advice for a v8 engine

Dear Jeepsters,

i am thinking to upgrade my 4.0l straight six to a v8.
i run a Yj 92 model. Main use for road.Secondary light offroad and overland.

what is the best i can go for?

suggestions welcome.

Thanks  

So far my 350 has been great. If you go that direction just make sure gears are set up right, or dont plan on going over 60, if you want to be able to afford to drive it.I came from driving imports so I love being able to put the power down when I want it.  

If you go with a V8 you'll have to upgrade your axles or you'll trash um the first time you mash on it a little to hard. You'll have to probably swap in Dana 44s or something similar. If it was my jeep id keep the 242ci. (4.0) and get a header,new exhaust with high flow muffler,  high spark electronic distributor and a cold air intake. You should be able to get around 50hp. and 50 ft.lbs of torque increase, which is a very noticeable amount in power. And you'll get better millage too.  
Get a real jeep! (pre '75)

I'm very interested in any facts that you have about needing new axles for a V8 swap or a 50 hp and 50 ft. lbs. of torque increase for the 4.0L with a cold air intake and exhaust changes.  

Well i forgot to mention taking off and gutting the catalytic converter which ive heard will give you 5-10hp and about the same torque. An ive read reports that with magnaflow compleat exaust system you can get 15hp and 12ft.lbs of torque. The Hei electronic dist. will give you gains of 8hp. and 5ft.lbs of torque. The cold air intake will give you 15hp and 10ft.lbs of torque. I did however mistype the estimated torque increase. I ment 35ft.lbs. and added up the HP increase with all those mods is 48 and i did say around 50. Now to the axle swap thing, a 4.0 on a good day will probubly get about 160hp to the ground where as a healthy 350 will probubly get around 240 to the ground according to how its built. So thats 80hp difference not to mention the extra torque. Perhaps you have a lighter foot than i do but i just dont think that a 30 and 35 will withstand that much power.  
Get a real jeep! (pre '75)

Next time you read some advertisement for power building bolt-ons, be careful about what the ad is trying to make you think vs what the ad really says.

Ads like to say UPTO 15 hp increase. If you only got a 5 hp increase, is it a true statement.

Even if the claims were true, you can't just add them all up. It doesn't work that way.

So, click here for some facts and data for bolt-on performance for the 4.0L.

And click hear for some realistic expectations written by a company that sells all the bolt-on stuff.

If you want to understand about airflow through a tube, and how the tube needs to be "tuned", and just being bigger is not necessarily better, click here.

The following is from Novak Conversions, which has nearly 40 years of Jeep engine conversion experience...

Axles
Many people mistakenly think that a more powerful engine demands stronger-than-stock axles. This is not necessarily the case. The factory Dana 35 and Dana 44 rear axles (the latter usually being found on towing package option Jeeps) can withstand very ambitious engines. Such is the case for the front Dana 30 as well. Whether your converted Jeep needs stronger axles is more a question of how you use them, and usually in terms of off-road considerations more than on-road use.  

With a modern fuel injected V8, you can get approx the same mpg you now get from your inline 6. It won't matter if your getting 275hp or 325hp, because the hp increase over the inline 6 will not leave you at a loss for power. Axels break with 4cyl engines also, but it not something you have to change. I run a 5.3l v8 & a stock Dana 35 with a detroit tru trac. It's been intact for a year now, with no issues. Driver, and throttle control play the biggest part in the axel game. The best part about a swap such as your considering, is how much driveablity a v8 gives a jeep. On the road, you can cruise at 75 up & down the hills without moving your foot. Wheeling, the power needed for the situation is there at idle, or at the floor.
Down side of a V8 in a jeep, to do it right, it expensive. With the items you must change,(radaitor, motor mounts, exhaust, Gauges, Adaptors, Drive shafts, ect..) You can pretty much figure on using about $7500.00 if you do it yourself.  
ohhhh!! sooo!!! AWESOME

Another fact that you guys failed to consider is the amount of wear on each particular axle. A very worn axle will probubly not withstand a V8 for very long. And yes the most important factors are driving style and wheeling conditions, i.e terrain.  
Get a real jeep! (pre '75)

ftgiles:
Next time you read some advertisement for power building bolt-ons, be careful about what the ad is trying to make you think vs what the ad really says.

Ads like to say UPTO 15 hp increase. If you only got a 5 hp increase, is it a true statement.

Even if the claims were true, you can't just add them all up. It doesn't work that way.

So, click here for some facts and data for bolt-on performance for the 4.0L.

And click hear for some realistic expectations written by a company that sells all the bolt-on stuff.

If you want to understand about airflow through a tube, and how the tube needs to be "tuned", and just being bigger is not necessarily better, click here.

The following is from Novak Conversions, which has nearly 40 years of Jeep engine conversion experience...

Axles
Many people mistakenly think that a more powerful engine demands stronger-than-stock axles. This is not necessarily the case. The factory Dana 35 and Dana 44 rear axles (the latter usually being found on towing package option Jeeps) can withstand very ambitious engines. Such is the case for the front Dana 30 as well. Whether your converted Jeep needs stronger axles is more a question of how you use them, and usually in terms of off-road considerations more than on-road use.

And when i said "Ive read reports" I read about people who actually tested the products not just what the manufacturer said the increase would be. Im just as skeptical as the next guy about estimated power increases. So don't think what i said is unproven or an estimation.  
Get a real jeep! (pre '75)

From JP's 10 proven power plays article:

Power Play Combo:
Performance Distributors 4.0l Firepower Ignition Kit, Pn 4.0 Kit
Performance Distributors Harness Adapter, Pn 1728-Ah
K&N Fuel Injection Performance Kit, Pn 57-1518
Gibson Stainless Steel Header, Pn Gp400s
Gibson After-Cat Exhaust, Pn 617200
Rubicon Express 62mm Throttle Body, Pn Re1062
Hypertec PowerProgrammer III

1999 XJ sport
4.0L
aw4 auto transmission
4.88 gears
33-inch tires

Power Gains:
stock: 133 hp, 176 lb-ft*
Modified: 152 hp, 200 lb-ft*
*Note - numbers taken at rear tires


What's missing from the above bolt-ons that would yeild another 31 hp?

Most of these gains were accomplished with the programmer, of which you don't mention in your list of things that will gain a combined 50 hp.  

The cold air kit (15hp) . And the removal, gutting and reinstallation of the catalytic converter as i said 10hp. Thats 25 plus JPs figure of 19 and equals 44hp overall increase which is only 6hp away from my "around 50hp" estimation. So ill leave it at that.  
Get a real jeep! (pre '75)

Oh about the programmer, I did forget to mention that. But one more thing, I read a different test with a YJ 4.0 and different brands of upgrades so theres really no comparison.  
Get a real jeep! (pre '75)

The K&N Fuel Injection Performance Kit, Pn 57-1518 is the cold air intake.

Post up the facts so others who read this thread are not misled!  

Very well. The bottom line is that every engine in every jeep is different. You could get 5 consecutive sequential serial numbered 4.0 engines and put the exact upgrades on them and get completely different numbers from them. I read a particular person that put certain up grades on his jeep and got the following numbers out of it. 48hp. and 36ft.lbs of torque increase. Id link you the web page but recently the website can not be accessed for some reason. So what I said, I don't personally think is a inaccurate estimation. But obviously you disagree.  
Get a real jeep! (pre '75)

Don't forget the change in the torque curve when you add all that stuff. It may end up in an undesireable curve depending on which way you are using your Jeep. It may be great at the high end but most of the time you will loose low end.