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Non HO 4.0L to HO 4.0L

C

canook2u

NAXJA Forum User
Location
North Carolina
I've got an '89 XJ, non HO 4.0L.
1st) What is the hp/ lbs/ft difference between
the HO and non?
2nd) Does making the conversion require an
entire engine change, or just top-end
parts?

Please, either point me in the direction of
this information, or let me know what all
needs changed for the conversion.
Thanks in advance.
 
According to DC, the outputs are 177hp@4500rpm/224lbft@2400rpm for the non-HO and 190hp@4750rpm/225lbft@3950rpm for the HO. The difference is due to the higher flowing cylinder head and the larger TB on the HO.
You can install an HO TB (bore out the taper so that the whole bore is 60mm) onto the non-HO manifold using Joe Attardo's adapter spacer http://www.rockmodified.com/2003/april/TB/tb_perf.htm

You can adapt your Renix sensors to the HO TB and make them work.
The next part to deal with is the head. You don't need to bolt on an HO head but if you find one cheap, that's OK. You can improve your existing head by porting it and getting a 3-angle valve grind done to it. You can also mill the head surface and install a thinner head gasket to increase the CR for a further performance improvement.
Take a look around my website. You'll find a lot of useful info.
 
HO vs Non Ho

Ya, I understand porting will help a lot, but
wouldn't it be better to start w/ an HO head
and port it? Will an HO head fit my '89
block? Are there ANY differences in the bottom-
end? Thanks for your help.....
 
Addition to the Question

I noticed, the '91/ '92 have different exhaust
PNs. Then,'93 & later have a different PN again.
What are the differences?
Are the intakes different for the pre and post
'91s? This is why I'm wondering about going
to the HO head. I know this is a lot of
questions, but I have an obsesion w/ having to
know all about all models, especially under
the hood.
Thanks folks, I appreciate your patience.

Fred Rupert
 
The HO head's airflow advantage is almost entirely on the intake side because the intake ports were raised, giving air a straighter shot into the cylinders.
If you port the non-HO head and raise the roof of the intake ports, the ported non-HO head will produce similar airflow numbers to a ported HO head. That's why I said it's better to make the best use of what you have rather than spend lots of money on new hardware.
Guys like Robert Salemi and Rav are testament to the fact that porting the non-HO head yields excellent results.
 
Dr. Dyno said:
The HO head's airflow advantage is almost entirely on the intake side because the intake ports were raised, giving air a straighter shot into the cylinders.
If you port the non-HO head and raise the roof of the intake ports, the ported non-HO head will produce similar airflow numbers to a ported HO head. That's why I said it's better to make the best use of what you have rather than spend lots of money on new hardware.
Guys like Robert Salemi and Rav are testament to the fact that porting the non-HO head yields excellent results.
Click to expand...

:) do what the BOSS Said.

Rav
 
Ok, Ok, I got it......do what the BOSS said!!!!!
I'm new to the club, gimme a minute to get w/ the program... already.
I will probably do a stroker when I re-build, I just want to
maximize the intake/ exhaust manifolds as well as head
breathability.
Now, back to the different manifold questions, do they bolt-up
differently? Are the ports different?
Are there any better, (years), than others???
I don't mind porting, (Ok, BOSS), but, if there are manifolds
that compliment the porting, I'll find them.

Fred Rupert
 
The '99 and later intake manifold is probably the best, but you'll need to adapt it to make it fit onto your non-HO head. The PS pump mounting bracket and serpentine belt tensioner are also different on the new manifold so you'll either have to adapt your existing items to the new manifold or get the newer PS pump and belt tensioner as well as the manifold.
 
for just a few extra HP, why bother?

run it as is, save all the time/money you'd put into your old mill and dump it towards a meticulously built stroker.

the 91-95 heads have larger exhaust ports than the 96+, so they're the ones you want to get the best possible flow numbers.

99+ intake manifold + 60/62mm throttle body.

the block was reworked in 96 (IIRC) to make it stiffer.

so pick up used parts, combine all the best stock stuff, add the aftermarket goodies where needed and get some real bang for your buck!!!
 
Non HO to HO 4.0L

Cheap XJ,,,,,,,,,,,,,,thanks, that's what I was looking for, taking
advantage of the best parts to start with, then going form there.
I appreciate your help.:)
 
I have not seen it specifically stated, so to be sure you know -- the intake ports on the HO heads are higher than on your Renix head, so if you replace the head you will have to do some adaptation. IMHO you would be better served to do a,light port and polish on your head.

Nobody has mentioned that the camshaft is fifferent in the HO engines. It has been reported that the cam specs in the FSM are not accurate so I won't cite what the books says, but starting in 1991 when the torque peak went up 2000 RPM, they no longer used an EGR in the system. They did that by using a dual-pattern camshaft that supposedly has improved exhaust scavenging to eliminate the need for an EGR.

So the block is basically the same, but the cam is different. Don't know how much of that small increase in power for the HO was due to the head and intake, and how much can be attributed to the newer cam grind.
 
It's a popular myth that the cam was changed during the changeover from non-HO to HO engine but it is, in fact, exactly the same for all the '87-'95 4.0 models. The FSM definitely got the duration and lift specs wrong. The correct duration is 197* @ 0.050" (equivalent to 253* advertised) for both intake and exhaust, the valve lift is 0.424" (cam lobe lift 0.265"), LSA is 112*and ICA is 120*.
The cam specs changed in '96 with the introduction of OBD II. It became a dual pattern cam with an advertised duration of 253/259* (the longer exhaust duration was to compensate for the smaller exhaust ports in the newer head). Lift is 0.408"/0.415", LSA 107*and ICA 114*. The upshot was that the torque and HP peaks were reduced to lower rpm.
The torque peak of the '91-'95 HO engine is much lower than the 3950rpm that DC claimed according to real world dyno tests. It comes in at about 3200-3500rpm.
 
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