Still chasing 10s. New PB 11.38@123.5mph

[acammer]

Originally Posted by sr530

Every single car in NMRA's Coyote Stock class runs a clutch release device on a diaphragm clutch, and they all dead hook with 20+ psi in bias slicks. NA 302cuin factory sealed crate engines on spec fuel and tune running mid 9.70's @ 140 carrying 3000lbs, launching at around 7400. The only thing that keeps those guys from launching even higher is a factory ECU tune that closes the throttle blades if the engine goes over 7800.

NMRA's Coyote Stock is a sister class to NMCA's Chevrolet Performance Stock class that runs the sealed crate DR525's also @ 3000lbs. The CS and CPS sealed engine classes have many common rules and run against each other at the combined NMRA/NMCA World Finals.

Grant

No doubt those guys have it figured out the way to real maximize those power limited combos by tuning every other element. Fairly different car - 25% lighter with the weight they do have in the right places, (mostly) solid axle, purpose build race cars. Love those kind of classes.

I'm not arguing your points - I agree that a controlled release is optimal, and the more energy you can store to use in that release has the potential to be converter to even more acceleration. In the case of my car, the only release device I have is my left foot - and as you noted the RXT has a narrow, fast engagement window, so it's tricky. I'm using the wheelspeed as a crutch for sure - fortunately the bias plys with a lot of starting line ratio works pretty well. I think I can squeeze a half a tenth from the 60' with the technique I'm using now, and that's going to be better than what most of the street driven IRS manual 5th gen guys are seeing. More than good enough for me.

I'm sure I'll try it on radials again at some point, and then I'll be using a much slower release. I've done 'em before - with the stock clutch, 275/40/17 DR2 and 100lbs more weight I was in the 1.6x 60' times, no doubt that can improve.

[sr530]

Originally Posted by acammer

No doubt those guys have it figured out the way to real maximize those power limited combos by tuning every other element. Fairly different car - 25% lighter with the weight they do have in the right places, (mostly) solid axle, purpose build race cars. Love those kind of classes.

I'm not arguing your points - I agree that a controlled release is optimal, and the more energy you can store to use in that release has the potential to be converter to even more acceleration. In the case of my car, the only release device I have is my left foot - and as you noted the RXT has a narrow, fast engagement window, so it's tricky. I'm using the wheelspeed as a crutch for sure - fortunately the bias plys with a lot of starting line ratio works pretty well. I think I can squeeze a half a tenth from the 60' with the technique I'm using now, and that's going to be better than what most of the street driven IRS manual 5th gen guys are seeing. More than good enough for me.

I'm sure I'll try it on radials again at some point, and then I'll be using a much slower release. I've done 'em before - with the stock clutch, 275/40/17 DR2 and 100lbs more weight I was in the 1.6x 60' times, no doubt that can improve.

The Coyote Stock sealed crate engine cars are 25% lighter, on the other hand you have 25% more displacement as well as engine mods. There are lots of little things that make those CS cars so quick, but they will tell you the biggest thing is what happens inside the bellhousing.

The RXT's narrow engagement window is a by-product of clutch/engine mis-match, as it's far more appropriate for an engine that puts out around 850-925ftlbs. Even the RST would be overkill for your application, but it's engagement window would be much wider and easier to hit. It would also inflict less abuse on your drivetrain.

Grant

[acammer]

Originally Posted by sr530

The Coyote Stock sealed crate engine cars are 25% lighter, on the other hand you have 25% more displacement as well as engine mods. There are lots of little things that make those CS cars so quick, but they will tell you the biggest thing is what happens inside the bellhousing.

The RXT's narrow engagement window is a by-product of clutch/engine mis-match, as it's far more appropriate for an engine that puts out around 850-925ftlbs. Even the RST would be overkill for your application, but it's engagement window would be much wider and easier to hit. It would also inflict less abuse on your drivetrain.

