mechanical engineers - how would I calculate this? (((long thread)))

[260ZRED]

I'm studying ME but this is WAY WAY beyond me @ this point. I would really appreciate if someone could give me a reference to read or a way of calculating what I need. Anything will help.

 

What I'm trying to do is figure out what kind of gas mileage I can get out of a CUSTOM, towing rig I want to build.

 

Here's the setup now:

 

91 Toyota Pickup - 2.4Liter 22RE, 2WD, 5speed,

curb weight 3000lbs

coefficient of drag: 0.44

112hp @4600 rpm

142 ft-lbs @3400 rpm (stock)

 

empty: 26-27 mpg @ 70-75mph

loaded with trailer (1100lbs) ONLY: 17mpg @70-75

loaded with a trailer & car: 16 mpg @ 58-60mph

 

trailer weights exactly 1100lbs, car weights on average ~3200-3400lbs

 

 

New potential powerplant specs:

 

engine swap candidate #1: 1.9L VW TDI Turbo Diesel Intercooled

100hp@4000rpm

177ft-lbs@1800 (bone stock)

 

from: a 2003 Jetta

curb weight: 3200 lbs

Coefficient of drag: 0.32

hwy: 49 mpg

city: 42 mpg

 

I want to put the TDI engine in the Toyota and keep everything else the same, keep the Toy 5 speed tranny, the diff, 2wd, etc.

 

What would be the ROUGH mpg I can expect from this towing rig? Empty/Loaded? Assuming I can swap engines only and the drive train losses from transmission, etc. remain the same?

 

The TDI diesels are very de-tuned for the US market for emission reasons. Chipped, better intake & exhaust they are making ~110hp and 220 ft-lbs of torque (sourced from forums.tdiclub.com) AND get over 55mpg hwy (better than stock ratings). Its kind of like putting a 2.5" down pipe on a L28ET I guess..

 

Please explain your logic and reasoning for figuring out the potential MPG once the TDI engine is in & running.

 

All ideas/advice comments are VERY welcome.

 

This is a long term project with a healthy budget and a strong will to see it through.

 

I will be concentrating heavily on reducing the Truck's COD as well. No weight reduction will be possible, however, because it will be set up for towing. I've been told that's a big no-no altho it would help with MPG considerably.

 

thank you in advance for any ideas or advice.

 

Igor

[olie05]

Are you taking ME at UH? Thats what I am doing...

 

anyways, I'm sure you are hip to this equation:

F = (1/2)*(p)*(A)*(Cd)*(v^2)

 

F = Force of drag

p = Mass density of medium the object is moving through

A = cross sectional area

Cd = drag coefficient

V = velocity

 

Now what do you do with all this?

 

I would get the cross sectional area first, then calculate how much force it takes to move the car at ooo lets say 70mph, assuming your engine is producing the most amount of torque there (with proper gearing). then compare that with how much torque the new engine will make at that same speed (assume gearing puts it there) and get a ballpark highway estimate. Lets assume your found that the car only needed about 40ft-lbs of torque to keep it at 70mph:

 

(40/142)/(40/177) = 1.24647

 

... then, you could multiply this with the old gas mileage in the truck,

26.5mpg * 1.24647 = 33.031455mpg with new engine

 

Thats a really easy way to get a very inaccurate value, but at least it would give you an idea of how much you should at least expect. The way I did it doesn't take into account gearing, and it just estimates engine eficiency based on maximum torque output. I'm sure there are better ways to do it though... however, I'm a first year eng. student so cut me some slack

[260ZRED]

I found a great program that helped out a lot, CarTest. It actually spits out a very similar value as to what Olie calculated.

 

I've messed around with it, pluggin in know values for cars I have/had, and it is VERY accurate, the output it has given me falls within 2-3 MPG that I have actually seen.

 

It's an awesome program, even though its a little old.

 

http://www.cartestsoftware.com/cartest4.5/

[JMortensen]

Just as an aside, my friend put a freshly rebuilt 2L Toy turbo diesel in his 87 4x4. It has a solid front axle swap is lifted, dual transfer cases, and 35" mudders. Weighs in at 4500+ lbs. He took on a LONG road trip and got 26 mpg, not loaded per se, but with luggage. The point is there are diesel parts available from Toyota and they came in the pickup trucks from 87-89 I think and that might make it an easier swap. There definitely isn't any aftermarket though, so you kind of have to be inventive about modding it. IIRC he was hoping to get 180hp when it's all said and done.

