Inliners International Forums General Discussion Engines 235 vs. 261 vs. 270

Hey all,

I've been reading back in the archives for a few hours, and have learned a lot. However, I have some very situationally specific questions.

Here's my situation.

I'm restoring a rare pickup. At this point, I want it to appear stock in every way. It's a 55 1st series with the original, very well running 235 in place. It runs quite well, even though it has 94,000 original miles!

I'm curious what kind of horsepower, (read noticeable increase in performance) can I expect out of a purely internal rebuild of the 235?

I have a line on a 56 261 shortblock and an 848 head that would need the steam hole mod, at a very reasonable price for the two. Again, I want a pre-58 block so I can maintain stock appearance. (pre-58 doesn't use the full flow oiling system)
If I were to take this block/head combo and do internal work on it, what kind of hp can I reasonably expect?

Now, this truck in particular, I'm looking to restore to a visibly perfect representation of stock...but i want to be able to drive it in today's traffic at a reasonable pace. This is the only reason I'm not dead set on using the OE 235. I wanna sneak some extra ponies in.

Next question is this. I have a 54 3100 that has had a 55 1st rear end put in it. (open driveline.) It has a 55 2nd 235 in it.

I have a 61 261 that needs a home. I'd like to build that engine out and possibly use it in this pickup. This one, I don't care what it looks like visibly, as I'm not concerned with originality. What kind of horsepower could be achieved on a very street friendly hop-up? I'm not planning on racing anyone any time soon...I just wanna have a nice healthy potential for acceleration.

Last question. I also have a line on a pair of 58 270's also at a very reasonable price. I know there is a bit of surgery to stuff one of these under my hood. Does the 58 270 have an appreciable advantage over the 61 261 in terms of hp potential?
What is the cost comparison between the two? Is the 270 considerably more or less expensive to hop up vs. the 261? I know that both are more expensive that an U.R.E. But, I do believe that 6=8. So, enlighten me. I have some options, but I need to make an educated decision, and the "lines" I have on these engines won't last long.

Thanks so much for your patience with my ignorance!

A answer to your question about your second truck,I would build the 261 engine over the 270. 261 parts both stock and high performance are much cheaper and easier to find.Gmc heads are getting scarce and expenseve.Price a GMC head vs a 235/261 head.And by installing a 235/261 you don't have to hack your truck.
EvilDr235

Dear Josh;

Your plan use the 1956 261" engine is a good one and the best all around for keeping the "original look", & it bolts right in too.

There's no way to really tell how much extra power you can/will get as no 'dyno test' were done way back then.

An 'educated guess' would be around 50 Hp. more 261 vs 235 if you raised the compression & added a mild 3/4 cam, 75+/-.

If the 270 GMC engines are good, I'm sure there's a buyer here.

Good luck,

John M,

Thanks for the advice. I was going through some old posts, looking for some gold, and I think I struck it. It was one of your old posts regarding building a 235. Basically, you said that a 235 could be punched out .125" to a 252". So, is this where the 50 hp figure comes from? In your above reply? If I were to punch my 235 out to a 252, and use an 848 head, put a mild cam in it...would I be safe to use the original carburetion setup? Or maybe I should put it this way. What can I do as far as an internal hop-up (goal is to get some more horses without compromising the stock appearance.) I may just dump the idea of a 261, if I can get a good build out of my OE engine.

Thanks!

Jish,
The 261's real advantage is the beefier rods and approximately 35 foot pounds of torque. Put one in my 55 1st series and what a difference in the low end pulling power.

Dear Josh;

"Punch out the 261" to 278 & get even more.

The 261" is about 50 Hp.+/- more that the 235 & well worth the switch. These were used in the large trucks/buses of that era & rarely run hot because of the 'steam holes'.

Josh,

Just rebuilding a motor to stock specs is going to net you what the stock specs in your shop manual say. There would be no significant increase in performance unless the engine was on its "last legs". Stock specs are 123HP for the '55 235, and 148HP for the '56 261 for comparrison.
Both engines can be bored and stroked per Tom Langdons article, you can also increase compession with custom pistons, an 848 head, milling the head, or filling the chambers. Porting the head and using larger valves and camshaft can increase flow, but unless you're willing to improve the induction and exhaust systems, most of the potential of these internal mods will not be realized.

My opinion would be to leave the stock truck stock, and use the money to "build up" the other truck. If you want it to do highway speeds, adding HP isn't what you really need, its gearing. Since it is a '55 with an open driveline, I would suggest getting a set of aftermarket 3:36 gears from Patrick's, Randys Ring and Pinion, etc...

The GMC engines are definitely better for HP, but unless its a 270H or 302 (because of port size), I don't think I could justify the extra cost over the 261, in your situation. Just my opinion.

John M, Gearhead, drevil...

