Shouldn't my car be quicker?

[morepowerjoe]

I replaced my axles with some cheapies from rock auto because I was hearing a clang sound from the rear end while shifting gears like from drive to reverse. After the replacement I still had the sound so I thought it must be something else and drove it that way for over a year. Then I had a local shop check it out for me and they said it was from the axle. So, instead of going with the cheap stuff this around I decided to go with the ac delco oem ones and presto the sound was gone immediately. Granted the are like $700 for the oem ones I now know that they are way better than those cheap ones.

[acammer]

Originally Posted by LS1Formulation

Right now, I'm at my wit's end with this car. I replaced the broken axle with a parts store special, and it blew apart at the inner CV on a 1-2 shift on the street, 3 days after installing it. After talking to an axle company about upgrading it, I feel that the effort is futile. The car is lowered and I don't want to raise it back up, and offset diff bushings can only do so much. I already have a '98 Firebird Formula M6 that's getting a turbo Gen IV aluminum block 5.3 and that has a Strange S60 with a spool. I could dump the clutch at 6K and dead hook and wouldn't hurt that axle. My SS wasn't meant to be a full on drag car, just something fun to play with and take to the track occasionally. But breaking axles on the street just grabbing gears is ridiculous. Going to the track would just mean another expensive tow bill, because there's no way it wouldn't break on a prepped surface. The clutch might actually be the culprit here, because it bites hard as hell. It's a 6 puck ceramic with a sprung hub. Pedal effort isn't noticeably different than stock, and I have to really be slow releasing it to have any sort of chatter. I'd read and watched numerous reviews on the clutch and people complaining of chatter during the break in had me ready to experience it, but I had absolutely zero chatter during break in. As I said, this thing grips like crazy, every time I shift I can feel it shock the driveline. Not healthy, I'm sure, but the window of engagement on this thing is damn near non-existent. I should have went with something less aggressive, but I figured I'd get something better in case I did decide to add some power down the road. But if I can't stop breaking axles, there's no point in increasing power. Obviously, the cheap parts store axle didn't help, but I figured it would be at least as strong as OE. Apparently not. As an aside, I already have BMR diff bushings, a Eaton Truetrac, and an LPW cover, so the center section won't be a problem. Should I buy another factory axle instead of a parts store one? The axle company kinda steered me away from buying their axles (shocking, a lot of places wouldn't care, they'd just sell you whatever ), just because with how my car is set up, I'd experience too much wear in the joints and I'd have more problems. Not something I'd want to deal with after shelling out $2K.

Well, that sucks. From what I have observed, the aftermarket replacement axles are noticeably weaker than OEM. You have identified the other big issue - ride height. The CV angle is already poor in factory trim, and lowered it just gets worse. As you mentioned the offset bushings help, but only so much.

In my direct experience, the OEM axles are at least as tough as the ring and pinion itself, as I've never broken an axle, but I've had a few ring gear tooth failures. When you go to aftermarket axles it seems like they keep the ring gear safe, but fail with painful regularity.

It also sounds like the clutch is not doing you any favors - that abrupt engagement can be incredibly hard on parts. My RXT can be a bit like that - it has a pretty reasonable slip window, but it tigthens up sharply as it comes to the point of full engagement, and it will bite if you're not careful with it. I feel similar about chatter, I get a little here and there, but nothing troubling, and can definitely be driven around.

My G-Force 9" is supposed to go in this weekend. After fighting the same fight you are now for years, I'm ready to hopefully stop worrying about the rear end and just SEND IT for a while. Trans will probably be next knowing the way it goes for me.

For you, I think you find some factory axles, and just try to enjoy the car. Or, stock up on axles, and figure out how to tame that clutch down to where it doesn't hurt stuff.

[LS1Formulation]

Originally Posted by sr530

Clutch engagement rate is key to getting the most power possible thru a manual drivetrain in a drag race setting without breaking parts. It also happens to be the key to being quick. Hard for some to believe, but the weakest clutch that you can get away with is also the one that will give you the best ET.

