Okay, I'd like to figure out the advantages of having a roller cam. I know there is a little more hp gain but can somebody show me two identical engines with the same size cam on a dyno. I've heard that rollers last longer because of the less friction. But is it worth the extra $$$ coming from a college student?

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, Jon (91 RS too many mods to list)

 

Im a college student also and Im switching to a roller cam. Car craft did a test on a mopar 440 and HP jumped from 480 to 530. Thats a 15% jump in HP in a cam that Idles the exact same. Not to mention the roller makes more power throughout the whole rev range

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91 RS W/carbed 350, Vortec heads, performer rpm, Comp cams Xtreme energy 280 grind. BFG Drag radials. 3.42 posi,Corvette servoed 700r4, ****ty stock converter
13.24@104

 

ive herad mixed responses about roller cams, some people(magazines) love them, cnat say enough. however, the people ive talked to in the 'real' world, ie. mechanics that race, say they dont noticed a terrible difference. you decide.

 

Rev most,

Good question; here's what the pro's say:

Beyond 240* or so duration - yes, a roller makes a big difference. Below 240*, go with a one-step larger flat tappet cam to get approximately the same area under the curve.

I've spent literally hundreds of hours researching this topic, and I'm a real believer in the roller cam conversion - for super hot street or drag use. This applies to the old standard flat-tappet application blocks. Obviously, if you have a roller block already, keep it.

Here is my problem in a nutshell - the damned roller lifters and complete kits are SO GAWDAWFUL EXPENSIVE. I'm in the middle-engineering stages (paper only) of a 406 SBC buildup - and it will have AFR 195cc heads, single-plane intake, and Holley 850 cfm carb, along with 1-3/4" primary tube headers.

I've seen plenty of dyno tests that show a roller with 246 - 260* duration at .050 will plot 50-60 horsepower better than the same-spec flat tappet cam.

I've also priced the conversion cost - and this is INCREMENTAL costing (the springs, locks, retainers, etc. have to be replaced anyway, so I did not add the cost).

I come up with (including machining)an incremental cost of $600 - $800. Jeez, the lifter set alone costs $250. So.....

what to do?

Take a look from some other perspectives - and ask some questions.

1)Using the $10 per horsepower rule (it's an old estimation of a fair price to pay for extra power) does it fit the budget?

Well, if you get 50-60 HP for $600, yes.

2)What else could you do with that $600 ?
If you've already planned AFR heads, like I have, well, I'm looking at nitrous or supercharging for the motor.

$600 pays for the spray, but it will not refill the bottle. That's $8-$10 PER RUN.

No go there champ - not unless I'm really unsatisfied with the power of this 406.

3) How much is enough? This may be the most important question of all. In my case, I can wring 550 HP out of this 406 with a conventional solid-lifter design. Here is why I'm STILL very interested in a roller....

Roller cams do not just add high-RPM power, they add gobs of bottom-end torque. How?

Well, remember I mentioned "area underneath the curve"? Roller cams have extemely aggressive ramps that accelerate the valve open at a high rate. The difference is dramatic at the lobe - especially when the valve just begins to lift off its' seat. In the vicinity of an intake lobe where a flat-tappet cam is midway on its' journey up to max lift, say at .200 lift, is the place to look.

That is to say, given equal specs on both cams, what is the difference in valve timing at .200 lift?

Look at a solid roller and you won't believe it. Where a flat tappet cam shows 154 degrees duration at .200 lift, a roller will show 176. That roller cam fairly whacks the intake valve open.

That is a ton.......and THAT is what makes torque and horsepower. Yes, a roller is brutal on valvesprings and other components, but that is also why the conversion costs so damned much.

Lastly, look at one last secondary benefit....specifically, look at piston speed compared to valve opening rate (on the intake side).

At, say, 20 degrees BTDC, where a piston is on its' intake stroke, a high-performance motor wants every last molecule of O2 packed into it as fast as it can get it. The downward travel of the piston ATDC is going to create the vacuum, and at 15-20 degrees ATDC, it's demanding a bunch. The crankshaft/rod angle is becoming severe, and the acceleration of the piston away from TDC is acting as a "pump". So, the "opportunity" to fill, or even OVERFILL the combustion chamber with O2 is there. What our cam does with the opportunity is the difference.

Roller cams in excess of 240* duration, when combined with a free-flowing cylinder head and the right exhaust headers, very often exceed 100% volumetric efficiency. Your typical L-98 factory stock GM 350 operates on about 82%-86% VE.

A roller-cammed honker with 11 to 1 compression operates at 103%-110%.

There is the difference. So, unless someone has a red-hot price on a used supercharger in the next 6-8 months (and, hey that could happen), I will probably do a roller motor.

Remember when I asked "how much is enough"?
608 HP with 560 Lb. Ft. in a 3000 lb. car with a built 700R-4 and 3.70 gears and a 3000 Vigilante converter should do the trick.

