luvofjah

iTrader: (2)

Thanks, I got a 10.3 with the 1.433 compression height and 5.7 rods, 56cc heads, etc...

So that is .3 higher than TunedPort335 was running with iron heads (58cc), should not be a problem for aluminum heads...

Now my question is the dynamic compression with the above cam... will that be a problem...??

MoJoe

iTrader: (5)

Cam lift only requires heads/valves/springs that can handle that lift.
Intake duration (in degrees, either advertised in the 260*-280* range or 220*-230* range for measured at 0.050" lift) will affect the dynamic compression ratio (DCR) which determines pump gas tolerance and overall drivability.
I don't know "high lift but setup for low end torque" marketing translates into degrees of duration...

Static CR (SCR) can be calculated simply, while DCR also takes the cam spec into account. (I haven't run these through a DCR calculator, such as this or this, so don't take the numbers as gospel, just follow the trend).

• For a stock 205*-ish cam, and say SCR is 9.4:1, DCR is 7.8-8.0:1
• Crank the cam up to a 230* stick and that 9.6 SCR bleeds off to a 7:1 DCR and is sluggish.
• Or, rebuilt the engine at 10:1 with the "mild", stock-ish cam at only 210*, and you don't bleed enough of the SCR and end up with 9:1 DCR that pings like mad and needs race gas to run.
• Then take a well balanced performance build. Build the SCR at 10:1, add the 230* cam, and DCR is a responsive, and pump gas friendly 8:1.

Note: a confusing problem with the DCR calculators is what cam spec to use? Do you use the @0.050" duration measurement? Or add X degrees to it? Or use the advertised duration? Roller cams and their steeper* lobes use a duration closer to advertised than flat tappet cams which, due to their slower* lift lobes, should use a number closer to @0.050" duration.
* steeper...but the deceleration zones at the end of the lobes are flatter/slower like flat tappet cams to prevent valve bounce
* slower = less lift per degree of rotation
I haven't found a definitive answer. And, I am not sure there really is a definitive answer. Because: how much pressure is bleeding off for 5* at 0.010" lift?

These discussions can turn into rocket-science, hence why "packages" list "10:1 compression" even when there are 14 other factors that affect CR and DCR and therefore overall usefulness.

TxTtopZ

Mojoe... I have been using the actual cam card for when the intake closes to where it start s actually building DCR. An open valve will not create any compression that is substantial enough. For instance he is using a cam that has the intake valve close @ 63*.

luvofjah

iTrader: (2)

"high lift, but setup for low end torque"
Higher lift than the 335 in question, but duration seems the same, where rpm range is stated @ 1200 to 5200 for both cams... his being .48 lift... Not designed for high rpm power...

TF Heads can handle .6 lift, that is fine...

It's a 260 cam...
Duration 260 intake, 270 exhaust
@.050 210 intake, 218 exhaust

MoJoe

iTrader: (5)

Correct. The faster heat transfer of aluminum over iron reduces the hot-spots causing ping/detonation, therefore AL heads can benefit from higher SCR (and therefore higher DCR).

I didn't see if/where you listed the cam specs, specifically the intake duration. Flat vs roller makes a difference too (see my previous post). Grab the cam specs and your 10.3 SCR and plug into one of the DCR calculators I linked.

• Less than 8:1 DCR is sluggish response and/or leaving performance and economy on the floor.
• 8-8.5:1 is the sweet spot.
• Above 8.5 DCR requires race gas to prevent detonation.

These are general guidelines that depend on the rest of the package (cam lift, head flow, operating temp, etc).

luvofjah

iTrader: (2)

Roller Cam... the waller racing calc gave me a static compression ration in the 13 range... the other one did 10.3... but it doesn't have a dynamic compression calculator...

With 0 boost and 0 altitude...

Static compression ratio of 10.3:1.
Effective stroke is 3.07 inches.
Your dynamic compression ratio is 8.61:1 .
Your dynamic cranking pressure is 174.81 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 8.61 :1.
V/P (Volume to Pressure Index) is

MoJoe

iTrader: (5)

Exactly. And thanks for pointing out it is the cam closing timing that is the critical data. And thanks for the 63* number.

This is a mild cam, and won't bleed off much CR. (Not as much as a 230* @ 0.050" cam would).
BUT... plugging the 63* that TxTtopZ mentions into the Wallace DCR calc, the result is 8.39 for the DCR. This falls into the "pump gas tolerant" range as I understand it.

Static compression ratio of 10.3:1.
Effective stroke is 2.98 inches.
Your dynamic compression ratio is 8.39:1 .
Your dynamic cranking pressure is 169.07 PSI.

luvofjah

iTrader: (2)

My spec sheet says 59 ABDC, not 63.

MoJoe

iTrader: (5)

See the difference of 4*? I put in 63* and got 8.39 DCR, while your 59* says 8.61 DCR.

luvofjah

iTrader: (2)

So will that be ok with more tolerant aluminum heads?
91 or 93 octane gas?

TxTtopZ

This is why I specd out the cam given the earlier specs on what cam would work good. Its a 1800-5800 cam. It will work

If you go for a smaller cam as stated earlier your going to run into issues. I am trying to get the cam card for the other cam I like which is the Lingenfelter piece that is spec'd out 211/219 .530/.560 HR112 74211.. IF the valve closing events are later than the smaller one you listed then we might have something else you can use... It's made for Corvettes using the 113 aluminum heads so it might have some DCR in it.

There is also another one thats tried and true from those guys and thats the 213/219 .493/.502 HR112 74216... about the same duration with less lift but again.. I cant find a cam card. The 219/219 .560/.560 HR112 74219 is not bad either.

Edit... I am a big believer in a decent cam and good flowing heads vs a bigger cam and crap heads. All the LSX stuff uses a decent cam and makes big usable power because the heads are so damn good.

luvofjah

iTrader: (2)

I PM'd TunedPort335, he doesn't come on here much... but he's had his stroker kit for 10 or more years...
I did read in one of his posts, that he had a comp cams 1200 to 5200 rpm range with .48 lift... I checked the CC website, and the ABDC for a similar cam is 58, one less than the cam I have (which raises it for HIS cam), but again, I have 2 less CC's in the head chamber...

I asked to see what model he has...

Since my 8.6 is on the line, I read you can run lower thermostat, run cooler plugs with aftermarket ignition system, run cold air induction kit, and even if needed, retart timing.... & with aluminum heads being more tolerant than iron...

Looking forward to what TunedPort335 reports back...

FireDemonSiC

I'm actually already halfway through this build. Just need to buy valvetrain and machine engine block. See this thread:

https://www.thirdgen.org/forums/tech...-camshaft.html