Ideal Rev range for 100km/hr

Post by **Zol** » Fri Sep 12, 2008 4:05 am

Hi all.
I have just converted my GQ to a 4.2 Diesel from th 2.8.
I have 35's & will possibly go 37 or 8
I also have 4.6 difs

My question is...What is the ideal revs a 4.2 should be doing at 100kms?

ATM it revs at 2200 RPM at 100km/hr. Feels a little high. First gear is short tho I have plenty of grunt & pickup. Once I install a Turbo it will surely feel like it is even shorter between gears. I do a bit of medium to heavy 4wding but I mainly need it to run effectively on freeway for work.

I would love to hear what others run in revs at 100km/hr & with bigger tyres as well.

Cheers
Zol

Post by **dave_str** » Fri Sep 12, 2008 8:48 am

TD42 + 35's + 4.6 gears = Just about standard ratio.

Leave it how it is.

Dave.

Post by **coxy321** » Fri Sep 12, 2008 10:17 pm

If your putting a turbo on, i'd just leave it.

I have 4.1:1/TD42 and currently sits on 2700RPM at 110km/h on my 31" HT's. Speedo is 15km out (it actually reads 125km/h).

With 35" ET's speedo is spot on and engine does 2150RPM at 100km/h.

I'm happy with my current gearing, as a turbo should bring the power/torque equal to or greater than that of the gearing when i run the 31" tyres.

The only reason i would personally go 4.6's and/or transfer reduction is if i got into crawling/rocky stuff - which i dont see happening anytime soon.

Coxy

Fri Sep 12, 2008 11:28 pm

coxy321 wrote:If your putting a turbo on, i'd just leave it.

I have 4.1:1/TD42 and currently sits on 2700RPM at 110km/h on my 31" HT's. Speedo is 15km out (it actually reads 125km/h).

With 35" ET's speedo is spot on and engine does 2150RPM at 100km/h.

I'm happy with my current gearing, as a turbo should bring the power/torque equal to or greater than that of the gearing when i run the 31" tyres.

The only reason i would personally go 4.6's and/or transfer reduction is if i got into crawling/rocky stuff - which i dont see happening anytime soon.

Coxy

that doesnt sound right , sounds like you might have 4.3 ratios

Post by **Tony WestOZ** » Sat Sep 13, 2008 2:30 am

My stock everything TD 42 N/A GQ with 4.1 ratio`s does 2400 rpm at 110 km/h.
100km/h is approx 2200 rpm.

Post by **Zol** » Sat Sep 13, 2008 3:00 am

coxy321 wrote:If your putting a turbo on, i'd just leave it.

I have 4.1:1/TD42 and currently sits on 2700RPM at 110km/h on my 31" HT's. Speedo is 15km out (it actually reads 125km/h).

With 35" ET's speedo is spot on and engine does 2150RPM at 100km/h.

I'm happy with my current gearing, as a turbo should bring the power/torque equal to or greater than that of the gearing when i run the 31" tyres.

The only reason i would personally go 4.6's and/or transfer reduction is if i got into crawling/rocky stuff - which i dont see happening anytime soon.

Coxy

My Speedo is right on 10km/hr out. Shows 110 when I am really doing 100km/hr

Wow 2700rpm seems pretty high. Your first gear must be soooo short but your tourque would be pretty beefy?!

I'm assuming that once I put 37's & turbo she should have a good balance. Will sit at 2000rpm at 100km/hr & turbo will hold some power. At the moment I keep pushing the clutch in to change to 5th when I realise that I already am in 5th.It's feels like the revs are still high....but it could also be from that damn viscous fan. It is noisier than the engine.lol

I dare say that the first gear would feel a good length for normal driving but won't loose too much power while towing a 3 tonne boat. I'm thinking that the fuel consumption might be the next test.

Post by **canuck** » Sat Sep 13, 2008 9:08 am

Tony WestOZ wrote:My stock everything TD 42 N/A GQ with 4.1 ratio`s does 2400 rpm at 110 km/h.
100km/h is approx 2200 rpm.

The same here.

Post by **coxy321** » Sat Sep 13, 2008 10:23 am

I generally dont use 1st gear unless i'm offroad. You'll find the added diameter and also the extra mass of the bigger wheels will change things dramatically for you.

Why dont you see if you can borrow someones 35's for a test??

As i said before, the only reason you would probably want to go lower is for rock'n and crawling.

As for my 2700RPM cruising speed, it was a choice between that or wasting my ET's on the bitumen (along with twice twice the fuel consumption, and 90km/k top speed).

Doesn't seem to be using any oil, and only uses about 10L/100km.

Post by **Tomo_89** » Sat Sep 13, 2008 10:33 am

my N/A td42 with 35's and 4.11 gears sits on about 2000 revs at 100k's and reads 90k's on the speedo

Post by **Zol** » Sat Sep 13, 2008 3:18 pm

coxy321 wrote:Why dont you see if you can borrow someones 35's for a test??

