What are your opinions on oil viscosity? Amsoil? Diesel spec ?

I've been reading lately about mod engine owners running 5w 30 instead of 5 w 20
Also running 15/ 40 diesel spec? And is amsoil a gimmick?

http://www.mach1registry.org/forums/showthread.php?t=112712

ive started running the 15/40 diesel in my gt and will be running it in my mach when it is running.

i've never heard anything other than great things about amsoil from guys that do actually use it. i personally use royal purple in my 07. all of our other cars get mobil1

ive been tossing around going to red line, but so far its been good old ford motorcraft 5w20

I generally use whichever full synthetic is on sale at autozone when I go for my chance.

Amsoil is actually a really good product. It's just sad that it's coupled with a pyramid scheme. Have a friend that sells it to me at cost if I ever need it, but everytime I ask he tries to get me to sign up to sell it... meh.

medrick wrote:ive started running the 15/40 diesel in my gt and will be running it in my mach when it is running.

What made you decide to try diesel oil and what made you decide to stay with it?
Can you tell a power diff?

I know I will stir controversy with this, but. 15/40 is too heavy for these engines. They carry great oil pressure on 5w20 and 5w30. They have very tight clearances on the mains and rods. So viscosity is not a issue. Check your oil pressure stone cold, it is very close to 100 psi. Most mods run 40psi at idle. You will actually rob power with heavier oil, it takes more parasitic to turn the pump. I have built a bunch of high power mods and have not seen any failures from viscosity. If you just have to run something heavier, run the 5w50 synthetic for the Shelby. It will at least flow properly when cold. There is a lot of talk about diesel oils and ZDDP, they are not as high in ppm as they once where. If you really want to do something for your engine add ZDDP to every oil change or better yet run synthetic and ZDDP. I am not a believer in Amsoils claims of extended oil changes. Yes they use a great base stock, but you CAN NOT effectively filter out the byproducts of combustion. They are a chemical contaminate not particulate. Take this for what it is, my opinion.