Underwhelming Lap Times

[Twisted46]

My main goal with the cage work was to protect myself  but also to eliminate the work of the body between the rockers. There clearly isn't a lot of meat there so I tied the frame rails to the rockers at the T/C rod mount points and the roll hoop legs are only about 3 inches from the rear frame so that was an easy box weld with some plate to connect the rear suspension to the rockers. Door bars are there to triangulate the rocker structure and provide side impact resistance with vertical bars that come down behind the front seat brackets. I plan to add some material that connects those vertical bars to the tunnel and figure out something stronger at the firewall. I also want to add a bar that connects my rocker to TC bars to the upper frame horns. I don't expect to feel that difference very much but I do think it will be critical when running 400 in/lb springs. 

 

In other news, I got tired of the 280zx rear brakes overheating and went with a SM wilwood kit.  

[260DET]

Yes, looking at modern cars can be a lesson in where additional bracing can be done on the Z car, MX5 is a good example.

[heyitsrama]

@Twisted46 Thanks for the recommendation of the NCRCA, I'm very impressed with how much better the steering feels over bumps and within hard turns. It no longer feels like i have to fight the car in the corner.

I have to weld my strut brace up, from what Jon also says there appears to be a lot of improvements to be had. ( and hopefully shaved time in the corners). October 12th is the next day, plenty of time to do some testing before then.

[Twisted46]

You guys that have long track seasons are lucky, we are pretty much limited to 5 months here and two of those you can almost grantee rain. I have 2 more weekends this year, hopefully those Wilwoods pay off!

[heyitsrama]

@Twisted46 get some video footage if you can! 

[HowlerMonkey]

Tires are 225 but i didn't catch the other important size numbers.

 

Lots of guys have track records on 60 series tires because they maintain a bigger footprint through non-optimal camber changes than a square shouldered 60 series tire.     

 

Rim size vs tire size matters in contact patch area.

 

 

Edited August 20, 2020 by HowlerMonkey

[Twisted46]

8 hours ago, HowlerMonkey said:

Tires are 225 but i didn't catch the other important size numbers.

 

Lots of guys have track records on 60 series tires because they maintain a bigger footprint through non-optimal camber changes than a square shouldered 60 series tire.     

 

Rim size vs tire size matters in contact patch area.

 

 

 

True,

The Subaru had 225/45 300tw rubber on 17x7 wheels. The Datsun has 245/45 100tw rubber on 16x8 wheels. I think the problem was down to front end geometry being out of whack and me getting used to the car. The tires are glue after 2 laps now and let me take corners faster than I am brave enough to. 

 

I will be sure to get some footage this weekend.

[260DET]

Pic of my 280ZX front end bracing, what can't be seen is the square tube running the length of and under the sill, great for jacking too.

 

[Twisted46]

@heyitsrama As requested: https://drive.google.com/file/d/1ZMTusthPTrX-YXbRUJZl4vM3uAgz9SC8/view?usp=sharing 

Ignore the tires rubbing the front flares  a bi-product of wider front track I will need to address this over the winter. 

Also ignore the very incorrect time stamp, no idea how I did that. 

 

So this was my first full lap out and sadly ended up being my best of the day. Coming on to the front straight to end my second hot lap I got black flagged for spilling fuel out of the fill cap. Sure enough it was soaked so I taped up the gasket and that fixed the issue. Session 2 I started good but got black flagged again because of smoke coming from under the car. Turns out a plug in an unused dipstick port came out and was misting oil down on to the exhaust, fixed that.

