Stock chassis with slicks

[Monzy]

Been a while since i've posted or been on the VMF but back daily reading all your posts I've been doing some track time with my 69 Fastback but have never attempted running a slick on the back mainly due to the car being stock underneath... I've got a fairly healthy 428 wiht 4spd toploader and a 3:91rear going to Estimate about 400-450HP at the rear wheels. I'd love to put a good sticky tire on the back and have a true launch but I'm afraid the car will twist with no frame connecters or added support. Everything is in sound condition expect for the back frame rails which are a little scary at the ends only. Anyone have experience on this? Should I add some support to the car before attempting slicks.

[Maxum96]

I would strongly recommend putting frame connectors in. I used to race the brown car in my signature on wrinkle wall slicks. I had a mild 351c with a C6, 4000 stall converter, and 4:56 gears. I didn't have frame connectors or a rollbar in the car. I ended up getting wrinkles in the roof right behind the doors. My current car is running a stroker windsor that should make at least 550hp with a 5 speed and 4:11 gears. I'm running frame connectors and a 8 point rollbar. Hopefully this will keep the car from flexing when I run it at the track on slicks.


Link to video of me racing my previous Mustang

[CrisAnderson]

Originally Posted by Maxum96

I would strongly recommend putting frame connectors in. I used to race the brown car in my signature on wrinkle wall slicks. I had a mild 351c with a C6, 4000 stall converter, and 4:56 gears. I didn't have frame connectors or a rollbar in the car. I ended up getting wrinkles in the roof right behind the doors. My current car is running a stroker windsor that should make at least 550hp with a 5 speed and 4:11 gears. I'm running frame connectors and a 8 point rollbar. Hopefully this will keep the car from flexing when I run it at the track on slicks.


Link to video of me racing my previous Mustang

A big +1.

It doesn't take long to twist these cars up without subframe connectors. Mine still twists (no cage yet) at the track with a 2500rpm, drag radial spinning 1.80 60' launch. Not badly, but it definitely twists. The 10pt cage should be going in shortly.

I know guys who run for years launching hard on slicks with no subframes...but the cars are permanently ruined for any trueness. Not something I think you want to do with your classic =D.

Cris

[brianj5600]

How do you know if the body is twisting? All my panel gaps are still good. No Wrinkles in the quarters or roof. I never dynoed my car, but I would guess 550 fwhp/tq. http://videos.streetfire.net/video/69410045_177035.htm It is getting frame connectors and 10 pt cage now along with 200-250 more hp.

[CrisAnderson]

Originally Posted by brianj5600

How do you know if the body is twisting? All my panel gaps are still good. No Wrinkles in the quarters or roof. I never dynoed my car, but I would guess 550 fwhp/tq. http://videos.streetfire.net/video/69410045_177035.htm It is getting frame connectors and 10 pt cage now along with 200-250 more hp.

Get someone to take video from the drivers or passenger side rear corners. Make sure you can see down the line of the car. That's the best place to take chassis tuning video anyhow =D.

It'll be pretty apparent if it's twisting enough to do any damage!

Cris

[jimeast]

A friend of mine that had several classic Mustangs over the years had a built 289, (He was a drag racer, fairly serious dragster at one time) and he tweaked his frame on the street messing around so the doors did not line up.

I was surprised, and he told me it's not that hard to do to a Mustang.

[johnniedice]

A guy down the street from me is selling a 1970 Fastback but i never thought about buying one before. I'm going to take a pic of it later this week and upload the pic along with the details so i can get some feedback from you guys.

[Maxum96]

Originally Posted by johnniedice

A guy down the street from me is selling a 1970 Fastback but i never thought about buying one before. I'm going to take a pic of it later this week and upload the pic along with the details so i can get some feedback from you guys.

You ought to post that in the Vintage Mustang Forum under General Discussion.

[ChristianaMuscleCars]

I think frame connectors are a good idea for you. A big heavy engine with a bunch of power...something is going to twist. I recommend TCP frame connectors. They fit pretty well and look good too.

[blkfrd]

I would not think that subframe connectors by themselves are going to do a whole lot to prevent body twist. If the connectors were tied together with an x brace or the aftermarket braces that i've seen, then I could see how this would help with reducing body twist.

[camachinist]

Also, consider a suspension control device which changes the loading points on the chassis as well as the instant center of the car. We did well for years in 10 second cars with a six point roll bar and a four link with subframe connectors. Look at an old C/SA or B/S Mustang and see how they did it.

Here's a couple of examples from back in the day:

Ed Terry's '69 427SOHC

A still of Ed's car leaving the line:



Note: The SOHC '69's were re-fitted with '70 trim for the '70 season, indicating the durability of the chassis modifications.

Aldon Miller's C/SA '68 'vert.... ran 10.60's back in the day:



Personally, I had more issues with shock towers cracking than I did with chassis flex, since the connectors, roll bar, crossmembers and four link were the first modifications I made for track use.

Good luck with the project