Gas vs PSD
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Modular motor junkie
Joined: May 2009
Posts: 6,190
Likes: 8
From: Texas
in the all the comparisons you all are making, the v10 is outpulling the psd because of gearing and not because of power. when you say "my v10 in 3rd gear can outpull your psd in 5th gear going up a hill" you think that its because its in its powerband and making more hp, when in reality its because it has a HUGE gearing advantage of being in third gear. i can take my 225 hp 7.3 with 4.10 gears and put it in 3rd gear and outpull a 350 hp 6.4 with 3.55 gears in 5th gear going up a hill. no matter what rpm i am at, he is going to be making more hp than me, but yet i will still accelerate faster than him. because of the gearing advantage. and thats with less hp and less tq.
my family owns a wrecker business and we have several gas and diesel rigs. one of our gassers(~350 hp and 400 tq) has a 2 speed rear axle, and let me tell you, from a dead stop that thing will get a load moving just as easily as our diesels with 350-400 hp and 1000 lbs of tq. why? because with that kind of gearing, it doesnt take much power to get anything moving. BUT, there comes a time when you have to change gears. the more gears we run through on the gasser(and get into more normal final drive ratios), the more it pulls just like a regular pickup truck. thats why i keep saying that for a fair engine vs engine comparison you need to have the engines in the same truck with the same parameters(gearing, each in peak powerband, same final drive ratio, etc.) you cant compare one with 4.30's in 3rd gear vs one with 3.73's in 5th gear and say its engine vs engine.
my family owns a wrecker business and we have several gas and diesel rigs. one of our gassers(~350 hp and 400 tq) has a 2 speed rear axle, and let me tell you, from a dead stop that thing will get a load moving just as easily as our diesels with 350-400 hp and 1000 lbs of tq. why? because with that kind of gearing, it doesnt take much power to get anything moving. BUT, there comes a time when you have to change gears. the more gears we run through on the gasser(and get into more normal final drive ratios), the more it pulls just like a regular pickup truck. thats why i keep saying that for a fair engine vs engine comparison you need to have the engines in the same truck with the same parameters(gearing, each in peak powerband, same final drive ratio, etc.) you cant compare one with 4.30's in 3rd gear vs one with 3.73's in 5th gear and say its engine vs engine.
You cant compare them with the same gears because you cant compare them at the same RPM.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,852
Likes: 39
i can take my 225 hp 7.3 with 4.10 gears and put it in 3rd gear and outpull a 350 hp 6.4 with 3.55 gears in 5th gear going up a hill. no matter what rpm i am at, he is going to be making more hp than me, but yet i will still accelerate faster than him. because of the gearing advantage. and thats with less hp and less tq.
If you take two Superduties that are going the same speed up the same hill, but one truck weighs 1000 lbs more, the heavier truck is making more horsepower. Again, it does not matter what engine, gearing, or anything else. Heavier truck at the same speed = more horsepower.
Finally, you can never have more horsepower at the rear wheels that you do at the engine, and in fact the horsepower at the engine and the wheels are the same at any given moment (ignoring gearing loss, which will be almost identical from truck to truck anyway).
You cannot go faster or heavier without an increase in horsepower.
Postmaster
Joined: Apr 2008
Posts: 4,724
Likes: 4
From: Rogersville, TN
my argument was to put both engines in their peak powerband, but have them use the same gearing. on my infinite 10% hill climb, for instance, take my 225 hp 7.3 with 4.10 gears in 3rd gear at 2500 rpm and start piling the weight to it. take your 360 hp v10 with 4.10 gears and put it in 3rd gear at around 4k rpm and start piling the weight to it too. you will start out at about 15-20 mph faster than me(so you still have a momentum advantage), but which one is going to peter out first? we are both at our peak hp point, have 4.10 gears and are in the same gear(so same final drive ratio). that just seems a heck of a lot more fair to me.
Postmaster
Joined: Apr 2008
Posts: 4,724
Likes: 4
From: Rogersville, TN
ive been saying all along that hp is what makes you go faster. i dont deny that one bit. but i can tow heavier with less hp any day of the week. take my 7.3 again. it has 425 tq at 2k rpm and 225 hp at 3k rpm. say i put a chip in it that bumps me up to 500 tq at 1500 rpm but it puts a rev limiter around 2200 rpm. my stock 7.3 with 225 hp will outrun it in an unloaded drag race because it can turn more rpms and has more hp. but pull out my infinite hill again and tell me which one is going to do a better job towing a HEAVIER weight up the hill.
