Re: Engine, Tach, and Speedster Questions

Posted by Jim On 2009/1/4 1:19:01

Ron wrote: "...320 cu in 90 HP 8 (according to the engine numbers and owners manual) and want to know the normal operating rpm range..."

Ron,

Good question. I also wonder what maximum sustained rpm is healthy for these engines. I have a 39 320 that seems very unhappy if pushed over what seems like about 2100 - 2200 rpm. These engines make lots of torque. I currently have 4.36 : 1 gearing with overdrive (28% overdrive ratio) for a final drive ratio of 3.14 : 1. With 7.00 - 16 Firestones that are approx. 30 inches tall. The car seems very pleasant at 60 mph. I honestly believe it would pull taller gearing with no trouble at all. I look to drop to 4.09 : 1 rear gears giving a final ratio of 2.94 : 1.

Owen is spot on about the babbited connecting rod bearings being of concern in your engine. As light as your speedster will be, I would gear it to the moon if you want to go over 60 mph for sustained periods.

I would be very curious to hear other opinions from experienced operators of 320 8 cyl. engines on max. sustained rpm.

Your project looks very interesting.

Best of luck,
Jim