You want a clutch that barely holds after a wot shift into high gear, that same setup will also inflict the least impact after the 1/2 and 2/3 shifts. For your best launch though, clutch engagement rate needs to be even softer than what's needed after the shifts. The easiest way to consistently achieve a clutch with two different engagement rates is to add an external clutch hit controller. Lots of Drag Week type builds using my ClutchTamer and Hitmaster products to soften the hit and widen the sweet spot of diaphragm clutches with ceramic and iron discs.

Grant

So, from what I've read and watched about your product, I'm sold. I have zero interest in trying to get consistent with clutch release using my left foot, I'm just not good at it. More power to you, Acammer, for working on perfecting that skill. My question is, after what I've just experienced ( snapping an axle on a 1-2 shift on the street ), is there a way to set the Hitmaster up so that I can soften the clutch hit on shifts, but NOT have the launch feature engaged? Basically, I know I can have two timers set up to have different release rates, one for launching and one for shifts ( for use at the track ), but on the street I'm not going to be doing any high RPM launching and would only need to soften up how hard this clutch grabs between shifts. Would it be as simple as wiring in a second switch to activate the timers independently? I feel like this could actually eliminate my broken axle problem just by reducing shock loads through the drivetrain.

[sr530]

Originally Posted by LS1Formulation

So, from what I've read and watched about your product, I'm sold. I have zero interest in trying to get consistent with clutch release using my left foot, I'm just not good at it. More power to you, Acammer, for working on perfecting that skill. My question is, after what I've just experienced ( snapping an axle on a 1-2 shift on the street ), is there a way to set the Hitmaster up so that I can soften the clutch hit on shifts, but NOT have the launch feature engaged? Basically, I know I can have two timers set up to have different release rates, one for launching and one for shifts ( for use at the track ), but on the street I'm not going to be doing any high RPM launching and would only need to soften up how hard this clutch grabs between shifts. Would it be as simple as wiring in a second switch to activate the timers independently? I feel like this could actually eliminate my broken axle problem just by reducing shock loads through the drivetrain.

You could soften the hit after the shifts by swapping out that Spec 3 disc for a dual friction disc. But not a Spec 2+ style dual friction with Kevlar on one side, I would recommend a Ram Powergrip style dual friction that uses organic on the soft side.

For softening the hit of your existing Spec 3 after the shifts, the much less expensive ClutchTamer could do that for you. It activates automatically every time you stroke the pedal, and during slow casual pedal modulation you won't even know its there. But as pedal strokes become quicker, it takes over controlling pedal release rate. It will also help you consistently hit the sweet spot between bog/spin when launching the car. Downside is its typically a little tougher to install on an airbag car.

If you used the Hitmaster, i would just use a pressure switch to activate a shift timer any time the clutch pedal is released. Like the 'tamer above, you won't even know its there during slow casual clutch release. Easier to dial in than the 'tamer, but initial bleeding can be a pain.

Grant

[LS1Formulation]

I've had the rear axles/diff out in this car at least 8 times in the past 3 months. I'm definitely not going to swap in a different clutch. At a certain point, having to work on something due to repeated breakage sours you on doing work to your car. I'll just focus on softening up the shifts. I tried to go check out the clutch tamer, but the link doesn't work... Got one that does?

[sr530]

https://grannys.tripod.com/clutchtamerinfo.html
https://grannys.tripod.com/hitmaster.html

Grant

[LS1Formulation]

Thanks for the links. One question I had that I haven't seen addressed much is, how much do these devices reduce clutch life? I'd assume they reduce it at least somewhat, but I watched one video ( discussing AWD Subarus ) that said the clutches only last 10-12 passes. That's not going to be acceptable, as this isn't a race car, just a street toy I take to the track sometimes.

[sr530]

Clutches are much like brakes, they will last a long while until you start exceeding their thermal capabilities. That said, it's hard to fit a high HP drag race capable clutch inside a Subaru bellhousing! Any idea which clutch controller they were using? If it was a Magnus style valve, those are not clutch hit controllers. Magnus style simply slows the rate that the clutch pedal returns, even the dead-band area of pedal travel before the clutch actually engages. They are used for launch only, not suitable for softening shifts. Old tech at this point.

