The Stovebolt Site Forums The Shop Area Engine Shop Can an engine breathe better and still have good low end torque

I have shared with you all what my plans are for my 292. It's in the Hi-Po Area, as the questions I was asking was better suited for that area. This is engines in general, so I am starting it here, and if it needs to be moved, please do. Thanks.

I know the engineers know way more than I do. They crunch numbers, adjust this, tweak that, test this, toss that out, etc. Being a curious individual, and thinking outside the box, I tend to go about things differently, think about things differently, and do things differently.

I own a Jeep Cherokee with 4.0. Jeep improved upon their inline six design, by making the engine breathe better, and also increasing the torque output. I have to say that the 4.0 is a fine engine, and with mine having 207k it still runs strong, doesn't burn or use oil, and gets decent mileage (20-22 mpg) for a wheeled-brick. Yes, it has EFI, which is a huge improvement all by itself.

We all know an engine is just an air pump. In my mind I am picturing my 292, which I have been told varying things about the mileage they can get, but this really applies to all engines when I ask this, as there are engine improvement items for all the makes and models. Other engines that come to mind are the tuna boat car engines with tons of torque and got great mileage, while able to cruise down the road as fast as you wanted to, usually hitting 80 mph without even trying to. Unless the engine is offered up as a performance package, it will be woefully under powered, but will get the job done. Hence the huge aftermarket for performance improvement parts. Say one has one of these non-performance engines, and does improvements to it to make it breathe like it needs to, not like holding your hand over your nose and mouth with a slight gap in your fingers while running a marathon at 8,000 feet in elevation. And since the camshaft is the brain of the engine, if one gets a cam designed for torque, will this not effectively improve the torque, all the while having a better-breathing engine?

The car manufacturers are bean-counters, and want to save as much per unit as possible, yet they still need to adhere to federal regulations which typically drives up costs because of the extra restrictions.

Is it feasible to have an engine that breathes really well, but maintain low end torque? Or does improving the engine automatically make it a racing engine?

Inquiring mind wants to know. You guys have way more track time, drive time, tinkering time, performance adder time, and any other kind of car/truck tweaking time than I do.

I look forward to hearing back from all y'all.

"Breathing", AKA "volumetric efficiency" is the engine's ability to move its cubic inch (or CC) displacement in and out of the cylinder head effectively. It's largely a function of intake and exhaust manifold design, cylinder head port shape and size, number and arrangement of the valves, and duration and lift of the camshaft lobes. Everything from the air cleaner to the tailpipe must be considered when "improving" an engine's breathing ability, and like in a lot of other situations, "There's no free lunch"! Improving low end torque usually has a trade-off in decreased top end horsepower, and vice versa. Simply changing or modifying one component without making corresponding changes both upstream and downstream might result in a small gain one way or another, but generally speaking the whole system from end to end must be considered to show any worthwhile gains.

Straighter port shapes, more valves per cylinder, overhead camshafts, computer-controlled variable cam timing, and fuel injection can be combined to get some pretty impressive performance over a wide range of RPM, but trying to apply that kind of technology to a primitive design like a 292 is like making a silk purse from a sow's ear- - - -"It can be done, but afterwards the pig doesn't hear very well, and it looks funny!" 292's were designed to move heavy loads on medium-sized trucks around, with little or no consideration to high speed performance or fuel economy. They do that job very well, and they can be modified to run somewhat faster, while sacrificing some of the low-end torque that they were designed to produce.
LOL!
Jerry

Yes they will perform better with more air flow, BUT you have to know how to make air flow and still keep the air velocity high. Most racing engine run a very small rpm range, so making power is kinda easy if you know what range you are after. Street cars need to have power at all rpm ranges, thus what you call underpowered is more like well tuned for what it was intended for. Adding high flow heads does nothing if you don't improve the valve train, induction system, and exhaust system. You can't use the improvements if the air can not get into or out of the " air pump " fast enough. Really good heads are those with high flow numbers and really small ports, this keeps the air speed really high. The higher speed air piles up under the valve waiting for the valve to open, this piled up air can actually fill the cylinder over 100% on really good running engines. Really big ports have relatively slow moving air and just can't fill the cylinder fully until the rpm is high enough to over come the port size, this is the low torque at slow rpm you mentioned.

