easy question for cam experts

steel1212 · Nov 22, 2005

Ok, explain to me again what duration does for the cam and what lift does for the cam? Does more duration run to more hp numbers if matched up right with parts and more lift move the power band higher up in the rpms?

302 coupe · Nov 22, 2005

more duration raises the rpm range, more lift increases the torque. Given that horsepower is a function of torque and rpm, increased duration and lift will increase horsepower and torque, while raising the powerband.

SoCalCruising · Nov 22, 2005

Also, take note that the lift should be coordinated with the flow characteristics of the heads. That is, if your heads stop flowing at .400" lift, using a .500" lift cam will likely hurt power because the flow from .400-.500" lift may be of such poor quality that power suffers. This might be true of unported stockers on older engines, which may have decreased flow past their peak. In general, I have read that it is wise to pick a lift value that is at least 5-10% less than the peak flow value of the heads. This insures that flow characteristics will be good.

steel1212 · Nov 22, 2005

Thanks guys thats what I was wondering. I was looking at the retro fit roller cams for my car and most of them with the same duration as the cam I have now have more lift and I was wondering how that would affect performance. I have a 280H 230/230/ .512/.512 and I think the ones I was looking at went to .560 if I remember correctly.

.100 57.8 53.4

.200 111.4 95.7

.300 156.7 122.2

.400 189.3 137.3

.500 199.5 143.1

.550 203.6 146.0

.600 203.8 147.3

those are the flow numbers for my heads.

302 coupe · Nov 22, 2005

you don't want a retrofit (reduced base circle) roller cam. You want a regular hydraulic or solid roller cam, and link bar lifters to go with it. Cost is the same either way, but you have a far superior setup with the link bar lifters and full base cam. For lifters, check out Comp 838-16 (mech roller), Crower 66335-16 (hyd roller), or Crane 44518-16 (mech roller). With the link bar lifters, theres no need in using the dogbones/spider/reduced base cam to run a roller cam in a non-roller block. The reduced base circle cam's pitfall is it's lack of being able to support agressive lobe profiles, the core is too small and doesn't have the strength of a full base circle cam. A regular base circle cam can support far more agressive lobe profiles.

I think you need a head swap more than you need a cam swap at this point. Note that if you switch to the link bar lifters, the heads have to come off to install them due to their height.

D.Hearne · Nov 22, 2005

In comparing a roller to a flat tappet cam, the duration figures are misleading. A roller with the same duration as a flat will have more effective flow, due to the ramps being "faster", this opens the valves sooner and closes them later, giving it more flow "under the curve". It will also at the same time idle smoother than the flat tappet. Going to a roller with the same or close to the same specs in lift and duration will improve your performance with the heads you now have, due to the better low lift flow, as the valves will open sooner. I also agree on the choice of using the link bar lifters, simply due to the fact that they're reusable with other std base roller cams. If you're not happy with the one you choose, you will have more choices to swap to.

steel1212 · Nov 22, 2005

Yeah, I'll probably go with afr 165 or 185s at the same time if I switch cams. When I said retro fit I really ment the bar lifter setup.

SoCalCruising · Nov 22, 2005

If you look at the flow numbers on the AFRs, you'll see that the box-stock head is about all done at .600" lift. You don't need a cam with more than the .560" lift you are contemplating. You should invest in upgrade springs, though, if you go with a roller cam.

D.Hearne · Nov 23, 2005

SoCalCruising said:
You should invest in upgrade springs, though, if you go with a roller cam.

Well there's one thing I didn't need to do with my Canfield heads. The springs they came with are still at it, doing fine with a Z303 cam with 1.7 rockers. They've been up to 7 grand with it and 7500 with the B303 on the old motor. Never missed a beat yet.

57fairlane · Nov 23, 2005

If you really want to get confused, for a given set of duration figures we could narrow the LSA for a 'higher' powerband and widen it for a 'lower' powerband. For a given set of gross duration figures, we could increase the lift and raise the powerband. We could fatten the lobe ect . . . Really what happens is that you end up looking at valve timing events. Yes you could have a cam that is a generic 226/226 at .050 but you could make quite a few that have completely different timing events.

The 'new age' thinking is that high lift and radical ramp rates combined with a wide lsa with short duration and very good flowing heads get you the best of both worlds . . .

Gas mileage and performance that pulls to 6000+ at this point I am thinking Ls-1

steel1212 · Nov 26, 2005

Well I plugged the XE274HR comp cams hdyro roller into my dyno2000 last night. I know its just a desk top dyno but I've got every plugable number plugged in so I think its close. Anyway, with everything that I have on it now and if I just switched the cam from the 280H to the roller above I go from 339HP at 6k and 344 torque at 4500 as it sits now to 351HP at 5k and 399torque at 3500/4k with cam change. If I switched to afr165s I get 387hp at 5500 and 411torque at 4K. The afr185s move the power up more but the numbers go up as well to 418hp at 6K and 420torque at 4500.

