Valve Spring Recommendation for BBC Pro Comp Heads - Chevelle Tech
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post #1 of 13 (permalink) Old May 22nd, 20, 10:23 AM Thread Starter
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Valve Spring Recommendation for BBC Pro Comp Heads

Looking for recommendation for valve springs for my 496. Running pro comp rectangle port heads. Mild cam with 0.541" lift, ~290 duration. Would like to rev to about 6k rpm. Planning to add a turbo in the future.

Randy Johnson
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post #2 of 13 (permalink) Old May 22nd, 20, 10:28 AM
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

Flat tappet? Roller? Hyd or solid?
What brand cam? What springs do they recomend?

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post #3 of 13 (permalink) Old May 22nd, 20, 10:32 AM Thread Starter
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

It is an older comp cams grind. Hydraulic flat tappet. Lost the cam card.

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post #4 of 13 (permalink) Old May 22nd, 20, 2:20 PM Thread Starter
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

Correction: It is a Crower 01243 cam. Crower recommends their 68340 or 68302X2 springs. 68430 are 118lbs at 1.9" installed height and a rate of 452 lb/in. 68302X2 are 107 lbs at 1.850" height and 342 lb/in. Crower catalog says 68302X2 are good "up to" 6000rpm. 68340 are for "over 6500 max".

I think I'll go with the 68430s or something similar.

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post #5 of 13 (permalink) Old May 22nd, 20, 2:38 PM
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

Quote:
Originally Posted by rlchv70 View Post
Correction: It is a Crower 01243 cam. Crower recommends their 68340 or 68302X2 springs. 68430 are 118lbs at 1.9" installed height and a rate of 452 lb/in. 68302X2 are 107 lbs at 1.850" height and 342 lb/in. Crower catalog says 68302X2 are good "up to" 6000rpm. 68340 are for "over 6500 max".

I think I'll go with the 68430s or something similar.
Before you order springs pull one or two and check the installed height.

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post #6 of 13 (permalink) Old May 22nd, 20, 3:16 PM
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

Randy,
You really need to do what Marcus said and not only check height but also the size of the spring pockets etc etc etc. Once you know what size spring will fit, then you can find one that will have the correct open and closed pressures to work with your camshaft.

At least once a month I will have guys bring a set of heads for me to do and along with the heads they will bring the cam "kit" that they bought with springs etc etc. At least half the time the parts they purchased will not work with the heads they have

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post #7 of 13 (permalink) Old May 22nd, 20, 3:35 PM
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

Are you going to be running this engine at high RPM all the time? Keep in mind, manufactures will recommend valve springs based on you using this engine in it's peak range for extended periods of time. Or in drag applications. Valve spring pressure is to prevent valve float at the upper RPM range for a run down the strip 4 to 5 times a day. So they are designed for that purpose. Think about how you want to use this car. If your spending most time cruising around town, going to the car show and occasionally running from stop light to stop light, there is no need to run the max spring pressure. Just make sure the spring has the correct bind and lift. The lower lbs. on the spring will lighten up the load and ware on your valve train.
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post #8 of 13 (permalink) Old Jun 6th, 20, 2:12 PM Thread Starter
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

Still looking for help. My installed height without shims is 2.153" with these heads. I bought a set of the 68340 springs, but they recommend a 1.900" installed height. That would be 0.250" in shims!

Any recommendations? Should I get different springs? Offset retainers and/or keepers?

Thanks.

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post #9 of 13 (permalink) Old Jun 6th, 20, 3:27 PM
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

Quote:
Originally Posted by rlchv70 View Post
Still looking for help. My installed height without shims is 2.153" with these heads. I bought a set of the 68340 springs, but they recommend a 1.900" installed height. That would be 0.250" in shims!

Any recommendations? Should I get different springs? Offset retainers and/or keepers?

Thanks.
You can get -.050" locks, I don't know about retainers with reduced height, you may have to call somebody, like Howard's Cams/Competition Products.
That .250" is a lot to make up though.

Sounds like you've got the wrong length valves for mild cam use...usually that kind of tall installed height/longer valves is used for Solid Roller cams that need that much spring.

If you try to stay at that 2.150"-ish height you are likely not going to find a mild enough spring....no market for it. Every spring list I looked at when you went to 2.00" installed height or more the seat pressures were 200lb+ and open pressures above 550 lbs.

You are including the spring seat locator in your installed height measurement, correct?? Not measuring to the bare aluminum spring seat??

Did you buy the heads assembled complete?? If so, sounds like you bought a head set-up for solid roller.
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post #10 of 13 (permalink) Old Jun 6th, 20, 3:50 PM Thread Starter
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

2.153" is to bare aluminum. Seat locator is only about .058", though.

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post #11 of 13 (permalink) Old Jun 6th, 20, 6:16 PM
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

Quote:
Originally Posted by rlchv70 View Post
2.153" is to bare aluminum. Seat locator is only about .058", though.
So you've basically got 2.100" right now because you can't run it without a spring seat.

You can lose .050" with the locks, but you're probably not going to find a retainer that will lose more than another .050". Still puts you .100" away and that is too much shim.

Reality is you've got the wrong length valves for a mild spring installation.
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post #12 of 13 (permalink) Old Jun 13th, 20, 1:42 PM Thread Starter
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

Found these 0.300" valve spring spacers and some different valve retainers. Compressed height is right at 1.900".

https://www.summitracing.com/parts/crn-99459-8

Randy Johnson
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post #13 of 13 (permalink) Old Jun 13th, 20, 1:57 PM
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Re: Valve Spring Recommendation for BBC Pro Comp Heads

I hadn't considered using BBC exhaust rotator eliminators under all springs.
Looks like you found a way.
Make sure it fits the guide or pocket OD fairly close so you don't risk the positive stem seal getting beat up from that seat moving around and the inner spring hitting it..
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