benefit of 4.0L strokers

[streetpirate]

could it be air drag from rust holes? my renix got 19-22 mixed/mostly highway. but whenever i wasnt cruising you can bet i drove the piss out of it. still got 19. now its like 16-17, and im getting massive blowby. tim efor a stroker.

 

[Dr. Dyno]

The only downside is that I believe more power is needed. Quite frankly, I'd love to see a rig with 35" tires on a chassis dyno. I bet there would be about 170 HP at the rear wheels of most strokers.

Maybe for those Renix strokered Jeeps with 35" tires. Forget about MrShoeboy's 168rwhp. That was on a Mustang dyno (reads lower than a Dynojet) and he has 32" tires.
According to the SmokemUp.com HP calculator based on 1/8 mile trap speed (the most accurate HP calculator I've found), mine should be putting down 220rwhp (input 3622lb weight including me, 1/8 trap speed 76.5mph). If I input the numbers from 10 years ago when my XJ was bone stock (3692lb, 1/8 trap 68.5), the number is 161rwhp.

 

[CRASH]

The difference, on a number of dynos, between a Renix and an HO stroker is about 15 hp.

Large tires and big axles really sap power. On the order of 30-35%, in my experience.

A bone stock XJ weighs about 3100 pounds, so I take it you weigh 592 pounds?

 

[Dr. Dyno]

A bone stock XJ weighs about 3100 pounds, so I take it you weigh 592 pounds?

A bone stock base 2.5 XJ with 2WD might weigh 3100lb but definitely not mine. Mine weighed 3525lb bone stock (1/2 tank of gas) and I weigh 167lb. Don't believe it? Here's why:

4.0 engine = ~150lb heavier than 2.5
4WD = adds a further ~140lb
UpCountry package = adds another ~80lb
Laredo trim = adds more weight over base trim

The Limited model with auto tranny, NP242 (mine's a 231), and electric leather seats is even heavier (just over 3600lb stock).
Anyway, whatever you think the real weight of my Jeep might be doesn't really matter. It's still 70lb lighter than stock (~2%) and the change in 1/8 mile trap speed indicates a ~39% increase in HP/weight ratio over stock, so my stroker is putting out ~37% more HP than stock.

 

[CRASH]

And I quote from the 1994 Jeep Brochure:

Curb Weights:

2 door, 2wd: 2808
4 door, 2wd: 2850
2 door, 4wd: 2985
4 door, 4wd: 3028

Mass/acceleration/power equations are readily available on the net, you should check them out. Hint: Mass plays a much more important role in acceleration than HP. So knowing your mass is quite important.

 

[Dr. Dyno]

Mass/acceleration/power equations are readily available on the net, you should check them out. Hint: Mass plays a much more important role in acceleration than HP. So knowing your mass is quite important.

Thanks. I did physics at school so I already know about F=ma. Since a=F/m, acceleration is directly proportional to rwhp/weight. Regardless of what my vehicle weight is, the rwhp/weight ratio is still 134rwhp/tonne and my stroker still makes ~37% more HP than stock. Since the combined weight of my Jeep and myself is 3622lb, that's 1.643 tonnes so that equals 220rwhp.
If it makes you happy, input 3028lb + 167lb for myself instead (combined weight 3195lb or 1.449 tonnes). That'll yield 194rwhp but it'll be wrong. I've had my Jeep weighed on two different scales at vehicle testing stations and I doubt both of them were wrong because they came within 10kg of each other.
If you find a 4WD 4-door 4.0 XJ Laredo with the UpCountry package that weighs anywhere near 3028lb with 1/2 a tank of gas and all fluids added, let me know. The weights that you quoted are for the 2.5 model in base trim and they're dry weights (no gas, no fluids). Add 120lb for a 1/2 tank of gas & fluids.

 

[60thAnivrsryXJ]

Are you guys drag racing your jeeps or somthing, seriously why do you give a fawk about horsepower. If I wanted to drive a suv that was powerful I'd borrow my mom's trailblazer (275hp inline 6). I had my jeep on a chassis dyno last week and the 135rwhp and 195 lb ft of torque it measured satisfies me just fine. I would rather spend my money on a more things to make my jeep hold up on off road trips than stroking the engine. That's just my opinion and I know I opened up a can of worms but I had to say it.

 

[krakhedd]

You call that fast?

I smoke those 4.2s all day long. They weigh c.5000-5500 lbs.

My friend who has one readily admits my Jeep accelerates far more quickly, and goes faster. His is a 2005, just got it about 5 months ago.

I think my Jeep is pretty quick, but I'd still like the extra 50-75RWHP I anticipate making out of any stroker I build. I have a line on a built 360 that I'm considering putting in at this point, though. I don't *NEED* that extra power, but I'd definitely *LIKE* having it. Kinda like do you *NEED* a supermodel for a girlfriend or do you just *WANT* one?

Remember, a stock, late-model XJ like mine puts out c.190HP @ the flywheel, which translates to around 150-160RWHP. The parasitic losses remain relatively the same building a stroker, so all the HP you gain is free. It doesn't take any more power to move the vehicle the same speed, but you have the option of moving it MUCH more quickly at the discretion of your right foot.

