LS5 versus LS4 camshafts

[Duke W.]

It turns out that Sealed Power actually offers the '73-'74 LS4 camshaft. I found it by crossing the OE 353040 part number at www.napaonline.com and it came up as CS660. The high level specs are as follows (I/E durations @ .050"/IPOML/EPOML/LSA/lobe lifts, inches, inlet data listed first)

210/213/109/117/113/.258/.258

The CS1093M, which is the replacement for the early 3883986 (with a rear journal groove) and 3904359 (no rear journal groove) is as follows:

214/218/110/120/115/.271/.282

As far as I know the CS1093M has no rear journal groove, so one will have to be machined for use in '66 390 HP engines.

The 343040 has slightly less lift and the lower LSA on similar durations means it has slightly more effective overlap. My hunch is that more overlap was designed in to help meet federal NOx standards that went into effect in 1973 (1971 in California). Any added overlap would increase exhaust gas dilution and lower NOx, but degrade idle quality and low end torque.

I don't know if the relative durations of either cam are suitable for the cylinder head E/I flow ratios, because I have no data for either as-built or massaged heads, either open or closed chamber. On balance the early design probably offers more broad range performance, but without head flow data for both as-built and massaged, open and closed chamber configurations, it's impossible to conduct accurate simulations.

It's my understanding that all hydraulic lifter Corvette big blocks had 2.06/1.72" valves, and heads up to 1970 were of the closed chamber variety and open chamber from 1971-1974.

Duke

[Joe L.]

Re: LS5 versus LS4 camshafts

It's my understanding that all hydraulic lifter Corvette big blocks had 2.06/1.72" valves, and heads up to 1970 were of the closed chamber variety and open chamber from 1971-1974.

Duke

Duke-----


That's correct.

[Richard M.]

Re: LS5 versus LS4 camshafts

Duke,
How would the GM 10185060 cam that was used in the 454 HO crate engine, compare with the 3883986 cam if used in a 66-69 427 390 0r 400 hp
performance wise?

Richard

[Duke W.]

Re: LS5 versus LS4 camshafts

The data from the GMPP catalog (220/220/-/-/115/.500/.500 valve, not lobe lift) means that its a bit more aggressive with little more overlap and 6 degrees more inlet duration than the L-36 cam. It's very near the L-79 small block cam in terms of duration and overlap.

POMLs are not listed, but the catalog note implies that this cam is the same as the the 14096209 used in the 502, but advanced five degrees. The note also says to use valve spring 10185058, but I could not find this spring in the spring chart.

It would take specific head flow data to determine from simulations which of the three would best meet the user's target torque, power, and idle characteristics, but my hunch is that the OE L-36 cam (retarded four degrees in a 454) in conjunction with massaged heads would offer the most useful road engine torque characteristics.

As I've always said, you massage the heads for top end power within the maximum engine speed limit and work valve timing to meet the low end torque requirement, and low overlap in conjuction with a relatively late phased inlet valve closing usually works best.

Duke

[Richard M.]

Re: LS5 versus LS4 camshafts

The 1994 Performance parts book says to use spring 3970627, with this cam.

Richard

[Duke W.]

Re: LS5 versus LS4 camshafts

That brings up an interesting dilemma, but the solution might solve a problem.

The ...627 spring was the second design production spring (dual with integral unbrella valve seal) that appeared circa 1969 to replace the prone-to-break early single spring/damper design. However this spring appears to be out-of-production/unavailable from any source - GM or aftermarket, and no one has been able to cross reference it or find a supercedeing number as far as I know. Maybe this 10185058 spring referenced in my 2006 GMPP catalog is effectively a replacement for the ...627, but I can find no data on it.

I tried cross referencing it at napaonline.com and came up blank. You big block guys need to research this further as we currently don't know of an equivalent replacement for the ...627 for big blocks running OE camshafts,

BTW, multiple rates have been speced for the ...627 depending on the data source. Joe Raine had a couple tested and the calculated rate was 454 lb/in, which jibes with some listed specs. The rate stated in my 2006 GMPP catalog is 267 lb/in, which is clearly wrong, however, this is higher than the 358 lb/in rate quoted for the HD spring used with L-88/ZL-1. Go figure!

Big block valve springs are very confusing.

P.S. napaonline.com shows the VS708 as applicable to all big block corvettes but it doesn't have the integral retainer and umbrella seal of the OE ...627:

http://www.napaonline.com/Catalog/Bu...rtNumber=VS708

Dimension data is specified, but no forces/rates:

http://www.napaonline.com/Catalog/Ca...671_0194499105

[Richard M.]

