The Stovebolt Site Forums The Shop Area Engine Shop Consideration with 261 Engine

I have a 1949 Chev 3600 truck with a tired 235 and through help on this forum I've found this is not the original engine. I've posted questions on ways to improve my top end speed to enable occasional longer distance highway trips which is not possible with my current 235 engine ... which tops out at about 45 mph. I've received suggestions on converting to a 261 engine and wanted to get more information on what modifications I'd need to consider in making this change. Depending on what I get back, I'll turn my attention to the parts forums to ask about 261 engines for sale. Thanks.

Regardless of which engine you choose, 216, 235, or 261, the practical RPM limit of a stovebolt six is somewhat less than 3000 RPM. Simply making the displacement bigger isn't going to do much, if anything to increase the top speed. At 2500-3000 RPM, any of them is going to sound like it's over-revving. It's not. People are just too timid to run the engines the way they were designed. In the bigger trucks, stovebolts ran wide open, all day, every day, carrying loads that today's snowflakes with lace on their manties would never consider hauling in their pampered toys. Either figure out a way to switch to a 3.50-something rear end ratio, or find a 5 speed overdrive transmission to increase your road speed.
Jerry

There is an article here on the Stovebolt site Tech Tips titled "The Need For Speed" that will direct you the way you need to go. Probably the cheapest and easiest way to go faster.

I've read replies to improving top-end speed by changing out transmission with OD to changing out rear-end gears. Through the help and wisdom of this forum, I've come to find-out I'm running a RPO 235 engine out of a 1949 4000 series engine. My interest is to find the most practical solution to increasing top-end from current 45 mph-ish, to having the ability to drive at 55-60 mph. Not looking for high performance speed, just practical and modest highway speeds to stretch my occasional travel distance options. My current engine isn't far from needing re-build. Stay with the 235 and rebuild plus rear-end gear change ... and/or find a 5 speed OD transmission. Thanks in advance of the worldly advice from the Stovebolt members.

Shortly after I graduated from high school in 1963, I inherited my late grandfather's 1958 Chevy coupe. It was the bare-bones "Delray" model, nothing fancy at all, but I loved it. It had a 3.73:1 ratio rear axle and a 3 speed manual transmission, 14" wheels, and fairly low profile tires. I had no problem whatsoever keeping up with traffic at 65-70 MPH, and I saw the high 80's on the speedometer more often than an 18 year old kid really should have. It had a box stock 235 engine. Yes, it made some tortured noises, but it stayed together! I'm going to guess you can run 55 or so with the rig you've got with no modifications, IF you'll get the steering and brakes in top shape and keep the engine tuned well, and run some fairly tall tires.
Jerry

"The Need For Speed" tech tip article
https://www.stovebolt.com/techtips/axles/1%20Ton%20Upgrade/

That will give you a 4.10 center section. Not great but better.

There is one glaring error in that "Need For Speed" tip- - - - -if you attempt to adjust the backlash on a rear end that's been in service for any noticeable length of time, you're going to interrupt the wear pattern of the ring and pinion gears, and create a howl that will make a set of earplugs required equipment at that new 60-something MPH top speed!
Jerry

Now you tell me ....

I drove a 53 gmc pickup on a 1000 mile elk hunting safari in western MT back about 1983. We had the 55 mph speed limit then. Did it all day long coming and going on that trip.. Should be able to sing along alright.

Another way to go is use a Saginaw all synchro 3 spd. with an overdrive. I see these all the time a swap meets cheep. I put one in a 53 car and it worked good, I have also put the o/d on a Saginaw 4spd. I have a friend that did the 3spd.o/d in a 51 pickup with a 261, what a sweet driver it has the kick down and oem column shift.
Jay D.

When I've jacked up the front end, the suspension on passenger side wheel has a little play and may suggestion bearings, or ...? On steering, what is the advice to look for or check. I have minor free play in the wheel and I can barely detect a slight knock when I turn the wheel when in my driveway. I understand to make sure running gear and brakes are in top shape if/when I increase my speed to 45 + mph.
Sorry for bad Stovebolt forum etiquette to mix tops within a given forum topic ... thought I'd stick with this thread. Thanks.

