how fast can we go roundy round

[85_IDI_4x4]

*NEW EDITED POST*
Governor springs aside what part of these engines would be the limiting factor on how high of RPMs they can turn? My guess would have to be the the stock bolts holding the connecting rod caps on would be the first part to let go. In that case a set of stronger rods with studs could be used to eliminate that.

A member on this board has replaced his governor spring with the higher RPM spring from the GM idi and has iirc spun @ ~4500rpm for sustained periods of times. I would be interested to know how much his connecting rod bolts have stretched if he ever does a tear down of that engine. It has also been mentioned that his valves were floating but there has been discussion of using PSD springs which could be used to prevent that (you can also find places that will make you custom push-rods, valves and rockers if you give them specs, i have looked)

Just as a teaser if this engine was gas there is calculations you can do to determine what maximum rpm is possible using stroke length. it is based on what your mean piston speed would be and what is considered max safe speed for different levels of internal engine components.
Level: max rpm, mean piston speed
Stock: 5023 rpm, 3500 ft per min
Heavy duty: 5741 rpm, 4000 ft per min
Race: 7177 rpm, 5000 ft per min

http://thefirstgensite.com/code/maxrpm.htm

 

[Michael Fowler]

Certainly not an expert, but my guess that the limiting factor is how fast or how slow the fuel burns. Gasoline burn faster than diesel, so I suspect the calculation you referenced would not be valid.

 

[85_IDI_4x4]

Well some of the big hp pull trucks can spin 6k so its not that diesel does not burn fast enough. If you had the right governer spring im sure an 6.9/7.3 would spin that fast but then detonate seconds later.
But what part would be the one to let go first at that rpms? I know the pull trucks run some $$$$ parts to spin 6k.
And the calculations are for how much stress the parts can handle. It just happens the guy is talking about gas engines. but diesel parts are normally much stronger but heavier than gasser parts

 

[sle2115]

One of the big factors is weight of the rotating assembly, etc. Think about swinging a hammer, a 16 oz hammer versus a 32 ounce hammer, that kind of the differnce between gas and diesel (or even some hd gas engines). I'm not sure what the max RPM is, I don't think anyone knows, but apparently IH thought 3400 would be fine and hold things together, of course, it's been proven they can go more, but for how long, etc. Then I guess you see multiple "wants" here, some of us want all we can get without reliability issues, others want to see what they can get until it breaks. I used to fall into the latter, but these days, I just want to start my truck and work it as needed.

 

[85_IDI_4x4]

i do not wish to discuss the whole "want vs realiabilty" issue. That has been gone over and brought up more times than i can count on this board. What you and i want and consider reliable are going to be different so it is not worth discussing.

My question is about maximum rpms and what the limiting factor is. I would like to keep this thread about that.

i will be editing my orignional post to make my question clearer and easier to understand when i can get to a computer instead of my phone

 

[Goofyexponent]

Uh, about the fuel burning.....my brother calims his old 1.6 VW diesel would spin 7000 RPM........

He also claims that you can make 500 horsepower out of a 5.9 cummins with only a screwdriver.....

So take that as you want.. ....yea, my brother isn't the smartest thing going around these parts.

Anyways, I think a lot to do with max ROM DOES have to do with fuel combustion rates. Also, you need to think about the rotating mass you have going on in there. That is a LOT of weight to have spinning around at anything over 4000 RPM. The rods, the pistons and the crank all weigh comsiderably more than a racing gasser which would use super strong, but light weight pistons and whatnot.

Factor in the valve springs being a weak link, and you now are asking for trouble.

The pumps fall FLAT on their faces after about 3000 RPM IIRC, so anything above that would be converting fuel to noise and valve train parts coming out the exhaust.

I would just leave the top RPM as it stands and try to make my power within those parameters. If memory serves me right, Mel's Moose pumps are governed at 2800RPM or so?

I am not saying not to spin them up, I am saying do whatever you want with it...but when it does fly apart, can you sell us the good parts that are left over? lol.

 

[The Warden]

I think SLE hit the nail on the head with the rotating assembly...one thing to keep in mind is, as a general rule, the larger an engine is, the lower RPM's it's designed to turn, and this is doubly true with diesels since the rotating mass is considerably heavier than on a gasoline engine (think about how much stronger/heavier the pistons, conrods, and crank have to be to routinely handle 21:1 compression ratio as compared to 8 or 9 to 1). I once worked on a boat with a big inline-8 Caterpillar engine (don't remember the model number or displacement, but the engine was about 10 feet long and the individual valve covers were about the size of my face), and that engine wasn't meant to turn faster than 1500 RPM ...and bigger engines turn even slower; IIRC the low speed diesels that power the big freighters don't turn over 300 RPM.

