Thread: V8 guys with big tyres.... i have some questions

Originally Posted by shayne86

Its an 04 facelift model with 4.0 and according to the vin its a low compression block. Roughly 280k on the clock.

The V8s aren't my thing, but from what I read that's a fair innings for a 4.0 without refreshment. Blokes like Pedro might have something to say on this.

Try a few extra psi in the tyres.

Has anyone else been through this or should be looking at refreshing the old motor?

It would be rare indeed for a V8 to NOT need a new camshaft and lifters at that mileage. ( the original design of the V8 By GM made the camshaft Base circle diameter very small to get a compact engine, but the loads on them are therefore greater than later V8s say with roller lifters.)
The bottom end is usually OK , but the heads will usually need a clean up and valve reseat.

One of the issues with overgearing a V8 is that to reduce Nox they are retarded at low revs so at highway speeds you have dropped out of the best torque band.

My TD5 is light years ahead of my highly modified 3.9 (for torque with Thor manifold, chip, dyno tune modded heads but stock cam) towing up a hill.
Regards PhilipA

I don't know where this 3% figure is coming from, it's more like a 10 % difference from where I'm looking.

Here's some figures from the ExplorOz wheel size calculator

Tyre Size Calculator @ ExplorOz Articles

Using the standard D2 tyre size of 235/70R16 or 255/65R16 (both pretty much the same dia.) these are the results I get.
Results for tyre 255 / 65 R 16

Rolling Radius	368.95mm
Circumference	2318.18mm
Diameter	737.9mm
Wheel Cover Size	Size 005

Results for tyre 275 / 65 R 18

Rolling Radius	407.35mm
Circumference	2559.46mm
Diameter	814.7mm
Wheel Cover Size	Size 009

Differences between Wheel/Tyre 1 & 2

Rolling Radius	38.4mm
Circumference	241.28mm
Diameter	76.8mm
When your speedo reads 100km/hr you're actually at 109.43km/hr

Rolling diameter has been increased by around 3" (76.8mm) and the circumference by around 10" (241.28mm). On the ground this is a difference of 9.43%

No wonder the poor oldLandy V8 is doing it hard

Deano

Originally Posted by DeanoH

I don't know where this 3% figure is coming from, it's more like a 10 % difference from where I'm looking.

Here's some figures from the ExplorOz wheel size calculator

Tyre Size Calculator @ ExplorOz Articles

Using the standard D2 tyre size of 235/70R16 or 255/65R16 (both pretty much the same dia.) these are the results I get.
Results for tyre 255 / 65 R 16

Rolling Radius	368.95mm
Circumference	2318.18mm
Diameter	737.9mm
Wheel Cover Size	Size 005

Results for tyre 275 / 65 R 18

Rolling Radius	407.35mm
Circumference	2559.46mm
Diameter	814.7mm
Wheel Cover Size	Size 009

Differences between Wheel/Tyre 1 & 2

Rolling Radius	38.4mm
Circumference	241.28mm
Diameter	76.8mm
When your speedo reads 100km/hr you're actually at 109.43km/hr

Rolling diameter has been increased by around 3" (76.8mm) and the circumference by around 10" (241.28mm). On the ground this is a difference of 9.43%

No wonder the poor oldLandy V8 is doing it hard

Deano

Your figures are valid, but he is comparing the new biggies with 31 inch tyres on 16 inch rims, not standard D2, so bit of a halfway house issue.

Originally Posted by shayne86

I knew there would be a bit of a performance drop but i was not expecting this much of a drop compared to my other set of 16's with 31's.

Originally Posted by DeanoH

I don't know where this 3% figure is coming from, it's more like a 10 % difference from where I'm looking.

^^ this is where the figure came from Deano

I suspect there may be a bit of all the previous answers, generally, the difference in feel to say 265/70/16's from stock is usually acceptable ( TD5's less noticeable than the V8's ) but from there up it's pronounced on both ( comparing stock TD5 and V8 ) .
It's been very hot in Perth as well, so that will also contribute.

Edit , hah beat me to it Gavin

Originally Posted by discorevy

^^ this is where the figure came from Deano

I suspect there may be a bit of all the previous answers, generally, the difference in feel to say 265/70/16's from stock is usually acceptable ( TD5's less noticeable than the V8's ) but from there up it's pronounced on both ( comparing stock TD5 and V8 ) .
It's been very hot in Perth as well, so that will also contribute.

Yeah i think you are right with the heat component of this little dilemma of mine. Driving around today without the camping gear on board with a slightly lower outside temps felt a little nicer to drive. But there aren't any big hills near home to test this theory.
Maybe im just not use to old girl yet.

I have a heavy D2. Lifted, sliders and steel bars front and rear. 31 inch Duratracs on 16's. Roof racks. Pulls like a steam train with a 1 tonn boat on the back up hills and did very well with a 2 tonn dual axle boat on the back too. Stock high comp 4.6 5 speed manual. My 2.4 triton has more torque when towing the same 1 tonn boat up hills but the 2.4 variable vane turbo Triton motor outguns the stock TD5 in a big way, and has a very nice Aisin 6 speeder behind it. I know that very tricked TD5's go hard too. As a matter of passing interest as to how motors have developed- stock TD5 in auto is 315nm (1950rpm) and 101kw (in Disco)(4850rpm). Stock MQ and MR Triton 2.4 MIVEC is 430nm (2500rpm...so likely more torque but certainly no less torque as TD5 at 1950 but then keeps building) and 133kw (3500rpm so nice and low too). Cheers