Owner of a broken cart
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.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.
Im kinda embarassed, you said it better than i should have. Ya. lolI'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.
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.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.
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.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.
Basically, i guess im asking, how can I improve the bottom end torque (idle to 3000rpm) of my stock 305, AND improve mpg.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 ?
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...I managed to find my stock cam specs.
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.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
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.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!