Outer Limits 4x4 Board

Lads,

I'm thinking of flattening out the torque curve in my 3.5DOHC V6

Has anyone out there done anything with replacement cams or regrinds in this engine?

I heard a whisper that the EVO Pajero has adjustable cam cogs (ie timing)like TRD works ones

Any thoughts

Secondly has anyone replaced the valve stem seals in the DOHC - how much pain is it?

Ado

You can't regrind the cam and change the profile as the computor will not know what is going on unless you change to unichip etc and reprogram
Sorry

Actually, thats not entirely true. You can re-grind a subtle cam profile and the computer will still be happy, its only when you start to use high lift and long duration cams that the computer will scream thats enough... You could use a vernier cam gear to play with the cam timing on a dyno, that might be enough to give you better bottom end.

I haven't thought this thru, so it could be crap, but here goes:

DOHC = one cam for inlet, one for exhaust.

Should be easy to adjust each in opposite directions to reduce valve overlap (or adjust one only? - maybe inlet?) to move the torque peak to lower revs. Trade-off would be in top-end power, and I don't know how the computer would react.

Scott

South and Scott,

Yeah, thanks you've confirmed what I thought -

With the existing arrangement I could only move each cam by a tooth - prolly too much

It would be easy with vernier cam cogs - Know where I could get some?

I heard that the EVO model has them

Ado

If you know how much you want to move them by, just drill another hole for the locating dowel.

Working out where to put the hole could be a bit tricky, and I'd never get the hole where I wanted it anyway, but clever people can apparently do this quite successfully.

Cheers,

Scott

Guys,
The Pajero's and all mitsu's run a Karmen Vortex air flow meter. This will allow you to change the airflow into the engine (ie cams) and it will cope quite well. High lift isn't the problem it is overlap between the exhaust and intake and to a certain extent the duration of the intake that will effect the ability of the computer to cope. So if you keep the same duration and over lap but increase the lift the engine will cope just fine. As stated the torque band on an engine can be moved by changing the overlap between the intake and exhaust to improve efficency at a given RPM. The only way to increase power is to increase torque at a given rpm. The only way to increase torque to to increase the break mean effective pressure (ie stuff more air into the engine).

Cheers
Paul

Paul,

Now you've done it

What your saying is that the ECU won't cope with changes to the Overlap

and that's what I wanted to change

The DOHC is plenty powerful and torquey enough but the power and torque curves are more suited to rallying (paris-dakar) than crawling in heavy terrain i find that if I'm at lowish revs and I apply more right foot it either bogs down or spins

I want get more torque at lower revs even if it means loosing peak torque

and before anyone says it I don't want a bloody diesel

Ado

HI ado,

Newbie here but I have a 3.5 DOHC 5 speed as well and I reckon the thing has great low down grunt. The biggest improvement has been made with a k&n replacement panel filter and a 2.25 exhaust with one muffler.

It will pull 2nd up some pretty steep hills at less that 1000rpm - I have been very impressed, and having never been a Mitzi person, I'm well chuffed with its ability.

ANd I agree with ya - I don't want a bloody diesel either!

regards

Adow,
The computer won't cope with big changes in the amount of overlap that doesn't mean you can change where the overlap occurs. The reasons that it has problmes is because as you increase the amount of overlap you end up with a rougher idle, this in turn makes the airflow through the AFM pulse which causes it some confusion. Not as much a engines that run a MAP sensor though.

Paul

NJV6,

Yeah Roger the diesel not with the low range gearing of Pajeros - I drive a 3l turbo diesel Prado at work and its hopeless below 1600rpm but it compensates well with almost 3 to 1 low range.

Paul - I don't understand, how do you move the overlap - advance or retard inlet and outlet cams together..., what effect does advancing and retarding have on torque delivery respectively?

I remember getting huge improvements in the old rally car by increasing the lift and increasing the overlap (ie the inlet duration was extended (to let more air in) so that inlet and exhaust valves were open at the same time more), the cost was the engine lost all its bottom end - fine for a race car.

so I thought that if I could increase the lift and reduce the overlap in the Paj I could flatten out the torque curve and get less overall but better average across the rev range.

Ado

PS most performance shops only know how make race not lugging engines and don't know what specs to cut the cams to

Adomw wrote:NJV6,

Yeah Roger the diesel not with the low range gearing of Pajeros - I drive a 3l turbo diesel Prado at work and its hopeless below 1600rpm but it compensates well with almost 3 to 1 low range.

Fair comment, they are geared a bit 'through the roof'

Adomw wrote:PS most performance shops only know how make race not lugging engines and don't know what specs to cut the cams to.

Perhaps you could pull an old 2F Land Cruiser engine to bits and have alook at its cam!!!

Cheers, Glen

Glen,

It's funny you should say that....,

I was going to check out the SOHC Mitsi V6 cam

Apparently they are less peaky to drive

Ado

Great minds think alike,
fools seldom differ