[joes455]

What spring should be needed for a sr 262/268/112 .600 lift ,IH 1.9.?Thank joe

[Steve C.]

What did the cam manufacture recommend ? And keep in mind heavier valves require more seat pressure, as an example a 2.110" vs 2.190" size. How aggressive are the lobes. Type of retainer material factors into its weight. Rocker arm ratio. Lot's of factors.


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[steve25]

What rpm is your bottom end built to handle?

[AG]

I used a CC 262/266 at 0.050" SR cam in a 461. I installed the springs with 220# seat pressure when new, which lost some pressure after being in service. Shifted the motor at 6500 rpm and it never skipped a beat. Got to 10.2 in the 1/4 with a 3450# car.

[Steve C.]

Not necessarily a recommendation here but conversation why it might be a good idea to speak to the cam manufacture with pertinent information involved.

The previous solid roller cam in my current 505 was a custom from Crower with 292/298 @.020, 260-266 @.050 , about 180/184 @.200 and .4250 lobe lift. With 1.65/1.6 rocker ratio. With it I spent time on the phone with Dave Crower about the combination, it made peak power at 6000 rpm. With that cam if raced and banged on he wanted 240 seat pressure and up towards 600 open. If limited street use only, no racing, and at that lower 6000 rpm then for the most part he said ok to 220-225 seat pressure. So it depends so much how the car is driven and the rpm range.

Later I changed cams to a UltraDyne MSP solid roller cam from Bullet Racing Cams, similar to the Crower but with additional .4300" lobe lift. And also a similar discussion with Bullet Racing about the spring pressure. Interesting to note that fellow also wanted the same 240 seat pressure if raced and limited street use. His recommendation was the PAC-1243 rated 240 at 1.900". Also fwiw, that is the same spring as the Comp 943.

A side note to consider, and related to comments by Paul Carter. He has stated in threads if your heads have a 30 degree valve seat, then the seat pressure should a bit higher. The flatter 30° seat has a tendency to bounce the valve more when closing so more seat pressure should be run.


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[joes455]

Thanks Steve Cam is a custom Sr intk opens 22 close 58 and/ exhaust open 70 bbdc close 18 atdc.There is no recommended spring on cam card.Bottom end forged crank Ross pistons,eagle rods floating pin arp stud 2 bolt main 73 400 no extra holes drilled for 4 bolt in block, 6000 rev limit .Purpose for street and some track time for tuning

[Steve C.]

For interest post the manufacture and specs of the cam in question. If a comp Cam list the lobe numbers ( in the grind # ) this way we can look up the duration at .200 lift and the rated duration.

Also it my not necessarily apply but with spring selection in conjunction with a 1.900" IH watch the distance from coil bind at net valve lift, too far of a distance is not a good thing ! I presume the .600" is net lift after valve lash.

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[Steve C.]

Below from input here:
http://www.wallaceracing.com/camcalc.php

Intake Duration is 260.00 degrees.
Exhaust Duration is 268.00 degrees.
Installed Intake Centerline is 108.00 degrees ATDC.
Installed Exhaust Centerline is 116.00 degrees BTDC.
LSA is 112.0 degrees
Overlap is 40.00 degrees.


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[joes455]

Grind #4017b/[email protected] and thanks for your help Steve c

[Steve C.]

Those Hi-Tech .420 roller lobes would not be as aggressive as my similar 260 degree Crower cam was. This from looking at the intensity number derived by subtracting the .050 duration from the .020 duration and the duration at .200 lift. And with less lobe lift, .4200" vs .4250". It would be interesting to know what a Comp Rep might recommend. I can say Comp for their TK Series solid rollers which is their most aggressive standard rocker ratio series will call for 240 lbs seat pressure, at least the Rep I spoke with did so with a similar application as mine. That would be the Comp 943 spring. Again, not necessarily a recommendation for that specific spring as I'd call a Comp Rep to discuss it. If you have one you can trust

Also note the total lift capacity of that spring in conjunction with your distance from coil bind with the net lift involved here. I don't know how much valve lash your using but my notes suggest the Comp Hi-Tech .420 series typically uses .024". With .4200" lobe lift that is 0.630"gross lift and therefore I'd use 0.606" net valve when evaluating spring choice. This based on a 1.5 rocker arm ratio in use.

