u channel in some places (top of window and a-pillar) and working out a way of keeping the lexan up in place. Are there safety concerns with not being able to open the passenger window? Do you need side view mirrors? I've never used one, but I've seen people in race cars have a full length mirror running at the top of the windscreen inside the cabin. Good luck, Dave

Clifton, I should've been more clear sorry, I wasn't talking about just under power. tube80z, So what I'm picturing is Richard's car rolling, the top of the inside suspension moving both inward (relative to centreline), and upward (relative to road). If the upward component of that movement exceeds 10mm, I don't see how the tyre is still on the road. Dave

Correct me if I'm wrong, the instant one tyre looses touch with the road, is the instant the other tyre is then taking 100% of the load, and providing 100% of the lateral force. This doesn't sound like a good way to set things up to me. You'll have shared load, then as soon as the inside tyre lifts the outside will see a massive spike in load, and I'd be very surprised if it didn't understeer like a pig as soon as that happens. There is an article in this month's RCE where Ortiz talks about this very thing, albeit on the rear of a mustang. Not to even start to talk about the case where you go over a sharp rise which results in the front of the car lifting >10mm. I foresee severe badness, but I am often wrong.. Dave

Sweet, just checking. Did you account for increased SoS with pressurized air charge when calculating runner length/harmonic rebound/ram-effect rpm range? Probably not much that can be done about it now, will be interesting to see if there is any noticable power peaks at or above your predicted rpm range. Dave

You run lean in #6 because its getting too much air, not too little. I think what happens is the air has inertia in flowing that makes it harder for it to make the right angle turn on the way down the plenum, but easier after its already stationary after hitting the end near 6. Also, as air increases in temperature, so too does the increase in particle excitation, and hence the speed at which pressure equalizes, as indicated by an increase in the speed of sound. This is likely to affect your ram-effect RPM range. Here is a potentially handy calculator: http://www.sengpielaudio.com/calculator-speedsound.htm Regards, Dave

Nice find. Dave

Can you get some square 4" and cut one side off to give it more volume? Dave

Aside from the RB25/VG30 (RB25 has smaller turbine which I think would make it better suited to twin application) `T3' based turbos, and seeing as you're somewhat handy with the fabricationer, I'd keep an eye out for the IHI VF22 turbos. They have been known to pop up on ebay for ~AUD500. Good luck, Dave

Tony, Thats a good bit of information. The reason it works is because cross sectional area is determined by the square of the radius. I know its pi r squared, but the pi's cancel each other out, so what you're left with is identical to So it starts like pi*C^2 = pi*A^2 + pi*B^2 all divided by pi gives you the pythagorean formula you mentioned. Dave

Not citing your references is called plagiarism. http://www.ami.ac.uk/courses/topics/0123_mpm/index.html Dave

Actually `yield' is point at which the material stops deforming elastically, and starts deforming plastically. Dave

Cool, back onto the topic of rods, I have no first hand experience, but do remember reading somewhere comments by someone more experienced than I that went like this: Most rod failures result from oil starvation and the resulting heat buildup. Taking that, and Tony's comments about elasticity and the resulting little, and big end deformations, it would seem plausible that if the big end becomes elongated, (in addition to heating it up), it would affect the oil supply with more oil leaking out past the points which are further from the crank journal. As I understand it larger clearances are a good thing as the oil flow (and hence cooling capacity) is increased, but I would have to guess that the additional flow and cooling capacity do not outweigh the additional heat in the rod due to deformation. That, and ensuring that your crank is cross-drilled so the `centrifugal' forces aren't pulling the oil out faster than the pump can supply it. I envy your machining shop, and skills 1 fast z. Dave

In chronological order: Dave

CFD is just a somewhat educated guess. If you have the skills, build it and test it. Will be no mistake that way. Dave

Arrogance versus talent.

Dude. Wtf. Dave

Noone is arguing that a heavier car isn't harder on the drivetrain (atleast not me). I am arguing your reasoning. The reason is that the heavier car has more load on the tyres, which makes them less likely to spin, in addition to requiring more torque to move it. Experience is worthless to us here if you can't explain it properly. Noone is going to take your word for it. Dave

Jeff, I would probably recommend making it a sandwich design so the bit that seperates the plenums is simply bolted together between the two halves. Then you can not only adjust the shape/profile/size of the slot, but you can remove it altogether, all by undoing a few bolts. Would also allow you to do back to back dyno testing, hint hint. Dave