weedburner

Nice project! 60' is mostly about high launch rpm and then getting your clutch to slip just right. Hit and miss trying to do that with your feet, much more consistent and far less wear/tear on the clutch with a 2-step and a clutch hit controller. Grant

The ratio difference between 1st gear and 2nd gear is going to be a huge factor in keeping the stock stubs/flanges alive thru the shift. It's basically the energy stored in the rotating assy at shift point rpm vs the energy stored in the rotating assy after the shift. The difference between those two energy levels equals the amount of energy released during the shift. Eric JB's use of a 700R4 and a 2500 converter puts more stress on stubs/flanges than just about any other common sbc combination, especially with drag radials and a tire chirping shift kit added to the mix. The tighter splits of the T350 are a far better drag race choice over the 700R4, not only less 1st gear ratio but about 12% less energy release on the 1/2 shift. To help make that statement easier to understand, lets say you have an entire rotating assy (crank/flywheel/pressure plate) out of the engine and spinning on bearings at 1000rpm. That rotating weight spinning at 1000rpm contains a fixed amount of energy that can be put to work. One way to measure that stored energy is to apply a braking force to the rotating assy and then measure how long it takes for that braking force to bring that rotating assy from 1000rpm to a full stop. Lets say a braking force of 100ftlbs can take that rotating assy from 1000rpm to a full stop in 1 second. Basically the energy contained at 1000rpm is 100ftlb/seconds. Sounds pretty reasonable so far, right? Now consider that the energy stored within that rotating assy is an exponential function of it's rpm. Spin that rotating assy up to 2x the speed, it will contain 4x the energy. Spin that same rotating assy all the way up to 6500rpm, now it contains 4225 ftlb/seconds of energy! Now further consider what happens when the transmission shifts from 1st to 2nd gear. The ratios in a 700R4 indicate an rpm drop to 3450rpm in 2nd gear after a 6500rpm shift. At 6500 before the shift, the rotating assy contained 4225 ftlb/seconds of energy. After the shift at 3450, the rotating assy only contains 1190 ftlb/seconds. Now the question- where do you think that 3035 ftlb/sec of energy released during the shift goes? Same thing applies to manual trans gear splits. Grant

Still going to be a 4-1/2" 1350 shaft that's only a couple feet long connected to a cast 4 bolt Spicer flange Grant

To me, 4-1/2" with 1350 u-joints is an almost comical mis-match of parts for something like your Z-car. That 4-1/2" dia tubing will do absolutely nothing for you as far as critical speed at your length, but that bigger tubing also drastically cuts down on the available room to route the exhaust. Why saddle yourself with those monster parts that will only slow you down? My car is similar in that it's an '85 RX-7 w/ small in/out Toploader 4 spd. It uses 1310 up front with a similar sized 3R rear joint. Also uses a common Spicer 28spl slip yoke and 2-1/2" dia x .065" tubing that's 26-1/4" long center/center. Grant

New bests are always a great time But drag racing is addictive and I think you will find yourself looking for more. Your current best is 9.84, but 143mph is enough power to run 9.20's. For an automatic car, most of what it takes to achieve a 9.20 level of efficiency comes from finding a proper torque converter that slips just enough to let the engine make the most of it's power band. For a manual trans car, the equivalent to the right torque converter is finding just the right amount of clutch hit that doesn't cause bog, spin, or broken parts. All three of those things will reduce your fun factor, and all three are caused by a clutch that's allowed to hit too hard. Yours is also a nitrous car, so the definition of a clutch that's allowed to hit too hard changes when the bottle is turned on or off. Some may find it hard to believe, but a proper hitting clutch will hit your halfshafts with less intensity than the equivalent auto/converter. Proper clutch hit management also makes it possible to use radial tires effectively. This also tends to improve the fun factor, as you pick up a few more mph while eliminating the need to swap tires between street/strip. All just friendly suggestions, took me a long time to figure it all out. Grant

Might as well go straight to auto now, that will be more fun than the hit and miss results of trying to control the hit with your left foot. Grant

