New at this, trying to understand horse power

Both. The GC uses an ancient design that has been reconfigured numerous times over 50+ years but does not benefit from overhead cams, 4 valve/cyl etc. There is a lot more resistance inside the 4.0 than the 3.5. It's unfair to compare 21st century technology with an engine designed in the early to mid 1900's. You can not bring fuel consumption into the arguement because now we are comparing the GC to the FX... a brick to a bullet. There is added weight and rolling resistance in the GC... if you had the 3.5 in the GC, the fuel consumption would probably be almost comparable.

-Brian

From Infinity websight. FX35 with 2wd is 4,110 lbs

from my GC ownersmanual 2wd 4.0liter weight is 3791 lbs

The Infinity is 319 lbs heavier and has a smaller engine and gets same gas milage with 80 more HP.

Depends on what you want from your engine really. The only figures I can find for the infinity engine is VQ35 DOHC 24-valve

OT: I second that depends on what you want ... I like the fact that my old

There are oodles of factors involved that determine horsepower. Without going into depth, here are a few things to consider:

A Honda Accord has 220some HP. This just means it has a lot of take-off power and can probably pull a fair-sized load. However, this car is designed for higher RPM and smooth operation. For the sake of explanation, add a 6" lift and put some 33" tires on the Accord and try and go through a mud hole. The car has little low-end torque and a completely wrong set of gears. So, given that the GC (about 190HP?) and Accord have comparable HP ratings, they are designed to do completely different things.

Next up, consider gas mileage. I'm using the Accord VS GC example again because it is more black VS white. The car is aerodynamic whereas your GC is like driving a barn through a headwind. The car is designed for high-RPM shifting, quick power transfer to the wheels for a fast take-off, and a smooth, light ride. The GC is designed to pull my house off the foundation, tear the pavement to shreds upon take-off, and is unsmooth (good word, eh?) enough to burp a child. Similar HP but completely different purpose. Also on the topic of gas mileage, consider the engine design. The GC engine is based on an old design which is less concerned with conservation of fuel and more concerned with "gimme lotsa power right-bloody-now and turn it into low-end torque!!" The Accord engine is based on "must be able to post 35mpg on the sticker to sell the car quickly" and only delivers the extra fuel when you stomp on the gas. Not to mention, (awaits argument from Bill), those Jap engines are extremely efficient when it comes to injection.

Third thing, consider my poor 4cyl rust-bucket, driven-to-hell-and-back '85 CJ7. I doubt that thing has any more than about 60HP now-a-days but when my buddy's '91 YJ was up to the fenders in mud, I had absolutely no problem pulling him out. For comparison-sake, I'd challenge any Infinity driver out there to a 30 foot long X 1 foot deep mud bog and despite having 200HP, 2 extra cylinders, and an extra litre of displacement, I would still put my $ on my old CJ. Why? Cuz my little baby is designed to turn that 60HP into "plow-power" and the Infinity is designed to carry Mrs.Anderson and her 4 kids to the grocery store.

As for technical info ...best bet is to just look it up on google. A lot of high performance sites will have lengthy technical data, comparisons, and diagrams. As a quick answer to your question though, I wouldn't call it "better" engineering or technology. It *is* newer and more efficient ...but it's just a "different" design for a different purpose. I can't say I know a person who bought a Jeep because they wanted good MPG. I'm usually happy with anything over 8mpg ;p One day I'm gonna do the engine/tranny/EFi swap. One day.

----- Original Message ----- From: "Brian Foster" Newsgroups: rec.autos.makers.jeep+willys Sent: Sunday, January 02, 2005 12:29 PM Subject: Re: New at this, trying to understand horse power

First off, I thought you were talking about the glorified Nissan Maxima - I don't know the Infinity line up that well. Getting back to the question, you can't expect a prehistoric pushrod engine to perform anywhere near that of a high compression DOHC 24 valve engine.

The 3.5 utilizes modern age technology to take advantage of;

Volumetric efficiancy - high flow tuned induction, polished intake, 4 valve configuration, DOHC, electronic variable valve timing etc. Thermal efficiancy - aluminum block, intake and heads, high compression etc.

Is it any wonder why the IRL used them? Mass produced, affordable race engines. You won't see too many 4.0's racing except of course for JeepSpeed where they need cast iron to keep the front end on the ground!

-Brian

Thanks for the insight. So the infinity uses "newer" technology if I understand you right?

The other responses almost all dealt with low RPM tourque in the old fashioned Jeep Engine VS the newer design infinity power plant. The lower end tourque is preferable with a Jeep type vehicle than the additional HP at higher RPM?

Perhaps another stupid question, but couldn't gearing (transmission) take advantage of the higher HP at higher RPM without sacrificing tourque?