The other thing to think about are the valve springs...at what point do the valve springs stop being able to close the valves quickly enough and the valve start floating/risking contact with the pistons? Certainly, you can upgrade the valve springs (IIRC some people were considering using upgraded PSD valve springs; not sure what came of it), but what sort of strain will that put on the rest of the valvetrain (pushrods, rocker arms, etc) that it wasn't designed to handle? Those may be upgradeable also, but AFAIK no one's currently making an upgrade for the pushrods or the rocker arms that's compatible with these engines, so that'll need some R&D and fabrication.

Yes, dyoung did it with an otherwise completely stock engine and his engine didn't fly apart...yet. With that said, you could hear the valves floating in the video he took of it...and nobody really knows what kind of long-term damage there may have been, or how long it could have been sustained for. Based on that, and based on the fact that Ford's ALREADY running these engines to a higher RPM than IH designed them for (IH designed them to govern at 2800 RPM; Ford changed it to 3400 RPM because they figured it'd be more pleasant for mass consumers), my strong opinion is that you're better off not messing with the governor, and if you're going to, either be prepared to heavily modify the engine or be prepared to rebuild/replace it when it lets go.

Just my $.02...

 

[Goofyexponent]

Well said warden......lol.

 

[The Warden]

Uh, about the fuel burning.....my brother calims his old 1.6 VW diesel would spin 7000 RPM.......

I agree with you overall, and certainly 7K is too high, but FYI the smaller European diesels DO turn a higher RPM...my old M-B'***** the governor at about 5000 RPM, and my TDI's governor kicks in at around 4500 RPM (although I've never pushed it that far). But, these are MUCH smaller engines (the TDI's 1.9l and the M-B's were 3.0l's) that were designed for passenger cars and were designed to turn at that RPM from the get-go. Completely different animals than our IDI's...

 

[hairyboxnoogle]

Ive thought about this and talked to some about it, IH origional governor spec was 2800, Ford increased that to 3400. I plan on running between 4 and 4400 after being balanced and blueprinted, studded bottom end, main girdle ect. Yes upgrading the rods, mainly to lighter ones would be a huge help. Thing is no one makes any. My guess to have a set of rods made... haha ya right.

But more on your topic, in stock form. I would say rod bolts would be my guess at the weak spot. After being balanced, BP'd. i would say wrist pins. Anything above 4400... youre starting to really put a beating on the injector pump oil pump and numerous other things, that just werent designed to go that fast.

 

[fordf350dually]

i saw one turn 10k. it was my buddys 7.3 idi. the gov spring broke and the tach went around 2.5 times then the crank went threw the oil pan.

 

[The Warden]

i saw one turn 10k. it was my buddys 7.3 idi. the gov spring broke and the tach went around 2.5 times then the crank went threw the oil pan.

Holy Mary!! That reminds me of all the stories I've heard over the years about 2-stroke Detroits running away...sometimes the only thing you can do is put as much distance between yourself and the engine as possible. Thank goodness nobody got hurt...when an engine blows up after running away, the shrapnel can be dangerous ...

 

[towcat]

the GM 6.2/6.5's can spin faster due to lighter stuff all around. fully dressed, the IH idi weighs 1100lbs. a fully dressed GM weighs 800lbs. outside of a rash of broken cranks last year, there is very little trouble with IH bottom ends even though they weigh three times as much compared to a GM. GM otoh, will tear out main webs without a second thought. Still, I have no hesitation in hotrodding a GM 6.5 versus doing the same to a IH. IH's aren't supposed to run that fast and the stoutness of the bottom end is explaintion enough. that is why I am looking into a bypass type supercharger for the IH plus a turbo. On the GM, a large hairy balls turbo that can ramp up quickly is enough for me.

 

[RANOVRU]

I think SLE hit the nail on the head with the rotating assembly...one thing to keep in mind is, as a general rule, the larger an engine is, the lower RPM's it's designed to turn, and this is doubly true with diesels since the rotating mass is considerably heavier than on a gasoline engine (think about how much stronger/heavier the pistons, conrods, and crank have to be to routinely handle 21:1 compression ratio as compared to 8 or 9 to 1). I once worked on a boat with a big inline-8 Caterpillar engine (don't remember the model number or displacement, but the engine was about 10 feet long and the individual valve covers were about the size of my face), and that engine wasn't meant to turn faster than 1500 RPM ...and bigger engines turn even slower; IIRC the low speed diesels that power the big freighters don't turn over 300 RPM.

^ = money.


If youre talking about an all out build, aka aftermarket engine, then things change. A stock GM 454 doesnt turn much over 4-4,5k, but stroked to say 468 for a drag application they can spin 8k+.

 

[icanfixall]

About those big cargo freighter ship engines... The ones I know about spin up to 82 rpm and the overspeed rpm test is around 102 rpm.... Look at utube for... The largest Diesel Engine.... Back a few years valve springs lost the ability to open and close around 14,000 rpm. Some Indy engine designers were working on some solenoid operated electrical valve springs. At 12,000 rpm the piston is moving up and down 200 times a second. So how many times is a valve opening any closeing.