88 4.2 + 88 4.0 +7120 Head + Carter AFB ???

[KnacK]

First post so be gentle

I've got a complete 4.2 in my 88YJ with the original Carter AFB. I also have a complete 88 4.0 Renix longblock plus a 7120 head. I do not have the wiring harness for the Renix FI.

With that being said, I've got all of the parts for a stroker. I know I'll need oversized pistons for the rebuild and a new cam. Both has 200k miles on them.

My question is: Can I still run the Carter AFB if I decide to build a 4.5? I also have no interest in feeding this thing premium fuel. I have no interest in going FI. This is basically a DD and to run around my ranch with. I'm trying to keep this as simple as possible ( read $$$$$$ ).

The 7120 is in great shape. The 4.0 block needs the cylinders honed and new bearings. Both cranks need a little bit of machining.

If I am off base on this, then I'll just toss the 7120 on the 4.2 and leave it at that.

From those in the know, what do you think?

Thanks,

Chris

[Mgardiner1]

i hate hate HATED the 4.2 with a carb on it.... see if you can get a handle on how much CFM is required for 4.5 liters of displacement, and see if the carter carb can flow enough air. If it can't, and you don't want to do FI, then just toss the new head on and call it a day

[KnacK]

I agree. I will eventually get FI installed on it.

What about running regular fuel? Am I going to have a detination issue using essentially stock parts to build this?

[Mgardiner1]

Tough to say. One advantage you'll have if you stick with the carb'd system, is you can manually retard your timing if light pinging is present

[IH 392]

I've got a complete 4.2 in my 88YJ with the original Carter AFB.

Since when did ANY 258 come with an "original" Carter AFB????????

[mendelmax]

And how about using 4.2 block, boring it to stock 4.0 bore instead of overboring the 4.0 (lower displacement = less CR = less chance to ping), putting 7120 head on it, having mechanical fuel pump left there and putting some good carburetor like webber or something? Still budget build, no electronics- seems cool to me.

[eliv1]

I speak here only from hard learned experience.

1. the carter original carb, is not big enough for the 4.5L stroker, i ran a carter carb on my 4.5L overboard 0.125" 258 and had nothing but trouble. the air flow will be enough for it to run, but will suffer in performance in the upper end, lower end with a carter carb is excellent. the thing that makes the carter carb unbearable, is that the fuel compartment is too small, and i will bog down under hard acceleration. there are several suitable carbs for the 4.5, an MC2100 (suffer's from medium low-end performance), the holley 470CFM truck avenger - good but pricey.

if you want your stroker to be carbed, i would choose the MC2100, I ran my stroker for a bout 2 years with the MC2100 and it is one of the best carbs i've seen, simple, reliable but with only decent low-end performance, upper and mid performance are very good with the 1.08 venturi version. also this carb will run at very steep angles.

2. as for overboring the 258 to accept 4.0 STD slugs - just dont do it, although this is my engine setup, which is running very reliably for about 5 years now, and about 50,000 miles, i would not reccomend it, espcielly when you've got a 4.0L block. the overbore is way out of recommended specs, and will leave a very thin cylinder walls.

mmm... if you got any more questions, dont be shy.

[KnacK]

So its looking more and more that I will probably go 30 over on the 4.2 block, find a good cam, toss a 7120 on top, and then get a MC2100.

I'll still keep the old Renix block around for when I get FI.

Thanks guys.

[1bolt]

I'm sure he meant BBD.

IMO why go for more powerful engine at all if performance fuel is out of the question? The cost difference between low and high octane is around a buck or two per tank. I use to be caught up in wanting to run 87 octane until I got a DOHC 4.6 32 valve Mustang Cobra that ran on premium... a couple bucks more per tank was so worth it over the detuned performance on lower octane

The ultra budget stroker will ping on mid grade in all likelihood.

I would rebuild the 4.0 with stock stroke before I put the 7120 head on a rebuilt 4.2... the 4.2 is a dog and lipstick (an HO 4.0 head) wont change that. The stock 4.0 is nearly doubling the power output of a stock 4.2 (flywheel, to flywheel numbers) and don't anyone say that the 4.2 has more low torque, it doesn't. It has a lower torque peak, but that peak is still less than the 4.0 makes at the same RPM.
<-- me beating on the 4.2

[1bolt]

So its looking more and more that I will probably go 30 over on the 4.2 block, find a good cam, toss a 7120 on top, and then get a MC2100.
Thanks guys.

having done this twice I can tell you you're wasting money. The cost of stock rebuilding a 4.2 is nearly identical to building a stroker and the stroker will put out well over double the power at the wheels than a 4.2 does at the flywheel.

Wheel horsepower to wheel horsepower you're talking 60-75 horses (NO SHIT!) versus 190-200 horses, for the same basic cost. Even a stock 4.0 is going to double up on a stock 4.2. at about 145 horses at the wheels. The HO head wont get the 4.2 anywhere near the 4.0... I've seen 20 horses on dyno tests.

I apologize if I seem a little vehement or strongly opinioned about this subject but literally dozens of people come to this same poor conclusion here and on the email list over the last couple years, and it's IMO not even worth entertaining... Let alone deciding in favor of.

You're talking:
Same machining = same cost
Oversized pistons = same cost
Aftermarket cam = same cost
Gasket set = same cost
Build time (or labor) = same
Electric fuel pump = 4.2 about $60-100 dollars cheaper

And on top of that you're going to modify a carb intake to fit on a 4.0 HO head EITHER WAY.

So is saving $60-100 bucks worth losing 125 horse power and a hundred foot pounds of torque over?

[KnacK]

(crap I lost everything that I typed......... )

Simon, I agree 100% with everything that you said and you make an excelent point. My main concern is running 87 octane fuel in a stroker. I know that running a carb gives be a bit more room with a/f ratios and timing, but I have not been able to find anyone that has done this without a detonation issue.

But, I have not finished my search yet either.

[1bolt]

When you finish your search if you find someone they will have zero decked the block for tight quench spec (gasket thickness or around .043-.050) and reduced the compression to under mid 9's static with dishing, and/or a high overlap cam that will produce good horse power at higher RPM's but sacrifice some torque in the low to mid RPM range because of the overlap and longer duration.

This is your best bet in terms of cheap initial build and if you don't mind the street style cam it's a good deal for pump gas. If you want optimal off-road and towing performance there's plenty of low and mid range torque to be had by accepting 93 octane and 3 extra bucks at every fillup... TO put it in perspective with gad around me:

87 = $2.45 = $36.75 a tank
93 = $2.75 = $41.25

Or 4.50 per fill

1, 15 gallon (average) fill per week x 52 weeks
87 octane = $1911.00
93 octane = $2145.00

Or $234 dollars per year difference.

[IH 392]

87 = $2.45 = $36.75 a tank
93 = $2.75 = $41.25

87 (E10, it's mandatory here) came DOWN to $2.83 this week!, last time I bought good gas (Shell V Power for my Yamaha) it was about $38 for 5 gallons!