Supercharged 4.2 - JeepForum.com
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post #1 of 16 Old 05-06-2021, 06:14 PM Thread Starter
JeepinGeo
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Supercharged 4.2

In a world where everyone wants to be like each other, I want to be different.

If a V8 were free and ready to swap, it would be a no brainer. But until then, I'm sticking with my trusty old 4.2. It's a '79 258 in my CJ5. I just rebuilt it, everything minus new pistons and rods. The engine and engine bay is immaculate and is ready to be blown.

Anyway, truly helpful articles on this specific subject are few and far between. I am looking for anyone that wants to genuinely give advice, especially from those w/hands on experience working w/a supercharged inline 6.

The supercharger I have is a gen 3 Eaton M90 from a 2000 pontiac gran prix. I got it cheap from a junkyard. Was the only one there, and it's in perfect shape. I currently have the stock 2 barrel intake manifold with a Weber 38 carb. I am going to remove the stock blower pulley in exchange for my v-belt setup. Once that is pressed on, I'll line it up with my belts and measure for adapters. This will be draw-through. I do not care about running fuel through the rotors. I can weld and was planning on an adapter plate from the carb to the charger, and from the charger to the intake. Also, this blower does have the butterfly valve bypass. I am also aware of the consequences of backfiring through the intake, and will deal with that via installing a pop-off valve or the alternative in adatper plate or intake. Mind you, the Jeep already has a 3" body lift installed by the PO and therefore should NOT require me to cut the hood once installed. As of right now, the Jeep is tuned well and runs well. Lastly, I am looking for a convervative 5 psi without the use of an intercooler. This is not intended to be a crazy upgrade, but rather a more conservative and unique approach to a little power increase on my daily driver.

Ultimately, I am looking for a similar write up or any legitimate pointers on this entire process.

Thanks.

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post #2 of 16 Old 05-06-2021, 06:37 PM
BagusJeep
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Never done it myself but plenty have done it to the later 4.0 such as:

https://www.boostedtech.com/solution...-supercharger/

Thing is, they all use fuel injection.

BagusJeep lives in Bali with far too many 4x4s:
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
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post #3 of 16 Old 05-06-2021, 07:09 PM Thread Starter
JeepinGeo
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Thanks Bagus. I know "fuel injected" and "supercharged" has a better ring to it, but I'm going to keep it carbed. Do you think 5psi s a good # for stock pistons?
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post #4 of 16 Old 05-06-2021, 07:12 PM
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When you rebuilt the engine did you build it for a power adder? The bottom end will not last if it is not built for boost. Pistons, piston to cylinder wall clearance, rings & ring gaps, connecting rods...an NA engine verse a power adder engine will have different requirements if you build it right.

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post #5 of 16 Old 05-06-2021, 08:37 PM
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Even high output alternators have problems with V belts. Unless you have several V belts on the supercharger, you are going to have problems. You would probably have much better results with a SBC or a GM LS Motor. Better performance and much more reliability.
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post #6 of 16 Old 05-07-2021, 12:45 AM
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The 4.2 will take the boost if mild. 5psi is fine on an older engine and is about what an Eaton with no intercooler will give. It is not a very effcient supercharger but it will do what you want.

A 4.0 is no better built or uses fantastic materials, it is nothing more than a 4.2 with different stroke and bore and some better flowing heads. If a stock 4.0 can take it, so can your stock 4.2.

The Vee belt is a concern. There is a lot of horsepower driving that superharger, you may want to think about a ribbed drive belt and a pulley change.

What I was thinking about over coffee is your choice of carburettor before or after supercharger. If before then it has to be above the supercharger and manifold to allow fuel to run down into the engine, a puddle of fuel being an explosive danger. A carb on the manifold and after teh supercharger is easier to plumb in, so what do you need to change on a Weber 38 to make it run? This kinda question used to arise in my pilot ground school days, as an aircraft flies into the air, how does the carb keep on working? (talking Cessnas here)

The float bowl must be pressurised by the supercharger. In this case you could run a hose from a ported vaccum source on the carb across to the top of the float a chamber and put in a tapping. I cannot recall on the 38 DGAS there being a vent.

The carb would then need sealing up pretty good, good gaskets etc. Air can escape and it will do no harm but you want the boost going into the engine. There will be some loss around throttle shafts but minimal if new. A leaky carb would be a nuisance, the leak would squeal.

