SCCA EMod MGB GT V12 Build

In reply to GameboyRMH:

I only raised front ride height, I don't think rear RC would change much.

I still think the cause was a change in roll axis inclination, but I'm surprised you got such a big difference at the front. Sounds like you could get a lot more front grip with 1" drop spindles, but then you'd have to improve rear grip to get a decent handling balance.

In reply to GameboyRMH:

I have 2" drop spindles on it now. I have no problem getting more front grip, the problem is that it always comes at the expense of inside rear tire spin. The site where I got extra grip last weekend doesn't generate enough grip to reveal this problem so I don't know if the raising of the front would result in a better car in Lincoln. I messed around with my suspension program a bit and it gives the ability to raise or lower the car and see dynamically what happens to everything. Raising the car 1" in the front only results in the front roll center rising by 1.3" and the rear roll center rising by .41" so I think the roll axis is not what caused the increase in front grip. Over the course of a weekend, I have raised rear RC by several inches and I doubt I could feel .41" rise in RC. It could be the change in camber at the different ride height but I don't know until I do some testing.

Is there somewhere close by to do hot laps without CMP oversite...

759NRNG wrote: Is there somewhere close by to do hot laps without CMP oversite...

There is a local guy who rents the entire road race track once a month and charges $100 for a whole day. I should try to get out there and bring a bunch of pylons to do some testing

Loose, all this roll center, axis inclination mumbo jumbo makes my head hurt .....are there pictures, alternative webb sites for a more digestible conclusion? I may be old ,but I learn something new everyday. Peace out.

How horizontal are (were) your lower front control arms??

759NRNG wrote: Loose, all this roll center, axis inclination mumbo jumbo makes my head hurt .....are there pictures, alternative webb sites for a more digestible conclusion? I may be old ,but I learn something new everyday. Peace out.

I experienced the same thing when I started this. I got actual headaches from trying to absorb what I was reading. I don't know any good online explanations, even the ones that are supposed to be simple are still kinda complicated. Imagine that you have a video of a car coming straight at you going through a slalom. On that video, you could find a spot in the middle of the car somewhere that doesn't move up or down, left or right as the car pivots from side-that is the front roll center. There is a similar roll center for the rear of the car and the imaginary line between the two is the roll axis (the line that the whole car pivots on when leaning left and right). Roll axis inclination is the angle of the roll axis and most solid axle cars have the roll axis higher in the back. Center of Gravity is the point where if you could attach a string to that point and hang the car from it, the car would balance perfectly. If your center of gravity (Cg) is higher than your roll center (RC) then weight is transferred when the car changes direction. The greater the vertical distance between your Cg and your RC, the greater the weight transfer. So, let's say my Cg is 16 inches high and my rear RC is 12 inches, it's like a 4 inch arm with a large weight hanging off it trying to twist my car left or right when I turn. The lower my RC is, the longer the arm and the more the weight transfers. I tune over/understeer with rear RC because it's so easy. By lowering the RC with the Panhard bar, I am transferring more weight in a turn, just like if I ran softer springs or a softer sway bar. Raising the rear RC reduces weight transfer, just like if I installed stiffer springs or a stiffer rear sway bar. All things being equal, the end of the car with the least roll resistance will have the most grip. A low roll center loads the tires slowly and is good for road racing where tire life is important. Autocross cars run a higher roll center because it shocks the tires by transferring weight harder and getting heat in them faster. My front RC is about 4" and rear RC is about 12", I have no idea what my Cg is with the new engine but IIRC it was 17" with the V8.

loosecannon wrote: In reply to GameboyRMH: ... the problem is that it always comes at the expense of inside rear tire spin. ...

Which pages do you have pictures of current rear design?

Also- when you say inside tire spin- is it more during right or left?

If it's more when you turn right- it's possible that some anti-torque wedge designs can help- as they can help prevent the engine torque from rotating the axle and lifting the right side tire.

If it's equal- one thing than can mechanically help that is a lower panhard bar- so that the moment generated by the bar as it loads laterally will generate more torque to counter the inside tire lifting.

I don't have a good picture of the rear suspension because there's so much stuff back there. I haven't noticed a difference in which tire spins this year but last year it was definitely the drivers side tire that would spin easier. That was because the car was 90 lbs lighter on the left rear than the right rear, now they are the same. Lowering the Panhard softens the rear suspension and does eliminate wheelspin, but it also turns the car into an understeering pig.

Does tire pressure play a part at all in this..side to side/front to rear ?

loosecannon wrote: I don't have a good picture of the rear suspension because there's so much stuff back there. I haven't noticed a difference in which tire spins this year but last year it was definitely the drivers side tire that would spin easier. That was because the car was 90 lbs lighter on the left rear than the right rear, now they are the same. Lowering the Panhard softens the rear suspension and does eliminate wheelspin, but it also turns the car into an understeering pig.

Since you can reduce the wheelspin, have you tried reducing the limited slip action?

In reply to 759NRNG:

We run less pressure than most in the front. My tire guy (Ron VerMulm from R&S Racing) has recommendations on how much the tire should roll in turns and you can see on the sidewall what is going on. I had to drop pressures on the front a lot to get it to roll over a little and this did improve front grip.

In reply to alfadriver:

Not possible with a Torsen style diff

loosecannon wrote: In reply to alfadriver: Not possible with a Torsen style diff

So you need to get enough traction, but not too much, then.