With the wheel jacked up, grab the tire top and bottom with the grease cap removed, and look for play between the hub and the spindle. That would be bearing wear and/or preload adjustment problems. If the whole spindle moves, you have kingpin and/or bushing wear problems. With the steering wheel locked in the straight ahead position (I use a bungee cord to the seat frame) try to shake the wheels by grabbing the front and rear of the tires. Look for looseness in the tie rod ends, drag link (between the left front spindle and the steering gear, and/or movement of the Pitman arm that comes out of the side of the steering gear and hangs down next to the frame. Sometimes slack can be fixed by tightening adjustments, otherwise you'll need to rebuild or replace the worn steering parts. There can also be looseness in spring shackles, spring pivots, and other suspension parts not directly involved in the steering system. Once you find the source of the looseness, post a new thread in the "Driveline" forum. You'll get plenty of help there to make your truck safe to steer and stop. That's always the first concern to address, before making it go faster.
Jerry

Just to pipe in with some first-hand experience with a very similar truck ('49 3804)... if anyone is still interested at this point ...

A big foot stomp to everything Jerry and Coilover said.

If you're changing the engine anyway, upgrading to a 261 is a great way to go. That's what I did. I did two very simple upgrades that were as easy as they come with *zero* modifications required. I now have plenty of power in stop and go traffic, and the ability to cruise 60-65 effortlessly, plus ability to dash to 70-plus when needed.

Upgrade One -- 261 install. For zero modifications required, look for a 261 from the 1954 mold. These engines were built for the '54 and '55 1st series trucks, so they have the provision for the front engine mount and the high-mounted water pump. If no front mount, merely use the front plate (what the timing cover attaches to) off your old engine. Look for a 261 with the casting code of 3733950. NOTE: Some of the 261's with this casting code will have date codes later than '54. Mine did. Threw us for a loop on the bearings. But it was because it was built as a crate motor for the '54 and '55 trucks. You can read about the group effort to rebuild this engine (under Jerry's tutelage ) in our "Rebuilding the 261" tech tip.. Some interesting things we found out about the engine so read the tech tip BEFORE you order parts ... like bearings ... Using this engine requires no mods -- it just bolts right in. You can even use all the peripherals from your old engine, except the manifolds and carburetor. No need to move the radiator, fiddle with engine mounts, reroute accelerator linkages, or drill holes for water pump relocation plates or any of it. If you use a '55 or later 261, it will require some mods, as will a 235.

Also, when trying to identify the '54 mold 261... you will read on this site about the "Captain's Bars" being an identifying mark of the 261. This is not entirely true. The '54 mold did not put Captain's Bars on the block, so don't bother looking. Look for the casting code and don't let the absence of Captain Bars throw you off. But if you *do* see the Captain's Bars, it will probably mean that you have found a 261 that will require some modification to work in your truck.

Upgrade Two -- Replace the rear axle third member with a 4:10 ratio from a '68 to '72 C-20 (with auto tranny). That upgrade is covered in the TechTip Coilover referenced. Oh, as a 3600, are you running 16 or 17-inch wheels/tires? I'm running 17's on my 3800. If you run 16's, you might not get the speed bump I did.

Note to remember -- A lot of advice given by 3100 owners is well intentioned, but remember that those trucks are different than our 3600 and 3800's -- we have the HO52/72 rear axle, which makes the ratio improvement an insanely simple upgrade. Their rear axle gear upgrade is not so simple Neither is finding/adding overdrives or any of the other add-on speed equipment. The very simple HO-52/72 3rd member swap is as simple, and relatively inexpensive, as upgrades get.

Lastly -- Jerry covered it well, but ... we are deadly serious about the brakes and the steering -- neither of which were expected to deal with modern highway speeds, so make sure they are tip top condition before you break the "AD Barrier" of 50 MPH.

