The Stovebolt Site Forums The Shop Area Engine Shop 235 rpm range ???

I am building a 235 with a mild performance cam. What is it's best RPM operating band? How low can you go without lugging the engine and what is a reasonable redline?

I need to know this to calculate the best rear end gear ratio.

I just bought a T5 transmission out of a Chevy S-10 and need to figure out it's gear ratios. I also bought a 12-bolt from a 71 Chevelle. It has 2.73 gears with a posi in it. I am going to assume a tire diameter of about 27-28 inches. So what is a 235 good for? 1000-2500 RPM or more like 1500-3000 RPM. I am just guessing. Let me know your experience.

Thanks

I believe 3200 rpm is about the top rpm you would want to run for a long period. If you build a 235 correctly you could get it to spin in the 6000 and 7000 range, but that would be a race motor and you would be eating up main and rod bearings very quickly. When it comes down to it the 235 only has 4 main bearings and a long wobbly crankshaft. The faster you spin the engine the more wobble you get.

Run all day at 3200, redline at 4000, absolute redline at 4500.

The 235 is not very economical spinning at 3200 rpm, so you don't want to be near there for cruising rpms. I would think you would be happy if your engine was right at 2000- 2400 range at 70mph. That means the 2.73 gears with overdrive will not suit your needs. You would probably want to be in the 3.55 through 4.11 range if you are running an overdrive, but that also depends on the overdrive ratio.

What does this all mean? Give us more info on how you want to use your truck. If you want economy, you would choose higher gears... say 3.55 with overdrive. If you want to use your truck like a truck for towing (doubtful with the selection of a t5) you would use the lower gears like a 4.11. Midrange gears like the 3.73 may give you the best of both worlds. The 2.73 gears would work well without an overdrive assuming you have a steep first gear. It may be hard to get your truck started on a hill with such a high gear ratio. Towing would be out of the question.

sound like my big V-6 cruz at 3,000 all day redline at 3500 4,000 it all comes unglued in seconds. . .

Mike

I used to run my stock 235 on the highway for hours between Denver and Santa Fe, probably about 10 trips, cruising at about 3500 rpm. With 4.56 gears, I wasn't keeping up with traffic, but I was getting about 16 mpg.

I'd like to know what kind of power a built 235 is capable of.

I have a 52 Belair with a 235, mild cam, dual intake with Carter/Webers, fenton headers, engine was balanced when rebuilt.
Stock inclosed drive line, 355 rear end, 27 in tires.
I am at 2900 RPM at 65 MPH and it just purr's along.
Has plenty of power to maintain speed pulling hills.
Driving the freeway's I get 16-17 MPG, if I have a lot of around town driveing it's not so good (i like to hear the glasspacks).
I think balancing the engine makes a big difference.
The 235 is never going to be a real power house unless radical things are done to it, but I find mine is good for what it is used for in a 3600 lb car.
I also have a 46 pickup that I'm going to start a frame off on this winter, I have a 323 posi traction rear and a 261 eng, I'm still reasearching what I want to do with the transmission.
Gary

Right now, I have a mostly stock 235 (HEI, fentons w/ water heat for stock intake/carb) and a stock sm420 4speed tranny/Gear Vendors Overdrive combo that gives me the best of both worlds. I still have 3:90 posi rearand, a super low geared granny, and I can overdrive 2nd which is hardly ever needed, 3rd, which is a nice split between 3rd and 4th, and of course, overdrive 4th, which puts at me 2800 rpms at 80 mph. That's the same rpms as 60mph in 4th. 70 is much more comfy w/ stock suspension/brakes and I can actually have conversations and listen to the stock AM radio due to much lower cab noise-dynomat also helps. I am getting 16-18 mpg as opposed to 11-13 previous when truck was all stock. I am also running 29.8" radials. Coming Soon... disc brakes, restored suspension w/poly bushings, and mildy hopped up 261 stroker.

I had a 1961 Dodge D-300 the that ran 55mph@3250rpm with a 361 engine lasted 239,000 miles. . . Truck got stole 2 or 3 year's ago. . .

My 62 GMC K-3000 runs 62.5mph@3000rpm with a 379M-V6. . .

My 59 Mack runs 72mph@2,000rpm with a 711END+T<<altered the triplex, still a 2 stick 15spd but now has .61:1 OD. 5SPD OD mack trans $3,000 3spd auxy $750 seeing the look on trucker's faces when you past them on the interstate with a 59' B61T Mack loaded with a D9R CAT! priceless :crazy: :crazy:. . .

My 80 dodge D-30 runs 65mph@2,750rpm with a 360 2bbl

My M123 ran 42mph@2250rpm with 903 V-8 cummins, Should now run 58MPH@2,000RPM with the KT-635 I-6 cummins with 13spd OD. . .

not sure what my 79 Chevy run's 250 3spd i'm guessing 65mph@2,500rpm about. . .

My 95 ford run's 67.5mph@2250rpm with 351W EFI. . .

a 235 should run 3250rpm all day long. . .

