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I want straight answers

XJRunner

NAXJA Forum User
Location
San Diego
Ok I've read a bunch of threads and searched but I always came away confused. I want to know a few things.

ok first, I'm buying a rebuilt 89 4.0L. It's been bored .030 over in the rebuild. I wanna boost its power a little. I've read about using a later model intake. which years do I want to look for? And will it bolt right up? Also I want to do gasket matching, is this hard to do and worth it? Then on the intake I want to bore the throttle body and intake and also put a bored throttle body spacer, do you recommend this? And finally, I read that LT1 injectors are a replacement for the newer injectors and Ford 5.0 are replacement for the older Renix engines, which ones do I use with the later intake? Also what cam would you recommend for more torque and mid range? Thanks for your help and sorry for the million questions.
 
First problem you're likely to run into is the fact that you're here in CA. While you could make the top-end swap look OEM, you're going to end up deleting the EGR, which can and do make you fail smog (even if the damn thing creates more emissions than it's purported to eliminate. Per reports from the Smog people, on my 87...)

Later intakes can be adapted to the RENIX head, but it's easier to just drop on a later top end (head and manifolds) and call it good. Either way, you delete the EGR - but the later heads flow more air, and the ports were raised 5/8" for 1991 (which is why the manifolds don't just "drop on" - a little work is necessary.)

The Ford SB injectors (Blue tops, I believe) work well on the 4.0L, and the LT1 should work quite well as well - there was a thread on this recently, when someone decided to do the swap. He had an HO engine, but there's no reason to suspect that the RENIX won't benefit from the swap. Both cases show some small benefit from more effective fuel atomisation, which encourages compleat combustion. As long as the injector fits physically and electrically, and the flow rate compares favourably to stock, you'll be fine (RENIX injectors, I believe, are rated for 19#/hour at 39psi. There is a formula to correct that flow rate for different pressures, but I don't have that handy at the moment, either.)

"Port matching" (matching the ports via the gasket) is fairly simple - just time-consuming, and easier with air tools. Match the intake to get a nice, smooth flow, and leave a "step down" at the exhaust port (the port in the head should be slightly smaller than the port in the manifold. This helps prevent "exhaust reversion," which decreases scavenging.) Be sure to "ramp" the increase in size as you go into the port to make for smoother flow - a 3:1 to 5:1 ratio seems to work well (if you have to enlarge the port by 1/16", then use 3/16" to 5/16" of port length to blend it back into the lines. Should have a gradual "funnel shape" and a clean transition into the original port lines.) A good article on DIY port work can be found at Standard Abrasives' website - I don't have a link handy, but it's well-written and illustrated well.

Boring the throttle body will probably improve part-throttle response, but the OEM throttle body can flow plenty of air to supply even a stroker - so your +.030" engine won't have any trouble. Spacers are of dubious utility, at least to me (there is some benefit to increasing plenum volume in an intake system - but a spacer isn't much of an increase.)

Did I miss anything?
 
APN header 2.5 inch all the way back would be ideal for your stroker IMO.
 
XJRunner said:
thanks. so no bueno on the intake swap? Would a cam help me out more

It can be done - but one way or another, you'll run afoul of the California Air Police doing it.

I honestly think that I should answer your question with a question - "What, exactly, are you trying to do?" Until you have a fairly specific goal in mind, you'll have a difficult time getting a straight answer to pretty much anything.

I'm perfectly willing to help you (and so is pretty much everyone else here!) but if you don't know where you're going, how will you know when you get there? (Not being a smartass - it's a perfectly reasonable thing to ask.)

Besides, the more work you do on paper, the less money you'll end up spending on parts - and the happier you'll be with the results.
 
I just did the manifold swap on my 91 last weekend. Still haven't worked the kinks out getting the pullies to line up right, infact I'll hafta replace my water pump again after only 7 months. I noticed a slight difference in power but..with a stroker idk if it would be really worth the hassle. But if you wanna grind for hours on you power steering bracket it will work...
 
yea no stroker. I just want more power. I just want to know all the little power secrets. injector swap, cam,intake swap. I want more low end and mid and top if possible but it don't matter as much
 
XJRunner said:
yea no stroker. I just want more power. I just want to know all the little power secrets. injector swap, cam,intake swap. I want more low end and mid and top if possible but it don't matter as much

You can't usually have it both ways - either top end horsepower, or low-end torque. While an increase in one will net you an increase in the other, you're going to target one or the other more.

