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Owner of a broken cart
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Discussion Starter · #21 ·
I'll bet the folks at Comp can come up with a recommendation given the parameters of his 305 buildup. :)
I wished i could get David Freidburgers advice. lol After he stops laughing ofcourse. Since this is at the complete opposite end of the spectrum he frequents.
 

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Your earlier post said you are operating at "one notch above idle". I'm not sure what rpm that equates to. The thing that you should understand is that most modifications you will make will have little to no effect at extremely low rpm levels. The way to create more torque at lower rpms is to increase displacement. The money that it would take to upgrade what you have would be better spent buying a larger engine and reselling your 305. A 350 Chevy would provide more torque than a modified 305 operating at 1500(?) rpms. You just can't effectively gain torque at low rpms because most modifications provide no real benefit at that rpm level. You might take a look at obtaining a 472/500 Cadillac engine and adapting it. Torque out the a** at low rpms and they don't weigh but maybe 50 lbs more than a Chevy with iron heads. You can usually find them with low miles and about a $500 price. A simple tune up and probably a carb rebuild and I guarantee they will have way more torque than the Chevy........especially at low rpms.
 

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Owner of a broken cart
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Discussion Starter · #24 ·
Your earlier post said you are operating at "one notch above idle". I'm not sure what rpm that equates to. The thing that you should understand is that most modifications you will make will have little to no effect at extremely low rpm levels. The way to create more torque at lower rpms is to increase displacement. The money that it would take to upgrade what you have would be better spent buying a larger engine and reselling your 305. A 350 Chevy would provide more torque than a modified 305 operating at 1500(?) rpms. You just can't effectively gain torque at low rpms because most modifications provide no real benefit at that rpm level. You might take a look at obtaining a 472/500 Cadillac engine and adapting it. Torque out the a** at low rpms and they don't weigh but maybe 50 lbs more than a Chevy with iron heads. You can usually find them with low miles and about a $500 price. A simple tune up and probably a carb rebuild and I guarantee they will have way more torque than the Chevy........especially at low rpms.
Good point. I have access to a 355sbc with 12:1 pistons, rv/rock crawling cam. I just didnt want to run 91gas all the time.
And everyone i know with a 400sbc has it turned into a 421. :(
 

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Just for comparison, here are a couple of random dyno charts. They basically give you a reasonable comparison of displacement vs 2000 rpms as most dyno charts never show the results below 2000. First is a 305, then a 383 Chevy, and finally a Cadillac. The 305 basically has 330 ft/lbs with about 125 hp. The 383 has about 385 ft lbs. at about 150 hp. The 500 Cad has 450 ft/lbs at 170 hp. They are all turning 2000 rpms. Do you see the trend here? The Cad has the lowest compression of all with a 9:1 (some are lower) and burns regular gas. Anyway, I don't want to push my opinion any further, so I will add the dyno info for your viewing and then maybe stir a little thought about what you can do cheaply.
616798
616799
616800
 

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Hates: Liver. Loves: Diesel
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I'll try to offer my input as a tractor person myself.

The stock engine in that tractor was likely all done by 3300 RPM. This is not just because it was a wheezer, it has to be. The gearing, PTO, and all the associated equipment is matched to the engine's RPM range. There are industry standard PTO speeds and sometimes gearing to increase or decrease PTO based on the engine's output, but suffice it to say... He needs to make his torque within the RPM range that the rest of the tractor was designed for.

If he keeps a 5500 redline and his torque peaks at 4000, he's just wasting potential. He is also lugging the engine below peak VE and below a BMEP that is comfortable. Heat, detonation, and carbon issues can result.

This is no different than the thousands of questions here when people ask this is my cam, heads, compression, what gears do I need? Except this is the opposite. He's trying to get the engine to make more torque in the RPM band he can USE. 327amc... correct me if I'm wrong, I'm just trying to slow down the "why would you do that" posts.
 

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Curtis73, I agree with what you said about the engine must produce enough torq at the correct rpm range. In this case he has a larger engine than stock, so he should have at least as much torq as before. He is also concerned about cost to modify the engine and the ability to use regular fuel.

The easy answer to the last question is.......low compression ratio. Its not cost effective to use a high ratio that requires high cost premium, and its not cost effective to use an aftermarket injection system to run a higher ratio and still be able to burn regular.

Second thing is that most modifications to virtually any engine do not produce increased torque at rpms below 2000 with the exception of engine displacement. Increase displacement and you will increase low end torque. Again, I am unsure exactly what rpm the OP is currently running but he wants it to be less. If he is running the 3300 you mention, then modifications can help increase the torq available. But again, he wants less rpm.

