roller camshaft opinions please.

[Terry F.]

If you had two camshafts with identical grinds and one with hydraulic lifters and the other with hydraulic roller lifters, would there be a significant increase in performance? Example would be a 390hp with factory grind.

I suspect the engine might run a tiny bit cooler and there would be less horse power used to rotate the moving assembly but other than that I can't see much benifit?? Opinions appreciated as always! Terry

[Michael H.]

Re: roller camshaft opinions please.

Terry,

It would require two different cam grinds to end up with the same specs when using a roller design lifter instead of flat tappets but to answer your question, there probably wouldn't be a measureable difference in power, even on an accurate dyno. The roller lifter was just part of the package that reduced HP losses in the engine, but it wasn't frictional losses that brought about the roller cam and lifters in production. Lot of money out the window for an old engine if you want the same cam specs in a roller design cam instead of a flat tappet design.

[Duke W.]

Re: roller camshaft opinions please.

Roller cams have more aggressive flanks, so you get more area under the lift-crankangle curve compared to a flat tappet cam of equal .050" duration, but the trouble with most aftermarket roller conversions is too much overlap - just like most aftermarket flat tappet cams.

The additional overlap makes for a lumpy idle and less low end torque without a significant improvement in top end power. Too much overlap and exhaust backpressure from a reasonable street legal exhaust system is a poor combination that reduces torque bandwidth.

If I had a 390 I would pocket port/port match the heads, multiangle valve seats - all the prep I recommend for SB heads - use the OE/OE equivalent cam and everything else OE (or OE equivalent) with careful attention to assembly detail including achieving a CR in the range of 9.5-10:1 determined by actual measurement and proper head gasket selection for the final assembled deck clearance.

If anything, a higher overlap cam will make the engine run hotter, not cooler. Your best bang for the buck is to put your budget into the heads and use quality name brand OE replacement parts, which are cheaper than GM for what is probably the exact same part made in the same Federal Mogul or Dana plant.

Duke

[Terry F.]

Re: roller camshaft opinions please.

Thank you for your comments. I will be pulling my engine apart and I had just started to toss the idea around. I think I will just go with the original grind and roller tip lifters. Thanks, Terry

[Terry F.]

Re: roller camshaft opinions please.

Thanks for giving your opinion. I think you have answered my question for me. I am really interested in just having a very sound running engine. I could just see myself not having enough vacuum to open the headlights at idle and having to change carbs, etc.

Who is a good supplier of headgaskets that come in different thicknesses? Does this style of gasket typically have to be retorqued after warm up? Terry

[Duke W.]

Re: roller camshaft opinions please.

I don't know about BBs, but for SBs I'm aware of shim gaskets from .015" to .018", which is the OE shim gasket thickness, and .028" and .038" composition gaskets.

Changing the gasket thickness .010 changes the CR about 0.3, so within this range of gaskets, the target ratio range can usually be achieved, and the shim gaskets will seal okay as long as the block and deck measure level, and many do.

Prior to disassembling your block, measure the deck clearance of all eight cylinders very carefully, and mutilple times if you are a novice at this until you have consistent data sets. These measurements will tell you if your block decks are level, which they usually are within a few thou.

Use the your measured deck clearance along with head chamber volume, available piston compression height and dome volume to compute the CR using available gaskets of varying thickness to arrive at your target CR range. Be sure to factor in any difference in compression height of the installed pistons and replacements.

Then when the short block is assembled, remeasure deck clearance, and select a suitable gasket. It's not unusual to see five to ten thou difference in deck clearance side to side, and it can often be "equalized" by using different gasket thicknesses side to side to negate the difference and achieve near equal CR on both sides.

Duke

[Mark #28455]

Fel Pro head gaskets

They are commonly available in .038" and .041". In addition, I have used the .051" that you can get from Summit or Jegs and I also think a special order .061" might be available. The .051" costs about twice that of the .041".

Good luck,
Mark

[Mark #28455]

The whole point of a roller cam

is to use a cam with even LESS duration at .050 lift and still be able to flow as much air as the hydraulic lifter cam with longer duration at .050 lift. I have seen a 502 with oval port Vortec heads and a stock pickup truck cam make the same horsepower and torque numbers as a 502 HO engine with the rectangle port heads. We're talking 560 ft lbs torque and 450 HP with a butter-smooth idle at 700 RPM. You could probably make more power than a stock 435 HP engine with an idle at least as smooth as the stock 390 HP cam - but your bigest challenge would be to convince the cam grinder that you really want to buy a cam that "wimpy". As Duke has said, the aftermarket caters to cams with too much duration and overlap because the "street heroes" want an engine that idles like crap!

Mark

[Duke W.]

Re: The whole point of a roller cam

Very good, Mark! Folks are starting to see the light.

How's this for a wimpy roller cam - 211/230, Points of max lift 123/117 for a whopping LSA of 120 degrees. Well, at least it's "retarded", but who the heck came up with such a screwball design.

GM Powertrain, that's who - for the LS7!

