Davidgmcman

Having trouble figuring compression ratio out. I have iron block 9.230 deck height bored to 3.904 100% flat top pistons compression height of 1.328 stock stroke 3.622 stock rods 6.09 ls6 cnc heads 63.5 cc chambers and .051 head basket need help horrible with math remember the aluminum ls1 block is 9.240 and this one is 9.230

ss performance

iTrader: (17)

Check out this site.

http://www.bgsoflex.com/auto.html

It has a bunch of calculators for automotive applications.

Davidgmcman

Thats giving me 11:1 pretty good site thanks

.boB

iTrader: (1)

Now calculate your dynamic compression ratio. If it's over 8.0, you'll have some trouble with pump gas in the summer.

redtan

iTrader: (5)

Wut? Plenty of people run DCR in the high 8s just fine on 93 pump gas.

Davidgmcman

When I worked it out I come out with 10:9:1 static and 8:01 dynamic right were i had originally planed it

.boB

iTrader: (1)

This is 8.35 on pump gas. Sometimes you can get away with it, and sometimes you can't. Unless you're racing, keep it closer to 8.0.



And this is what can happen with E-85 at >8.5. It detonates up under the first ring land.

ss performance

iTrader: (17)

I have found that website very useful many times.

Good Luck

RezinTexas

I'm running 8.500 DCR with zero issues on 93 octane through the brutal Houston summers. Patrick G is my tuner

redtan

iTrader: (5)

That's called a shitty tuner my man. Again, plenty of people on this site have ran in the mid-high 8s on 93 gas for thousands of miles, including myself, without as much as a hiccup.

I scan everytime I drive the car and I get no knock anywhere in the RPM range and I'm sitting dead on 8.8 DCR. Oh and this is on shitty winter blend no less.

.boB

iTrader: (1)

That's not a "shitty tune", that's a race engine running on the edge, lap after lap. No timing retard, so max power every lap.

You can get away with a high DCR, especially if you have a electronic ignition with a knock sensor. If there's any pinging, it will retard timing to protect the engine. But then you lose power. Do your dyno run on a hot day, with coolant temps above 200* or so and see what you get.

Keeping the DCR below 8 or 8.5 will maintain max power on pump gas. Especially if you keep it cool.

You can bump that up even a little bit more if you've polished the chambers a bit, and kept your quench down to 0.035-0.040".

Play with programs like Desk Top Dyno, and see what the power difference is between 8.5 and 8.0. It's such a small amount that you wouldn't even notice on the street. On the drag strip, it would be measured in thousands of a second.

If you're racing and need every HP you can get your hands on, it's worth it to push the edge. If you're looking for a fun street car that makes good power and will last forever, it's probably not worth it to push it that hard. All depends on what your goals are, and what risks you're willing to take.

But, that's just my opinion. I could be wrong.

redtan

iTrader: (5)

Ok race engine running 7000rpm for an extended period of time you may be right to keep the DCR down for safety and logentivity.

However, I don't see the guy asking for a specific setup (aka circle track or road course engine). Thus on a regular street/strip engine where it doesn't see 7000rpm for hours on end, mid-high 8s DCR is more than doable.