Multipart question, 4.2/4.0 hybrid, dyno numbers...

[EFIeagle]

First, if you feel this thread is off topic, boot it out the door (lemme know if ya do), second, I figure this would be the best place for it, since most of the parts and principles apply....

AMC 4.2L .030 over, unknown (but fairly deep) dish size
7120 head, stock valves and passages (no porting done)
92 cam with same pushrods
92 manifolds
2.5" exhaust from bellhousing back (2.5 cat and Flowmaster 40)
95 pcm
94 ZJ 5.2L injectors on 98 single line rail
Adustable FPR (coming soon)
Adjustable map (cuz Dino is a genius)
Hand ported (62mm I believe, is same width as intake manifold opening exactly) tb
3" intake tubing all the way + cone and MAT sensor relocation
AX15 + NP249J

I live at 5400 ft above sealevel.

It's almost completely put together, except for the wiring, fuel pump/fpr, muffler-back exhaust and few sensors, and I am literally losing sleep wondering what that motor's gonna do...

So first question: Motor has been very recently rebuilt, as I found out when I started this project, so I know there's no blowby or leaks. Approximately what wheel and crank numbers can I expect this motor to put out, if tuned more on the close to stock/economy side? This is going to be my (only) dd.

Second: What's the most power I could get out of it as is?

Third: Which parts give the largest gains? Cam? TB? etc

Fourth: I'm fairly sure I'm going to need an aftermarket universal adjustable FPR, since the rail does not have a return but has injectors that came from a rail with one. Will I still need that map adjuster? Is one option better than the other, or can I get the same results with either, and would using both be better than just one or the other?

Fifth: I spotted a late model intake manifold on a cherokee in a junkyard today. Considering what I've already got, how much power would I gain, and how would it affect the hp/torque curve?

[EFIeagle]

I should also mention the head has been shaved approximately .025 as well (tried to weld the jackets m'self the first time....), and I'm using the stock head gasket. The block appears to be decked, the piston tops are level with the top of the block.

[1bolt]

Well I seem to be on a crusade lately with this... I've been twice burnt by 4.2 builds so... I'm not sure where these 4.0 head and fuel injection on a 4.2 block builds are coming from but IMO that's a whole lot of work to polish a turd... Especially when the same work/money will net you from 90 to 150 more horses.

Keeping the 4.2 block is a big mistake, if you're going to rebuild a AMC I6 and it's not some nostalgia/stock restoration type of thing, the 4.0 block with larger bores that actually mate up to the 4.0 head properly, is the way to go... and putting the 258 crank in their while you rebuild it is a no brainer, which costs almost nothing more than rebuilding the 4.2 stock would (if you have a 4.0 laying around anyway, and if you're putting 4.0 injection on the 4.2 you probably do)...

I'm not saying this to dog on you, there's been three or four of these lately (last couple weeks like 3 people have brought this up) so please don't take this personal You are unfortunately the first person recently to actually come here (or the Yahoo email group) who's already tossed money at the 4.2 block. Others were asking if they should rebuild the 4.2 block and put the 4.0 FI and head on, so they weren't "too late" so to speak to find out there's better options. Namely building a stroker or rebuilding the 4.0 block and setting the 4.2 block aside for a later stroker build.

The reasons are simple, the 4.0 has larger bores, and can be safely overbored more than the 4.2 even with these larger bores the 4.0 HO heads combustion chamber is a little outside of the cylinder bore, on a 4.2 this mis-match is very pronounced, it means valve shrouding and inefficient combustion as combustion heat will be wasted on the protruding ledge created from the mistmatch.

It cost basically nothing more to stroke a 4.0 block with a 4.2's crank than stock rebuilding a 4.2 (or 4.0) does... for this reason alone rebuilding the 4.2 is a poor choice... Even stock rebuilding the 4.0 and bolting it in instead is a better choice than rebuilding a 4.2

4.2 stock flywheel horsepower is 100-110 hp 4.0 flywheel horses = 190-195hp. There are a lot of reasons for this but larger bores that match the better breathing HO head, higher compression with better quench and a better cam are big ones... you can change the cam and machine for compression and quench but you'll never out bore the 4.0. simply because they both have about the same cylinder wall thickness, so the one that starts out bigger has the advantage.

I feel for you having put money into it already, but hey don't feel too bad I built two 4.2's and threw money at them too before I learned my lesson and built a stroker. The stock 4.0 in my wife's XJ is worlds better than my last and final 4.2 build which had a .60 over bore 4.0 HO head, fuel injection, aftermarket cam, header, dual exhuast flow master etc. etc. I mean it would just walk all over that last 4.2 and it doesn't have so much as one mod done to it. No wonder at roughly 90 more horses than a stock 4.2 and my mods MAYBE improved the 4.2 by 40 horses (if I was lucky) it still would have had FIFTY horses on on the 4.2.

With a Stroker even cammed for low torque (which sacrifices higher RPM horses) we're talking more like 100 horses over a similar built 4.2... You can see why I'm pasionate about this. There's a lot that can be left on the table for the same money and effort!

[EFIeagle]

Here's my reason:

bought the car for 1300 dollars, didn't pass emissions because of a combination of the BBD and bad cat (that I didn't know about until after the following), so I converted to the MC2100. STILL didn't pass, found out it was overbored when I pulled the head. A week after that, I found a 92 4.0 with head, cam, internals (that were completely shot), manifolds and distributor....for 20 bucks, which of course led me to converting to mpi.

