GM L31HD and cam choice

[slowburb]

Hello, any progress on this build? I just took shipment of a new L31-R HD yesterday and I too am looking for a cam. I'm looking for off Idle torque to 4-5000 rpm in a 97 Suburban on 35" tires and 3.73 gears. I've read this several times and I think what I understand is that the GM# 14097395 HT838/Marine cam is the choice for no cylinder head machining and new springs? If that is correct, would this combination benefit from roller tip rockers?

Thanks in advance?

You'll want new springs with the cam to do it *right*. No head machining is necessary. I wish this myth would die.


*********MACHINING IS NOT NECESSARY TO RUN A HOTTER/BIGGER CAM ON VORTEC HEADS!!!!!************


Roller tip rockers aren't really worth much. Look at Scorpion roller rockers or keep your stamped OEM's.

 

[slowburb]

Hello, any progress on this build? I just took shipment of a new L31-R HD yesterday and I too am looking for a cam. I'm looking for off Idle torque to 4-5000 rpm in a 97 Suburban on 35" tires and 3.73 gears. I've read this several times and I think what I understand is that the GM# 14097395 HT838/Marine cam is the choice for no cylinder head machining and new springs? If that is correct, would this combination benefit from roller tip rockers?

Thanks in advance?

You'll want new springs with the cam to do it *right*. No head machining is necessary. I wish this myth would die.


*********MACHINING IS NOT NECESSARY TO RUN A HOTTER/BIGGER CAM ON VORTEC HEADS!!!!!************


Roller tip rockers aren't really worth much. Look at Scorpion roller rockers or keep your stamped OEM's.

 

[davkenrem]

You'll want new springs with the cam to do it *right*. No head machining is necessary. I wish this myth would die.


*********MACHINING IS NOT NECESSARY TO RUN A HOTTER/BIGGER CAM ON VORTEC HEADS!!!!!************


Roller tip rockers aren't really worth much. Look at Scorpion roller rockers or keep your stamped OEM's.

Much Thanks!!!

 

[L31MaxExpress]

Hello, any progress on this build? I just took shipment of a new L31-R HD yesterday and I too am looking for a cam. I'm looking for off Idle torque to 4-5000 rpm in a 97 Suburban on 35" tires and 3.73 gears. I've read this several times and I think what I understand is that the GM# 14097395 HT838/Marine cam is the choice for no cylinder head machining and new springs? If that is correct, would this combination benefit from roller tip rockers?

Thanks in advance?

For that cam there is absolutely no reason to swap the springs. GM runs the same OEM springs on the Marine engines that came with the 395' cam. GMPP also took that same Marine 350, put 1.6 roller rockers and the Ramjet EFI intake on it and it became the Ramjet 350 crate engine. When GMPP discontinued the 1.6 rockers, GMPP switched out the Ramjet to 1.5 roller rockers and revised both the part number and power ratings of the engine. GM also uses the same springs for the 151' roller cam that is in the SPO 357 HP 350 HO engine. Ramjet had .461/.481" lift and the SPO .474/.474" lift.

 

[slowburb]

For that cam there is absolutely no reason to swap the springs. GM runs the same OEM springs on the Marine engines that came with the 395' cam. GMPP also took that same Marine 350, put 1.6 roller rockers and the Ramjet EFI intake on it and it became the Ramjet 350 crate engine. When GMPP discontinued the 1.6 rockers, GMPP switched out the Ramjet to 1.5 roller rockers and revised both the part number and power ratings of the engine. GM also uses the same springs for the 151' roller cam that is in the SPO 357 HP 350 HO engine. Ramjet had .461/.481" lift and the SPO .474/.474" lift.

Mmmmmkay buddy.

 

[Supercharged111]

Mmmmmkay buddy.

He's right. I researched part numbers when I did my marine cam with 1.6s and that's why I kept the stock springs vs installing LS springs .050" too short.

 

[davkenrem]

You'll want new springs with the cam to do it *right*. No head machining is necessary. I wish this myth would die.


*********MACHINING IS NOT NECESSARY TO RUN A HOTTER/BIGGER CAM ON VORTEC HEADS!!!!!************


Roller tip rockers aren't really worth much. Look at Scorpion roller rockers or keep your stamped OEM's.

Much Thanks!!!

