VETDRMS

I'm in the process of building a 406, and I need to decide on which cc AFR 195 head to use. I will have ~.010 deck, and when I ran the 68cc chambers in a CR calculator I came up with 10.8:1. I'll be at ~10.3:1 with the 74cc chambers.
Should I just not risk it and go with the 74cc's?
The cam is a Comp Xtreme Roller 288 Hydraulic roller (236I/242E@.050;.520/.540)
What is the highest you can run on premium?
Thanks :cheers:

gkull

You need to figure your DCR.

But, just off hand 10.8 and your cam is just about right.

VETDRMS

Gkull Thank you, how would i figure my Dynamic Compression Ratio? I have seen how to do it, but can't remember. So how are things with your motor? crane straighten out the lifter problem?

1979toy

Here's a link to the dynamic compression ratio calculator program. http://cochise.uia.net/pkelley2/DynamicCR.html
Sounds to me like you are going to be right on the edge of being able to use pump gas. That assumes that you maintain perfect tuning. I'm setting my engine way below that level because I know how bad my tuning skills are.

Brettmc

Remember you can get away with a skosh higher cr with aluminum heads.

Brett :thumbs:

MotorHead

Use desktop dyno and see how much hp/torque a half a point compression gets you, probably not that much :D

gkull

Vetdrm I have a down loaded version of a DC Ratio calculator. You need the .006 or advertised cam duration numbers for the calc. They say that 8.5 dynamic is max with aluminum heads for street driving 91-93 unleaded super. Mine is 8.43 or something like that. I also have a slow advance curve and it runs fine on 91.

I am buying a new custom sollid roller. I ask Smoked tires to post my DD2000 run on the cam I ask Crane to build. The profiles Crane came back with are reverse spit durations. With 250 degrees intake and 238 degrees exhaust @ .050. I ran some simulations on their two cams and they are just under 40 more hp peak and about 40 less foot lbs of tq.

So I think a torque monster is better than 40 extra hp at 6000 - 7000 rpm. The idea sounds intriguing. Does anybody know anything about these style of cams?

PatsLs1vette

gkull i just instant messaged you about those style cams.ive used them before.

Jvette73

Im runnin 10 to 1 with XE262 and have no negitive issues using high octane pump gas. I also run full agressive advance curve and have no ping or detonation. Like gkull said, with that 288 cam you should have no problem. The bigger cam with longer duration holds the valves open longer which reduced the cylinde pressure. I heard some claim to run 12 to 1 on pump gas in conjunction with 300 duration cams. The only thing with a 300 duration cam is, to get the most of it you need an engine thats willing and worthy to rev to 7000rpm and beyond.

VETDRMS

Thanks for all the great info!

1979toy Thank you, that was just what i was looking for. I ran all the specs for my motor and and will have a static compression ratio of 10.87:1 and a dynamic compression ratio of 8.32259267850636. I think I am going to go with the 68cc heads.

Brettmc I wanted to figure that in as well, and at the DCR I found I think the 68cc's would be a good choice.

MotorHead This cam may like the extra compression, and they say 1pt is usually worth 4% increase in hp, so 2% of 510 is ~10hp. Not much to scoff at.

gkull I used the .006 numbers from comp (288/294) And like above the DCR was 8.32259267850636. So I think i'll be on the ragged edge, but should be ok. I"ll be buying a timing retard unit for my Crane ignition, so if it pings it won't be hard at all to fix.
Sounds like an interesting profile for sure! If that is your intended rpm range then it would probably work pretty good.

JVette73 Thanks, I think i'll go on the edge with the 68's. One motor that suprises me is the 16:1 pump gas motor entered in the Engine Masters series... :confused: I should make peak power around 6200rpm, and for my bottom end i'll be just fine [SCAT crank/SCAT H-beam 6" rods/SRP Forged Flat top pistons] :cheers:

The Money Pit

I went with the 74cc chambers and have just over 10.1:1 cr with flattops.Been running for 8 months now with no sign of detonation.
I'm still trying to dial in the timing via distributer recurving,but with the recent snow,I've not been able to road test.My commute is 400 miles a week,and I've driven this in 95 degree heat,and also 10 degree cold. Be advised when you reach this level of power you will find the need to upgrade the cooling system. Check out my website. :cheers:


[Modified by The Money Pit, 5:04 PM 3/2/2003]

VETDRMS

The Money Pit
I was going to get the 74cc heads and mill them down to 72cc (.012) This would put me just at the 10.5:1 I'm aiming for. I will be running a Crane Hi-6 with LX-92 coil with a MSD Pro billet or similar distributor, from what i can see these heads like 34-36* total.
I was going ot use the griffin circle track aluminum radiator (31x19), I know of a few other forum members who have used it, but can't remember who.

The Money Pit

I ran a dyno program and tried cr's from 9.0 to 12.5:1 and saw very little gain with the cr being the only change to the combination.Seems to me the price of milling perfectly straight heads would not be worth it. When they warp and you need the material removed,it would not hurt you.
Also in reguards to the cam choice,keep in mind the intended purpose of the car. I drive the hell out of mine(20,000 miles yearly) and so street manners is a must.It can pull 6500 rpms the way it sits,and the trade for top end power would leave me with much less power brake than I already don't have.


[Modified by The Money Pit, 7:36 PM 3/2/2003]

rponfick

What is your altitude in Billings. If it is similar to Denver (mile high), you will have no problem with your CR. The altitude here effectively reduces CR by about 20%. The gas companies already know this because they reduce the octane ratings avalilable at high altitude accordingly.

ZD75blue

So what would the max compression be with 87 octane?

Cough... sorry for hi-jacking, air shocks needed an adjustment :jester