JMortensen
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Posts posted by JMortensen
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4 minutes ago, JMortensen said:
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We don't need to guess here. The wind tunnel testing did the MSA spoiler (BRE spoiler) and a 5.25" tall spoiler. At 120mph, the BRE made 22 lbs downforce. The 5.25" one made 30 more lbs downforce. Without a spoiler at baseline, it made 55 lbs of lift.
The much bigger thing with regards to Z car aero is to do something in the front. Cover up that huge hole in the front and I expect you'd see some real gains at the drag strip. Stock, the test car made 320 lbs LIFT. That work that the air is doing is slowing you down. If you look at the wind tunnel results the stock test #2 the car had .471 CD. If you look at the last test with the car with the most aero mods was .407. The hp to drive the baseline car at 120 was 102. The hp to drive it with the front end mostly blocked off was 88. So closing up the front is like giving yourself another 14 hp at the fast end of the track.-
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I wanted something around 10.5:1. I cc'd the chambers and did all of that and was going to hit my numbers. On the first build of this motor I used the wrong machinist. He installed the previous, smaller cam and there was coil bind. Rather than replace the springs he cut the crap out of the valves to lower them in the head, so the "margin" on the valves was zero. from the cut part of the valve to the top was pretty sharp, and the valves got hot and tuliped because of this. Set them on a table and they rolled funky, but the engine still made pretty good power when the harmonic damper failed and keyway on the crank broke. After the crank took a crap I went for a rebuild with flap tops.
Anyway I had everything just where I wanted it as far as chamber size, then replaced the valves. the new valves had no dish in them and sat much further into the chamber so it jacked the compression up, and then the head needed to be surfaced just a hair, and between the two that bumped it into race gas territory.
Mark's car is easy to drive around the grid. I don't think the cam will be your problem. It will be the clutch. Mine is much harder to move around at low speeds. You can do it, but you just don't even try to be smooth, because those tiny clutches wear quickly, so just be rough and don't slip the clutch.
I don't know if you were here when Monzter was an admin, but he had I think a triple disk 5.5 on his street car. He made a crazy intake manifold and actually seemed to get decent numbers out of the MSA Stage 3 cam (only person I've ever seen make that POS cam work). Might be worth looking up his old threads. -
I can answer some of these. I'm running a dual 7.25" button clutch on my V8. There are smaller 5.5" ones also and you can get 1, 2, 3, and 4 disk units (maybe more) to hold more power. They use a flex plate to engage the starter in the standard location. For the super hardcore racers they'll have a smaller starter that goes in backwards on the transmission side and hits a smaller diameter flex plate. You can get button clutches for the L6, don't think I've seen the tiny bellhousing and flex plate for them though. Regardless, a flexplate and button clutch reduces the weight a lot because the pressure plate is smaller, the clutch disks are smaller and lighter, etc.
I believe Cary was running steel wheels, but when you get them down that small they just don't weigh that much. The Formula Atlantic tires are not that expensive for slicks. I understood that my Yokohama 15" FA slicks I used in the 90s and 00s had a kevlar strip down the center and was told that this prevented them from expanding and changing the effective gear ratio at high speeds. FAs can get going pretty fast on super speedways, and used to run before CART cars at their events back in the day. Wasn't aware they had kevlar belts too.
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Mark has the strongest L6 I've ever driven by a long shot, it's hard to say it's lacking power. But yeah, the "area under the curve" is WAAAY bigger with the V8, and it's most noticeable when I don't shift in slow corners and he does. I also have a lot more tire than he does. My springs are about twice as stiff too. They're just different. He always raves about how my car turns in a lot harder than his. His is easier to drive, just does everything a bit slower and more calmly.
I would suggest you get that 300+ duration cam. I had an 11:1 L28/E31 .490/280 cam with the chambers polished and valves unshrouded and all the stuff done and it pinged really badly until octane got to about 95 or 96 (had to mix race gas). It both pinged and could have used more top end. I was planning for a bigger cam and all that and then finally succumbed to the V8 temptation. -
Mark Haag and I have driven each other's cars many times. Here's a cool shot of his, with mine going around the autox course (I'm driving Mark is passenger) in the background.
He has a high strung 12:1 stroker that pushes a little over 300bhp. I have an L33 which is an aluminum 5.3, makes about 370 whp. I've got more tire, obviously. Both cars are built to autocross, mine more seriously.
You can make arguments for both, and they're both fun to drive. I have to say if you were looking for the best noise, his wins hands down. But mine is faster at autox and I think if we went to a big track I'd just drive away. I know he wouldn't trade me, and I wouldn't trade him either. We both are big fans of each other's car. Different strokes... -
We had a guy here 20 years ago, gramercyjam was his user name I think. I believe his L24 autox car was 1800 or 1850. Cary, aka Tube80z, might have been even lighter in his autox car. 1750 or so. Those two always stuck out as the lightest. I don't think either of them swiss cheesed their cars to get that weight. Just stripped out race cars with nothing that wasn't needed.
