The Right Cam

[Ponyrider]

I have a 95 Z28 with Trick flow heads, 1.6 rocker what would be the best cam for me. 383 stocker eng

[fastTa]

It's going to depend on alot of things.

1. Head Flow Data
2. Compression Ratio
3. Headers?
4. Stall Speed (if auto)
5. Rear End Gear Ratio
6. How much power are you looking to get?
7. How much is "steetability" a factor?

The 2 most important factors to consider when looking at different cams are duration @ .050" and LSA (lobe separation angle). These will both be the primary factors in dictating the characteristics of the cam. The duration will be a strong determining factor in the overall power the cam can make, the RPM's to which the cam will make power, and the driveability, specifically down low in the RPM range.

LSA will be a strong determining factor in the cams idle characteristics and will also affect the cams power potential. The numerically lower the LSA the closer the intake and exhaust lobe centerlines are. The closer the intake/exhaust lobe centerlines are the greater the valve overlap. More overlap generaly means more power poetential because the scavenging affect is increased and will thus "draw" in a greater a/f charge. Again generally speaking, usually the idle and low RPM characteristics will be less "streetable" as the LSA is lowered numerically.

Another thing that needs to be considered is the overall lift of the camshaft along with your 1.6 rockers. Piston to Valve clearance should be looked at depending on the amount the heads are milled and the type of piston you are going to use. Additionally you will need to make sure the valve spring that you will be using will be able to efficiently handle the overall lift of the cam with a 1.6 rocker. The valve spring coil bind tolerance can me found by subtracting the solid height of the spring from the installed height of the spring. This will give you a good idea of how much lift the spring can accomodate before coil bind.

[Ponyrider]

Okay
1. 64 cc
2. 10.1
3. hooker super comp
4. 2800
5. 3.73
6. 475 -500 if possible
7. No

[fastTa]

Okay
1. 64 cc
2. 10.1
3. hooker super comp
4. 2800
5. 3.73
6. 475 -500 if possible
7. No

By head flow data, I meant a flow chart which shows the air flow measured in units of CFM at increasing lift heights. Generally speaking with significant port work and larger valves, a split pattern cam in the low 230's on the intake and a 112 LSA should easily get you roughly 410 RWHP which would be close to 500 at the crank. It would also be a streetable cam. Idle would have some lope, but nothing extreme. Shouldn't be much cam surge either. Good tuning can do wonders.

But again, in order to choose an exact grind, it is a good idea to go by the head flow numbers to pick the perfect cam for your motor.

[Injuneer]

Assuming they are "out of the box" you can get the flow data off the Trick Flow website. They are the same as the Gen 1 SBC TF heads, since all they really did was alter the cooling passages. As a result, you get an overly large combustion chamber (62cc according to TF) that was intended for blower motors and strokers. For a rough number, the TF's are 195cc heads and flow about the same as a stock LT4 head.

[fastTa]

Assuming they are "out of the box" you can get the flow data off the Trick Flow website. They are the same as the Gen 1 SBC TF heads, since all they really did was alter the cooling passages. As a result, you get an overly large combustion chamber (62cc according to TF) that was intended for blower motors and strokers. For a rough number, the TF's are 195cc heads and flow about the same as a stock LT4 head.

Assuming they ARE out of the box, and assuming the flow curve of the TF heads are similar to a stock LT4 head, then he would have to go with a larger cam to get the 500 at the crank he is seeking. The fairly low compression ratio doesn't help either.

[TimeLord]

The TFS TW that I am getting have been planed down to 56CC,can this be done to your heads to help the CR?

[Injuneer]

I'd be interested to see how he got 10.1:1. That would take a thin head gasket and flat top pistons, as a minimum. TF shows the 64cc combustion chambers for there Kenny Dutweiler "signature" series CNC heads. The rough cast are 62cc.

[fastTa]

My old link to a compression ratio calculator with the provision of the gasket bore is now dead. So ignoring the gasket bore and assuming a .030" deck height, a flat top piston with a -2cc valve reilef, and a .039" compressed gasket thickness, I come up with a static compression ratio of 10.68:1

So with the gasket bore he should be around 10.45:1 according to the above "assumed" data.

He may have a much taller deck height, more valve relief volume, or a thicker gasket or a combianation of either of these.

ponyrider, do you know your deck height, compressed gasket thickness (or just the actual part number would help), and piston volume?

[Ponyrider]

No, not right now I don't. The short block is at the machine shop for decking and to be stroked to 383. I was thinking of making the block a 396 but unsure if that's better then a 383?

[fastTa]

No, not right now I don't. The short block is at the machine shop for decking and to be stroked to 383. I was thinking of making the block a 396 but unsure if that's better then a 383?

Depends on whether you have plans for a power adder or not...especially nitrous. If you plan to just make a nice strong naturally aspirated motor, then yes a 396 or 409 would be fine. However if you plan to use a power adder, the 383 would be a good choice as far as reliability.

If you do plan on going n/a with the motor, the compression ratio needs to really be focused on like Injuneer and I have been trying to help with. Lots of things that the machine shop does will affect the final static compression ratio, such as deck height and the amount the heads are milled. If they are doing a true square deck then the piston will be very shallow in the bore. Roughly .000" - .005". This will significantly raise your compression over say a non zero decked "deck height" (.000" - .005"). Additionally, the more the deck of the head is milled the more it will raise compression as well.

Another thing to consider will your pushrod length neccesary based upon how far the go with milling the heads. Generally speaking if they go the common .025" - .030", then you would go with a 7.150" pushrod. If they take less than that you will be able to use the stock 7.200" pushrod length.

Just rambling now , but just trying to think of the little things that commonly get shuffled to the bottom of the list of importance.

BTW what is your target CR?

[Ponyrider]

I hope CR means comp rate. If so my target is 10.5 to 11.00 if that is capable for this application Im trying?

[fastTa]

I hope CR means comp rate. If so my target is 10.5 to 11.00 if that is capable for this application Im trying?

Absolutely. Well within the range of possibility.