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Twisted46

Underwhelming Lap Times

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On 9/18/2019 at 6:00 PM, Twisted46 said:

 

Here is a clip my wife took, It was lap 1 so not full out but you can see how much the car is leaned over. 

https://drive.google.com/open?id=1lHUmts9dnRvONSdJXeCmxB1UYCDN7UCe

 

Here is a session I recorded in the forester last year

https://drive.google.com/open?id=1_cOSLhnecTk7zxuCZ1SZRiydYeTxENpG

 

 

Not trying to be critical, but do you drive the Z like you do the Forrester?  I noticed from your Forrester video that you turn the wheel into the corner and hold it for a long time.  To be fast in a Z you need to get used to the rear of the car moving around a lot, especially when stock.  The trick is to learn what's too much and what's just right.  To someone that's never lapped a Z hard before this can feel like the car is going to kill you.  You will be unwinding the wheel after turn in much faster in the Z.  If you're not then it's like driving around with your foot on the brakes.  It also helps to get the entry speed up, which looks lower across most of your data.

 

Cary

 

 

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Cary, in my opinion if you are worried about being criticized then you shouldn't be posting things on the internet so don't worry about it lol. I also know you have no way of knowing I raced BMWs for 7 years and only tracked the forester for the 2 years I was working on getting the Z together. 

 

That being said I am used to RWD sports cars and let me tell you getting a forester around a track takes a very special approach to handling, when your weight is 2+ feet off the ground you don't dare move the wheel mid corner, you purely steer with the pedals. 

 

Yes the Z required a lot more wheel work but I think I found my primary issue which is a front alignment that is all out of whack. Even the toe which I had set at a dealership is messed up (toe out at over 1 degree different each side.) Combine that with woeful camber and body roll and it makes sense why the car felt loose and was squealing tires at low speeds. I really think I will save 5 seconds when i get the alignment and body roll sorted. Another 5 when I start to brake later because I can carry more speed in the corners. Then another 5-10 as I learn the car more.

 

I am going to counter your entry speed comment. If the car is already pushing in understeer more entry speed is going to slow your exit speed down. 

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Well I may have found the true root cause today. I had the front in droop while changing oil and was playing with the drivers side wheel and noticed a huge amount of play. The new moog rod end is shot, couldn't tell with weight on the front. Thank god it did not let go at speed mid turn.  

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first off get a laptime simulator ( more than willing to help with this / offer my services...) see what the car is capable of doing on the track with the inputs see if it really is car or you..... see what difference is then start by optimizing car for said track.... optimimum lap is a great start. dont throw money at things you think could be the problem without knowing what it actually is.... can easily find the cg of a car, and a rough estimiate of torsional stiffness and mass dist at home with some help. plug that and suspension into simulator see what it spits out. then start tweaking car, some software can tell where improvements can be made others cant... at end of the day picking up a book on vehicle dynamics is never a bad idea. 

 

more than happy to help a fellow z owner!

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16 hours ago, heyitsrama said:

any updates to this? i just tracked my Z after a long time, i was actually really impressed with the handling from my buddies CRX, and was kinda disappointing to get back into the Z.

 

I would like to hear as well.  For years I have tracked an E30 BMW with fantastic handling.  I am scared to death I will finish my very expensive years long "Z" build and wind up with an unwieldy dog of a car with a big engine that only goes fast in a straight line.

Edited by Ironhead

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1 minute ago, Ironhead said:

 

I would like to hear as well.  For years I have tracked an E30 BMW with fantastic handling.  I am scared to death I will finish my very expensive years long "Z" build and wind up with an unwieldy dog of a car with a big engine that just goes fast in a straight line.

I think i have a shit setup for the track tho, its essentially just poly bushings with KYB struts... perhaps my expectations were too high ha..

I blame being a poor college kid  when i started my build. 😂

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You can sort a Z and make it handle. Just takes more work than it does on a newer car with a better suspension design. Took 2nd overall at an autocross this summer, along with 5th on another occasion. But if you're expecting to put poly bushings and KYBs in one and be at the front of the pack, eh, not so much...

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Hey guys, IIRC Greg Ira holds the S30 fastest lap at the same track nearly 20 seconds faster so yes they can be VERY fast. 