Thanks for the replies. I definitely have some thinking ahead of me.

gearhead: Now, bear in mind, my NAPCO is a 55 1st. The door plate says the hp is 105. So, the stock 56 261 would give me a 43 horse boost. Is that right? I know it's not going to be a race truck, but what I'm thinking is this...It's carrying 4.57's...obviously low gears. However, it'll be riding on 34 inch tires...that's using the stock 19.5" rims. With tires that are between 4 and 6 inches taller than a conventional 2wd truck would have been equipped with, i'd think the gear ratio would get picked up a fairly decent amount. Now, couple that with a some more horses and some more torque...Am I out of my mind, or in theory, shouldn't putting a 261 with no mods gain me quite a bit in terms of driveability...at least considering the uniqueness of my application?
Please correct me if I'm wrong.
Now, I think I'm definitely going to be building a 270 for my 3100. I bought a military 302 head today. Should be here in a few days. So, that'll be my hotrod project. I use the term hotrod very very loosely. I'm not made of money, so it'll be a very modest hotrod.
Truth be told, I'm doing the 270 thing more for my dad, and because I want a project he and I can get into that's not a stocker. He used to work with his buddies back in the 50's on 270's and 302's and race them. He never had one of his own, because that was for kids with money. He was the sole supporter of his family by the time he was 16...
So, anyway, he seemed to be real excited at the prospect of putting a 270 together for the old pickup. He's 69 now, and retired, and it was really nice to see the spark in his eyes at the prospect of getting his hands on a 270. So...I'm willing to incur the extra expense, because the nostalgia of it means so much to him.
I'll tell you this though, I'm definitely going to be picking everyone's brains throughout these multiple projects on how to do this stuff.
I really really appreciate you guys, and your willingness to help.

Thanks so much!

I didn't realize that it was a NAPCO, so whether or not the rearend gears can be changed, I can't say. 123HP is the gross HP listed in my books, so is the 148HP on the 261.
If you are turning too many rpm's for the 235 to handle, the same will happen for the 261. Adding more HP will obviously make it take off quicker, but it's not going to improve the top end speed much, especially in stock trim. If you do decide to rebuild any of these engines, I would recommend getting it balanced if you intend to turn more than 2500 on a regular basis. There are gear calculators available online at some of the places that sell differential parts.

Seems Tom Langdon told me once that putting a 302 head on a 270 will require special pistons. $$$$. Thats why I would recommend a 302 in the first place. I read once that a 270 can be punched out to a 302, but Tom says no. I guess, sonic check the block and consult your engine builder.

Dear Josh;

Don't try to "re-invent the wheel" here.

A 4X4 has low gears purposly. It's for climbing around in the desert sand/snow and not driving down the highways 70+. Also; There's a special relationship between the front drive section and the rear. The rear can't push any harder than the front pulls etc.

Gearhead is correct in that a 261 will produce more 'low end' which a 4X4 needs.

You can put OD behind your 270/302 for fun on the road.

Thanks John. I'm not trying to reinvent the wheel...I'm just trying to help them move a little faster. I should clarify what I meant by "decent pace." I'd honestly be quite happy if I could keep my napco on the road at 55-60 without straining. I have no interest in pushing it to 65 or 70...That'd be crazy without changing to 4.11's or higher. And I just don't have any interest in ripping the OE gears out right now... I suppose it's worth investigation. I know there's a 4.11 kit available now...Tall dollars, and I need two. Granted...I'm not planning on working the truck. It did enough of that in it's former life, and quite honestly, the 4wd parts are far to hard to replace to chance breaking something. So, it may not be sacrilege to ride around for a bit with 4.11's in there.
So, basically, what I should take away from this discussion is this.

If my goal is:

A) improved highway speeds, then really higher gearing is what I need. Couple a 261 with 4.11's and it'll be that much better.

B) more low-end power, then a 261 is for me, but
any improvement in hwy speeds should be taken purely as a happy accident because any improvement in gear ratio that my taller tires will give me.


Thoughts?

Josh

The 270 block can be bored .125-inch oversize to 292cid. A 302 head will require pistons of the 302-type. Since the standard 302 bore is 4.0 inches, pistons of the slightly smaller size may cost a little more.

There is currently a 270-H head advertised in the "Classifieds," but there was quite a bit of interest in that relatively rare item, and it may now be gone. Typically these heads are much more expensive than the 302 equivalent. The 270 crank and rods should fit in a 302 block with no problems, and boring the 302 .125 oversize yields 320cid.

i hope that you and your father will have the opportunity to enjoy that GMC-powered "hot rod." i know just how he feels. In the sixty-fifth year of my age, after hauling heavy pieces of cast iron around for many years, i'm almost up and running with a fine piece of machinery. We learn patience and continue to hope.

God's Peace to you.

d
Inliner #1450