Fast? Trailblazer? You should be shot for using those words in the same sentence.

 

[60thAnivrsryXJ]

Fast? Trailblazer? You should be shot for using those words in the same sentence.

If you'll reread my post you will see the word was powerful not fast. I never called it fast. The difference between powerful and fast is where the weight thing comes in. The trailblazer was just an example and I am not trying to praise it by any means, thats why I said "If I wanted to I'd borrow..." But the fact is that I don't want to. I'm fine with a 190 hp motor that puts 135 to the ground.

 

[snow drifter]

I would definatly like to have a stroker! One thing that kills my power is ELEVATION! I'm at 10,000 ft. Sorry off topic

 

[53guy]

One thing to think about is that power can equate to efficency (given a lighter foot). Think about pulling a trailer full of crap by youself...sucks, takes a while, your back hurts, can't go very fast, get tired real quick...Now think of that same load but with 5 of your friends helping you. That load is moved that much faster, that much easier, less wear and tear on yourself and the others, and overall, everyone isn't as tired in the end....So think of that in a jeep. Add more power (torque and hp) and you will ease the strain on the motor, requiring less effort to pull the same weight and move it the same speed. Now will you get the same gas mileage as before? NO. You may get better, you may get worse. It all depends on your driving habits. If you get all excited about the "New" power your jeep has, you'll burn through gas like its cool, but if you ease off the gas, you'll most likely get better mileage. just my .02.

 

[WobblesXJ]

You guys talk about mass but then show numbers in lbs. What a shame.








(stir stir stir)

 

[SCW]

You guys talk about mass but then show numbers in lbs. What a shame.








(stir stir stir)

LOL

 

[theksmith]

18-19 MPG highway with my 4.6, 65k on it and no signs of slowing or losing fluids. Cools just like the 4.0, runs at @ 195-205 regardless of outside temp. If you are doing a rebuild anyways, I really cannot think of a good reason not to stroke it while you're in there...

Do you have to run a higher octane gas on a 4.6/4.7 stroker? Or does it depend on how you build it? If so, with today's gas prices, that's a minus.

 

[Dr. Dyno]

My stroker runs great on the cheapest gas available locally (91 octane). I would have to try really hard to make it ping (lug it at low revs in 5th gear on a steepish hill on a hot day) so I'm sure it would still run fine on 89 octane.
As far as gas mileage goes, on the highway I'm getting the same mpg from my stroker as I was from my old 4.0, but in the city the stroker is slightly thirstier.
My driving habits haven't really changed since I've had the stroker in my XJ but the performance is effortless and I can hang onto a higher gear in the city more of the time. I seldom need to rev it beyond 2500rpm, it's that effortless, but I do rev it occasionally to 5150 just to hear the engine sing.
Did I need the extra performance of the stroker over my old 4.0? No.
Do I love having that extra performance? Absolutely yes.
Would I recommend a stroker? Definitely.

 

[CRASH]

That's the beuty of a Renix stroker, the knock sensor takes care of any knocking issues. I run 9.5 to 1 compression, and run 87 octane all the time with no pinging. Since I live at 3,000 feet and wheel much higher I shouldn't have any detonation issues any way. Occasionally I do long road trips at sea level with no issues either.

 

[CRASH]

Are you guys drag racing your jeeps or somthing, seriously why do you give a fawk about horsepower. If I wanted to drive a suv that was powerful I'd borrow my mom's trailblazer (275hp inline 6). I had my jeep on a chassis dyno last week and the 135rwhp and 195 lb ft of torque it measured satisfies me just fine. I would rather spend my money on a more things to make my jeep hold up on off road trips than stroking the engine. That's just my opinion and I know I opened up a can of worms but I had to say it.

When all other mods are done, what do you suggest I mod?

 

[xj-grin]

That's the beuty of a Renix stroker, the knock sensor takes care of any knocking issues. I run 9.5 to 1 compression, and run 87 octane all the time with no pinging. Since I live at 3,000 feet and wheel much higher I shouldn't have any detonation issues any way. Occasionally I do long road trips at sea level with no issues either.

Ditto that, no pinging with 87 all the time. I actually live above 5000 feet, and occasionally (i.e. $3.00/gallon) run 85 octane without ping, although I stick to 87 darn near all the time...

 

[Highmiles]

And I quote from the 1994 Jeep Brochure:

Curb Weights:

2 door, 2wd: 2808
4 door, 2wd: 2850
2 door, 4wd: 2985
4 door, 4wd: 3028

If Jeep brochures are anything like the advertised weights the sport bike manufacturers use, those curb weights are way light. Those guys always weigh their rigs dry - no oil, gas, dry (or no) battery, etc. The sport bike guys will actually drain the oil from the shock and forks just to advertise the lightest weight and greatest HP per lb.

 

[gcurtis]

I know in automotive that many mfg's do exactly what was mentioned above, plus the stripped down packages to up fuel economy base numbers (with help of curb weights) for CAFE (smog related) standards. Figure those numbers to be the lowest of the low, dry, without battery and with the most stripped down of packages.