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Topic Review (Newest First)
08-31-2008 01:12 PM
Morgan22
re: Small base circle cam

Thanks again for all the replies!

This place is great for getting some solid information

Morgan
08-30-2008 07:49 AM
ScoTFrenzel Your small base circle cam is for lifter positioning only. Not a problem in your situation.
I would think that fuel injection should be a major consideration at your altitude variations. Having an ideal closed loop mixture has benefits in every realm.
Yep, my rods are fuelies. Great torque with the only downside being lesser power above 5500 rpm. Inconsequential to me.

For myself, roller cams and fuelies only.
08-28-2008 09:33 PM
TorkMonster400 I spoke with Lunati A while back when researching cams and they told me their are no adverse affects of running a small base circle. The cores are only weekend buy a minimal 3% maybe. I even spoke with Howards cams and got the same response. hope this helps
08-28-2008 08:11 PM
oldbogie
Quote:
Originally Posted by Morgan22
Thanks Bogie, I was hoping you would chime in on this.

I don't want to date myself but I remember when factory roller cams came out. The rumor was that the cam profiles themselves didn't really change much from the flat tappet profiles and the gain was really only in the reduced friction of the roller lifters compared to a flat tappet. Don't have a clue if that was true or not but that is what I remember.

I will try to use the factory roller set up and see if I can find a grind to fit my 393 combo in the 1500-4500 or 2000-5000 range with about 10 to 1 compression ratio. I live in the Rockies at 5000ft so I think I can push the compression a little more up here. From here in the city you can drive to the top of the mountain just outside of town and go from 5000 to 10,000 ft in about 10 to 12 miles. Pretty dramatic change in engine performance.

Thanks,

Morgan
At the valve there wasn't any significant change in lift or timing. The roller served two purposes:

First was to provide (or maintain) existing durability compared to flat tappet cams against the reduction and final removal of high pressure organic metallic lube from engine oil such as ZDDP. This was done to enhance catalytic converter life.

Second was a side benefit where the reduction in friction between the lobes and lifters provided a bit more power but more importantly for the factory improved fuel mileage, which the Feds grade them against, so called CAFE "Corporate Average Fuel Economy" standards.

Bogie
08-28-2008 08:03 PM
Morgan22
re: Small Base Circle Cam

Thanks Bogie, I was hoping you would chime in on this.

I don't want to date myself but I remember when factory roller cams came out. The rumor was that the cam profiles themselves didn't really change much from the flat tappet profiles and the gain was really only in the reduced friction of the roller lifters compared to a flat tappet. Don't have a clue if that was true or not but that is what I remember.

I will try to use the factory roller set up and see if I can find a grind to fit my 393 combo in the 1500-4500 or 2000-5000 range with about 10 to 1 compression ratio. I live in the Rockies at 5000ft so I think I can push the compression a little more up here. From here in the city you can drive to the top of the mountain just outside of town and go from 5000 to 10,000 ft in about 10 to 12 miles. Pretty dramatic change in engine performance.

Thanks,

Morgan
08-28-2008 07:27 PM
oldbogie
Quote:
Originally Posted by Morgan22
Can someone educate me of the mechanics of small base circle cams?
What I keep hearing is that they should be avoided like the plague.
Something about harmonics and deflection?
If they are so bad why do they make them?
Since they do what are they intended for?

I have a 351w that I'm going to stroke, 393 and am considering using a small base circle cam to convert to hyd rollers of the stock ford type w/spider.
This is a street motor that won't see past 6K rpm not a high rpm screamer that from what I hear so far is where small base circle cams seem to have a problem with flexing.

Will it work well and be durable?

Thanks.

Morgan
There are a couple problems with small base circle cams.

First, the lobes are sized smaller but the lift over duration remains the same. This places a higher contact load between the lobe and lifter which is a durability and wear issue. A roller is probably a better solution in this case as rollers are better able to absorb larger amounts of contact loading, but like anything else it's not an infinite capability. The flat tappet Ford is probably better able to handle this than the Chevy by virtue of its larger diameter lifter. But I'd still go with a roller given the choice.

Second is related to the first in that the forces on the shaft are greater since the reaction area of the lobe to lifter is less. This increases the torque or twist moments in the shaft. Not a problem with a mild street engine, but when you start getting into high pressure springs especially when combined with high RPMs these factors can arrive at broken cams.

Bogie
08-28-2008 05:36 PM
Morgan22
re: Small base circle cam

Thanks for the replies,

I am aware that they use flat tappet small base circle cams in stroker SB Chevy a lot to clear the rod bolts.

In this instance I'm told that a 351w block (393) has room to clear with no problem with a regular HYD flat tappet. So I have a 3 choices, running a regular HYD flat tappet or running a small base circle cam with stock HYD roller lifters, dogbones, spider, or regular HYD roller with link bar lifters.

The link bar setup is the most expensive and the best I know. But this is no high RPM motor and I'm wondering if I can run the stock HYD roller and gain the benefits of the the roller cam profile and gain some power and still have some usability/durability.

Is it worth it or should I just run a flat tappet and be done with it if I don't step up to a link bar set up.

Has anyone run a small base circle HYD roller and had good results?

Morgan
08-28-2008 01:28 AM
jbvcw71 The ammount of defection really depends on the open valve spring pressure.
More aggressive profiles require stronger spring pressures.
It's safe to assume that the less metal there is to stabilize the cam's going to flex easier.
Some flex is actually normal & depended upon (keeps parts from being brittle & breaking).
Too much flex & bad things happen.

I'd just build it and follow the manufacturer's specs.

It should be fine as long as you don't "ride the limit".
(go with the biggest profile cam you can stuff in it)

BTW I'm just a novice.
08-27-2008 10:23 PM
SDLuck
cams

This, is I feel , is a question for a cam grinder or a cam company. I see many responses on here that scare me to death.Small base circle cams are usually for stroker motors for rods to clear.
08-27-2008 10:06 PM
Morgan22
Small Base Circle Cam

Can someone educate me of the mechanics of small base circle cams?
What I keep hearing is that they should be avoided like the plague.
Something about harmonics and deflection?
If they are so bad why do they make them?
Since they do what are they intended for?

I have a 351w that I'm going to stroke, 393 and am considering using a small base circle cam to convert to hyd rollers of the stock ford type w/spider.
This is a street motor that won't see past 6K rpm not a high rpm screamer that from what I hear so far is where small base circle cams seem to have a problem with flexing.

Will it work well and be durable?

Thanks.

Morgan

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