BBC Daily Driver Cam Question

[burbfixer]

When adding a cam to enhance a stock, or close to stock engine, at what point does duration begin to affect idle quality, vacuum, and off idle torque?
Some factory cams are so tiny, it seems substantial improvements can often be made and will help power everywhere, from idle speed to redline. I suspect that for many standard small and big block domestic V8s the duration where compromises begin is somewhere in the 205-215 range, but don't really know, so was hoping to tap in to some of your experience.
I know more info is needed, so for the sake of this discussion lets assume the following : 87 octane fuel, heavy tall geared street and highway cruiser with a manual trans, so it will at times be asked to pull from near idle speed. Assume a close to stock 454 long block with compression about 8.5 or 9 to 1, headers and good exhaust, and a decent intake and carb. The exhaust port and system are not particularly weak, so a flat hydraulic cam with a single pattern, or close to it, is desired. So the engine is 'stockish' but better. Also assume a common 110-112 lsa. What duration number would enhance the engine, but preserve the idle, vacuum and off idle torque? Likely not everyone will agree, but I'd still like to hear your thoughts.
Thanks in advance!

[lefty o]

with 454 inches, id say you can do about 220@.050" without any compromise and likely wont notice it at idle or cruise. as always pick a cam guy and give him a call.

[Kenny M]

I just had Crane grind me one for my driver. Its a 74 Trans Am 455 Super Duty. The lobes I used were BBC lobes on a HY Roller I used them to keep the lift out of the engine..OEM valve springs and 1.52 rockers. 323 gear with auto trans. 9.5to1 180 lbs cranking compression, 17" Vacuum @900rpms, Very mild cam sound with No shake. Idles like a baby at 700 rpms in gear. Runs perfect on California 87 fuel, no knock or run on.. timing is 12 36 and 45 with vacuum advance. Tons of power from off ideal to 5600. 224 230 .490.500 114 in at 110

[Newold1]

I have learned over the years especially with more education of my tiny brain by great camshaft makers that duration alone is a short place to start when planning engine power and torque ranges. Other specs. such as LSA, IVO, IVC, EVO, EVC have to be considered and designed to produce the best possible result. Just considering duration will most of the time lead to a camshaft that does not provide top performance.

[Roadknee]

with 454 inches, id say you can do about 220@.050" without any compromise and likely wont notice it at idle or cruise.

Agreed. I have a 268 Comp (218 @ 0.050") in a 7.6:1 468 in a heavy truck. Idles smooth 625 rpm in gear and pulls hard to 5,000 rpm.

[CamKing]

What duration number would enhance the engine, but preserve the idle, vacuum and off idle torque?

Cam# BBCH, H68305-69310-112
216/220 @.050"
.519"/.527" Valve Lift
112 LSA

[GOSFAST]

You should consider setting it up with a hyd-roller if you're thinking cam change!

Not a real big deal on the BB's, most BB blocks are already drilled/tapped for the cam plate! No cam buttons or "chasing" cam end play to worry about. Would be no big deal doing a spring change.

Thanks, Gary in N.Y.

P.S. An "added" plus by changing over to the hyd-roller yields about 30 "free" HP. The initial cost is more BUT, if you manage to "flatten" a lobe or two it will prove to be a moot point!

MkIV Block - MkVI Cam Thrust.JPG

[burbfixer]

Thank-you everyone for the replies. Appreciate the 'personal experience' comments especially. Anyone else care to chime in on the initial question? More input is welcomed!
In the latest episode of Engine Masters (love the show) one of the hosts almost seems apologetic for using the 'smallest cam he's ever intentionally installed' - a 218 degree cam. Admittedly, my experience is very limited, but I've never had one even that big - but I'm trying to learn!
CamKing,
I understand you do this for a living, so thanks very much for the specific recommendation. It fits with what I had suspected. I assume as compression changes, so would that number? So at the risk of over-simplifying it - is there any rule of thumb for adding/subtracting duration if compression moves up or down? For example, for each 1/2 point compression, add or subtract about X degrees for a similar result?
Newold1,
You raise some good points about other factors. With such a vast array of cam choices out there, I needed to start somewhere, and thought most of us understand duration as the fairly standard cam sizing 'language'. If duration isn't it, what do you feel is a good starting point in making cam decisions? I know Mr Vizard teaches it's overlap and lsa, and that duration is a byproduct of those two numbers. Do you have experience using that method? Or another that has worked for you?

[Kenny M]

You make a very good point. My concern on pump gas stuff is detonation. Sure you can go with 212 and 108 cams and make amazing bottom end. But if your In the 9.5 range your on the edge of trouble if your running 87 to 91 fuel. Here is a example, when I built my Super Duty 455,(See Previous post) I wanted to use a standard HY camshaft. A summit 2802 was a very nice SD replacement 224 234 114 .460 lift.. I installed the cam, plenty of lifter offset. I always mark the pushrods to make sure they spin. I fire her up on the run stand . And two lifters are not spinning. I caught it immediately. It seems like the left bank of the cam was ground wrong. Because it put the lifter contact back in the center of the lifter. The cranking compression was 175.. I had a Crane HY roller on the shelf 212 222 112 .500. in at 108.. I installed it and checked number one compression 225 LBs.. that would be trouble.. I backed it up to 112.. 205 LBs.. Still trouble. So being I had oem springs 125,290.. that is why I made my low lift roller.. Again she runs amazing.

Ken Maisano
Mascar Classics

[burbfixer]

Kenny M,
Thanks for the cranking compression info. It's all info I can apply to my build. 220ish psi will be right in the ballpark for me because... in my actual build, I'll be building for propane. I intentionally left that detail out so more people with personal experience would reply. With lpg fuel, I should be able to increase the compression mentioned in my first post by 1.5 to 2 points to compensate for the fuel octane, and still consider the replies from everyone very valid. When it comes time to buy a cam, I will likely email CamKing and go with him. I've read many posts of his on several sites and am fairly convinced he's a true expert when it comes to optimizing a cam for an application. Should be interesting!

[gnicholson]

I would go 210 to 215 single pattern on 108lsa . Ton of off idle torque

[burbfixer]

gnicholson,
Thanks for the suggestion!
At one point in my quest for info, i was stoked to try a narrower lsa as you suggest, likely with a similar duration as you mention. Vizard books, and other comments on various threads had me convinced that a narrower lsa is the way to go for torque and best power. What holds me back now from going that route now is this : I'm not clear on the effect narrower lsa's have on fuel efficiency. Piecing together the few statements I've seen on it, it sounds like fuel efficiency might suffer, and I'm not willing to give up several mpg for the added power. If you or anyone else have input on this, it would be appreciated!

[pdq67]

One way to look at this is to compare dynamic compression ratios of several cams.

I figure that for a good 454, Erson's HI FLOW AH is a dandy mild high lift, hy-cam.

Spec's: 284/218 or 220, (depending if it is an older cam or a newer cam is all), 111/111, .542" lift.

The only deal is that you will need to install high lift valve springs because stock springs won't work.

I have a new 284/218 Erson, new old stock, cam in my closet that I never used because I went 496". I was going to make a 475" engine until the dreaded, "More power Scotty", bug bit me!

As well as a new old stock set still in the box K-B Silv-O-lite .100" over 454" hyper flat-top pistons.

pdq67