The costs to modify an existing engine would exceed the cost of selling the existing engine and replacing it with a larger engine.....probably by a significant amount. Then we get back to compression ratio. The larger engine needs to have not only more displacement, but a low comp ratio as well. He mentioned a larger Chevy with a high comp ratio being available. I don't think that would be a cost effective choice and he may have problems with spark knock even if using premium gasoline.

I may be wrong, but the simple answer seems to be large displacement and low compression........as well as not having to purchase a lot of expensive parts to get it up and running. I know I said I wouldn't beat the Cadillac drum anymore, but I'll say one more thing. You can find these engines, often ready to run with minor repair. They usually have way less than a 100,000 miles on them. I'd say 60,000 on average. Upgrade the distributor with a Pertronix, and put new valve seals on it without removing the heads. Knock the freeze plugs out and flush the coolant system and replace the plugs. New spark plugs and plug wires and probably a new water pump. Carb will most likely need to be rebuilt. Decent engines usually about $500 and the wide torq band will allow you to run the tractor at virtually any rpm of choice from idle to 3300 rpm. The one part that will be expensive is a standard flywheel. Probably about $1,000 total investment.

The bottom line is that even if he switches to a larger Chevy smallblock, he will have to find something with low compression or pay for it every time he buys gas. Thats my objective opinion, so I hope I didn't offend anyone.
 

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Hates: Liver. Loves: Diesel
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I don't disagree with anything you mention, and you can ALWAYS beat the caddy drum around me. By far my favorite. The one thing I will re-mention though is lugging. If you are calling for torque when you are too far below the peak torque RPM (below VE peak) you are lugging which causes vibes, excessive cylinder pressures, excessive heat, etc. On the street its rare. If you have a manual, you downshift. An automatic takes care of it for you. In tractors and boats, it's a genuine problem - hence why tractor engines are designed with such low torque peaks and beefy internals. Go back far enough to the 2-cylinder Puttin Johnnies, some of those were 450+ cubes with two cylinders and made 22 hp. They idled at 180rpm and redline was about 900 rpm.

I think if he wants to keep the 305, he should get the compression to about 7.5:1 and find a cam in the 175-180 duration range with an LSA that produces next to zero overlap. That should get a torque peak around 2250, right in the sweet spot for dragging a plow and PTO.
 

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Owner of a broken cart
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Discussion Starter · #29 ·
I'll try to offer my input as a tractor person myself.

The stock engine in that tractor was likely all done by 3300 RPM. This is not just because it was a wheezer, it has to be. The gearing, PTO, and all the associated equipment is matched to the engine's RPM range. There are industry standard PTO speeds and sometimes gearing to increase or decrease PTO based on the engine's output, but suffice it to say... He needs to make his torque within the RPM range that the rest of the tractor was designed for.

If he keeps a 5500 redline and his torque peaks at 4000, he's just wasting potential. He is also lugging the engine below peak VE and below a BMEP that is comfortable. Heat, detonation, and carbon issues can result.

This is no different than the thousands of questions here when people ask this is my cam, heads, compression, what gears do I need? Except this is the opposite. He's trying to get the engine to make more torque in the RPM band he can USE. 327amc... correct me if I'm wrong, I'm just trying to slow down the "why would you do that" posts.
Im kinda embarassed, you said it better than i should have. Ya. lol
 

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Owner of a broken cart
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Discussion Starter · #30 ·
Curtis73, I agree with what you said about the engine must produce enough torq at the correct rpm range. In this case he has a larger engine than stock, so he should have at least as much torq as before. He is also concerned about cost to modify the engine and the ability to use regular fuel.

The easy answer to the last question is.......low compression ratio. Its not cost effective to use a high ratio that requires high cost premium, and its not cost effective to use an aftermarket injection system to run a higher ratio and still be able to burn regular.

Second thing is that most modifications to virtually any engine do not produce increased torque at rpms below 2000 with the exception of engine displacement. Increase displacement and you will increase low end torque. Again, I am unsure exactly what rpm the OP is currently running but he wants it to be less. If he is running the 3300 you mention, then modifications can help increase the torq available. But again, he wants less rpm.

The costs to modify an existing engine would exceed the cost of selling the existing engine and replacing it with a larger engine.....probably by a significant amount. Then we get back to compression ratio. The larger engine needs to have not only more displacement, but a low comp ratio as well. He mentioned a larger Chevy with a high comp ratio being available. I don't think that would be a cost effective choice and he may have problems with spark knock even if using premium gasoline.
All great info. However, the caddy engine is a not go, as the engineering and fab work it took to get a chevy to bolt up was pretty much a pita. All be it a fun one.

The cost to modify the existing engine would exceed the cost of selling the existing engine and buying a larger one (of the same family) ONLY IF someone actually wanted to buy my 1986 305. Which they do not. lol

Honestly, any local SBC ready to run around here is rare, and costly. This is dirt track country. :(
 

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All great info. However, the caddy engine is a not go, as the engineering and fab work it took to get a chevy to bolt up was pretty much a pita. All be it a fun one.