 

I then started having fuel starve issues for the rest of the day that I had previously only noticed when I was running the fuel level too low but I was running around half a tank of gas (trying to prevent more sloshing out). Basically when I would get out of a hard braking/turning zone the engine would sputter if I tried to give it any throttle and AFRs shoot up in to the 20's. This was very noticeable down the back straight where I could get on it for corner exit but by the time I would shift to 4th I would basically coast along for about half the straight and then get power back. Obviously this killed my times and just threw my focus off in general and I ran in the high 1:50s the rest of the day. My assumptions are that either the stock pickup and baffle are just not able to take the Gs or have broken off. When I cleaned the tank they were in place but who knows. I don't THINK it is a carb issue because it acts fine mid corner and corner exit which to me rules out a slosh problem. It seems like the carb is not getting enough fuel during hard corners and uses up what reserve is left in the bowls before the system can catch back up. I testing the pump in car last night and it pushes 5.5 PSI and plenty of volume when sitting flat. 

I am already planning to add a fuel cell before next season so in an attempt to temporarily alleviate the issue I am going to run a bigger needle and seat to help with recover and try to properly seal the tank so I can run it near full without any issues. I know another quick fix is to raise float level but I would rather not. 

 

Good news, the brakes felt amazing and I had not overheating or dragging issues with the rears. I only have 1 track day left this season so hopefully I can get through it without issues. 

Edited August 26, 2020 by Twisted46

[jhm]

Yeah, you probably already know that fuel starvation is an issue under heavy g-loading....even with as much as half a tank.  The fuel cell should def fix it.  A small surge tank in conjunction with the stock tank is another possible solution.  (Or just keep the tank at least 3/4 full all the time! )

 

I've had issues with fuel spilling out of the gas cap with certain locking caps, but never with the stock non-locking cap....they seem to really lock down tight and prevent any spillage even with full tank and long fast left-hand sweepers.  Are you having any pressure build-up in the tank; and if so, maybe consider how you have the tank "hosed" to allow venting?

 

Sounds like you've got a nice "to-do" list building for this winter!   

[Twisted46]

@jhm I have a rollover/vent with loop coming off of the top rear port in the OEM tank. I have never noticed any pressure build up, sadly my OEM cap is not very snug. I have been on the hunt for a new gasket but can't find them. 

 

I absolutely do haha, although I do not plan on doing a surprise engine rebuild again this winter  

[heyitsrama]

I ran into three issues in my last track event.

1. overall trust in the chassis, although the NCRCA helped with the turn in and significantly reduced the bump steer, the chassis still feels like it’s flexing a load. I think it’s time for a triangulated front chassis brace to help address this.

 

2. damn fueling issue, I realize that there is a leak in my system, I think it occurs at the fuel filer neck. I noticed fuel on the quarter panel, and coming out at the fill as well. I think the actually fill tube might need to be replaced. So can’t let the fuel get below 1/2 tank, can’t fill it past 3/4 😒.

 

3. hesitation at 3.4K rpm, occurs at ~1/2tank. I noticed this happens when the track gets hot. I was thinking it could be related to fueling, but I really have no idea what to look at here. Street driving the car runs great, and I was not able to replicate that issue on my drive home. 
 

On the plus side I got my lap times down from 1:54:00 to 1:48:16! 🥳

next track event Dec 6th, hopefully the rain holds back.

Edited October 11, 2020 by heyitsrama

[Twisted46]

@heyitsrama 

1. Hands down the biggest issue with these cars, I love my T3 bar but I am sure other work great too. Makes an unbelievable difference for the price.

2. HAHAHA, it is not funny but interesting that we seem to have the exact same issues with different setups, I used gorilla tape liberally and had no more leaks out of the filler neck. I am going fuel cell next season. because having to run in the sweet spot of fuel level is annoying at best. 

3. I had the same issue , bowls would drain empty on the next straight after a tight corner. I have a Holley so the simple fix was raising the float levels just a bit and installing higher flow needle and seats. That does solve the problem but did solve the side effect. 

 

Good luck at the next event, we are already approaching below freezing at night here so car season is over  

 

Now for an update, and probably my last for a few months. 

