GlenL

I guess it depends on how it's jacked. With the car lifted on the jack points the engine bay spreads open so it pulls on the ends of the bar. I think that during jacking the jacked side pulls and the floored side pushes.

Rob Edwards

'78 5-speed, Low-G tires, brakes, and engine. Utterly stock, never hit (I've been staring up its skirt for 2 days now). Bent downward in the middle. What are the vector forces that bent it this way?

mark kibort

leaning on the cross bar to change the air filter?

thats just it... there should be just as many bent down as up, statistically if it was due to the chassis flexing, but its not. probably a mechanic puling up on the bar, or down on it over its hard life at the shop.

mark kibort

I think youre right.... might also be the forces on the car in high g loading situations too then, right. either way, dont think you need much more than compression or extension control and the stock bar does a good job of that, no?

Carl Fausett

This is what I believe:

That cornering forces pull on the cross-brace, so the brace is in tension. It is not getting bent that way. It can be quite light and still strong in a straight pull like that.

BUT: I think sharp upward shocks on one side of the suspension (pot holes, curbs, rumble strips at the track) put the cross-brace in compression, and that's how it gets bent. To withstand a yield in compression, the cross-brace has to be much stronger.

You can kind of see how it would be so if you look at this picture. Cross-brace visible on top, forward frame tubes in the center, and cross-brace that connects the two frame tubes at the bottom (aka lower radiator mount) Hard to see behind that is our chrome-moly cross brace from lower a-arm mount to same mount on opposite side.

Upper cross-brace definitely helps keep the tubes in the frame that the lower a-arms are mounted to from twisting. Lower frame brace does so even more. In this accident, the lower frame brace kept my frame from being bent when the tire hit the wall. Saved my ***. The Ackerman arm bent, but not my frame.

GlenL

That bent-down bar is weird. The compression forces are along the bottom of the bar and most bars (every other I've looked at!) are bent upwards. "Leaned on" sounds plausible.

The bars are light tubes as the force vectors it's designed to counter are running end-to-end. The tube and mounts aren't capable of counteracting the up/down motion of the sides; it's holding the sides a specific distance apart.

With the "sharp nosed" profile of the car, they couldn't put a box at the front to control these forces and added the bar. I wonder if they started with the bar or added it after finding the hood getting squished in trials.

hwyengr

I swear it was posted somewhere that early development mules didn't have the cross brace, and that they'd have to pry the shock towers apart to be able to remove the engine.

mark kibort

the main function is for that bar to resist compression. its a stretch to think that there is any twisting going on, (pun intended) especially with the forces acting on the chassis ... the proof is how light and how straight the bar is. sure some are bent, but we have no idea what caused that as it might be external forces like a mechanic lifting it, or the car being jacked up.. ( I lean toward the car jacking because that induces more twisting forces on the bar... but it could also be stretching forces as Carl says...
bottom line, I don't think anyone has produced more compression force than Scot, Mark A, Joe fan, Dean Krenz, Chuck and the devek car, while visiting Laguna seca. all these cars had stock bars, Mark A and Joe changed when they did the intake.
if there is compression and its happening to bend the bar the 1/4-1/2" that it bends, the Carl's cross bar is going to fix that for sure, and it looks pretty cool too.. that's why I want one. (as long as its not too heavy)

axis of evil

what is the consensus on the efficiency of this bar?
the original would not fit as it would have passed through the inlet trunking, had to have the forward lean to clear both the hose and the hood.
no trouble with flexing , it's a cut down solid front sway bar from a 260Z Datsun

RennPartsDirect

The cross-brace is probably fine. I'd be more concerned with the engine...

Carl Fausett

UPDATE ON UNENGRAVED CROSS-BRACES

We have hit our magic "10" pre-order level. So the un-engraved bar can be a reality as discussed.
Gretchen is now trying to contact each of the buyers to take their deposit so we can proceed.

If you are one of the ones who have called in or emailed in your reservation to Gretchen, call or email her now to make payment so we can keep this rolling forward.

Thank you!

Carl Fausett

Update on delivery/shipping status: they are due back from the machinist on 11/25, then they go to the welder (allow 7 days) then back here for polishing if that is requested.

We expect we should be able to ship to you on or about Dec 1st.

Carl Fausett

They are here and we are shipping them now.

Ones in blue tape have been polished.

Andy Kay

Carl, if for some reason you end up with an extra non-polished bar, I'll be happy to purchase it. Obviously I'm not on Rennlist as often as I should be.

Carl Fausett

I made 20 of them, Andy. So I have a few extras.

The webmaster is fixing this page
http://www.928motorsports.com/parts/crossbrace.php
and then you will be able to order them from there. Wait about a day...