I already run 35's

Post by **Zol** » Sat Sep 13, 2008 3:25 pm

Tomo_89 wrote:my N/A td42 with 35's and 4.11 gears sits on about 2000 revs at 100k's and reads 90k's on the speedo

Aha.... Tomo...That's prolly the balance I'm looking at ending up with once the 37's are on.

I'm really interrested to know how your truck feels with your setup?! Eg First gear, through gears, 5th gear & overall power & fuel consumption. I would assume that it feels pretty much on the mark....yes???

Post by **Tomo_89** » Sat Sep 13, 2008 4:34 pm

first throught to third seems fairly good but it loses a fair bit of power in fourth and fifth. Fuel economy with extractors and pump tweak is about 15l/100k's. I'm thinking of going to 4.3's when i turbo it so i would say 4.6's would be ideal for 37's.
Let me know how it goes with the 37's as i would like to do this but don't want to lose too much power.

Post by **Zol** » Sat Sep 13, 2008 7:09 pm

Tomo_89 wrote:first throught to third seems fairly good but it loses a fair bit of power in fourth and fifth. Fuel economy with extractors and pump tweak is about 15l/100k's. I'm thinking of going to 4.3's when i turbo it so i would say 4.6's would be ideal for 37's.
Let me know how it goes with the 37's as i would like to do this but don't want to lose too much power.

That's great fuel economy. Yeah I'm thinking the same. I have to saythat I'm suprised that people hik tht th 4.2's are sluggish. or a stock diesel I think they do well Comparing itto the 2.8DT hey are about he same but without the Turbo kick.

Will keep you posted mate. Will proly throw an add in to sell 35's while they are newish & make sure someone has stock of 37's before they sell.

Post by **MyGQ** » Sun Sep 14, 2008 1:17 am

Mine is a slug that's for sure

it won't hold 110K's with 35's on and 4.11:1 ratios, maybe my engine is dying or something.

Post by **Zol** » Sun Sep 14, 2008 4:33 am

MyGQ wrote:Mine is a slug that's for sure

it won't hold 110K's with 35's on and 4.11:1 ratios, maybe my engine is dying or something.

Wow. That's interresting. I've been driving a 2.8dt with 35's with 4.6's & it held up. I'm sure that a 4.2d should manage with 4.1's. Has it always been like that?

Post by **macneil** » Sun Sep 14, 2008 2:20 pm

is there any reason u want to run a set of 37's if ur only doing light 4wding.. leave the 35's and save fuel..

Post by **Zol** » Mon Sep 15, 2008 12:36 am

I think that with Turbo & lower rev on freeway with 37's it will be more economical. That's my thinkin.....Seems sorta logical....don't know.

Post by **Tony WestOZ** » Mon Sep 15, 2008 1:18 am

Zol wrote:I think that with Turbo & lower rev on freeway with 37's it will be more economical. That's my thinkin.....Seems sorta logical....don't know.

Not really.
You could be doing 2000 rpm but the throttle could be open more to keep the engine at those revs.
Think of a generator. The throttle opens to increase the power output needed for the increased load, but the revs stay the same.

37`s might cover more distance per revolution but there size and weight require more energy to turn them.

Post by **Zol** » Mon Sep 15, 2008 2:48 am

Tony WestOZ wrote:
Zol wrote:I think that with Turbo & lower rev on freeway with 37's it will be more economical. That's my thinkin.....Seems sorta logical....don't know.
Not really.
You could be doing 2000 rpm but the throttle could be open more to keep the engine at those revs.
Think of a generator. The throttle opens to increase the power output needed for the increased load, but the revs stay the same.

37`s might cover more distance per revolution but there size and weight require more energy to turn them.

I totally agree with you Tony & for all I know...You could be right. The only reason why I think that it might work is because it feels like it could do with a drop of a few hundred revs & feels like it has heaps of power (tourque). Maybe even too much. At the moment I can fairly comfortably overtake in 5th gear on the freeway straight. Dropping down to 4th would be slightly too high as well. Feels like it's almost balanced but not quite. Just shy of it's "sweet spot" This is all on feel.

I'm wondering if these engines vary much between each other depending on "wear & tear"???? As my engine feels capable.

I adjusted the tappets yesterday as well & seems to have increased it's power a fraction too. Next step is towing. I am hooking up the boat this morning & heading off for a fish. It will be the first tow with the 4.2 setup. I am very curious to see what she does with a 2.5 to 3 tonne load. First gear will be an absolute dream compared to the 2.8DT. This was one of the major reasons for upgrading. First gear on the 2.8 was terrible for taking off on a hill & impossible to pull the boat up a ramp without low gear....Even with standard wheels. But I have to say it did well through the rest of the gears. It's just that dreaded first gear that was painful. Will post a result when I come back.