The cost to modify the existing engine would exceed the cost of selling the existing engine and buying a larger one (of the same family) ONLY IF someone actually wanted to buy my 1986 305. Which they do not. lol

Honestly, any local SBC ready to run around here is rare, and costly. This is dirt track country. :(
The Caddy was just an example I used because I am familiar with them and know they are legendary for their torq production. As far as adapting any Buick/Olds/Pontiac/Cadillac, the bellhousing is similar to a Chevy where it bolts to the transmission. Don't know how you adapted the Chevy to the tractor. but if you used a Chevy bellhousing, the front end of the bellhousing can be adapted to fit any of the engines mentioned above. You do have to check and see which side the starter mounts though. Now, I understand that you went thru a lot of effort to adapt the Chevy and are reluctant to convert to anything else. No one likes to do a job twice.

The thing is, there really isn't much that you can do to increase the torq on your 305 and at the same time reduce the operating rpm. At least, I don't know of any way.....but I have been wrong before.

What is your idea of how to go about doing this if you want to stay with your 305 ?
 

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Here is something that may help you. I was actually looking for something else I saved a long time ago, when I stumbled across this. Its coincidental that it happens to mention a Caddy engine, not meant as trying to continue beating the Caddy drum. Its about displacement and about cylinder filling and cam timing. It may still represent an rpm level above what you want, but its some food for thought.
616836
616837
 

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Owner of a broken cart
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Discussion Starter · #34 ·
The Caddy was just an example I used because I am familiar with them and know they are legendary for their torq production. As far as adapting any Buick/Olds/Pontiac/Cadillac, the bellhousing is similar to a Chevy where it bolts to the transmission. Don't know how you adapted the Chevy to the tractor. but if you used a Chevy bellhousing, the front end of the bellhousing can be adapted to fit any of the engines mentioned above. You do have to check and see which side the starter mounts though. Now, I understand that you went thru a lot of effort to adapt the Chevy and are reluctant to convert to anything else. No one likes to do a job twice.

The thing is, there really isn't much that you can do to increase the torq on your 305 and at the same time reduce the operating rpm. At least, I don't know of any way.....but I have been wrong before.

What is your idea of how to go about doing this if you want to stay with your 305 ?
Basically, i guess im asking, how can I improve the bottom end torque (idle to 3000rpm) of my stock 305, AND improve mpg.
1. It may be contradictory and therefore impossible,
2. It may be already there (by the factory)
3. It may be completely possible.

In the end, what i have works great. But why go this far IF you can make it work more greater.

Oh, and thanks for the article, Jeff Smith was one of my child hood heros! So knowledgeable!!
 

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Discussion Starter · #35 ·
I forget who asked, but the reason i was interested in a solid flat tappet cam, was because from what im told, they are able to be machined with a slightly more aggressive profile, coupled with a short duration cam (for the torque) seems like would be a way to make a short duration cam breath better, and squeeze out a tad more efficiency.
But alas, i cannot find any short duration solid flat tappet cams.
But my thinking there could be way off.
 

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I managed to find my stock cam specs.
OK, your current cam looks about like what I suggested above: a 1950's truck cam... at least on the intake side... at your RPMs level, the exhaust doesn't need to be so much bigger, should be same as the intake... and LSA is way too narrow, should be 115 - 125 degrees somewheres... once the cam is optimized, carb. and ignition tuning gets your MPG... engine hours per gallon...
As I also mentioned above, the 305's torque and HP is monstrous compared to the original engine, surprised you'd want more... unless I'm missing one of your intended uses... and your top speed is likely well over 100 MPH... but I have offered further tweaks...and the hydraulic cam can also be reground down more, but may go through surface hardness and reduce cam life... and regrinding can't easily fix the LSA... extensive/expensive welding would be needed...
Any SBC 400 made after 1970-71 would have a compression ratio down in mid 7's:1, torque peak at 2000 RPMs, and HP peak at 3600 RPMs... 194/202 durations cam(cars, maybe smaller if a truck engine).. an added even much smaller 1950's truck cam would make it even more suitable...
 