 

EDIT--put a big honkin air dam on the front. That will help a lot with the cd.

[260ZRED]

I've thought about that, but the Toyota 2L-T (turbo diesel) engines are nearly impossible to find.

 

here's a truck I've been watching, it's an 85 Toyota Turbo Diesel:

 

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=4633716148&sspagename=STRK%3AMEWA%3AIT

 

as you can see, they dont go for cheap!!

 

A 50,000mi TDI motor can be had for ~2000.00-2500.00 complete, with many parts available and a limited but existing aftermarket support. It makes the exact same power as the bigger Toy. Diesel.

 

ACME Adapters makes a transmission adapter to mate the TDI engine to the Toy. pickup 5 speed tranny. And TDI aftermarket support is slowly growing.

 

The main problem is.. is it worth it? I want to get at least 35-40mpg fully loaded, towing 4500lbs @ 55mph. Empty I would like to see 55mpg. I dont think thats unrealistic, but if it takes too much $$$ then its not worth it.

 

All in all, a good challenge!

 

Any other engine suggestions??

 

thx,

Igor

[ZROSSA]

Jon's right. There are toyota turbo diesels that will bolt in there. I had a landcruser parado as a co. car for a while with a 3l turbo diesel in it. It moved along nicely for a heavyer the 2000kg truck. We have some pretty large hills ( some may call them mountains) around here and I used to love the way you could leave it 5 th gear and blast up the hills at 140kph. They are better now with common rail fuel systems and intercoolers. I wouldnt touch the VW.

 

Douglas

[JMortensen]

I've thought about that' date=' but the Toyota 2L-T (turbo diesel) engines are nearly impossible to find.

 

here's a truck I've been watching, it's an 85 Toyota Turbo Diesel:

 

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=4633716148&sspagename=STRK%3AMEWA%3AIT

 

as you can see, they dont go for cheap!![/quote']

Jesus. My friend was GIVEN a truck just like that one (but rusty), and has bought a couple engines for basically nothing. I guess he just got lucky! I wouldn't pay $6K for that powertrain either.

[260ZRED]

I would love to use a Toy-diesel but again, they are $$$ and very hard to come by over here in any form. So it's really not an option for me. No diesel's were legally imported in the US after 1985, when the EPA banned their importation because of emissions.

 

Importing a half-clip is an option but the TDI will cost less and parts are available here.

 

So I still think a built & tuned TDI motor would be my best bet.

 

Do you suppose 35-40 mpg @ 55mph towing a 5000lb trailer is possible? (upped boost, better IC, improving the trucks aerodynamics, etc?)

 

Or am I being over optimistic here..?

[boodlefoof]

I'm not an ME, nor an expert but something strikes me about your engine swap proposition. I may be completely wrong, but it is food for thought.

 

If you're putting in a smaller turbocharged engine into the pickup, and you will be putting a lot of load on the engine (from towing), you're constantly (or very often) going to be in a positive boost scenario. The smaller engine and increased load is also going to require that you give the car much more throttle than an engine with more displacement and torque.

 

Now, at highway speeds perhaps this won't be the case and you will get increased fuel economy. But, in stop and go traffic, it seems like you would probably get worse fuel economy than, say, putting in a larger V6, cammed to make most of its torque down low.

 

If you consider the throttle position and vacuum as your analogs to fuel consumption, it appears that the smaller engine may be detrimental.

[Kennysgreen280zt]

My 91 toyota V6 gets 23 mpg unloaded. Mostly 35-55 mph with some in town driving. Personally I wouldnt need more than the 4 cyl for what I do with the truck, but its what I got.

 

The TDI swap is an interesting idea. You are aware that in europe they got a whole host of TDI engines, inline 5, V6 and V8's came in Audi sedans and would require a similar adapter to fit in the truck. Im sure there are euro market importers just as there are JDM importers, so getting a slightly larger diesel may be a possiblity. Also, I bought a diesel Audi from this guy http://dieselhead.net/dieselHead_inventory.html and it seems he has a few toyota diesel motors there as well.