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I spy a necroposting spammer.
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The wheel wells are pretty stout. Not the wells, but the walls that the connect to. There are 3 or 4 layers of sheet metal on the inside of the dog leg area. I know because I picked the seam sealer out to stitch weld in there. Huge PITA. Should have skipped it. I've seen some people lay a piece of sheet over the gap and then stitch there, that would have been a million times easier.
Those NHRA rules probably make sense on a ladder frame car, but that bar that you're showing doesn't make a whole lot of sense on a Z. Same with the main hoop supports connecting to the floor. -
Gonna be really low on my priority list. Maybe next winter. Was supposed to do the flat floor two winters ago...
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Shit. Now you got my brain rolling on this. Thanks a lot.
I don't think there is room for this front brace, I think the oil pan and bell housing would be in the way, but I'm thinking the rear one would definitely work. Maybe if there is too much crap in the way up front I could make a single horizontal bolt in xmember possibly bent to go under the oil pan, and then I could do the sheet AL on the bottom. -
Yeah, I think all of this hit home when Cameron (heavy85) was building his car for Pike's Peak. When you have to consider rolling off of a cliff, then suddenly your cage looks like it protects from top impacts but does almost nothing for bottom ones. I think really a full tube chassis is the way to go if you want bottom impact protection. If you're just looking to stiffen the chassis though, a butterfly brace on the bottom would probably do a lot. Would love to see this tested in FEA.
My plans include eventually doing a flat floor, and if I ever get there I'd like to incorporate a simple bolt in brace between the subframe connectors. Maybe just a big X across the bottom with a front and back straight member. There isn't a lot of room on my car and it's really low so was thinking about something like a .5" x 1" rectangle tube, and then just welding some angle iron feet to the corners that would overlap the SFCs and bolt on, then attach the flat floor to the bottom of the brace.
I also had the thought that I would use sheet aluminum between the frame rails (non-flammable) and that alone would probably stiffen things up quite a bit. Again, some testing would make this less guesswork, but I have zero cad drawing experience and not much desire to figure it out, so will probably just do what should work and see what happens, just like the rest of the car...
This is all cribbed from the Flying Miata braces. https://www.flyinmiata.com/default/flyin-miata-butterfly-brace-v2-0.html
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We're getting off topic, but what I did to strengthen this area was to run an X from the strut towers to the bottom of the main hoop like so. In retrospect if I had to do my cage over I'd put a horizontal bar across the top of the trans tunnel as well, I think that would give a lot of strength in a side impact. The main diag and the X would have to move up. Might have to make huge plinths to make this compliant so the cage attached to the "floor."
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1 hour ago, NewZed said:
Pretty pretty pretty sure that @JMortensen looked at that in the past.
Yeah, I asked that question in the past. I don't think I got a firm answer from anyone else about it. I ended up running monoballs instead of bushings, and welding the monoball holders into the chassis, so I didn't need the crossmember. What I ended up doing was using a piece of 1" square tube across the span, just to tie the chassis together. It's lighter and straight so probably more rigid. If you wanted more clearance for exhaust, could make a short little crossmember that bolted in at the strap mounts, on top of the RT mount, and get it a little further out of the way of the exhaust pipes, not sure if how much that gains, but I think the stock crossmember is probably 1.25" or 1.5" tall and those bolts are higher than that, so might be worth it.
If you're just street cruising, I think you can live without the crossmember and use your bolt on caps. The RT mount won't add much if any rigidity, that's not what it's meant for. -
The old school bubble flares were shaped in such a way and tall enough that you could get a lot more wheel movement, but I don't know a current supplier. The other option would be a flared quarter panel. For a narrow one, something like ztrix's Subtle Z or 940Z, or even the old California Z kit from Jim Cook Racing. For a wider one could do ztrix's YZ or IMSA flares, or one of the old box flare setups (most people find these ugly). There are other makers too, but it's really hard to find a good fiberglass supplier and ztrix.com actually ships orders in a reasonable time with good quality.
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20 hours ago, Popeye1 said:
JMortenson: I actually did not know that about the original ZGs. I do not believe I will be going so far as to go hella flush, I would like to maintain functionality. I assumed proper placement, proper trimming of the fenders (hurts to say that after all that paint work) would offer enough room to at least prevent rubbing for the majority of the suspension travel?