Re: LS5 versus LS4 camshafts

Duke the 1994 GMPP catalog gives part # 14097002 as the spring used in Gen 5 454 & 502 HO engines, 1.487" OD. but no other specs.
also retainer # 14096274 is used with this spring.

[Richard M.]

Re: LS5 versus LS4 camshafts

Duke, I just found this spec. for p/n 14097002, The dual spring is 1.487" O.D. diameter 1. The pressure at installed height is 110# @ 1.88". Use with valve spring retainer P/N 14096274.
Richard

[Joe L.]

Re: LS5 versus LS4 camshafts

That brings up an interesting dilemma, but the solution might solve a problem.

The ...627 spring was the second design production spring (dual with integral unbrella valve seal) that appeared circa 1969 to replace the prone-to-break early single spring/damper design. However this spring appears to be out-of-production/unavailable from any source - GM or aftermarket, and no one has been able to cross reference it or find a supercedeing number as far as I know. Maybe this 10185058 spring referenced in my 2006 GMPP catalog is effectively a replacement for the ...627, but I can find no data on it.

I tried cross referencing it at napaonline.com and came up blank. You big block guys need to research this further as we currently don't know of an equivalent replacement for the ...627 for big blocks running OE camshafts,

BTW, multiple rates have been speced for the ...627 depending on the data source. Joe Raine had a couple tested and the calculated rate was 454 lb/in, which jibes with some listed specs. The rate stated in my 2006 GMPP catalog is 267 lb/in, which is clearly wrong, however, this is higher than the 358 lb/in rate quoted for the HD spring used with L-88/ZL-1. Go figure!

Big block valve springs are very confusing.

P.S. napaonline.com shows the VS708 as applicable to all big block corvettes but it doesn't have the integral retainer and umbrella seal of the OE ...627:

http://www.napaonline.com/Catalog/Bu...rtNumber=VS708

Dimension data is specified, but no forces/rates:

http://www.napaonline.com/Catalog/Ca...671_0194499105

Duke-----

You could look for a long time for specs on the GM #10185058 valve spring and I don't think you'll ever find any. As far as I can tell, GM #10185058 was a Mark V ENGINE ASSEMBLY. So, I expect this number is an error in the GMPP Catalog.

As far as I can tell, the GM #3970627 valve spring was discontinued without supercession. However, the valve spring retainer with integral shield used with it is still available from GM under GM #3964264 (for about 15 bucks each, GM list).

I think the GM #14097002 is probably the closest thing available from GM. It might even work with the 3964264 retainer.

[Clem Z.]

Re: LS5 versus LS4 camshafts

That brings up an interesting dilemma, but the solution might solve a problem.

The ...627 spring was the second design production spring (dual with integral unbrella valve seal) that appeared circa 1969 to replace the prone-to-break early single spring/damper design. However this spring appears to be out-of-production/unavailable from any source - GM or aftermarket, and no one has been able to cross reference it or find a supercedeing number as far as I know. Maybe this 10185058 spring referenced in my 2006 GMPP catalog is effectively a replacement for the ...627, but I can find no data on it.

I tried cross referencing it at napaonline.com and came up blank. You big block guys need to research this further as we currently don't know of an equivalent replacement for the ...627 for big blocks running OE camshafts,

BTW, multiple rates have been speced for the ...627 depending on the data source. Joe Raine had a couple tested and the calculated rate was 454 lb/in, which jibes with some listed specs. The rate stated in my 2006 GMPP catalog is 267 lb/in, which is clearly wrong, however, this is higher than the 358 lb/in rate quoted for the HD spring used with L-88/ZL-1. Go figure!

Big block valve springs are very confusing.

P.S. napaonline.com shows the VS708 as applicable to all big block corvettes but it doesn't have the integral retainer and umbrella seal of the OE ...627:

http://www.napaonline.com/Catalog/Bu...rtNumber=VS708

Dimension data is specified, but no forces/rates:

http://www.napaonline.com/Catalog/Ca...671_0194499105

with a higher lift cam like the ZL-1 would not you want a spring with less pounds per inch to keep the over the nose pressure down ??

[Clem Z.]

Re: LS5 versus LS4 camshafts

Duke the 1994 GMPP catalog gives part # 14097002 as the spring used in Gen 5 454 & 502 HO engines, 1.487" OD. but no other specs.
also retainer # 14096274 is used with this spring.

• Spring type: dual
• OD: 1.487"
• Pressure at installed height: 110# @1.88"
• Solid height: 1.37"
• Average rate (lbs @ in): 316
• Retainer: P/N 14096274
• Valve seal kit: 12550422