Sid447

Pewterme,

It's possible you are hitting dfco rpm or map. You might want to check what it's set at and if nec, re-adjust to different datums.
If that isn't it; try adjusting throttle follower and or cracker to get rid of it.

Pewterme

Yes, the first time it was installed dot to dot. I then had to buy an adjustable timing chain so I could have it degreed. The only bad part of this was having to pay labor charges again. Any other cams I have installed will be degreed. The only difference in my cam is that is is a +1. Looking forward to hearing your results.



I'm supposed to be going back to Nashville sometime soon to let him tweak it a little more and will ask him about this. Does the C5 have a throttle cracker?? Seems there was something different?? Anyway, appreciate the suggestion.

GuitsBoy

iTrader: (4)

I think he reduced his bucking by 97%.

The bigger displacement probably helps out too...

Im along teh same lines, ive got a huge majority of it tuned out, but every once in a while my right foot does the magic combination to make it buck.

WKMCD

iTrader: (2)

I agree. That's how my car was done. 230-236 XE-R 112 +2. No bucking. I drive my M6 3.90's car in bumper to bumper DC traffic any time I want.

Gauge

iTrader: (3)

So...

Can anyone describe exactly what causes the oscillation? I know what factors can affect it, but can anyone explain exactly what is going on when this surging occurs?

PREDATOR-Z

Too much fuel, not enough air, too much timing or all of the above.

GuitsBoy

iTrader: (4)

Too little fuel, too little timing are what I usually hear, but im sure you can overshoot this too...

PREDATOR-Z

I reduced my surging by decreasing timing and fuel. Maybe my base tune was overshot as you said.
I'm sure there are more factors to consider, like SCR as well.

Gauge

iTrader: (3)

I was hoping for something a bit more specific. There's an oscillation going. At one point the engine is surging and putting out more power than you want, and at another point the engine lulls falling in RPMs and not putting out the power you want. What's happening at each point and why?

EDIT -- Inquisitive nerds can be a real PITA, can't they?

muncie21

iTrader: (14)

Not sure about your (or others) situation, but on my car it was fueling related. It would surge/oscilate based on AFR values, which changed from ~11 to 17 during low RPM steady state driving. This change in AFR made the car lunge forward and stumble back as the PCM tried to add/remove fuel to maintain stoich.

jegten

iTrader: (22)

thanks for the clarification.
initially, i had your cam, and changed to this particular one.
we'll see what happens.

jegten

iTrader: (22)

anyone-and sorry if hijacking

the setup i was installing included the tsp torquer 2 cam, stock rocker arms, and the stock length on the pushrods (7.40) was fine.
now that i changed to this cam, 228/232, .588/.595, but mine is on a 110+2lsa, will the stock length PR (7.40) fit fine?
it just occurred to me since i got the cam last week.

thanks

GuitsBoy

iTrader: (4)

Anyone want to share what the timing is at low map?

Im right around:

800 - 28*
1000 - 33*
1200 - 39*
1400 - 40*
1600 - 42*
1800 - 43*
2000 - 44*

As MAP goes up, timing falls off.

Does this look about right? Ive seen a lot of people say to jump right up into the 40's where the bucking takes place...

PREDATOR-Z

yeah, but cam only i would run 7.425

jegten

iTrader: (22)

thanks, Pred!

Gauge

iTrader: (3)

That's a small LSA, but the duration is pretty low, so the overlap is not very big. I'm not surprised there was no surging.

eamador11

You know what also, that bucking may not all come from the cam. I actually have slight bucking now after i swapped to 4.10s (i only have a 224 cam) Its possible it could be due to the very low final drive gear on first and the low speed you are doing. (ie I have to keep slight pressure on the gas when cruising through a parking lot)

You will however experience hot starts where after you re-start a hot motor the idle is very erradic until it finishes hunting.

GuitsBoy

iTrader: (4)

Hot Idle start issues and idle hunting are far easier to tune out that this blasted bucking... I dont believe the two are related. I have no idle hunting or surge, hot or cold start.

jay_99z

iTrader: (5)

That's where I'm at too. I have a 383 with TSP Giant cam. Idle is perfect....in park or in gear. In fact I can't get it to stall. No surge at all.

Only problem area is part throttle between 1400 and 1800 RPM's. I have the fuel dialed in with wideband. I have played with the timing and have gotten nowhere. It sits dead on timing and fuel cells (not switching between two cells) but still bucks. For the time being I have the converter lockup adjusted to keep me out of that range. I'll try again when I get more patience

GuitsBoy

iTrader: (4)

Until a tuning genious can lay out a step by step procedure on how to tune a big cam to not buck, im gonna have to say that no tune will ever completely eliminate it. Sure I can easily drive around the problem areas, but that dosnt mean its eliminated. Im very particular about my tune. Ive tried positively everything and I read constantly in the tuning forum and the HPT board. Nobody that I know of has sufficiently explained how to aleviate bucking. The best ive seen is a few coverups. They seem to work fairly well (although not entirely) but then once the weather changes, its back to bucking hardcore again. Wont somebody fess up and let the magic spell out of the bag?