 

[davkenrem]

Well my research indicates the same. GM takes the L31-r that I bought for $1750, slides this camshaft in it.

https://www.summitracing.com/parts/nal-12677151

They rename it the SP350-357-base and charge an extra $1550.00!! Oh wait, you get a Chrome Timing Cover, Flex Plate, Dipstick and oil filter.

https://www.chevrolet.com/performance/crate-engines/sp350-357-base
https://www.summitracing.com/parts/nal-19367080/overview/

Think I'll buy this cam.

 

[davkenrem]

Pace Performance sells this,

L31-R HD 12530283

https://paceperformance.com/i-23836...0-cid-vin-r-3-4-1-ton-replacement-engine.html

$2069.88

and...


GMP-12530283-4

https://paceperformance.com/i-23869...t-main-no-mechanical-fuel-pump-provision.html

$2869.96

Which appears to be the 12530283-L31 -R HD engine, with the only change I see is the cam.

Running this spring.

https://paceperformance.com/i-6484546-10212811-small-block-chevy-475-lift-350ho-spring-single.html


I did a search on Pace Perfomances website for the spring and the results list every engine that has this Valve Spring in it. There is about 30 of them.

https://paceperformance.com/search.html#!sq=10212811

Some things I noticed:

>The GM SP350/357 appears to be the same engine as the L31-R with the only difference being the compression ratio is listed as 9.0:1 vs the L31R at 9.4:1. GM's site list Cast Aluminum pistons for the engine where as the L31R list Hypereutectic . Is that a true value or was it GM's way of hiding that the SP350/357 is the L31R with a hotter cam??

https://paceperformance.com/i-23888652-gmp-19367080-2x-pace-performance-sp350-357-w-black-trim.html


>The GM RamJet 350 appears to be the exact same engine as the L31-R with a slightly milder cam than the SP350/357 but has the exact same specs as the L31-R other the cam and induction.

https://paceperformance.com/i-6255304-19355815-gm-ram-jet-350-crate-engine.html



>GM Parts direct list the application for this valve spring as the following:

Valve Springs - GM (10212811)

• Express, savana. Astro, Safari. All models. 4.3l. S-series. Silverado, sierra.
• Applications:4.3L. 5.0L, 5.7L. 6 CYLINDER. 4.3L, 8 CYLINDER. 4.3L W/BALANCE SHAFT. 4.3L, W/BALANCE SHAFT. 8 CYLINDER - 5.0L, 5.7L.

https://www.gmpartsdirect.com/oem-parts/gm-valve-springs-10212811

>What I cannot verify is that this is the same spring that is used on the L31. But for 30 years I've read of GM "reaching into their vast parts bin" to find some part they already have. My conclusion is that that GM takes a Longblock (L31-R) that they probably have less that $500-$800.00 of cost in and make several crate engines from it by using 2 or 3 different cams and adding on external accessories with a huge mark up.

If this theory is true, you can buy all the parts to build the Ram Jet 350 Crate Engine for around $4850.00 and GM sells it at around $6275.00, a $1400 mark up.

The Pace Perfromance GMP-12530283-4 - 390HP is another good comparison, for $2869.96 You get the L31-R and the SP350/357 Camshaft.

https://paceperformance.com/i-23869...t-main-no-mechanical-fuel-pump-provision.html


Or you can buy the NEW GM 1996 - 2000 5.7L 350 CID (L31-R) and the 12677151 - Hydraulic Roller Camshaft - SP350/357 for $2385.42 and have the exact same thing.


https://paceperformance.com/i-23836...0-cid-vin-r-3-4-1-ton-replacement-engine.html

https://paceperformance.com/i-23849469-12677151-hydraulic-roller-camshaft-sp350-357.html


I'm beating a dead horse. This was mainly for my own information and I'm just sharing it with you guys.

Conclusion, the L31-R is one of the best deals on a crate engine on the market. You can virtually build any GM Vortec based crate engine from it, just buy swapping the cam and adding accessories.

 

[slowburb]

By the standards I'm accustomed to, the stock L31 springs are inadequate for an L31, so there surely inadequate for a warmer version of the same motor, and I'm not calling you Shirley. When you have to warranty a motor for however many miles, you look at a slight performance drop for valvetrain longevity as an advantage, not a disadvantage. I'll take GM engineering's stance on a lot of things, but not this, or the gov-bomb, or the 4L60E. I don't care which springs GM put in which motor. I'm concerned with open/close pressures, rates, and valve control, with anything "LS" out of the considerations.