Thread: Thumpy Idle

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Hi guys/gals!

Camshafts are still a bit of a mystery to me.

About what duration do cams make a engine thumpy at idle/poor vaccum?

Is there a general formula/guide I can follow?
Is camshaft duration porportional to vaccum loss?

In a nutshell, what I am asking is, for a street engine how much duration is too much? Or does it come with years of engine building like you guys have?

lol i'm all questions,
thanks in advance,
-CJP

I would say on a SB Chevy 218 at .050 and up 450 Lift and up . You can hear the cam from there-up and start to drop Vaccum .

a well built engine is usually planned around the cam .. the cam is the heart

The cam in my El Camino is 276/286 at .0045", 221/230 at .050", .454"/.454" valve lift, and 110 LSA, and is best with 9.0-10.5 compression to 6000 rpm's (a low end cam) It has lots of lop, and pulls 16lbs of vacuum, power brakes work normal, the more duration the more compression that bleeds off, which I wanted to do with my 58cc heads, so that I could use 87 octane gas. It never knocked with 87, even when it was 100 degs out

Pat

That was a good idea with that camshaft pick . With the cost of gas this is a good way to still run an engine with high C/R . with out having to change heads or pistons . I had a 1969 Pontiac 400 that was way up on the C/R I did the same thing . COOL

Depends on cubic inches too. The smaller the engine, the more radical the cam will sound. For example, the old Duntov cam in a 350 will sound pretty mild. In a 283, it will sound pretty radical.

Get a P.A.W. catalog (Performance Parts Warehouse). They carry everything, including cams from different manufacturers. They will list the applications for each cam profile and what you will need to reap the benefits. (ie: cubics, compression, convertor, gears, etc...)

You can make any cams to have thumpy idle is by closing down the lobe center line down to smaller number...

I am definitely writing this info down!

276/286 at .0045", 221/230 at .050", .454"/.454" valve lift, and 110 LSA
Now that is a torqey/low range cam. How did you come the conclusion of using that camshaft HemiTCoupe? Street/daily drive El-Camino?

-CJP

Originally Posted by dhemi1

I am definitely writing this info down!

276/286 at .0045", 221/230 at .050", .454"/.454" valve lift, and 110 LSA
Now that is a torqey/low range cam. How did you come the conclusion of using that camshaft HemiTCoupe? Street/daily drive El-Camino?

-CJP

I put the motor together back in '94, I had it for my '37 chevy pickup, that I sold with the mock up motor in it, it had sat in the corner on a stand wraped up, I put it in my El Camino 3yrs ago.
I wanted a motor with lots of lop and not a lot of lift so that I could use 87 octane, this is the one I wanted, it does have lop, it also worked with out changing the TQ, I drove it everyday for 2 1/2yrs (I sold it), I pulled more weight than I should have at times, it had lots of low end pull.

I talked to Harold , (He's always on the forums at Team Chevelle) He was the designer of the cams & owner of Ultra Dyne cams , then Lunati bought him out and he has been designing cams for yrs there, he makes alot of the factory stock & hp cams.
I lost the papers on my cam and I just told him the number on it, and he wrote this back to me : (In another thread he said it's good in a 350/383/400 , and in a 283/305/307 use a different cam)



#1 Aug 15th, 05, 10:25 PM
HemiTCoupe
Tech Team Join Date: Jun 2005
Location: Maplewood, Mn.
Posts: 41


UDHarold "E8239"

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I bought one of your cams about 10 years ago, and I lost the papers and I don't remember anything about it.
On the end of the cam it says "E8239" stamped on the gear end along with 276-286-H10 and "UD"
I have it in a 406 with dished pistons, 60cc 202/1.6 heads, early 80's spread bore intake, Q-Jet, headers. stock torque converter with a 350 tranny.
Could you please tell me if it's good for low end or mid range. How it should idle. lift duration. or even if it's good for this motor or not!

Thanks Pat
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HemiTCoupe

Pro Street Full Fendered '27 Ford T Coupe -392 Hemi with Hilborn injection
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#2 Aug 15th, 05, 11:50 PM
UDHarold
Senior Tech Team Join Date: Oct 2002
Location: Senatobia, MS, USA
Posts: 1,467


Re: UDHarold "E8239"

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Sure.....

Your cam is 276/286 at .0045", 221/230 at .050", .454"/.454" valve lift, and 110 LSA.
Yours is the 58239th cam that UltraDyne ground.
It should be in the engine on a 104° to 106° ATDC ICL--ie, 4 to 6 degrees advanced. It should work with anything between 9:1 to 10.5:1. Power in a 406 should be from just off idle to 6000, with peak around 5200. Idle should be around 750, and there should be enough vacuum to work power brakes. I still make this cam, only on 112 LSA.
It's a good one.....

