Inliners International Forums General Discussion Engines 292 Dynamometer Question

My first post.

Wanted to first say what an amazing resource this place is. I’ve been a lurker for a long time now, and I only recently registered to the forum.

I’m collecting parts and trying to put the final plans in place for a complete rebuild of a 292 that will power a 2-Ton truck. I’ve read a lot of threads here at Inliners on how to extract more torque and horsepower from these engines. All super helpful.

The most basic modifications I am reading here for making a 292 make more power and torque, is installing larger valves in the head, bolt-in lumps for the siamese intake ports, bump the compression a little, and a camshaft that’s happy at lower RPM. Top-off all these free-flowing improvements with a new intake/carb and headers. Sounds great to me.

It’s my understanding that when you can get an engine to breath easier, it will make more power. It’s also my understanding that the higher levels of power and torque from these modifications now peak at a higher RPM. Please correct me if I’m wrong.

I’ve seen a few dyno results for these types of modified 292’s on this forum. The problem is, these dyno results typically start at 2,500 RPM and higher. What I want to know is what’s happening between 800 RPM and up. I’m interested to learn what I’m potentially loosing at those lower RPM from these types of modifications.

I’ve read that the modern water-brake engine dynamometers commonly used today are not able to effectively control the engine and give accurate results below about 2,500 RPM. In fact, it’s not uncommon to see a published dyno sheet that starts at 3,500 RPM, or even 4,000 RPM. For the hard core race engines, this is not a problem. For a street engine? Or how about a truck engine?

Because this engine I’m going to build will see most of it’s usable life between 1,600 RPM and 2,600 RPM (with a max peak of 4,000 RPM), is it unreasonable to want to know what is happening starting at 800 RPM? Maybe I’m asking for too much.

Your thoughts would be greatly appreciated.

David

I think you are exactly right. My 292 "truck" build is still in pieces so my ideas are still theory. I think that even the big valve/lump port are mods that don't help at low rpm. It seems that stock or near stock valves and ports will supply enough fuel mixture and maintain velocity on the bottom end. I am even thinking of using a 194 head with minimal port work and just narrowing the bolt bosses. I have pistons advertised at 8.5-1 and with the small head I'll be around 9 to 9.5-1. I have a low end Crower cam that will deliver the torque from idle to 2500 and top out around 4000. I'll run headers into a single pipe and eventually GM TBI & stock GM HEI ignition. My truck was only a C20 heavy camper special and now has a flatbed. It has a worn out 350/T400 now but hopefully will get the 292/700R4 in the near future.

Like you I would like to see a dyno test for a "truck" built 292. A friend here had an excavation business and his dump truck towed his backhoe all over this mountainous area and even over the Sierras. It had a 292 that he had built. I wish I knew the details. Another friend with a similar business had to borrow this truck and was so impressed he had Eddie put a 292 in one of his older trucks. I borrowed that one and here we are today.

A link to a thread of my planned build: Truck 292

It's so difficult to get HP and torque numbers at that low of an RPM range either with an engine dyno or chassis dyno because you with basically just stall the engine, that readings at 2000 RPM and above are the norm. So it basically becomes just your best guess what the engine is doing down at those lower RPM's.

Thanks for the replies!

Beater,

That link you provided is one I've read several times. I have no doubts that the modifications others talk about will bring great gains in both horsepower and torque. Like you, my concern is where in the RPM range do these increases, and decreases actually happen.

CNC-Dude,

What you say supports what I understand about the dynos that most use. I'll do some more research to see how the Diesel engine builders test their engines.



Well,

I read somewhere years ago (in an actual book!) that GM uses something called "Steady State" dynamometers for engine development. The idea is they can hold an engine at a steady RPM, then try different spark advances, throttle openings, fuel ratio's, etc to see what combination gives the best output. I'm guessing by testing at incremental RPM levels, this helps them develop correct distributor advance curves and camshaft profiles and who knows what else. The GM engineers where not dummies, that's for sure!

Thank you Gentlemen.

David

Keep us informed of what you find out and what course you take. To me this is the most interesting use of these engines.

I absolutely will. When I finalize the recipe for this build, I would be happy to create a build thread if that helps.

I'm likely to have a few more questions for this community before I begin.

David

The engine's port and valve sizes, cam events, manifold design etc. were all developed to produce efficient power in the RPM range you want.
The engine's VE at those speeds is already over 90% (and drops off sharply after 3,000), so the most effective method of increasing torque are:
1, displacement
2. static CR
Both expensive.
Most conventional methods (porting, cam event duration, big valves, rocker arm ratios) just move the torque curve ahead to higher RPM.

How about a turbo? That was my original plan when I went thought my Megasquirt phase a few years ago. That would probably work beat with stock compression but need forged pistons?

Panic,

A increase in static compression ratio would be my first choice.

