Just wondering.. at which lift or duration or whatever does your idle get lumpy and sweet soudning? Thanx,
Matt

 

Duration of 230* starts giving you a fairly lumpy idle.

 

what about 256*.. what does that sound like? What kind of cam gives you that lumpy, scare the sheeit outta your diapers, 67 Z28.. feel it in your chest from a mile away, making the car shake violently, type of duration?

 

The cam I just took out of my BBC was .637/.637 lift and 270/280 duration and it idled smooth at 1000 rpm.

LSA and valve overlap also plays a part in idle quality. You can have 2 cams with the same lift and duration and they'll have different manners if the LSA and overlap are changed.

 

Rob: I am talking about a 305.
Stephen: How was your's smooth at 270 lift, but a 230 is starting to get lumpy?

 

For your '85 I suggest the Comp Cams XE262H or the XE268H cam, which both have a nice lope to them. I've used both. I currently have the XE268H in the engine, but I think I made more overall power with the XE262H.

In fact, I think I have some XE262H 305 cam sounds laying around here somewhere:
http://www.ws6transam.org/tasound2.wav
http://www.ws6transam.org/tasound3.wav

Through Hooker cat-back: http://www.ws6transam.org/tasound5.wav

 

The displacement of the motor makes a big difference as well. A 230/236 .540/.555 112 cam sounds pretty bad *** in a small block 350. If you stuck that cam in a 383 or a 406, it wouldn't sound as mean. If you stuck something similar into a 468, it would sound down right tiny.

A 305 doesn't need a very big cam because it can't make use of all the air/fuel the cam can provide. An LT4 hot cam would probably sound very mean in a 305.

 

I have found me a great cam.. has 256/268 duration. How would that sound? Those all sound AMAZING.. (the sound files) I htink the first 2 are the best.. but they are ALL nice! But what lift/duration would you need to get that classic muscle car shake, and cam-stutter?

 

hey 97ws6charged.. that all makes very good sense; thanx for the description

 

Keep in mind that that rumpity-rump sound is just the sound of an engine having a hard time running. A noticeable lope will almost always mean poor low end grunt, believe it or not.

It gets old REALLY fast on your daily driver

 

That's why they make 4.10:1 rear end gears and stall converters.

The last car I had like that was a 77 Z28 with a built 355 in it. I thought it was cool to watch the air cleaner dance through the 4" cowl hood. It definately got attention. The only thing that sucked worse than the mileage (9/gallon with the th350, 15/gallon with the 700R4 which broke too many times) was not having AC and living in Florida. Driveability was fine with the 2800 stall and 3.50:1 gears.

One last thing, usually poor low end performance is caused by mismatched parts. Too big a cam, not enough compression, crappy heads, wrong rear end gears. When you pick a cam, you need to pick one that will work with your setup, not because it's the biggest cam Comp offers or because it works in your buddy's car. There is actually a science behind this stuff.

 

Why does the "rumpity rump" cause the engine to have a hard time breathing?

 

That rumpity rump is the sound of exhaust gas being pushed into the intake tract, diluting the air/fuel mixture with inert, already-burned gases. As you increase duration, the intake and exhaust valves stay open at the same time for a longer amount of time and exhaust reversion increases.

The stacatto sound is partly the sound of combustion gases "popping" up past the intake valve into the intake manifold runner. Another part of the sound is from a combustion cycle on one of the pistons that goes unfired, because the air-fuel mixture for that particular cycle wasnt strong enough to light off and push the piston down the bore. As you increase RPM though, the incoming air column gets enough velocity (and inertia) to reduce the effects of reversion.

 

So why do muscle cars tend to have this type of cam? Isn't it true that cams with this type of lump are high-end power-making cars?

 

in my 305 i have a 480/480 lift 210/220 @50 and 112 lsa. it dosent have a heavy lope, it has a choppy lope-idle which i like more than a heavy lope.