I have a 250 head I worked over using my dad's SuperFlow flow bench. I gained about 20% more air across the valve opening range on the intake side and just a bit more then that on the exhaust side. I added 1.6" exhaust valves from stock 1.5". When I had the head on the truck ( stock 250 ) it ran really good at full throttle and cruise. Try to climb a hill or pass with out going full throttle, it lost all power and shook so bad it broke the shifter mount. My conclusion to this problem was the exhaust flowed more air then the intake, and at part throttle it was pulling the fuel mixture from the intake during valve overlap leaning the engine so bad it couldn't run. The head is headed for the scrap bin this week!

Joe, that's a classic example of doing "race engine" stuff on a street machine- - - - -and your experience proves the point I've been making here, and to a couple of decades' worth of high school students- - - -"Have a good idea of what you want the engine to do before you pick up a wrench"! Make it work on paper before you invest a lot of time and money whittling on metal!
Jerry

Good stuff!

In my 1981 C20, it is a low mileage truck, I'm the third owner. With it being low mileage I wasn't concerned with replacing the heads. I installed vortec heads and a spreadbore vortec intake. That improved the power, while using the stock single exhaust and exhaust manifolds. Vortec are known for great flow at lower rpms. About a year later I removed the engine to re-seal everything. I figured while it was out, I would swap in the 300hp/327 cam I had, and that really increased the power. That truck will pull hills much easier than it did before, and using much less pedal to do it. The 4.10 gears help there, too, I'm sure. I like the single exhaust for the scavenging effect, and this truck is the first one I had with single exhaust on a v8. I've never been disappointed with how it performed, even in stock form, but I like the improved performance the vortec setup made. Better exhaust would improve it more, but for visual emissions testing criteria, I plan to leave it alone as it passes the sniffer and visual with flying colors.

My 4.0 Jeep, it runs great as-is, so it will be left alone.

The head for the 292 will get 0.030 shaved off, has 1.94/1.60 valves. Exhaust will be freer-flowing than stock, while having scavenging. Ignition will be HEI. The sweet spot for this engine is 2,200 rpms. We'll see if it happens.

I've heard when porting, not to reshape the ports, just smooth them out some, knocking off the cast-flash, and gasket match for smoother less restricted air flow between the intake manifold/head and head/exhaust manifold(s).

I’ll join the fun. I was thinking about this the other day.

Inline 6s with Siamesed ports have some significant limitations. Most of the typical stuff that backyard hot rodders do is sometimes applicable to SBCs but not very applicable to the 235 and later 230/250/292.

However, rather than trying to make one of these engines into something it’s not (power at higher RPM)....can a guy optimize/improve what they are already good at?(decent power and torque down low)

And if so, what would those mods be?

Edit: I’m not supposing these hypothetical “work to its natural strength” mods will be worth the time/ money/ effort. Just trying to understand what gains are even possible.

Very true in my experience, but if you study GM's records regarding the development of your particular engine, you might discover some of what it sounds like you want has been done already. I don't know about the 292, but it did happen for the 235. Not the breathing part, Shane. Some Chevy inline sixes aren't going to breathe much better than an asthmatic chain smoker in a Death Valley dust storm with a potato stuffed in his mouth, but you might discover some versions of your engine have answered the question of higher torque at lower rpms. They did this with the 235 in 1959...and it is interesting. Maximum torque increased to 217 at 2000 rpm where horsepower declined to 135 from 140, but max horsepower occurred at 4000 rpm. In 1956, max torque was 210 at 2400 rpm (~17% faster) and max horsepower was 140 but at a higher 4200 rpm. What changed? The camshaft changed, according to GM Heritage data. They were going for more economical power, so they changed the camshaft They changed from .400 lift on both intake and exhaust to one with .320 on intake and .328 on exhaust and also changed from 185 degrees duration to 174 degrees duration. So at 2000 rpm, you have all the torque you're going to get out of the stock 235. They left it this way until 1962.