BTW, I developed what turns out to be a very accurate model for the LS7 on Engine Analyser. I shortened the stroke to 327 territory, and the power curve ended up "off scale" at revs that the valvetrain won't take. So I advanced the cam about 8-10 degrees and voila - a reasonble torque and power curve for a short stroke engine.

There is a message there!

Duke

[Terry F.]

Re: The whole point of a roller cam

I was thinking that if I went to a roller cam my goal would be to slightly increase peak horse power and increase torque across a wider RPM range. I would not be interested in making the engine run higher RPM's to get the added horse power since I am not into breaking things but I like the feel of useable power and friskiness. I hope that makes resonable sence? I am not an engine builder if you know what I mean. I figure there was a reason the new engines use this engineering and I thought of taking advantage of it for the fun of it. Terry

[Duke W.]

Re: The whole point of a roller cam

Theoretically a properly designed roller cam should make broader torque bandwidth than a flat tappet cam, but the operative phase here is "properly designed".

As far as top end power is concerned it's about 90 percent head flow and ten percent cam. You can't make up for poor flow efficiency with a cam, no way!

That's why I try to pound into to guys' brains that head flow is where it's at, and judicious modification of heads as has been documented for over 30 years is the first and sometimes only "modification" that should be made.

The LS7's CNC machined ports yield flow efficiencies of about 60 percent on both sides, and with a relatively mild cam it makes excellent torque bandwidth and high specific top end power.

Duke

[Mark #28455]

more grunt, no loss in HP @ high RPM

With a properly designed roller cam, you still get enough flow to keep your high RPM power, but you also are able to minimize the overlap and close the intake earlier so you don't loose cylinder pressure - that boosts the lower RPM power/torque - the best of both worlds!

Trouble is convincing the cam grinders - the specs you come up with will "appear" to be really wimpy, but run great. Look at the TPI engines, they were making great power with aftermarket cams in the 210 to 216 degree duration at .050" lift. Nobody would have EVER considered that a performance cam 30 years ago.

Like I said before, the 502 with Vortec heads had a stock pickup truck cam with 204/209 degrees duration at .050 lift and still pulled 560 ft lbs torque at 3500 RPM, although it was down to 500 ft lbs at 4500 RPM. That cam only had .480 lift, so if we brought the lift up to about .530, it would have likely had a better top end - but that would have required machining a new lobe master (8 years ago, likely off the shelf now).

Mark

[Michael H.]

Re: The whole point of a roller cam

If we're talking about a short/medium duration cam, there's still no difference between a flat tappet and roller design, "all else being equal". Either design can be ground to produce the exact same specs throughout the valve opening/closing cycle. The only benefit of the roller design is the fact that it allows a much faster rise per degree than a flat tappet design when radical lift curves are used. The limiting factor with a flat tappet design is the point at which the lobe would run off the edge of the lifter face with an aggressive lift curve. (that's why wide base mushroom face lifters, or larger diameter lifters, are used in racing engines that require flat tappet cams, such as Nascar/cup) However, in an engine with a reasonably tame lift curve, such as the 390 HP that was originally discussed, the roller design offers absolutely no improvement over a flat tappet design, all else being equal. As I've previously stated, unless the lift per deg exceeds the physical dimensions of the flat tappet design, rollers are a waste of money.

Now, we know why this roller design was used for decades in racing engines but does anyone actually know the real reason why the new car mfg's began using it in production engines? Less friction would be a great answer, if it were true, but that's not the reason. Everyone is under the impression that a lot of things inside the engine with little roller bearings automatically increases HP, but that's not the case. The bearings are part of it, but not for reasons that you would think. Bet Duke knows the answer.

[Clem Z.]

Re: more grunt, no loss in HP @ high RPM

the LS-1 corvette engine switched to the 6 liter truck cam in 2001 for more grunt. i think a lot of the performance of the TPI engine has to do with the intake design coupled with the cam design. i know my 2005 LS-2 will stretch your neck when full throttle from a dead stop and still pull like a train at the upper 6500 RPM range. anyone who drives or take a ride in a new ZO-6 will know what power feels like. with the addition of long tube headers and a different cam the ZO-6 engine will pick up close to 100 HP so that tells you the cam is very mild. katech has a 660 HP street drivable engine package for the ZO-6

[Duke W.]

Re: The whole point of a roller cam

Maybe not. The OEMs have always claimed lower internal friction, and a roller design will take greater force at the tappet-lobe interface, which allows more rapid acceleration. Even if velocity is keep at the same level as a flat tappet design, higher acceleration yields maximum velocity sooner, and you can use milder deceleration, which will increase valve float speed and still yield more area under the curve.

Look at the LS7 - 7100 RPM limiter with roller hydraulic lifters, but the light weight valvetrain helps a great deal.

It's interesting that a lot of DOHC designs use roller rockers rather than direct actuation, which adds a lot of cost and complication to the valvetrain, so there must be some advantage, but sometimes I wonder. All my DOHC engines are direct actuated shim over bucket designs, which is a pretty simple and bulletproof architecture.

Duke