Mike

The following information is based on my 54 truck which is driven every day....in fact, I just returned from the Turkey Run in Daytona, a round trip of about 300 miles. I am running a low torque cam, bored .060, a little head work, Fentons into 1-7/8 pipes, dual Carter/Webers and a stock distributor. The engine has been fully rotationally balanced, which I HIGHLY recommend. The transmission is an "85" T5 with a .72 OD and the differential is a Camaro 3.42 and the tire height is 28.5"

My 1960 235, makes it's power in this configuration between 1500-2400 rpm's. It cruises at 70 mph at 2100 rpm's and in 5th gear you can drop down to 45 mph in 5th and accelerate with traffic with no lugging. However, if you wanted to drop down to 4th gear it will comfortably wind to 65 mph at under 3000 rpm's. The truck will easily run 80 mph but has a sweet spot at 70 mph. Average mpg is 17.5 for both city and open road driving. My truck is still running a straight axle and 65-70 mph is the most comfortable cruising speed. At 80 mph the 4 wheel non-independent suspension becomes acutely obvious.

I tried a 3.08 diff which was totally unsatisfactory with my .72 combo. It made for a good 4 speed but lugged in OD at 55 mph and didn't "feel" right until you were at 70-75mph....too fast for comfortable cruising. The 3.42 is as tall as I would go with a .72 OD and a 28" tire. I would recommend a 3.42 as the tallest choice, with a 3.55 being a good option and a 3.73 if you live in a hilly region or plan on cruising at lower speeds.

Your first task is to determine your T5 OD ratio....the TAG on the front bolts will ID the year and a "search" will lock in your numbers. If your tag is missing, put the transmission in 5th gear, mark both front and rear shafts and rotate the rear output shaft 360 degrees. If the front shaft spins less than 270 degrees you've got a .72, if it spins more than 270 degrees you've got a .86 OD. If you by chance, have a .86 OD gear, you might be able to run the 3.08. I find the following site helpful:

http://csgnetwork.com/multirpmcalc.html

The lower calculator has proven to be very accurate.

My rationale, when building my engine and drivetrain was to maximize the original design potential of the 235. I saw no reason to try to spin a 4 main engine above and beyond it's capabilities and opted for a combo that lets the 235 breath and spin effortlessly, without a lot of unnecessary revs. I realize that pumping out horsepower and revs on a 235 is possible, but torque, economy and getting max. benefit for my bucks, made more sense to me. After all, the real joy of owning an AD is in driving it!!!! I hope this helps you sort out your options.

Dave

My stock 1954 truck 235 runs at 2800rpm at 55mph just thought I would give you my 2 bits worth

Dave,

Handy calculator. Thanks

When I'm running my 51, 235 at 50 mph she sounds like she's ready to blow. 55 is about as fast as she'll go. She runs great but boy is she loud. Do most of you find that? I have a 411 rear end. A 51, 235 is a low pressure engine. Mine has hydralic lifters (car engine).

Glenn,

Thanks for the replies. I have been out on a trip and am anxious to get home to check out the transmission that just got delivered. It does not have a tag as there are no front bolts. I don't plan to tow with it. I have a new Silverado for that. I want a decent cruiser that can keep up with traffic. If I could get teh 17 MPG some quote, that would be great as well. I do live with hills in south central PA, but don't mind shifting. It sounds like it is best to plan on keeping the revs low in the range of 1500-2400 with runs up to 3500 for acceleration. It has a very broken original suspension, but I am amlost sure that I will use the Jom Meyers front IFS and the TCI spring kit on the rear. I want to lower it as little as possible but still get tha benefit of a modern IFS. So, I will have to do some research to find out waht ratios I have and then what rear end will get me a good operating range. I figure that to keep up with traffic, I would like to be able to cruise at 75, so I guess I should target about 2200RPM at that speed and see how the rest splits out.

My 235 was on a 4.56 rear end, and I was able to physically drive it at a maximum speed of 74 to 75 mph, but at a dangerously high rpm. I routinely cruised it at 65 mph at around 3200 rpm, but would sometimes increase that to 70.

What really helped me with the additional rpms was upgrading the Rochester 1 bbl carb with a Holley/Webber 2bbl from Langdon's Stovebolt. I gained a lot of top end capability with that swap and it worked really well for my 235.

Yea i should have thought about that !

you think by kicking up my carn on the old 379 i could get it to handle run up to 3250rpm or is 3,000rpm still going to be max cruzing speed ?

Mike

Just a note: 4 main bearings obviously isn't the best design, but it's not an inherent RPM limiting factor.
The "slant 6" 225 has an even longer stroke than the 235/261 (4.125" vs. 3.9375") and does 5,500 RPM quite nicely.
An industry guideline for highest sustained cruising speed (assuming water & oil temperature are OK) is 2,500 feet per minute average piston speed (15,000 ÷ stroke = RPM). For a 235/261 this is 3,810 RPM.

I gotta jump in here. I have a 1960 stock 261 engine. I am trying to keep all the drive train pretty much stock but my car is a daily driver and I speed some on the highway. According to my calculations I am turning about 3100 rpm at 70mph. This is with a 3.55 rear rear and 27" tires. From what I am reading here this should be ok without damaging the engine? I want to , at least keep the engine but if I can't maintain highway speed I might upgrade to a 200 r4 with open drive line. I just installed a tach so when the weather breaks I can get a better idea of true rpm.

Thanks , Pete