Dynamic compression ratio & cam timing

Go down

Dynamic compression ratio & cam timing Empty Dynamic compression ratio & cam timing

Post  AUDIOADDICT02 on October 19th 2013, 11:48 pm

Ok guys, so I'm real close to getting my 460 running, but after reading, reading, & reading about engines, I learned that dynamic compression ratio is very important when it comes to running pump gas.

Engine specs:
460 bored 40 over-4.40" bore
Stock crank
4.20 cc flat top pistons
Zero decked
D3ve heads
Ford racing .038 hg's
Summit racing g6630 timing set
Lunati voodoo 61605 241/249 cam

With all this, I'm at 9.83 static cr(although the cam asks for 10.5) & 8.6 dynamic cr.
Apparently 8.5 is the safe max cr for pump gas, I only have 91octane available.

Am I calculating the dynamic cr correctly? My cam sheet says the intake closes at 46.5 degrees abdc(I'm guessing at .050 lift)... I have read that my number would be calculated: 241-180+15 = would equal when the intake valve will close.

Also, I have my timing gear set at "6 & 12" position, which is apparently advanced on this timing set, but shouldn't it be 0 degrees adv/retard?

Can somebody please help me & review my combo to see if I'm doing it right? Before I crank it & end up blowing it up or breaking something...

AUDIOADDICT02

Posts : 44
Join date : 2012-05-11

View user profile

Back to top Go down

Dynamic compression ratio & cam timing Empty Re: Dynamic compression ratio & cam timing

Post  LivermoreDave on October 20th 2013, 8:33 am

With pump gas this combination I believe will be marginal. Although a prepped combustion chamber and a tailored ignition timing curve (rate & amount) will assist in detonation control or elimination. The camshaft has 4* ground into it and advancing it farther may only contribute to detonation. With all that said, it will sure sound good and I wish your performance goal satisfied.

Dave.

Below is the Lunati specification.

Hydraulic Flat Tappet Cam. Designed for very hot street/bracket race applications, this cam requires a mini- mum of 10.5:1 compression,
4.11 gear- ing and 3500 RPM stall converter. Works with up to 250 HP nitrous, and pulls very hard past 6500 RPM when coupled with the correct parts.•Advertised Duration (Int/Exh): 284/292
•Duration @ .050 (Int/Exh): 241/249
•Gross Valve Lift (Int/Exh): .582/.600
•LSA/ICL: 110/106
•Valve Lash (Int/Exh): Hyd/Hyd
•RPM Range: 2500-6600
•Includes: Cam Only

Part Number: 10340705
Previoius Part Number: 61605

LivermoreDave

Posts : 972
Join date : 2009-09-27
Location : North of the Equator.

View user profile

Back to top Go down

Dynamic compression ratio & cam timing Empty Re: Dynamic compression ratio & cam timing

Post  Paul Kane on October 20th 2013, 11:47 am

Generally, flat top pistons and D3VE heads should be able to run on pump gas premium with the camshaft you are using, however we don't know what vehicle the engine is in, where your cam is phased, etc, and cannot draw any final conclusions without that information (and more). By the way, that's quite a bit of cam for most D3VE headed engines and the kinds of uses they are typically utilized.

It seems you are trying to evaluate dynamic compression ratio "on paper," and that you have not evaluated your valve timing events as they are in the real world (ie, have not degreed your camshaft).  And so one cannot know precisely when your intake valve is truly closing.

If the entire OEM valve train is being used with OEM length pushrods, no pedestal shims, etc., then the valve timing events are probably not exactly as the cam card specs indicate they are at the lobes, nor is it likely that the engine will have as much valve lift as the camshaft can provide.  Further, if you have not modified your D3VE heads to accomodate the lift that your camshaft is supposed to provide, then your engine will almost certainly have valve train clearance issues between the valve spring retainers and the valve guides...which will break the stamped steel pedestal rocker arms.

If all these matters have already been addressed, then you're probably ahead of the curve.

Paul
Paul Kane
Paul Kane

Posts : 876
Join date : 2009-09-15
Location : San Francisco Bay Area

View user profile http://www.highflowdynamics.com

Back to top Go down

Dynamic compression ratio & cam timing Empty Re: Dynamic compression ratio & cam timing

Post  AUDIOADDICT02 on October 21st 2013, 12:41 am

Thanks for the responses guys.

How should I set my ignition system up to try & avoid detonation?

Paul: My heads are being machined to accommodate the extra lift the cam provides.
The cam is positioned with the dot on the cam sprocket facing down & the key way on the crank pointing straight up.
Isn't that how the cam company would figure when the intake valve closes? I have not degree'd the cam & can't afford a degreeing kit at the moment.
Also, should I use a longer rod, or would the oem length be fine?(hardened rods will be used, of course)


AUDIOADDICT02

Posts : 44
Join date : 2012-05-11

View user profile

Back to top Go down

Dynamic compression ratio & cam timing Empty Re: Dynamic compression ratio & cam timing

Post  LivermoreDave on October 21st 2013, 9:03 am

AUDIOADDICT02 wrote:Thanks for the responses guys. How should I set my ignition system up to try & avoid detonation?
AUDIO when your engine is complete and installed in your vehicle, then you can tailor your ignition needs as your application requires. Most modern aftermarket distributors and ignition modules have adjustments that allow timing curve adjustments with ease. Ford Duraspark ignitions are good street ignitions although adjusting the timing curve in the distributor will require a bit of "trial and error" approach. When using the Ford Duraspark ignition system, be patient it may require multiple adjustments or/and changes.

Dave.

LivermoreDave

Posts : 972
Join date : 2009-09-27
Location : North of the Equator.

View user profile

Back to top Go down

Dynamic compression ratio & cam timing Empty Re: Dynamic compression ratio & cam timing

Post  AUDIOADDICT02 on October 23rd 2013, 3:51 pm

I guess I'm just paranoid about detonation & breaking a piston(that's why I had to rebuild my engine in the first place) since I'm going to be using sealed power h535cp hypereutectic pistons. I have read a lot about hypers not holding up to detonation very well, but I got a good deal on these & I couldn't afford forged.

I guess I'll just back off the timing a bit & go from there once its up & running.(I'm using the stock distributor for now)

AUDIOADDICT02

Posts : 44
Join date : 2012-05-11

View user profile

Back to top Go down

Dynamic compression ratio & cam timing Empty Re: Dynamic compression ratio & cam timing

Post  quick 52 on October 24th 2013, 10:39 am

Im running close to what you have 10.14-1 com. and use pump gas cam is a solid flat 258 .615 square but did run the voodoo cam your running... my timing is at 34* total

quick 52

Posts : 612
Join date : 2011-01-14
Age : 68
Location : leonard mi.

View user profile

Back to top Go down

Dynamic compression ratio & cam timing Empty Re: Dynamic compression ratio & cam timing

Post  AUDIOADDICT02 on October 30th 2013, 11:32 pm

Nice, how'd you like voodoo cam? I kinda just chose it thinkin outta my a$$ since I saw bigger numbers & thought that will give me more power. What difference does the timing make?

AUDIOADDICT02

Posts : 44
Join date : 2012-05-11

View user profile

Back to top Go down

Back to top


 
Permissions in this forum:
You cannot reply to topics in this forum