Here's a shot of my 261 all nestled into the 3804 engine bay. Note the high water pump. The engine color (Detroit Diesel Alpine Green) and the Rochester Carb are the two main "tells" that this isn't the original 216. I did use the kit to mount the 216's valve cover -- something that I am now starting to regret. It looks cool, but it blows oil all over the place

Hope we've helped!
John

I had a warmed over 261 in my 1957 3600 for a while. I also had a 3 speed synchro over drive with split gears (becomes 6 speed) and 3:38 differential gears (NAPCO). It was a great combination, I actually seldom used the OD since the diff gears gave me 70 - 75 mph no problem all day. The engine had enough power to handle the gearing. I got my diff gear's from Patrick's, he actually gave me a discount because I bought two sets of gears (front and rear). I was also able to call him a couple of times to verify some install procedures, a very nice man. Unfortunately, I thought I read he passed away. He'll be missed.
don

My story much the same on my 53 1/2 ton with a 4.11 axle ratio.
I found a stock bore 261 and had it machined .030 over and polished up the crank then I assembled it with new insert mains and rods bearings, Best neoprene rear main.
Around the same time installed an okie bushing replaced axle bearings and seals and found NOS pinion bearings and carrier bearings. Next I purchased a Mother Trucker 3.55 ring and pinion. Set it all up in the garage ,which went really smoothly, there are some good articles on the stovebolt on this.

Bottom line is now I have an engine with more power, taller gears and taller tires and I can easily cruise with the traffic on the freeway.

Jerry is right you know, before that, the engine just seemed to be over revving but it is not, with stock gears it is operating out of the sweet spot though at anything above 50-55 mph.

I'm about to make the change from my tired 235 to a 261. My intention beyond the engine rebuild, is to get higher top-end speeds. It's been a while since I ventured out to the Stovebolt community with this ask. I wanted to ask for any current best advice in changing to this engine and making the appropriate other changes to hit 65+ mph. I started with front disc brake conversion a year ago and I love the confidence in quality braking power. Highly recommend. I jumped to 245 R7016's. I like the ride and look of these bigger wheels and tires. Any current help on the engine, gearing and OD change would be appreciated.

TGill, lots of great advice posted above that's directly related to your question. Here's mine, find a S10 T5 transmission with a .72 overdrive. Your engine will think the stock 4.57 rear gear suddenly morphed into a 3.29 ratio. If you're running 31" tall tires, you'd be turning 2500 rpm at 70 mph. With that one change, 60 to 65 will be a breeze, faster than that is no problem with a 261 I'd think. On level ground (and no headwind) I run 60-65 with my stock 85 hp 216 in a 3600.

Best of Luck,

RonR

"1949 Chev 3600 truck with a tired 235"

A tired 235 can mean an engine with worn rings and lost power/torque. If you are often at full throttle at 45 mph then yes, more power/torque will increase top end. You need the power/torque to overcome wind resistance and haul the weight of the truck and occupants. But there is a point (Jerry's comment) where the torque of even a rebuilt good engine will start declining on the RPM/torque curve. The analogy is a team of horses pulling a light load can only run so fast. Adding another horse doesn't mean it will run faster.

A 1949 will have a torque tube drivetrain. Upgrading transmissions or rear axles means converting to an open drive shaft which involves $$$. If you want to drive your truck often on the expressway then yes, I vote upgrade. You also should think about upgrading your braking system (bettering stopping power) and do all you can to the original steering to make it perform optimum. There are crazy drivers on our expressways today so you and truck may need to react quickly.

Changing to taller tires is cost effective. You may have to change the gearing for the speedometer.

buoymaker did add an element I glossed over. Cost of conversion to a T5. I'll ballpark a few numbers which are open for debate. A T5, I've bought 4 over the past 6 years. Prices ran from $100 to $300. Two I pulled from wrecked trucks. From what I read, 400 to 500 "might" be an entry point today. My new driveshaft to replace the torque tube was $150.00. A new clutch disk (you can use the original pressure plate if it's good) and input shaft....$100.00.

So, if a transmission can be had for $500 then drive shaft $150 and clutch and input shaft for $100. You're looking at $750.00. Depending on how skilled/lucky one was at finding bargains
and doing all their own work, it's possible to make the upgrade for half that amount. Or it could be twice the guesstimate above.

Goodluck,

RonR