Power to weight Ratio: Why are XJs slow?

[CherBear]

Lets consider the following:

A 2000 Xj has 193 hp and weighs about 3050 lbs.
Thats comes to a p/w of 15.8 lbs/hp
0-60 in about 9 flat. mid to low 15s on the 1/4 mile. (that was the lowest number i could find on a stock XJ)


A 2006 VW GTI has 200 hp and weighs about 3150
p/w of 15.8 as well
GTI can do 0-60 in about 6.3 seconds and run a 1/4 mile in the mid 14s.

So why so slow?
I know a big factor in these times are the aerodynamics of both vehicles. The Xj is brick compared to the GTI.
How ever, i want to ask you fellow jeepers how to increase my acceleration to more satisfactory levels. I know it has the power to do it, but i would like to hear what you guys think of shorter gearing or anything other ideas you might want to throw around.

 

[swbooking]

Arent those ratings HP at the crank?

I would assume that if you looked at the WHP of each the XJ would probably have a lot lower dude to the loss of power through its drivetrain. I would also assume that the VW has a much more efficient/compact drivetrain therefore allowing more of its estimated HP get to the wheels.

and as you said, im sure the aerodynamics has a huge effect on the XJ.

 

[IslanderOffRoad]

IH8EPA... cute.

Are you a reincarnation of purple cherokee?

 

[swbooking]

IH8EPA... cute.

Are you a reincarnation of purple cherokee?

:roflmao: I didnt even think about that! Seems to me that you might be right John

 

[IslanderOffRoad]

I'm an intarweb detective!

 

[swbooking]

Just to entertain myself since im bored...

IH8EPA: What are your goals with this gain in acceleration?

 

[CherBear]

about 131 at the wheels for the XJ albeit high-ish miles

And about 178 for the VW.....

You are correct. Let me then ask you how i can get more ponies to the ground then?

And no, i am not a reincarnation of "purple cherokee"
My jeep is green thank you very much.

My goals would be... to go fast? Beat those damn rice rockets perhaps?

 

[IslanderOffRoad]

Driveline loss is much higher in 4wd vehicles.

 

[Boostwerks.com]

yeah the AW4 drivetrain sucks up a rediculous amount of power. I'm honestly thinking about doing a NV3500 swap just because of this.

 

[CherBear]

Yea thats like a 27% (<-- shit) drivetrain loss. for the Chero
And an 11% (?) for the V dub, which is much lower than i expected. I thought most cars were around 20% loss
i guess thats the advantage of having fwd.

 

[swbooking]

Off the top of my head:

Fix the aerodynamics problem. If you look at that hideous YJ (I forgot the name of it Renegade maybe) due to all its plastic cladding etc, it has the best MPG and aerodynamics of any of its kind (IIRC). Make not only the air passing over the Jeep more efficient but also the air passing under it. Lower it, install some type of under body diffuser, etc...

Gears: If your just looking for quick acceleration. Move to a deeper gear.

Unsprung weight: Keep it light. Aluminum wheels, smaller contact patch on your tires, disk brake swap, etc...

Figure out where the loss in power is to the wheels: Is the AW4 more efficient over the AX-15? the NSG370? 42RE? NV3500? NV4500? etc...? Hows the transfer case efficiencies? Whats better? 231? 242? 249? etc...? Should you ditch the whole 4WD all together?

Those are a couple of the places i would start.

 

[CherBear]

Wow now cowboy. There will be no ditching of the 4wd.
Nor will i be adding any type of body modification. I want to beat the Rice rockets, not become one.

Hell ill just swap in a whole Chevy drivetrain with a built 350. That will show them!!

 

[swbooking]

I didnt go into motor modifications cause it seemed that you were satisfied with the 4.0s power output and just wanted suggestions on how to get that power to the wheels.

If you want to go into motor swapping there is A LOT you can do:

Stroker/V8, Microtech/Haltech/etc programmable ECU, headers, exhaust, CIA, and so on, and so on...

 

[IslanderOffRoad]

Wow now cowboy. There will be no ditching of the 4wd.
Nor will i be adding any type of body modification. I want to beat the Rice rockets, not become one.

