WHATS THE HIGHEST COMPRESSION RATIO THAT I CAN PUT IN MY 400EX?
DO YOU GUYS KNOW ANYTHING ABOUT THE 500KIT FOR THEM FROM FST?
IF I PUT A 440 KIT INTO IT AND THEN PUT A 12.5:1 COMPRESSION RATIO WILL I WRECK ANYTHING??
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you will throw a rod, you can put a 13-1 compression piston in them from LRD, I have heard of the 500 but don't know anything about it. You can put a carillo rod in your motor to hold up to the compression. It isn't just overevving the motor throwing the rod it is the big heavy piston two.
Hope I helped

 

15.3 to 1 is the highest you can go. But you have to run good rave gas. Don't worry about the rod it won't break he don't what hes taking about. The 400ex rods are one of the strongest stock. The 505 kits are a little unreliably. And it cost alot of money. But I think they make it water cooled. If u look a one, the head looks like has no fins on it.

 

It won't throw a rod, Can you tell my engine that, oh wait it is to late, it already did it, along with hundreds of other high compression 440's. Call Lrd performance, or Curtis Sparks racing.
Both these guys build alot of 400's they'll tell you who knows what they're talking about. WON'T THROW THE ROD....RIGHT!!!!

 

When I had my 400EX I was thinking about going big or staying home. With the bigger piston and higher compresion you will have two places which to look for problems. You will throw a Rod time and RPM more time less RPM, more RPM less Time. You will also need t look at the Cases, I asked Sparks Racing, and CT racing and they did confirm that.

Good luck, I just traded mine in and got a 440, 12.5 and water cooled for less than the cost of my 400EX with the Kits.

Smitty

 

P.S. For the record, I know it all, and you will loose a stock connecting rod bearing, if not the complete crank, in under 50 hours. Get the Corrilla, or stay below 12:1. Dont say I didnt warn you.