RA23/28/40 and AE71 engine crossmember comparison

[brett_celicacoupe]

well i took some measurements today of both AE71 and RA40 xmembers. i am told (source: omanra23) that RA40 xmembers are the same as RA23/28 just to clear that up.


so here are my measurements, estimated to have tolerances up to 5mm depending on which measurement.

the measurements taken were to look at the depth of the crossmembers, the relative positioning of the LCA mounting points, and the overall width.

the overall shape of the xmember is not to scale but the things with dimensions are drawn accurately (as possible) WRT each other.


pics are biggish but ill leave them as is to preserve readability.

judging by the relative positions of the LCA mounting points, im assuming that when fitting the AE71 xmember, it would be be best to keep the LCA as close as possible to the stock position.

in the overlay picture, the front view is fixed, thats exaclty where the xmember will be mounted (WRT up-down and side-to-side ways).

however the top view does have some lee-way to move foward or back. positioning the LCA mounts as close to the old position is only limited by the amount of metal surrounding the rear holes on the AE71 xmember.

in the case that the xmember is fitted such that the LCA mount is moved backward 15 from the factory position, what suspension characteristics would be expected from this? especially after some castor is dialled in. the LCA might start to make a serious foward-pointing angle


i measured a height difference of 25mm between the LCA holes on the AE71 and RA40, where the AE71 LCA hole is the higher one. im assuming this is a very good thing since the car can be lowered further than normal without seeing the LCAs make bad angles that would usually require RCAs to fix. any thoughts on this?


something else to note is that the LCA mounts are 40mm wider overall on the AE71 xmember. i roughly ran the tape across the LCAs and low and behold the AE71 LCAs are exactly 20mm shorter than the RA40 LCAs. the MX62 LCA is about 65mm longer than the AE71 so something around -5deg of camber would be expected in that case. i hope to end up using RA60 struts with R32 callipers and rotors so camber will probably be back to
-3deg by default. hopefully some adjustable strut tops will be able to dial it back to 0deg for road driving.

in the next few weeks i may begin to look at the characteristics of the steering setup on the AE71 re bumpsteer and ackerman angles







cheers

brett

[TurboRA28]

Great diagrams and info mate!

AE71 LCA's being 20mm shorter than RA items? Hmm not sure.. I was pretty sure AE71 and AE86 LCA's were the same, being 300mm which is same as RA28.

Or does this mean RA40 LCA's are longer than RA28/AE86/AE71?

[TA-022]

overlap above has raxx being longer (well mounting more inboard) than ae71.

you gained track didnt ya joel with the 71 rack setup???



nice work Brett! ive got RA60 and most these measurements already if you
wanted to do your thing with em ... just let me kmow. Either way top job!

[TurboRA28]

Yeah I gained track but I used the KE70 xmember and RA28 control arms (300mm). It wasn't a substantial amount, 20mm more each side or so.

[TurboRA28]

Also note on the diagrams above how much higher the inner pivot point for the LCA's are! I found RCA's are not really needed when using KE70 xmember and lowered springs..

edit.... oops i skim read that too quickly.. this point has already been raised!

If you went all hectik low you might still need them.

[TurboRA28]

I got the LCA location (forward backward direction) very close to the RA28 stock position.

I redrilled the hole as far back on the KE70 xmember as possible but also welded angle in around this area for strength.

[brett_celicacoupe]

I got the LCA location (forward backward direction) very close to the RA28 stock position.

I redrilled the hole as far back on the KE70 xmember as possible but also welded angle in around this area for strength.

good info again mate.


im wondering if you trimmed the outer edge of the AE71 xmember because my hazed memory tells me there is a lip on the chassis..... so the AE71 xmember might clash with it?

feel free to post up your before and after modding pics joel im interested to see


it definately looks like the rack of choice.


i think its going to be a bitch to measure balljoint positions and pivot to look at the akerman etc

[TurboRA28]

Yeah I did trim the outer edge off the ae71 and replaced with the angle.
I only can find after pics...

[o_man_ra23]

Brett, Ill be doing some balljoint and akerman dynamic drawings when I get the 23 up on stilts. Can you email me the acad version of those drawings though so I can have a starting point??

After driving around with an RA40 xmember on my RA23 for 2 years... yeah, they are identical.

Good work otherwise, just saved me a bit of work... Though I may re-measure some things for greater accuracy.

Cheers, Owen

[brett_celicacoupe]

looks like 5mm thick angle there?


is there any gap between the inner edge of the angle and the xmember, considering the xmember tapers down pretty quick?

your engineer was obviously happy with the result?

[brett_celicacoupe]

just having a quick think,

im expecting there will be a couple 3D plots with vertical suspension position on 1 axis, steering angle on 2nd axis and the 3rd axis will be toe/ackerman.

sounds fun


i need to buy some race car dynamics textbooks now so i know what needs to be changed to make things better

[TurboRA28]

Do you mean the gap here?

[brett_celicacoupe]

yepo ....

[TurboRA28]

Yeah there is a decent gap in there.. We put a couple of spot welds in there.

Engineer has seen pictures and had no complaints.. It's not all signed off yet though as i am waiting until the brakes are done and any other mods that come along the way. Officially the RA28 still has a 3t-gte in there.

[TurboRA28]

Should we discuss roll centre heights in this thread seeing as the xmember does change this?