IRS vs Solid Axle weight comparison

[Tob]

While visiting George at MGW I received a text from my good friend Tom Wenstrom. Tom serves on Dean Martin's crew at Rehagen Racing and just happened to be there when an opportunity arose - to accurately measure the weight of a typical S197 axle assembly (including the UCA/LCA's, etc) as well as that of a '15 assembly with an iron center section.

About 110# difference. Not too shabby, and the un-sprung weight difference should be pretty significant as well but we didn't get into tearing apart the IRS as it will be getting bolted into the new race car in the near future hopefully.

 

[bpmurr]

The 110 is worth it. Best Stang I've owned!

 

[SID297]

It sucks about the added weight, but at least it's all in the right place.

 

[BlackBolt9]

It was pointed out to me that it's not even 110# since I forgot to weigh a sway bar and end links with the solid axle.

 

[SID297]

Probably closer to 100 lbs. The s197 rear sway isn't super heavy.

I bet there's a 5lb difference in just the gears as well.

 

[SID297]

Also Tom, are you guys planning on switching to an aluminum center section?

 

[BlackBolt9]

Probably closer to 100 lbs. The s197 rear sway isn't super heavy.

Yeah, I think that's a pretty safe guess. I'll try and weigh one in a couple weeks when I head back over there again.

I bet there's a 5lb difference in just the gears as well.

That would be accounted for in the weights taken above. Unless you are talking about switching the IRS gears out for the older style gears from the solid axle, which may happen since we will probably switch ratios and won't be able to get the newer gear sets yet.

Also Tom, are you guys planning on switching to an aluminum center section?

Not as of right now. I have been talking to Dean about it, but from what I understand we currently can't get the parts without buying a whole car since Ford isn't producing much for service parts yet. Maybe something has changed recently but I don't see it happening any time soon for us.

 

[BlackBolt9]

S197 Sway bars - Seems there is a rather large weight difference from one size to the next that I didn't expect. Heavy bar was 25mm, lighter bar is 18mm.

And this isn't a perfect comparison since this IRS didn't have brake hoses or wheel speed sensors, but that shouldn't be a huge difference in weight. Still have yet to see if the housing is the complete cause of the weight difference or if the aluminum housings use standard 8.8 gears instead of the super 8.8 gear set and how much difference in weight there is between the two.

Travis - sounds like we won't be tempting fate with the aluminum housing on the race car. Don't want to have one explode on a standing start or some other similar high load event. Just don't think it's worth the 40# especially since that 40# is in a pretty decent place and not part of the un-sprung weight.

 

[Tob]

Tom, is it legal (at this point) in AI to change the IRS subframe bushings if you want to?

 

[BlackBolt9]

From the 2015 rule book:

"Control arms and bushing material are unrestricted, but the location of the cradle cannot be changed in
relation to the OEM mounting point. The OEM brackets must remain in place and the IRS cradle must
mount to the chassis using those points in the OEM location. Bushing material for the brackets and
mounts is free (Aluminum, Delrin, etc.) but the mounts must remain as stock."

Of course they don't list the 2015 Mustang in their approved IRS list but I assume that's due to no one running one yet. Maybe we'll have the first one for them to look at???

As of right now the car is being built to run in the Trans-Am series which crosses over fairly closely with American Iron, so I assume again that we will run it in American Iron at some point this summer.

 

[SID297]

All the 2015s use the Super 8.8 so the earlier gears will not swap into the pumpkin. I understand the concerns on the Al diff, but considering how much power they cut out of the car I don't think there will be much danger of popping it. I plan to switch to the Al one myself fairly soon.

 

[Eatonualive281]

This is interesting. That's about the same weight difference between an 03 cobra and an 03 sra. Pretty neat

 

[BlackBolt9]

All the 2015s use the Super 8.8 so the earlier gears will not swap into the pumpkin.

Ok, good info.

I understand the concerns on the Al diff, but considering how much power they cut out of the car I don't think there will be much danger of popping it. I plan to switch to the Al one myself fairly soon.

