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Discussion Starter · #1 ·
71 Chevy C10 Fleetside. 3.73 gears. Turbo 350, stock converter. 350 Chevy, bored .60. headers, Edelbrock Performer RPM intake, Holley 670 Street Avenger Carb.,
RHS heads, 2.020” Intake/1.600” Exhaust.

Rebuilt the motor, new cam, heads etc. ended up wiping the cam. Heads, springs etc. are “relatively new”

Ordered a new Comp cam.
Operating Range:1800-5800 RPM
Duration Advertised:270° Intake / 270° Exhaust
Duration @ .050'' Lift:224° Intake / 224° Exhaust
Valve Lift w/1.5 Rockers:.470'' Intake / .470'' Exhaust
Lobe Separation Angle:110°
Got the kit with springs. Springs are smaller diameter then my current set up and do not sit over the spring locators.
Called Jegs tech support and was told that the difference between the old and new springs was not enough to worry about changing them. (Would make my life easy!)
Can any one tell me if I should go with this? Or do I need to find a different spring that fits? Different locator?

New springs;
Comp 981-16
Single Outer Valve Springs
  • Rate: 373 lbs
  • .880'' ID, 1.254'' OD
  • Seat Load: 105 lbs at 1.700''
  • Open Load: 273 lbs at 1.250''
  • Coil Bind Height: 1.150''
  • With Damper
Existing springs;
Comp 972-16
Single Outer Valve Springs
  • Rate: 308 lbs
  • 1.060'' ID, 1.460'' OD
  • Seat Load: 124 lbs at 1.800''
  • Open Load: 293 lbs at 1.250''
  • Coil Bind Height: 1.195''
  • With Damper
 

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They are right, what you've got is fine and actually a little better.
The smaller 981 spring is just the lowest cost way good enough to run with that cam.

They also won't be the cause of a wiped cam, if that was your worry.

New 981 is 105 lbs seat, 280 lbs open @ the actual .470" valve lift.
Old 972 is 124 lbs seat, 270 lbs open @ the actual .470" valve lift.

The higher seat pressure will be better able to control any seat bounce, which is what creates "valve float" .
 

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You probably already knew this, but after wiping the first cam, that engine needs to be completely disassembled and all the cam shavings thoroughly cleaned out. Then find out why????. There are lots of reasons a cam can be wiped.
 

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That is also quite a bit of cam duration for a heavy vehicle with a stock TH350 converter and 3.73 gears. It will work fine for most normal driving, and may sound good, but will probably be pretty “soft” for acceleration at low RPM.
 

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Discussion Starter · #5 ·
Thank you guys for your input. Helps a ton.
I will be adding a stall. I am only looking for cruising. 20 miles to town and then cruising main street.
I believe the last cam was wiped from bad break in, poorly adjusted valves. I know I never used break in oil or zinc additive. Probably didn’t change the oil out very well. (I built it in a shed with little knowledge and even less money) Then took it to a shop, they tightened the valves some more assuming that took them the rest of the way out.
 

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Comp is trading the damper’s contribution for less main spring pressure.

The damper adds a bit spring pressure and of rubbing friction between it and the outer spring.
The pressure contribution is probably not all that much; but the rubbing friction between it snd the outer spring is a function much like suspension system shock absorbers in that it dampens the run away natural oscillations of the bare spring. The result is more stability with less total pressure which these days reduces impact loads on the valve train that eventually end up at the lifter to lobe interface which add to the wear on these items. This is just plain smart engineering. It is the point of beehive springs which use a variable wind in both diameter and coil spacing to produce the same effect as a dampened coil without the frictional losses between damper and spring.

If you look at competition type nested springs that often consist of either an outer spring with damper and an inner spring or an outer spring and two nested inner springs; you will see the damper and or the nested inner springs are wound in counter directions. This is done to develop countering natural frequencies to damp the frequency modes that result in natural vibrations ganging up to cause spring surge.

As far as digested cam and lifter clean up through engine disassembly I’m not convinced this does much. This failure mode mostly creates fine particles rather than larger chunks of metal. To a high degree the filter traps most of this stuff. The damage done is the damage done as not all the oil is filtered all the time. So if the circulating wreckage was large enough to cause damage to the oil pump gears and bearings that damage is what it is. If the engine has held normal oil pressure through this whatever the damage is it is nominal. So opening the motor up to just clean it probably has little value, At the other hand if there is visible damage then some level of rebuild is in order which goes beyond cleaning the pan with a solvent soaked towel.

Oil changes are vitally important, they always have been. Engines are mighty hard on oil. The combustion process subjects oil to high temperatures with acid and water contamination that doesn’t exist in gear boxes and rear axles. The temperatures bake the oil molecules to failure, these are mostly found on the underside of the pistons where oil mist is a need to cool the underside of the piston crown. The combustion process through blow-by (simply a name given to engine exhaust that escapes into the crankcase) puts the waters of combustion and burnt as well as unburnt fuel products into the crankcase. These mix with oil to create all sorts of undesirable compounds from acids to semi-poly compounds that form sludges and varnishes. To some sensible degree this stuff is like pouring pouring polyester resin and alkyd paint into your crankcase. So the concept of oil changes is to get this stuff out of the engine before the acids etch the metals mostly bearing and piston and the esters and varnishex goo and glue everything up. For those of use that have opened up engines from people who never changed oil we know that you are first greeted by a crankcase full of what looks like jellied grease.

