Overhead Cam

[Mals BA XR6T]

Many years ago I owned a 1984 Nissan TRX bluebird. Anyway after many hours/kms of hard driving something bad happened to the motor but as it turned out it was a good thing. A total rebuild was called for (I told you it was bad) and I ended up putting in a "lumpy Cam". After a few mods to the carby (remember those) and timing gear (remember adjusting that too) I had the car back on the road.

Well blow me if it didn't improve things!!

Anyway, is this something that you do to cars like ours today?? Twin Overhead Cam jobbies I mean??

[Cobra]

no mate ... please no .... wait till they have been out awhile ....

(beware the modification salesman !!! B) )

[Mals BA XR6T]

I'm not thinking about doing it... not in the near future anyway, just wondering if it's still done in general

[Cobra]

  Mals BA XR6T said:

I'm not thinking about doing it... not in the near future anyway, just wondering if it's still done in general

a great quote ... with the amount of science in "variable" engine management nowadays, the cams are often over looked ....

their roll has become somewhat fundamental, but they can still have major impact on the running of the car, the jump to VCT was one the last big impact ...

some say there are too many variables .. probably right ....

IMO new cams cost a truck load in comparison to an exhaust or interceptor chip and can't make near their gains ...

cheers

[Macktheknife]

Not too much can be gained from a practical point with mods to the cam profiles/lifts etc if you've got forced induction.

Take a look at what Dynoe Steve is achieving with what are relatively simple (but well evaluated) mods.

Remember you've got double VCT already.

Mackthe....

[rjn]

yeah that is the beauty of VCT, it kinda gives you different cams when you need them I.e. when you put your foot down the profile change, so it's better than changing them for some "lumpy" ones as they are only lumpy when they need to be and not lumpy when you are just cruising.

Honda have this pretty well sussed with the VTEC thing, incredible amounts of HP out of a 2 litre in the S2000, nearly all down to some serious cam changes "on the fly" and extreme (for a road car anyway) revs (9000 max).

It wasn't that long ago you would have been pretty happy having 176kw (240ish HP) in your 5.x litre V8

[Mals BA XR6T]

VCT is timing, "lumpy Cam's" refer to lift. Unless I'm mistaken?

I'm just thinking about this out loud really, and what, if any benefit would you have?

[Turbo6man]

  Mals BA XR6T said:

VCT is timing, "lumpy Cam's" refer to lift. Unless I'm mistaken?

I'm just thinking about this out loud really, and what, if any benefit would you have?

lumpy doesn't refer to the cam at all - just the effect the cam has on the way the engine runs especially at idle.

The timing of the cam, the lift of the cam and the overlap all have an effect on the "lumpiness", but cam timing is the most critical.

You can achieve good improvements with older motors by using a higher lift cam and not changing the cam timing too much. But for all out performance you need the alter timing to correspond with the engine rev range, the compression, and the type of inlet runners you will want to use - there are a lot of variables as you might imagine.