14 replies to this topic

[NTSOS]

So, we have a SBC, street driven, max rpm 6000 + (?), .502 lift......cam grinder recommends a minimum of 140# seat pressure and 400# open spring pressure for a hydraulic roller.

*Generally speaking*.......does that seem like excessive spring pressure for a reliable street driven motor using premium pieces and parts?

OTOH, It's probably an apples to oranges comparison and the LS7 is know to have a very
stiff valve train, titanium valves, beehive springs etc. but the spring pressure difference is quite dramatic considering the rpm potential and lift for the LS7.

LS7

211 - intake duration @ .050

230 - exhaust duration @ .050

.591 - intake valve lift

.591 - exhaust valve lift

Seat - 101#

Open - 310#

Max RPM - 7100
_____________________________

SBC - iron 327

222 - intake duration @ .050

228 - exhaust duration @ .050

.487 - intake valve lift

.502 - exhaust valve lift

Seat - 140 - 160#

Open - 400 - 425#

Max RPM - 6000 + (?)

Above setup using Morel rollers, Manton pushrods, PAC springs/retainers

Opinions please........thanks!

John

[McGuire]

That's more than I would run. I would ask the cam grinder why he wants so much nose pressure. I would think 320-340 lbs over the nose would be sufficient for 6500 rpm with that cam grind, given the general specs, but it's his camshaft.

[NTSOS]

Mac.....I made it clear to the cam grinder that the intended use was strictly street with an emphasis on reliable operation.........I have asked for a more complete technical explanation for the spring rates assigned to this particular profile and especially as it relates to reliability.

John

[McGuire]

Huh. I've recently done two 400ci SBCs (one aluminum, one iron) with .550" lift, 240-ish duration Comp hydraulic rollers. Ran to 6000-6500 with around 340 lbs of open pressure.

Valve spring selection is sort of an interesting topic in that when push comes to shove, it is largely experiential. It so happens that a few of us were kicking around this very subject last week, whereupon somebody observed that cam grinders seem to go conservative, apparently to save parts, while engine builders tend to go big to stay out of float on the dyno. Where that all fits into your tableau, I don't know.

[Lee Nicolle]

That's more than I would run. I would ask the cam grinder why he wants so much nose pressure. I would think 320-340 lbs over the nose would be sufficient for 6500 rpm with that cam grind, given the general specs, but it's his camshaft.

Me too, 350 open should be heaps @6500. Some grinders seem to like too much then bitch when you lose a lobe. Others are usually too soft, particularly on proper performance cams. In my experience Crane are usually too soft, put another 20 lb on the seat and a bit more open means the engine will turn another 500 useable RPM. Might be ok with Titanium vaves but us mortals only use stainless!

[NTSOS]

Yes, I know....I have been "bouncing" back and forth between two or three spring sets, one that follows the cam grinders recommendation and then lighter versions that look similiar to what your setup looks like.

I have researched several forums exhaustively and the general consensus is to go heavy and avoid valve train seperation and the result is *less* chance of part breakage......if your pieces and parts are up to it.

OTOH, I look at the LS7 stuff and the GM PowerTrain solution is very elegant with the relatively light springs and all......it's always there, occupying a space in my brain.

Heavy ass springs for the street just seem so brutal.....like they are trying to mask a not very well designed cam profile.

It's making me crazy.....I don't want to screw up a reliable street machine!

How much does a SpinTron cost?

John

[McGuire]

Rollers can stand more spring (to allow more valve rate) but actually require less spring for a given rate. This seems to cross folks up. Aside from the mechanical benefits of a roller, the performance advantage here is in its quicker ramp -- increased dwell in the final ~.200 of lift. That's where the money is. A big spring essentially trades float and potential associated breakage for constant wear. However, any hydraulic lifter roller or not is sensitive to spring pressure as in collapse. I took a quick peek last night and the roughly equivalent Comp brand grind calls for a spring with 110 lb at 1.700 and 278 lbs at 1.250. That seems a bit light but on the other hand, the LT1 and LT4 roller engines used similar spring rates if I recall. If the supplier can't explain why he requires that much spring pressure, I would step off his cam.

[NTSOS]

If the supplier can't explain why he requires that much spring pressure, I would step off his cam.

Yes, I agree.........now we wait!

Thanks mac!

