[JSH]

We're tearing down the engine in July, so I decided to use the opportunity to change to CID heads and an updated cam. Here's the cam spec summary:

Proposed CID Camshaft:
Comp Cams LTX Custom
Hyd. Roller Camshaft 1.8 1.8
38% Fuel Lob
248 / 264 .640" / .630" 1.8 / 1.8
116+4

Current LT4 heads Camshaft:
Cam Motion Billet Core GM
Gen V LT High Lift Custom Hyd. Roller
Camshaft (38% Fuel Lobe)
235 / 248 .644" / .631" 1.8 / 1.8
118+4

My question is, do I go with LME's proposed specs? Does anyone know of a cam that works better?

[Joshinator99]

Originally Posted by JSH

We're tearing down the engine in July, so I decided to use the opportunity to change to CID heads and an updated cam. Here's the cam spec summary:

Proposed CID Camshaft:
Comp Cams LTX Custom
Hyd. Roller Camshaft 1.8 1.8
38% Fuel Lob
248 / 264 .640" / .630" 1.8 / 1.8
116+4

Current LT4 heads Camshaft:
Cam Motion Billet Core GM
Gen V LT High Lift Custom Hyd. Roller
Camshaft (38% Fuel Lobe)
235 / 248 .644" / .631" 1.8 / 1.8
118+4

My question is, do I go with LME's proposed specs? Does anyone know of a cam that works better?

Where do you shift now for RPM? That’s going to push the power band even higher by a good bit which is fine if you have the airflow and valve train to support it…

[JSH]

Originally Posted by Joshinator99

Where do you shift now for RPM? That’s going to push the power band even higher by a good bit which is fine if you have the airflow and valve train to support it…

The 2/3 and 3/4 are close to 6500, and the rest are 6950-7000. I've got enough air to make 21-22# boost at sea level

[Joshinator99]

Originally Posted by JSH

The 2/3 and 3/4 are close to 6500, and the rest are 6950-7000. I've got enough air to make 21-22# boost at sea level

That new cam will probably want you shifting in the 7300-7400 range if I had to guess. Hopefully King will chime in. Does your boost drop off at all as you approach 7,000 RPM? If so your blower might not be happy supplying the motor at higher RPM. If your boost is rock solid right to the redline then maybe you’re good to go. Just need valvetrain to be setup for that.

[KingLT1]

Do you care how well the car drives and behaves on the street? That cam is going to want more rpm and converter. It has 24 degrees of overlap which is race car stuff imo. Your current cam has 5.5 degrees of overlap which is much better suited for street use and a blower. 24 degrees of overlap is going to bleed off boost.

[JSH]

Originally Posted by Joshinator99

That new cam will probably want you shifting in the 7300-7400 range if I had to guess. Hopefully King will chime in. Does your boost drop off at all as you approach 7,000 RPM? If so your blower might not be happy supplying the motor at higher RPM. If your boost is rock solid right to the redline then maybe you’re good to go. Just need valvetrain to be setup for that.

Yes, boost ramps up all the way through 4th, and stays constant through 5th.

Originally Posted by KingLT1

Do you care how well the car drives and behaves on the street? That cam is going to want more rpm and converter. It has 24 degrees of overlap which is race car stuff imo. Your current cam has 5.5 degrees of overlap which is much better suited for street use and a blower. 24 degrees of overlap is going to bleed off boost.

I'm fine with more rpm, but have not considered another converter. What overlap do you suggest? As I've said many times here, this is my first DI car, so every topic raises unknowns for me.

[KingLT1]

I do think positive overlap is beneficial in a PD application where you are spinning the blower hard as it will kill some bottom end torque in trade for more high rpm power, but 24 degrees is a lot imo. You also might see the boost drop some. And you are going to trade off a lot of drivability for more top end. That cam will probably want 72-7500rpm shifts and 1000-1100rpm idle. For example, The BTR stage 3 is around 13-16 degrees of positive overlap. You do have a 390 which allows for more cam, but I think I would try a cam in the 12-16 degrees range. The combo will probably want a 32-3600 converter. I would look at something like BTR's stroker gen V cam... 233/25x 115. As Josh mentioned there will be some variables to consider. Will your current supercharger and valvetrain support more RPM? I think you might consider contacting someone like Jason Levia on a build like that.

