Baddad

Omg! That's gotta be a good part of my power problem from another thread I started! How do you decipher these numbers?

cruiser54

You want an ECU out of a 89 or 90 ending in 428.

Baddad

Found one! Gotta love craigslist! Gonna try and install this week, I'll post results. Thanks again Cruiser!

cruiser54

Great. You'll like it.

XJdryva

So having a 89 Comanche is good? Throw a H.O. head on it and heart intake and boogie?

cruiser54

No need for the head.
Here's why:

HO myth buster


Renix in 90 made 182 HP. HO in 91 made 190 HP. That's 8 HP difference.

HO only made more HP than Renix at higher RPMs and not a bit more torque. HO had a 58 mm throttle body versus a 52 mm throttle body on a Renix. That’s 20% more air available through the HO throttle body. The HO also had a better design header. See where I'm going with this?

It’s only a 4% horsepower increase…..

The whole 8HP was not mostly from the head, but from the bigger TB and better exhaust manifold.

Put a 60mm TB from www.strokedjeep.com on your present manifold using the Renix head, eliminate the "crush" in your headpipe with proper re-routing, and go for it.

HO stands for Highly Overrated.
__________________

Dumajones

HAHA,, Highly Overrated So true. Im going to steal this HO myth buster quote..

LadyKenai

.

XJdryva

Oh, I wasn't really going off numbers. I was going off of how hard the thing pulls you back in the seat. I have had many vehicles that said they made a certain amount of power to keep the insurance companies happy.
I had a 89 Comanche with a 94 motor and I can absolutely promise you without a shadow of a doubt that that thing had more power than any of the other 14 XJ's or 2 MJ's that I've owned spanning from 87-99.

cruiser54

I don't get the logic. some of those others surely had an HO motor........

89Laredo

I ran a manual ecu in my 89 for a while, works fine. I let the smoke out of it, only reason I'm not still using it.
429 code.

cruiser54

How did you smoke it?

I've also run 429 ECUs. Only thing I noticed was when shifting the trans into gear too soon after starting, the idle was a bit wonky for a few seconds.

XJdryva

That's the point. The actual H.O. Cherokee with the Chrysler opp system didn't run as good as an H.O. on a Renix system. I have seen this more than once. It is not common for a 4.0 Comanche to keep up with a 5.3 Silverado, but mine did.
I have a Renix and Chrylser version right now so I can tell the difference first hand. I have a H.O. motor with a good head laying in the front yard. It will literally cost me a head gasket and antifreeze to do the head swap.
I suppose I could make a video of my 2 Jeeps racing to prove the point about how much more power the H.O. makes, but the real point would be if the 89 is faster after the head swap (which I promise it will be)

cruiser54

Here's my experience.
90 MJ 60mm throttle body, exhaust "crush" eliminated, dizzy indexed, grounds done etc.

88 XJ with all the same and a 90 ECU but with an HO head port matched to the intake.

MJ is faster.

XJdryva

Either way, you're increasing air flow to the head. That's all a H.O. head is anyways, It's like a LS6 head on a LS1. The advantage is minute, but an advantage none the less. Increase air flow, increase power and gas mileage.

FYI, I have been ripping that crushed part of the exhaust off of every Jeep I've had for the last 15 years. I have a guy that makes them for me and installs them as well if I happen to not have access to a welder. I've been putting a header on them for the last 7 years. Just did it to my XJ. The only reason the MJ doesn't have it yet is because I got it 2 weeks ago and it has several other issues to address first.