The fuel pressure will need turning up to around 8 - 9 psi as the 5psi boost will be opposing it. An electric pump and FPR.

You would need to change the mixture. This is one of the drawbacks. A carb delivers fuel by air volume, not density. A 30% increase in density at max boost would require 30% more fuel. You can rejet enough that it will run but the mixture will not be as well controlled as with fuel injection.

Just a few thoughts
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BagusJeep lives in Bali with far too many 4x4s:
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
1980 Land Rover Series III 109" troop carrier - ROVER
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post #7 of 16 Old 05-07-2021, 09:20 AM Thread Starter
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Thank you again, Bagus. You're about the best help I've found. To cover a few of your concerns:

1. I have decided to aim for 5psi without an intercooler. It's not a race Jeep by any means.

2. I currently use high quality Gates ribbed V-belts. Water pump, alternator/power steering bearings are tip top shape. I keep everything tight like it should be, and am not concerned with slipping. Once adapted for pulley alignment, I intend on fabbing an idler/tension pulley inline. A V-belt should be just fine.

3. I have done extensive research on draw-through vs. blow-through. I have seen draw-through many times and am going that route for ease. As for safety, I will install a backfire valve either off of my intake or off of the blower-intake adapter. I am also aware of boost referencing the carb, and will do so accordingly.

4. Take a close look at this picture. This is one of maybe 3 Jeep CJs in total I've seen with a supercharged setup. Now, there's no behind the scenes article, but from what I can tell, it's a draw-through Eaton M90 supercharger on a 4.2L using a V-belt pulley. Everything I want to do. Care to point anything out about this picture? Thanks!!!
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post #8 of 16 Old 05-07-2021, 09:35 AM
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My previous post was in no way meant to discourage you. If you have the will and the money it will be an interesting project. My only motive was to point out the problems that can come up and also the hidden costs with such projects. You said if you could get a V8 for free, you would swap that. That sounded like you did not have to have a supercharged Jeep and you just wanted more power. Having a supercharger on the Jeep motor is going to make working on it more difficult. You may have to cut your hood, You may haver intake leaks when it comes to adapting an unproven setup. If something happens to the supercharger that you got for a really good deal, a replacement may be very expensive. I have convinced several people to look for a rusted out Jeep with a SBC conversion (at a good price) to get all the adapters to install a SBC in their Jeep for a very reasonable price. It has worked out for a couple of them. We will be interested to watch your progress on your project. It will be something most of us have not seen before.
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post #9 of 16 Old 05-07-2021, 01:14 PM Thread Starter
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Thanks for the feedback StoneTower. I am not oblivious, by any means, to all the benefits that come with a V8 swap, but my location here in central florida leaves me with few decent swap options. SBCs are out there on Craigslist and Marketplace all day, but they're blown up or people are asking way too much...almost like a used Cummins owner! And I figure that because I already have the junkyard supercharger, my only real investment is the adapter plates which I can fab up myself. There are always additional costs of course, such as a backfire valve, gaskets/sealants, pulley, etc. and I know it sounds like a CRAZY idea. But I'd like to freak out my local Jeep club members with a little underhood surprise. On a side note, just for added information, my drivetrain is a T18 (granny first) followed by a Dana 20 with the standard Dana 30 up front and AMC 20 rear. Nothing crazy, but I look forward to proceeding with this project and I will certainly keep yall updated as I progress. Thanks again.
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post #10 of 16 Old 05-07-2021, 02:11 PM
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@JeepinGeo

Will you be tuning for low end torque or higher RPM power?

I would consider adding a good aftermarket intake like the Clifford 4bbl.
and an exhaust header to help the supercharger make the engine breathe.

I know it's more $$$ but the performance will improve,
4 bbl flange will also make a more stable base for the supercharger.

5 Pounds of boost will be fine without an intercooler. Corvair and many other early SC/turbo cars
didn't use one. just be sure to avoid detonation.

This will be interesting to follow, Good Luck with your Project.

Whats over that next ridge?
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post #11 of 16 Old 05-09-2021, 06:08 AM
Shawn Watson
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Is it even possible to modify a 38 for boost reference at the s-port to the power valve?