In reply to alfadriver:

No, I think I need a clutch style diff that will put power down even if one tire is a little unloaded. I took a pole of diffs in EMod at SpringNationals and the only cars that did not have a clutch style diff were me and Ron VerMulm, who has the exact Eaton TrueTrac that I have. Even the Tunnels, with a stock BMW clutch diff, do not have a wheelspin problem like I have. Ron had problems with wheelspin but thinks he has it solved now.

Yeah, generally torsens and the like are only useful if you can guarantee that both wheels will be on the ground at all times. They work by guaranteeing an upper bound on the torque split ratio between the wheels (TORque SENsing = Torsen, get it?), so if one wheel is in the air, it behaves like an open diff. They're more progressive and smoother than a clutch LSD, but they do have this crucial limitation.

An open diff always applies the minimum of both wheels to both wheels. Call this a 1:1 ratio. A Torsen has a bias ratio > 1:1, so the more heavily loaded wheel receives a multiple of the torque on the one trying to spin. If the inside wheel is zero though, you still don't get much. A 3:1 bias ratio can deliver 75% to one wheel, with 25% to the other, for example. If the 25% side has no grip though, you're still limited to only 3x that much tractive effort on the other side.

A clutch type on the other hand can go to nearly full lock, even with one wheel in the air, but the lockup might be a bit more sudden and aggressive. With a spool or an aggressive clutch type LSD, you can do a nearly infinite bias ratio, putting 100% to one side or the other.

tl;dr: You want a clutch LSD.

In reply to mck1117:

Awesome explanation, thanks. I don't know if I mentioned it but I have ordered a Variloc diff and here is an explanation of how it works: https://icpcitation.com/variloc_theory.htm

Craziest dyno experience happened today. I need to remind or share a little background info first. This EBay engine has been randomly going into a limp home mode, which means no boost. And neither the old engine or this one would make any boost at all below 4000 rpm. The wastegates on these engines are set for a really low opening pressure (6 psi) so for the last event I just added a spring to the arm of the wastegate and it upped the opening pressure to almost 9 psi and it made boost at 3700 rpm. For the dyno session, I added more spring pressure and it now opened at 12 psi and was fully open at 20 psi. They strapped my car down like normal and I warmed it up then shifted up to 4th gear and mashed the throttle. The car started to rev then violently went to redline, like the tires were spinning or something. It turned out that my new for 2017 ceramic clutch was slipping under load in 4th gear. Right there on the dyno, I removed the trans to adjust the hydraulic release bearing and put it back together. This changed nothing, it still slipped like mad (see YouTube video) so Brian Wall suggested I try a pull in 3rd gear. Since this was just a test to see if the clutch would hold, I didn't start the GoPro, but I sure wish I had because it would have made for an unbelievable video. I stomped on the gas in 3rd gear, boost came up, the front tires came right off the ground and the car danced around the dyno-it was crazy!! While they double strapped the car down, I looked at the data logs and the car was making 10 psi by 3000 rpm and peaked at 31 psi. On the next run, when I was actually able to go all the way to redline under load, the car was breaking up from being too lean. Jerry from Bad News Racing was hooked up remotely to my laptop so he looked at the logs and saw that the throttle was actually opening just 50%. I was making a lot of power for just 50% throttle opening. Just to be sure, I disconnected the extra spring on the wastegate and we tested again. It wasn't as lean as before but it also wasn't making the boost and the throttle was still only 50% open. Jerry made more changes and we tested and re-tested but only had moderate success with the throttle opening problem. Then the fuel pump solenoid, which controls the high pressure fuel pump, failed and put the car into limp mode. We found our problem. There was no point testing further because data logs showed that the solenoid was not allowing the fuel pump to get to the pressure it was supposed to. Fortunately, I have a spare solenoid, and I have another clutch so I hope to make it to the next race event. Enjoy the video https://www.youtube.com/embed/YZNCPuIWXNU

Your wastegate scenario sounds like time to move to an external gate. I have gotten nothing but headache and heartache anytime I tried to force an internal WGA to perform at more than 10psi above the preset spring pressure.

In reply to gumby:

I have an adjustable wastegate coming but it still uses the stock flapper valve, we'll see how that works out

loosecannon wrote: In reply to alfadriver: No, I think I need a clutch style diff that will put power down even if one tire is a little unloaded. I took a pole of diffs in EMod at SpringNationals and the only cars that did not have a clutch style diff were me and Ron VerMulm, who has the exact Eaton TrueTrac that I have. Even the Tunnels, with a stock BMW clutch diff, do not have a wheelspin problem like I have. Ron had problems with wheelspin but thinks he has it solved now.

I went with a clutch type differential for this reason, even though I had never lifted a rear wheel on my MGB before this year I am glad I did because in hairpins I am now. I am on the fence if I want to adjust it to lock a little sooner, it seems perfect except for really tight hairpins. I was impressed though, I can control the lockup pretty easily with the throttle.

Its a bummer that your engine and clutch have been giving your fits this year.

looseC sorry, been losing sleep over the waste gate debacle.....NOT Aren't all the components turbo ,intake, exhaust, part of one complicated casting on the LHU? Can one really plumb a 'remote' waste gate with this setup? zzzzzzzzzzzzzzz good night

In reply to 759NRNG:

Here is a picture of my turbo. The stock wastegate pod cannot be opened to change springs but the new one I have replaces it and has 6 different springs that push the rod and open wastegate at different pressures

[URL=http://smg.photobucket.com/user/loosecannon/media/MGB-GT/zz_ko4oema_1_zpslvf0baql.jpg.html][/URL]

On it boss, dyno time this weekend?