So .5 sec quicker in the 1/4 for less cost than re-filling a nitrous bottle doesn't sound like fun to you? Grant

With a hit controller you will be able to launch at 7500 off the 2step with a quick clutch dump, and rpm won't fall below your torque peak. You have the potential to shave about .5sec off of your ET and I think you can do it with your existing halfshafts. Although not IRS, my car has been 5.73 in the 1/8 with a 1.30 60' , also manual trans + radials and dead hook launches. About 225hp plate on a 1 sec delay. Super aggressive full face sintered iron clutch, but it's hit controlled to the point that the hit is spread over about 1.0 sec vs about 0.3sec without a hit controller. Without a hit controller, my car twists a 2-1/2x.065" driveshaft almost instantly. With the clutch hit controller, same 2-1/2"x.065" driveshaft has been in the car since 2012. Grant

Add something like my ClutchTamer and you will likely be able to get a lot more from your halfshafts. Pretty easy to diy a similar solution once you understand how my solution works, here's a link to my version of a clutch hit controller... LINK Grant

Your Z and my RX-7 would look good sitting next to each other. What weight, rear gear, and tire size? My RX is 2325 without me, 3.73, 275/60-15 also with a manual trans, ran 5.73 back when it had 700whp.

When I convert the FC RX-7 from IRS to solid axle, I go with a torque arm suspension. Basically a couple lower control arm chassis brackets that attach to the same place that the original IRS subframe mounted to, along with a torque arm that extends forward below the driveshaft. The nose of the TA anchors to the top of the trans tunnel (driveshaft passes thru the middle of a shackle style arrangement), easy to do in an RX-7 because there's a lot of room above the driveshaft in a piston powered RX-7. Here's a link to my page on converting the FC to solid axle... FC/8.8 Solid Axle Conversion I have also seen IRS cars converted using basically stock geometry FOX body Mustang triangulated 4 link suspension. It appeared that they simply stuck the rear under there, then fab'd chassis brackets in place to fit the links. Fox Mustang rear just happens to be the same width as the FC's IRS. Grant

Launching at the dragstrip reliably with a manual trans can be challenging, but most of the magic in getting it all to work reliably is getting the clutch to hit with just the right intensity. Too much clutch capacity can make the car tend to either spin, bog, or break. I came up with a device using a hydraulic screen door closer that allows me to easily adjust how hard my clutch hits. Without it, my car instantly twists it's driveshaft in two. With it, my car dead hooks and does 1.30 60's without bogging. My page on my car (linked in my post above) shows the cylinder installed and attached to the clutch pedal, it also shows the dash bracket. The RX-7 is similar to the 240 in that the distance from the dash to the pedal is fairly long, so you should be able to slightly modify an off-the-shelf Wright VH440 closer to do the same thing. I make a shortened version of that same cylinder, very popular with the stick shift NMRA guys.

My RX-7 is similar to your car in size/weight/power. I went with a narrowed GM 8.5" 10 bolt solid axle and added a torque arm. If i were doing it again, i would go with a Ford 8.8 just because they are so much easier to find and about the same strength. With the torque arm setup you will need to fab some brackets to attach the lower control arms to the chassis, a panhard bar or watts link to center it, and an anchor bracket for the nose of the TA up in the tunnel. Not sure how big your stock wheelwells are, but my stock RX-7 wheelwells hold 28" tall 275/60-15 drag radials with very little room to spare. I have over 700hp to the wheels with a manual trans, here's a link to a page featuring my car... http://grannys.tripod.com/20102.html . Here's a pic of a similar setup that i added under a 2nd gen RX-7 to replace it's original IRS... The vertical bolt is actually the large stud that the original IRS subframe bolted to. In addition to the large stud that located the bracket, there are (4) 3/8" bolts in the bottom plate and (4) more 3/8" bolts that attach the bracket's backside to the chassis. Both sets of 4 bolts also have a 1/8" thick backup plates to spread the load on the inside of the car. Here's what the overall set of brackets look like to convert an IRS 2nd gen RX-7 to a solid axle... The torque arm does not weld to the axle housing, it simply slides over the pinion area and attaches thru a plate that fits over the lower section of it's rear cover. The two odd shaped brackets on either side of the torque arm are anchor points for the watts linkage, the one brachet with the stud is a pivot point for the watts linkage's bellcrank which welds to the right side axle tube. The (4) unpainted brackets weld onto the axle tubes to attach the lower control arms, as well as the shocks. This setup was designed to use the original lower control arms and watts linkage from a '79-'85 solid axle equipped RX-7 to keep cost down. Here's a link to a page that shows converting the IRS second gen RX-7 to a solid axle... http://grannys.tripod.com/TASAinstallguide.html I don't make anything for a hybrid Z, just thought the pictures might inspire someone Grant

