Non-Ho to Ho redline difference?

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summitlt

NAXJA Forum User

Location

Maine

• Oct 6, 2005

• #1

What between the two makes the 250RPM difference in redline? the bottom end are both the same. So what makes the HO version ble to handle the extra RPM. Differences in the head?

 

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XJ Buzzard

NAXJA Forum User

Location

Birmingham, AL

• Oct 6, 2005

• #2

I believe there was a difference in the intake manifold. The HO manifold has a better air flow than a non HO.

 

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summitlt

NAXJA Forum User

Location

Maine

• Oct 7, 2005

• #3

I dont think so, but that wouldnt effect redline, just top RPM that it could achieve.

 

old_man

NAXJA Forum User

Location

Loveland, Colorado

• Oct 7, 2005

• #4

On at least some of the later HO's they added a girdle over the crank caps, but red lines are somewhat subjective anyway.

 

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Dr. Dyno

NAXJA Forum User

Location

Al Ain, UAE

• Oct 7, 2005

• #5

summitlt said:

What between the two makes the 250RPM difference in redline? the bottom end are both the same. So what makes the HO version able to handle the extra RPM. Differences in the head?

Click to expand...

The HO has a better flowing cylinder head and a larger TB so maximum HP was raised from 177hp @ 4500rpm to 190hp @ 4750rpm (190hp @ 4600rpm on '96+ XJ's). Maximum torque increased by only 1lbft from 224lbft @ 2400rpm to 225lbft @ 3950rpm (225lbft @ 3000rpm on '96+ XJ's).
The rev limit was increased in the HO simply because it can breathe better at higher rpm.

 

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summitlt

NAXJA Forum User

Location

Maine

• Oct 7, 2005

• #6

So how far can a I6 rev to? Without throwing a rod? Or does valve float occur first?

 

langer1

NAXJA Forum User

Location

Mineral City,Ohio

• Oct 7, 2005

• #7

summitlt said:

So how far can a I6 rev to? Without throwing a rod? Or does valve float occur first?

Click to expand...

Point is any time you go over 190Hp@ number you loosing horsepower.

 

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summitlt

NAXJA Forum User

Location

Maine

• Oct 7, 2005

• #8

true, but you want to be able to shift and land back into peak power

 

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Dr. Dyno

NAXJA Forum User

Location

Al Ain, UAE

• Oct 8, 2005

• #9

summitlt said:

true, but you want to be able to shift and land back into peak power

Click to expand...

...and that's why the HO rev limiter is set at 5250rpm. By then, the HP output is falling and the TQ output is dropping off rapidly so going beyond that is pointless. Valve float occurs somewhere around 5600rpm.