 

I have not had the car back to the track, full winter here in Ohio now. But if you read some of my posts I am pretty sure I found the major issues. Aside from braking much earlier than I should have my front tires were only using about the outside 1/4 in turns due to camber and probably some flex. I bought NCRAs and a triangular front brace. I also found a new tie rod end that was floppy that could have ended very bad.

 

Have to wait until April to see results but I am expecting to cut 10 seconds with camber and braking.

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Well I ended up getting the NCRCAs and T3 front triangulated bar installed. Two new tie rods and a fresh alignment (2mm toe out) in the front, I did find that the rear has a pretty big toe in issue. Nothing I can do about that at the moment but the tires don't seem to upset so I will just run with it. I did some more cage work in the mid and rear including a welded STB and connecting the main hoop to the roof rails. I still want to tie the front of the rockers to the frame rails and up to the strut towers but can't find time. The car feels extremely tight and planted now even a lower speed. The Hawk HT-10s should help in the braking department and give me more confidence. 

The biggest change though was an unexpected engine rebuild. I started to loose a rod bearing so why not just rebuild the whole thing and give it more power. I followed COMPs XE274 cammed vortec build and holy S does this thing scream now. I can tell I will easily be 30 mph faster down the back straight just based on how fast 4th gear is over. I plan to do some logging this weekend but I am estimating that 40-90mph in 4th takes less than 6 seconds which is roughly my hairpin exit speed. I haven't tested 5th gear out yet since I am only running up and down the highway and try to keep things safe and reasonable but if it pulls anything like 4th I will easily be over 130mph before I need to get on the brakes. 

 

Only two weeks left until proving day. 

 

 

 

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I have some lap data to sift through but the car (and me) were much faster, around 10 seconds without getting 100% clean laps since the track was really busy. I didn't get much seat time because it rained all morning but I have 3 more weekends lined up. Most importantly the car feels GREAT now. I wish I could explain better how the car felt before but images driving around on 2" wide tires. Now it feels like a car should again with amazing predictability in the corners and improved grip in the front. The additional reinforcement is very noticeable and turn in is awesome with the NCRCAs. The fronts are wearing evenly now which is probably where 90% of the change that I feel. It also tucks the nose in really nice mid corner if I ease off throttle a bit. Anyone that has seat time at the track understands just how important confidence is to lap times and I feel comfortable in the 260 now. 

 

As for the engine and brake upgrades.. hoboy does she fly now, actually slightly terrifying going 136 down the back straight with no ABS to rely on :). But seriously there were very few cars on track that pulled harder in the straights. The HT-10s are amazing and will lock up the tires pretty easy at higher speeds so I buy in to the guys who say that you only need better pads in most cases, If I was running longer that 20 minutes I would looks for upgrades to manage heat but that is a non-issues for the time being. 

 

I may look at getting some spacers for the rear this season but am largely happy with improving my times in the car as-is this season. The next big project is coilovers to reduce roll and rear end replacement. 

 

I will get some video next time and post it. 

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Had another good day out this past weekend, dry with temps in the 80's so it was near perfect. I beat my previous personal track record by 4 seconds and was hanging around with some prepped spec Boxsters, they were faster in the corners I was faster in the straights. I am going to have to go to different rear brake setup though. The 280zx kit has been giving me issues with dragging/sticking that is causing me to miss some track time to adjust and bleed, keep warping rotors. I don't think they can handle the heat and abuse of slowing the car from 140 mph so I am gong with the kit I probably should have in the first place, Wilwood 2 piston.  

Other than that I am really happy with the car's balance still.

 

@heyitsrama I am running a fairly stock rear end with just KYB struts and German springs. I am planning on A-arms and coilovers this winter mostly for alignment tuning. I am not sure if you consider a suspension mod but I have a welded rear tower brace that ties in to the roll hoop I replaced every bushing with poly stuff. Also running no rear bar. In the front I have the same strut/spring combo with T3 NCRAs and the triangulated brace, and 280Z bar. The last two, and to answer your question, are mandatory in my book on a Z that gets driven hard. Those were my two latest additions and completely transform the car for a few hundred dollars. The best way I can explain how the car felt before is vague, disconnected, and unpredictable which I would attribute to poor suspension geometry (after lowering) and very weak suspension connection in the front. I think you could get to the same place with control arms but those are 3-4x the price of the NCRAs (comes down to how much adjustment you want) and . I don't know that the brace actually increases grip but it makes the car FEEL better and respond more consistently corner to corner which is worth way more that a few seconds off a lap to me. 