It's not the 300ft/lbs that kills the transmission, it's the intense inertia energy release that happens when engine rpm is pulled down quickly. Even a 250hp engine can easily generate a 700+ft/lb torque spike at the input shaft, all it takes is an aggressive clutch coupled with sufficient traction. A T5 can easily live at 400whp, you just need to pay attention to what clutch is in front of it. If clutch capacity is < 500ft/lbs or so, you will probably be fine. The T5 input shaft i have here on my desk has a minor dia of around .760" in the spline area. I'm not sure what alloy it is, but a treated 8620 shaft of that size would have a yield strength of about 1000ft/lbs. Mustang Cobra clutches are a pretty good match for a T5, lots of Mustangs running low 11's to high 10's 1/4's with a T5 using that clutch...they have a 10.5" organic disc and a PP load of around 2124lbs, shouldn't be too hard to come up with something close that will fit. Bottom line is you don't have to be afraid to run slicks if you choose the right clutch.

A 113 mph trap speed has potential for around 1.60 sec 60'. With that much improvement in your 60, you would probably be around 11.50 et. I run 100 lb/in springs up front. That gives more rise up front on launch, which raises the CG resulting in more weight transfer. I've even added 200lbs of lead inside the back bumper when it's needed. Basically you want all the weight transfer you can get until the tires hook, you can always decrease the weight transfer later if wheelies become a problem After you get all the weight transfer that you can get, adjust your staging rpm until you find the sweet spot between bogging and spinning. Don't give up on your ST-10 just yet. Here's something to think about... ...what happens to engine rpm when an automatic car launches? rpm basically rises from staging until the transmission shifts, no torque spikes created to knock the tires loose. ...what happens when the typical stick car is launched? rpm quickly dips down from the staging rpm, indicating a torque spike was created. The larger the dip in rpm, the larger the torque spike the input shaft and tire patch will see. Eliminate that torque spike, you can get more power down before killing the transmission or knocking the tires loose. In the past you had to buy an expensive adjustable clutch to consistently achieve this, but not anymore. You can probably use the clutch you already have.

This is a 3000rpm no-prep launch with 3.73 gears, 2.78 1st gear, and 28" tall 275/60 radials... Without the clutch slipper, it would be bog city.