[RobZL1]

For what it's worth, I like that recommendation. I did a decent amount of research on my cam selection. I went with Katech's 233/250, 119+4. It has about 4 degrees of overlap, and the dyno graph I have seen pulls hard up to about 7000-7200 where it then starts to flatten. The cams I saw with tighter lsa (113 to 115 like the BTR 3) peaked earlier around 6000-6500.

With this, I concluded while it would sound nasty with a tighter lsa, I'd rather have the power continue to carry. I can only assume the wider lsa is responsible, per conventional cam wisdom.

Take that for what it's worth. I'm no cam guru, and I know it depends on a LOT of factors like your displacement, your head flow, your desired characteristics, etc.

[JSH]

Originally Posted by Joshinator99

If your boost is rock solid right to the redline then maybe you’re good to go. Just need valvetrain to be setup for that.

Current valve train:

Cam Bearings-Dura
Bond LTX CH-26T
Cam Bearingsura Bond LTX cam
bearings CH-26T

Timing set.:MOD GM LT1/LT4 Wet
Sump Crank Gear

Timing set.:LME LTX Billet Timing Chain
Guide

Timing set.:Cloyes C5R Single Roller
Timing Chain

Lifters.:Johnson High RPM Tie Bar Hyd.
Roller Lifters w/.700" Captive Roller. For
Use In Extreme Hyd. Roller
Applications, Designed For 200+ lbs.
Seat & 550 lbs. Open Pressure. Highest Quality Lifter Available

Push rods:Smith Brothers One Piece
3/8" x .080" Wall pushrods 381-xxxx (might not work with CID heads)

CUSTOMER SUPPLYING ROCKER ARM (I do not remember what rocker I have now, it might be the one HPE installed. It's not stock.)

Trunnion Mod.:CHE Bronze Trunnion
Modification For All GM LS & LT Rocker
Arms (installed

Cam Bearingsura Bond LTX cam
bearings CH-26T

[JSH]

Originally Posted by KingLT1

The BTR stage 3 is around 13-16 degrees of positive overlap. You do have a 390 which allows for more cam, but I think I would try a cam in the 12-16 degrees range. The combo will probably want a 32-3600 converter. I would look at something like BTR's stroker gen V cam... 233/25x 115.

Here's BTR's Hot cam"
BTR RED HOT CAMSHAFT

221/24X, .619/.617, 113 LSA

INTAKE LOBE LIFT @ TDC: 0.04730

[JSH]

Originally Posted by RobZL1

I went with Katech's 233/250, 119+4. It has about 4 degrees of overlap, and the dyno graph I have seen pulls hard up to about 7000-7200 where it then starts to flatten.

Katechs 233 / 250 @ .050, . 649/ .658 lift, 119+4 LSA, 38% fuel lobe makes sense for mine. Particularly when you read the write-up for the cam. I think they call it LT4 track day cam. What's the overlap?

I need to better define the car for LME because they appear to believe that I'm going to ask a lot more of it than I intend to.

Im not sure how my low DA factors into the calcs. For example, I'm going to be running at least 2 and 1/2 lb less manifold pressure than a car like mine runs in Houston.

[RobZL1]

Yep. That's the one I have. The overlap calculates to 3.5 degrees. My cam card is pretty spot on for the published numbers. I think my particular cam's overlap is 3.8 actual. Barely any overlap, really.

I would think cam specs would be the same at any altitude. Again, not a cam guru by any means.

[JSH]

Originally Posted by RobZL1

Yep. That's the one I have. The overlap calculates to 3.5 degrees. My cam card is pretty spot on for the published numbers. I think my particular cam's overlap is 3.8 actual. Barely any overlap, really.

I would think cam specs would be the same at any altitude. Again, not a cam guru by any means.

We try to run more advance and more cylinder pressure up here. So I was saying that you could design a cam for elevation where it had, for example less overlap and more cylinder compression, but I'm definitely not a cam guru either

[JSH]

Originally Posted by KingLT1

Do you care how well the car drives and behaves on the street? That cam is going to want more rpm and converter. It has 24 degrees of overlap which is race car stuff imo. Your current cam has 5.5 degrees of overlap which is much better suited for street use and a blower. 24 degrees of overlap is going to bleed off boost.

Both LME and Katech agree that the cam proposed by LME is a race car/motor cam, but that's not mine. I'm going with KaTech's Race Day cam, which has minimal overlap. You saved me from myself, again.