I imagine it would take a special flat top piston with a compression height that allows a zero deck after a minimal block deck cut. Then some careful material removed with a ball mill on the top of the piston "just" under the opening formed above by the combustion chamber to bring static compression down to something closer to 9.00/9.25 to 1. This would preserve as much quench area as possible. I'm reading that the turbulence created from quench helps reduce pre-ignition when compression is raised.

Beater,

Your idea would most likely obtain the best results and even higher gains in torque and power compared to a strictly NA approach. I've read where a smaller turbo can be used to just bump the lower RPM performance. I'm guessing if either forged or cast pistons are used, it would still take a good EFI system to manage it all safely. Especially if I'm 20,000+ pounds combined climbing a mountain pass.

I think you are going to have several large challenges ahead of you if you are considering a 292. One is you are going to be excessively overweight for what your expectations are for a relatively underpowered gas engine, compared to a comparable diesel engine like a Cummins. And second, with that extreme weight, you also have the much higher elevation which will effectively lower the power and torque the higher you go. At the very minimum a turbo may be your only saving grace to offset and compensate for those challenges you face.

CNC,

I completely agree with everything you said.

The heavy loads this truck will see will be on very rare occasions. Most of this trucks useful life will be with lighter loads. The truck will be treated more like a super heavy duty one ton.

I used the heavy load example to drive home the idea of how important a really good engine management system would be needed if I did go the 292 turbo path.

I've got a 489 (0.030" overbore, with a 4.25" stroker crankshaft) Big Block Chevy here that would be a better choice if I was needing to haul super heavy loads on a regular basis.

And just to share more information, my project is based on a 1953, 2-Ton GMC, with a 161” wheel base. I will be adapting more modern medium-duty truck disc breaks on all four corners, with an updated rear axle for a more highway friendly gear ratio, and longer leaf springs with shocks on all four corners. All of these updates will be from parts I've taken from a more modern 16,000 GVW medium-duty truck.

The truck will look stock on the outside and inside the cab. If you crawl under the truck or look under the hood, then not so original looking.

My first plan was to use the Big Block Chevy. Because the truck will not see heavy loads for most of it's life, I have rethought this project, and I'm going to try and make this 292 work.

If using the 292 ends up being too much trouble, I have the Big Block to adapt instead.

I hope I don't get banned for mentioning a V8...

David

My pistons are off the shelf 8.5 to 1 and with the 194 head should be 9-9.5 to one. I think they are Silvolite I can get you the number if you want. I have a turbo from a Fire Bird that I had planned to use. There have been great developments in EFI systems since I began thinking and gathering parts. Now I think one of the new systems would simplify the turbo/EFI interface. The turbo plumbing is simple with plenty of room.

I used to have a 1940 International D40 rated at 2-3 tons (stamped on the ID plate) It had a Blue Diamond six 260 ci, 89hp @ 3200, 192 foot pounds @ 800- 1600. It weighed around 7,000 lbs. It had a fifth over transmission. It would fairly comfortably travel at 55 mph 3 tons of hay. I once hauled a load of railroad ties stacked to the top of the headache board and two max loads of salvaged barn board over the Sierras. Steep hill slowed it but I never had to go below 3rd gear and 30-35 mph. It was a very good truck and ia still on the road today. Just mention this as some Idea of what these old trucks will do. Of course it is no match to what my son's Ram Cummins gan do.
The biggest issue was brakes. I don't think the vacuum booster worked but better brakes would have helped a lot.
It was a cattle truck and had a full set of stock racks with a loading ramp and had a pintle hitch & vacuum brake lines for a trailer. It came from the central valley in California and probably hauled cattle as truck & trailer. I researched the previous owner and that was his business.
Your truck should do better.

Beater pointed out another challenge and you are likely to encounter others. But stopping is going to be a serious consideration if your loaded to the upper end of the target weight. Also, in many states, 16,000 lbs is the maximum GCVW(gross combined vehicle weight) that a dually(one ton)truck can legally operate with in public roads. So a half ton style truck trying to tow that much can get you a hefty ticket from the DOT...

Beater,

That old D40 sounds like it was a cool truck. I picked the 53 GMC because I loved the look of it. My efforts to update the drive train and brakes was just because finding the parts for these older heavy duty trucks is a real problem. Especially brake parts. There are a fair number of companies supplying brake parts for the 1/2-Ton to 1-Ton trucks, but anything bigger than that is left to dumb luck finding anything. I will start to look closer at the turbo idea.

CNC,

No problems on my end. My truck is rated to 16,000 lbs GVW, 26,000 lbs combined. Any modifications made, including brakes are from a similar class 5 vehicle. The tires this truck uses are 9R-22.5. This thing is bigger than a 1-Ton that's for sure.

I have a 51-52 GMC 3/4 ton in it yard and it is in play as part of "the truck" dream with the '68 and a '90 4x4 2500 Suburban. That plan would only involve the bed & dually axle from the '68 and still leave me with 2 piles of just in the yard.

The Art Deco styling on the D40 is an eye catcher.
D40