Cruising revs on a 6.5 chev

All,

I have a 1999 wagon with 4.65 diffs, and a 2005 manual gearbox from a 3.0 TD, running on 33's. The 6.5 chev that I had installed currently sits on about 2230rpm when cruising at 100kph. These revs don't seem that high for other motors but the 6.5 seems to have a sweet cruising speed at 2000rpm and 'feels' like it is revving high when at 100-110kph.

Has anyone else with this conversion noticed this or am I imagining it? I think the sweet spot would be around 1900-2000rpm in my uneducated opinion.

One piece of advice I had was to change the diffs out to 3.5's, but that seems a bit counter-productive for the slow stuff.

Another option looks like the 10% rev reduction overdrive gears from Marks 4WD adaptors.

Any thoughts would be appreciated.

Hi Ben,

to be honest mate you have a Beast on an engine there with a whole different Torque Delivery. IF it was me? I'd be taking the 4.6s out and selling them and fitting some 4.11s.

f you tried hard enough you could find someone keen to swap their 4.11s for your 4.6s with maybe $300 to $500 your way or something. swap them in the drveway ;

If neither of you are up for the task of the swwap and want to pay then ask them to pay for the strip and fit of both cars and get the swap done.

3.5s seem pointless but if your engine is happy at 1900 then dropping to 4.11 seems ideal i'd say.

So you think doing the diffs is better idea than the 5th gear changeout? Costs and swap opportunities aside.

For sure! The 4.6s are sort after by TD42 owners wanting to run 35 " tyres. They give us back our Torque Curve. You don't have a problem there! Infact it sounds like your a little to far into it at cruise and would be happy with a lower ratio all round.

The 4.1s are a dime a dozen and you should have little trouble finding some. If you drove it down to Brisbane you might find ok mate Bene or Newby might even grab them off you!

4.11 should drop it nearly 400 revs so it will sit quite nicely then. You have heaps of torque with that donk so could even go as low as 3.9s.

Yeah, torque is certainly not the problem.

Am keen to know how others with the 6.5 have got theirs set up as well. Sounds like 4.6's are not the way to go with this engine.

Quote:

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Originally Posted by BenK

Yeah, torque is certainly not the problem.

Am keen to know how others with the 6.5 have got theirs set up as well. Sounds like 4.6's are not the way to go with this engine.

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Companies like Brunswick and bullet swap the 4.6's out as part of their conversion.

Hmm, perhaps I am wrong about the diffs then. It went in with 4.6's, but I just checked the Brunswick Diesel site and your right, they seem to fit the 3.9's as part of the conversion. If that is the case, and I am not convinced going to a 3.5 diff ratio is a better idea, then perhaps the 5th gear (overdrive) mod is the way to go to bring those revs down a bit.

5th gear mod from Mark's adaptors went in yesterday. I opted for a 10% reduction in revs. Engine now cruises at about 1850rpm on 100kph which was slightly less than I thought it would. On the positive, there is still ample torque for overtaking but I'll update once I have had a chance to tow the boat (2 tonne) on the highway. So far very pleased with this mod and I think it will suit this engine nicely.

After an 800klm highway run, I am definitely pleased with the change. Revs are at 1850-1870 on the 100kph mark, and at around 2000rpm for 110kph. Still plenty of torque if a quick overtake is needed.

When towing, it did require a few extra downshifts to 4th on the hills, but I'll take that as an acceptable consequence.

Is there any way of telling the age of a transmission, Marks adapters website states 'Nissan updated all GU Patrols as of 08/2004 with a longer spline main shaft and 5th gear'. Is this what that modification is trying to achieve? Although mine now has a 4.2 box in it, how would I know if the box has the new spline. My rpm at 100 sits at about 21-2200 so it probably hasn't got it.

You cant tell from the outside, and the way you can tell if it is ok or not, is by checking the colour of the oil

Mic

Quote:

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Originally Posted by BenK

After an 800klm highway run, I am definitely pleased with the change. Revs are at 1850-1870 on the 100kph mark, and at around 2000rpm for 110kph. Still plenty of torque if a quick overtake is needed.

When towing, it did require a few extra downshifts to 4th on the hills, but I'll take that as an acceptable consequence.

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G'day Ben,

I am curious what your fuel consumption figures are like, ie city, hwy and towing?

Regards,

RLI

I haven't filled up since putting the new 5th gear in and driving that last 800klm trip, so can't compare that yet. We also did a stack of hard low range driving, but the low range stuff is mainly all just idling or slightly above, with short bursts of acceleration.

My best fuel consumption has been 14.3litres/100klm, which was a combination run on around 650klms of highway, good dirt roads and a little 4wdriving. I have also had figures of 14.6/100 and when towing it gets into the 16/100, but again, I haven't done a long highway run with the boat on to accurately gauge that yet.

I'm currently away with work, and have to drop the fuel tanks to remove contaminants when I get back home, so I am unlikely to have an accurate figure for a while yet. I would be very surprised if the fuel consumption comes down too much from where it is, but Brunswick reckons it should get into the high 13/100. I'm dubious of those sorts of figures, but keen to put it on a dyno to get the best out of it soon. No doubt it would also benefit from a mandrel bent exhaust instead of what is currently on it.

I'd be interested to see what sort of figures others with this engine are getting as well.

I haven't done a fuel comparo yet that's on the highway only... The last one I did was highway/off road and towing a camper trailer... About 18/100.... Was still pleased as my old 4.5l GU was 22/100 and no where near the torque the new beast has!

I was initially told not to get one as they over heated, cooked heads and blew turbos and drank fuel like there was no tomorrow....

Bloody glad I didn't listen. I've had my wee beastie for about a year and still giggle like a school girl when I hit the loud pedal!


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