Cam selection for TT setup

[jjump59]

anyone have any tips on selecting a cam for a turbo engine? i'm looking at a TT Pontiac deal and have found a fairly mild hyd roller, just wonder if it would be ok. thanks

[ty1295]

http://www.cammotion.com/

They will spec a custom cam for you for very little more than an off the shelf. Well worth the money.

Lots of theories on turbo cams, in general you want little to NO overlap.

With fuel injection 114 deg. lobe seperation angles.

[Y-TRY]

A lot of the turbo cams I've seen are using split duration, with the long side to the exhaust.

What is the theory on this?

[PhillipM]

Why go with a 114 lobe sep with FI??? I don't know much about cams so I am just asking to learn a little bit.

[ty1295]

114 = less overlap in general. With turbo being things are forced in, you don't need the scavange effects.

114 though on a carb can sometimes not work well from what I have heard. I am by far NOT a cam expert though. I think has something to do with vacuum signals, etc. Again no cam expert.

[Y-TRY]

I have a carb and 114 LSA. It's important to remember that the actual degrees of overlap is relative to duration as well as just the angle. For example: A cam with 240 @ .050 and a 114 has more overlap than a 230 @ .050 with 112 LSA (generally speaking), even though you'd think "114 has less overlap than 112". That's true with a given duration, but make sure not to assume a big ol' 250 @ .050 cam with a 114 has little overlap, because it will still have a ton. Big duration cams need an even larger displacement angle to seal it up. (Just throwing that out there)

[jjump59]

how does this cam sound for a 800 hp 461 twin turbo, heads flow 320 cfm at 600 and 700.

Gross Valve Lift 0.502 0.510
Duration At 0.006 Tappet Lift 276 282

Valve Timing At 0.05
Open Close
Intake 6 38
Exhaust 49 1

These Specs Are For The Cam Installed At 106 Intake CL
Intake Exhaust
Duration At 0.05 224 230
Lobe Lift 0.335 0.34
Lobe Separation 110

[Y-TRY]

You really need to know what the heads flow at .500 and lower lift. Those heads will never see that flow with that cam.

[jjump59]

Heads flow,

int exh
88 62 at .100
166 127 at .200
230 185 at .300
279 230 at .400
315 255 at .500
320 268 at .600
326 272 at .700

If you need any other information, I can probably provide it. Thanks

[camcojb]

Heads flow,

int exh
88 62 at .100
166 127 at .200
230 185 at .300
279 230 at .400
315 255 at .500
320 268 at .600
326 272 at .700

If you need any other information, I can probably provide it. Thanks

Those are great exhaust numbers. I've got a couple of turbo grind hydraulic rollers here, but they're for a small block Chevy. Both on 114 lsa, 4-6 degrees of overlap. One is installed straight up and the other is only 2 degrees advanced. On a turbo cam either the intake and exhaust @ .050 is the same, or the exhaust is shorter than the intake. The bigger of the two is for a 1000+ HP Brodix build and has close to .600 lift and 232/227 @ .050

Jody

[Y-TRY]

Those are great heads! Wow. I have ported AFR 220's that flow about the same, but my cam is about .600 lift. But 315 @ .500 is still pretty good.

The usual issues with velocity vs. big cc ports pretty much goes out the window with forced induction, too.

For what it's worth, I had my cam custom ground. It's like Jody said, with a split duration, but it's kinda big: 242/250 @.050, .588/.608 lift, on a 114 LSA, installed at 106. The cool thing is, since it's a solid roller, I actually only have 282/290 seat-to-seat duration, so it really runs pretty mildly. Solid roller allows the ramps to be pretty steep, as you see with mine. If/when I go EFI I'll re-think the cam.

[Matt]

something with about .5-.6 lift and pretty much no overlap is what you need.