02-17-2023, 07:15 AM | #29 | |
GPI Sales Consultant
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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.
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GPI Max Package 2.0: Brodix BR7 heads/GPI porting, MAX3 cam, ST2116LSR, BSR Max Lift rockers, LS7 LSXR with 103mm TB, Vararam OTR, Mcleod RXT, G-Force/Strange 9" IRS setup with 4.63 gear. 551whp, 11.1@124mph.
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02-17-2023, 11:49 AM | #30 | |
Drives: Chevy Astro Join Date: Jun 2020
Location: PNW
Posts: 25
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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 |
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02-17-2023, 12:28 PM | #31 | |
GPI Sales Consultant
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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.
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GPI Max Package 2.0: Brodix BR7 heads/GPI porting, MAX3 cam, ST2116LSR, BSR Max Lift rockers, LS7 LSXR with 103mm TB, Vararam OTR, Mcleod RXT, G-Force/Strange 9" IRS setup with 4.63 gear. 551whp, 11.1@124mph.
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02-18-2023, 11:29 AM | #32 | |
Drives: Chevy Astro Join Date: Jun 2020
Location: PNW
Posts: 25
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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 Last edited by sr530; 02-18-2023 at 06:50 PM. |
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05-16-2023, 11:49 AM | #33 |
GPI Sales Consultant
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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.
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GPI Max Package 2.0: Brodix BR7 heads/GPI porting, MAX3 cam, ST2116LSR, BSR Max Lift rockers, LS7 LSXR with 103mm TB, Vararam OTR, Mcleod RXT, G-Force/Strange 9" IRS setup with 4.63 gear. 551whp, 11.1@124mph.
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05-17-2023, 06:38 AM | #34 |
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Drives: 2015 Camaro 2LS, 2015 Camaro Z/28 Join Date: Nov 2019
Location: Mesa, Az
Posts: 2,382
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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.
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2LS: a TREMENDOUS machine. Z/28: it's a BIT MORE POWERFUL, of course.
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05-17-2023, 07:26 AM | #35 | |
GPI Sales Consultant
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__________________
GPI Max Package 2.0: Brodix BR7 heads/GPI porting, MAX3 cam, ST2116LSR, BSR Max Lift rockers, LS7 LSXR with 103mm TB, Vararam OTR, Mcleod RXT, G-Force/Strange 9" IRS setup with 4.63 gear. 551whp, 11.1@124mph.
Got a question about a GPI product? Feel free to shoot me a message! |
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