Since the inline six in general (and the AMC six in particular) was designed from the ground up for low-end grunt, focus on that. Besides, when you're cruising or trying to get moving, it's low-end torque that will do that for you.

Here's a question - do you have an automatic or a manual? While an automatic is geared fairly well (3.54/3.55 from the factory,) it could benefit from a bit lower gearing - like 4.10. If you've a manual, the gearing (3.07) just plain sucks - someone wasn't thinking. Going to 4.10 or 4.55 could net you a noticeable improvement in performance, and it's an easier job.

There are a number of camshafts that fit in the AMC six block, but many of them are listed as "not for use in computer-controlled vehicles." I need to start contacting these vendors to find out why - is it a genuine incompatibility with computer controls, or are they just not certified for emissions? Still, you've about a half-dozen options from Crane, Crower, and a couple of other outfits, so we're not totally out of the running.

A lot of external engine mods that would normally be available to you will cause you to fail smog - not because they'd increase emissions, but because no-one's really bothered to get their add-ons certified by California for RENIX (1987-1990) XJ and MJ, and that's why the field suddenly opens up from 1991 (with the introduction of OBD-I.) Sucks, but that's what we're stuck with. And, why I do plan to leave California (and when I do, I plan to leave California to the Californians! I've had it with this place...)

Things you'll probably want to consider:
1) Re-gear. Especially if you have a manual. (If you have a manual, check to see if it's the Peugeot box of the Aisin. The Peugeot has a longwise split down the case, and should be replaced with the Aisin. I went through four Peugeots in three years...)
2) You can bore the throttle body out, but the power gain would be minimal. The advantage would be in throttle response.
3) Consider adding a "cold air" intake - there's one certified for use on RENIX in CA, and it's made by XJ-Armor. Reports from the field on ordering from him are mixed... If you build a sheetmetal baffle around the thing and open up the hole that it breathes through behind the grille, you may see a slight increase in power (and a probable increase in throttle response as well.)
4) "Port-matching" will probably net you a minimal gain as well - but if you're willing to do the work, go for it! I'd suggest you get at least another intake before you do - so if you do screw up, you've got a spare...
5) Replace your fuel injectors. If you've still got the OEM ones (metal bottom/plastic top,) you're at risk of having them leak anyhow. Replace with Ford "blue tops" I think - you'll get better fuel atomisation, a little more power, maybe a few points added to your MPG, and the Smog Monkeys won't notice...
6) Re-gear. I know I said this earlier, but you're in CA - which limits your engine options. Therefore, you have to look at other solutions to your problem...
 
XJRunner said:
thankyou soooo much!!! this has cleared up everything.

The performance world is not as simple as people like to think - unless the aftermarket has caught up. Since we don't have Small Block V8s, and we don't drive "sport compacts" - or "tuner cars," or whatever they're called this week - it's especially important to think before you start buying parts...

California doesn't help things, either.
 
XJRunner said:
yea. I already have to take all my intake crap out and reinstall the factory stuff to smog it every two years. its dumb

Are you "profiled" to "Test Only" stations yet? They hit me with that - and my rigs are RENIX as well.

Never mind that I found out (through a conversation with CARB recently) that my rigs run cleaner than most vehicles ten years newer - the computer has profiled me based on displacement and age, and there's nothing I can do about it but shut up, and pay twice as much for the test as my tags...
 
XJRunner said:
yea I know. We have the strictest smog laws

Who's "we" - ya got a frog in your pocket?:gee: I don't consider myself a "Californian," I'm a "temporarily expatriated American." I'm a transplant - I grew up in Indiana, the Air Force put me out here - but I refuse to change to fit in with the mentality out here.

I plan on leaving someday (once I've gotten rid of the last of my entanglements, one way or another...) and I won't be bringing California with me. I just want to live somewhere where we can be left the Hell alone! I'm tired of the busybodies in Sacramento (and, let's face it, Washington) getting involved in everydamnthing I do and making things difficult all around - for no real good reason (let's face it - anything that shouldn't be done is already illegal or difficult anyhow, so why make it worse? See other discussions on malum in se vice malum prohibitum for my opinions on that, I've gone into it elsewhere in depth.)

I still consider America to be the "last great hope of the world," but we've got a lot of work to do to make up the ground we've lost over the last 30-40 years or so.

Meanwhile, if the suggestions I've given you aren't found to be enough, go ahead and ask more questions! At least the answers are free...
 
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