Shawn

Live in a way that those who know you but don't know God will come to know God because they know you.
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post #12 of 16 Old 05-09-2021, 09:05 AM Thread Starter
JeepinGeo
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Hey Shawn. That's a great point actually. I have seen many people boost reference a 32/36 progressive, but never a 38. I'm sure it can be done, but it'll take some time to figure out. Im considering swapping a 4 barrel intake on it for better breathability (head was ported as well) and then may just as well use a 4 barrel carb on top of the charger anyway.
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post #13 of 16 Old 05-09-2021, 10:18 AM
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Quote:
Originally Posted by JeepinGeo View Post
Im considering swapping a 4 barrel intake on it for better breathability (head was ported as well) and then may just as well use a 4 barrel carb on top of the charger anyway.

That would be a good idea, and it is good that you ported your head. The 4.2 will only benefit from the SC as much as the intake is capable of delivering.

No experience with superchargers, but I once added a Banks turbo to a stock non boosted engine and it ran up to about 10 psi. 5 psi should be plenty safe for your 6 banger. The 4.2 has a very strong bottom end. Definitely install a boost gage on the intake.

The carb you install will likely have a direct impact on your bottom end response. If you go 4 bbl I would consider keeping it somewhat conservative regarding CFM with manual secondaries for ease of tuning.
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post #14 of 16 Old 05-11-2021, 09:55 PM
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Quote:
Originally Posted by JeepinGeo View Post
In a world where everyone wants to be like each other, I want to be different.

If a V8 were free and ready to swap, it would be a no brainer. But until then, I'm sticking with my trusty old 4.2. It's a '79 258 in my CJ5. I just rebuilt it, everything minus new pistons and rods. The engine and engine bay is immaculate and is ready to be blown.

Anyway, truly helpful articles on this specific subject are few and far between. I am looking for anyone that wants to genuinely give advice, especially from those w/hands on experience working w/a supercharged inline 6.

The supercharger I have is a gen 3 Eaton M90 from a 2000 pontiac gran prix. I got it cheap from a junkyard. Was the only one there, and it's in perfect shape. I currently have the stock 2 barrel intake manifold with a Weber 38 carb. I am going to remove the stock blower pulley in exchange for my v-belt setup. Once that is pressed on, I'll line it up with my belts and measure for adapters. This will be draw-through. I do not care about running fuel through the rotors. I can weld and was planning on an adapter plate from the carb to the charger, and from the charger to the intake. Also, this blower does have the butterfly valve bypass. I am also aware of the consequences of backfiring through the intake, and will deal with that via installing a pop-off valve or the alternative in adatper plate or intake. Mind you, the Jeep already has a 3" body lift installed by the PO and therefore should NOT require me to cut the hood once installed. As of right now, the Jeep is tuned well and runs well. Lastly, I am looking for a convervative 5 psi without the use of an intercooler. This is not intended to be a crazy upgrade, but rather a more conservative and unique approach to a little power increase on my daily driver.

Ultimately, I am looking for a similar write up or any legitimate pointers on this entire process.

Thanks.
Hello Jeepin Geo,
Based on your 1st post above and what you requested I can refer and recommend this person who is a intelligent and creative individual (below) I hope you get as much out of this guys channel and his mechanical knowledge as I have.

Although its not a exact match for you, the closest step by step EATON M90 SuperCharger Inline-6 retrofit is on-

YouTube (YT) under **** ( Thomas Beyer ) **** channel. His name typed into search will get you there

He did IMO, a pretty darn good and thorough 2 or 3 part video series on a complete DIY supercharger, head PORT with exhaust and intake head re-flow and BANKS TYPE hi-pro header plus intercooler install on a 1996 Grand Cherokee and even he also did some Dyno testing afterward with a good detailed discussion on boost and tuning. Yes, he is a 4.0L Fuel Injected and not carberated yet, most of the critical install, troubleshooting, mounting, intercooler fab and more is covered very well.

If you find his project helpful please let me know and be sure to give me a thumbs up.

I havent read all the posts here but scanned thru to see if anyone else mentioned this fellows project and didnt notice so I posted this in order to hopefully help your build along or help someone else.

I hope your project is well underway and all the best.

DW



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Last edited by 95-ZJ; 05-11-2021 at 10:36 PM. Reason: Added additional info
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post #15 of 16 Old 05-12-2021, 01:50 PM
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" Only 3 CJ's that I seen with this set up "

That's most likely 'cuz we don't like cutting holes in our hoods. I am very pleased with mine. Fastest CJ5 that I Know of & looks good , don't' you think ?
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I was Schooled as a Mechanic 45 years ago. Then I became a Locksmith....... Who Knew ???
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