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Discussion Starter · #1 ·
my '89 4.2 only has 51,000 miles on it. I would like more power. Here's the situation: I have an '89 Firebird with the chevy 305 and TBI fuel injection. It has 147,000 miles on it I was thinking rebuilding it and putting it in the '89 YJ. Think the money would be better spent putting the 5.0 in rather than trying to squeeze all the power out of the 4.2 by maybe putting a 4.0 H.O. head on it? how would the 4.0. H.O. comapre to the 5.0 chevy TBI?
Tas
'89 YJ 4.2L, 5-speed, Flowmaster, Euro taillights.....

 
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from what i hear the tpi is a sweet motor but it carries a complex wiring harness, well you should relize that u already own the motor, plus i would recomend using a chevy tranny and not what your jeep has in it know because it will not like the 350 and AA wants almost 600 bucks for any adapter than even if u use a chevy tranny u have to buy an adapter for the tranny to tcasse unless u use a chevy one, One thing to consider is what do think of your motor know and what would u like out of a motor?


 

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yes what do you want out of your engine? a 4.0 head on a 258, is great.. especially if you get the fuel injection with it. 305? mmm.. you will need a tranny and transfer case then.. and you have to rebuild it. and its still only a 305. my friend has a new 305 in his, its stock but new, and my old 258 had more balls than that has. i would stay with the 258, put a carb, intake and headers on it, and if you think its still not up to it. get the head done. will work awesome, and its only got 51k on it.. mine had 170k when i sold it, and was still strong. but i had the head done, 500 holley 2 barrel, offenhauser intake, and headers.. with dual exhaust.
like i said, it kicked the hell out of that 305 my friend has.

survival is instinct, but living takes guts
 

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one other thought, those little add ons.. you can do one or two at a time and still drive.. you dont need them all at once, vice putting the 305 in you will need tranny and transfer case to drive it.. just a thought..

survival is instinct, but living takes guts
 
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jeepgod
i would say that the 305 has a slight advantage! where did the jeep kick @ss over the 305? and i would suspect that the 258 had better gears that matched the tires better than the buy with the 305, he probbably did not have the money after doing a v8 swap right they are expansive but it is up to the owner to decide if it is a worhty upgrade, gears will make a vehilcle that much better! not only that if u keep the 258 get a hei setup on it!!

 

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well he has gears.. and tires.. also running a t-18.. that 258 just had more umph... that might be what most call torque.. hey.. like i said to each his own.. was just giving you my thoughts.. and i just never liked the 305 much.. sorry.. am biased..lol. . no i got rid of the 258, i found a 401..

survival is instinct, but living takes guts
 

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Discussion Starter · #7 ·
the reason I'm considering the 305 is:
1. I have it
2. the sweet V8 exaust note
3. I know camaro/firebird guys that have them up to 240hp wihtout taking off the valvecovers by:
a. intake mods
b. full exaust system
c. ignition mods
4. much better gas milage than a 350
5. I leery of spending money on performance mods on the 4.2 since it is so weak now and hard to believe there could be a world of difference with a fixed up one.
6. most mods for the 4.2 won't be smog legal.(I'm in Los Angeles)

Reason for not putting in the 305:
1. the 4.2 will most likely always get better gas milage.
2. the 4.0. head might make a world of difference
3. 4.0 might be the best choice
reasons for putting in the 4.0
1. for the price of the EFI conversion I could find a whole used engine for the same price.

Would it be a good idea to use the 700-R4 with the 305? is auto better for offroading?
thanks
Tas
'89 yj 4.2L, ax-15, Flowmaster, Euro taillights


 
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I like my 88 YJ with an AMC 401 in it... It really gives you that UMPH!!!
Do what you want... Your cash your truck. Most people in this town
think I'm just a crazy kid out to kill myself in the jeep. Ok so they are
somewhat right... But anyways, I was talked and griped at up one side
and down the other for the v8 and it not being a chevy. All you gotta do
is sit down look at what you got, how much money you got and let things
fall into place. I did mine this way and am only in the hole $1000 but I did
end up with a new tranny and a HD D44 and D60 in the deal too. Do the
math and you will see that I came out ahead... Its late and im rambling...
To Each His Own... Whatever Floats Your Boat..and my favorite...
Different Strokes for Different Folks.
Later
Dustin


JeepChild
 

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living in LA.. used to live there myself. i would still highly consider keeping the 258, mine sounded awesome. .and remember you will need a tranny, and transfer case.. possibly driveshafts.. depends on how you mount it in. you will need a radiator, or some fancy hoses.. since the output on the engine is on the opposite side.. depends on the motor there i think.. i know friends that run amc v'8's with 258 radiators just fine.. but trust me a 258 can out perform that 305, but i am not sure on the emission laws there. moved some 4 years ago. and i knew a guy that would inspect my jeep.. but like i said, and been said before.. think about the whole picture.. and its up to you on what you want to spend. good luck with it..


survival is instinct, but living takes guts
 

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One thing that you might want to think about is emissions. The 258 thing can use the existing feed back system and keep your YJ legal. If you go the small block in California, it might not be legal, you may want to check.

 

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Why not go with a AMC 304? They are cheap to find , they do cost a little more to rebuild , but I have had several and they can really
run. An AMC engine got that 305 beat. Remember that even the 400 engine used in 1978 Firebird only put out 180 HP.
Besides they bolt right in.

 
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I have a 258 and it blows 305's out of the water. There is so much torque, its amazing. What I have is a Lunati cam, pistons and crank, stock intake mainfold, .060 bored cylinders, ported and polished head, weber 38/38 carb, and Heddman dual exhaust. I would keep the 258 just because the v8 is such a pain. It is amazing what the right cam and some porting can do. It also helps to remove all of the emissions crap, but you will be shot for doing that in California.

 

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Discussion Starter · #13 ·
Thanks everybody for the replies.

For those that don't know about engine swaps in Cali: the engine has to be the same year of the car or newer with all emissions left in tact and from the same class. so no AMC engines and no v10s from 2500 dodges.

If I was keeping the 258 I was thinking about a polished 4.0 head, header, 2.5" mandral bent exaust, 3 chamber or delta flow Flowmaster, HEI or MSD blaster coil. I just got the stock carb rebuilt.
how much would a 4.0 H.O. head go for?
Tas


 

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Stroking that puppy is real easy. Just use a 4.2 crank and rods, and put them in the 4.0. Brings it up to about 4.5l. You can have the best of both worlds for the price of a rebuild.

 
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i do not think anyone is really considering this point if u do a v8 a swap and do not have enough money to put gears in your rig than, just skip the v8 and go with gears towards accomadating the size tire u are running, well if u do both i think u have one great combo but... i also think that a 258 or 4.0 is great geared i know so many people who do v8 and have power but they could be top dogs if they had gears, (gobs of power) and and the right tourqe curve! hmmm sound like a setup to me

 
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