Rear Sub Frame Brace

[Jackhammer]

I would like to solicit some advice and or comments on a rear sub frame brace I am considering having fabricated and then bolting it in. I have included below a picture of my idea and placement of the brace.

 

Here is my situation. I am finished with the restoration of the chassis and suspension (pictures are in my gallery). In addition the outside paint work is done as well. Bottom line is I have decided to install a SBC... possibly a crate Ram Jet in the 300-350 HP range. I was... up until this month just going to modify an L28 and be done with it.

 

But... I have the V8 bug. I am now concerned that the rear sub frame needs reinforced/tied together. Since I have completed the chassis, I do not want to do additional welding and causing burnt paint,grinding and all the related redo. Thus.. I thought I could get the needed reinforcement by fabbing up a brace inside between the rear wheel wells with 1/8" steel plate and then bolting it through into the sub frame cross piece that holds the differential front brace. The picture should give you a pretty good idea of what I am considering.

 

Initially, when I had the car on the rotesserie... I welded in 1/8" channel (cap over)on the front frame rails from the firewall to the radiator brace. I also welded in baddog frame/floor rails underneath on the new floor pans. I am confident the front 2/3's of the car is strong. It is just tying into the rear sub frame that I am attempting here. I will also be using strut braces.

 

So... if I do what I am proposing do you think I will have enough structural strength to prevent the usual stress related problems associated with the V8 conversions?

 

I am only going to be using it on the street... no repeated hard launches and track racing. Maybe... an occasional track day every now and then.

 

Thanks for your input.

 

Jack

 

http://album.hybridz.org/data/500/medium/Sub_Frame_Support.JPG

[fastzcars]

If your concerned about flex I would get triangulated strut tower barces.Like the ones that "Top End Performance " sells. I know that some members here have had problems with TEP, but they'r in my area.I think they make a light and strong set. Don't get the ones with the hiemjoints on them. They'll just pivot around. One thing though, I did have to jack up the front of the car to get the front bar to bolt in, you'll be surprised how much the tower's move when you lift up the front of your car from the center of your crossmember.

[JMortensen]

That piece that you're talking about reinforcing is one side of a triangular "torque box" that makes up the main structure in the rear. The deck, the vertical piece, and the floor inside the toolboxes make up the torque box. I stitch welded mine to stiffen it. I think your brace might do something, but stitch welding might do almost as much without adding weight.

 

It sounds like you're basically spending all of your effort to strengthen the frame rails. This is a car with struts, so bracing the strut towers is just as important. As fastzcars says the strut towers are really flexy, so you'd probably FEEL strut tower bars where you might not feel the benefit of the brace you're talking about. I don't think your proposed brace would hurt.

[The Rototiller]

I would like to solicit some advice and or comments on a rear sub frame brace I am considering having fabricated and then bolting it in. I have included below a picture of my idea and placement of the brace.

 

Here is my situation. I am finished with the restoration of the chassis and suspension (pictures are in my gallery). In addition the outside paint work is done as well. Bottom line is I have decided to install a SBC... possibly a crate Ram Jet in the 300-350 HP range. I was... up until this month just going to modify an L28 and be done with it.

 

But... I have the V8 bug. I am now concerned that the rear sub frame needs reinforced/tied together. Since I have completed the chassis' date=' I do not want to do additional welding and causing burnt paint,grinding and all the related redo. Thus.. I thought I could get the needed reinforcement by fabbing up a brace inside between the rear wheel wells with 1/8" steel plate and then [b']bolting[/b] it through into the sub frame cross piece that holds the differential front brace. The picture should give you a pretty good idea of what I am considering.

 

Initially, when I had the car on the rotesserie... I welded in 1/8" channel (cap over)on the front frame rails from the firewall to the radiator brace. I also welded in baddog frame/floor rails underneath on the new floor pans. I am confident the front 2/3's of the car is strong. It is just tying into the rear sub frame that I am attempting here. I will also be using strut braces.

 

So... if I do what I am proposing do you think I will have enough structural strength to prevent the usual stress related problems associated with the V8 conversions?

 

I am only going to be using it on the street... no repeated hard launches and track racing. Maybe... an occasional track day every now and then.

 

Thanks for your input.

 

Jack

 

http://album.hybridz.org/data/500/medium/Sub_Frame_Support.JPG

 

 

what is your interior painted with?

[Pop N Wood]

If you capped your frame rails through the engine compartment with 1/8" steel, then the down braces on the top end performance strut bar are uneeded weight. A triangulated strut bar connecting the two towers to the firewall is always good, but the bars going from the front of the towers down to the strut bar seems sensless in you case.

 

If it were me, I would forgo the brace you drew in your picture and find some way to connect your subframe connectors to the back subframe. If I am interpreting your drawing correctly, bolting a brace in that position will help keep the car from twisting along it's axis. I would think a rear strut bar or bolt in roll bar would be much more effective than a brace placed down low like that. Plus you are trying to brace what is probably one of the strongest areas of the car.

 

But in my opinion your bigger worry will be keeping the front and back halves from moving like an accordian. That is why connecting the subframes to the back is what I would want to do.

[Jackhammer]

I appreciate all of the input so far. To recap... I am hearing triangular strut bracing on the front, tying front floor rails to the rear sub frame and the proposed brace may help some at least it would not hurt.

 

Then would the solution be... use the proposed brace and tie (bolt) it together with 1/8" steel frame rails to the existing floor frame rails. They would be bolted from the inside just behind the front seat cross brace to the existing floor rails and conform to the floor and attach to the rear sub frame cross piece and proposed brace.

 

Does that sound like overkill or should I eliminate the proposed brace and just run the bolted in rails to the rear sub?

 

I have also noted the emphasis on the triangular strut bracing up front. What do you recommend for the rear brace.... just a straight one connecting them together?

 

Thanks Again,

Jack

[Jackhammer]

what is your interior painted with?

 

 

POR 15...it was used inside and out. I have since applied Dupli-Color truck bed liner and dyna-matted it.

[The Rototiller]

POR 15...it was used inside and out. I have since applied Dupli-Color truck bed liner and dyna-matted it.

 

did you use bed liner on the inside and outside too? did you sandblast the entire car? just curious. i am in the process of building a rotisserie to work on the underside of my 240z...i have seen lots of great work on here (yours included) and it always gives my inspiration.....

 

thanks

[fastzcars]

Here's the link to Top End performance. TEP . If you notice the rear strut brace ends are welded and the strut tops are connected to the base of the opposing tower.

[Jackhammer]

did you use bed liner on the inside and outside too? did you sandblast the entire car? just curious. i am in the process of building a rotisserie to work on the underside of my 240z...i have seen lots of great work on here (yours included) and it always gives my inspiration.....

 

thanks

I just used the bed liner on the inside floor boards. Sandblasted everything that could fit in a 4 ft. blast cabinet. Everything else was scraped, wire brushed and sanded down to bare metal with a mud buster.

 

Best of luck to you on your project. Inspiration is good and so are some deep pockets.

[Jackhammer]

Here's the link to Top End performance. TEP[/url'] . If you notice the rear strut brace ends are welded and the strut tops are connected to the base of the opposing tower.

 

 

Thanks...I checked out their sight. The braces look good. I am wondering though if the cross brace will clear the carb/air intake on a SBC? It looks like it could be an issue. I will have to call them to find out.

 

Jack