Also often with a "B" suffix code after the part number as here the lobe lift can be, but not always, altered with an additional 0.001" lobe lift. So here from .4200" to .4210". If so a small change but something to consider. Also on my solid roller cams ordered with a "B" code the rated duration has been slightl differen than what is listed in the Comp catalog.



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[joes455]

Thanks Steve Lobe lift is as you say 4210.I could muster about 12 " vac when I was running this cam in sig.Did idle smooth in spite its duration.

[joes455]

What would it be @ .200 ?

[joes455]

Just received heads from Butlers ,he had to go to a taller valve.IH is now 2" ,need advice for a 2" ?

[Steve C.]

Now you have increased the weight of the valve further needing additional spring pressure. And for only 0.606" net valve lift. Typically many of the springs rated for 2.000" IH are good for a .750 or more max lift. Again presenting further potential issue of being too far away from coil bind at that 0.606" lift.


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[Steve C.]

Sorry, I did not mean to space your question regarding the 0.200" duration.

Your lobes are listed in page 76 here:

http://www.compcams.com/Technical/Ca...terCatalog.pdf

Again keeping in mind the "B" suffix codes can, but not always, alter the rated duration and lobe lift in some.


Here are two valve spring companies I would suggest:

http://www.racingsprings.com/

http://www.kmotion.biz/springsintro.htm


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[Steve C.]

Related side topic.... Pushrod flex. Heavier valves require higher spring pressures, which increase the risk of pushrod flexing. If you are not already doing so use a pushrod with a thicker wall section. Example if 5/16 pushrods instead of the typical common 0.080-.083 wall upgrade to 0.118-0.125 wall. Also a fwiw, if you were to build a 5/16 pushrod and a 3/8 pushrod at the same length and same diameter the difference in column strength is 96.7 percent different. If you go up in wall thickness from say .083 wall to .118 wall only about 5-6 percent better so always go with the larger tube if it will fit.

"Do not be overly concerned about pushrod weight. The pushrod is on the slow moving side of the valve train. The additional weight of a heavy wall pushrod usually provides a much needed increase in valve train stability."
Manton Pushrods
http://mantonpushrods.com/tech-info/facts/

Stiffness often trumps lighter weight when it comes to valvetrain component design.

Rhetorical questions... Did Butler go to a higher installed height because they had 2.190 diameter valves already on hand sitting on a shelf that had a length required for the increase in installed height. Did he consider custom made valves with the same diameter but with a shorter stem length.

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[joes455]

Butler said I needed the longer valve......,that was good enough for me,he is the man.I could always shim up to a 1.95 or even a1.9,I know coil at max lift needs to be close to coil bind

[joes455]

Could also go with the HS 1.72 rocker,to close the gap

[Steve C.]

Comp 955 double spring / no damper

1.550" dia / will work fine in the Edelbrock heads
812 rate
Rated 240 at 2.000
1.230 coil bind

.4210 lobe lift x 1.72 = 0.724 - .024 lash = net 0.700" valve lift in theory
0.070" from coil bind

( these spring specs here from old catalog / not verified

If done right your proposed cylinder heads should flow beyond 0.700" valve lift.

A 2-valve engine responds to high lift. Bottom line, the engine wants all the lift it can and thrives on it so run as much as mechanically achievable or unless prohibitive because of cost limitations. If it's a street only application or race application will have a bearing on the situation, this is the "race section".
Many would be hesitant to run 0.700 lift on the street ! But from input here I'll presume this is a race car with some weekend cruising.

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[joes455]

Im gonna stay with the 1.9 IH .050 neg retainer and .050 shim