Lead Driver
Joined: Jul 2007
Posts: 7,868
Likes: 9
From: Rhode Island
this is where i have the problem with the gasser argument. yes, your engine makes peak power at a higher rpm. but instead of comparing your gasser engine at its peak rpm vs the diesel at its peak rpm, you want to put your 3:1 reduction unit on the gas engine AND run it in its peak power band. that gives it the advantage of not only being in its peak power band, but having 3 times the gearing as the diesel.
my argument was to put both engines in their peak powerband, but have them use the same gearing. on my infinite 10% hill climb, for instance, take my 225 hp 7.3 with 4.10 gears in 3rd gear at 2500 rpm and start piling the weight to it. take your 360 hp v10 with 4.10 gears and put it in 3rd gear at around 4k rpm and start piling the weight to it too. you will start out at about 15-20 mph faster than me(so you still have a momentum advantage), but which one is going to peter out first? we are both at our peak hp point, have 4.10 gears and are in the same gear(so same final drive ratio). that just seems a heck of a lot more fair to me.
my argument was to put both engines in their peak powerband, but have them use the same gearing. on my infinite 10% hill climb, for instance, take my 225 hp 7.3 with 4.10 gears in 3rd gear at 2500 rpm and start piling the weight to it. take your 360 hp v10 with 4.10 gears and put it in 3rd gear at around 4k rpm and start piling the weight to it too. you will start out at about 15-20 mph faster than me(so you still have a momentum advantage), but which one is going to peter out first? we are both at our peak hp point, have 4.10 gears and are in the same gear(so same final drive ratio). that just seems a heck of a lot more fair to me.
It still doesn't matter, the argument is, more HP will allow you to pull more with the proper gearing. Put a 16:1 reduction on it, and that 400HP 16,000 RPM racecar engine will pull as much as the 400HP 1500 RPM diesel.
You simply can't allow both engines to use the same gearing and run them in their peak power band RPMs up a hill, because the gasoline powered vehicle will always be going faster then the diesel, which puts a higher load on the motor. Put a reduction on the gasser, run both trucks at the same physical speed, and let each motor be at their maximum HP, and the higher HP gasser will outpull the diesel every time.
Postmaster
Joined: Apr 2008
Posts: 4,724
Likes: 4
From: Rogersville, TN
compare my 5.4 to my 7.3. my 5.4 has 260 hp and my 7.3 has 225. with both of them empy, my 5.4 is faster than my 7.3. no questions asked. but put some weight on them and it becomes laughable. ive done tests with both of them pulling the same trailer up the same hill and its not even close. for example, i took my 5.4 and put it in 3rd gear with a ~6k lb trailer hooked to it on a small hill. i ran it to 3500 rpm and then floored it. it had almost no acceleration at all and could not hit 4th gear. i took my 7.3 and hooked the same trailer to it on the same hill and did the same thing in 3rd gear, but at around 2k rpm. it had no problem at all accelerating and was still accelerating in 4th gear when i topped the hill. my 5.4 was making more hp than my 7.3 the whole way up the hill and was in its peak power band, but it couldnt pull more weight or faster than my 7.3.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,852
Likes: 39
Those two "advantages" you cite are one and the same.
Lead Driver
Joined: Jul 2007
Posts: 7,868
Likes: 9
From: Rhode Island
if you want to access your powerband, why dont you just speed up a little bit and raise the rpms? you can access that sweet spot without having a 3 to 1 gearing advantage. just like the example i showed in my other post.
compare my 5.4 to my 7.3. my 5.4 has 260 hp and my 7.3 has 225. with both of them empy, my 5.4 is faster than my 7.3. no questions asked. but put some weight on them and it becomes laughable. ive done tests with both of them pulling the same trailer up the same hill and its not even close. for example, i took my 5.4 and put it in 3rd gear with a ~6k lb trailer hooked to it on a small hill. i ran it to 3500 rpm and then floored it. it had almost no acceleration at all and could not hit 4th gear. i took my 7.3 and hooked the same trailer to it on the same hill and did the same thing in 3rd gear, but at around 2k rpm. it had no problem at all accelerating and was still accelerating in 4th gear when i topped the hill. my 5.4 was making more hp than my 7.3 the whole way up the hill and was in its peak power band, but it couldnt pull more weight or faster than my 7.3.
compare my 5.4 to my 7.3. my 5.4 has 260 hp and my 7.3 has 225. with both of them empy, my 5.4 is faster than my 7.3. no questions asked. but put some weight on them and it becomes laughable. ive done tests with both of them pulling the same trailer up the same hill and its not even close. for example, i took my 5.4 and put it in 3rd gear with a ~6k lb trailer hooked to it on a small hill. i ran it to 3500 rpm and then floored it. it had almost no acceleration at all and could not hit 4th gear. i took my 7.3 and hooked the same trailer to it on the same hill and did the same thing in 3rd gear, but at around 2k rpm. it had no problem at all accelerating and was still accelerating in 4th gear when i topped the hill. my 5.4 was making more hp than my 7.3 the whole way up the hill and was in its peak power band, but it couldnt pull more weight or faster than my 7.3.