John

[NTSOS]

My question:

Just curious..........do you have a technical explanation for the recommended spring rates on this particular cam profile.......IOW, I'm trying to determine why this particular profile has so much more seat and open spring pressure than most other SBC *street* hydraulic roller cams I have had or have compared to recently, all with very similar specs and operating ranges.

Their answer:

I am surprised your other motors don't have that much spring press. A little more press will make your cam more responsive on the bottom and work well on the top end also.

All perf. hyd. rollers and low lash solid rollers work well with those press.

Thanks

John

[McGuire]

I am surprised your other motors don't have that much spring press. A little more press will make your cam more responsive on the bottom and work well on the top end also.

All perf. hyd. rollers and low lash solid rollers work well with those press.

How in the world does greater spring pressure "make your cam more responsive on the bottom"? That doesn't mean anything, not that is true anyway. Who are these people? Please PM me if you don't want to dish in public.

[Lee Nicolle]

My question:

Just curious..........do you have a technical explanation for the recommended spring rates on this particular cam profile.......IOW, I'm trying to determine why this particular profile has so much more seat and open spring pressure than most other SBC *street* hydraulic roller cams I have had or have compared to recently, all with very similar specs and operating ranges.

Their answer:





John

Big springs normally help top end power as early float saps power but will make negligible difference in bottom end and midrange power. If any thing those big springs are eating power in mechanical effort.. Normally roller requires a little less seat pressure, as do hydraulic cams of any type.
Though for all out race track power you will never beat a solid lifter cam.
But for street use and light race use hydraulic is simpler,quieter and easier on the whole valve train and generally more responsive at lower RPM and gives the benefit of increased vaccuum as well.

[McGuire]

Rollers require less spring pressure but can withstand more, thus tripping people up. Roller? Oh goody, let's pile on the spring rate.

I've been looking around and so far I haven't found anyone using this much spring with a hydraulic roller SBC. I've run more cam rate with considerably less spring (like 100 lbs less) to 6000+ rpm. So why do we need more spring than we need to get the job done? More is better? I'm willing to listen, but I don't see how the bottom-end response claim could hold water. Would be nice if he had described HOW it achieves that -- that would be an interesting theory. I can understand more spring in engines that will be drag raced or see lots of dyno pulls, but for a 1000-mile road trip, not so much.

[NTSOS]

When I called Isky to ask if their retro hydraulic roller lifters were made by Morel (they are), the tech guy stated that the *HIGHEST* recommended open spring pressure was around 400 psi for Marine applications and typically 340 - 360 for street applications, the limiting factor was supposedly non-pressure fed needle bearings for the Morel HR lifter.

I have also read that high spring pressures do not incur a power penalty because of the stored rebound energy especially with multi cylinders........kinda like the oposite of a jake brake where cylinder pressure is released at or around TDC, circumventing the air pressure assist for the decending piston.

Maybe I should just go with a pressure fed, plain roller bearing solid lifter.....except I would rather sit around and drink Budweiser than run valves.

In any case, I think I'm switching cam people.

John

[McGuire]

I have also read that high spring pressures do not incur a power penalty because of the stored rebound energy especially with multi cylinders........kinda like the oposite of a jake brake where cylinder pressure is released at or around TDC, circumventing the air pressure assist for the decending piston.

Quite so. The penalty is in increased friction and wear. The loss in fhp is typically not a concern in a street engine but the wear is.

Maybe I should just go with a pressure fed, plain roller bearing solid lifter.....except I would rather sit around and drink Budweiser than run valves.

I adore hydraulic rollers. Only way to go in a SBC street engine anymore, as I see it. Quieter, more reliable, superior power, no more flat tappet lubrication or break-in hassles, no more lash adjustments. The '87-on factory block with provision for roller lifters is especially nice as the Delphi lifters are dirt cheap and work great. The Dart SHP iron block also incorporates the OE lifter spiders. 4.125+ bore for 400 CID with a 383 crank (350 main journals), can't beat that.

[NTSOS]

I agree, that would be a great combo.......only problem is, I have decided to build a dual quad 225 HP *externally* accurate motor and I'm stuck with a '56 block and heads.

My '56 Chevy currently has a completely stock 170 HP/Powerglide combo and since I show it in both stock and hot rod classes by simply swapping out the wheels and tires.......I thought the 225 HP motor would give it a little more pizzaz in each class.

John

John's '56 Sedan