Rear squat is not your friend if you gain camber. The bigger dia your wheels the less forgiving is the sidewall, and more the tire will be edge loaded with camber gain. You want the rear contact patch as perpendicular as possible to the track at the point of maximum acceleration. Don't limit your front shock travel, maybe even extend the travel of your front shocks to get as much front rise and weight transfer as possible. Looser worn out front shocks would be better, as would softer front springs. Your rear spring rate is stiffer than ideal for a solid axle car, but that works in your favor to reduce the amount of irs induced squat. Balancing "torque vs clutch" will help your ST10 live longer. Remember- your crankshaft/flywheel assy is an energy storage device. Any change in rotating speed represents a change in the amount of energy stored within. As an engine gains rpm, some of it’s output is diverted/stored as inertia added to it’s spinning crank/flywheel assy. Inversely anytime that engine’s rpm drops, the inertia energy removed from the spinning crankshaft/flywheel assy must go somewhere to make that happen. Example- say a vehicle is launched at 5500rpm and rpm is pulled down to 3500 as the clutch locks up. That 2000rpm drop directly represents inertia energy removed from the spinning crankshaft/flywheel assy that was directly discharged into the transmission’s input shaft. This discharge of energy is added alongside the engine's output, creating a momentary "spike" of increased torque output. As rpm begins climbing while the vehicle continues to accelerate, some energy is diverted from the engine output to recharge inertia back into the spinning crank/flywheel assembly. The speed with which the rpm change occurs has a direct effect on the intensity of this energy exchange. If the duration of the exchange is doubled, it's intensity is cut in half. This is where the balance of "torque vs clutch" comes into play. If the torque capacity of the clutch is closely matched to the engine's torque, any extra torque "spike" will be dissipated as additional clutch slip and not passed along to the transmission's input shaft. This added clutch slip is actually helping in a few ways, extending the duration of the energy exchange (less intensity), and reducing the amount of rpm change (less overall energy to discharge). Instead of changing clutches everytime i want to experiment with something different, i found it much easier to get some of the same advantages by installing more clutch capacity than required, then adjusting the duration of clutch slip using a small adjustable hydraulic cylinder attached to the clutch pedal. It's proven very effective. My Shop Mule is running 5.70's with 1.30 60's (700+ to the tire) using a 1-1/16" input / 28 spl output Toploader and 28 spline axles using a 2900# diaphragm PP for several years without failure. I've since started producing a more compact version of the cylinder used by the Shop Mule, here's a link. An interesting note- if rpm remains constant from launch until clutch lockup (controlling clutch slip can make this happen), no energy is recovered or spent changing the speed of the spinning assembly. Because having a torque "spike" requires leaving enough reserve strength in the drivetrain to deal with that surge of energy, removing that temporary energy surge allows one to actually add more engine power while still staying below the ultimate strength limit of the drive train. This is the area i'm exploiting with the Shop Mule.

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Western WA, near the North Cross Hwy.

Placing the weaker grease passage area in compression (rather than tension) as power is applied will make it less likely to fracture. For u-joints that have a grease fitting in the cross, the drilled hole from the fitting to the center of the cross is a weak area. If viewed from the front of the car, power from the transmission is transferred in a clockwise direction into the u-joint. ...Placing the grease fitting ahead of the slip yoke ear (as it rotates) will compress the grease passage area as power is applied. ...Placing the grease fitting behind the slip yoke ear will place the weak area in tension, making it easier for a crack to form. For the rear u-joint, the grease fitting should be placed ahead of the driveshaft ear as it rotates.

I have built thousands of driveshafts for V8 swapped RX-7's over the last 20 years...1310 u-joints and 2-1/2" diameter, same materials that i use in my personal car (manual trans, 275 drag radials, good for 5.73 w/ 1.30 60'). 1350 u-joints and 3-1/2" tubing are brutally strong, but the bigger/heavier parts only slow you down if 1310 and 2-1/2" can do the job. These cars are short, so no need for larger dia tubing w/ regards to critical speed. Smaller diameter driveshaft also allows for larger dia exhaust in the small rear portion of the tunnel. Use quality 1310's (I recommend Spicer) and orient them so that the grease fitting passage is compressed under power. The cold forged Spicer Life 1310 joints are the strongest (and no grease fitting), there are people getting 1000hp thru those.