If you want to get maximum drag strip performance out of a manual trans car, the clutch needs to be able to endure some slip. Same is true for automatic cars, small mechanically inefficient torque converters are quicker as they allow the engine to operate up where it makes the most of its power band. The additional power produced more than offsets the reduction of mechanical efficiency.

During casual driving with an actual 2-stage clutch hit controller in place, clutch life will not be affected at all.

For a guy that hits the track a few times a year, using a clutch hit controller will enable him to safely/consistently sneak up on a suitable compromise between clutch life and maximum performance. There's a hit/miss aspect to trying to master that skill with your foot, and with every miss it's either your clutch or your drivetrain that will suffer.

Bottom line is less wear/tear on your clutch/drivetrain with a clutch hit controller vs trying to do the same with your foot.

Grant

[LS1Formulation]

Well, rather than let my car sit or worry about it breaking again, I went ahead and bought a pair of G-Force Renegade axles, BMR cradle bushings, and Hendrix offset diff bushings. of course, I gotta wait a couple weeks until there's an open test and tune, but in the interim, I'm going to find a spot to go hone my ability to let the clutch out. I'll worry about the clutch master install over the winter. Maybe I'll finally get to see what this thing can do!

[LS1Formulation]

Update: Finally was able to hit the track again, but the surface was crap and actually scary to drive on, spinning the tires and getting loose through the traps. Finally switched lanes last pass and ran a best of 12.57@113.55, with a 1.82 60' time, still getting some spin throughout the run. I was spinning so bad in the left lane that I picked up 6 MPH by switching lanes, 107.4 to 113.5. I'm still getting a bit of wheel hop on the passenger side of the car, maybe about 30' off the line, but it's pretty mild. I have to lift slightly and it immediately goes away. I'm thinking I'll install some BMR upper control arm bushings, as every other part that's been recommended to control wheel hop has been upgraded, so that's seemingly the only thing left to do, unless someone has any other ideas. All in all, I'm decently happy with what I got out of it, because getting my 60' down into the high 1.6's - low 1.7's should get me a 12.2-12.3, I'm thinking.

[LS1Formulation]

Went to the track again yesterday, much better surface prep this time, ran a new PB of 12.45@113.9, with a 1.85 60' time. I'm still spinning a few feet past launch, which is killing my 60' time, but it's pretty mild. Still have a tiny bit of wheel hop too. Also ran a 12.49@114.4 with a 1.87 60' time. Both of those passes were an easy slip off the line, launching at 4000 RPM. I'm finally happy with where it's at, and know there's room to improve.

[wastepile]

Originally Posted by acammer

I also have a lengthy video on launch techniques for these heavy M6 cars. You might find this valuable as well.

@acammer - Incredible video, thank you for putting this together.

For folks who have raised their RPM limit within the ECM, is there any street driveability cons to just having it at 7500 RPMs all the time?

[acammer]

Originally Posted by wastepile

@acammer - Incredible video, thank you for putting this together.

For folks who have raised their RPM limit within the ECM, is there any street driveability cons to just having it at 7500 RPMs all the time?

RPM limiters should be based on what your valve-train is reasonably capable of controlling. They also should be understood as a imperfect, and defeatable. There are a few scenarios where the RPM limiter can be exceeded.

The first is not common, and fairly obvious - when the car is placed in the wrong gear and mechanically over-revved. No limiter is going to save you there, and that can be catastrophic. I've had it happen one time, while making a gear change with substantial lateral G-Force applied, and selected second instead of fourth. I was lucky that I was not making an aggressive release on the clutch, and so I caught it fairly quickly. This was back when the car was just bolt ons, and I sent that OEM valve-train to probably 7500 or so - about 1,000rpm over the rev limit at that point. I suspect it was fairly out of control, but the mild factory lobes and cam timing probably saved me, as I suffered no ill effects other than being tightly puckered for the next hour or two.

