What Makes The Cam Lumpy?

[LOCO]

I got a question i always wanted to know
what makes the cam have that lumpy sound?





Cheers, Serg

[GMMAD]

LSA gives it the lumpyness low LSA 108/110 gives a very nice lump
higher the LSA the smoother it is standard is 119 I think
it can also be tuned to be more lumpy as well

[MattJ]

I got a question i always wanted to know
what makes the cam have that lumpy sound?





Cheers, Serg

The overlap of the exhaust valve closing and intake valve opening causes the engine to be inefficient at low speed which results in the lumpy idle. The closer the Lobe Seperation Angle the more the overlap, the more duration the more (typically) the overlap. There is more to it than just that but that is the basics. You can have a large duration cam with wide LSA and have a resonably smooth idle, or you can have a small duration cam with close LSA and have a lumpy idle.

[LOCO]

So Just say the 114 lsa would be more lumper than the 112 lsa?
Is that correct?

[A^K^T]

So Just say the 114 lsa would be more lumper than the 112 lsa?
Is that correct?

It's the other way around , high LSA number for mild idle and low LSA number for rocking and snorting like a mad bull (duration has an affect too)

[SS-355]

Its the other way around mate ,112lsa would be lumpier than a 114 lsa.As has already been said the lumpiness can be altered through the tune.My cam is on a 112 lsa and you definately know its in there.

[ATOMIC MALOO R8]

Its the other way around mate ,112lsa would be lumpier than a 114 lsa.As has already been said the lumpiness can be altered through the tune.My cam is on a 112 lsa and you definately know its in there.


i was told by PT that tuning lump in to the cam was not advisable ?

[LOCO]

propz ppl u really help me out





Cheers, Serg

[macca33]

i was told by PT that tuning lump in to the cam was not advisable ?
I would imagine that tuning in/out some lope would relate a fair bit to idle speed and timing/fueling at particular idle points. Tuning, however, does not and cannot alter the valve events - they are fixed by the cam-timing and cannot be altered in our vehicles (our cars are not VVT/VTEC, etc).

Maybe PT don't like to do it, as it lowers idle and that could have other impacts upon the way the engine operates at idle with A/C, alternator, water pump, etc.

Cheers,

Macca

[JezzaB]

To make it lumpy in the tune you have to push the spark and fueling from their optimal positions. It can have an effect on drivabilty because you are effectively putting in a "bad" tune to make it lump and jump. So it is possible it may stall when cold etc.

Ive got a friend with a GTS cam and an A4. Ive got it to idle in Park like it has a largish cam and it rocks and rumbles but when you put it into drive its smooth as silk.

He likes to stand around the car chatting while its lumping away thinking its a big cam :lol:

Jez

[BLACK 346]

i was told by PT that tuning lump in to the cam was not advisable ?

I reckon they would know :)
What would be the point of tuning in the lump anyway, I guess if
you picked the wrong cam and it wasn't lumpy enough. Just make
sure you get the right cam and it is not an issue.

[macca_779]

I reckon they would know :)
What would be the point of tuning in the lump anyway, I guess if
you picked the wrong cam and it wasn't lumpy enough. Just make
sure you get the right cam and it is not an issue.

Alot of people actually like it. My 220 cam can be made to be quite lumpy with a lower idle and less fuel and timing. I don't do it because I like it smooth but others do. Each to their own but of all the cam's I've tuned only myself and Dug's Senator have wanted it to idle stock. Although I have been known to screw around with mine at times to show off its flexibility with EFI LIVE's real time Bi-Directional Controls.


To make it lumpy in the tune you have to push the spark and fueling from their optimal positions. It can have an effect on drivabilty because you are effectively putting in a "bad" tune to make it lump and jump. So it is possible it may stall when cold etc.

Ive got a friend with a GTS cam and an A4. Ive got it to idle in Park like it has a largish cam and it rocks and rumbles but when you put it into drive its smooth as silk.

He likes to stand around the car chatting while its lumping away thinking its a big cam :lol:

Jez

Jez one thing I did discover a little while ago and I don't think I told you about is when dialing in idle timing and then setting timing for maximum MAP vacuum it can bite you in the arse with the underspeed timing values. Normally as you know spark will be added to help control a low idle but if its already at max it will work against you and you get hunting that is difficult to filter out. So by dropping about 4deg from Max vacuum I've found that you can once again use timing to help control idle speed and idle quality isn't too much worse off for it.

[JezzaB]

Alot of people actually like it. My 220 cam can be made to be quite lumpy with a lower idle and less fuel and timing. I don't do it because I like it smooth but others do. Each to their own but of all the cam's I've tuned only myself and Dug's Senator have wanted it to idle stock. Although I have been known to screw around with mine at times to show off its flexibility with EFI LIVE's real time Bi-Directional Controls.



Jez one thing I did discover a little while ago and I don't think I told you about is when dialing in idle timing and then setting timing for maximum MAP vacuum it can bite you in the arse with the underspeed timing values. Normally as you know spark will be added to help control a low idle but if its already at max it will work against you and you get hunting that is difficult to filter out. So by dropping about 4deg from Max vacuum I've found that you can once again use timing to help control idle speed and idle quality isn't too much worse off for it.

Already pegged it bud ;)

Got a 234 234 112 cam idling very nicely.. well as nice and a cam like that will :lol:

[Banks_vz]

whats the standard cam for a vz ls1? i watched this video on youtube: YouTube - vy ss ute with cam idle (http://www.youtube.com/watch?v=GochUzGmYOI)

and that tickles my fancy :)

[huggies]

if you want a nice lumpy cam sound
texas speed Magic Stick 3 or 4 will give a great sound
MS4
YouTube - MS4 Cam in 2003 Z06 (http://www.youtube.com/watch?v=CP5uefxVh8U)

MS3
YouTube - MS3 2002 Camaro SS (http://www.youtube.com/watch?v=NT85QB9j55U)

[ATOMIC MALOO R8]

great stuff love that black vet

2300 for go
big stick for sound that's what its all about
YouTube - V8 (http://www.youtube.com/watch?v=3mL_ga3M13w&feature=related)