 

I have two conclusions (which are much the same as those before me) the S30 needs major help in front suspension connection (side to side) and frame to frame connection (front to rear) once you start eliminating the unibody as the main carrier for suspension loading the car feels much better. Second the front suspension geometry is a mess when you lower the car, I would wager that given the same spring rate a standard ride high Z is faster around a track than a lowered one, all other factors being equal. 

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Interesting comments and I think that you have nailed the crucial weaknesses in the stock S30 body for race use. Basically the fire wall does not sufficiently connect forward to the front suspension load points. Also the attachment of the front X member which bolts to the rails, the stock four bolt setup allows flex, it's simple to add a couple of brackets forward to bolt to the rails.

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Totally agree, and thought I'd throw my $.02 in as well.

Re: front strut bar, I did my own about 20 years ago and I've relayed the experience many times, but after installing I took a test drive on my favorite curvy road and nearly drove off the inside of the road because the front end responded so much better. Night and day. People tend to think that the strut bars hold the strut towers apart, and it might do that when you go over bumps, but when turning the load comes in at the bottom of the tire which pulls the top of the strut tower out, reducing neg camber. So strut towers help to preserve your static neg camber setting under load and that's why the front end grip is much better. Learned this out of a Porsche Owners Club magazine where they had tattle tale dial indicators on the struts and did some skid pad testing before and after.

From personal experience I would suggest that the Z chassis is VERY weak in beam loading (fore/aft). When I used to put my car on jackstands I'd set them under the TC rod boxes and I could literally watch the front end droop about 1/2" under the weight of the motor and hear the metal creaking. When braking at 1g and the forces trying to both pull the front strut towers forward while simultaneously folding the car in half around the firewall are much greater than the static weight of the motor. I'm not convinced that subframe connectors do a whole lot to help, either, even though I have them on my own car. There needs to be a strong load path between the front and rear struts that prevents a lot of flex under braking.

To that end, any well designed cage for a Z should connect the strut towers front and rear, IMO. Can be done through door bars, or with bars down the center of the car, but I think it's a shame to build a cage and not take advantage of the opportunity and I always shake my head when I see a car that has main hoop supports that don't connect at the strut tower. I'm also increasingly convinced that I did my front strut/firewall supports in a suboptimal way, and that an X from the strut towers to the dash bar with the V's connecting at the firewall is a better way to go than a V to the middle of the dash bar like I did. Eliminates the need for the bars down the middle of the car to connect the front and rear struts. This encroaches on the space above the engine and might make it harder to get the engine in and out, so I'd do a bolt in V in the engine compartment and weld it in on the interior side.

 

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1 hour ago, JMortensen said:

From personal experience I would suggest that the Z chassis is VERY weak in beam loading (fore/aft). When I used to put my car on jackstands I'd set them under the TC rod boxes and I could literally watch the front end droop about 1/2" under the weight of the motor and hear the metal creaking. 

 

Don't have anything worthwhile to add but I can't remember if you have a 240Z or a 280Z.  When I first got my 76 280Z I was surprised at how stiff the unibody was.  Before I knew better I lifted from the back of the front frame rail and could get the whole side of the car up with no apparent flexing.  I was used to old chevys that creaked and groaned and bent as you lifted them. 

 

The difference between the 240 and 280 bodies is often a topic of discussion.

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On 7/31/2020 at 12:08 AM, 260DET said:

Interesting comments and I think that you have nailed the crucial weaknesses in the stock S30 body for race use. Basically the fire wall does not sufficiently connect forward to the front suspension load points. Also the attachment of the front X member which bolts to the rails, the stock four bolt setup allows flex, it's simple to add a couple of brackets forward to bolt to the rails.

 

Do keep in mind that the way the crossmember is bolted in is considered a safety feature.  It's designed to shear in case of a heavy frontal impact and allow the engine to go under the car rather than through the firewall.   The downside to all this as you mention is there isn't a lot of stiffness available for the strut tower or the front suspension points.  When you look at newer cars it's interesting to see just how much additional structure they have put in place in these locations.

 

Cary

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