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Unread 02-13-2012, 02:59 PM   #1
MegaCabMan
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Thinking about an Engine Build

I'm looking for some input.
First off... if you are thinking V8 then don't even post, I'm not going to do it.

Here are my criteria.
Keep the original block (1988 4.2L).
SUPER reliable, 100k mi engine
89 octane max.
$1500-2000 budget (closer to 1500)

Things I'd like:
Offy 4bbl manifold
Holley 600 cfm 4bbl


So here is the plan so far... A straight forward rebuild w/ 0.060 over pistons stock compression. (New rings, pistons, cam, timing set, oil pump, bearings (rod, crank and cam), cam, lifters, wrist pins, etc...)

I'm thinking about upgrading the intake to an offy and putting a Holley 600cfm W/ vac secondaries. Cost wise I think it will run about and extra $600 for new parts and I'm leaning this way over FI for the simplicity of it (I'm a big fan of the K.I.S.S theory). This will also eliminate the EGR valve, not that it is hooked up now anyway. Oh and I checked and acording to the CFM calculator I used @100 VE a 266CID (258 bored 0.060 over) engine running at a redline of 6500 RPM needs 502CFM. Why a 4bbl and not a 2bbl, you ask? a 4bbl is like running a small 2bbl for everyday driving, but when you need some extra power, you have another 2bbls that will open up.

I'm also thinking about headers but will stick with the stock manifold for now to save some $$.

The longterm vision for this jeep is to make it an over-lander so ease of repair is essential as is fuel economy but I still need enough power to run down the interstate at 80mph.

So here are my questions:
Will the advantages of a 4.0 HO head be enough to offset the cost, or should I just have the original head ported?

What cam should I go with? Like I said, the jeep will ultimately be an over-lander so I'm not going to be doing any mud racing or hard-core rock climbing. I have 3.55 gears, 32' tires, AC, power breaks and an auto trans and all are going to stay. It also needs to be able to run at 3000-3200 rpm for hours at a time for highway travel. Again reliability is paramount in this build.

If anybody has any input on the internal parts I'd like to hear it. You know stuff like those pistons suck or I had really good luck with that oil pump.

What else am I forgetting?

Thanks in advance for your input!

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Unread 02-14-2012, 07:45 AM   #2
jeepdaddy2000
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Quote:
So here is the plan so far... A straight forward rebuild w/ 0.060 over pistons stock compression. (New rings, pistons, cam, timing set, oil pump, bearings (rod, crank and cam), cam, lifters, wrist pins, etc...)
Too much. Boring should be done to true the cylinder walls, not increase displacement. Your not going to get enough cubes out of this to warrant the thin walls.

Quote:
I'm thinking about upgrading the intake to an offy and putting a Holley 600cfm W/ vac secondaries.
Too big. Large carbs are only good at extreme RPM's. A 390CFM will give you better performance through the powerband. You already did the calculations. Given your criteria of reliability, fuel economy, and daily driving parameters, too big is, well, too big.

Quote:
What cam should I go with? Like I said, the jeep will ultimately be an over-lander so I'm not going to be doing any mud racing or hard-core rock climbing. I have 3.55 gears, 32' tires, AC, power breaks and an auto trans and all are going to stay. It also needs to be able to run at 3000-3200 rpm for hours at a time for highway travel. Again reliability is paramount in this build.
First, I am a bit confused about your RPM's. Given a general OD trans with the stated gearing and tire size, your engine speed puts you up in the triple digits. I would rethink/calculate this. Be sure not to mix up a direct (1.0) drive ratio with an OD (.75??)one.
That being said, I'm pretty sure 2100 will give you a speed in the 75 MPH range. Again smaller is better. An RV cam grind will usually pull from the 1000K mark up past 3500RPM's. This is especially true since your planning on retaining the stock exhaust manifolds.

I am a firm believer in high volume oil pumps.
Are you doing the build yourself or having an engine builder do it for you?
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Unread 02-14-2012, 11:13 AM   #3
1SASjeepster
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If you go to Holley's web site, they have a carburetor selection guide. You just answer the questions and they show you the carburetor they recommend. I would decide what camshaft company you trust... hopefully one that is built here in the good old USA and contact them. Their customer service is usually top notch and they can steer you in the right direction...PLUS they can tell you if the camshaft you chose will require new valve springs and such.

Good luck.
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Unread 02-14-2012, 02:49 PM   #4
MegaCabMan
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Quote:
[Given a general OD trans with the stated gearing and tire size, your engine speed puts you up in the triple digits. I would rethink/calculate this. Be sure not to mix up a direct (1.0) drive ratio with an OD (.75??)one.
Well the trans is just the TF999 so no OD. But your right, Ive got something fowled up and I'm betting that the tach is screwed...I never ran the numbers before and just assumed the tach was correct, I've gone fast in the jeep, but I know I've never gotten to triple digets...Hell even if it never shifted out of 2nd gear I'd still be doing over 100mph at that RPM. I'll be checking that out!

