DREAMZ28

iTrader: (1)

That would be great, I love reading those threads. I've been reading the cam discussion threads for the past few days whenever I have the time, cars are overly addicting.

LilJayV10

iTrader: (39)

I re read the last email from Brian. He said 61cc. I don't know what that is with a .040 or .045 gasket.

JakeFusion

iTrader: (7)

11.1 would put you around 8.5:1 DCR which is what you want. 8.7:1 is pushing it and 9:1 is beyond what most feel comfortable with...

I ended up with 11.2:1 because of that. That's enough while being safe.

DREAMZ28

iTrader: (1)

How do you calculate dcr? I'm about to search to see if there's online calculators.

And is having a high static compression, say, 11.5 plus and a dcr of 8.5 better than having, say, 10.7 scr and 8.5 dcr? I heard someone in a thread say they wanted to run a high static and drop the dynamic down to reasonable levels by manipulating valve events/duration/overlap. Is either way advantageous to the other?

I'm trying to imagine it in my head and the only thing I can see is it helping quench, since to raise static compression ratio with a stock bottom end, you have to get the combustion chamber closer to the piston.

JakeFusion

iTrader: (7)

DCR is a calculation. Some engine guys hate it and others are ok with using it for a rough estimation of cranking compression. Point is a later IVC point from a bigger duration or wider LSA or combination of them kills bottom end and part throttle drivability.

Going with more static compression raises dynamic compression by default if the cam remains the same. Either way you want to optimize your dynamic compression for the gas you will be running. Huge cams needs more static compression to have the same dynamics compression of smaller cams (which also have lower static). Like I said, it's a calculation and part of determining the best combo. That's why cams that excel for stock heads are not really optimized for aftermarket heads in terms of compression (not even getting into airflow) and vice versa.

Compression is your friend most times tho... Helps with drivability and overall power and especially in the low end and midrange.

DREAMZ28

iTrader: (1)

I understand that, my question was more of a hypothetical.


Say you have Cam A and Cam B.

With cam A, you have a 11.5 compression, and because of your IVC, it drops dynamic down to 8.4.

With Cam B, you have 10.9 compression, and because of your IVC, it puts dynamic at 8.4 also.

With all other variables ignored, what would the effect of having a high static compression vs a lower static compression, but the same dynamic compression have? I'm trying to see if it's advantageous to run a high static compression with a reasonable dcr vs an average compression with the same dcr.

JakeFusion

iTrader: (7)

Cam B is smaller and will therefore provide better midrange and low-end torque at the expense of some uptop.

Because we don't have variable valve timing, we have to pick where we want power.

Cam B will not make a lot more torque than Cam A. The specific energy of 93 only allows so much torque with 346cid. Just where to do you want that torque?

Also, the bigger a cam, the more overlap it produces. Overlap means power with cathedral port heads and allows the exhaust charge to help pull in fresh air. This is another advantage of a bigger cam uptop.

DREAMZ28

iTrader: (1)

OK, so the difference in power isn't dependent on the difference in static compression, but just the fact that the cam has to be bigger and more aggressive to get dcr to a reasonable level.

I've been thinking about running stock 243 heads, being on a budget. I know they bump my compression up to 10.5, head gasket remaining the same thickness. I want to be very involved with my cam selection, how do you get valve events from a certain cam?

I was playing with the idea of this cam, but thinking for my compression, it might be a tad too much.

intenseblue

iTrader: (1)

Wallaceracing.com has a calculator to find valve events if you know the cams duration, lsa, and icl. Dynamic compression is determined using advertised duration at .006, not .050.
Uempistons.com has theeasiest to use dcr calculator i've found but they say to add "x" amount to .050" duration numbers if you dont know .006" and thats trouble and should be removed imo, so find the true duration and valve events and have fun lol

LilJayV10

iTrader: (39)

If this was explained I wasn't able to grasp it.

LilJayV10

iTrader: (39)

Maybe Brian's Stage 3 cam would be better suited?

JakeFusion

iTrader: (7)

See post 67.

intenseblue

iTrader: (1)

This is probably a horrible attempt to make this simple but ill stab at it open to correction.

Assuming 93 octane 8.8 dcr is a max reccomended number for an ls1/ls2/ls6. Dcr in a way represents cylinder pressure which represents torque potential and responsiveness. By enlarging the camshaft, you lose dcr and cylinder pressure of the ivc is later, when in most cases it is, and torque also. If you increase static compression with the larger cam to reach the same dynamic compression, youve now restored the cylinder pressure and torque output to same level but now have added airflow and horsepower from the larger cam. Torque numbers may be the same, but at a higher rpm. 11.8:1 engine with 8.8 dcr can run as easy on 93 as a 9.9:1 8.8dcr ls1 one has a small cam and low comp, one has high compression and larger cam.

this is probably flawed but the concept should be understandable

DREAMZ28

iTrader: (1)

Basically, a high static compression with a 8.5 dynamic compression vs a lower static compression with a 8.5 dynamic compression, would there be any benefits to either method with all else equal.

99wssixm6

iTrader: (3)

Perhaps I'm missing something in this post but I just wanted to point out that the camshaft profile will never change Static Compression; it will only effect dynamic compression. Static compression is simply a calculation of cylinder volume at bdc vs tdc.

JakeFusion

iTrader: (7)

The bigger the cam the more compression you can throw at it... that helps low-end torque and drivability of the big cam.

DREAMZ28

iTrader: (1)

I understand that. I should've said engine a and b. Its basically a comparison between one build and another build, and the only variables being dcr/scr. Say, one person runs a thin head gasket and mills the crap out of his heads, and his scr ends up being 11.7, yet his cam gives him a 8.6 dcr. another guy runs a stock head gasket with unmilled heads, giving him a 10.6 scr and his cam gives him a 8.6 dcr. Is the first person benefiting from the higher static compression even though his dynamic compression is the same as the second person?


As a side note, ignore the effects the different cams and valve effects would bring.


I know, it's a confusing question.

DREAMZ28

iTrader: (1)

OK, so having a higher static compression will aid in low end torque and drivability, even if your dcr ends up being the same as it would if you ran a smaller cam with less static compression?






OK, basically, I'm asking if static compression has an effect on anything, or is dynamic compression the only thing that actually matters?


I know you can run a bigger cam when you have more static compression, that's not my question. I'm trying to see if there are gains from just having a higher static compression alone, even if your dynamic compression ends up being the same because of cam specs.


Does having a 11.7 static and a 8.6 dcr have an advantage of having a 10.5 and a 8.6 dcr. See what I'm saying?

A.R. Shale Targa

iTrader: (2)

This is not a yes/no question, rather the rest of your entire combo determines which way is better for you. If you only have 2.73 gears and a 2800 converter then the 10.5 combo where the cam is smaller and has a powerband of 25-6500 would have an advantage. If you got 4.10s and a 4200 stall then the larger cam/higher comp would be in it's 3800-7200 range.

DREAMZ28

iTrader: (1)

OK, I was trying to see if there was any advantage to running a higher compression besides being able to run a bigger cam