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Postmaster
Joined: Apr 2008
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From: Rogersville, TN
That is not fair, because the V10 is being worked harder, not only does the V10 have to be pulling that load up the hill faster (which requires more power), but for every doubling in speed, wind resistance increases 4x, so that V10 has a much higher load on it from the start hauling that truck up the hill faster.
). with both of us in third gear and me at 2k rpm and you at 3500 rpm, you are only going to be doing about 10-15 mph faster than me. i would even think it would be a lot more fair if say, my 7.3 had 3.55 gears and your v10 had 4.10 gears. that way at the same speed we would both be at our peak rpm. but when you start talking 3 to 1 and 4 to 1 gearing advantages, thats not even close to being fair.
Postmaster
Joined: Apr 2008
Posts: 4,724
Likes: 4
From: Rogersville, TN
i have the 2v 5.4, so it doesnt make peak hp at 5k rpm. if i remember correctly, its peak hp is at 4k rpm. even at 3500 rpm it was still making more hp than my 7.3 at ANY rpm. point is, it still had more hp and the same gearing, but it couldnt pull as much or as fast. i can still assure you though, that at no point in the powerband will it pull as good as my 7.3. my 7.3 can maintain speed up hills with a load at 2k rpm in 5th gear that my 5.4 loses speed going up in 3rd gear and wide open.
Lead Driver
Joined: Jul 2007
Posts: 7,868
Likes: 9
From: Rhode Island
i have the 2v 5.4, so it doesnt make peak hp at 5k rpm. if i remember correctly, its peak hp is at 4k rpm. even at 3500 rpm it was still making more hp than my 7.3 at ANY rpm. point is, it still had more hp and the same gearing, but it couldnt pull as much or as fast. i can still assure you though, that at no point in the powerband will it pull as good as my 7.3. my 7.3 can maintain speed up hills with a load at 2k rpm in 5th gear that my 5.4 loses speed going up in 3rd gear and wide open.
Postmaster
Joined: Apr 2008
Posts: 4,724
Likes: 4
From: Rogersville, TN
physics and formulas dont pull my trailer though. at 3500 rpm my 5.4 makes more hp than my 7.3 at any rpm. whether its peak hp or not, its still more hp by a LOT(also leadhead, 2k rpm is far from the peak hp of my 7.3 too. it makes peak hp at 3k rpm). but in 3rd gear at 3500 rpm i can floor my 5.4 and it goes nowhere. in 3rd gear with my 7.3 at 2k rpm i can floor and hit 4th gear and keep climbing. at 2k rpm my 7.3 is making 162 hp and 425 tq. 425x2000=850,000/5252=162. at 3500 rpm my 5.4 is making 233 hp and 350 tq. 350x3500=1,225,000/5252=233. shouldnt having more hp and the same gearing help it accelerate faster? by the "physics" my 5.4 has 71 more hp than my 7.3 at the instant i floored them, but yet the 7.3 ran off and left it. how is that? because even though it had less hp it had 75 more tq.
Senior User
Joined: May 2004
Posts: 407
Likes: 0
From: Humble, Texas
I disagree with phillips91 regarding the hp argument but he makes a solid point that with a 4.30 rear end, a psd can theoretically go about 85 in 4th gear and 110+ in OD. Of course, I did not do any wind resistance calculations because that would take me longer than 1 min to calculate and I don't care enough, plus you'd really need a dyno sheet. My point is that the loss in speed due to a diesel running "gasser" gears is at a speed that most of us would never go anyway, and without a tuner, the pcm wouldn't even allow it. 35 mph is not even in the same county, let alone the same ballpark. In fact, rpm with 4.30's at 35 mph isn't even high enough to get to the top gear anyway.
At highway speeds, hp WILL make the difference. The V10 WILL end up faster but if they are geared the same, it will take longer for the V10 to pass the psd because it will be out accelerated.
Postmaster
Joined: Apr 2008
Posts: 4,724
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From: Rogersville, TN
Wind resistance quadruples for every doubling in speed, so that means the 5.4 powered truck was under 3 times the load, just pushing the truck through the air. Since you were pulling the trailer up the hill 75% faster, that means the 5.4 truck was also under 1.5x more total load just pulling the trailer up the hill.
in 4th gear (1.0 tranny ratio and 4.10 rear end=4.10 final drive ratio) at 2k rpm(162 hp and 425 tq) my 7.3 will still accelerate faster than my 5.4 in 3rd gear(1.61 tranny ratio and 4.10 rear end=6.6 final drive ratio) at 3500 rpm(233 hp and 350 tq). my 7.3 is going faster(more wind), has less hp and much worse gearing, but yet it still accelerates faster. i know you all like your physics and all that, but thats coming straight from my butt sitting in the seat and my foot hitting the go pedal.