The second scenario for exceeding the rev limit is far more common. This involves some uncoordinated shifting where the driver is approaching the rev limit, and depresses the clutch before releasing the throttle. Many would assume that the rev limiter would "catch" this behavior and cut spark/fuel/throttle as needed to control this, and while the ECM will make every effort to do so, when you disconnect the engine load right near the limiter at full power the engine accelerates RAPIDLY and that acceleration/inertia can carry it several hundred RPM over the limit even after the ECM has cut the power. This can happen on a missed shift as well, where the gear does not engage, but the driver fully commits to wide open throttle and the revs rise so rapidly that the ECM is unable to catch them in time. This is a good reason not to attempt power-shifting unless everything is properly configured for it. I don't think there is a benefit from power shift vs. good coordinated shifting - but we'll leave that for another debate.

How dangerous this second scenario is depends on how tightly the rev limiter is set to the actual limitations of the valve-train, and how much piston to valve clearance the combination has. If your combination is already on the edge of control for the valve-train and you suddenly send it a few hundred RPM beyond that point, you're likely losing some control of the valve-train. Take that too far, and the pistons will start assisting the valve springs in closing the valves, and that doesn't typically end well. My preference is to overbuild a combination so that you have 3-500 rpm of decent valve-train control beyond your intended shift point, so that even if the driver goofs pretty good, you've got a margin of safety to work with.

In my combination, I have "stages" of rev limiting, as well as having a shift point and final limiter about 3-500rpm under where I think the valve-train is still stable out to. At 7700rpm I bring in a soft rev limiter, which is basically a rapid decline in ignition advance once you cross it. The effect of the soft limiter is to rapidly kill power, without completely killing the engine. This makes for a limiter the driver can easily feel, but is not at all violent like a spark or fuel cut. Hard cut limiters are hard on everything in the motor and driveline, and my goal is to avoid them if possible. At 7800rpm, I have both the ECM and my N2MB 2-step setup to bring in hard cut, ignition based limiting. One or the other would be satisfactory, but I have both available, so I'm ok with having a fail-safe.

The valve-train in my car consists of Johnson ST2116LSR lifters, Comp BSR Max Lift shaft rockers, PSI 1513 springs (~170# closed 475# open), and hollow stem stainless intake valves. It is well equipped to run to 8,000rpm or even a little beyond and be stable. I'm fairly tight on piston to valve clearance on the intake valve, but I have short travel lifters with only about .035" of preload. With deflection, I'm confident that I couldn't pump up a lifter enough to make intake piston to valve contact. I have LOT of exhaust piston to valve clearance, so I would need to massively float the exhaust to have a concern for contact there. So, all that to say, shifting at 7700rpm, even if I miss and send it to 8,200rpm somehow, I'm not real concerned.

So, I guess that was a LONG way to answer your question. Said shortly, you should keep the limiter no higher than necessary for a given combination to achieve it's best potential performance safely.

[LS1Formulation]

Okay, updating this as I learn some things and try some things. Got my PB down to a 12.41@112.73, with a 1.86 60' time. Upped my shift points to 7000 RPM. Still not getting a good 60', but I am pretty sure I know why now. My car is lowered, and I failed to buy camber bolts to allow it to be adjusted to 0 degrees in the rear. It's at 0.6 degrees presently. So my contact patch is uneven, and the small amount of hop I'm getting from my passenger side is due to the inside of the tire biting harder than the outside. Ordered camber bolts from Phastek, hope to get them by this weekend so I can install them and get a fresh alignment. My Nittos also show significantly uneven wear on the passenger side inner tire from this. Live and learn, I'm still getting used to having an IRS car. I'll also be buying brand new tires, as mine are pretty much toast.

Since my last track outing, I installed a GPI ported rod mod intake - To say that it woke my car up is an understatement. I only have a mail order tune, so my assumption is that they set it up safely rich. Well, the additional airflow the new intake provided has allowed all that extra fuel the opportunity to burn, and holy crap! It feels like I gained at least 30 HP. Don't know for certain, but I've scheduled a dyno tune in a couple weeks to see if it can be further optimized. I'm probably going to hit the track tomorrow just to get an apples to apples comparison, but it feels significantly quicker.

Also, I ordered an LNC-2000 and CTAP so I can concentrate more on clutch release and throttle application instead of hoping I'm launching at the correct RPM. I'll be having my tuner raise my limiter to 7500 because it's at 7100 right now and I am tickling it on occasion due to my slow shift light reaction times. As well as fully disabling the factory launch control, which is basically worthless.