BTW did I notice that the 05 GC has a different engine with less displacement than before? Something like 3.5 or 3.7 to the old 4.0.

I like my Jeep but I also like the looks (and specs) on the Infinity FX. I don't do any offroading with my jeep. The Infinity looks like a brute road handling machine. 20 inch tires and 280 hp is pretty impressive. The pricetag is in the mid to high 30s and you can buy a lot of Jeep (or a Jeep & a boat) for that kinda $$.

Absolutely. The 4.0 design is a cast iron push rod engine that dates back several decades. It's seen improvements over the years with fuel injection and computer controls but the basic design is prehistoric. There are so many wear areas (timing chain, lifters, pushrods, rockers) that the DOHC (dual overhead cam) design eliminates (or reduces in the case of the timing chain).

It depends what the engine is designed for. In the most basic way of thinking, lower RPM produces more torque to initiate movement - higher RPM is where horsepower is calculated. This statement is not completely accurate but it might help you a bit. Think of an 18 wheeler. It uses a 12-14 litre diesel engine that might put out 400 hp at 1500 rpm. That same engine will also produce 1000+ ftlb torque at 1100 rpm. Now lets put a 3.0 litre 900 hp F1 engine in that truck... rev it up to 17000 rpm and dump the clutch... hey, where did the clutch go?

Now, to make matters even more confusing. Torque is a twisting force measureable by a dynomometer. Horsepower is a calculation derived from torque (RPMxTORQUE/5252). To base engine performance strictly on horsepower, you have to consider it's ability to create RPM. How does this apply to the

The 4.0 with a larger displacement has to push heavier pistons up and down, turn a hug crankshaft that's proably a foot longer than the V6 counterpart which in turn drives a lunky timing chain to spin a massive camshaft. Wow, lot of work so far but it's okay, the 4.0 has the torque to do it. Now, the cam shaft converts the rotery motion back into reciprical motion and has to push those 12 heavy lifters up and down all day. The lifters in turn push the pushrods up to the rockers which pivot and push the valve down into the combustion chamber.

The advantage with the 3.5 is; Smaller pistons, smaller crankshaft, rubber timing belt vs. steel timing chain, no lifters, no pushrods, no rockers, 2 small camshafts, lighter valves. Every moving part in the valvetrain absorbs energy. The 3.5 has twice as many valves but they are much lighter than the 4.0 valves and are able to move quicker. A major restiction on a 2 valve engine is the valves floating (not returning to their seats fast enough). The way to avoid this is with a heavier valve spring. The trouble with a heavier valve spring is that it takes more energy to open the valve.

Absolutly... but.... when you play with ratios you either get better take off or better top speed, not both. You may have noticed that most new vehicles these days are equipped with 5,6 and 7-speed manuals or 4 and 5 speed automatics. Gone are the days of the 2-speed powerglide, 3 speed autos, 3,4 speed manuals. Like a truck (9-18 speed transmissions), the newer transmissions are able to better keep the engine in its peak operating rpm range. With less gears, you have to wind it out beyond the engines peak hp range or risk shifting back in well below the engines peak torque range. Theorhetically, your best fuel consumption will occur if you shift out at your engines peak hp range and back in at peak torqure range. RPM above or below that window is wasting fuel.

It's about time! However, there is nothing wrong with the 4.0 if you can deal with it's fuel consumption... they last forever.

If you're not off-roading then the FX line is a pretty cool way to go. Personally, I don't think I would want a GC for off-roading anyway... I'd rather have an old Cherokee or Wrangler for the dirt and a 300C for the ashphalt.

I hope I haven't further confused you,

-Brian

Many thanks!!!!

Very well described!

Hey Bill, it didn't take too long to offend you this year! lol The OP was asking how/why a 3.5 could have more hp than the 4.0. Fact is that hp ratings are derived from torque and rpm. If you can build a small engine that spins really fast, you can support a claim for higher horsepower.... like a 3L F1 engine putting out 900 hp at 16000 rpm. Don't worry, I'm still a big fan of 400-500 cu-in motors, I was just answering his question. There's no replacement for displacment.

-Brian

That is about right for a F1 engine although, I think the Ferrari one can rev up to around 18,000 rpm.

Dave Milne, Scotland '91 Grand Wagoneer, '99 TJ

Busy bee ? Now, I *know* you have never heard a F1 engine. They don't sound the same live and up close as they do on the telly.

FWIW, on a wet runway, Schumachers 2003 Ferrari did:

However, unlike Indy cars, F1 cars can go round more than one "hand" corner, and generate over 2 ton of downforce to enable them to do it (3 times their mass). Therefore, the above times don't show how quickly they can go (since that amount of downforce isn't required in a straight line).

Dave Milne, Scotland '91 Grand Wagoneer, '99 TJ