Jump to content
HybridZ

Z car IRS vs the NHRA


Eric JB

Recommended Posts

I know there is a lot of fast Z's on here that run down the 1320. (or 660) But with the single trailing arm rear suspension, we are only legal to 10.99.

I am wondering if anyone has built an upper trailing arm set up (even mock) with halfshaft loops to get past the rule. I see a lot of you guys spending time and $$ to make them live. How do you get past tech? Thanks.

Link to comment
Share on other sites

It appears I am at the crossroads, between sinking $$ into the IRS, or going to a solid. ( I really don't want to cut my car up) I am still .8 seconds away from trouble, but my car is stock back there, except for the ZXT axles. Not sure if I want to commit to making the IRS live, when the rest of the car is already legal to 10.00. I have motor upgrades sitting in the shop, but the car is already too fast for Sportsman (footbrake) and if I jump to the next class, I want to make the car run 10.90's, so I can run it in the Lucas series, in S/ST.

 

If upper control arms were fabbed up, with halfshaft loops, and a set of wolfcreek style axles were used, I wonder if they would let me slide to 10.90. WHOLE lot less work than going solid.

Link to comment
Share on other sites

right out of the rulebook.

 

 "Cars running 10.99 (*6.99)or quicker that weigh more than 2,000 pounds with independent rear suspension without upper and lower (both) control arms must replace swing axle differential with conventional differential housing assembly (Example 1963-1982 Corvette). Cars with independent rear suspension with upper and lower (both) control arms may retain swing axle assembly regardless of weight or e. t. "

 

Yes, sorry for the confusion. The point I was trying to make was, since the Z only has one trailing arm, transverse arm, control arm, (you choose) there is no way to mount halfshaft loops between the upper and lower, since the upper doesn't exist.

Link to comment
Share on other sites

Hmm, that seems shitty.  My guess is that the rule was really intended for suspensions where the axle is used to locate the wheel laterally in place of an upper control arm, which isn't the case on the Z since the upper strut mount does that.    I think even building a mock one would take some careful measuring, since you would want to make sure it doesn't bind during travel.  I don't have a solution for you, but good luck.

Link to comment
Share on other sites

Namor is calling that right. But you can't count on an inspector to understand it. We really should have axle retention loops if only to reduce carnage should we break at speed. It's just a matter of figuring it out and dedicating the time and money. Something always seems more important to me (though this is pretty important). The trick is to make it serviceable. And the NHRA rule book is pretty restrictive on how you could build it: 1/4" thick strapping. Several people have contrived versions using u-bolts, which would probably get the job done. But they don't comply with the rule book.

Edited by RebekahsZ
Link to comment
Share on other sites

The driveshaft loop I built for my truck was a 1/4" wall piece of pipe cut 2" long, and then welded to a bracket. The one on the Z is two pieces of strap bolted together. Since the Z isn't a swingaxle design, I am thinking a couple of clam shells bolted to the transverse arm might appease them. Kinda surprised no one else has run into this issue.

Link to comment
Share on other sites

Way pro active. I'm just thinking about where I want to go with my racing. Right now I am in Sportsman. (12.00 and slower) but the car will go 11.8x. So I spent the last year trying to slow it down to stay in the class. Not much fun. I could move up to Pro, but I really don't like racing from the rear view mirror. Which leads me to making the car go faster. (way more fun)

 

I like racing the Z, and have done pretty well with it. It works well and runs the number, but I know there will come a time when I have to do something about the ass end. It might be due to breakage. But it might be due to rules. 

 

I don't care much for the big tire solid axle thing. I like the way it looks, and drives right now. The easiest thing to do is add weight, choke it off and stay in Sportsman. Not my style. 

 

So as you can see, I'm waffling back and forth.

Link to comment
Share on other sites

Try going to a stick and race the numbers-it sucks! At my local tracks they are happy just to have enough cars show up to justify firing up the grill to sell a few burgers. So far I've never had anybody get dirty enough T to check for a driveshaft loop (which I have) or a SFI Bellhousing (which I have). Seems like belt dates and a sufficient number of bars on the roll cage are what get most folks. I'm pretty sure Josey did Drag Week last year without axle restraint system. But, when an axle breaks, it usually does a good bit of damage to the brake lines and sheet metal. I may come looking for you next year for a couple slices of that 1/4" pipe to build a system. I hope to be putting 800hp thru Z31 axles in the next couple of years, and I'm scared about it. But not scared enough....

Link to comment
Share on other sites

I would agree that even real NHRA inspectors are very much on the honor system. I have been asked if I have a driveshaft loop, and saying yes was good enough. Even when they find something they don't like, they usually let you run, but ask you to change it for next time. But I have also seen where they will give you warnings about approaching a milestone ET and not being equipped for it.

 

et-quick-reference.png

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...