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Guest Message by DevFuse
 

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horsepower or torque?


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10 replies to this topic

#1 Uberoo

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Posted 29 July 2009 - 02:19 PM

Offroad which is more important, HP or TQ? Ive always thought of it as "HP is how fast you can go,TQ is how fast you get there". I know TQ is a twisting force,acceleration for lack of a better word.Where does HP play into that?

With that in mind, I have two engines that i might like to put in my offroad subaru toy. Engine A is a two cylinder diesel. It has like 16 HP but about 85 Lbft of torque by 1500(or less) RPM.It revs to 3600 RPM. Engine two is a EA81. just guessing but it has 80 HP at 5K RPM or so and 90(ish?) Lbft of torque at about 2.5K rpm or so.

Which is a better engine offroad? one one hand the diesel has more TQ from idle, where as the subi has way more horsepower. In the mud there are two reasons why someone might press the gas more, other than just wanting to go faster. Those are: get engine into torque band to better deal with the drag of the tires in the mud, and to spin the tires faster to get them to self clean.The diesel would have the tq at low RPM to not bog down as much at low RPM.The gas engine however could rev much higher to get the tires clean and maybe keep going by the "paddle" effect. Each lug of the tire acts as a paddle to give some forward momentum.

Im kinda thinking the diesel, but I know know if it could spin the tires fast enough to get the tires to self clean.I dont really want to put the diesel in just to get stuck a mudhole that having lots of wheelspeed would have been all it needed to get through.

What engine would you pick?Is TQ or HP more important offroad?

#2 TheSubaruJunkie

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Posted 29 July 2009 - 02:59 PM

From everything the seat of my pants has told me, torque likes to kick in at much lower rev's. And when you are off-road, that is very... very good.

#3 nipper

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Posted 29 July 2009 - 04:04 PM

Torque gets you moving, HP keeps you moving, so you want torque :)


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#4 Uberoo

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Posted 29 July 2009 - 10:12 PM

so then the little diesel might just be the hot ticket offroad..

#5 nipper

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Posted 29 July 2009 - 10:36 PM

Yes diesels have the grunt. When doing off road you want as much power available at low RPM as possible. Now if it was a street vehical built for speed, the gas engine would be best.

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#6 The Beast I Drive

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Posted 29 July 2009 - 11:26 PM

How big is the Diesel? Im thinkin you could multiply the torque if you used 2 of them in line with each other, so the output of the crank on the 1st one coupes to the front of the crank on the second one, but if they are too big and too heavy then it wouldnt work too well... The deisel definitely has the torque where you need it most for off road, especially with larger tires

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#7 nipper

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Posted 29 July 2009 - 11:34 PM

there is another part of this equation, what transmission are you using, A troque converter multiplies torque as well as transmits power, while a clutch can always be started in gear.


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#8 Numbchux

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Posted 30 July 2009 - 12:31 AM

if you're rock crawling, and will never be exceeding ~10mph. the diesel you're talking about would work wonderfully.


but if you EVER plan to drive it on the road. even just down the street to fill up the tank. 16hp isn't going to do it.

also, if you ever have a hillclimb, or anything else that requires momentum, you'll be screwed.

or, if you are ever in a situation where you have to clean the tires, again, screwed.



I really don't think you'd be happy with THAT diesel. now, if you were talking about a '70s or '80s VW diesel 4-cyl. where we're talking about 50-60hp and 100-120 ft/lbs. yea, that'd be pretty slick. you'd be wishing you had more poop occasionally.....but most of the time it'd be pretty sweet. But you're talking about LESS peak torque, just 1k rpm sooner. IMHO, at stock subaru gearing, 1500 rpms isn't low enough.

#9 nipper

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Posted 30 July 2009 - 09:56 AM

if you're rock crawling, and will never be exceeding ~10mph. the diesel you're talking about would work wonderfully.


but if you EVER plan to drive it on the road. even just down the street to fill up the tank. 16hp isn't going to do it.

also, if you ever have a hillclimb, or anything else that requires momentum, you'll be screwed.

or, if you are ever in a situation where you have to clean the tires, again, screwed.



I really don't think you'd be happy with THAT diesel. now, if you were talking about a '70s or '80s VW diesel 4-cyl. where we're talking about 50-60hp and 100-120 ft/lbs. yea, that'd be pretty slick. you'd be wishing you had more poop occasionally.....but most of the time it'd be pretty sweet. But you're talking about LESS peak torque, just 1k rpm sooner. IMHO, at stock subaru gearing, 1500 rpms isn't low enough.


Even the earliest VW's had 25 hp, so yes if you are going to ever want to do anything over 70, or get there in less then an hour (to 70) you will need bigger. But for even 30/45 it will be ok .

nipper

#10 bigo1966

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Posted 30 July 2009 - 10:00 AM

Just put the diesel in and if you dont like it take 30 min and put the EA81 back in.

Edited by bigo1966, 30 July 2009 - 10:06 AM.


#11 Uberoo

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Posted 30 July 2009 - 10:24 AM

now to see if I can get the head off the diesel without breaking the studs...it has a glow plug that was installed to far in.They tried to back it out but it broke.Then it sat outside for a long time, and now has a lot of rust on it.Engine turns over freely though...

as far as coupling two engines together, one engine is 19" long if you include the massive crank pully.The engine weighs 300 lbs, but because its aircooled its only about 50 lbs heavier than stock...because its so big and heavy only one will fit in the engine bay.it will however sit 6" above the hoodline...perfect for getting air to the cylinders for cooling...




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