I forgot to mention the bolt bosses being removed and lumps installed. I can see where these engines have breathing problems. It was in their design, with a "potato" stuck in the middle of their wind pipes...lol... I have read it can be improved, not much, but improved over stock. In any engine I build or do improvements to; torque is my main goal along with maximum vacuum at cruise rpms. I can't care less about horsepower.

I wonder if they had improved the head design for better flow, if these engines would have still fallen from popularity. I mean, we love them because we want to keep our trucks stock for the most part, but if we can get a tad more power, why not, right? Nowadays everybody is worried about laying rubber on the road, racing to the next stop light and stop sign and making as much noise as possible.

Change the stroke. My "258 that looks like a 216" will have either 5/16" or maybe 3/8" extra stroke. I'm not looking for more RPM, because that's a virtual impossibility. More leverage on the crankshaft translates to more low end grunt, and less off a need to downshift. However, it's about the most expensive way to get that extra torque!
Jerry

First, I have absolutely no brand loyalty so I go with what works best for the effort expended. If one must stay with a push rod inline six at least start with a 12 port head and seven main bearings, then we can talk modifications that give noticeable results.

One of my former students has a basket case Toyota Supra stored out in my pasture. I wonder how much work would be needed to graft that 24 valve twin overhead cam cylinder head onto a stovebolt block??????

Jerry

I think from the previous 292 video posting of EASY bolt-on performance items, a 20 horsepower increase is about it, as shown by the dyno tests. Never the less, the engine still has to move a heavy 1/2 ton (or larger) truck that has a wind resistance characteristic of billboard. GM designed our beloved vehicle (AD truck etc.) with great low end torque, that can carry loads at a reasonable lower speeds. I think we should respect the capability it was designed for. If we want "all around better" then simple logic tells us to buy a new GM truck.

That's a good question, Jerry. I'd think it might take some creativity and imagination, but you have both of those.

Shane...the 292 wasn't short on torque at all. I've always thought most of those could be made to run a lot more economically if you put something good behind them rather than try to put something good in them. Most of the ones I saw were connected through 1:1 final gears to a rear end like the 4.11 or 3.90 or in some cases the 4.56. Always looked way out of whack to me.

Those gear ratios probably meant that the slide rule jockeys were counting on the trucks they were powering to run heavy overloads most of the time. The owners of most of those big box trucks considered "GVW" to be a "suggestion" at best!
Jerry

I know the gains are minimal, at best. That video was a stock engine, stock exhaust, stock 1bbl intake with a slew of fuel delivery options thrown on.

Safe to say, if done right, better breathing can result in good low end, just need the right items and mods to make it work.

On my particular rig, the 4.11 gears, multiplied by 0.73, equals 3.00. 3.00 is my overdrive/final drive ratio, which is in the low 2k rpm range.

At that RPM range, the only thing your head work has accomplished is putting a big drain on your checkbook. The stock head already has enough volume capacity to produce all the torque you'll ever need at 2K, with nothing more than a little bit of smoothing with a die grinder and a few cartridge rolls.
Jerry

I have seen the lump ports everyone always talks about and do understand why they install them, but if you look at the whole port over all, the bolt boss isn't hurting the head at the rpm the engine was intended to run at. Sure the port opening is small going around the boss, but there are two of them per cylinder. By that I mean each cylinder can draw from both sides of the boss, and since the intake has only one runner per pair of cylinders, there is no torque lost or gained by the boss in the middle of the road, it actually splits the air flow directing it towards each cylinder. The real problem with the head is the floor of the port is to low and there is no room for the air to turn down into the cylinder. The air shoots straight across the valve blocking the other side. Lump ports raise the floor up and give the port a half decent short turn radius the air can follow, the down side is you open the whole port up bigger just to install them thus loosing the velocity. The good running 292 run at high rpm, 250 go even higher, just look at what the Australians have done with the 250's.