Does this seem reasonable or am I just blowing smoke up my own ass?

D.Hearne · Nov 26, 2005

Sounds about right. The roller has more bottom than the 280H because it opens the valves sooner. But to use it, you'd need screw in studs and guide plates with your stock heads, if you don't have them now. That and a spring change. I think those numbers are off though as far as the rpms with a 302, seems to me, the hp and tq peaks would be a lot higher with the 185's and the XE274. With my Canfield's and a 1.7 rockered B303 cam, it didn't make power till 3000 and pulled to 7500. Never dynoed this, just my obsevations from behind the wheel. My Canfield's are the equivalent of 165's.

steel1212 · Nov 26, 2005

The only thing stock about these heads are the names. They have screw in studs, guide plates, new valves (wish they where 1.9s), little flow job, magnum roller tip rockers 1.6. Yeah, I got as close as I could in the math and flow numbers with the afrs as I could I'm sure it doesn't calculate some other things in there as well. I was expecting it to be higher up on the 185s as well. Hp hits 226 on both at 3k and the torque curve is pretty much flat starting at 377 2k on the 165s and 370 2k on the 185s. The funny part is my heads with this cam make 225hp at 2k but only go to 351hp total and make 376torque at 2k but only go to 399. Again this is all on a desk top dyno so I don't expect it to be 100%

jbuening · Nov 28, 2005

Not to hijack this thread, but does an engine with a mechanical roller valvetrain need frequent valve adjustments like the mechanical flat tappets? One other question, i've seen used mechanical roller lifters sell for a decent buck on ebay. I know that you should always use new flat tappet lifters, but what is the consensus on roller lifters? I know there is less friction and wear on roller valvetrain but is it safe with used roller lifters? Not trying to be a tight arse, but just curious as i see them sell on ebay all the time.

57fairlane · Nov 28, 2005

jbuening said:
Not to hijack this thread, but does an engine with a mechanical roller valvetrain need frequent valve adjustments like the mechanical flat tappets?

Depends on the lobe. Many "racing" grinds use extreme ramp rates and therefore valve spring changes are needed twice if not three times a year.
Yes, lash has to be set but your frequency depends on the lift and lash setting.

jbuening said:
I know that you should always use new flat tappet lifters, but what is the consensus on roller lifters?

Rollers are fine for re-use. Just check the rollers themselves obviously.

D.Hearne · Nov 28, 2005

The frequency in lash adjustement depends on the ability of the locknuts in holding a setting under load and also wear on the valve train. On my 427 I had twenty years ago, it had the factory rockers that had an interference thread to hold the setting on the adjuster screws, no locks, I usually had to set them once a month or more depending on how much I drove it.

KillerKittyCat · Dec 4, 2005

steel1212 said:
230/230/ .512/.512 .

This is where I get confused. My A block cam (stock) has the small base circle but matches the lift of this cam. (Very little duration on the stock cam)

I put a 234 duration 512 lift cam in the car and it ran great until I got on the road. I was in second gear doing 30 mph,on a six lane road,approaching a red light when the light turned green. The shop that sold me the cam told me not to baby it on break in. So I nailed it. The backend broke loose and it took me all three lanes to recover. I went back later and measured. 27 feet of positraction rubber left on the road. I do some dumb stuff but that scared me!

So back to my confusion. My stock cam gives me good performance as a daily driver. Just changing cams made the car a monster. My CJ Cougar will not do that. I put the stock cam back in that day. So if horsepower is the combination fo the two components did I somehow go beyond the natural curve???? My car is stock and a daily driver. I have 340000 miles on it and am waiting for it to die so I can restore it. I am getting almost 25 miles per gallon which I do not understand. The only upgrades are the pertronix and Edelbrock carb. 300 gears in the back. It starts everytime on the first turn and I do not have to clean the engine because everything is still black and gold. The front tires have 27000 miles on them and look perfect yet I have not had a front end alignment in 250000 miles.

I thought cams would improve performance with an overall upgrade of the engine and related systems. Why did mine become undriveable?

HistoricMustang · Dec 4, 2005

D.Hearne said:
The frequency in lash adjustement depends on the ability of the locknuts in holding a setting under load and also wear on the valve train. On my 427 I had twenty years ago, it had the factory rockers that had an interference thread to hold the setting on the adjuster screws, no locks, I usually had to set them once a month or more depending on how much I drove it.

Today, the adjustments should not occur:

http://www.badasscars.com/techtips.html#LIFTERS

HistoricMustang
www.historicmustang.com

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