As far as the bore, I was just assuming worst case.

I'm still shopping for a shop to do the work, Ive used a race engine builder here several times but that was 15 years ago and I just want to be sure that they still do good work.

Do you think a 470cfm truck avenger carb would be OK or it still too big? 470 is as small as they make in that model. http://www.holley.com/0-90470 I kinda like the idea of the high angle ability. and according to the Holley interactive carburetor selector, it should work.

Last, what about the head. What should I consider doing there?
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Unread 02-14-2012, 03:57 PM   #5
jeepdaddy2000
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Quote:
Well the trans is just the TF999 so no OD
Well, don't I feel silly...
Here is my personal opinion.
There are 3 basic types of builds. Low RPM, mid RPM, and high RPM. The information below is a GENERALIZATION of the builds and what they do.
Low RPM usually runs from off idle to 3500.
Mid range builds typically run from 1500 to 4500.
High end builds really start making power in the 3500 range and pull all the way to the 7K range.
Low RPM builds are stock to mild upgrades. They usually revolve around slow speed wheeling, pulling loads, daily driving, and fuel economy. They are the best running of the three, providing almost no difference in drivability except a boost in power. Small 4BBL's, dual plane intake, RV cam, stock exhaust manifolds or headers with small pipes or slightly larger than stock single pipe.
Mid range builds are more street performance oriented. You will loose a touch off the bottom, but the midrange surge will be much stronger. Larger carbs, X style intakes (V8, open for inlines), bigger cams, higher compression, mild headwork, shorter collectors with larger dual exhausts. Most fun running between stoplights. Fuel economy will begin to suffer, cold weather starting can become a chore, and the engine can develop a mild lope at idle.
High end builds entail a lot of work. Large carb/s, open manifolds, high lift/long duration cams, extensive headwork, high compression pistons, heaver rods, huge exhaust, the list goes on and on......Very fast. Not for daily driving. Poor economy, high maintenance, vibrations, no low end power.
The criteria for picking a build:
What do you plan on using the rig for. DD, weekend trail riding, rock crawling, mud bogs, sand drags, pulling a boat, show and shine, hunting etc.....
An HONEST assessment of your max RPM's. Everybody wants the biggest and the baddest, but usually, too big is too much and everything suffers.
Avoid mixing and matching components from the different builds. Huge carb with mild cam. highrise dual carb intake on a DD, etc...If in doubt of what you want, talk to your machinist. Give him an honest explanation of what your doing, and he can recommend a course of action.
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Unread 02-14-2012, 04:55 PM   #6
40dog
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have you checked out the jeep strokers website? putting a double pumper big a$$ toilet bowel carb on it will be a waste of money.i see guys putting bis a$$ carbs and cams in and on engines all the time and they suck.If your building a jeep engine go to a shop with experience with them " this may not be as easy as it sounds" A stroker set up will net the power and performance your looking for. Don't go over board with the bore out it may overheat easily and or have cylinder wall problems . have a shop build the short block and install the head ,intake ,water pump ,and tins yourself. many say they don't believe the 4.0 head swap was really worth it. idk. I have driven a stroker and would swear the jeep had a mild v8 in it if i didn't know it was a stroker.just my thoughts they are not worth much but there free.
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Unread 02-15-2012, 10:20 AM   #7
MegaCabMan
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40dog, thanks for the input!
With the 258 I already have the 3.9" stroke..the only thing bigger is a $1800 4" stroker crank or I could have one custom cut...not worth the $ in my opinion and will reduce the reliability of the engine.

As for the carb, I'm not going with a double pumper; just a small 4bbl with vacuum secondaries. When running a 4bbl you are only running on the front two venturi, which are much smaller than the venturi of the stock carter 2bbl. So I should see a boost in throttle response and better fuel economy (as long as I keep my foot out of it)

@jeepdaddy
No need to feel silly, it's a jeep--no telling what has been done to it unless your told. I 100% agree with your summary of possible builds. My build will be of the LOW RPM variaty...right now my only quandary is about the head...I'm really leaning toward just keeping the stock head and having a good 3 angle valve job done on it. BUT if someone can make a good case for the 4.0 head I'd sure listen!

