[bcjjones]

A while back I had a buddy flattened a cam lobe on his 355. We tore down the motor, cleaned, replaced the cam and all has been well since, but he's worried about it happening again. 355 with aluminum heads, 1.6 rockers about 10.3:1 compression, 5 speed, 3.73 gears, 28" tire, 1 5/8 long tube out a dual exhaust.. all in a Silverado. Very similar build to mine. Currently has a Lunati bare bones flat tappet 224/234 Duration at .050". 112 Degree Lobe Separation Angle. 0.465"/0.488

He wants to change it to a retro fit roller and has found a custom cam grinder who has shot a couple options over to him. Curious on y'alls opinion.

Cam# SBC, HR71360-72360-110
276/280 @.006"
228/232 @.050"
.360"/.360" Lobe Lift
.576"/.576" Valve Lift w/1.6 rockers
110 LSA

272/276 @.006"
224/228 @.050"
.340"/.340" Lobe Lift
.544"/.544" Valve Lift w/1.6 rockers
110 LSA

With both cams he is recommending these lifters:
Lifter# XLR-8H01
.842" SB Chevy Hyd.Roller Lifter, 16set
Tie-bar, Retro-fit, Slow Bleed Rate


He claims both cams are good for a gain of 40-50 hp and 30 lb/ft of torque over the current cam. Sounds optimistic but wanted y'alls opinion?

 

[lmsport]

the power gain will depend on the flow capacity of the heads

 

[BogiesAnnex1]

Does depend on port flow and what you use for fuel.

In the end a port can only move so much mixture, most peak around .5 inch of lift. Not that they quite but the flow drops off pretty fast.

The other is fuel, if you guys are using corner gas station fuel with upper octane in the 91 to 93 range then a combination of less total duration with more packed into the .050 range with higher lift is more effective than lots of duration spread over the .006 range with less lift. The point here is to close the intake earlier to get the most compression pressure out of more limited compression ratios.

If your running higher octane fuel like E85 or race gas then you can pursue more old time compression ratios which are favorable to long duration cams and a little less lift.

These are the games you play within the flow limits of the heads you have. A way to get a port to deliver more flow into the cylinder is to use the cam to hold the valve open over more time. This works pretty well on a peak flow limited port but back into needing more compression to deal with reversion that happens with a late closing intake but with more overlap can be used to compensate as well. This drives you to operating at higher RPMs to take advantage of this set of dynamics. The other way is to use better flowing ports and less total duration but more across the .050 adventure, this is a huge advantage of roller cams. As I stated before the usefulness of this is how much CFM the port can deliver to the valve. This is where the Gen III and up engines shine as the port tends to keep feeding the valve when the valve is at lifts above .5 inch because the short side turn is less radical so there isn’t a flow separation on the short side that stalls the overall flow to the valve.

Bogie

 

[2001Blazer4x4]

Don't forget that roller cams take different stronger valve springs because of the heavy valvetrain. So be ready to change them when going from flat tappet to roller cam. Often requires different retainers as well for different diameter springs.

On the other hand, sometimes people use roller cam springs with a flat tappet cam and end up with flat lobes from the excess pressure.

Dont make these mistakes



Sent from my moto g power using Tapatalk

 

[johnsongrass1]

Your cam guys will know what spring they intended for you to use.