BTW...Thanks to you all for a great discussion. I've learnt alot from all of your responses & looking forward to more. Who knows...we might even end up making a chart for best diff/tyre combos for the bible after we're done.lol

Post by **coxy321** » Mon Sep 15, 2008 9:15 pm

As far as getting better fuel economy on a "loaded" diesel, my thoughts are that with equal load, you're better off running a higher RPM (within reason, say 2500RPM) compared to running at a lower RPM (say 2000RPM) and labouring the motor. The only thing running at a lower RPM would acheive is hotter EGT's and more fuel usage.

I know that would personally preffer to have too short of a gear setup as opposed to too tall of a gear setup.

Coxy

Post by **GUJohnno** » Mon Sep 15, 2008 9:21 pm

Mine sits at 1,900 RPM @ 100Km/hr and cruises very nicely. I depends on how you have you turbo set up at.
I have mine set now that with slight accelerator pressure I can quickly be doing 120Km/Hr.
With the torque down so low it makes for easy cruising and towing and great off road.

Post by **coxy321** » Mon Sep 15, 2008 9:26 pm

GUJohnno wrote:Mine sits at 1,900 RPM @ 100Km/hr and cruises very nicely. I depends on how you have you turbo set up at.

Very true. Are you running a .64 or .86 A/R on your exhaust housing?

.64 is probably spot on for what you said.

Post by **GUJohnno** » Mon Sep 15, 2008 9:34 pm

I recently changed from the .56 down to .46 and added a 3" dump and exhaust and had it tuned by Andy.
By doing this it has lost a little top end power but it's fantastic down low where I wanted it for towing the camper.

Post by **MyGQ** » Mon Sep 15, 2008 9:40 pm

Zol wrote:
MyGQ wrote:Mine is a slug that's for sure

it won't hold 110K's with 35's on and 4.11:1 ratios, maybe my engine is dying or something.
Wow. That's interresting. I've been driving a 2.8dt with 35's with 4.6's & it held up. I'm sure that a 4.2d should manage with 4.1's. Has it always been like that?

hard to tell, i have swapped over from 33's to 35's but the decrease in power is remarkable, and its slowly going slower up hills lately, maybe its time for an Injector pump and injector service.

Post by **coxy321** » Mon Sep 15, 2008 10:29 pm

GUJohnno wrote:I recently changed from the .56 down to .46 and added a 3" dump and exhaust and had it tuned by Andy.
By doing this it has lost a little top end power but it's fantastic down low where I wanted it for towing the camper.

OK. Thats fairly small, is it on a T3 or T28 unit?

Post by **Tony WestOZ** » Mon Sep 15, 2008 10:34 pm

GUJohnno wrote:I recently changed from the .56 down to .46 and added a 3" dump and exhaust and had it tuned by Andy.
By doing this it has lost a little top end power but it's fantastic down low where I wanted it for towing the camper.

Good move there.
To many people go bigger turbos chasing HP rather than looking at real world applications.
Torque at the right revs is were it`s at.

Post by **GUJohnno** » Tue Sep 16, 2008 5:28 pm

coxy321 wrote:
GUJohnno wrote:I recently changed from the .56 down to .46 and added a 3" dump and exhaust and had it tuned by Andy.
By doing this it has lost a little top end power but it's fantastic down low where I wanted it for towing the camper.
OK. Thats fairly small, is it on a T3 or T28 unit?

Denco Switzer unit

Post by **Zol** » Tue Sep 16, 2008 11:11 pm

Hey guys.
Towing went well. First gear was absolutely brilliant. Didn't even need to drop into low gear on the ramp at Tunks park...and that' a pretty steep ramp. Freeway was good. I could cruise nicely on about 80 to 90km/hr in 4th on some hills & even fifth & could manage 100 in 5th no dramas (& more but not a good idea & illegal)

It is in need of a turbo just to get that extra grunt through the gears after second gear. Fuel consumption was great. Not a huge difference between normal driving & towing. Don't know extact figures with tank meter yet but let's say....I have done about 230kms on a full tank so far. Out of that I have done approx 100kms of towing & I still have over half a tank left. That's pretty good. About the same as the 2.8 without towe. The 2.8 absolutely guzzles on load. Much more than the 4.2.

Was looking at Turboglide for installation of a Turbo. Not a bad price. I was recommended but I still have time to research more. If anyone has strong recommendations please let me know.

Cheers

Post by **GUJohnno** » Wed Sep 17, 2008 10:13 am

I would suggest talking to Andy at Diesel-Tech regarding turboing the truck

Post by **Zol** » Wed Sep 17, 2008 9:28 pm

GUJohnno wrote:I would suggest talking to Andy at Diesel-Tech regarding turboing the truck

Where abouts is he & do you have his number?

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Ideal Rev range for 100km/hr

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