is 11:1 compression ratio to high for pump gas....396 .60 over...

What will be the vehicle use?,,,track,,,street? IMO think for street/ cruzing ur asking to run hot especially with .60 over

is 11:1 compression ratio to high for pump gas....396 .60 over...

Need more information on engine/drivetrain to make a determination.

Your cam duration can greatly effect your dynamic compression.

I'm currently running 10.76:1 static compression with a Lunati Voodoo 60104 cam...

I'm getting ready to bump up to 11:1 and a better quench while installing a larger cam that will actually drop my dynamic compression by about .70 from where it is now.

I've been adding a little Kemco 130 octane booster as a precaution on the street although I've never heard it ping.

comp cam 520 intak 520 ext kit..sagnal 4 speed...373 12 bolt pos rear...69 chevelle...cast iron passenger heads 65-66...looking at headers for this motor now

David, cam lift doenst mean much, but from that small number it cant be very big. It'll run, but with the engine timing very reatrded. Might want to opt for newer version open chamber heads. 781/049 etc, to get you to 9:1.
Anyway, give the cam specs, duration adn LSA so these guys can give a reply.

4 speeds are less tolerant than autos, btw. The torque converter helps.

230 230 duration 520 520

Sir, thats going to be an issue. You'll need to limit advance severly to get it to not detonate.

ok, COMP 280 Magnum cam + 11:1+ 396=:sad::sad:

How did you determine 11:1 CR?

IF you have factory 11:1 pop-ups, they get this CR from 106cc heads and a hefty dome. You state mid-60s passenger car heads....have 96-98cc chambers.... So with a smaller dome, you"ll have a buncha compression on your hands!!!!!:yes:

I had this situation with my 68 Vette, 101cc closed chamber heads and L-2268 11:1 domed slugs...roughly 11.75:1 CR

IF you do have the domed slugs, get some 781 or 049 heads to get the CR down to 10:1 territory......so you can run some advance.

Go up in cam size and get kemco additive.

BTW, the SAGINAW 4-spd was designed for cars with 300 ft lbs torque, base small block engines. it will blow the first time you get traction and try to launch hard.....

i'm trying to understand what the mashine shop is telling me...

do I wont to change out the pistons or mashine the heads? I dont know...

Can you post the engine specs ?
Piston brand/part number
How far down the hole is the piston at TDC ?
Head gasket thickness
Cylinder head casting number
Cam brand/part number

That info will let us calculate the static & dynamic compression ratios to answer your question correctly.
Or you could calculate it yourself with this program:
http://members.uia.net/pkelley2/DynamicCR.html

Get ALL the specs from the machine shop first. You need the casting numbers off the head and piston, deck height and head gasket. Then someone can tell you what you have for compression. If your cam has enough duration, you might be ok. I have an 11-1 454 that I put 2000 pump gas miles on last year with no problems. But the cam is 314/324 duration, thus dropping the comp down to a safe level.

With the complete specs, you can get alot of help from this site. :thumbsup:

rodger that

many thanks
DP

My boss's L78(375 hp) with a 282 crane cam will NOT run 93 without DETONATION or Deiseling-with a L88 cam it would(barely)-I don't know the piston to head clearance or other tidbits that help run high compression are but I don't think it would help much-high octane gas or some thing like KEMCO or the old C5 will make it work.

Better plan on Aluminum heads then.....

...or Calico coatings on the piston tops, chambers, valves, and ports. It'll help a lot more than you think.

can a good mashine shop open the head chamber?

DP,

While you 'could' open the chamber up, you could also hit the water jackets.....
And you also could spend a lot of money getting the chambers opened...
Buy a set in the size that you need....