Great idea, did you have to do anything special to pass tech?
BUILD THREAD 86 GP 2+2~Blown 6.0
- Thread starter 81cutlass
- Start date
Looks like you need to get your 2 step off from the clutch pedal or make it adjustable. I think it will make your clutch happier. Didn’t you have a pressure sensor in the clutch system somewhere previously? That would be some great info for testing, even street testing so you can make the most of your track hits.
Was the tracked prepped?
Was the tracked prepped?
Not much special.
All have probably been to 7 tracks with this car and they only check these things regularly
1. Helmet with Snell rating in date
2. Battery fastened down firmly, I replaced the stock plastic hold-down with a 1/8x1 steel bar bent to shape
3. Coolant overflow bottle (stock)
I have been asked if I have a driveshaft safety loop but beyond that, nothing.
I never had a sensor in the clutch line before. That is new.
I have been thinking and agree I need to make the engagement point adjustable on the 2 step. I certainly don't want to run it manually but I do want too switch it on and off at different times. Currently it turns on with the clutch pedal pushed down maybe 5% so if the pedal is down even partially the 2 step is activated. Looking back at my logs when I had that 1.8 second clutch clamp time (my first pass) the launch RPM carried significantly above the set of 3500 even though the clutch pedal wasn't at the position where the 2 step should be off. I need to look into that.
The track was (lightly) prepped. They prepped it in the AM and after lunch. I wasn't close enough to the track to see if they were dragging or spraying it after a few runs or not. It was a bracket weekend so a lot of 11-13 second NA cars of bias slicks so it wasn't super sticky by any means.
I pulled the snap ring and the push rod out of the master cylinder yesterday.
I ran to the hardware store and bought a 1/2" heim joint and 1/2-20 grade8 bolt. I had to neck it down to the small 1/4" diameter to allow the push rod to swivel through its full range. Duplicated the ball end on the lathe.
The grade 8 bolt should be a lot stronger than the stock rod, and the thread is 1/2" so not the weakest part anymore.
I need to get a jamb nut and it should be back together. The next problem I have is that I thought the pivot shaft on the clutch pedal was 0.5", so I got a 0.5" bore heim, but the pivot shaft is actually 0.505", so I have to somehow sand the OD of the pin down.
You're almost there (wink).
Set up a pressure switch to run a relay that controls the 2 step. Basically move the manual switch from the clutch pedal to the pressure switch. Thus, you can kick off the two step at the preferred amount of pressure via your adjuster screw.
Wow, that sounds painful to dial in. But I think you need to do something before you're swapping clutches because of 6000rpm clutch releases. Personally I'd try it on a thumb switch and control it via feel until I got the clutch to work how I wanted it.
Set up a pressure switch to run a relay that controls the 2 step. Basically move the manual switch from the clutch pedal to the pressure switch. Thus, you can kick off the two step at the preferred amount of pressure via your adjuster screw.
Wow, that sounds painful to dial in. But I think you need to do something before you're swapping clutches because of 6000rpm clutch releases. Personally I'd try it on a thumb switch and control it via feel until I got the clutch to work how I wanted it.
I do have 2 additional 2 step activation inputs. Right now I'm switching the 2 step with ground, but I have a 12v activation wire and an entirely additional 2 step setting. I can set the first rev limiter to say 4k and the second rev limit to 5k and switch either on independent. Maybe thats why is called a 2 step? There are two steps of rev control!?! I hadn't realized that before today haha.
I agree, I don't want to spin 6000rpm before the clutch locks up. The challenge, and you relayed it well, is how. I'm not sure.
You bring up a really good point I hadn't considered. On that first run where the engine spun to 5500 even though there was still pressure in the clutch, the 2 step should not have turned off. If there is pressure in the clutch system the 2 step should still be active. The 2 step turns off when the pedal returns to the top of it's range and it only returns to the top when there is near zero clutch pressure. Or that's how I think it works, I need to confirm.
It took 1.8 seconds for the clutch pressure to bleed off on that run and it was able to over-rev the 3500 limit very early on. I need to look into that better. I should be able to test that at home not on the track.
