Inliners International Forums General Discussion Engines 235 & 261 RPM Limits

I am building a 261 with a RV cam, the crank has .002 bearing clearance, the rods are stock 261 rods, the pistons are flattop Egge .030 over pistons and the head is a 1959 848 head decked .010. The block has been decked to align it with the centerline of the crankshaft.

The 1950 Chevrolet Styleline deluxe car the engine will be installed into has 15' tires, a 3:55 to 1 rear end, and a Saginaw 4-speed.

I have no idea what the RPM Redline should be for this engine or for the 235 in my truck with a similar setup;

what do you think maximum RPMs should be?

I do not intend to drag race with the car but want to "get on it going onto the freeway" to reach 70 miles per hour.

Thanks,

Ted

Given 70 mph, tire size, rear end ratio and transmission, you can do the math and find out what rpm the engine will be turning to do this.

In the McGurk article, he recommended keeping keeping RPMs below 5000 for engines with stock components and under 5500 for engines with stiffer valve springs and other modifications.

I know the article is from 1955, but I think it's still pretty good advice. Especially when you consider the newest 235/261 is over 50 years old.

As far as your setup goes. At 70 MPH you should be turning between 2800 and 2900 RPM depending on your tire height.

http://www.ringpinion.com/Calculators/Calc_RPM.aspx

http://www.selectric.org/55chevy/soup.html

You'll need to know the diameter of the rear tire. then you can use one of the many on line calculators to figure things out, such as http://wahiduddin.net/calc/calc_speed_rpm.htm. (there are others)
To try to answer your main question, cruse speed rpm... I'm thinkin' 3000 sustained would be as much as I'd go, and I'd prefer less than that. My daily driver is right at 2000 at 70mph (with the overdrive engaged) Others will have more first hand info. Typical redline for a street engine? Probably mid to high 4's. Stay tuned..

Paul

Agreed. 4500 would be a maximum only approached with consideration. I usually shift at 3000. there well be a need to do some work on the rotating and reciprocating stuff if you want to get past the 6000 rpm harmonic barrier more than once.

Fair enough gentlemen, 3,000 for traveling and not more than 5,000 even though I've got stiffer springs to match the RV cam.

Appreciate the help and have a great holiday season!

Ted

The 235 rods are generally thought to be good to 5200 rpm max. I have cruised at 3400 rpm with the 411s out back (depending on the tires ), generally shift max 5500-5700 rpm at the track, although I have gone as high as 6K at the drag strip on a very few occasion (did not make much difference performance wise as the head simply runs out of steam I think at around 5300 rpm and maybe not even that deep. but I have not done that for quite a few years, too hard on the parts). The 261 rods presumably would go a little higher but the weak link is that funky split small end. But I think the others are right, 3000 for crusisng, 4800 shift max are nice safe numbers.

The stock '54 Chevys with standard shifts (1:1 high gear ratio) and those 6.70 X 15 tires (26" dia)would run 70 mph for long stretches in their day. Those tires/gears equal out to 20.9 mph per 1000 rpm in high gear. 70 mph divided by 20.9 mph equals 3.348 thousand rpms, or 3348 rpms. No hill for a stepper! Or 3212 rpm with 3.55 gears