Way back when John Coffey fixed Amir's car. I can't remember Amir's screen name, but he had an SR20DET swap in a 260 I think. Anyway he was chewing up the rear tires on track, brought it to Beta Motorsports and John moved the flares up quite a bit. The problem is that the ZG flare is styled to be installed the way that Amir had it installed. It fits the body line when mounted too low to be functional. So I would suggest if you want functional, find a flare that has room for the tire to move. Not sure if the pics are still here of Amir's car, but that would be the place to look for how to do it. They look weird installed higher though, and if you have sectioned struts you'll probably still have issues. I would assume that Stance struts have travel similar to a sectioned strut.
The way to check it is to pull the spring and compress the suspension and look for interference. I had my car cut for flares, did that test while setting up some new control arms and found major interference. Had to cut again. Second time I cut all the way to the top of the wheel well arch. If you do that, ZGs and probable most other smaller flares are not going to have enough vertical space for the tire to move. So again, the best way to solve the problem is to limit the travel, or get better flares.
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Business is great, thanks. You get that anal fistula sorted out yet? Seems like not yet...
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Yeah, you're right. Which got me thinking, how the hell did they make that work? So I searched for a picture, and found one. Looks like the front doesn't need the flare at all, and the rear is going to cut the tire, just like all the people running ZGs today. So ZGs never really worked correctly for the intended purpose.
https://dattosankureiji.wordpress.com/2013/12/02/some-datsun-racing-history-goodness/
Thanks for piquing my interest. Always a pleasure. -
11 hours ago, Michael said:
4. Tires "fully" filling flares raises the question of suspension travel... rates, damping and so on. Too much travel and the tires will rub (or even shred). Not enough, and the ride is harsh, or even worse, the orientation of the tire contact patch with respect to the pavement is bad. Maybe good aesthetic fit results, unfortunately, in poor traction.
The purple car above, and 99% of the ZG flares people install have this problem. The have the tire all the way out to the lip of the flare in hella flush style, and because of the shape of the flare there is no way for the suspension to move an inch without the tire hitting the flare. On ZGs in particular people tend to mount the rears too low and not cut enough of the fender. I think this is because the flares were originally useless: the old 70s Japanese Zs that ran them had wheels and tires that fit into the stock fenders anyway. Why they put them on in the first place is beyond me, but I don't bolt fake vents or scoops on my cars either.
https://www.sportscarmarket.com/profile/1972-nissan-fairlady-zg
[img]https://www.sportscarmarket.com/wp-content/uploads/2016/08/1972-nissan-fairlady-zg-drivers-front.jpg[/img]
Looks like putting the image tags in doesn't work, but there's a good shot of an original ZG at the link and you can see that the flares are totally unnecessary.
If you were inclined to go hella flush, I'd suggest you run a huge stack of packers and a big foam bumpstop so that the suspension rode on the bumpstop all the time and the packers kept the suspension from compressing so far that you'd smash the tire into the flare or cut it on the not trimmed enough original fenders. Lots of newer cars ride on the bumpstops all the time, or as soon as there is any body roll at all. You can do that pretty well, surprisingly. -
There is a similar video of the Janspeed car with the hood blowing up like a balloon:
Love the duct idea, did it myself. Louvers work too, if you can do that too...
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I have the front crossmember 2.5 inches off the ground and the pan is slightly higher. I made my mounts so if you're using off the shelf stuff YMMV. My goal is to eventually run a paneled bottom. I had to raise the drivetrain because the T56 was hanging down below the frame rails (Bad Dog SFCs). 280 rails are taller so there is a little wiggle room there.
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I did the 2.66 Woodward rack. I don't drive it on the street, but I would. I don't think it's too sensitive, although you might be in trouble if you were leaning down to get something off the floor and weren't paying attention. Much nicer in slaloms.
I also did the Holley 302-2 and and Improved Racing baffles and a 3qt Accusump. I have a 30 lb low oil pressure light, haven't seen it come on when autoxing on 14" wide slicks.
More info on my swap here:
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I was out of town, thanks for posting this info Arttu. I have this end: https://www.ebay.com/itm/381257941708 which came off of a sway bar for an E46 that I bought used for an extremely good price.
Here are some details on my blade end from Hoerr Racing Products: "The GC1042 blade is a 950L blade which is the longest one we offer. The .310 thickness is a bit heavy for a 1 ¼” dia bar, a .270” blade would be more ideal. Let me know which direction you end up going with, I’ll be glad to help out if you choose to buy new items."
So that would be 7.75mm thick, tapers more dramatically, and is also shorter at 190mm. Now I'm mulling selling and buying the thinner .270 blade which is 6.75mm thick, or just making an adjustable bar end and leaving it be. I'd love to have the in cockpit adjustability, but not sure how much effort I want to put into it.
Rear spoilers, opinions and comments welcome
in Body Kits & Paint
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DM me your email address I'll send you the full size ones, or you can find them in my albums on FB: https://www.facebook.com/Jon.E.Mortensen/