I've got a 230 stashed away that's going to get the "go fast" treatment, but it's not headed for a truck. Several years ago someone gave me a partially-finished "Excalibur" roadster project, the fiberglass-body kit car that looks like a mid-1930's Mercedes. I'm planning to install a V8 pattern bell housing that will accommodate any GM engine from a Mercruiser 4 cylinder to a 454 big block V8. The short stroke 230 I-6 will probably run 6K RPM or more with the head work, cam, and carburetion I'm planning to use. It won't have enough torque to twist the cap off a wine bottle, but it will probably sound like a bumblebee on steroids when it's wound up!
Jerry

Ironically I am where I am with the engine from comments on here. I was told the mileage isn't great, and that I wouldn't like the engine. Of course this was after buying it, and it was bought for a specific purpose, and that was for highway cruising as the main goal. My Pop told me about the 292 and the torque monster it is. So I thought, "Great! This engine will work for what I am wanting to do.", as torque is my main goal to be able to push those gears and propel the truck in any situation. I was ready to install it in 2019. Then the comments made me question my purchase, and I didn't want my mileage to drop from 12-14 to 6-8, 10 if I was lucky. So, I did a bunch of research, bought parts for the sole purpose of having a torque plateau, not having the torque drop-off. The dyno charts show the torque dropping off beginning around 3,000. We all know an engine needs to be revved at certain times to get moving, pull a hill in a lower gear, etc. Having never driven a vehicle with a 292, the only vehicle to get a feel for on L6 is my Jeep, and I like the way the Jeep performs. I figured I could, with a spot of luck, get the 292 to perform similar to the 4.0. Having already done a ton of number crunching for the Jeep to get the gear ratio correct for the tire size I went with, all to get the rpms back to what the factory had them at with 3.55 gears and tiny tires. I used the same approach to get the end goal of my truck to be somewhat close to what the Jeep does on the road. The Jeep does weigh more than the truck does, so they should be close performance-wise. I'll have 8 forward gears, really only 6 because granny low is not used for taking off unless loaded down or towing something heavy, so I should be able to get the sweet spot at any speed, loaded or unloaded, and still have some extra mid-top if I need it. That was my approach, and after the online conversations, I realize it may be a giant flop. But then again, it may end up being exactly what I was striving for. It was definitely not intended to be a hotrod speed demon truck, although, if I am on the highway, I need to be able to keep up with traffic to some extent.

I never thought of a 250, but after all my research, a 250 is a valid option and can be modified using sbc parts. I can't find a 250, but if one surfaces I may buy it, build it with a similar mindset, and see how it does. We'll see. It's only money, right...lol... For some reason my money trees that I get from the nursery keep dying no matter how I care for them, sad.

I'm sure you've already seen this, but if not, please take a look at the torque and horsepower curve for a 1968 292...the year picked at random (page 85):

https://www.gmheritagecenter.com/do...hevrolet-Trucks/1968-Chevrolet-Truck.pdf

My goodness, gross torque (around 270) tops out at what...16~1700 rpm and runs pretty much on a plateau from around 1300 until 2400 rpm? Not bad in stock condition.

Jon, you're spinning your wheels- - - - -'My mind is made up- - - - -don't confuse me with facts!" Hotrodders are kind of like Marines- - - - -they have a tendency to believe their own propaganda, and any effort to suggest that they're not 10 feet tall and bulletproof isn't even considered! There's a very profitable industry based on the idea that factory designers are a bunch of dummies, and installing the latest version of digitally designed doohickey (which I just happen to have on sale this month, BTW) will triple your power and double your gas mileage! P.T. Barnum is alive and well, and he's selling hotrod parts these days!
Jerry

I haven't seen that. Impressive. Mine being a 1966 may be close to that. Now to go look it up.

