sen2two

im finally going to lower the renesis into my FC. (was going into a 1st gen, but traded it for a better condition 1990 GTU)



so since it was going into a 1st gen, it has a 12a front cover. i was going to make the motor mount a flat peice of 1/4 inch 6061 T-6 aluminum on the front cover bolted to the frame. kinda like if you were putting a 12a into a older toyota or other ol'skool car.



but is it strong enough to hold the motor without breaking or cracking? maybe 3/8in to be sure? i dont want to use steel to keep weight down.

j9fd3s

some observations.



1. if you look at any factory mount, they are always boxed, or built so that the structure is strong. like the driver side mount bracket for the fc, its reenforced. they really want the rubber to flex, not the mount bracket. vibration is an issue too.



also the load on most mounting systems are setup so its only near vertical. there is very little side load on an engine mount, either there is another mount for that (FWD) or theres a V type shape to both mounts.



the greater side loading, and less reenforced the mounting design, the beefier it needs to be

mazdaspeed7

The engine will impart a twisting force on the mounts when you launch hard, shift gears, or anytime you are on the throttle. Every ft lb of torque that makes it to the transmission is also trying to twist the engine out of the car. Look at the way the entire chassis of an old fox body mustang on slicks twists during launches when they are making good power. Lots of torque and a weak chassis make it very noticable, but it happens with anything with an engine. You also have to deal with the forces of gravity, multiplied by bumps. You will a few G's for an instant on big bumps. The engine mounts need to absorb this to keep it from falling out of the car.



Aluminum isnt a bad choice, but it does not have the fatigue resistance that steel does. It has to be engineered with a higher safety factor than steel would. If you are concerned with weight, use 1/2" plate, and mill out areas in the center to form a pattern similar to a truss. A quick google search will give you load graphs for the various types of trusses. Also, you dont have to mill all the way through. You can leave the open areas with even as little as 1/16" for added strength. Use a ball mill so you have filleted corners. Stressed concentrate in sharp corners and transitions, and will be the first area to fail.

sen2two

thanks for the good info.



but after making a few measurements. i will not be able to use a flat piece across the front like i was going to. the steering rack is in the way. so now i will be waiting until i lower the motor in the car. i have another idea to still use the 12a front mounting bolts. but i'll wait until im lowering it to know for sure.



i'll post pictures when its in.