Hell ill just swap in a whole Chevy drivetrain with a built 350. That will show them!!

You could always make a nose cone and wing like the Daytona Charger

 

[MaxxXJ]

... the reason the GTI is much faster is a mixture of things...
1st, rolling resistance, their wheels and tires combined prolly weigh as much as one of our tires alone
2nd gearing, their geared to rev all the way upwards of what 8000rpms and were setup to 5500...
3rd their lower to the ground so the aerodynamics are better.
4th their DOHC
5th their 200hp came turbocharged
6th im assuming stick vs automatic
... thats all i can think of for now, but yanno what my 2000 xj stayed with a 3000 gt yesterday, my auto vs his manual...

 

[CherBear]

What does 2, 4 and 5 have to do with anything
2. I dont care how high u can rev your engine, it still has a max hp
4. maybe ill have triple overhead cams, it still doesnt give me anymore hp.
5. I dont care if it was supercharged or turbo charged. it still only has 200 hp.
might even be slower due to turbo lag.

I do agree with your other points and yes i should have pointed out #6. Manuals are much more efficient.

 

[Mr_Random]

Swap in an ax-15, learn your power curve, and how to use it best! Because you're switching from auto to manual, you'll also be getting a better gear ratio and be able to beat them stoplight to stoplight much easier.

There's probably nothing you can do for 45+ speeds though, wind resistance, rolling resistance, lack of top end, etc will kill you... but then again, rice burners don't go on the freeway, they don't know how to get further than two blocks from home...

Ditch excess weight! Buy a set of cheap "road" tires to tear up the 'burners while around town (and get your better gas mileage), and keep your offroad tires in good condition for the real fun! leave tools at home, take out your rear seat, get rid of your girlfriend/wife, leave your homies at home, etc!

Ditch your roof rack! If it's stock it's crap anyways!

Run them off the road before you can even race them...

Only drive on dirt roads, that will work.

 

[IslanderOffRoad]

I still think you're purple's alter ego.

 

[BBeach]

... the reason the GTI is much faster is a mixture of things...
1st, rolling resistance, their wheels and tires combined prolly weigh as much as one of our tires alone
2nd gearing, their geared to rev all the way upwards of what 8000rpms and were setup to 5500...
3rd their lower to the ground so the aerodynamics are better.
4th their DOHC
5th their 200hp came turbocharged
6th im assuming stick vs automatic
... thats all i can think of for now, but yanno what my 2000 xj stayed with a 3000 gt yesterday, my auto vs his manual...

1, yeah
2, they dont rev that high (I dont shift my 1.8t past 6500, a vr6 maybe 7k)
3. aerodynamics are rather insignificant in 0-60's
4. dohc or not, it's still 200hp
5. 200hp is the 2.8 vr6, 180hp is 1.8t
6. prolly stick

If you look around some more OP, the Jeep is usually low 8's for the auto, and mid 7's for the standard. It's all amount gearing and traction really.

On the purple cherokee note, I'm guessing you lost to your first vee dub??? :rof:

 

[MaxxXJ]

What does 2, 4 and 5 have to do with anything
2. I dont care how high u can rev your engine, it still has a max hp
4. maybe ill have triple overhead cams, it still doesnt give me anymore hp.
5. I dont care if it was supercharged or turbo charged. it still only has 200 hp.
might even be slower due to turbo lag.

I do agree with your other points and yes i should have pointed out #6. Manuals are much more efficient.

2 matters because your power curve is alot shorrter than the gti because once he hits boost its a solid 200 hp from say 2000 rpm to 8000 as to where your building 193 hp all the way up until redline
4 matters because a dohc rev's faster than sohc motors so while your still accelerating to 5500 rpm, the gti has already shifted and moved onto a new gear
and i also thought of another one... gearing, i havent found out yet but a jeeps first and 2nd gear i bet are alot longer than the gti's so it will take more time to get thru your gears... and if the jeep only has a 4 speed automatic and the gti has a 6 speed manual...

theres alot of factors to look at in a drag race, just accept thier somewhat slow and move on.