I think I'll swing by the machine shop today and chat with them about this. BTW the shop I'm thinking about using did a lot of the R&D machine work for Mercury Marine when they developed the first ZR1 engine--now the northstar. So they have some industry cred, or at least they did back in the day.
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Unread 02-15-2012, 04:56 PM   #8
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First off, who is machining/building this motor? The 600cfm is big, you will never be running 6500rpm in a overlander. I think holley has a offroad one @ 470cfm. Overlanders need good fuel economy too. Mostly for a cam I would go with as mild as possible, for reliability and economy. In the 4.7 strokers we built, we used Crane cams, Both Crane and Competition cams have tech lines and such for making sure you get the right cam for what you need. Your engine builder or machinist should have some good ideas.
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Unread 02-16-2012, 06:05 PM   #9
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i wasn't telling you to get a stroker crank for your 4.2 though that would be nice . i was referring to placing your crank and rod assembly from your 4.2 in a 4.0 block set up as a jeep style stroker engine. i know you want to rebuild the 4.2 but this is a option .just a thought. have you checked out jeepstrokers.com they have a ton of 4.2-4.0 jeep engine performance build info "real info" stock part combinations and after market.check it out.there is more info there then you will be able to read in a few weeks time.excellent site I'm planning on building a stroker for the 88yj im building right now using the 4.2 as a parts donor "since it has a fist sized hole in the block from where the motor mount was riped off"
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Unread 02-21-2012, 01:19 PM   #10
MegaCabMan
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Well the RPM thing was really bothering me. At first I thought that I must have misread the tach or the tach was acting up. So over the weekend I took it for a drive and noted the the RPM's 2800 at 82mph (~75 MPH corrected for tires) Then I dug around on the internet for calculator and found several one said I was doing 160 mph and another said 75 mph. I guess you just can't trust everything on the internet...Hmmmmm.

Next I wanted to make sure that I didn't have a hole in one of my pistons so I did a compression test...I'm not sure how my engine even runs! I had three cylinders at 75psi, two at 60 psi and one at 30psi!

I found out today that I am getting a nice bonus here at work so, looks like I got some money to throw at this.
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Unread 02-23-2012, 01:18 PM   #11
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well it looks like the 4bbl and offey are out of the picture. I cannot locate them used and paying over $800 for this mod doesn't make sense and will severely bust my budget.

For now I think I'll just locate a pre-egr stock manifold, I already have a non-eletronic carter carb.
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Unread 02-25-2012, 01:37 PM   #12
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First off, a holley 66 is too big. The best carb for a built 258 is a holley TA 470 4 barrel. On my 87 258 I installed a holley 470 TA 4 barrel, offy intake, comp cam, rollor rockers, ported head, hipo pistons, header, DUI, MSD and a holley fuel regulator, It screams!!! I tried the 4.0 head, I found that a ported 258 head works better when using a carb setup. The 4.0 had a little more power at full throttle in the upper rpm ranges, the ported 258 head had better responce in the low to mid rpm ranges where I mostly operate at, better off road with my setup. If I was drag racing I would of stayed the 4.0 head, but for 4-wheeling, crawling a round, the reworked 258 head seemed to perform better. I think the 4.0 head works better with FI setup than a carb, at least in my experience. I paid over 400.00$ for a ready to install 4.0 head from clearwater, It only cost me 250.00 to have my 258 head flowed and polished. With a little work, you won't be disapointed in the way the 258 performs, you don't need a V-8. I t has the power of a small V-8 and the lowend torque of an I-6.
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Unread 02-27-2012, 11:02 AM   #13
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@ Idwheelthat
Quote:
First off, who is machining/building this motor?
Buddy Rice Performance Engines in Oklahoma City. They helped Mercurser develop the heads for the first (1990) ZR1 engine. I saw a few prototype heads in his shop back in 86 or 87. When I saw the dual overhead cam heads on the bench and asked about them he said "Just a little project for mercuser" Then when the ZR1 came out in 89-90 I put two and two together. Years later I asked and Skip Rice confirmed that's what they were.

@wendell
Quote:
you don't need a V-8. I t has the power of a small V-8 and the lowend torque of an I-6
I will take your advice and port/polish the 258 head. the external performance parts will have to wait till I get some more extra $, but at least I'll have good bones to work off of.
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Unread 02-27-2012, 11:21 AM   #14
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IMHO for a rebuild and looking for a bit of a boost in power.

Lower compression ratio to 8.5-9.0 (probably 500$)
Cam for boost (quicker closing exhaust valve) (about 180)
Check the deck for true-ness same with cylinders(machine chop dependent)
ported heads (about 300$).

Super charge to about 10psi with an intercooler. Custom tune and SRT4 injectors, probably be pushing close to 400crank if you're tuned right and assuming free flowing exhaust.
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Unread 02-28-2012, 03:28 PM   #15
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Thanks for the input but I'm thinking that forced induction is out for two reasons. First cost, second I would take a hit in the reliability department. The engine may run great, but I'd destroy the rest of my drive-line unless I upgrade it also; and then we are back to reason one, cost.
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