I have a offshore mount that bolt through L brackets that are cross bolted into the stringers. My question is the bolts that hold the engine mount to the Angle brackets (Aluminum) should you use High stregnth steel or Stainless steel bolts? I think Stainless steel bolts are more brittle but does it really matter?

3 or 4 1/2" stainless bolts will work just fine. You won't ever reach the tensil strength of a grade 8 as the stringer will crush first.

Raypanic, your talking about the mounts to the brackets, correct?
Not the brackets to the stringers.

I used 1/2" stainless on mine. Mounts to brackets and brackets to stringers.

Also, I don't think that the stainless is more brittle, I think the stainless bolts are softer. Grade 8 would be a harder bolt making it more brittle

Raypanic,
I agree with the prior responses. If you are using pedestal style motor mounts 1/2 " stainless bolts will do just fine. What ever you do make sure you put anti seize on the stainless bolts when running the nuts on. If not they will gulled up and thats not fun. The reason I think these are ok is you are not supporting the load of the engine just stopping it from moving back and forth.
If you have an offshore style race Mount I would suggest using 7/16" or 1/2" grade 8 fine thread bolts with a locking nut. JUST MAKE SURE YOUR BOLT IS LONG ENOUGH THAT THE BOLT STICKS ALITTLE OUT OF THE NUT WHEN TIGHTENED UP. Reason being fine thread bolts hold tighter and the grade 8 bolt has a better shear strength. Especially in a go fast big power offshore boat.

If you have any other questions feel free to call the shop.

Pwrbt33- John S.
Offshore Performance
1-877-GOFAST1

You can get hardened stainless.

Jon

ARP makes hardend stainless bolts. In agreement with what was stated earlier in this tread, MAKE SURE TO USE ANTI SEIZE!. especially when you are using self locking (nyloc) nuts. Failure to do so will cause the nut to seize up on the bolt so tight that you will have to use a cut off wheel to get it off...Roger

shouldered hardened, stainless bolts are the choice. strength, use and esthetic's make them the bolt of choice, especially if you have a trick looking functional bilge , in a boat that you run on the hard side, oh, 7/16 is the size too.....