Good engine mods for the 4.0 V8???

[DM74]

Hey guys,

I was reading the 4.0 to 4.6 post and instead of high jacking it I thought I might do this seperately.

Does anyone have any great mods or ideas to improve economy and power on these engines without wrecking the reliability or their intended use? (ie off roading and pulling my 1800kg boat). (ie not superchargers, but that would be awesome....)

Generally, headers and exhaust are the first point I'd look at but I'm concenred that I'll lose back pressure and make 1st gear crawls on downhills a disaster? Anyone done a 'cat back' exhaust or full system?

Also, I see heaps of diesel computer mods, but do they have the same for petrol - 15% power up, 30% economy improvement??? Sounds too good to be true, but these are the numbers I'd like - or 30% power up....

I haven't towed our boat with it yet, and I really hope its not going to be as much of a slug as I think it will be? It does feel like it has plenty of lazy torque ready and waiting and is kind of deceptive once you give it some stick, but I sure as heck wouldnt want to give my wife a run from the lights in her Mazda 6...... (only up to the speed limit of course!)

regards
Darian

[big guy]

I suggest a cam for towing but best is to get a 4.6 with high compression motor and good computer like Haltech or similar.

Huge improvement, I realise its only 600ccm but it just rocks.

Pull yours out and sell seperately if it still runs well and or do exchange or similar.
Have a look at trs website.

[Tombie]

Cam
Head clean up and unshroud valves
Port match heads to manifold and Exhaust
Haltech
& 4.6 bottom end....

[Pedro_The_Swift]

back pressure?

anyway,, before you spend ANY money on it,, think about liners.

any decent improvement would be more than a D2 V8 is worth,,
not that that should stop you--
or me:angel:
but to get any decent torque figures you'll need 4.6 or 5L.

tophat it and stroke it to 4.9.
bullet proof and will go forever.

[BigJon]

back pressure?



:Rolling::Rolling::Rolling:

[DM74]

I guess the back pressure???? hasnt been noted before?

Small exhausts will have plenty of back pressure / restriction so when you put it in a lower gear (no accelerator) and back off, it is more likely to hold its revs - or put you through the windscreen. Eg going through the Burnley tunnel in Melbourne, or down a hill.

With a bigger more flowing exhausts in the same car, when you drop it into a lower gear the revs a more likely to build and will gradually speed up.

I'm no mechanic but have changed a few exhausts on my Falcons over the years, and I wouldn't want to modify it andt bugger up what I guess would be an important thing on decents - without having to use the 'hill descent' button which seems painfully slow....

Would love to have the spare cash around to throw some more 'Cubes' at it, but really looking for any cheaper mods that may free up a few ponies that are already lurking in there!

[bee utey]

Sawing a muffler off SOUNDS like you have more power but it's an illusion on a standard V8. The best way to increase your power/engine braking is to drive everywhere in 3rd gear instead of 4th. Multiply your flat torque curve by 30% extra revs and you get more power:D.
Seriously, save your pennies and get a 4.6 or 5.0 conversion.

[PhilipA]

I guess the back pressure???? hasnt been noted before?

Small exhausts will have plenty of back pressure / restriction so when you put it in a lower gear (no accelerator) and back off, it is more likely to hold its revs - or put you through the windscreen. Eg going through the Burnley tunnel in Melbourne, or down a hill.


Seeing the injectors switch off on overrun over 1500RPM , it is hard to see how back pressure has any effect as there is no/little hot gas exhausting.
Regards Philip A

[Traco]

Not sure about the D2 but it made a noticeable difference to my D1 when I fitted 2.5 inch free flow system using a Supercat straight through muffler. More torque and revs out freer. I retained the standard exhaust manifolds, which are quite good.

The Rover V8 usually responds to exhaust tuning. The works racing 3.5 SD1s picked up 30 bhp when they ran open exhausts.

[Hardchina]

Fit an 82 degree thermostat then modify the temp senders to the ecu so they read 98?(or whatever the stupid high 4.0 temp is) at 82. (just a thought....????)

[PhilipA]

Going from my experience with my RRC you DO gain some power with a free flow exhaust but only at full throttle high revs. At cruise there is little exhaust gas backpressure.

By 1992 or so the manufacturers had worked out how to have a low restriction but quiet exhaust by increasing the volume of mufflers which flowed quite well at light throttle.
Look at cars now and you will see humungous mufflers for even 2 litre cars, as noise regs get tougher.

From what I have heard it is difficult to cheaply get extra power from a Thor as the Motronic is quite efficient, even sensing misfire by measuring the crank acceleration between firings. The knock sensors ensure that max advance is always there. I understand that the Thor always runs at Lambda so an afternmarket ECU may yield extra power at WOT, but you would lose the refinement .

However there is a question on the low comp engines as to whether they are tuned for 89 octane or 91 so an interceptor may be able to add some advance. I haven't spoken to Graeme Cooper about Thor piggybacks for a long time but sveral years ago they found it quite difficult to gain much.

So I tend to agree that a bigger capacity is probably best to increase power significantly.

Head mods will help but in my case yielded 6% across the board on a 14CUX and I think similar on a Motronic. I do not have a flow bench so it is possible that a professional with a flow bench may get an extra couple of %. I haven't yet matched and ported my Thor manifold as I was afraid of losing some of my low down power but I would think you may gain another couple of % there as AFAIR it was pretty sloppy around the ports and injector monts.
Regards Philip A

[DM74]

Thanks guys.
I hoped there was something magical and cheap to do but it doesn't sound like it? Will leave it alone for now i guess....

regards
Darian