Camshaft characteristics

Hi, I have a mildly build 455 (425hp, 517 lbsft) with a 227/238 cam, .481/.492 in my 1971 GS.

How would you describe the characteristics of such an engine at idle, low speed, higher speed? No headers, Lock-up Converter at 2800.

I feel it`s "rumbling" quite some compared to a stock 1974 Century 455 I recently drove that was all stock.

Between 900-1800 rpm it seems to transmit some "virbrations" to the car, it`s rocking a little, but seems to keep the "rhythm", stabilizes as the rpm get higher, cruises nicely above, lets say, 2000 rmp.

As I have no comparison, neither personal experience with different cams nor other modified engines to rely on, I`d like to ask what you think about this? Would a cam with the above described parameters behave like I describe?

Thanks

Jens

 

It sounds spot on for a Cam of that size in a motor which is that amount of CID, especially with low compression 1971 heads!
For how many miles has this Cam been in the motor?

 

I would question the exhaust. It almost sounds like an exhaust vibration or drone.

 

Like Sean said, it sounds like exhaust drone. What size pipes are you using? Larger pipes like 3" drone quite a bit, and some mufflers as well. Change the mufflers and see if that changes the sensation.

 

I wouldn't think that engine or that cam would be that bad as long as it didn't lock up the converter below 1800-2000 RPM. I'm going to go with the majority and suggest it might be exhaust related.

If it is exhaust and it isn't welded up solid, you can sometimes loosen a clamp and torque the pipes in different directions to give them a slight spring action. I've used floor jacks and ratchet straps to pull and push them around. One of my pipes used to rub the transmission cross member under load. We loosened some clamps, tugged and pushed with pry bars, retightened the clamps and watched it spring back a little but it bought me 1/4" of clearance and quit vibrating against the cross member.

Also, make sure your hangers have rubber isolators. I've seen shops weld the exhaust hangers to the frame and the pipe with no isolation. The engine and trans mounts allow movement and the pipes need some leeway, too. We have a body-on-frame design and the muffler shop treated it like a unibody.

 

Thanks for your infos so far, gives me a direction to check that wasn't on my list.

Had it up on a lift recently, asked the mechanic about the engine mounts, said they "looked" ok, but then I think I'll have to jack it up und see for myself if it rocks out of it's foundation while shifting. Scared of being overrun by my car though

Additonal info: the car was converted from a 350 to 455, it still has the original SBB exhaust. No X- Ort H-pipes, nothing fancy there, cast exhaust manifolds.
Heads are big valve-converted.

Jens

 

Lucky for me, I can't hear the loud, thumping, rumbling from the TA-413 Roller, over the squeaking of my polyurethane bushings...

 

Hey Larry, spot on for me, it's an AM&P build Street1, up to max. 5500 rpm street engine. I think you can still get the specs on Mike's page.

Yeah, thought also it might be typical for such a cam, car runs strong and all, but then,that slight rocking and rumbling...
It's a little bit like the scene in American Graffiti where Harrison Ford sits behind the wheel of the '55 at the lights,you can see the steering wheel moving and shaking in his hand while idling.

Jens

 

Is it "uniform/even"? If it is hitting correctly on all holes and fuel/air distribution is good, even all bumpy, it should be even. Having a hole missing, or uneven fuel air distribution can make it rough and annoying.

Can you get a video that helps show what you are experiencing?

 

Thought about that too, the video might be the way to go...better than movie analogies Won't be before the coming week, car's not at home right now.

I THINK it's quite even,and like I said, above 2000rpm it gets smooth, no more rocking. Might have to do another compression test to check on everything being equal.

Jens

 

You can fine tune the idle quality by adjusting the idle mixture screws or raising the timing a bit. If you have a vacuum advance setup try switching to a manifold vacuum source. This will add a bit more timing at idle and smooth it out. You can also slightly raise the idle speed a bit to smooth it out.

 

Hi Sean, thank for the hint.

No vaccum advance, it`s not meant to be hooked up for the setup as I can read in the instructions. I`ll go for the idle speed and mixture screws, a tune-up won`t hurt at all.

 

Hi everbody, quick update: after seeing my mechanic he adviced me to replace some ignition components as they looked quite worn, though not too old. Did the cap, module and rotor, waaaay more smooth right now, that "annoying" roughness seems gone for now.

Thanks for all your help and inputs

Jens

 

Another update: Found air leak at the carb`s front, fixed, again improved, runs so much smoother in idle, all around driving is tighter, more spontaneous, feels good..


Thanks for your help.

 

Sounds like you've got it sorted out. Good job.