If I hadn't been told about the 6-8 mpgs, 10 if I was lucky, I wouldn't be where I am. It may be driving habits that got them the 6-8, or maybe the 292 is just a gas hog, that I do not know from actual experience. I have they are not the most economical, of course this was after I set off into uncharted waters. Uncharted for myself, that is. I just have a hard time accepting it is that bad. And if it is that bad, then all of this was for not, and a v8 will have to go back in eventually. I was wanting an engine that came as a factory option, was told about the 292, bought the 292, and now have been walking around in the Alice in Wonderland's rabbit hole.

It's all good, I have options. Stock 292, altered 292, 350, just wanting to go away from the v8, been driving trucks with them my entire driving career...lol...

Far from being a hotrodder. My wife on the other hand, lead foot...lol...

This is the dyno chart I used...

It appears the torque is improved. Maybe not.

12 Bolt Dyno Chart with and without lumps

I worked on 292 engines in step vans for many years. There is no reason you can't get 12-15 mpg in a pickup that is tuned right & geared right. They are a rugged engine. We used to drive them with the throttle to the floor mile after mile & never blew one. They can be noisy though. The heavy duty versions have forged pistons that rattle when they get worn some.
I still would prefer the 350 v-8 though.
George

I've posted this here about a hundred times. You can buy a brand spanking new 250 six with HEI ignition and manifolds, water pump, spark plugs right here for $2300 (non hardened seats) or $2500 (hardened seats). These are stationary engines, so you may have to first install it as an irrigation pump engine to make certain people happy. Go to the bottom of the page...

https://www.donhardyengines.com/specials.htm

Where is the Clifford intake and sweet headers?

I had never heard of a stationary engine. Interesting way to get a new engine. The sbc and bbc get the headers, why no love for the 250...lol...

The Clifford intake and headers are in one trunk and the finely engineered Fenton stuff is in the other trunk. A man grinning from ear to ear down by the river in a trailer park in Newark, NJ has them and he's waiting for you. Just wink and tell him you know me and Jerry and he'll give you a discount. I'm sure he will. He's selling them out of the back of his van. His name is Phineas Barnum.

Tempting, but not sure I need that stuff any more. Just got me some triple prong iridium spark plugs that will add 15-20 horsepowers.

And they'll make your hair thicker, increase your testosterone, give you a natural musk scent and add 20% muscle mass to your upper torso...

Don't forget the high octane unicorn farts for the ultimate boost

For the record, my last response was meant to be funny as everyone else had turned towards the comical side of things. We definitely have a mixed bag of personalities in this forum, and that is what makes it entertaining, and sometimes frustrating, but always educational.

As a Frenchman once said: La plus perdue de toutes les journees est celle ou l’on n’a pas ri. Translated by many as "a day without laughter is a day wasted" and more literally translated as "the most wasted of days is when we haven't laughed."

Did you know France owned Texas (part of it anyway) for roughly 5 years?

I inherited the funny bone from my grandma, she always had a great attitude. Grandpa was the hard ***. But he earned it fighting in WWII in the 106th Inf. Div., 423rd Reg. Company B.

I did not know that about Texas. Interesting.

Read up on the Louisiana Purchase. France "owned" a large chunk of the current US, including most of the Missouri River basin, stretching up into Montana.

Um, well...actually the Louisiana Purchase only included parts of Northern and Northwestern Texas, didn't it? The US tried to claim...well you can read some of it here (including Spain's agreement regarding Florida and what the treaty of 1819 said the US had to do regarding Texas:

https://en.wikipedia.org/wiki/French_colonization_of_Texas