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Discussion Starter #1
alright so iv had my 89 yj for for three years now and like most people after a couple years i now have the urge to obtain more power and be able to once again be able to travel at highway speeds with my oversized tires.
so heres what i got so far..
1989 yj with the 2.5 low output
4 in suspension lift
1.25 shackle lift
33x12.5x15 mickey thompson baja claws on 15 inch mickey thompson sidebiters

so i began to think about all the engine possibilities and first thought about the usual chevy swap but then found someone with a 74 amc 304 with the matching 3 speed manual t15 tranny. i like the idea of using this engine because as far as i know it is the only factory offered v8 ever available in a jeep wrangler with the earlier year being more powerful. however i am by far no jeep expert.

i planned to keep the 304 mostly stock with the only mods being a 4 barrel/new ignition/milder cam ect but then found a supercharger kit available for it and fell in love with the idea of having a "sleeper" and opening the hood to shock people with my amc blue painted beast.

now i know everyones first reaction will be to just go get a 360 or 401....
and i am not interested in that so with that being said i would like to start getting some answers to my main questions before i begin to get the machine work done and continue planning this thing out.

first of when building the engine is there anything specific i need done knowing that eventually a supercharger will be equipped?

what kind of power can i honestly expect out of such a engine?

will i be fine just replacing the reared with a maybe built ford 9 inch?

what gear ratio should i be looking at considering this is and still will be my dd?

i have only read other v8 swap stories and have no experience with any myself so any help will be appreciated and the questions will increase as the build developes

once i figure out how i post pictures i will
thanks in advance
 

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As for the rebuild, forged pistons would be a good idea, along w/ improved ignition & a radiator upgrade....at minimum.

A ford 8.8 is a much cheaper swap than a standard 9" & will put up w/ 300hp if you don't get crazy. 300 dependable HP w/ good low end TQ numbers should be easy w/ a small blower on a 304.

The main problem w/ using that tranny is that the outputs are on the opposite sides as your YJ....requiring a new front axle/drriveshafts, at least.

You might want to think about a different tranny/adapter to gain a few gears, simplify the swap and be able to use the readily available 4:10 final ratio found in 4-banger YJs & Explorer 8.8 rears.

To be nit-picky, a V8 never came stock in a "Wrangler"....they were in CJ Jeeps before the Wrangler name was used.

I love to see AMC motors in Jeeps....props on that. & Good Luck.
 

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Im more of a motor head, but of such that thinks if you cannot do it with the easy parts then it doesnt need to be done. :)

That being said, 300 hp should not be too hard to get to, good pistons like what was mentioned, have the rods checked cleaned, and balance the parts. To get to 300HP you will need a hot cam (that will require a little research, but I suspect something like a crane 272 would be close). You would need a good flowing intake and heads, a properly tuned carb and exhaust system. 300 hp would like a good set of headers, with a Y pipe crossover and probably a 2.25 or 2.5 inch pipes out back. If you Y into a 3" exhaust it might help you with the torque curve.

I think that would be pushing 300 if not more, and then having the blower would be a bonus.

But, here is the thing; you need to decide what you want to do. The 300hp could be attained with the right machine work and some decent parts; if you go blower you should replace your rods, pistons, and possibly crank with a set that can handle that. You will also need to keep in mind the kind of compression ratio you would need to obtain good hp ratings with a blower. For example, if you build the motor to maximise tq and HP, you might loose the ability to run a blower without getting special fuel, read significantly higher octane. A well built motor can push 10:1 compression and run on pump gas, like 93 octane rated with little problems, you add a blower on that comp ratio and its not easy to find octane that high. Depending on your blower, you would need about 8.5:1, but that changes things and will probably lower your static HP until the blower kicks in.

And, another thing to think about, if you are building it like this for that kind of power, you are basically building a racing motor. You will need to keep the revs up to make use of it and that is where your gas mileage, and low end get funny. You may need to really evaluate what you want for your Jeep and what you realistically will be doing with it.

I also agree think about stronger axles.

Wow, now that I write that out, there is a bit to building up a performance motor especially if you want it reliable, and streetable.
 

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The type & size of the blower makes a huge difference, as well.

The centrifugal type favored by the go-fast 5.0 crowd requires RPM to make max power, much like a big turbo.

The smaller ones like the baby roots/whipple type can give a 100HP jump at modest RPMs w/ a mildly built motor and be quite drivable by keeping max power under 5500rpm.

Big HP numbers sound cool, but in reality they are expensive to actually make & use on a regular basis. Be realistic about what you need, unless this is a big budget toy.

