300 H.P. valve springs

[Joe L.]

Re: 300 H.P. valve springs

[ATTACH=CONFIG]68871[/ATTACH][ATTACH=CONFIG]68872[/ATTACH]Duke and Joe, The photos might not be as clear as needed, but the retainer on the left came off the 1962, 250 H.P. The retainer on the right has the C marking.
Ken

Ken-------


I do not know what these are. There were only 4 valve spring caps used for small blocks over the 1955-1991 period. These are as follows:

early 1955----GM #3711176

1955-66-------GM #3729363

1967-79-------GM #3896934

1980-91------GM #14003974 (also SERVICE for 1967-79)


I have pictured the 3729363 and 3896934 above.

[Duke W.]

Re: 300 H.P. valve springs

Thanks guys for all the dimension data and photos. What I'm trying to figure out is the functional difference between the 56-66 and 67-up caps.

My tentative conclusion is that the caps are interchangeable, however the early cap will result in a lower installed spring height by about .030".

That may be why the '67 I referenced in post #11 required so many shims to achieve 0.90-.100" coil bind clearance on the relatively low lift McCagh Special Cam, which is just the OE '67 "300 HP" (CS-274) cam with the lobes swapped and indexed very late. A couple of "327 LT-1s" didn't require excessive shimming to achieve this spec, but they were '65s, so they have the early caps and the LT-1 cam has more valve lift, which is calculated by subtracting clearance ramp height from gross lobe lift and multiplying by 1.44, which is the maximum (measured) rocker ratio at maximum valve lift. Max hydraulic lifter cam valve lift is calculated using gross lobe lift times the 1.44 rocker ratio.

Do you guys agree with my tentative conclusion?

Duke

[Joe L.]

Re: 300 H.P. valve springs

Thanks guys for all the dimension data and photos. What I'm trying to figure out is the functional difference between the 56-66 and 67-up caps.

My tentative conclusion is that the caps are interchangeable, however the early cap will result in a lower installed spring height by about .030.

That may be why the '67 I referenced in post #11 required so many shims to achieve 0.90-.100" coil bind clearance on the relatively low lift McCagh Special Cam, which is just the OE '67 "300 HP" (CS0274) cam with the lobes swapped and indexed very late. A couple of "327 LT-1s" didn't require excessive shimming to achieve this spec, but they were '65s, so they have the early caps and the LT-1 cam has more valve lift, which is calculated by subtracting clearance ramp height from gross lobe lift and multiplying by 1.44, which is the maximum (measured) rocker ratio at maximum valve lift. Max hydraulic lifter cam is calculated using gross lobe lift times the 1.44 rocker ratio.

Do you guys agree with my tentative conclusions?

Duke

Duke------


The way I see it is as I stated: if GM considered the 1955-66 caps and the 67-91 caps interchangeable, they would long ago have consolidated them into one part number. Also, they certainly would not have superseded the 1955-66 with a new part number, GM #10038209, applicable only to 1955-66.

[Bob W.]

Re: 300 H.P. valve springs

I stopped by a local engine rebuilder Saturday and he said a 1.250 od valve spring will work in a small block head with out any problem.
Bob

[Kenneth F.]

Re: 300 H.P. valve springs

I installed longer springs Sealed Power recommended for the CS-274 camshaft. I set the valve spring installed height to the specs. from the 1966 GM manual, which was about .100 shorter than what I originally had. What a difference in performance. With the pedal about 2/3 down in 2nd gear, the RPM's jumped past 4500 RPM's and showed no sign of slowing.

[Bob W.]

Re: 300 H.P. valve springs

Kenneth so what # spring did sealed power recommended ? Also did you change the lifters push rods &rocker arms ? I plan on using the same cam in my 283 / 245 hp motor
Bob.

[Kenneth F.]

Re: 300 H.P. valve springs

Hi Bob, Sealed Power recommended VS-521 springs for the CS-274 camshaft. I used Sealed Power hydraulic lifters, generic rocker arms and push rods.
If I were having heads rebuilt, I would take the valve spring installed height specs. to the shop. I got my specs. from a 1966 GM shop manual.
You might start a new thread with your plan, and see what Duke Williams and Joe Lucia say.
Ken

[Bob W.]

