renix 258 ?

Does any-one know if the RENIX inj. will work on the 258? I know the head has to be swapped, but will the computer be able to compensate for the bigger cubes? what about the fuel press. regulator? I plan on moving the I.A.T. sensor to the cold air tube, and use injectors for the G M quad 4 motors (higher flow 34lbs/hr vs. 19).

I don't see a problem with it, but you'll find that 34# injectors are a little excessive. You should be able to run with about a 24# injector without too much trouble, and just swap the entire top end (you'll also get the benefit of a better-breathing head and intake manifold.)

I can do the math to check, but a 24# should do nicely. No need to overdo it.

5-90

The biggest hassle putting the Renix on the 4.2L is that you need a crank shaft position sensor and will need to swap distributors, wiring harness, and add the sensors and ECU. The CPs is mounted in the bellhousing, so there are two ways to go. Either buy the aftermarket CPS reloaction kit and mount it on the crank shaft dampener, or do a bellhousing swap along with the corresponding flywheel or flex plate as the tranny dictates. You will also need to change the fuel pump to a high pressure pump. Not rocket science but a fair bit of work. All in all, having heard all the horror stories about the carbs on the 4.2L, I think it would be worth the effort. Google should yield you more info.

okay, similar question; I have a Renix MJ, are there any complications to swapping a 258 shortblock rather than a 242 shortblock?

If I remember correctly, there is an issue with a water jacket that needs to be plugged. Yahoo strokers might be the place to search.

BrettM said:

okay, similar question; I have a Renix MJ, are there any complications to swapping a 258 shortblock rather than a 242 shortblock?

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The 258 issues are simplified if the block is a late (87-91) wide deck YJ 258.

The RENIX 258 is simplified because the early YJ 258's had a flexplate or flywheel with the RENIX tone ring (what the cps is triggered by). The Mopar crank balancer kit (the normal balancer end cps kit you read about) is for the 91-95 OBD1 MPI, not RENIX MPI. HESCO used to make a similar RENIX balancer, but it was $$$$. When in doubt swap over the 4.0L tone ring (on the flywheel or flexplate) and use a trans with the cps mount.

The YJ 258 blocks came from the same casting molds as the 4.0L. These blocks have a wider deck surface that better matches the 4.0L head. Earlier 258's came from different mold plugs that have a narrow block deck that can leave water jackets exposed on the 4.0L heads. When you use a narrow deck 258 and a 4.0L head you need to seal the exposed water jacket ports in the head.

It is also best to match the head with the MPI system intake manifold (RENIX or OBD1/2). The 258 heads are not as efficient as any of the 4.0L heads (unless you have an early large port 258 head that has been worked over), so do not waste your time keeping a 258 head.

i'm thinking in the next year I will need to do something with my engine; rebuild, used low mileage, or order a short or long block.

so it sounds like I can just order an 87-91 YJ 258 shortblock and bolt up everything else already in my MJ, right?

BrettM said:

i'm thinking in the next year I will need to do something with my engine; rebuild, used low mileage, or order a short or long block.

so it sounds like I can just order an 87-91 YJ 258 shortblock and bolt up everything else already in my MJ, right?

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Sounds like you need a Stroker! Start saving your pennies

AARON

MrShoeBoy said:

Sounds like you need a Stroker! Start saving your pennies

AARON

Click to expand...

NO!



I don't know nearly enough about engines, I've never even done a basic rebuild. I only wish my 4.0 with 220k miles had a little more power, any more and it would just get me in trouble.

BrettM said:

so it sounds like I can just order an 87-91 YJ 258 shortblock and bolt up everything else already in my MJ, right?

Click to expand...

You can, if you trust the rebuilder to identify an 88-91 258 block.

BrettM said:

NO!



I don't know nearly enough about engines, I've never even done a basic rebuild. I only wish my 4.0 with 220k miles had a little more power, any more and it would just get me in trouble.

Click to expand...

It's not real hard, 4.0s are actually pretty good to learn on , find a good machine shop and a stroker is as cheap(or was for me) to build as a stock rebuild. I used all new parts comp cam, rockers, crank, rods, pistons,etc... and had about a grand in mine including machine work.

BIGWOODY said:

It's not real hard, 4.0s are actually pretty good to learn on , find a good machine shop and a stroker is as cheap(or was for me) to build as a stock rebuild. I used all new parts comp cam, rockers, crank, rods, pistons,etc... and had about a grand in mine including machine work.

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you got a writeup with more details? $1000 I can handle and I'm certainly ready to learn. How much was your machine shop work and what was done?

I can't say that I have a write up, I'm one of these people who does heavy research via the web and then does it all in a matter of a couple of weeks with out much documentation. But, what I can remeber is I look at all the web pages having anything to do with building a stroker. Bought every part that I could from an engine parts supply house (the ones that the machine shops around here use) but could have bought all the parts of the net. I used a 258 crank, pistons, with 4.0 rods. The 258 crank was from the last year or so of the YJ that used it (serpentine belt motor). Did minimal head shaving and zero block decking, valve job on the head, bored cylinders to accept new pistons. I didn't get into swaping on a later intake or even an HO head, but did use mustang injectors and adjustable regualtor. I had the benefit of having a shop around the way from mine that has a chassis dyno where I tuned the regulator and tweaked on mine a bit. I'm sure I could've built one with more power, but I already own fast street cars and I'm not one to fool myself into thinking an XJ is a "hotrod". Mine has worked well, has way more power than stock, will cruise at 85mph all day long with 5.13s and 38.5 swampers, as well as smoke them down from a light. I'm sure I could have put a header on it, swapped intakes, heads, etc... but for what I needed it does the trick and was cheap to build.

Re: renix 258 ? PART 2!!

BIG thanx to all for 411 on this. I really mean it! if anybody is ever in ky., and wants to go play, let me know I dont mind playing tour guide. Also, as soon as I get the AW-4 rebuilt I will let everyone know how this works out. The tranny is waiting on some parts from a company in australia that has figured out some tricks with the 'verter and valvebody for better wheeling. till next time, thanks. ren