Awhile back we put a competition cam in my coupe and now, when I cruise at low speeds, the resulting lumpy surge seems to load and unload the u-joints and the tranny and rearend gears giving a kind of whiplash effect that gets stronger and stronger until I push in the clutch. Is this pretty standard or does it indicate that I need new driveline parts (excessive lash)? Is there anything short of downshifting and running at a higher RPM that a guy can do? JOE
It's usually the extra lead that tends to end up in your right foot right after installing a lumpy cam that is hard on drive line components.
That was my first thought. What gear ratio do you have, and what does the cam manufacturer reccomend? Is this a "bottom of the page" cam?
For this reason? Is it the higher pitch, or the fact that they would be new gears and newly adjusted? Either way, I might look into that. JOE
Not sure, offhand, on the ratio. By "bottom of the page" do you mean getting close to the biggest cam I could get? I don't recall the specs on the cam, but it was the second biggest one I could have gotten for my 350... then ended up using it in a punched out 283. JOE
To keep the rpm up. Since the longer duration cam makes the engine run poorly at low rpm....making it surge, etc.
Typically, the more radical a cam you have, the lower the rear end gear ratio (numerically higher) needed to support it. This is due to the higher RPM range that the cam operates in. For example, if the cam starts making power at 3500 rpm, then your factory 2.73 gears (just an example) are going to make the car virtually undriveable. It will be a sputtering slug up until the engine reaches its new power range, and then will come on like gangbusters. For example, say your car has 3.25 gears from the factory. Most of the cams listed in a mofern cam catalog show the gear ratio that is recommended to work best with it. The "bottom of the page" cams as I call them...the more radical ones...typically call for at least a 3.73, if not 4.11, gear ratio. If your cam is radical for a 350, and was put into a 283, its going to seem even more radical. It may be overcammed for your intended use entirely. Post up the cam specs, and try to get your rearend ratio...that would be a big help.
I've always been really happy with the gearing of this car, so I don't know if I wanna go there. I'll have to look at the ratio I have and the specs on the cam. Maybe I'll put some new guts in the rear this winter and tighten it up with some fresh u-joints and go from there. I appreciate the input. I didn't know if my car was trying to tell me something. It may just something I have to get used to... like riding the clutch a little more than normal to get it moving. JOE
It's related to the "no free lunch theorem" which says that if you gain more power at higher rpm, you give up low rpm driveability.
That statement right there makes a lot of sense. BULLDAWG- I'm not sure where the spec card is at the moment, but thanks for the offer. JOE
So you're saying there's a trade-off involved? That you can't have it both ways? You can't have your cake (or cam) and eat it too??? Wow, that gonna be a tough sell with some folks around here. I love it when somebody cuts right to the meat of things like this. If he's got s 3 speed in it, I wonder if switching to a 4 speed with a lower 1st gear and some more even gear spacing would help. Maybe advancing the cam a few degrees would bring back the low end driveability a bit as well.
Engine not tuned correctly will do the same. Mine galuped when I first got it running with a manual tranny. More initial timing and leaning the idle took it away for me.
Actually you can have your cake and eat it too. Look at the new SS Camaro and GT Mustangs. 420+ HP and 6 speed trannys getting 20 to 30 MPG and idle like your grandma's station wagon. And that's factory stock with a warrantee. Most of us would rather have the steep ramps and big overlap of the old skool cams tho. Mileage sucks, Steep gears needed, can't hear the stereo over the headers, crawling in traffic takes practice to just keep the damned thing running. That pine tree air freshener can't quite hide the burnt rubber smell in the car, but people bullshitting in the parking lot don't stand there and ignore you when you're comming at them. They get the hell outa the way.
