I just installed the Semi-Solid Urethane mounts in my mildly built 240z. It is tuned at 140 hp to the wheels with the l24, Cam, high compression head, headers, and SU carbs. It was rebuilt and able to withstand high RPM's, 7,000-8,000 range. I primarily use this car for Autocross, Gymkhana, Off-road Rally Racing that is Sanctioned by San Diego Club Racing and it is comfortable and reliable enough to drive to work. I drive Highland Vally Road (an extremely tight & winding mountain road) every day to work, so I tear apart stock mounts and go through sets of tires and brakes every 3-5 months on average. I have been looking for a set of Urethane mounts for my car for many years, I got tired of braking and replacing stock sets. I know it's time to get new mounts when my engine hits the strut tower brace. I have gone through 4 sets already and was just fed up with the hassle and wanted something permanent that I didn't have to worry about. I am also planning a high HP l-28, (400hp to the wheels..) But I was held back because there wasn't an easy solution for this problem. (I am breaking mounts with a stock motor!) When I saw the new urethane racing mounts I felt inner peace! Now there is a set of urethane mounts for the l-series thanks to Mckinney Motorsports! Call now and get a set, Don't waste your time with the stock mounts! Ask For Mack! Mckinney Motorsports Website Phone: 951-304-9300 email@example.com The installation went smooth without a hitch, Really easy to install! Took about an hour with basic hand tools and a jack to lift the engine, no need to raise the car on jack stands. They look really cool in the engine bay, very beefy, thick and strong and have very little vibration. I was expecting more shaking and resonating but was very pleasantly surprised that it has a near stock comfort level for a urethane mount. I noticed an increase in throttle response, when shifting and rev-matching and heel toe, I am able to chirp the tires in 2nd gear, I wasn't able to do that before. The mounts have very little movement compared to the stock mounts. Thank you Big Mack for developing these Urethane L-series engine mounts! Keep working on the matching transmission mount!