jt1

The same frontal area was used throughout the tests, for all cars. Bob gave me a quickie run thru of the conventions aerodynamicists use to determine frontal area while we were measuring the car. As I understand it, the silhouette of the car at the largest point, plus the area under the car, is the area used by all tunnel operators to keep it consistent between tunnels. So, if you were looking at the car from the front and could see the whaletail protruding around the cabin area, that doesn't affect the frontal area because it's not at the largest point on the car. This is like many of the conventions and definitions used in all engineering tests and calculations. Also remember that we were not looking for razor sharp absolute values, we were more interested in trends of the data. This let us get a lot more tests done in the time we had available. That is correct. The tunnel has four pads in the floor that the tires are strapped to, and the pads have sensors attached to them that give XYZ force vectors. Then, knowing the force exerted, wind speed and frontal area, the respective coefficents are calculated, then used to calculate forces at speeds other than the test speed. The tunnel has some sensors inside which monitor wind speed, pressure, direction, and more, but these are used to determine the performance of the tunnel itself. Any data related to the car comes from the force pads in the floor. It's possible to directly measure aero pressure at different points on the car, but the setup takes up a lot of tunnel time, at 490 $/hr. We didn't do any of the point pressure testing. The "rad" numbers you asked about were sensors used on the radiator in a previous group's test. Apparently they were picking up some breeze in the basement under the tunnel, which is where the sensors are located. John

Yup, that pretty much sums it up!!!!!!!!! There's some history behind the gnose car. We thought we were going to have a gnose to test, then it became obvious we were not due to complications. The, about two weeks before the test, I passed a moving sale in a nearby community. Among the stuff being sold was a pristine 69 vette, a 350/350 4spd conv., a tricked out Z71 pickup, a nice 300z with a well done 350 swap, the gnose Zcar, and a nice 78 trans am. The guy said where he was moving he couldn't keep all his toys, so all of a sudden we had a gnose to test. That's how it was called "the yard sale Z" The gnose is a two piece model, and does not extend all the way back to the radiator support. I have no idea who made it or what vintage it is. It turns out a local member has a set of the very rare, very expensive gnose headlight covers we could have tested. He didn't know we had found a gnose, and I didn't know he had the covers. John

I broke one at VIR last fall. Luckily it broke on the inside and at a slow speed, so the wheel didn't come off and there was only minimal damage from the halfshaft flopping around. It's a combo of sticky tires, more torque, and abuse. For instance, curb hopping under power is very hard on the axles because of the shock loads. I think if you're over 300 hp, and running R's or slicks you need the MM axles. John

CD and CL are coefficent of drag and lift, respectively. These are unitless numbers which are used in aero equations to calculate the forces at a certain speed. Basically the smaller the number, the less lift or drag is generated, so for our purposes smaller is better. Bob Smith and I measured the gnose car to come up with the frontal area. There are some conventions used, but it's basically the silhouette of the car, with the area under the car included. Using a jig he had, we measured the height at the roof, the height at the drip rails, the height of the rolls on the doors, and the widths at each of these points, then he has a program that gives the frontal area. The wind speed was actually 80 mph. As I understand it, the reynolds curve has a knee point at 80mph, so if you test at that speed you can interpolate up or down. The "REQD INPUT" is a value you can change on the actual spreadsheet to calculate forces at different speeds. In the case of the sheet Mike posted, all the forces are at 120mph. If you change the speed, the forces change, but the coefficents do not, they stay the same. So for the purposes of discussion, it best to talk about CD, CLF, and CLR, the coefficent of drag, lift front, and lift rear. The "RAD" numbers have no meaning for this test. As far as I know, the tunnel doesn't put out anything explaining the data, although it would be cool if they did. John

The bondo guy has some talent. Somebody should set him up making molds and laying mat. Those are some nice looking fenders. John

The gnose car had 225/50/15 tires, so I'm pretty confident that made a difference in the drag compared to the stock car. There is probably a lot of room for improvement on the gnose, you could seal the nose to the radiator support, add an air dam, add headlight covers, etc, like we did with the other car, but we only had so much time to work with. John

Two piece and one piece refer to the rear main seal design. Up to 86, blocks were two piece rear main seal, then GM made a running change in 87 to one piece seal blocks. You must use a crank that matches the block, they will not interchange. Grumpy's pic shows why, the cranks and blocks are very different in the rear main seal area. I think you're getting a really good deal, and I like good deals. I would but the stuff just because it's a bargain, even if i had to get another block. Are the pistons new or used? Still a deal either way. You need a two piece seal block to match the crank, that's standard bore and will clean up at 20. If it's a two bolt main I would use arp bolts in the main caps and line hone it. The 400 cranks mains have to be turned down to 350 size, usually the bottom of the cylinders have to be notched to clear the rod bolts, sometimes the pan rail too. Depending on which rod you use you may have clearance problems with the cam, so that has to be checked. You get to know your machinest pretty well doing a 383. There might be a clearance issue with the 400 damper if you use JTR engine mounts. You probably need to do a search and see, but you might need to use MSA mounts to get the 400 damper to clear the steering rack. The 400 damper is larger diameter than a 350 damper. Once again, I'm not trying to be negative, just letting you know some info you need to come up with a plan and make decisions. 383's are cool engines and make a lot of power. Mark has one in his beautiful yellow 240, and it's so much stronger than my 350 it makes my head hurt. John

lbhsbz, congrats on getting the car running. It's always great to get a new motor or new project running for the first time, and get it out and buzz around some. Now you can start refining all the little things. It's interesting the car weighs out that close with the scarab mounting position. I would have guessed a little more front weight. Do you know any history on the front fenders? Based on the WTT, that's a nice design, with some lip in front of the wheel, smooth transition into the air dam, and a big vent behind the wheel to evacuate air. Are they full fiberglass or modded steel fenders? John