To prevent your current bog, either your clutch has to slip or your tires have to spin. My suggestions regarding air pressure and shocks are aimed at going away from clutch slip and reducing traction to gain some spin and pick up some rpm. The less rear shock suggestion was assuming your car squats when power is applied, as less compression would allow it to squat faster, momentarily reducing traction possibly enough to get the tires spinning. Dropping air pressure isn't going to make much difference, at least as far as gaining enough rpm to prevent your bog. More air pressure will make a difference only if traction is reduced enough to let the tires spin, which will gain you some rpm. Here's what your rpm is at different lockup time intervals down the track, assuming 2.97 T56 1st gear, 3.54 diff ratio, and your car accelerating at a 1.76g rate (1.45 60')... .3 seconds in, 11.7mph 1590 rpm w/ 26" tire, 1476 w/ 28" .4 seconds in, 15.6mph 2120 rpm w/ 26" tire, 1968 w/ 28" .5 seconds in, 19.5mph 2649 rpm w/ 26" tire, 2460 w/ 28" .6 seconds in, 23.4mph 3182 rpm w/ 26" tire, 2955 w/ 28" .7 seconds in, 27.3mph 3713 rpm w/ 26" tire, 3448 w/ 28" .8 seconds in, 31.2mph 4239 rpm w/ 26" tire, 3986 w/ 28" As you can see, if your clutch locks up at .3 seconds in and the slick is stuck to the track, that bog to 1476 rpm with a 28" tire is only going to improve to 1590 rpm if you swap to a 26" tire. Even if you were to spray some nitrous to help off the line, without wheelspin the rpm would be pulled below the minimum recommended 3000 unless clutch lockup is extended out to .6 seconds. If you want to carry the wheels down track, the engine needs to be spinning fast enough at lockup to make some power. Just to be clear, my clutch slipper doesn't make it a slippy clutch, as the intent is only to delay lockup just until your car is going fast enough that lockup won't cause a bog. You still have all the original clamping pressure, just slightly delaying it's application. RPM does not have to flare up above the staging rpm if you don't want it to. If you are afraid of hurting your clutch, you can easily adjust so that you still have most of your bog, just not as much. Much more predictable than relying on wheelspin to overcome the bog. I know what you mean about driving around town knowing your car can pull the front tires. My favorite part about going to the track is driving back home late at nite with a big smile on my face.

With 3.54 gears and your clutch likely locking up at less than .3 seconds in, rpm is going to be pulled down to around 1500 unless you can get some wheelspin or clutch slip. Nitrous can't help when the rpm is pulled down that low, but there are a couple things that you could try to get some wheelspeed... ...more air in the slicks ...if the rear of your car squats on launch, less rear shock ...more stored energy thru either a heavier flywheel or more staging rpm can help break your slicks loose, downside is the added torque spike when that stored energy is released can easily become a parts killer. ...add some clutch lockup delay. Delaying lockup until about 1 second in will result in an rpm dip to around 3000, way better than the current 1500 or so. The added slip allows you to launch at a much lower rpm, so it's not adding as much clutch wear as you might think. If the added rpm nets you enough power to get a little wheelspeed as well, the resulting rpm at lockup of around 4000 will really make your car fly. This route is also much easier on the rest of your drivetrain, as it basically eliminates the torque spike from the flywheel effect of the spinning crankshaft/flywheel assy releasing energy during launch. Also makes it easier to hook up when the track isn't that great. Here's an easy/cheap DIY way to add some lockup delay... http://grannys.tripod.com/clutchtamerdiy.html . I use one to get 1.30 60's from 28" radials, 3.73 gears and a 2.78 1st gear 4 spd, just not possible without it. If you decide to make one for yourself, i'll send you $50 if you report back with results

I went about this clutch slipping in a little bit different way. I use an inexpensive screen door hyd cylinder to do basically the same thing. It's adjustable for the amount of "initial hit" that the clutch has, as well as the amount of "secondary delay" for final engagement. Also adjustable from the driver's seat. Here's a link to the DIY details, including PN# for the cylinder that you can get from the local Home Depot... http://grannys.tripod.com/hillbillyclutchslipper2.html Here's what happened without it... Hi Eric JB, i'm the guy from Concrete with the V8 RX-7

I use one of these clutch slippers, really helps reduce the torque spikes that kill parts... http://grannys.tripod.com/hillbillyclutchslipper2.html I have a solid axle 8.5" 10 bolt with 28 spline axles, no problem at 700whp with a manual trans and drag radials, 1.308 60'. It will help your IRS as well. Here's what happens to my car without the clutch slipper...