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Discussion Starter · #1 ·
I've been thinking of maybe replacing my valve springs, but I am not in a position to pull the engine. I seen a video of a guy pushing compressed air into the cylinder and using a funky tool to pop them out, so it seems doable. But how much of a PITA is it?

I'm thinking of this because of my dyno results. It's a Comp 280H cam that should hold better to 6000 IMO.

First time I dynoed the car I had a torn vacuum secondary diaphragm so it's not truely accurate, but it sure looks like valve float above 5500.



Second dyno test I didn't run it much past 5500.



Thoughts? Is it even worth it?
 

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IMO, I really don't see that cam peaking much higher (if any) than 5500 rpm in a 454. What is the rest of the combo?
 

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We did this here ; Mark J provided me the all new stiffer springs , shims and micrometer . I bought the tool from Summit - We used a plug wire to keep the valves up ( no compressor needed ) all the new spring were measured and installed at correct height . It was a fun job i did all the measuring , my friend the mechanic did the rest - it took about 4 hours :) slowly but surely !






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Discussion Starter · #6 ·
Are you using Comp #924 springs? If so that is a problem. They are their own rev limiter.
I think so. I didn't build the engine so I can't be certain, but I do know it has the yellow marking on the spring.
 

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Yes, after measuring every valve height, the springs need to be measured for height at full valve lift to have the correct pounds as per the cam specs. Adding shims of different thicknesses lets you attain that. Then every spring needs to go to the valve for that height.

And I'll tell ya, doing them in a big block car with air conditioning, with 620 pounds at full lift is no easy task.

 

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Yes, after measuring every valve height, the springs need to be measured for height at full valve lift to have the correct pounds as per the cam specs. Adding shims of different thicknesses lets you attain that. Then every spring needs to go to the valve for that height.

And I'll tell ya, doing them in a big block car with air conditioning, with 620 pounds at full lift is no easy task.


Yeah, mine have been in there for 5yrs now and looking to change them too.
225-240lbs seat pressure and 600-650lbs open pressure

So I feel ya.
 

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The last pic in post 4 shows the valve stem micrometer. You measure from the head to the bottom of a valve retainer with locks installed. Few valves will be identical.

It might be easiest to take the measurements to a machine shop and let them measure the springs and you'll have springs with shims for each valve. Don't mix them up!
 
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friend ran the smaller 268H in his 454 way back in the 1991 time frame.
Performer intake and we tried many carbs and timing curves.. it ran the same as my 350 with a 268H in it.. we both had 308 gears .. he had TH400 and I had TH350.
Mine was a 78 nova and his was a 78 camaro.

The 454 would rev to 6000 rpm with the little cam real easy.
I installed the 280H in a 396 with the 911 springs 122 seat pressure and 2.19-1.88 valves.. valve float is 6500-6700 it still needs more spring pressure with that 911 spring.

The 280H will rev to 7000 easy with the right springs.
Max HP on the 268H (the little cam) is at 5700... this is where the HP starts to fall off. The 280H should be more.

The 280H in a 355 will run 12.50's with junk in a 3000 lb ride with some gear.
I would hope 100 more cubes could match that.

This is a good case for you to purchase a book or 2 that explains all you want to know.
How to build and modify sbc cylinder heads.
How to Build and Modify Chevrolet Small-Block V-8 Cylinder Heads (Motorbooks Workshop): David Vizard: 9780879385477: Amazon.com: Books

You can use the same information on about any head.
There might even be a BBC head book out there.

Those how to books are very informative.
 

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mr 4 speed that 110 seat 330 open would be fine with the SBC
but this is the BBC you will need more.
I have read many people have issues with the 911 spring at 122 seat pressure going into valve float early and even being down on power earlier than valve float.. changing to what Strokerboats suggested (Isky 8005a springs) was done a few times and really fixed the lack of power and low RPM valve float issues.

I would have thought 122 seat would be plenty but I was dead wrong going with 911 springs and the OP has even lighter springs than the 911
 

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mr 4 speed that 110 seat 330 open would be fine with the SBC
but this is the BBC you will need more
I have no problems using that spec spring with .520 lift big block Chevy f/t hydraulic cam.Actually,the open pressure might be 340
FWIW,This spec (110/330 or 340) is used on the 454 and 502 HO cams,which are hydraulic roller. IMHO,that is weak for a hydraulic roller but fine for a hydraulic flat tappet street cam.
 

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maybe the harmonics come in early then on the comp 911 springs at 122 seat pressure.
Or maybe the 280H comp ramps are more aggressive than some .520" lift cams.
I never thought those magnum line of cams were aggressive though.

When does that HO cam peter out. I know that 280H will pull to 7000 really easy and 7200 with a good tune and enough spring and good head work..I do not mean just pull up there and not make any power..I am talking optimum shift point for best ET and MPH.

Maybe there is an issue with the 911 springs I used on that recent BBC, But i checked and set each one up myself.
I do know that particular cam in the BBC i did does not like the 911 spring.

Or could be the 2.19 -1.88 valves I used were way too heavy along with heavy retainers.
They are not under cut and they are stock stem size.
 

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I'm pretty sure I know the answer to this, but is there any benefit to some titanium retainers?
As they're a nice big chunk on the end of the valve stem, yes. But valve stem locks are so small, there's no reason to go Ti. BUT you may need to replace them to match the lighter retainers.
 

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Discussion Starter · #20 ·
As they're a nice big chunk on the end of the valve stem, yes. But valve stem locks are so small, there's no reason to go Ti. BUT you may need to replace them to match the lighter retainers.
I know the Ti retainers helps increase RPM limit, but by how much on a sub 6000 rpm engine? 100, 200, 500 rpm?

I also just read about Tool Steel. Apparently more reliable and only a few more grams than Ti at a lower cost.
 
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