I don't have any other car. I don't have a license (until next month). My other half does not have a car. Neither of us have easy access to transportation, and asking the roomates to help every now and then doesn't feel right. Perhaps if I had a pickup, and the money and ability to take the block to the machine shop, buy new internals, along with everything else that comes with, I would have. It's hard enough to walk a mile home from the bus station carrying a 4.0 head over your shoulder, I've done it.

Everything in the block and behind the covers was new in that 4.2 when I bought the car, because the po had been doing some restoration to it but gave up. I'm not looking to smoke tires or stoplight race ricers on friday nights. I'm looking to have something that gets good gas mileage ( a well tuned 4.2 w/BBD gets 30 mpg hwy), is easy to work on, easy to find parts for, inexpensive to drive and easy to fix up with minimal transportation needs for other parts, since this is my only car. I'm curious about the numbers because let's face it, that 4.2 is no longer stock, and there are a few things I've installed into it that I've researched on and have been told will make a big difference. There is another member of a different forum I'm on, with an almost identical setup to mine, and he gets around 330tq and 230 hp (I don't remember if that's flywheel or crank, but either would be fine by me, assuming 20% drivetrain loss).

I also purposely kept the 4.2 because the Eagle and the Wrangler were the last vehicles it was used in, and since I'm restoring mine, I'd like to keep it close to stock, if a bit modernized. Since I was in the process of parting out roomate's 94 bmw in the garage at the time of purchase, I've had to do every single bit of work on that car in the gravel side yard.

Don't let me pop yer bubble completely.... I have plans for that 4.0 block sitting on an old 31" TSL on my back porch. Lots of plans. But for right now, I'm gonna stick with something that once running, will last for a long time. Here's the kicker... it will have only cost me around 800 dollars to get my car up and running again.

I could NOT have used that 4.0 without some seriously expensive work. There's a good chance two of the mains have been worn beyond repair, but I'll get the shop's opinion on it next year. Cylinders 2 and 3 had SEVERE rod knock, and cylinder 2's rod bearings had spun inside of each other, their edges razor sharp, and the rods worn beyond repair. The cylinder walls had obvious blowby scarring as well. The difference between what I did and what I could have done is about 1000 dollars and a 4.0 block instead of 4.2, and some ungodly way of transporting said block and internals back and forth. Basically, I'm just going with what's easiest and least expensive for right now.

[amcinstaller]

no disrespect to anyone, but seriously, i think theres more 4.0 head on a 4.2 swap info on eaglenest than there is here. this is a stroker site, hence the name.

[1bolt]

It sounded from your first post like you had machine shop work done to your 4.2 so I apologize for presuming that you were doing a complete rebuild.

30 mpg on a carbed 4.2? how much does an Eagle weigh??? Anyway yeah if circumstances dictate going with the 4.2 I guess I can see why you went with it...

[EFIeagle]

Yeah, just doing a head/cam swap w/efi. Eagles weigh between 3400 and 3600 lbs. Factory mpg rating was 21 city 30 highway. I signed onto this list because I've been gathering information for my eventual stroker build, and information on my current swap.

[amcinstaller]

this is a very popular swap with eagle guys far as i can tell. a dude in alaska (i believe) boasted huge gains just from throwin on the top half of a 4.0, complete with FI. some have done it with just the head, and kept the carb, but im not sure why?

[1bolt]

It's all good, stroke it next time you'll be shocked how much difference doubling the hp will make

Did you know there was a year when the 2.5L fuel injected AMC 4 banger made more power than the 4.2? Honest 100% true. Jeep factory ratings!

I know all about having to do what you have to do. Still I am having a hard time with 30 MPG I'm not trying to kill the messenger though if that was the factory rating I'll take your word ... I'd have a hard time believing 25, I never got out of the teens with either of my 4.2 experiences, and that includes fresh builds, BBD (properly working if you can believe that! granted it didn't work properly for more than the usual year or two before it needed another rebuild... A 2100 carb with 1.08 venturi , Weber, Holley TBI injection, and factory 4.0 fuel injection... and a 4.0 HO head swap in there...

Amcinstaller, the only before/after dyno numbers I remember of a 4.0 head swap onto a 4.2 was about a year back and it was something like 20hp... My own experience seems to jibe with that... Now if a lumpy cam is installed I can see any 4.2 gaining some significant hp numbers, because the factory 4.2 cam is so far upside down on torque versus hp.

[amcinstaller]

pretty sure the only dyno used was the butt dyno on that one. it was on the eaglenest about a year ago i think.

[1bolt]

I've seen lots of butt dyno claims for that head swap including my own, no I'm talking about an actual dyno comparison before and after and It may have been posted here, or at least linked to. I remember making the comment: I thought so!

[eliv1]

Here's a dyno run for a 4.2 with EFI and 4.0L head, 60mmTB and 99 intake, by a guy namer Peter, who's a member of this site...
the number's aren't that impressing, but give's us an estimation.

http://www.jeepstrokers.com/forum/viewt ... 4&start=30

Eli.

[Plechtan]

This is not really a stroker subject ( 4.2, 4.0 head) , but maybe somthing should be posted in the FAQ section saying " don't waste your time and money"

[amcinstaller]

This is not really a stroker subject ( 4.2, 4.0 head) , but maybe somthing should be posted in the FAQ section saying " don't waste your time and money"

this is why i suggested asking at eaglenest.

[1bolt]

I think someone on the eagles nest should post that to their FAQ section