diesel engine rpms

ziemerj

Member
I was talking to a guy that has been pulling for a long time and he was telling me about how he's working on a new engine that he's hoping to get running up to 5000 rpm. I know a lot of pulling tractors are running around 4 thousand rpms. Is it really possible to pull at 5000 rpms and keep everything together? How are they getting that rpm out of engines that are only rated at 2250 to 2700 rpm?
 
Problem is to have enough compression to start . The engine looses too much compression when valve reliefs are cut in the piston top.
That is why you will see highly boosted Diesel pulling engines needing a snort of ether to start even in the summer time.
Without valve reliefs the cam can not be ground with enough lift, duration and overlap to allow high rpm breathing .without loosing too much compression due to both the long exhaust/intake overlap. with the late closing intake blowing air back into the intake manifold during the start of the compression stroke. And the size of the valve reliefs reducing compression.
Cam timing is why diesels are low rpm torquers. It's not because they are "diesel". Look at the days when a tractor had gasoline or a Diesel engine. The natural aspirated gasser made the same power as the natural aspirated diesel. Both the gasser and diesel had a short duration cam and similar displacement.
 
Rated same hp but the diesel produced far more torque. Mainly due to two factors. Higher cylinder pressure (compression) & longer burning fuel that is introduced over a longer duration, so it pushes on the crankshaft both harder & for a longer time on each combustion cycle. This is straight out of your john Deere R service bulletins (manuals)
Gas engines do not have as big a torque rise as diesels, on a dyno chart. Even with identical specs- except compression obviously. If you made a gasser at 15:1 & a diesel at 15:1 (started with either) it would be close, but I'm no expert on the combustion differences between diesel & methanol - not sure if you could find 'gas' to run on 15:1 ? I will find the John Deere tech bulletin I'm referring to & post it here since I know you'll want to see it :)
 
Diesel engines of the antique era made the same HP (with a greater torque rise) as a gas engine with 6:1 compression. Once gassers got up to 7:1, diesels needed more cubic inches to match power, until turbos came along.

As a percentage the diesel might have a better torque rise, but an equal cubed 15:1 meth burner would far, far, far out power a n/a diesel.
 
Hi
I will tell you 2 simple things i know from what Ive seen. Back in the U.k we used to put ford 2700 series 6cyl diesel motors in fordson majors for pulling.
A new group started up. a guy from the hills turned up and made out he knew everything. this guy told us, that new better you couldn't rev a stock ford 2700 turbo more than 3000 rpm with out mods other than steel clutch and flywheel with protection.
his was a 3000 limit tractor that had never been teched but tried on his yard at home. Well the 5000 rpm stock theory he had went right out the window. His was over. Never heard another word from him about it. Yes I am aware it was a bomb waiting for an explosion with the cast flywheel. when the tech said it passed 3500 rpm we all backed away quickly.

my buddy's fordson ran unlimited rev classes ie no governor/ rev limit other than the guy on the throttle, or the rodsn pistons comming out the block.
He had that at over 5000 rpm with steel clutch and flywheel. I know that was a stock 2700 series truck motor tuned, with big turbo and pump. I can vouch for the rest being stock it was my spare motor and I helped him put it in.
I guess reliability depends on how well the original motor was built and balanced at the start for a stock motor doing it. Basically how you can do it is, low compression, then bring it up with boost, component balance and re engineer the week parts as you find them.
Then hope you get it right before you go broke trying.
or if you get to being jacked as much as it will go on diesel and you can't keep it going. Convert to alky fuel Like Peter Clarke did with Red Alert back in the late 90's in the U.K. and cross the hp barrier again
Regards Robert
 
What if both had the same cam, stroke, bore & governed to the same rpm, say 3500, same compression? I don't know much about methanol except it's high enough octane to run 15:1. I'm not sure there is any gasoline that will go that high, there may be.
 
Neither one will work very well. Lets assume 8to1 on the gasser and 16to1 on the diesel.
Most people get all thrilled about the high combustion chamber pressure of the diesel and " torque".
The fact is it's the difference between the combustion chamber pressure before combustion. And the pressure in the combustion chamber after combustion.
If a diesel had 600psi compression and 1000lbs combustion pressure, the actual working pressure is 400psi.
A gasser with 250psi compression and 750psi combustion pressure would have a working pressure of 500psi.
The gasser with 500psi vs the diesel at 400psi would make more torque and power if both were were running at 1800rpm.
If the cam was optimum for the gasser at 3500rpm . The pistons would be slamming into the valves on the diesel. If the valves somehow didn't get the pistons. The diesel version would be a dog to start.
If both engines had a cam ground for 1800rpm . The diesel would be a good starting engine.
Odds are the 1800 rpm gasser cammed for 1800rpms would make similar to slightly more power than the diesel with the 1800rpm cam and operated at 1800 rpm.
Both engines with a 1800rpm cam would be wheezing dogs at 3500rpm due to low volumetric efficiency. The valves would not be open long enough , nor high enough . To provide enough flow to fill the cylinders.
 
Some of the very high end race gasses might handle 15:1.

As i said before, in otherwise equal engines from the antique era, n/a diesels made the same pto HP as gas burners at about 6:1 compression.

Increased fuel delivery and porting of the had and manifold would allow a diesel to keep up with maybe a 7:1 gasser. At 9:1 the gasser is leaving the diesel behind. Anywhere from a 12:1 gas burner to a15:1meth burner is miles ahead of the diesel.

However, add a pump, injectors, and a turbo to the diesel, and things get different.
 

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