 

The season finale started of great, car was running good and I wasn't having fuel issues. we were only going to get a half day since storms were coming in shortly after lunch. IMSA had just been at the track all weekend so it was pretty slick and the first two sessions were very short due to some black flags and wrecked cars. To make up for it they gave us a 40 minutes session right before lunch break and I was setting my best lap times yet, car was running great, I was feeling great. 37 minutes in and as I shifted into 5th on the back straight there was the unmistakable sound of an engine coming to the end of it's lift and lots of white smoke following. To make the story short I don't know what failed first but all of my coolant was in the oil pan and 4 lifters were completely disintegrated with pushrods down in the crank case. Watching back video the oil pressure looked fine and water temp never got over ~200. I don't have the engine pulled yet but I don't need to look at it to know the bottom end is toast.

 

FYI solid rotors in front were fine during that session with good pads and fluid. 

 

As tempting as it is to just sell the car as is and move on, I know I could never buy anther for what I paid for mine and would never recoup 1/4 of what I have put in to it. So a new engine it is, and probably not another SBC as I am learning they are not the best for my application without a fairly expensive build. I feel like I have rushed this build just to get it to the track up to this point and have decided my best path forward is to take a year off an build it properly to be reliable. My initial thought is going to an aluminum LS motor with a new stand alone ECM to clean up the engine bay and interior and hopefully be more reliable, but my mind will probably change 10 times before I actually go buy a new motor. I am not looking to make more power just to make it more reliable living at 4-7K RPM. 

 

I did not intend for this to be a build thread but what the hell, may as well keep it going now!

[jhm]

@heyitsrama, Hey Amar, do you notice the fuel leak all the time; or just at the track (e.g. long fast left-handers)?  Your fuel cap may not be making a tight seal.  If it's a stock cap, you can try bending the little metal tabs to tighten it.  If it's a locking cap, many of them don't fit tightly enough to provide a good tight seal.  Old BMW locking caps can be made to work nicely, but they're no longer in production and pretty hard to find these days.  I have the stock tank still, and have to use the stock non-locking cap to prevent leakage any time I'm at the track....I only use the locking cap for street driving.

 

Regarding difficulty filling your tank....have you modified the stock tank hosing?  If so, that may be the root cause of the issue.  The tank needs to move fuel freely within itself, and be able to vent air (both for ease of filling, and to prevent pressure build-up during operation.)  The stock evap tank allowed this, but lots of people (including myself) remove it.  The "hose loop" method mentioned by @Twisted46 usually fixes most of the issue.

 

Good luck with, and good job getting your lap times down! 

 

[heyitsrama]

@jhm I noticed there was a steady leak when i filled up the tank and parked the car on the driveway, it was dripping from the middle of the body, between the body and the fuel tank, right below the license plate... But that was on a slant, when i was at the track i noticed it was dripping at the corner of the rear wheel well on the passenger side. i think the leak could be at the fill neck, perhaps on the inside where is enters the body hole for the fill? I was using a flashlight to shine light inside and see for a hole, did not spot anything. ill test out with the bent tabs, that's a great call. I had this shitty locking cap that offered no seal whatsoever, i shoved a towel followed by a latex glove to keep the fuel down, actually worked pretty well ha.

 

I replaced all the hoses the last time i dropped the tank (excluding the fill), and retained all the stock evap tank, (although i dont have a smog pump or the charcoal canister hooked up). Perhaps this could contribute to the hesitation issue i was experiencing, i notice that this does occur when the track gets hot (later in the day, but i also might have low fuel, and can use a surge tank)

 

@Twisted46 The whole day i was at the track, i was thinking i should go find a ls1/t56 and enjoy fuel economy + power when i need it on the track. I dont need 500 HP, stock ~300 is enough to take the kids to school, and not have to deal with the carbs. I think its an option im going to keep on the table, but i would certainly go back and do more chassis bracing to support the torque.