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I wish you luck with what you are attempting to do as I always admire it when people try to learn and experiment. I've given you my best advice but I understand that you have a path you want to follow in your experimenting. I used to fool around with the idea of building a homebuilt airplane powered with an auto engine. General Aviation engines (Lycoming/Continental) generally operate in a range from 1800 to about 2700 rpms. This is because of propellor tip speed limitations. There are air cooled engines like the Volkswagen and Corvair that can work with direct drive in that rpm range. When you move to larger and water cooled conversions, many people are enamored with the ability of V8 engines to produce lots of HP at elevated rpms. It was kind of a confluted situation. With an airplane, weight (especially on the airplanes nose) is a major problem. The "trend" was to use an expensive reduction drive (more weight and complication). One fellow was building a VERY EXPENSIVE warplane replica. Anyway, the idea was that by turning 4,000 rpms he could harness 400/450 hp to turn his propellor at 1800 rpms. Propellors are more efficient at slower speeds. Most airplanes that are built at home cannot begin to utilize 400 hp. Generally 150-200 hp is sufficient. BUT, the current "trend" was to use some type of reduction drive even though it added a lot of weight. Again, weight is a MAJOR factor in an airplane. One fellow who was very experienced and knowledgeable and talented built an aluminum Ford with a reduction drive. He was able to pull it off and had a good flying airplane. One day he decided to try a full throttle take off. He locked the brakes and reved it up to full pull. When he released the brakes the airplane sprung forward and literally jumped off the ground. He hadn't considered the old law of physics that for every action there is an equal and opposite reaction. The airplane being so light was unable to resist the torque being applied and it immediately began to rotate toward upside down. Luckily the fellow was able to regain control before fully inverting. He never tried that again, and he cut the propellor size down so he wouldn't ever get surprised if he had to apply full throttle during landing. My suggestion to many builders during that time was that they did not need a reduction drive but should simply use a lighter direct drive and then increase displacement if they wanted more power. No weight penalty if you took an aluminum LS Chevy engine and went from 346 cu in to 383 or even use an LS3 block and stroke it to 415 cu in. They would easily make 200 (250)HP which is more than most homebuilts could use. But everyone wanted to follow the "trend". Now the reason I got off on this airplane tangent was to suggest that you might do some research into some of the Lycoming and Continental engines and see if you can find what cam specs they used to "optimize" (?) their engines. These are low compression air cooled engines using magnetos. Here is a video of one of my pioneering heros.......Steve Whitman. Well known for innovation and racing. The airplane is his own design and it uses an aluminum Oldsmobile 215. So keep experimenting and learn all you can. Oh, the airplane/Olds is direct drive............

and another homebuilder following the same route
 

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Now the reason I got off on this airplane tangent was to suggest that you might do some research into some of the Lycoming and Continental engines and see if you can find what cam specs they used to "optimize" (?) their engines.

and another homebuilder following the same route
Probably all he has to do is get past the first person to answer the phone at a cam company and ask to talk to a cam engineer that already knows how to do lowest RPMs torque! That cam engineer may not even work for the cam company full time. Just drops some designs in and goes on other projects.

WHY did that guy mount the Olds aluminum V8 upside down in that plane and thus create all the problems that entails?
Looks like the German way of doing things...

Best auto engine to use in a plane is the newer aluminum LS7 427" which already has a wide LSA cam that is strong at low RPMs.

Be damned if I'd fly in a plane that has an engine with a TIMING BELT !!!

Those auto engine conversions have insanely high prices! Probably mostly for insurance costs reasons!
 

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Probably all he has to do is get past the first person to answer the phone at a cam company and ask to talk to a cam engineer that already knows how to do lowest RPMs torque! That cam engineer may not even work for the cam company full time. Just drops some designs in and goes on other projects.

WHY did that guy mount the Olds aluminum V8 upside down in that plane and thus create all the problems that entails?
Looks like the German way of doing things...

Best auto engine to use in a plane is the newer aluminum LS7 427" which already has a wide LSA cam that is strong at low RPMs.

Be damned if I'd fly in a plane that has an engine with a TIMING BELT !!!

Those auto engine conversions have insanely high prices! Probably mostly for insurance costs reasons!
Actually there are several benefits to inverting the engine. First is that the airplane has an imaginary balance point thru the wings. As you raise or lower where the trust from the propellor occurs it causes the airplane to either tend to climb (or possibly dive) when additional power is added (or removed). A sea plane with the engine mounted behind the cockpit has a large tendency to dive as power is applied. In a conventional aero engine with opposed cylinders the engine is basically flat and can be mounted higher. The V shaped auto engine would block the pilots view if raised. Inverting when using direct drive raise the propellor but keeps the mass of the engine lower which helps when landing. Other benefits are that the coolant gravitates toward the heads keeping air pockets away. LS Chevy engines incorporate steam tubes to evacuate air in the heads. Invert the LS and no steam tubes needed. Oil can pool around the valve spings and valve stems to draw more heat away as well as several other beneficial effects.The LS7 basic engine is a great candidate to build, but I would not use a factory built one because of the titanium rods and about $14k price. I'd use the block and then populate it with a better crank and rods. Depending on the rpm range, that would decide which heads I would use.
 
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