The second run was another issue entirely. The clutch took 1.1 second to bleed pressure to zero but the clutch was not coupled. I saw the shift light and shifted, but it fell to 3200rpm because I essentially short shifted the thing, wheel speed was not where I wanted.
I definitely need to review when the 2 step is allowed to turn off. I like the pressure switch idea. I'm just trying to determine if that is more or less reliable or if there are conditions where it won't work for what I need.
I would LOVE to have the 2 step disengage when clutch slip % reaches a certain value as a second or primary input. Even if pressure in the clutch is zero and the clutch is still slipping Id really like to still rev limit.
I think 1.1 seconds is too long. I would guess that you're looking for something around .2-.4 seconds - again, a guess.
That is a right proper beefy boi solution.
For the pin, couldn't you just cut a new one on the... oh I dunno... lathe?
Yeah, 1.1 is too long. The system failed before I found the time that worked best.
1/4 turn got 1.8 seconds
1/2 turn got 1.1 seconds
3/4 turn got no data but the best 60ft of 1.85
1 turn it ripped the tire off and defaulted to 0.3 s
7/8 turn it bogged (pretty certain the system failed here or on the previous pass
3/4 turn it bogged
3/4 turn it ripped the tire off, went back to pits to diagnose and it broke the push rod.
0.2-0.4 is roughly the range where it is clamping now and results in bog or spin.
The guy with the LSA blazer at the track ran 1.55 60ft. Since I have the same power, that is my goal.
I want the clutch to fully couple at 32mph (4000 rpm) and I shift at 48mph or 6200ish. That 48mph shift time is about 2.2seconds into the run, and I need to target somewhere about 1/3-1/2 that time.
Long story short I THINK 0.6-0.8s is where it needs to couple.
I have a plan that does involve the lathe 🙂
So back to this, I did some testing in the garage tonight and I agree. I need to remove the 2 step control from the pedal. The pedal bounces up and turns the 2 step off when I release my foot when it's set around 3/4 turn, even if there is pressure still in the clutch, which is what my best launch was with.
That's a helpful suggestion! I'll search for a high pressure Hobbs style switch and tee it in. I bet if I can truly limit the rpm to 4k or whatever until the clutch pressure is low enough that it couples I won't slip the clutch so hard.
In other news I got the top end of the push rod installed. I had to weld an extension to the pivot shaft because the heim was too wide and I lost the place for the hair pin to install. I also welded a nut to the clutch pedal so I can put a travel stop in and hooked up the 'choke' light on the dash to the relay so when the valve is turned on, the light is illuminated.
The local arm chair car show formerly known as 'Car Craft Summer Nationals' is this weekend. I need to pivot and scrub the brake dust off the car and maybe bet the the car ready for the show.
I did the autocross last time I went to the show but they cut the time slots down this year and couldn't get a spot so I don't think I'll be and to autocross.
One step at a time!
I was thinking about you mentioning it bogging and it brought up some questions/comments.
You're making boost on the 2 step correct?
You don't have any launch timing retard with HP Tuners correct?
Can you see where the 2 step turns off in the logs and where is the boost and timing when that occurs?
Bogging - smh. I look at an LSA or blower of any type as instant boost that is rpm dependent, not load dependent. I thought of the heck of a time I have not spinning with my launch retard putting timing down to nothing and I'm still blowing the tires off. But bogging, I've never even came to close to that other than when I've added about double the fuel it needs. If I use a normal timing curve for boost where I'm at 20 degrees at 5psi, which is where I've been launching at, and I turn of off the launch retard, then I'll turn the tires to instant smoke with a 5.3. So when I consider that you have a 6.0 and you're getting it to bog on the hit has me thinking you have a tune issue or 2 step release issue.
The most boost I've been able to get on my 3rd gear spool mod with all of the Co2 pounding on the gate is 16 psi, and I've let go of the brake at that level twice - that was some very smokey events. I have taken out too much timing by a crap ton and made for a slow take off, but I'm talking about launching at 2 degrees.