:??: HUH?

 

[SID297]

Ok, good info.



:??: HUH?

You guys not going to have to run an intake restrictor in this one?

 

[BlackBolt9]

You guys not going to have to run an intake restrictor in this one?

We will have to do that, but even solid axles have exploded on occasion in World Challenge standing starts. We will be running similar power to that.

 

[SID297]

Yeah, I think that's a pretty safe guess. I'll try and weigh one in a couple weeks when I head back over there again.



That would be accounted for in the weights taken above. Unless you are talking about switching the IRS gears out for the older style gears from the solid axle, which may happen since we will probably switch ratios and won't be able to get the newer gear sets yet.



Not as of right now. I have been talking to Dean about it, but from what I understand we currently can't get the parts without buying a whole car since Ford isn't producing much for service parts yet. Maybe something has changed recently but I don't see it happening any time soon for us.

We will have to do that, but even solid axles have exploded on occasion in World Challenge standing starts. We will be running similar power to that.

That's surprising. Do you remember what part failed?

Think you'll have to run the 60mm restrictor, or are they going to cut you guys a bit of a break?

 

[BMR Tech]

Great info!!

As for the S197 RAA....I would figure in the 25mm rear bar (some came with 26mm) and also, I would try and throw the 05-10 style UCA/Mount out, in favor of the 11-14 UCA/Mount. Due to the 18mm hardware, stronger and larger UCA Mount, and the larger UCA.....it would likely be a few pounds heavier as well.

And I also believe the newer 11+ (13/14 for sure) LCA are a little heavier than the older style S197 versions.

 

[BlackBolt9]

That's surprising. Do you remember what part failed?

Think you'll have to run the 60mm restrictor, or are they going to cut you guys a bit of a break?

I'm not sure, I wasn't there when they took them apart. Just saw the aftermath and it looked like a bomb went off in the diff. From the parts and pieces I couldn't tell if it was gear or diff failure. I would bet it's a fatigue loading issue though because I'm pretty sure the couple we've had break were not on new parts.

This car we are building will originally be ran in Trans-Am and American Iron since the S550 hasn't been homologated into World Challenge yet. So we will have to run whatever restrictor is necessary to match the power to weight ratio required by the rules.

When the car does make it's way into World Challenge, I suspect it will get MORE restrictor. In theory, the S550 "should" handle better, so to keep parity amount other makes/models in the series, they will need to make less power. Keep in mind Dean is running the top of the leader board at COTA this weekend with the S197 so far.... we'll see when the other teams take out the sandbags though....

Great info!!

As for the S197 RAA....I would figure in the 25mm rear bar (some came with 26mm) and also, I would try and throw the 05-10 style UCA/Mount out, in favor of the 11-14 UCA/Mount. Due to the 18mm hardware, stronger and larger UCA Mount, and the larger UCA.....it would likely be a few pounds heavier as well.

And I also believe the newer 11+ (13/14 for sure) LCA are a little heavier than the older style S197 versions.

I was comparing these for mostly race cars, I don't know anybody that was running the 25mm bars. Most were around 18mm and some actually run without a bar at all. Doubtful you can get away with running no rear bar on the IRS. I figured I'd weigh the 25mm in case anyone was interested though, and because it was the first one I grabbed off the pile

Not sure on the different styles of upper and lower control arms. I did notice the larger hardware on the newer upper arm but it can't amount to more than a pound or two. We didn't get that picky because that's in the noise of how much everything weighs.

 

[me32]

Now i cant wait to see when people start figuring out how to swap the irs in the S197

 

[BlackBolt9]

I highly doubt you will see that unless someone REALLY wants the S197 look with an IRS. The rear floor plan is completely different, so it will take significant fab work (read $$$) to try and swap one in. It really wouldn't be any different than trying to swap in an IRS from a Termi other than being a different design. In the end it will be cheaper to just buy an S550.