JBurer

Questions for those of you familiar with FD 20B swaps. If the route is taken where the stock subframe is untouched, motor is mounted back ~ 3 inches (not far enough back to require firewall cutting) and driveshaft is shortened:

1. what is typically done to the powerplant frame, now that the transmission sits further back?
2. If the steering rack is moved down 1/2" to compensate (for not cutting the firewall), will this cause bump steer or have any negative effect on steering?

Thanks in advance,
John

bosscobra

iTrader: (1)

if you want to keep the stock subframe why move the rack down? if your gona move the rack down anyway just get an aftermarket subframe. and if you move the rack down on your stock subframe its then no longer "untouched" i think the cleanest and easiest 20b install would just be get the definedauto 20b mounts, run a dry sump so you dont have to modify the rack in anyway. and send them your intake manifold so they can shorten it or just have a custom manifold fabed up if your gona be running a lot of boost anyway, that way you get better and equal flow. just my 2 cents, hope it helps in some way

JBurer

Boss,
Thanks for the reply. Actually mis-spoke when I said untouched subframe - what I meant was OEM subframe in it's original location.

Lets say the 20B install is configured this way -
https://www.rx7club.com/20b-forum-95/20b-fd-stock-subframe-363842/

Bump steer issues?

t-von

iTrader: (8)

You can shorten the PPF or use the existing mounting points of the tranny and diff to make a custom brace to support them. It would be just like any other car with tranny and diff mounts. If your willing to make a complete custom intake manifold, you can drop the engine directly behind the rack and hammer the firewall to clear the tranny. You would also have to fab something for the oil filter section. Moving the engine to this position will actually give you a lower center of gravity (because it's lower) and is also better weight distribution than the stock car.

bosscobra

iTrader: (1)

anytime you relocate your rack you can run into issues, even just half an inch changes the steering geometry so i would say yes bumpsteer would be needed with that settup

hwnd

iTrader: (4)

From what I've read, that bumpsteer can be fixed with adjustable tie-rods or adjustable steering arms. Keep in mind that this is was coming from a circle-track car setup but I do not see why the same theory wouldn't apply.

I've also thought about moving the rack forward. no up/down changes but forward.
while the arckerman geometry would be temporally off, that too can be fixed with adjustable rod-arms. i'm very sure someone will give 50 reasons as to why these ideas are very bad (moving the rack) but, as long as your angles are correct once you bolt it all back together - who cares?.

i think by changing the rack's position (forward), the geometry becomes offset (neg ackerman) due to having to adjust the rod-arms but if you have adjustable arms, you really could dial the ackerman geometry back into play. i think the standard Race tire has about a 3* {degree} slippage area and the standard DOT tire has a 6* - 10* slippage area. so it doesn't have to be 0* perfect ackerman anyhow - besides, OEM cars are generally NOT setup with 0* geometry, the inner tire tends to be over corrected (by 1*/3*) to keep the rear tires in line with the path of the front wheels.

I'm still reading on this topic and asking questions.. there may be something else i'm not seeing that would affect the steering in such a way that we couldn't correct it.

bosscobra

iTrader: (1)

hinson supercars sells tie rod ends to correct for moving the rack down just a bit if you wanted to go that route. but ive just heard of some people still having issues. i know when i do my ls2 project i'm keeping the rack at the same hight and running a dry sump and moving the engine up just a bit to clear. that way all my steering stays the same