try these options Rhodes lifters mechanical lash give it 030 lash correct power valve or metering rod springs timing and advance curve sometimes it takes some tuning, and SOMETIMES other parts a raceing engine is not suitable for the street, unless you are a very skilled tuner i have had some 283 that werent suitable for the track and took 3 days to tune and that had a chev off road cam which is kinda mild first day it just stalled and coasted to door Powerglide! finally the last day laid rubber all the way out the door and off to the races
That could be a big part of your problem. A cam that is big in a 350 is probably going to be way too big in a 283.* 215-218 degrees at .050 and around .450 to .480 lift would be a pretty big cam to run in a street driven 283 and I'd be willing to bet if it was the 2nd biggest sbc cam they were offering it's a hell of a lot bigger than that. Look at something from the Comp Cams line in the 250-262 advertised duration range and you'll have a cam you're a lot happier with if you like street and highway cruising.
I just went and shredded my office and can't find the spec sheet on the cam. Sorry to be unable to supply information to help answer my own question. I love everything else about this engine though. Its powerful, loud, obnoxious, rumpity, revs through the roof in less than an instant, and as mentioned above... people get out of the way when they hear me coming (and they do hear me way before they see me). Other than the slow cruiseing issue I mentioned, it's awesome. CLAYMART hit on something too... I'm running a Saginaw 3-speed, so a 4-speed with closer gearing might be the answer for me.... and I'll try a timing tweak too. I live in the middle of the Chequamegon National Forest and don't do a lot of driving at city speeds, so as long as my car isn't telling me its about to toss a gear I can live with it as is, but if I can I'd like to make it smoother in town. Thanks guys... JOE
Rhoades lifters will improve vaccum at low speed, and eliminate any trace of "big cam" sound at idle...but not fix the problem, which is too big a cam (or not enough engine, however you want to look at it). Not to mention, changing lifters on a flat tappet cam isn't a good idea. If the cam is as big as I'm thinking, its either gear swap or cam swap. A cam swap would be cheaper.
Nobody likes the sound of a big lumpy cam better than I do, but they definetly come at a price and that's generally loss of low rpm performance. I believe what you are experiencing is just the effects of operating the engine way below the effective rpm range of the cam, it's just not going to run good down in that rpm range because it wasn't designed to, it wants to race. If you want to run smoother through town and keep that cam you gotta raise your rpms while your doing it. Drop a gear and let it wind up. A 4 speed like was mentioned above might be a big help, cruising in 3rd just might do the trick. Good luck!
The proper cam is the answer to this issue. The overlap is too much, and the duration is too big. The second biggest cam for a 350 into a 283 is FAR too large, and unless you have the head, intake, and supporting system to turn the RPM's needed, the gear change is going to take away from your enjoyment of your car. The proper cam besides being your least expensive option is also going to increase your performance, increase fuel economy, and provide the driveability that you want. The shock load on the driveline components will ead to premature failure over and over again. Big racing type cams are great for cars that spend 95% of their time above 4500 RPM, but on the street, and properly matched cam for the combination will provide everything that you want. You can even get a custom speced for your exact application that will provide the lumpy sound without causing driveability issues. The engine is a system, and you have a mismatched part in the system. Things will fail, and performance will suffer.
Rhoads lifters will only reduce by a certain amount, if you got too much cam then using Rhoads lifters will give you slightly less than too much..They are noisy and you don't know if they ever really give the full cam at higher revs as oil temp, pressure has a role..There is no reason why you can't change the lifters as long as they are new, the cam is good, and you still do the proper break-in..IMO think your surging problem can be corrected with tuning..I will guess that the idle speed is around 900/1000 rpm, if you are trying for much lower that in itself is a problem....I suggest a mechanical advance only distributor...18° initial, 10° in distributor [gives 20° actualy] which will give 38° total, coming in by 3000 rpm..Be sure the distributor starts advancing 100/200 rpm higher than idle speed, very, very important!! A lot of carb recomendantion can be given offhand but if you check and post the engine vacuum level at idle it can be way closer..
Ultimately this is the right answer, selecting the proper camshaft is always best. If you want a lumpier idle with a cam that has lift and duration that are a decent match for the engine you can go with a tighter lobe separation angle, although you might lose some vacuum.
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