Our jeeps are pretty light, and modest HP/TQ numbers go a long way in them. I've driven a buddy's TPI Chevy 350 rig w/ about 275 horses.....and that thing ROCKS! Gets better MPG on the highway than my old 4.2, as well.
 

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Agreed, I would personally build the motor for decent numbers with good parts. 300 streetable HP will beat 500 HP that you can only get into on the track. A YJ is not a race car, and with their low weight, 300 will feel VERY strong.

I would go for what I mentioned earlier, build a strong lower end with good pistons, rods and crank, find some good flowing heads and intake while matching the carb to the build. A decent cam with a power band of 1500-2500/3000 rpm, keep compression reasonable up to 9.5 or so, build the exhaust to maximize TQ numbers, and that will be a very impressive motor. Easy, much cheaper, and still very impressive.
 

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When I was doing a 360 for a CJ, I found this site for neat stuff. They have hot cams for your 304.

American Performance Products

Heres another excellent source of hipo AMC stuff.

Bulltear.com - Home

As mentioned, your going to make your YJ a rocket ship so you will need a lot of extra build up to handle the power. A mildly built free breathing 304 will generate great power without breaking the bank.

Keep us posted!
 

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Discussion Starter #10
as of now i am just trying to get quotes on cleaning the block heads and crank and i understand that 300 horsepower would be plenty of power but i was just thinking how awesome it would be to have a supercharged 304 because I'm sure i wouldn't probably run across another one like it. the supercharger i would be using would be a vortech supercharger not a blower because bulltear already has brackets made for using the vortechs. i realize that by doing this i would be spending a bigger chunk of money and it will probably take twice as long but i am just in love with having this engine setup and feel like it will all be worth it in the end. so I'm for sure gonna get forged pistons i haven't figured the cam out yet, as far as machine work i don't think i am in need of changing the original dimensions of the engine for the supercharger. i also realized now that it would probably be safer to just get 3/4 ton or 1 ton axles. i should be getting the machine work done here in the next few weeks so il keep you guys posted.
 

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I love these build threads, I get to see what actually goes into building one of these high HP wranglers.I hope you keep us updated as you go.Right now its a dream for me, but you have to start somewhere.Good luck with the build!!
 

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Interesting build, I hope you follow through. You best bet is to talk to the manufacturer of the supercharger for recommendations internal upgrades. I am certain they would have a recommended build list.

The supercharger is a great choice for an off road vehicle. While a turbo has lag and makes power in the upper RPM, the supercharger begins making power right off idle. This means a good increase in low RPM torque and a much flatter torque curve.

FWIW a blower and supercharger are the same thing. Although some people use the term blower to mean a certain type of supercharger.

Check in with the supercharger manufacturer for build specs.
 

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if you want it to last then leave the blower off . 304 with a 4 barrel and headers makes a jeep pretty peppy..forged pistons are going to slap around when cold
 

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Discussion Starter #15
i plan on having to contact the company for a lot of parts because i am a beginner when it comes to all of this thats why I'm trying to get a plan together now and build a parts list while i save up the money for the engine work
 

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and as far as the engine lasting? why should i have to worry about the engine lasting with the supercharger? as i said I'm a beginner and have no experience with superchargers at all. but was under the impression that if i build the engine specifically for using the supercharger it should be fine. please correct me if i am wrong.
 

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and as far as the engine lasting? why should i have to worry about the engine lasting with the supercharger? as i said I'm a beginner and have no experience with superchargers at all. but was under the impression that if i build the engine specifically for using the supercharger it should be fine. please correct me if i am wrong.
not trying to talk you out of doing this at all.I loved hotrods in my younger days.But,anytime you build more power,it puts more pressure on everything and creates more heat.forged pistons expand a lot as they heat up.because of that they are a sloppy fit when they are cold,which causes piston slap and wear
 

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x2 on what harley says... much like anything you do in a build (hot rods, Jeeps, etc) any time you build one system bigger and more powerful you have to compensate the others or you create weak points.
 

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and as far as the engine lasting? why should i have to worry about the engine lasting with the supercharger? as i said I'm a beginner and have no experience with superchargers at all. but was under the impression that if i build the engine specifically for using the supercharger it should be fine. please correct me if i am wrong.
To simplify, your engine is like a big air pump, the supercharger forces more air into the engine. This raises the compression in the cylinders which puts more pressure on the entire rotating assembly ( pistons, rods, crank ). A proper build will compensate for this extra stress with proper parts and assembly ( including a fully balanced rotating assembly). If your boast numbers will be low you can safely run hypereutectic pistons instead of forged.

A supercharged engine running low boast will give you a nice increase in power ( somewhere in the 50 hp range is likely) while not putting immense stress on your components.
 
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