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Old 02-10-2005, 06:29 PM
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Comp Cams hydraulic roller vs. solid flat tappet comparison

I managed to score another 400 block from my buddy for $600 CDN, and it was cleaned, magged for cracks (none found), and sonic tested, which showed a really well cast block. It is a 511 casting, so I'm feeling ambitious about finally replacing the 350 in my TA. My question: I'm looking at making some serious power, and since I am a loyal Comp Cams customer, I was browsing through their catalogue and noticed something rather peculiar about their cam lineups for SBC's. It appears from looking at the advertised duration to .050 lift duration ratio, that the solid flat tappet cams have a considerably steeper lobe profile than the hydraulic roller cams do. As an example, a retro-fit hydraulic roller cam (XR282HR) has 282/288 advertised and 230/236 at .050, and a comparable solid flat tappet cam (XS268S) has 268/274 advertised and 230/236 at .050. Both cams are from their respected "Xtreme Enegry" series, both cams have identical .050 duration and marginal lift differences, but the hydraulic roller has more advertised duration by quite a bit. As a result, the solid cam has a wider operating range than the hydraulic roller, with more low RPM capability. The same goes for pretty much their whole lineup, as comparing any range of cams from the list will show the same kind of profile difference between solid flat tappet and hydraulic roller (even the non retro-fit versions). The real kicker is that the solid flat tappet kits cost about half as much as the retro-fit hydraulic kits, making me more inclined to put up with adjusting lash every once in a while. Is there something I am missing in my assessment, perhaps the roller cams allowing for less smashing of the valves on the seat, or is this really in line with what I should expect from each type of cam? Maybe other cam brands do not show the same anomaly... your input will certainly influence my decision on which cam to buy.

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Old 02-10-2005, 07:22 PM
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My only guess is that the hyd roller lifter cant stand up to the abuse created by a really steep ramp. The solid lifter, may be stronger and more able to handle the abuse. This is just a shot in the dark. This is kind of counterintuitive because I have always thought that you could run a steeper ramp with a roller regardless of the design because a flat tappet cam will dig into the side of the lobe if the cam has a really steep ramp, so I really dont know.

Adam
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Old 02-10-2005, 10:42 PM
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If the roller lifters are really that weak, it sure makes me wonder about the solid roller cams, because the profiles on those cams are REALLY aggressive....
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Old 02-11-2005, 03:07 AM
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Phone Comp cams and ask your question, they designed them.
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Old 02-11-2005, 08:09 AM
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Roller cams have a smoother profile (IE not so pointed on the top)
but the same hieght so the lift coming off the bottom comes on faster stays open longer and closes faster.
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Old 02-11-2005, 08:15 AM
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Calling Comp would be a good idea. My point was not that the roller lifters might weak (if they are I dont know). It was that the hydraulic lifters, roller or flat tappet, may not be able to handle the abuse that a solid roller or flat tappet could.

Adam
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Old 02-11-2005, 09:19 AM
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cams

This is just my opinion,,,,,

But i really do not care for the hyd roller lifters. The problem is not in the lifters not being strong enough it has to do with collapsing the plunger when the lifter is opening the valve. Also the hyd rollers need attention paid to the proper spring set up. If you get to much seat pressure they will make some clatter at idle, but you need good over the nose pressure to control the heavy lifters... They are just a pain. Plus you need so much oil pressure to make the more aggresive ones work it's just not worth it to me.

I know there have been discussions about solid rollers on the street and i personally have never had a problem with a proper set up solid roller breaking parts.....

Keith
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Old 02-11-2005, 09:33 AM
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cam profiles

Quote:
solid flat tappet cams have a considerably steeper lobe profile than the hydraulic roller cams do.
Answer is very simple.
What happens when you hit a speed bump at 100 mph?

The wheel hops off the back side! So thats why rollers have a long arc instead of a quick bump.
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Old 02-11-2005, 09:36 AM
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While I like the hydraulic roller for smaller profiles, I believe the solid flat tappet is lighter and more reliable for the .550" to .600" lift range. Beyond that, a solid roller would be my choice.

tom

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Old 02-11-2005, 09:59 AM
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lifters

Hydraulic roller lifters must be pretty good, since a lot of the auto manufacturers are using them now, and you know how they hate to refit things that break, easily. On that point, knowing that SBF hydraulic roller lifters live quite well at extreme RPM, I dont think fragility is a problem.

However, in conversations with a couple different cam makers a few years ago, they both told me that for a hot street engine, or unless you are going to live at over 6000-7000 RPM all the time, that you are just as well off to go with flat tappet cams, as rollers in the milder profiles, dont offer much to offset the added expense.
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Old 02-11-2005, 12:58 PM
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thanks for the suggestion, I will email Comp and get their answer to this, then I will let all of you know what they tell me.
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Old 02-11-2005, 01:19 PM
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Quote:
Originally posted by rick458
Roller cams have a smoother profile (IE not so pointed on the top)
but the same hieght so the lift coming off the bottom comes on faster stays open longer and closes faster.


More area under the curve.
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Old 02-11-2005, 01:32 PM
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dyno results

Dyno results show that you get more torque from a longer duration but no substantial increase in HP. HP seems to come from the lift.
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Old 02-11-2005, 02:33 PM
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duration vs lift

Duration governs the RPM range that a cam works best in, and while it does have significant control over the amount of torque an engine puts out, once you reach a duration of roughly 230-235 degrees @ .050", the power curve starts moving up significantly in the engine rpm base, and significant losses of torque on lower end become noticeable. Lift doe have significant impact on the torque output of an engine as well as how it breathes on the upper end. One factor many overlook when considering the torque curve, is lobe separation. The wider the lobe separation, the broader the torque curve, while a narrower lobe separation thens to give more peak outputs, and generally in a narrower power curve.
It takes all three to come up with the power curve you want, as well as does lobe center timing.

Lift does have a significant impact on the torque curve, particularly on lower end with shorter duration cams.

This is one of the reasons why some of the manufacturers have gone to roller cams, due to the impressive increases in torque provided by doing so, by allowing more extreme lifts than provided with flat tappet cams. The higher lifts do dramatically effect torque.



Old rules of thumb:

10 degrees duration plus or minus will effect the power curve of the cam plus or minus 400 rpm.
50 cubic inches plus or minus, given the same cam grind, will effect the power curve by 500 rpm plus or minus.
Generally the more lift the better up to the point where the valves lift will no longer effect port flow. There is an aboslute point where it no longer serves a purpose to increase lift, as it will not, at that point affect power output. In fact, with some engines, to go above a certain lift will adversely effect port flow.

Last edited by Max Keith; 02-11-2005 at 02:33 PM.
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Old 02-11-2005, 04:58 PM
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runner size

Quote:
In fact, with some engines, to go above a certain lift will adversely effect port flow.
Edelbrock claims that their 170cc runner will handle .575 lift but I see all these people on the forum going to 200 and 220 cc runners with .500 and .520 lift cams. Putting on 800 and 850 cfm carbs to match the runners. Am I missing the point?
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