Once when I worked in an all night garage back in my flat rate college days I had a customer that had so much sludge and varnish build up in the rocker boxes of a small block Chevy that the guy brought it in because a few minutes after start up the good oil pressure fell to zip. Opening the valve covers was a pry bar project. Once inside the only space was where the rocker arms, pushrods and valve springs were working. Everywhere else was near solid goo. I left a note for the day boss to ask him about oil changes? The valley looked about the same When the engine was started the oil that pumped to the top end couldn’t drain back fast enough to resupply the sump so the oil pressure died. Left overnight the oil succeeded in oozing back to the sump so morning fire up showed pressure for about 10 minutes. The response to my question was he didn’t believe in oil changes “it’s just a rip off“ as he knew that oil lasted forever. My response was WTF? How about an engine rebuild?

Bogie
 

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In my opinion catalytic converter safe low zinc oil, higher spring seat loads, cheaper made cams & lifters, plus improper initial adjustment(more than setting lifter lash or preload, tune) are all factors in flat tappet cam failures these days.

Next time set the springs up at lower seat or use weaker/old springs for initial break in. Cheaper than break-in rockers, 80ish lbs seat Obviously don't rev it to the moon before swapping in the new springs. I like to prime the oil pump right before until all rockers show oil also, sometimes gotta turn the engine a bit to get em all to oil

Some cam lubes have the break in stuff needed but I like to also add redline additive to my oil instead of buying high priced flat tappet cam safe oil. and Lucas assembly lube is really sticky(wear gloves). Also like to use a box fan in front of the radiator.

As mentioned bit of stall should help.
 

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In my opinion catalytic converter safe low zinc oil, higher spring seat loads, cheaper made cams & lifters, plus improper initial adjustment(more than setting lifter lash or preload, tune) are all factors in flat tappet cam failures these days.
The most important one to note is the cam technology has evolved to more aggressive cams than ever before and higher spring pressures with added rpm then ever before.
It's hard to kill a long cam with a slow lazy ramp than a cam with higher lifts and short duration.
40 years ago the go too cam was the 292 cam with .450ish lift, 250lb springs at 6500 and now were looking at 270's and .550 lifts and 400lb springs at 8000.
 

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The most important one to note is the cam technology has evolved to more aggressive cams than ever before and higher spring pressures with added rpm then ever before.
It's hard to kill a long cam with a slow lazy ramp than a cam with higher lifts and short duration.
40 years ago the go too cam was the 292 cam with .450ish lift, 250lb springs at 6500 and now were looking at 270's and .550 lifts and 400lb springs at 8000.
Another good point. Still I'd say the most important one is, it's less common knowledge/skill to tune or break in flat tappets cams than 40 yrs ago.
 

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I’m old enough to remember when Isky broke the .5 inch barrier with the 505 cam. It was like “rocket science”!

I agree the old cams were bolt in and go, yeah they wore on occasion but it was rare. As I’ve said if you were having problems you bought a set of hard faced tappets which you can still do. The Ford Y-blocks ran a cam thrust plate with a mushroom shaped tappet that gave very little trouble in cam or tappet wear, which was fortunate because the the only way in or out for their tappets was through the bottom end.

But in today’s ‘brave new world’ of high output with lower compression ratios the emphasis is toward less overlap and earlier closing intakes using more lift to substitute for the breathing of these features.

A big problem with older engine designs was the fairly steep valve angles to the bore center these result in a fairly deep chamber that provide a pocket that hides a burnt mixture volume that is hard to vent out toward the end of the exhaust cycle. Both Chevrolet on the W engine (348, 409, 427) and the Ford MEL (383, 410, 430, 462) tried getting over this with a flat milled head which resulted in discovering other problems of mixture management in the cylinder that were detrimental to power.

There are compromises and other porting techniques that get around the flat milled head chamber or chamber in piston designs by flattening the chamber wedge angle and in the example of the early LS cathedral port head restoring good in cylinder in late flow management with achieving a high order or late cycle exhaust evacuation without so much overlap. The overlap being used for the incoming mixture to do the final evacuation of exhsust from the chamber and of course the exiting exhaust adds early velocity to the incoming mixture which helps fill the cylinder at the cost of increased fuel consumption and air pollution by the unburnt fraction. Which you can at least burn off in the exhaust system with air injection snd a cat converter but while scrubbing pollutants doesn’t do much for improving mileage. In the end Chevy realized that cathedral ports work well with carburetors and TBI but are unnecessary with port or direct injection so they went back to more conventional ports.

None of this is new the early Ford Indy engine used a 9 degree wedge chamber, this was an application not a discovery, as the effect of a flatter wedge chamber was already well known by the early 1960’s. The Chevy W motor and Ford MEL a case in point.

Back to cams and the reduction through elimination of overlap with earlier intake closing with fast ramping on the lobes, here it is especially advantageous to pay attention to improving flow across the back side of the valves, hence back cutting as this gets the early flow well increased. Along with this the elimination of old style valves with their glob welded head to stem greatly improves flows past the valve.

So there are a lot of elements to be considered in the never ending hunt for more performance, they all blend toward an optimal solution that is a set of compromises depending exactly what the designer needs for outcomes. We all tend to get stuck in our thinking and this really shows in the many years it took the OEMs to recover from the imposition of mandated emission and fuel conservation laws. However, the government thinking that every individual needs “ivory tower” guidance slowed much progress by putting the onus for wear compensation on the manufacturer designed system rather than mandating personal responsibility by requiring annual inspection and repair of failures, which maybe wouldn’t have flown well in our world of ‘rights’. But keeping up on maintenance as a requirement rather than a choice would simply removed the requirement for most of the damn emission gadgets and technical compromises of the 1970’s and 80’s made before the electronics technology was capable of carrying the needed number of instructions and fast enough to be real time useful plus reliable enough to do the engine management functions over the projected vehicle life span.

Bogie
 
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