Grant

I agree - but the "right" clutch from a drag racing perspective won't tolerate a season of this, let alone multiple seasons. How many passes do those guys get on a clutch? Probably the biggest maintenance item on the car. I lack the time to maintenance a clutch like a real stick-shift drag car requires. I also have plans for boost and 700+whp.

The RXT was chosen based on it's moderate cost, acceptable manners, holding power, thermal and abuse tolerance, and the ability to give me years of trouble free service - it's done all of those things well. If it needed replaced tomorrow, I would strongly consider another one. The car is ultimately a series of compromises - and the clutch is no different.

[sr530]

Originally Posted by acammer

I agree - but the "right" clutch from a drag racing perspective won't tolerate a season of this, let alone multiple seasons. How many passes do those guys get on a clutch? Probably the biggest maintenance item on the car. I lack the time to maintenance a clutch like a real stick-shift drag car requires. I also have plans for boost and 700+whp.

The RXT was chosen based on it's moderate cost, acceptable manners, holding power, thermal and abuse tolerance, and the ability to give me years of trouble free service - it's done all of those things well. If it needed replaced tomorrow, I would strongly consider another one. The car is ultimately a series of compromises - and the clutch is no different.

All what you said above are reasons why people use clutch hit controllers. They make an overkill clutch like your RXT hit more like a well matched clutch, without giving up holding power, thermal capacity, or the ability to grow without upgrading the clutch.

Here's a snip from a Dragzine article about Coyote Stock champ Clair Stewart, note the second to last paragraph:



I know you just want to see what you can accomplish with your foot, but i'm still saying there's a half second to be gained just by controlling what happens inside your bellhousing.

Grant

[acammer]

Hey guys - I thought I'd drop a little follow up in here. I was able to complete a bit of dyno testing a few days ago to get a feel for what the 9" diff is costing for horsepower. It's fairly commonly accepted that the larger hypoid offset of a 9" (which increases the tooth engagement) both results in increased strength and decreased efficiency. Most sources suggest 1-3% loss over more conventional ring and pinion setups. In general more gear ratio will consume some efficiency as well.

There is very little testing out there which actually documents the losses, so I was keen to do my own test. The combination has not changed since dyno'd at GPI, with exception that I'm running the complete Vararam, rather than just the open lid used on all our tests.

Pull #2 is the best comparison, Vararam with no filter. 538whp vs the 551whp at GPI would put the loss at 2.4%. That assumes the dynos read very close, there could be some variance there as well, and we probably have a touch more intake restriction now than when tested at GPI. As expected, the 9" is consuming a bit of power. But, for a stick shift car, getting the strength to handle the abuse, along with the aggressive starting line ratio and better rpm out the back all contributes to better performance and reliability.

For those curious on the other pulls:
#1 - Vararam with filter
#2 - Vararam no filter
#3 - open throttle body, iat reading about 25*F too high (helping keep the fueling right)
#4 - open throttle body, iat reading accurately (too rich)
#5 - turbo guard with velocity stack.

All tests were at about *84 ambient, 185* on water temp, and 200-220* oil temp. A more substantial cool down and hero pull might have made a couple more.

[ariZona28]

Some good results. That 2.4% reduction is probably well within the margin of variance in regards to two different dynos. It's quite possible you didn't lose any power but the added strength and reliability will allow you to launch a bit harder next time you're at the track. Looking forward to seeing how things work out.

[acammer]

Originally Posted by ariZona28

Some good results. That 2.4% reduction is probably well within the margin of variance in regards to two different dynos. It's quite possible you didn't lose any power but the added strength and reliability will allow you to launch a bit harder next time you're at the track. Looking forward to seeing how things work out.

Agree 100% that 2.4% could easily fall within the variance of the two dynos. I also think it's fair to say that some loss would be expected with the 9". Regardless, the added strength and reliability is welcome even at a 2-3% loss in power to the wheels. And, even with a loss in peak power, sustaining a better average power with the optimal gearing likely overcomes that loss as well. Definitely was the right move for what I'm into.