 

I would say getting a air dam might not be the best idea. I think the larger frontal area would hurt the aero more than help it. Maybe swapping out the lights for the later 4 runner lights would help. Also making the bumper smooth would help too. Blah blah blah all the same aero mods a Z needs to cut down CD. I run a conopy on mine, I dont know if that is better than a bed cover or open bed for MPG but its something to look into. Some of the VW diesel guys run super skinny tires to help out too.

[260ZRED]

Bone stock, the TDI has 40 ft-lbs of torque MORE than the original 22RE Toyota motor. And it has that torque available @ 1800rpm. Stock boost is set to 15-16lbs. I don't think it would require high constant boost once it's up to 55-60mph drving..

 

I need to talk to someone who's done this (or something similar) before... I just don't know anyone who has.

[ZROSSA]

Igor,

 

You need to think this one throught mate. You wont come out ahead by swaping a diesel into a petrol truck, particularly if you are going to use different companies engines and trans. You would be better off trading. I had a ford courier (Made in thialand) for about 3 years. It was a 2.5 tdi with 280nm of tourque at 1800 rpm. Not sure of the exact conversion but it should be close to what the vw tdi has in foot pounds. With my z on the trailer this thing struggled, big time! It would make power from just over 2000 rpm but you would have to slip the clutch to get it there. Dont pull out in front of traffic! The engine with a load on was always working hard. It had a lot better fuel consumption then a petrol engine would have in the same conditions but still a bigger tdi would have been the answer. It would have sat at 2000 rpm all day, mine was having to do 4000 rpm and constantly shifting to maintain speed.

 

Douglas

[Guest TegRacer324]

Hmmm this is also way over my head. I could maybe take a guess, but I'll get back to ya in about 2 years.

[Michael]

The component of horsepower needed to overcome aerodynamic drag is just P = D*V, where D is the drag given by Olie05’s equation. Assuming 30 ft^2 frontal area and the given Cd of 0.44, at 70 mph this comes out to around 30 hp. As a very rough approximation, the towed trailer and car will have about the same Cd and frontal area, so the required hp basically doubles.

 

More difficult to approximate would be the rolling resistance and the internal losses in the drivetrain and engine (cooling, pumping, exhaust); of course, it is only the latter will change when you swap engines.

 

The Jetta, meanwhile, with an assumed frontal area of 25 ft^2 would only need around 18 hp to overcome aerodynamic drag at 70 mph – and evidently it gets 49 mpg doing this. Presumably the gearing is such that the Jetta’s engine’s rpm at 70 mph is around 1800 (seems reasonable for a diesel?) – in which case it needs to make around 52 ft-lb of torque to produce the hp to overcome aerodynamic drag.

 

Now assume, very roughly, that100% of the horsepower goes into overcoming aerodynamic drag. Putting the Jetta’s engine into the pickup towing the trailer, to produce 70 hp at 1800 rpm is no longer possible, as it would require around 205 ft-lbs, and only 177 ft-lbs are available. But that’s not far off. 150 ft-lbs @ 2450 rpm give about 70 hp. Assuming that volumetric efficiency at 2450 rpm isn’t much worse than at 1800 (the torque peak), the fuel flow per unit time should just scale as the hp required – meaning, in our crude approximation, that the mileage of the Jetta’s engine in the truck would be a straight reciprocal of the ratio of the horsepower levels required. That is, 49 mpg * (18/70) = 12.6 mpg.

 

The actual mileage should be better, since the rolling resistance for the two vehicles doesn’t differ nearly as much as does the aerodynamic drag; so the total power required for the pickup isn’t as large as the ratio of drags predicts.

 

If the pickup and trailer will cruise at only 55 mph, then the hp to overcome aerodynamic drag is only around 34 hp, and the mileage (same assumptions as above) becomes 26 mpg. But I highly doubt that the truck doubles its mileage by slowing down from 70 mph to 55 mph!

[Moridin]

My brother had a friend in highschool with a mid 80's Toyota truck that got some pretty crappy milage on 33's. He did a vapor injection kit (water injection I believe) and saw at least a 30% increase in milage. I'm pretty sure it a was a carbed 22R, so he was able to jet it down along with some increased timing to get better fuel milage. It may help and be a far better alternative to swapping motors around.

 

Upping the output of the TDI motor is extremely simple. I don't think people realize how easy it is to get more power from a turbo diesel. Far easier than a gas motor IMO. Don't forget that with diesel motors that as power increases so does milage (unless big injectors and giant turbo are installed).