mr2guru

iTrader: (16)

Key question is it worth it and what side effects would this bring?

Putting together a hot 346:
ET215s
MS4 on a 239/242 110+1 (109icl)
Pistons have 3cc 11* reliefs
FAST90 for the intake
LT headers with cutout or bullets

Heads are milled to around 59cc which nets about an 11.4:1 SCR with .043 gasket. This equates to a 8.29dcr intalling the cam as ground.

Now if I advance the cam 4 more *, (lower the ICL to 105) it bumps the DCR to about 8.6:1. I lose some PTV (not a concern) and push the peak down? while creating more torque with the higher DCR?

Or would this impact high rpm hp that much? does the higher DCR achieved make up for that?

cost vs. benefit of advancing the cam in this situation?

Beast96Z

iTrader: (21)

By advancing the cam that much, you are going to make the cam extremley exaust biased. For most N/A applications, I like to keep the cam more intake biased, or no more than 2 degree's advanced. Espeacially with the great exaust port on the ET heads. Advancing a cam to gain a certain DCR, is not the way to go about it. I'd leave the cam as is, or advance 1 degree at the most. JMO.

Formulated

iTrader: (16)

I agree. You can just as well gain dynamic compression by raising static compression. I think getting caught up with dynamic compression ratio is a means to forgetting how the camshaft and cylinder heads really work. The exhaust port and valve timing need to be arranged well enough to achieve good blow down without chopping off the power stroke too soon. Likewise, the intake valve has to close at a timing that suites the intake manifold tuning. Get the induction and exhaust tuning sorted out using the camshaft, then set the static compression ratio to whatever your combustion chamber and available fuel can reliably support.

racer7088

You'd need to dyno it to see if it likes that or not but you might also be starting to get into more detonation. It might make more power everywhere or less or down low. Hard to say without testing it.

mr2guru

iTrader: (16)

I see your points. I am kind of stuck with the static ratio. I am not sure if I can mill these heads much more. They started life at 62cc. My quench is as tight as I am comfortable with ~.033
So that leaves cam dynamics to affect DCR to an optimum level for this cam.

I think I will start at +3 total, 107icl and go from there. I guess this is where the cloyes hex-a-just and QTP cover come in handy....

Patrick G

iTrader: (14)

106 ICL should give you the best performance balance. At 109 ICL, the intake valve closing point is around 48.5 degrees ABDC at .050". This is a little on the late side for a 346. By advancing the cam from 109 to 106, you will gain DCR and get the IVC closer to where the tuned-length runners of the intake manifold make best power.

Typically, advancing a cam past optimum will hurt you less than retarding a cam past optimum. In this case, you have much better odds of picking up area under the curve than leaving it at 109 ICL.

mr2guru

iTrader: (16)

Thanks Pat....