 

I see that people are retaining stock tanks and using these fuel pump that a fill bag that lays into the OEM tank, because of the surface area of the foam bag (sock?) its able to continue to pull fuel even when the fuel is sloshing around. I think MZR is using this in their EFI Z's they are building in the UK, i was shitposting chatting in their comments on their instagram, and it seems that they don't used baffled tanks, they just use these types of fuel pumps.

 

[JMortensen]

Just FYI, I've got an L33 aluminum block 5.3 with a small cam and carb setup because I can't wire a lamp and it should put down 370whp, so that's mid 400s at the crank. It's not hard to get power from the LS. It's glorious, runs on pump gas, not high strung like my previous L28 with triple 44s and 11:1 and all that stuff. Torque out of low speed corners is amazing.

On the tank, I would suggest NOT doing a fuel cell. I had similar issues with leaks, I think my tank split the seam or something. Wasn't rusty, never had issues with rust in the lines or any of that, but WOULD NOT seal after replacing everything, also never could seal the cap either so I'd always have fuel leaking out around the door from tight left handers. A cell did solve that problem but it was expensive, added about 20 or 25 lbs (friggin heavy), and was a serious PITA to install correctly with a barrier between the cabin and the cell itself, something most people don't do.

Surge tank is pretty easy to DIY. Have been thinking about FI for mine, and looking at options. There are a lot of AL catch cans out there with NPT fittings, would be pretty easy to set one up with some AN fittings, set up an inline pump for the FI and run the return plumbing back to the tank. If you have a tig would also be easy to make, just get a short length of tube, weld caps and AN fittings to it.

 

Edited October 13, 2020 by JMortensen

[heyitsrama]

I guess a tig welder really should be the next thing i look at getting, it seems to be a 'for life' tool.

 

@Twisted46 is it possible to get some closer picture of your t3 mount in the rear? I need to finish the firewall plate and make something that holds the 2 rods that come from the center of the trunk. For the trunk it looks like the way t3 does it is they want you to drill a hole and throw a nut on from under the car, seems you'd be drilling right above the differential.

 

I think i also should have used a studded rod end that will hold the rods that go down to the trunk rather than the rod eye..... a learning experience....

 

 

@JMortensen > so I'd always have fuel leaking out around the door from tight left handers

 

Maybe this is why newer cars have the little trap doors that you have to put the gas nozzle into to fill up. 🤔 I really dont want to do a fueltank swaps, id rather modify the original tank.. plus trunk space what if i want to take this car camping?    It looks like megasquirt can work on both l28 and ls series motors, maybe getting this L26 running on an EFI setup will get me closer to where i want to be with usability (its got a N42 head), and later down the line a ls motor will be an "easier"
modification. 

Edited November 5, 2020 by heyitsrama

[JMortensen]

I wonder if you could use a simple flap under the cap, like they do on fuel cells. I haven't seen a one way valve in the filler neck, if that exists that would be another option. I guess the filler hoses are all getting rock hard at this point. 20 years ago I had to remove my original with a hammer and chisel. LOL If you can still get a new one could measure and see if there is a one way valve for a 2.5" or 3" or whatever diameter hose it is.

[JMortensen]

https://www.ebay.com.au/itm/1955-1956-1957-CHEVY-GAS-TANK-FILLER-NECK-CHECK-VALVE-KIT-USA-MADE/133336309996?hash=item1f0b76a0ec:g:IxgAAOSwcB1eSbM0&frcectupt=true

 

This ebay listing is from Australia, but says the product is made in USA.

[heyitsrama]

Funny I was just looking at the same thing, can probably build something very similar that slips inside the tube and allows the flap to rotate downward, but weld in a tab to limit the flow up the fill neck.

 

I think todays project will be inspecting the fillneck for more cracks.

 

woah woah woah. look at this,

https://www.ebay.com/itm/DATSUN-260Z-280z-9-74-6-76-COUPE-FILLER-NECK-SUPERCLEAN/143555459622?hash=item216c927a26:g:4g4AAOSwNsdebXBL

This looks like there is a little flapper on the 74.5+ cars.