UDHarold


another guy asked him :


Jun 7th, 05, 08:57 PM
blue66 Join Date: Jun 2005
Location: WI
Posts: 19


UDharold cam reco

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I have a friend who is looking to change cams in his 406sbc, it is basically a driver but he is looking to have a nice lopey idle like my bbc solid roller but stay hydraulic and not change springs, rockers etc.
Anything out there that will make him happy?
its basically a stock 406, dual plane alum. intake, 4 barrel carb.
Thanks, BRian



#2 Jun 7th, 05, 10:09 PM
UDHarold
Senior Tech Team Join Date: Oct 2002
Location: Senatobia, MS, USA
Posts: 1,467


Re: UDharold cam reco

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Brian,

Not changing springs, I'd use either the VooDoo 262, with 219/227 at .050 and .468/.489 valve lift, or one of my older Lunati grinds, like the 301A5LUN, 272 at the seat, 217 at .050, .454 valve lift, 112 LSA, lots of vacuum, very long street life. or the 301A6LUN, 276 at the seat, 221 at .050, .454 valve lift, and 110 LSA, lopier idle, enough vacuum for brakes. I also have a 301A8LUN, 221/230 at .050, still .454/.454 valve lift and 112 LSA, that works power brakes.
All of the .454 lift hydraulics have a long history of long life on the streets, many over 100,000 miles. MY daughter used the 276 as an exhaust lobe in her 383, and it went 8 years on one set of springs, rockers, and lifters.
Tell me more about the engine and car and we can narrow it down.....

UDHarold



Harold is a nice guy and will answer any cam question, and not only about the cams he works with!!!



I'm no expert in camshaft theory, but I think a simple way to think of it is how many degrees of camshaft rotation there are between the midpoint of the exhaust valve lift and the intake valve lift. 110* is very common with a mild SBC cam. Assume that is a standard and all else is kept equal, 108* degrees would increase the amount valve overlap (ie. amount of time both valves are open at the same time) reducing lower rpm cylinder pressure and raising the rpm powerband of the motor. 112* has the opposite effect and would serve to build more low rpm cylinder pressure and lower the rpm powerband of the motor.

RPM range is also affected by the duration of the valve event (ie. 280* of duration will have a higher rpm range than 260*).

My .02 Worth!

Pat

Originally Posted by Racecar100

You can make any cams to have thumpy idle is by closing down the lobe center line down to smaller number...

This will really make the engine have a thumpy idle.
I would also favor the exhaust by 10 degree's.
In other words try and find a cam that is ground on a 106 L/S.

dHemi i too was looking and Denny found this one for me . Top link is the Comp Cam specs which are mild but this cam sounds great in the Vette in the second link. Just hit replay at you tube



http://www.compcams.com/Technical/Se...umber=35-218-3


http://www.youtube.com/watch?v=RJ_5NMiDJNA

I know,,, THIS damn v6 guy again,but this is the kinda question I'm asking.SINCE 90 DEGREE V6have different spacing than 8s ,how do I figure my cam specs to get the low end feel of big inches and still get good hp.to the 5500 rpm of these 262's ?Is there a way for v6ers to have as much gun as yiou aters? you know, sound and lope,thanks for lisyening phil the geezer

To reiterate some of what has already been said . . .
The last line kind of sums it all up.

This from http://www.superchevy.com/technical/...cam/index.html

LOBE SEPARATION ANGLE
By choosing a cam with the correct LSA for the engine's intended usage, you can have your cake and eat it too. First of all, the LSA is ground into the cam at the factory and cannot be changed without regrinding the cam. It represents the number of degrees, in crankshaft rotation, that separate the intake lobe centerlines from the exhaust lobe centerlines. A wider LSA figure, i.e. 112-116 degrees, moves the lobe centerlines further apart and will smooth your idle due to the decrease in overlap that it creates. The lower the figure, i.e. 106-110 degrees, moves the centerlines closer and will increase bottom end power, but your idle will suffer along with it. I did a test a few years back running five different LSAs on otherwise identical cams in the same engine. What I found was that the cams with a 108-110 LSA worked best all around. But idle vacuum was higher with the wider LSA cams (112-114) and this would translate to better idle quality. Bottom line here is that most cam companies have put lots of effort into selecting the proper LSA for the cam's intended usage so you'd be wise not to second-guess them.

Originally Posted by bluestang67

dHemi i too was looking and Denny found this one for me . Top link is the Comp Cam specs which are mild but this cam sounds great in the Vette in the second link.

Nah that's not a cam...here's a CAM!
Crank up your sound, it's worth it...

http://videos.streetfire.net/search/...5f014a00e4.htm

def a good sound .. should have put down a little water though .. thats a good site for the younger guys ..