And if you think good 'ol BOR is going to launch this monster at WOT the first time out, you're wrong. My 44-year-old ticker can't take that abuse. But I'll get used to it......quickly too, if history is any indicator of the future.

Besides that, I kinda' like scaring the SHIZZ out of all those babes that say "hey, can I have a ride"?

Makes 'em wanna hold onto something, or somebody, you know?

Want some candy little girl? (Salacious grin, as he eyeballs the young coed at the dragstrip)

Yeah, being old ain't all bad.

Please pardon the rambling, but it helps me to exercise the logic tool - and if I omitted anything, well Vader, GM, RB83, EDE, etc., please hop in and advise. Thanks.

BOR



[This message has been edited by Box of Rocks (edited November 10, 2000).]

 

To make a long story short, roller cams (can, if you buy a GOOD one) open the valves faster AND give higher lift for same/lesser duration than flat tappet cams, thus offering same/better horsepower (with the increased flow) with lesser advertised AND .050" durations, leading to better driveability/operability under normal (ie, street) driving conditions.

 

Box did a most excellent job of describing the potential that a roller system provides. I would add that there are simple geometric reasons for why a roller can have such steep ramps compared to a flat tappet. These facts effectively prevent a flat tappet system from being built having equal opening rates to a roller even with equally stiff springs, light components, etc.

Look at the shape of the cam lobe as it rotates under the lifter. As the ramp arrives at the base of the lifter, the "side" of the ramp comes into contact with the lifter; if you imagine making the ramp steeper and steeper, at some point you get to where the ramp is absolutely parallel to the lifter surface, and as you increase the steepness beyond that, the contact point between the lobe and the lifter no longer "rolls" across the lifter base, but instead a point farther up on the lobe contacts the lifter and begins to do the lifting action. So the lifter won't rotate in its bore like it must to survive. This drastically reduces the lifetime of the lifter and lobe.

A roller on the other hand has a very small contact area between the cam and the lifter base, namely the surface of the roller. There is not a large flat thing to be concerned with. So there is on reliability-imposed limit on that part of the system geometry.

Unfortunately when the factory "discovered" rollers and put them to use in the late 80s, they didn't alter their cam profiles to take full advantage of the possibilities that the roller system offers. They were only looking at the (minute) gas mileage savings. In fact, they could have steepened up the ramps quite a bit; shortened the .006" duration substantially, since they are now freed from the ramp slope limit of a flat tappet design; tightened up the lobe separation somewhat, since the overlap would be less anyway; and ended up with a motor that ran better than what they produced, used the same amount of fuel as the inferior flat-tappet design they copied over, and had the same or lower emissions. Oh well.

BTW I put my money where my math is... I have a Comp XR282HR in the 400 in my 83, and love it.

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"So many Mustangs, so little time..."

 

Hey RB !!

I was hoping you'd hop in......since you've BTDT with the 400 roller motor. I'm using the following numbers for cost comparison -

Hydraulic flat-tappet cam, lifters, springs, locks, retainers, etc. (The Comp full kit)
is about $400.

Roller cam, lifters, springs, retainers, locks, and rev kit $1,000.

Does that seem close?

Also, incredibly, I just saw a set of new Comp 818 roller lifters (new) and a set of 1.5 Comp roller rockers (new) advertised locally for $300 total. Somebody was going to build a motor and quit.

Enh, that #818 is the right lifter for a 400 SBC isn't it ?

Oh man, I'll bet this cat would take $275 for the works........which is about half price.

RB83 - please tell me you're using the 818 lifter - it checks out in the catalogue....

still, there is no substitution for BTDT. Thanks in advance.

BOR

 

Box--

That sounds like the right # for the lifters. It's the regular SBC "retrofit" roller, nothing special. Your cost numbers seem roughly in line for budget purposes as well.

You don't specify which Comp rockers you're looking at. I am using Comp's 1102. I discovered as I assembled and adjusted that the pushrods were WAYYYY short, to the point that they hit the inside of the rather liberally hogged-out pushrod holes (no longer slots) in my heads. I ended up with something like .150" over (7.550" maybe?)pushrods, and I still think I might have a couple that touch since I have some slight mystery valve train noise.

Yeah that roller stuff does add up, doesn't it? My setup didn't cost anywhere near what it should have, and I still have about $600 in it all. If I had paid full price for everything, especially the rockers, I would have over $1200 in it. And I didn't go with a timing belt, which I feel like I should have.

Oh well, live and learn, or die trying.

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"So many Mustangs, so little time..."

[This message has been edited by RB83L69 (edited November 10, 2000).]

 

All I have to say is that this board simply ROCKS.
Thanks for the great explination, probably the best responce I've gotten.

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, Jon (91 RS too many mods to list)

 

Holy sh!@#$T. BOX that was a killer response. Im opting out of a roller cam for my new engine mainly due to the cost contraints.

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Mark Lock
- 86 IROC-Z - Torn down for 383/SuperRam T56 setup
- -= IROC Online =- - The site dedicated to the IROC-Z