Sorry if this is the wrong spot I wasn't sure where to put it.
Ok so heres the deal. I am going to have my car dynoed on Sat. Currently I am using good old fossil fuel oil. I have heard the claims of synthetics offering you some gains due to lower friction rate. Has anyone actually back to back dynoed there car changing the oil in between pulls to verify if this is true? This is exactly what I am thinking. Get three pulls two back to back then a cool down, I might change my oil during the cool down to test this theory. I am also running a real thick 85/140 gear oil in my posi rear. Two questions here is this oil to thick? And I wonder how much if any I would gain by also going to a thinner gear oil like 80/90. Not sure if I will have time to do both. Any thougths or experiences in this area.

 

It's hard to get the conditions duplicated exactly. But, a magazine (I forget which one exactly, I believe it was an off-brand vehicle with a 347 stroker & 5-speed) did a chassis dyno test along those lines. I don't recall all the details, like what petroleum lubes they were using, but with Red Line engine, tranny, and gear lube, I believe they picked up in the range of 20 HP with no other changes. That's consistent with the various manufacturers' claims.

Several years ago, Smokey Yunick admitted to at least a 10 HP flywheel gain. Again, not sure of before/after brands or types.

You probably don't have any need for 85W-140. I've been using AMSOIL 75W90 for 20 years in all my gear lube applications with nothing but complete satisfaction. Their latest Series 2000 formula is even better than their original. Auburn doesn't recommend synthetic with their posi carriers, though (doesn't apply to you, but others should know that).