At which Lift or duration does your idle get lumpy?

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?

Are you talking about a 305 or 350?

More cubic inches lets you get away with more 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

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

The displacement of the motor makes a big difference as well. A 230/236 .540/.555 112 cam sounds pretty bad ass 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 :D

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

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 :(

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. :p

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?

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.

what do you mean a choopy idle.. glug..glug..glug..glug? Instead of an idle that sounds like it's gonna die?

what do you mean a choopy idle.. glug..glug..glug..glug? Instead of an idle that sounds like it's gonna die?

its kinda hard to explain. its like sped up lope with a crispy snap somewhat. when i pull up to a store , gas station or light it gets noticed. when i pulled in at work one of the constructtion guys re modeling the tech offices said "aint no stock cam in that thing" i turned back and said "wouldnt think it was a 305 ither!" and right about then he hadta pick his jaw up off the tailgate of his truck.

^ hmm.. I want a better-than-stock sounding cam.. (nice story though.. humored my quite well :lol: )

its far beyond stock sounding. not even close. going from a stock 89 305 and manifolds with only a cat back to headers and a MUCH bigger cam it was all the difference between pitch black and high noon.
im quite pleased with the outcome, now if i can get the dam thing fully tuned i'll be in good shape!!

I would also recomend the XE262 cam for your 305....it's a nice cam, and will provide plenty of power with the other mods you are planning.

I actually have that cam sitting in my garage, but my little brother is getting ready to slide it into the 305 in his '79 Malibu.

FWIW - the cam in my car is an XE274 (230/236 .490/.490 112 LSA ground +4 degrees). It's a pretty mild cam (esp. for a 400), but it's got a very sweet sounding idle @ 600 rpm :D


- Justin

Lift: .447''/.454''
Duration: 256°/268°
RPM Range: 1000-5200

That is the specs of the cam I want; seem any good?

Too much duration for street driving.....Is that duration at .050? If it is, wouldn't be my choice.....

That'll be a fine cam. Based on the lift, we can assume those are total advertised duration, NOT the duration at .050", which I assume will be in the 212/218 degree area, on what is probably a 110 degree lobe center angle. Install that cam on a 104 or 106 degree intake centerline and you'll be stylin'. Just remember to replace the valve springs, too, and clean up the ports on the heads to take advantage of the extra lift.

I dunno if it is "advertised" or "at .050".. I will try to find out. I am getting new v-springs, lifters, pushrods, rockers, etc.. and I will try to clean up the ports a bit. If I can find a die grinder, I will be in luck. All I do is ground out the ports a bit, right? Will that cam I gave the specs for sound mean in my car, or no?

I dunno if it is "advertised" or "at .050".. I will try to find out. I am getting new v-springs, lifters, pushrods, rockers, etc.. and I will try to clean up the ports a bit. If I can find a die grinder, I will be in luck. All I do is ground out the ports a bit, right? Will that cam I gave the specs for sound mean in my car, or no?

What cam is that? Do you have a brand name and part number?

- Justin

What cam is that? Do you have a brand name and part number?

- Justin

P/N 12-234-2 Comp Cams XE256H, 110 LSA, 212/218 @ .050"lift.

^ yup.
You have that focking memorized? lol.

^ yup.
You have that focking memorized? lol.
Heh, I got this thing about numbers, they stick in my head sometimes!

lol. Jeez.. you know your a Gear Head if you..

BTW Transam.. how will this cam treat me in my 305? I called comp about it a while back.. and they said this would be perfect for me.

With the 3.23 gears, I'd stick in a 2700 RPM stall converter. The cam will have a smooth idle but will lope a little bit, enough as to advertise that it's NOT stock. This will be most noticeable if you have headers. The cam will make decent off-idle power, especially if you upgrade the torque converter. As it happens, I have a 2700 RPM NEAL torque converter sitting here with less than 2000 miles on it, that I pulled when I converted over to the T56 manual. I'd box it and sell it for $150 plus shipping, if you wanted to pop it in while your engine is out. Duuh, whoops. I just remembered that you have a T5! :embarrassed:

Top-end punch will probably start about 2500 to 3000 RPM and continue through 5000 RPM, then drop off in the SOTPometer starting at 5500 RPM. You'll definitely shift before 6000. Make sure you check the intake centerline and try to set it up between 104 and 106 degrees. It'll help fatten up the low-end torque. My XE262H cam made peak power at 104 degrees.

If you want to really make it lively, swap out the 3.23's for some 3.73 gears. I wouldn't want any other ratio with a 305 third-gen.

I had the Crane Cams Powermax 2050 in my 305, loped a lot when cold and had that cool cam sound when warm.
here is a video of the car,
http://www.transamws6.com/video/ZepherWS6.mpg

The whole time reading that post (ws6transam) I was like.. "yup.. I have a T5" lol. But no worries ;)
whta is the SOTPometer? Why will setting the cam timing to that degrees help w/ low end punch? Will i need to put higher octane fuel in? What is the intake centerline?
Manny.. i have the vid on my computer. i LOVE the sound of your car :jelous: It does sound quite nice idling too :thumbsup:

whta is the SOTPometer?

Seat Of The Pants-ometer. Lots of people on this forum use them as their exclusive performance measurement device. Some people's SOTPometer's are so well-calibrated that they can feel the difference between a new AC spark plug, a Splitfire plug, and a Tornado intake insert.


Why will setting the cam timing to that degrees help w/ low end punch?


Setting the cam timing such that the intake valve reaches peak lift height at 104 degrees past top-dead-center will help fatten the torque curve while causing a little roll-off at the top end of the RPM band. Setting cam timing for intake centerline (ICL) is what is commonly called "degreeing in" the cam. You adjust it with three-way keyed cam chains, or with offset woodruff keys.

305's seem to like 104 degree ICL, whereas most 350's seem to liek 106 degree ICL, and stroker 383's like 108 ICL.


Will i need to put higher octane fuel in?

What is the intake centerline?


No, no octane requirement differences, unless you mess with the timing curve. Intake centerline is usually the point where the intake valve reaches maximum lift relative to piston position. "Centerline" is officially half-way from the point where the intake valve begins to lift from the seat, to where it returns to the seat. For instance, an intake lobe with 256 degrees of total duration will have its centerline at 128 degrees beyond the initial movement of the intake valve. If this centerline occurs at 104 degrees from top-dead-center, it means the intake valve will begin opening at (104 - 128) degrees, or 24 degrees before top dead center. If you dial in a 110 degree ICL, your cam will open the valve at 18 degrees before TDC.

Check the Comp Cams website, I think they have some illustrations online that help explain how this works.

Hm.. I think my SOTPometer is quite nicely "calibrated", lol.
I will tell the guy that is helping me w/ the rebuild about the degrees to set everything set to. THanx ws6!