1) You will have to get the 400 mains turned down to 350 main size; 2) Is your block a two piece seal block? the 400 crank won't work with a one piece; 3) You will have to get the whole show balanced. Not trying to be a downer, just trying to let you know some possible pitfalls to be aware of, you have the possibility of having a nice inexpensive torquer combo. John

If the spacers are made of quality material and fit properly, and the studs and nuts are upgraded, I don't think they present a problem at all. Usually the people who have trouble with spacers have some cobbled together mess. John

Several years ago Porsche had some wheels designed to pull air out of the wheelwells. Their idea was to improve brake cooling, with aero secondary. jt

Preith, that's some nice workmanship. Sweet car. John

I bought a set. I was mainly interested in quieting the car some without losing much power. At the time, my car had straight pipes on it, and it was LOUD. I ran them for several track events, and according to the butt dyno, they didn't affect power up or down. They did quiet the car some, so that was good. I changed them out for a set of race bullets, mainly because the sound of the inserts wasn't for me. They give the car a sort of high pitched exhaust note. They were the 3" 3 disc version, and could be purchased for a reasonable price if anyone wants to try them. John

http://forums.hybridz.org/showthread.php?t=118733&highlight=arp+studs

I should have been more specific with the drag comment, because I was thinking of the rear spoilers. I "expected" to see more drag from the rear spoilers, because circle track guys are always laying them down or shortening them. Several of the mods did increase drag, but they also had a positive downforce result. But, each of the rear spoilers produce a lower cd than the car with nothing on the rear. This amazes me, and I haven't been able to come up with a common sense explanation. jt

I'm curious to see how much it reduces the temps. I bet it will be a lot, but how much? Also, that brings up the question what's a desirable range for temps? All I can say about mine is it gets way to hot to touch, like burn you hot. jt

I wouldn't even think about the side force or yaw moments. Unless you take a lot of time centering the car in the tunnel, they are worthless. We didn't spend any time on that, thinking the time was better used on something else. I was pretty surprised that almost everything we did had some positive effect, some just more than others. Drag being fairly constant was also a big surprise. I thought the whaletail and wing would eat a lot of hp, but that's not the case. jt

Very cool pics!!!!! Thanks for sharing them. John

That was an eye opener. The hood raised up about 7 -8" and stabilized. The mule didn't have a safety latch, neither did the gnose car, and both did about the same thing when the hood flew open. Exactly what Bob Smith explained to us. If you know where the center of the ball of air is, the "stagnation point", that's the best place to put openings for cooling air in the front of the car. They are vented with perforated screen, just another one of the many cool details on Roddy's car. John

Great you had a good weekend. Keep looking for the sweet spot. I've started the V700's as low as 24 for a time trial. They hurt the edges a little and heated up quickly, but for about 3 laps they flew. John

I think our test cars had positive underhood pressure, and that air is flowing out the vents because of the pressure differential. The Bernoulli effect is helping, but it's effect is secondary. If I am understanding you correctly, you think the underhood pressure is negative, and air flows out the vents solely because of Bernoulli. What happens when the hood latch of a Z at speed unlatches? And why? John

The box doesn't create negative pressure. It separates the high pressure air headed for the radiator from the (hopefully) low pressure air under the hood. Then the low pressure air can work on the additional underside area of the hood & nosepiece, which was previously exposed to high pressure, and create additional downforce. Note the tests where we taped up the vents on Roddy's car. There was less front downforce with the vents taped. I think the box is a great idea, and my track car will have one on it. I just don't think it helps much until you get the underhood pressure to go negative. John

Jon, we didn't have time for any pressure data, but the yarn indicates we never did get a negative underhood pressure, even with Roddy's car with the grill almost completely blocked. There was air flowing out the vents in all tests. If we could get to the point of negative underhood pressure, then the radiator box makes a lot of sense, but there's a good bit of work to do on the frontend to get there. We're not even close at this point. John

...yeah, yeah, yeah...... Put some regular halfshafts in that thing and let's go harass the Porsche guys at CMP this weekend, I'll save you a spot. jt

The Vintage Z's were very nicely done cars, but they weren't "correct" restorations. You could find a number of incorrect things on the one I used to own. It ran, drove, and looked just like it was brand new, and had an awesome paint job. That car made me realize I am an enthusisist, not a collector. When you've got a perfect paint job, it can only go downhill, rock chips, door dings, etc. I owned it two yrs and put 600 miles on the clock. jt