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Late model manifold upgrade gains?

C

CW

NAXJA Forum User
Location
Coeur d'Alene, Idaho
OK, I am tired of cracking my header so I think the cast manifolds are the way to go. I am planning on swapping intake manifolds also and a mustang tb (if I can figure out how to adapt it to the renix). This is on a 4.6L stroker with ported and polished HO head, and a comp 250h cam. I will be replacing a '94 HO intake and exhaust and tb. What kind of gains should I expect out of the new manifolds. I know Jeep claims they produce a better exhaust note so that should be a plus.
 
I think I may have the answer. Take a look at the dyno plots of the stock 4.0 on the Hypertech Jeep Page and compare the plots for the '96-'99 and '00-'04 engines.
Both vehicles were 5-speed Wranglers and the dyno runs were done in 3rd gear. Both the '96-'99 and '00-'04 produce the same 146rwhp while the '00-'04 engine produces 4rwtq (5lbft at flywheel) more in the midrange. The newer engine does produce less torque from 2000rpm and below though.
The only differences between the two engines that affect the HP/TQ output are the intake manifold, smaller exhaust port head (on newer engine, this produces a flywheel 5hp/3lbft loss), and the slitter-vane water pump (on newer engine, this produces a flywheel 2hp/2lbft gain).
Since the head and water pump combined produce a 3hp/1lbft loss, then the intake manifold must produce a peak 3hp/6lbft gain with a small loss of torque from 2000rpm and below. This is exactly what you'd expect given the curved runners and larger plenum of the newer manifold.
 
Yes, they'll bolt straight on and the primary tube external diameter is still 1.5". The late model exhaust manifold has flexijoints that allow it to expand without the risk of cracking. Here's a pic:

33007072K.jpg
 
I was talking about using the two cast manifolds, because I keep cracking the tube manifold. When did they have the flexjoints? During the years with the new intake but before the cast manifold?
 
As far as I know, all the HO 4.0's until 2000 used stainless steel header-like exhaust manifolds. I think it was in 2001 when they were changed to cast with flexijoints (the last production year for the XJ) but I may be wrong.
 
If I'm not mistaken, that's the new two-piece unit that's fitted to the most recent 4.0's. That should work fine and it also won't be crack-prone. You'll need to add the dual collector pipes and two-into-one downpipe going to the cat (I think that one has two precats but you can do away with those).
 
The tube style header was available up to the 99 model year for the TJ and XJ. The cast iron exhaust manifolds started showing up in 99 on WJ's, and in 2000 on the TJ's and XJ's, and the pre-cats were a California only option.

I have commented before about the 99 style intake I installed on my 96 XJ. I lost some low end torque, but gained some at higher RPM's. I really felt it was a waste for my mostly stock 4.0l.

Bryan
 
Yeah now I'm wondering if I should go with the new ones with the flex joints ($175) that will bolt into my existing set up or go with the cast ones($86 & $96). I guess now I need to figure out what ones flow better. And as far as losing low end torque, on my stroker everything that was supposed to hurt the low end hasn't made a difference but the top just gets better. I think its because of my cam choice. After the port and polish head job, and 2.5" down pipe it really pulls hard after 3k and I can still break the tires loose through 1st and 2nd gear.
 
Last edited:
CW,
I have two sets of cast iron exhaust manifolds for the 4.0. I would take $25 plus shipping for a set. I also have the down or cross over pipe. It has been cut though. I does cross in front of the oil pan. I can check against my '95 head. From a previous look at it, you would need to grind some metal off the manifold to make the ports match. I am guessing 1/2 on the bottom. The crossover pipe is a two to one. It has no pre-cats. To my understanding the late XJs didn't have the pre-cats, but the ZJs did. I think the Wranglers had them a bit latter years.
Tom
 
How much material is around the ports on the manifold? I ported the head to match a '95 gasket and if I remeber right it was just short of 1.5" in diameter. If I could grind enough metal off I am definately interested.
 
You definitely DON"T want to match the exhaust ports of the head to the gasket. The ports will become too big and your engine will feel boggy at low revs. These are the port dimensions of the '92 head that I ported for my stroker and I think that's as big as you should go:

Intake port entries (rectangular): 44.0mm x 36.0mm (C/S area = 85.7% of valve head area)
Exhaust port exits (oval): 37.0mm x 34.0mm (C/S area = 86.7% of valve head area)
Intake port throat diameter: 43.0mm (88.6% of valve head diameter)
Exhaust port throat diameter: 33.0mm (86.6% of valve head diameter)
Intake port volume = 114cc (stock is 112cc)
Exhaust port volume = 80cc (stock is 73cc)

I reused the stock 1.91/1.50 valves since they were still in excellent condition.
 
It doesn't feel slugish at all at low revs at all. but honestly I can't how much I ported. I know I didn't feather the exhaut ports in 1.5" all the way around, do I probably didn't take too much off.
 
I compared the manifolds I have to a 95 gasket. The port outline on the gasket is larger than the manifolds. I think I placed these manifolds on my 95 head and it was iffy. I don't think they will work. I could send you a set for the cost of shipping since at this point I consider them only good for the 99+ heads, which should already have them. I have heard the ones with the flex joints also crack, but have no real first hand knowlege of that. What type of header did you use that cracked?
Tom
 
I've been going through 91-96 manifolds constantly since I dropped my stroker in. I think I am going to take a stab at fabbing my own header, since I don't really have enough money to buy an aftermarket unit, plus I think I can build something better than the typical borla unit. Im thinking a 1/2" flange and equal length 36" tubes and a 3" long collector.
 
CW,
The only things I can add, is maybe an exhuast manifold from a 258 might work. I looked at some pictures on E-Bay. The main problem is the center two exhuast ports share the same duct (for lack of a better word). Worth a look. I sense this is minimal cost, so this might not interest you. But as for after market, you might think of ceramic coated headers. I think they might not have as much thermal expansion, so less stress. I have been running Pace Setters for about 3-1/2 years with armour coat. No problems, except the coating is bubbling near the head. I am planning on getting some Cliffords. About $300 with ceramic coating.
Tom
 
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