Re: 300 H.P. valve springs

Kenneth do you have a phone number for their help line ?
Thanks Bob

[Kenneth F.]

Re: 300 H.P. valve springs

Bob, It appears that Sealed Power is now Federal Mogul. The listed tech line phone number is 1-800-325-8886.
Ken

[Bob W.]

Re: 300 H.P. valve springs

Kenneth Thank you for the phone number .
Bob

[David B.]

https://www.forums.ncrs.org/showthread.php?103388-Part-numbers-for-1970-LT1-cam

[Gene M.]

Re: 300 H.P. valve springs

David,
The 974 with the "v" marking on top is quite common on 60's SB heads. I have not payed particular attention to early and late just as to set spring height when done. The GM z28 style springs are a good choice. I have no idea what the p/n is. The engine shop I deal with does. The seals you mention I've not seen. As far as I've seen the stock Chevy used an "O" ring style seals on the top of the stem. Provided you have good guides that's all that is required. Reground and redone seats does increase the spring height. I always use 1.94" heads when building a restored 2.02" head when possible. But always use new one piece top quality valves.

L79 cam would be a better choice to the LT1, remember less cubes = less torque.

[David B.]

Re: 300 H.P. valve springs

David,
The 974 with the "v" marking on top is quite common on 60's SB heads. I have not payed particular attention to early and late just as to set spring height when done. The GM z28 style springs are a good choice. I have no idea what the p/n is. The engine shop I deal with does. The seals you mention I've not seen. As far as I've seen the stock Chevy used an "O" ring style seals on the top of the stem. Provided you have good guides that's all that is required. Reground and redone seats does increase the spring height. I always use 1.94" heads when building a restored 2.02" head when possible. But always use new one piece top quality valves.

L79 cam would be a better choice to the LT1, remember less cubes = less torque.

Gene, thanks for the input. I didn't provide all the background info here; I'm sort of emulating a '62 340 hp engine (visually, anyway), but the block is actually a 3959512 (service) block. It's the early vented style, but has large main journals, and a 355 ci rotating assembly. By my reckoning, the car is about 300# lighter than anything the factory ever built with a 350/LT-1. So, I'm hoping it will be torque-y enough get off the line OK.

I've read lots of discussion on springs, so I won't revisit that, but I didn't want to go heaver than OE. On the seals, I did consider the factory setup--however, the stainless valves the shop installed do not have provision for the O-ring stem seals. I was very careful, especially during disassembly, not to mess up the fresh seals on the guide bosses. The heads are 1.94/1.50--I thought about opening those up, but didn't. If I were doing it again, I might have gone larger on the exhaust.

[Duke W.]

Re: 300 H.P. valve springs

Thanks for writing the epilog to this story, David. It appears that using the "early" caps will require fewer shims to achieve mininmum installed height in order to maximize valve train limiting speed. Your 3.48" stroke engine should make at least 80 percent peak torque at 2000 as long as the spark advance map is set up like the 365/375 HP 327s. Max power and max useable revs is a function of head flow, but with properly massaged heads it should make close to 290 SAE corrected RWHP somewhere between 6000 and 6500 with a maximum useable power bandwidth close to 7000. Your valve spring installed heights will yield a valve train limiting speed of about 7200, so there is absolutely no need for stiffer springs, including the so-called "Z-28 springs", which were designed for the first design ...140 Trans Am racing cam. Production Z-28s used the 3911068 spring. BTW, Bill Clupper recommends against opening up 461X head valve seats for the 2.02/1.60" valve set. They were not designed with the larger valves in mind and may not have enough material. The 461 and later big port heads have different cores with more material around the valve seats to allow the larger valves. Nevertheless it's a good ideal to hand taper the both sides of the chambers with a die grinder to eliminate overhang. Since the LT-1 cam uses the long duration 30-30 lobe on the exhaust side indexed four degrees earlier, it mitigates the "restrictive" exhaust valve, but with proper massaging it's really not restrictive. The best set of flow numbers I have in my library is a pair of 462 heads with the standard valve size and an E/I flow ratio close to 0.80, so a longer duration exhaust event with an earlier opening isn't even necessary, but does no harm.